Mobile Communications Chapter 7: Wireless LANs

Mobile Communications Chapter 7: Wireless LANs
Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Mobile Communications Chapter 7: Wireless LANs Characteristics IEEE PHY MAC Roaming .11a, b, g, h, i … HIPERLAN Standards overview HiperLAN2 QoS Bluetooth Comparison Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.1 Prof. Dr.-Ing. Jochen Schiller

Characteristics of wireless LANs
Freie Universität Berlin Institut of Computer Science Characteristics of wireless LANs Mobile Communications 2002 Advantages very flexible within the reception area Ad-hoc networks without previous planning possible (almost) no wiring difficulties (e.g. historic buildings, firewalls) more robust against disasters like, e.g., earthquakes, fire - or users pulling a plug... Disadvantages typically very low bandwidth compared to wired networks (1-10 Mbit/s) many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE ) products have to follow many national restrictions if working wireless, it takes a very long time to establish global solutions like, e.g., IMT-2000 Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.2 Prof. Dr.-Ing. Jochen Schiller

Design goals for wireless LANs
Freie Universität Berlin Institut of Computer Science Design goals for wireless LANs Mobile Communications 2002 global, seamless /all in one operation low power for battery use no special permissions or licenses needed to use the LAN robust transmission technology simplified spontaneous cooperation at meetings easy to use for everyone, simple management protection of investment in wired networks security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation) Transparency/clearness concerning applications and higher layer protocols, but also location awareness if necessary Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.3 Prof. Dr.-Ing. Jochen Schiller

Comparison: infrared vs. radio transmission
Freie Universität Berlin Institut of Computer Science Comparison: infrared vs. radio transmission Mobile Communications 2002 Infrared uses IR diodes, diffuse light, multiple reflections (walls, furniture etc.) Advantages simple, cheap, available in many mobile devices no licenses needed simple shielding possible Disadvantages interference by sunlight, heat sources etc. many things shield or absorb IR light low bandwidth Example IrDA (Infrared Data Association) interface available everywhere Radio typically using the license free ISM band at 2.4 GHz Advantages experience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penetrate walls, furniture etc.) Disadvantages very limited license free frequency bands shielding more difficult, interference with other electrical devices Example WaveLAN, HIPERLAN, Bluetooth Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.4 Prof. Dr.-Ing. Jochen Schiller

Comparison: infrastructure vs. ad-hoc networks
Freie Universität Berlin Institut of Computer Science Comparison: infrastructure vs. ad-hoc networks Mobile Communications 2002 infrastructure network AP: Access Point AP AP wired network AP ad-hoc network Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.5 Prof. Dr.-Ing. Jochen Schiller

802.11 - Architecture of an infrastructure network
Freie Universität Berlin Institut of Computer Science Architecture of an infrastructure network Mobile Communications 2002 Station (STA) terminal with access mechanisms to the wireless medium and radio contact to the access point Basic Service Set (BSS) group of stations using the same radio frequency Access Point station integrated into the wireless LAN and the distribution system Portal bridge to other (wired) networks Distribution System interconnection network to form one logical network (EES: Extended Service Set) based on several BSS LAN 802.x LAN STA1 BSS1 Portal Access Point Distribution System Access Point ESS BSS2 STA2 STA3 LAN Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.6 Prof. Dr.-Ing. Jochen Schiller 9

802.11 - Architecture of an ad-hoc network
Freie Universität Berlin Institut of Computer Science Architecture of an ad-hoc network Mobile Communications 2002 Direct communication within a limited range Station (STA): terminal with access mechanisms to the wireless medium Independent Basic Service Set (IBSS): group of stations using the same radio frequency LAN STA1 IBSS1 STA3 STA2 IBSS2 STA5 STA4 LAN Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.7 Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science
IEEE standard Mobile Communications 2002 fixed terminal mobile terminal infrastructure network access point application application TCP TCP IP IP LLC LLC LLC MAC MAC 802.3 MAC 802.3 MAC PHY PHY 802.3 PHY 802.3 PHY Prof. Dr.-Ing. Jochen Schiller, MC SS02 7.8 Prof. Dr.-Ing. Jochen Schiller

Layers and functions Mobile Communications 2002 The IEEE standard only covers the physical layer PHY and medium access layer MAC like the other 802.x LANs do. The physical layer is subdivided into the physical layer convergence protocol (PLCP) and the physical medium dependent sublayer PMD . PLCP *sublayer provides a carrier sense signal, called clear channel assessment (CCA), and *provides a common PHY service access point (SAP) independent of the transmission technology. PMD Physical Medium Dependent sublayer handles modulation, coding /CODEC of signals PHY Management channel selection, MIB Station Management coordination of all management functions MAC- basic tasks Medium access mechanisms, fragmentation, encryption Station Management LLC DLC MAC MAC Management PLCP PHY Management PHY PMD Detailed IEEE protocol architecture and management Prof. Dr.-Ing. Jochen Schiller

MAC Management synchronization, roaming, MIB, power management **supports the association and re-association of a station to an access point and roaming between different access points. **It also controls authentication mechanisms, encryption, synchronization of a station with regard to an access point, and power management to save battery power. **MAC management also maintains the MAC :management information base (MIB). The main tasks of the PHY management include channel tuning and PHY MIB maintenance. station management interacts with both management layers and is responsible for additional higher layer functions (e.g., control of bridging and interaction with the distribution system in the case of an access point).

Physical layer Mobile Communications 2002 IEEE supports three different physical layers: one layer based on infra red and two layers based on radio transmission: 2 radio (type 2.4 GHz), 1 layer based on IR **PHY layer offers a SAP with data rates 1 or 2 Mbit/s transfer rate to MAC layer… Next to this slide …. presents the 3 versions of PHY layer defined in this std.. Prof. Dr.-Ing. Jochen Schiller

FHSS (Frequency Hopping Spread Spectrum)
is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. is a spread spectrum technique which allows for the coexistence of multiple networks in the same area by separating different networks using different hopping sequences original standard defines 79 hopping channels for North America and Europe, and 23 hopping channels for Japan (each with a bandwidth of 1 MHz in the 2.4 GHz ISM band). selection of a particular channel is achieved by using a pseudo-random hopping pattern National restrictions also determine further parameters, e.g., maximum transmit power is 1 W in the US, 100 mW EIRP (equivalent isotropic radiated power) in Europe and 10 mW/MHz in Japan.

The standard specifies Gaussian shaped FSK (frequency shift keying), GFSK, as modulation for the FHSS PHY. For 1 Mbit/s a 2 level GFSK is used (i.e., 1 bit is mapped to one frequency), a 4 level GFSK for 2 Mbit/s (i.e., 2 bits are mapped to one frequency). While sending and receiving at 1 Mbit/s is mandatory for all devices, operation at 2 Mbit/s is optional. This facilitated the production of low-cost devices for the lower rate only and more powerful devices for both transmission rates in the early days of Prof. Dr.-Ing. Jochen Schiller, MC SS

FHSS PHY packet format Mobile Communications 2002 The frame consists of two basic parts, the PLCP part (preamble and header) and the payload part. PLCP part is always transmitted at 1 Mbit/s, payload, i.e. MAC data, can use 1 or 2 Mbit/s Additionally, MAC data is scrambled using a polynomial for DC blocking and whitening of the spectrum ((DC) block is a frequency filtering device used in coaxial antenna systems. The DC block allows the passage of radio frequency (RF) signals while blocking audio and DC frequency interference that can damage the system. ) 80 16 12 4 16 variable bits synchronization SFD PLW PSF HEC payload PLCP preamble PLCP header . Prof. Dr.-Ing. Jochen Schiller

This system obviously does not accommodate today’s higher data rates.
Synchronization PLCP preamble starts with 80 bit synchronization, which is a bit pattern. This pattern is used for synchronization of potential receivers and signal detection by the CCA. SFD (Start Frame Delimiter) start pattern indicate the start of the frame and provide frame synchronization PLW (PLCP_PDU Length Word) length of payload incl. 32 bit CRC at the end of the payload. PLW can range between 0 and 4,095. PSF (PLCP Signaling Field) This 4 bit field indicates the data rate of the payload following. All bits set to zero (0000) indicates the lowest data rate of 1 Mbit/s. The granularity is 500 kbit/s, thus 2 Mbit/s is indicated by 0010 and the maximum is 8.5 Mbit/s (1111). i.e,data of payload (1 or 2 Mbit/s) This system obviously does not accommodate today’s higher data rates. HEC (Header Error Check)PLCP header is protected by 16bit checksum with standard Gen. polynomial G(x)=x16+x12+x5+1 spreading, despreading, signal strength, typ. 1 Mbit/s min. 2.5 frequency hops/s (USA), two-level GFSK modulation

DSSS (Direct Sequence Spread Spectrum)
Is the alternative spread spectrum method separating by code and not by frequency. key characteristics of this method are its robustness against interference and its insensitivity to multipath propagation (time delay spread). implementation is more complex compared to FHSS IEEE DSSS PHY also uses the 2.4 GHz ISM band and offers both 1 and 2 Mbit/s data rates. The system uses DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK) preamble and header of a frame is always transmitted with 1 Mbit/s, rest of transmission 1 or 2 Mbit/s chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code) max. radiated power 1 W (USA), 100 mW (EU), min. 1mW/MHz in japan symbol rate is 1 MHz, resulting in a chipping rate of 11 MHz. All bits transmitted by the DSSS PHY are scrambled with the polynomial s(z) = z7+ z4+ 1 for DC blocking and whitening of the spectrum. Many of today’s products offering 11 Mbit/s according to b are still backward compatible to these lower data rates.

DSSS PHY packet format Mobile Communications 2002 Synchronization first 128 bits are not only used for synchronization,but also gain setting, energy detection (for the CCA), and frequency offset compensation. The synchronization field only consists of scrambled 1 bits SFD (Start Frame Delimiter) This 16 bit field is used for synchronization at the beginning of a frame and consists of the pattern Signal Originally, only two values have been defined for this field to indicate the data rate of the payload. The value 0x0A indicates 1 Mbit/s (and thus DBPSK), 0x14 indicates 2 Mbit/s (and thus DQPSK). Other values have been reserved for future use, i.e., higher bit rates 128 16 8 8 16 16 variable bits synchronization SFD signal service length HEC payload PLCP preamble PLCP header Prof. Dr.-Ing. Jochen Schiller

Service: This field is reserved for future use; however, 0x00 indicates an IEEE compliant frame. ● Length: 16 bits are used in this case for length indication of the payload in microseconds. Header error check (HEC): Signal, service, and length fields are protected by this checksum using the ITU-T CRC-16 standard polynomial. Prof. Dr.-Ing. Jochen Schiller, MC SS

Infrared The PHY layer, which is based on infra red (IR) transmission, uses near visible light at 850–950 nm. Infra red light is not regulated apart from safety restrictions (using lasers instead of LEDs). The standard does not require a line-of-sight between sender and receiver, but should also work with diffuse light. Typically, such a network will only work in buildings, e.g., classrooms, meeting rooms etc. This allows for point-to-multipoint communication. The maximum range is about 10 m if no sunlight or heat sources interfere with the transmission. Frequency reuse is very simple – a wall is more than enough to shield one IR based IEEE network from another. Today, no products are available that offer infra red communication based on Proprietary products offer, e.g., up to 4 Mbit/s using diffuse infra red light. Alternatively, directed infra red communication based on IrDA can be used (IrDA, 2002). Prof. Dr.-Ing. Jochen Schiller, MC SS

Medium access control layer
Freie Universität Berlin Institut of Computer Science Medium access control layer Mobile Communications 2002 Traffic services Asynchronous Data Service (mandatory) The asynchronous service supports broadcast and multi-cast packets, and packet exchange is based on a ‘best effort’ model. Time-Bounded Service (optional) implemented using PCF (Point Coordination Function) While only offers the asynchronous service in ad-hoc network mode, both service types can be offered using an infrastructure-based network together with the access point coordinating medium access. The following three basic access mechanisms have been defined for IEEE : the mandatory basic method based on a version of CSMA/CA, an optional method avoiding the hidden terminal problem and finally a contention-free polling method for time-bounded service. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

The first two methods are also summarized as distributed coordination function (DCF), the third method is called point coordination function (PCF). DCF only offers asynchronous service, while PCF offers both asynchronous and time-bounded service but needs an access point to control medium access and to avoid contention. The MAC mechanisms are also called distributed foundation wireless medium access control (DFWMAC). Access methods DFWMAC-DCF CSMA/CA (mandatory) collision avoidance via randomized „back-off“ mechanism minimum distance between consecutive packets ACK packet for acknowledgements (not for broadcasts) DFWMAC-DCF w/ RTS/CTS (optional) Distributed Foundation Wireless MAC avoids hidden terminal problem DFWMAC- PCF (optional) access point polls terminals according to a list Prof. Dr.-Ing. Jochen Schiller, MC SS

Slot time is 50 μs for FHSS and 20 μs for DSSS.
For all access methods, several parameters for controlling the waiting time before medium access are important. Figure 7.9 shows the three different parameters that define the priorities of medium access. The values of the parameters depend on the PHY and are defined in relation to a slot time. Slot time is derived from the medium propagation delay, transmitter delay, and other PHY dependent parameters. Slot time is 50 μs for FHSS and 20 μs for DSSS. The medium, as shown, can be busy or idle (which is detected by the CCA). If the medium is busy this can be due to data frames or other control frames. During a contention phase several nodes try to access the medium. Prof. Dr.-Ing. Jochen Schiller, MC SS

MAC layer II Mobile Communications 2002 Priorities defined through different inter frame spaces no guaranteed, hard priorities SIFS (Short Inter Frame Spacing) for short ctrl msgs highest priority, for ACK, CTS, polling response PIFS (PCF IFS) waiting time between DIFS and SIFS (and thus a medium priority) is used for a time-bounded service. An access point polling other nodes only has to wait PIFS for medium access . PIFS is defined as SIFS plus one slot time. medium priority, for time-bounded service using PCF DIFS (DCF, Distributed Coordination Function IFS) used for asynchronous data service within a contention period, defined as SIFS plus two slot times. lowest priority, for asynchronous data service DIFS DIFS PIFS SIFS medium busy contention next frame t direct access if medium is free  DIFS Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

802.11 - CSMA/CA access method I
Freie Universität Berlin Institut of Computer Science CSMA/CA access method I Mobile Communications 2002 contention window (randomized back-off mechanism) DIFS DIFS medium busy next frame direct access if medium is free  DIFS t slot time station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment) if the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending (IFS depends on service type) if the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time) if another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness) This allows for short access delay under light load. But as more and more nodes try to access the medium, additional mechanisms are needed. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller 12

If the medium is busy, nodes have to wait for the duration of DIFS, entering a contention phase afterwards. Each node now chooses a random backoff time within a contention window and delays medium access for this random amount of time. The node continues to sense the medium. As soon as a node senses the channel is busy, it has lost this cycle and has to wait for the next chance, i.e., until the medium is idle again for at least DIFS. But if the randomized additional waiting time for a node is over and the medium is still idle, the node can access the medium immediately . The additional waiting time is measured in multiples of the above-mentioned slots. This additional randomly distributed delay helps to avoid collisions otherwise all stations would try to transmit data after waiting for the medium becoming idle again plus DIFS. to stop being involved in a situation, usually in order to allow other people to deal with it themselves

Obviously, the basic CSMA/CA mechanism is not fair.
Independent of the overall time a node has already waited for transmission; each node has the same chances for transmitting data in the next cycle. To provide fairness, IEEE adds a backoff timer. Again, each node selects a random waiting time within the range of the contention window. If a certain station does not get access to the medium in the first cycle, it stops its backoff timer, waits for the channel to be idle again for DIFS and starts the counter again. As soon as the counter expires, the node accesses the medium. This means that deferred stations do not choose a randomized backoff time again, but continue to count down. Stations that have waited longer have the advantage over stations that have just entered, in that they only have to wait for the remainder of their backoff timer

Figure 7. 11 explains the basic access mechanism of IEEE 802
Figure 7.11 explains the basic access mechanism of IEEE for five stations trying to send a packet at the marked points in time. Station3 has the first request from a higher layer to send a packet (packet arrival at the MAC SAP). The station senses the medium, waits for DIFS and accesses the medium, i.e., sends the packet. Station1, station2, and station5 have to wait at least until the medium is idle for DIFS again after station3 has stopped sending. Now all three stations choose a backoff time within the contention window and start counting down their backoff timers. Prof. Dr.-Ing. Jochen Schiller, MC SS

It shows the random backoff time of station1 as sum of boe and bor
The same is shown for station5. Station2 has a total backoff time of only boe and gets access to the medium first. No residual backoff time for station2 is shown. The backoff timers of station1 and station5 stop, and the stations store their residual backoff times. While a new station has to choose its backoff time from the whole contention window, the two old stations have statistically smaller backoff values. Now station4 wants to send a packet as well, so after DIFS waiting time, three stations try to get access. It can now happen, as shown in the figure, that two stations accidentally have the same backoff time, no matter whether remaining or newly chosen. This results in a collision on the medium as shown..i.e frames are destroyed Prof. Dr.-Ing. Jochen Schiller, MC SS

Station1 stores its residual/remaining backoff time again.
In the last cycle shown station1 finally gets access to the medium, while station4 and station5 have to wait. A collision triggers a retransmission with a new random selection of the backoff time. Still, the access scheme has problems under heavy or light load. Depending on the size of the contention window (CW), the random values can either be too close together (causing - collisions) or the values are too high (causing unnecessary delay). The system tries to adapt to the current number of stations trying to send. The contention window starts with a size of, e.g., CWmin = 7. Each time a collision occurs, indicating a higher load on the medium, the contention window doubles up to a maximum of, e.g., CWmax = 255 (the window can take on the values 7, 15, 31, 63, 127, and 255). The larger the contention window is, the greater is the resolution power of the randomized scheme. Prof. Dr.-Ing. Jochen Schiller, MC SS

802.11 - competing stations - simple version
Freie Universität Berlin Institut of Computer Science competing stations - simple version Mobile Communications 2002 DIFS DIFS DIFS DIFS boe bor boe bor boe busy station1 boe busy station2 busy station3 boe busy boe bor station4 boe bor boe busy boe bor station5 t busy medium not idle (frame, ack etc.) boe elapsed backoff time packet arrival at MAC bor residual backoff time Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Figure 7.12 shows a sender accessing the medium and sending its data.
However, under a light load, a small CW ensures shorter access delays. This algorithm is also called exponential backoff and is already familiar from IEEE CSMA/CD in a similar version. While this process describes the complete access mechanism for broadcast frames, an additional feature is provided by the standard for unicast data transfer. Figure 7.12 shows a sender accessing the medium and sending its data. But now, the receiver answers directly with an acknowledgement (ACK). The receiver accesses the medium after waiting for a duration of SIFS: so no other station can access the medium in the meantime and cause a collision. The other stations have to wait for DIFS plus their backoff time. If no ACK is returned, the sender automatically retransmits the frame. But now the sender has to wait again and compete for the access right. There are no special rules for retransmissions. The number of retransmissions is limited, and final failure is reported to the higher layer. Prof. Dr.-Ing. Jochen Schiller, MC SS

802.11 - CSMA/CA access method II
Freie Universität Berlin Institut of Computer Science CSMA/CA access method II Mobile Communications 2002 Sending unicast packets station has to wait for DIFS before sending data receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC) automatic retransmission of data packets in case of transmission errors Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

802.11 - DFWMAC-DCF with RTS/CTS extension
Freie Universität Berlin Institut of Computer Science DFWMAC-DCF with RTS/CTS extension Mobile Communications 2002 The two stations may sense the channel is idle, send a frame, and cause a collision at the receiver in the middle. To deal with this problem, the standard defines an additional mechanism using two control packets, RTS and CTS. The use of the mechanism is optional; however, every node has to implement the functions to react properly upon reception of RTS/CTS control packets.Sending unicast packets station can send RTS with reservation parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium) acknowledgement via CTS after SIFS by receiver (if ready to receive) sender can now send data at once, acknowledgement via ACK other stations store medium reservations distributed via RTS and CTS Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Figure 7. 13 illustrates the use of RTS and CTS
Figure 7.13 illustrates the use of RTS and CTS. After waiting for DIFS (plus a random backoff time if the medium was busy), the sender can issue a request to send (RTS) control packet. The RTS packet includes the receiver of the data transmission to come and the duration of the whole data transmission. This duration specifies the time interval necessary to transmit the whole data frame and the acknowledgement related to it. Every node receiving this RTS now has to set its net allocation vector (NAV) in accordance with the duration field. The NAV then specifies the earliest point at which the station can try to access the medium again. Prof. Dr.-Ing. Jochen Schiller, MC SS

If the receiver of the data transmission receives the RTS, it answers with a clear to send (CTS) message after waiting for SIFS. This CTS packet contains the duration field again and all stations receiving this packet from the receiver of the intended data transmission have to adjust their NAV. The latter set of receivers need not be the same as the first set receiving the RTS packet. Now all nodes within receiving distance around sender and receiver are informed that they have to wait more time before accessing the medium. Basically, this mechanism reserves the medium for one sender exclusively (this is why it is sometimes called a virtual reservation scheme). Prof. Dr.-Ing. Jochen Schiller, MC SS

The transmission has now been completed, the NAV in each node
Finally, the sender can send the data after SIFS. The receiver waits for SIFS after receiving the data packet and then acknowledges whether the transfer was correct. The transmission has now been completed, the NAV in each node marks the medium as free and the standard cycle can start again. Prof. Dr.-Ing. Jochen Schiller, MC SS

Two or more stations may start sending at the same time (RTS or other data packets).
Using RTS/CTS can result in a non-negligible overhead causing a waste of bandwidth and higher delay An RTS threshold can determine when to use the additional mechanism (basically at larger frame sizes) and when to disable it (short frames). The probability of an erroneous frame is much higher for wireless links than Fibre Optics .,assuming the same frame length. One way to decrease the error probability of frames is to use shorter frames. The MAC layer should have the possibility of adjusting the transmission frame size to the current error rate on the medium. Prof. Dr.-Ing. Jochen Schiller, MC SS

The IEEE 802.11 standard specifies a fragmentation mode
Again, a sender can send an RTS control packet to reserve the medium after a waiting time of DIFS. This RTS packet now includes the duration for the transmission of the first fragment and the corresponding acknowledgement. A certain set of nodes may receive this RTS and set their NAV according to the duration field. The receiver answers with a CTS, again including the duration of the transmission up to the acknowledgement. A (possibly different) set of receivers gets this CTS message and sets the NAV. Prof. Dr.-Ing. Jochen Schiller, MC SS

Fragmentation Mobile Communications 2002 DIFS RTS frag1 frag2 sender SIFS SIFS SIFS SIFS SIFS CTS ACK1 ACK2 receiver NAV (RTS) NAV (CTS) DIFS NAV (frag1) data other stations NAV (ACK1) t contention Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

packet ACK1 including the reservation for the next transmission
The receiver of frag1 answers directly after SIFS with the acknowledgement packet ACK1 including the reservation for the next transmission Again a fourth set of nodes may receive this reservation and adjust their NAV If frag2 was not the last frame of this transmission, it would also include a new duration for the third consecutive transmission. frag2 is the last fragment of this transmission so the sender does not reserve the medium any longer. The receiver acknowledges this second fragment, not reserving the medium again. After ACK2, all nodes can compete for the medium again after having waited for DIFS. The NAV specifies the earliest point at which the station can try to access the medium again.

DFWMAC-PCF with polling (PCF I)
The two access mechanisms presented so far cannot guarantee a maximum access delay or minimum transmission bandwidth. To provide a time-bounded service, the standard specifies a point coordination function (PCF) on top of the standard DCF mechanisms. Using PCF requires an access point that controls medium access and polls the single nodes point co-ordinator in the access point splits the access time into super frame periods as shown in Figure. A super frame comprises a contentionfree period and a contention period. The contention period can be used for the two access mechanisms presented above. At time t0 the contention-free period of the super frame should theoretically start, but another station is still transmitting data (i.e., the medium is busy). This means that PCF also defers/give way/ complies to DCF, and the start of the super frame may be postponed. Prof. Dr.-Ing. Jochen Schiller, MC SS

DFWMAC-PCF with polling (PCF I)
Freie Universität Berlin Institut of Computer Science DFWMAC-PCF with polling (PCF I) Mobile Communications 2002 After the medium has been idle until t1, the point coordinator has to wait for PIFS before accessing the medium. As PIFS is smaller than DIFS, no other station can start sending earlier. The point coordinator now sends data D1 downstream to the first wireless station. This station can answer at once after SIFS After waiting for SIFS again, the point coordinator can poll the second station by sending D2. This station may answer upstream to the coordinator with data U2. Polling continues with the third node. This time the node has nothing to answer and the point coordinator will not receive a packet after SIFS. PIFS stations‘ NAV wireless stations point coordinator D1 U1 SIFS D2 U2 SuperFrame t0 medium busy t1 Prof. Dr.-Ing. Jochen Schiller

After waiting for PIFS, the coordinator can resume polling the stations.
Finally, the point coordinator can issue an end marker (CFend), indicating that the contention period may start again. Using PCF automatically sets the NAV, preventing other stations from sending the contention-free period planned initially would have been from t0 to t3. . t stations‘ NAV wireless stations point coordinator D3 PIFS D4 U4 SIFS CFend contention period contention free period t2 t3 t4 Prof. Dr.-Ing. Jochen Schiller, MC SS

DFWMAC-PCF II Mobile Communications 2002 However, the point coordinator finished polling earlier, shifting the end of the contention-free period to t2. At t4, the cycle starts again with the next super frame. The transmission properties of the whole wireless network are now determined by the polling behavior of the access point. If only PCF is used and polling is distributed evenly, the bandwidth is also distributed evenly among all polled nodes. This would resemble a static, centrally controlled time division multiple access (TDMA) system with time division duplex (TDD) transmission This method results with an overhead if nodes have nothing to send, but the access point polls them permanently. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

MAC frames : 802.11 - Frame format
Freie Universität Berlin Institut of Computer Science MAC frames : Frame format Mobile Communications 2002 Types control frames, management frames, data frames Duration/ID: If the field value is less than 32,768, the duration field contains the value indicating the period of time in which the medium is occupied (in μs). This field is used for setting the NAV for the virtual reservation mechanism using RTS/CTS and during fragmentation. Sequence numbers important against duplicated frames due to lost ACKs bytes 2 2 6 6 6 2 6 0-2312 4 Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Data CRC bits 2 2 4 1 1 1 1 1 1 1 1 Protocol version Type Subtype To DS From DS More Frag Retry Power Mgmt More Data WEP Order Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Addresses Miscellaneous
receiver, transmitter (physical), BSS identifier, sender (logical) Miscellaneous sending time, checksum, frame control, data FRAME CONTROL FIELD Protocol version: This 2 bit field indicates the current protocol version and is fixed to 0 by now. Type: The type field determines the function of a frame: management (=00), control (=01), or data (=10). The value 11 is reserved. Each type has several subtypes as indicated in the following field. Subtype: Example subtypes for management frames are: 0000 for association request, 1000 for beacon. RTS is a control frame with subtype 1011, CTS is coded as User data is transmitted as data frame with subtype 0000. More fragments: This field is set to 1 in all data or management frames that have another fragment of the current MSDU to follow. Retry: If the current frame is a retransmission of an earlier frame, this bit is set to 1 The MSDU is the MAC service data unit that is received from the logical link control (LLC) sub-layer which lies above the medium access control (MAC)

Wired equivalent privacy (WEP): This field indicates that the standard
Power management: This field indicates the mode of a station after successful transmission of a frame. Set to 1 the field indicates that the station goes into power-save mode. If the field is set to 0, the station stays active More data: In general, this field is used to indicate a receiver that a sender has more data to send than the current frame. Wired equivalent privacy (WEP): This field indicates that the standard security mechanism of is applied. Order: If this bit is set to 1 the received frames must be processed in strict order MAC frames can be transmitted between mobile stations; between mobile stations and an access point and between access points over a DS (see Figure 7.3). Two bits within the Frame Control field, ‘to DS’ and ‘from DS’, differentiate these cases and control the meaning of the four addresses used It shows four possible bit values of the DS bits and the associated interpretation of the four address fields.

MAC address format Mobile Communications 2002 DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Special Frames: ACK, RTS, CTS
Acknowledgement Request To Send Clear To Send bytes 2 2 6 4 Frame Control Duration Receiver Address CRC ACK bytes 2 2 6 6 4 Frame Control Duration Receiver Address Transmitter Address CRC RTS bytes 2 2 6 4 Frame Control Duration Receiver Address CRC CTS Prof. Dr.-Ing. Jochen Schiller, MC SS

MAC management It plays a central role in an IEEE 802.11
all functions related to system integration, i.e., integration of a wireless station into a BSS, formation of an ESS, synchronization of stations etc. The following functional groups have been identified and will be discussed in more detail in the following sections: ● Synchronization: Functions to support finding a wireless LAN, synchronization of internal clocks, generation of beacon signals. ● Power management: Functions to control transmitter activity for power conservation, e.g., periodic sleep, buffering, without missing a frame. ● Roaming: Functions for joining a network (association), changing access points, scanning for access points. ● Management information base (MIB): All parameters representing the current state of a wireless station and an access point are stored within a MIB for internal and external access. A MIB can be accessed via standardized protocols such as the simple network management protocol (SNMP). Prof. Dr.-Ing. Jochen Schiller, MC SS

MAC management Mobile Communications 2002 Synchronization Each node of an network maintains an internal clock. To synchronize the clocks of all nodes, IEEE specifies a timing synchronization function (TSF) synchronized clocks are needed for power management, but also for coordination of the PCF and for synchronization of the hopping sequence in an FHSS system. Using PCF, the local timer of a node can predict the start of a super frame, i.e., the contention free and contention period. FHSS physical layers need the same hopping sequences so that all nodes can communicate within a BSS. Within a BSS, timing is conveyed by the (quasi)periodic transmissions of a beacon frame. A beacon contains a timestamp and other management information used for power management and roaming (e.g., identification of the BSS). The timestamp is used by a node to adjust its local clock. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

The node is not required to hear every beacon to stay synchronized
The transmission of a beacon frame is not always periodic because the beacon frame is also deferred if the medium is busy. Within infrastructure-based networks, the access point performs synchronization by transmitting the (quasi)periodic beacon signal, whereas all other wireless nodes adjust their local timer to the time stamp. This represents the simple case shown in Figure 7.18. Prof. Dr.-Ing. Jochen Schiller, MC SS

The access point is not always able to send its beacon B periodically if the medium is busy.
However, the access point always tries to schedule transmissions according to the expected beacon interval (target beacon transmission time). The timestamp of a beacon always reflects the real transmit time, not the scheduled time. For ad-hoc networks, situation is slightly more complicated as they do not have an access point for beacon transmission. In this case, each node maintains its own synchronization timer and starts the transmission of a beacon frame after the beacon interval. Figure 7.19 shows an example where multiple stations try to send their beacon. However, the standard random backoff algorithm is also applied to the beacon frames so only one beacon wins. All other stations now adjust their internal clocks according to the received beacon and suppress their beacons for this cycle. Prof. Dr.-Ing. Jochen Schiller, MC SS

On the top synchronization is to….
If collision occurs, the beacon is lost. In this scenario, the beacon intervals can be shifted slightly because all clocks may vary as may the start of a beacon interval from a node’s point of view. However, after successful synchronization all nodes again have the same consistent view. On the top synchronization is to…. try to find a LAN, try to stay within a LAN timer etc. Prof. Dr.-Ing. Jochen Schiller, MC SS

Power management Wireless devices are battery powered
power-saving mechanisms are crucial for the commercial success Standard LAN protocols assume that stations are always ready to receive data, although receivers are idle most of the time in lightly loaded networks. this permanent readiness of the receiving module is critical for battery life as the receiver current may be up to 100 mA basic idea of IEEE power management is to switch off the transceiver whenever it is not needed. For the sending device this is simple to achieve as the transfer is triggered by the device itself. However, since the power management of a receiver cannot know in advance when the transceiver has to be active for a specific packet, it has to ‘wake up’ the transceiver periodically. Switching off the transceiver should be transparent to existing protocols and should be flexible enough to support different applications. traded-off for battery life.* Longer off-periods save battery life but reduce average throughput and vice versa. Prof. Dr.-Ing. Jochen Schiller, MC SS

basic idea of power saving includes two states for a station:
sleep-mode without missing a message periodic sleep, frame buffering, traffic measurements basic idea of power saving includes two states for a station: sleep and awake, and buffering of data in senders. If a sender intends to communicate with a power-saving station it has to buffer data if the station is asleep. The sleeping station on the other hand has to wake up periodically and stay awake for a certain time. During this time, all senders can announce the destinations of their buffered data frames. If a station detects that it is a destination of a buffered packet it has to stay awake until the transmission takes place. Waking up at the right moment requires the timing synchronization function (TSF) **P.M. in infrastructure-based networks is much simpler compared to ad-hoc networks Prof. Dr.-Ing. Jochen Schiller, MC SS

Mobile Communications 2002 Infrastructure - Power management access point buffers all frames destined for stations operating in power-save mode. With every beacon sent by the access point, a traffic indication map (TIM) is transmitted. TIM contains a list of stations for which unicast data frames are buffered in the access point. TSF assures that the sleeping stations will wake up periodically and listen to the beacon and TIM. If the TIM indicates a unicast frame buffered for the station, the station stays awake for transmission. For multi-cast/broadcast transmission, stations will always stay awake. Another reason for waking up is a frame which has to be transmitted from the station to the access point. A sleeping station still has the TSF timer running. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Figure 7. 20 shows an example with an access point and one station
Figure 7.20 shows an example with an access point and one station. The state of the medium is indicated. Again, the access point transmits a beacon frame each beacon interval. This interval is now the same as the TIM interval. Additionally, the access point maintains a delivery traffic indication map (DTIM) interval for sending broadcast/multicast frames. The DTIM interval is always a multiple of the TIM interval. Prof. Dr.-Ing. Jochen Schiller, MC SS

destination for a buffered frame.
All stations (in the example, only one is shown) wake up prior to an expected TIM or DTIM. In the first case, the access point has to transmit a broadcast frame and the station stays awake to receive it. After receiving the broadcast frame, the station returns to sleeping mode. The station wakes up again just before the next TIM transmission. This time the TIM is delayed due to a busy medium so, the station stays awake. The access point has nothing to send and the station goes back to sleep. At the next TIM interval, the access point indicates that the station is the destination for a buffered frame. The station answers with a PS (power saving) poll and stays awake to receive data. The access point then transmits the data for the station, the station acknowledges the receipt and may also send some data Prof. Dr.-Ing. Jochen Schiller, MC SS

This is acknowledged by the access point
Afterwards, the station switches to sleep mode again. Finally, the access point has more broadcast data to send at the next DTIM interval, which is again deferred by a busy medium. The shorter the TIM interval, the shorter the delay, but the lower the power-saving effect. Prof. Dr.-Ing. Jochen Schiller, MC SS

ad-hoc networks In ad-hoc networks, power management is much more complicated than in infrastructure networks. In this case, there is no access point to buffer data in one location but each station needs the ability to buffer data if it wants to communicate with a power-saving station. All stations now announce a list of buffered frames during a period when they are all awake. Destinations are announced using ad-hoc traffic indication map (ATIMs) – the announcement period is called the ATIM window. Figure 7.21 shows a simple ad-hoc network with two stations. Again, the beacon interval is determined by a distributed function (different stations may send the beacon). Prof. Dr.-Ing. Jochen Schiller, MC SS

Station2 acknowledges this ATIM and stays awake for the transmission.
However, due to this synchronization, all stations within the ad-hoc network wake up at the same time. All stations stay awake for the ATIM interval as shown in the first two steps and go to sleep again if no frame is buffered for them. In the third step, station1 has data buffered for station2. This is indicated in an ATIM transmitted by station1. Station2 acknowledges this ATIM and stays awake for the transmission. After the ATIM window, station1 can transmit the data frame, and station2 acknowledges its receipt. In this case, the stations stay awake for the next beacon. Prof. Dr.-Ing. Jochen Schiller, MC SS

One problem with this approach is that of scale.
If many stations within an ad-hoc network operate in power-save mode, they may also want to transmit their ATIM within the ATIM window. More ATIM transmissions take place, more collisions happen and more stations are deferred. The access delay of large networks is difficult to predict. QoS guarantees can not be given under heavy load. Prof. Dr.-Ing. Jochen Schiller, MC SS

Association/Reassociation
Roaming Association/Reassociation integration into a LAN roaming, i.e. change networks by changing access points scanning, i.e. active search for a network MIB - Management Information Base managing, read, write Prof. Dr.-Ing. Jochen Schiller, MC SS

Roaming Mobile Communications 2002 No or bad connection? Then perform: Scanning (Passive scanning/Active scanning) scan the environment, i.e., listen into the medium for beacon signals or send probes/ enquiries into the medium and wait for an answer Reassociation Request station sends a request to one or several AP(s) Reassociation Response success: AP has answered, station can now participate failure: continue scanning AP accepts Reassociation Request signal the new station to the distribution system the distribution system updates its data base (i.e., location information) typically, the distribution system now informs the old AP so it can release resources The standard IEEE f (Inter Access Point Protocol, IAPP) should provide a compatible solution for all vendors. This also includes load-balancing between access points and key generation for security algorithms based on IEEE 802.1x (IEEE, 2001). Prof. Dr.-Ing. Jochen Schiller

IEEE b Depending on the current interference and the distance between sender and receiver b systems offer 11, 5.5, 2, or 1 Mbit/s. Maximum user data rate is approx 6 Mbit/s. The lower data rates 1 and 2 Mbit/s use the 11-chip Barker sequence. New data rates, 5.5 and 11 Mbit/s, use 8-chip complementary code keying (CCK) Figure 7.22 shows two packet formats standardized for b. The mandatory format is called long PLCP PPDUand is similar to the format illustrated in Figure 7.8. One difference is the rate encoded in the signal field this is encoded in multiples of 100 kbit/s. Thus, 0x0A represents 1 Mbit/s, 0x14 is used for 2 Mbit/s, 0x37 for 5.5 Mbit/s and 0x6E for 11 Mbit/s. Prof. Dr.-Ing. Jochen Schiller, MC SS

Optional short PLCP PPDU format differs in several ways.
The short synchronization field consists of 56 scrambled zeros instead of scrambled ones. The short start frame delimiter SFD consists of a mirrored bit pattern compared to the SFD of the long format: using || (Instead of long). Prof. Dr.-Ing. Jochen Schiller, MC SS

Only the preamble is transmitted at 1 Mbit/s, DBPSK
Only the preamble is transmitted at 1 Mbit/s, DBPSK. The following header is already transmitted at 2 Mbit/s, DQPSK, which is also the lowest available data rate. As Figure 7.22 shows, the length of the overhead is only half for the short frames (96 μs instead of 192 μs). This is useful for, e.g., short, but timecritical, data transmissions. As IEEE b is the most widespread version, some more information is given for practical usage. The standards operates (like the DSSS version of ) on certain frequencies in the 2.4 GHz ISM band. These depend on national regulations. For each channel the center frequency is given. Depending on national restrictions 11 (US/Canada), 13 (Europe with some exceptions) or 14 channels (Japan) can be used. Prof. Dr.-Ing. Jochen Schiller, MC SS

Figure 7.23 illustrates the non-overlapping usage of channels for an IEEE b installation with minimal interference in the US/Canada and Europe. The spacing between the center frequencies should be at least 25 MHz This results in the channels 1, 6, and 11 for the US/Canada or 1, 7, 13 for Europe, respectively. It may be the case that, e.g., travellers from the US cannot use the additional channels (12 and 13) in Europe as their hardware is limited to 11 channels. Users can install overlapping cells for WLANs using the three non- overlapping channels to provide seamless coverage. This is similar to the cell planning for mobile phone systems. Prof. Dr.-Ing. Jochen Schiller, MC SS

Prof. Dr. -Ing. Jochen Schiller, http://www. jochenschiller. de/
Prof. Dr.-Ing. Jochen Schiller, MC SS

WLAN: IEEE b Mobile Communications 2002 Data rate 1, 2, 5.5, 11 Mbit/s, depending on SNR User data rate max. approx. 6 Mbit/s Transmission range 300m outdoor, 30m indoor Max. data rate ~10m indoor Frequency Free 2.4 GHz ISM-band Security Limited, WEP insecure, SSID Cost 100€ adapter, 250€ base station, dropping Availability Many products, many vendors Connection set-up time Connectionless/always on Quality of Service Typ. Best effort, no guarantees (unless polling is used, limited support in products) Manageability Limited (no automated key distribution, sym. Encryption) Special Advantages/Disadvantages Advantage: many installed systems, lot of experience, available worldwide, free ISM-band, many vendors, integrated in laptops, simple system Disadvantage: heavy interference on ISM-band, no service guarantees, slow relative speed only Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

IEEE 802.11a IEEE 802.11a offers up to 54 Mbit/s using OFDM
The FCC (US) regulations offer three different 100 MHz domains for the use of a, each with a different legal maximum power output: 5.15–5.25 GHz/50 mW, 5.25–5.35 GHz/250 mW, and 5.725–5.825 GHz/1W. ETSI (Europe) defines different frequency bands for Europe: 5.15–5.35 GHz and 5.47–5.725 GHz and requires two additional mechanisms for operation: dynamic frequency selection (DFS) and transmit power control (TPC) Maximum transmit power is 200 mW EIRP for the lower frequency band (indoor use) and 1 W EIRP for the higher frequency band (indoor and outdoor use). DFS and TPC are not necessary, if the transmit power stays below 50 mW EIRP and only 5.15–5.25 GHz are used. Japan allows operation in the frequency range 5.15–5.25 GHz and requires carrier sensing every 4 ms to minimize interference. European Telecommunications Standards Institute:: Equivalent Isotropically Radiated Power:

IEEE 802.11a uses the same MAC layer as all 802.11 physical layers do
To be able to offer data rates up to 54 Mbit/s IEEE a uses many different technologies. The system uses 52 subcarriers (48 data + 4 pilot) that are modulated using BPSK, QPSK, 16-QAM, or 64-QAM. To mitigate transmission errors, FEC is applied using coding rates of 1/2, 2/3, or 3/4. Table 7.3 gives an overview of the standardized combinations of modulation and coding schemes together with the resulting data rates. Prof. Dr.-Ing. Jochen Schiller, MC SS

To offer a data rate of 12 Mbit/s, 96 bits are coded into one OFDM symbol.
These 96 bits are distributed over 48 subcarriers :: 2 bits are modulated per sub-carrier using QPSK (2 bits per point in the constellation diagram). Using a coding rate of 1/2 only 48 data bits can be transmitted. Prof. Dr.-Ing. Jochen Schiller, MC SS

7. 24 shows the usage of OFDM in IEEE 802. 11a
7.24 shows the usage of OFDM in IEEE a. Remember, the basic idea of OFDM (or MCM in general) was the reduction of the symbol rate by distributing bits over numerous subcarriers. IEEE a uses a fixed symbol rate of 250,000 symbols per second independent of the data rate (0.8 μs guard interval for ISI mitigation plus 3.2 μs used for data results in a symbol duration of 4 μs). As Figure 7.24 shows, 52 subcarriers are equally spaced around a center frequency. The spacing between the subcarriers is kHz. 26 subcarriers are to the left of the center frequency and 26 are to the right. The center frequency itself is not used as subcarrier. Subcarriers with the numbers –21, –7, 7, and 21 are used for pilot signals to make the signal detection robust against frequency offsets. Prof. Dr.-Ing. Jochen Schiller, MC SS

WLAN: IEEE a Mobile Communications 2002 Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNR User throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54) 6, 12, 24 Mbit/s mandatory Transmission range 100m outdoor, 10m indoor E.g., 54 Mbit/s up to 5 m, 48 up to 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m Frequency Free , , GHz ISM-band Security Limited, WEP insecure, SSID Cost 280€ adapter, 500€ base station Availability Some products, some vendors Connection set-up time Connectionless/always on Quality of Service Typ. best effort, no guarantees (same as all products) Manageability Limited (no automated key distribution, sym. Encryption) Special Advantages/Disadvantages Advantage: fits into 802.x standards, free ISM-band, available, simple system, uses less crowded 5 GHz band Disadvantage: stronger shading due to higher frequency, no QoS Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

IEEE 802.11a – PHY frame format
4 1 12 1 6 16 variable 6 variable bits rate reserved length parity tail service payload tail pad PLCP header PLCP preamble signal data 12 1 variable symbols 6 Mbit/s 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s pseudofield ::: Pad---extra bits

Operating channels for 802.11a / US U-NII
36 40 44 48 52 56 60 64 channel 5150 5180 5200 5220 5240 5260 5280 5300 5320 5350 [MHz] 16.6 MHz center frequency = *channel number [MHz] 149 153 157 161 channel 5725 5745 5765 5785 5805 5825 [MHz] 16.6 MHz Prof. Dr.-Ing. Jochen Schiller, MC SS

OFDM in IEEE 802.11a (and HiperLAN2)
OFDM with 52 used subcarriers (64 in total) 48 data + 4 pilot (plus 12 virtual subcarriers) 312.5 kHz spacing 312.5 kHz pilot -26 -21 -7 -1 1 7 21 26 subcarrier number channel center frequency Prof. Dr.-Ing. Jochen Schiller, MC SS

WLAN: IEEE 802.11 – future developments (08/2002)
Freie Universität Berlin Institut of Computer Science WLAN: IEEE – future developments (08/2002) Mobile Communications 2002 802.11d: Regulatory Domain Update – completed 802.11e: MAC Enhancements – QoS – ongoing Enhance the current MAC to expand support for applications with Quality of Service requirements, and in the capabilities and efficiency of the protocol. 802.11f: Inter-Access Point Protocol – ongoing Establish an Inter-Access Point Protocol for data exchange via the distribution system. 802.11g: Data Rates > 20 Mbit/s at 2.4 GHz; 54 Mbit/s, OFDM – ongoing 802.11h: Spectrum Managed a (DCS, TPC) – ongoing 802.11i: Enhanced Security Mechanisms – ongoing Enhance the current MAC to provide improvements in security. Study Groups 5 GHz (harmonization ETSI/IEEE) – closed Radio Resource Measurements – started High Throughput – started Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

ETSI - HIPERLAN Mobile Communications 2002 ETSI standard European standard, cf. GSM, DECT, ... Enhancement of local Networks and interworking with fixed networks integration of time-sensitive services from the early beginning HIPERLAN family one standard cannot satisfy all requirements range, bandwidth, QoS support commercial constraints HIPERLAN 1 standardized since 1996 – no products! physical layer channel access control layer medium access data link layer HIPERLAN layers OSI layers network layer higher layers logical link IEEE 802.x layers Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Overview: original HIPERLAN protocol family
Freie Universität Berlin Institut of Computer Science Overview: original HIPERLAN protocol family Mobile Communications 2002 HIPERLAN 1 never reached product status, the other standards have been renamed/modfied ! Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - Characteristics
Freie Universität Berlin Institut of Computer Science HIPERLAN 1 - Characteristics Mobile Communications 2002 Data transmission point-to-point, point-to-multipoint, connectionless 23.5 Mbit/s, 1 W power, 2383 byte max. packet size Services asynchronous and time-bounded services with hierarchical priorities compatible with ISO MAC Topology infrastructure or ad-hoc networks transmission range can be larger then coverage of a single node („forwarding“ integrated in mobile terminals) Further mechanisms power saving, encryption, checksums Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - Physical layer
Freie Universität Berlin Institut of Computer Science HIPERLAN 1 - Physical layer Mobile Communications 2002 Scope modulation, demodulation, bit and frame synchronization forward error correction mechanisms measurements of signal strength channel sensing Channels 3 mandatory and 2 optional channels (with their carrier frequencies) mandatory channel 0: GHz channel 1: GHz channel 2: GHz optional channel 3: GHz channel 4: GHz Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - Physical layer frames
Freie Universität Berlin Institut of Computer Science HIPERLAN 1 - Physical layer frames Mobile Communications 2002 Maintaining a high data-rate (23.5 Mbit/s) is power consuming - problematic for mobile terminals packet header with low bit-rate comprising receiver information only receiver(s) address by a packet continue receiving Frame structure LBR (Low Bit-Rate) header with 1.4 Mbit/s 450 bit synchronization minimum 1, maximum 47 frames with 496 bit each for higher velocities of the mobile terminal (> 1.4 m/s) the maximum number of frames has to be reduced Modulation GMSK for high bit-rate, FSK for LBR header HBR LBR synchronization data0 data1 datam-1 . . . Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - CAC sublayer
Freie Universität Berlin Institut of Computer Science HIPERLAN 1 - CAC sublayer Mobile Communications 2002 Channel Access Control (CAC) assure that terminal does not access forbidden channels priority scheme, access with EY-NPMA Priorities 5 priority levels for QoS support QoS is mapped onto a priority level with the help of the packet lifetime (set by an application) if packet lifetime = 0 it makes no sense to forward the packet to the receiver any longer standard start value 500ms, maximum 16000ms if a terminal cannot send the packet due to its current priority, waiting time is permanently subtracted from lifetime based on packet lifetime, waiting time in a sender and number of hops to the receiver, the packet is assigned to one out of five priorities the priority of waiting packets, therefore, rises automatically Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - EY-NPMA I Mobile Communications 2002 EY-NPMA (Elimination Yield Non-preemptive Priority Multiple Access) 3 phases: priority resolution, contention resolution, transmission finding the highest priority every priority corresponds to a time-slot to send in the first phase, the higher the priority the earlier the time-slot to send higher priorities can not be preempted if an earlier time-slot for a higher priority remains empty, stations with the next lower priority might send after this first phase the highest current priority has been determined IPS IPA IES IESV IYS transmission synchronization prioritization contention transmission elimination survival verification elimination burst user data priority detection priority assertion yield listening t Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - EY-NPMA II Mobile Communications 2002 Several terminals can now have the same priority and wish to send contention phase Elimination Burst: all remaining terminals send a burst to eliminate contenders ( , high bit- rate) Elimination Survival Verification: contenders now sense the channel, if the channel is free they can continue, otherwise they have been eliminated Yield Listening: contenders again listen in slots with a nonzero probability, if the terminal senses its slot idle it is free to transmit at the end of the contention phase the important part is now to set the parameters for burst duration and channel sensing (slot-based, exponentially distributed) data transmission the winner can now send its data (however, a small chance of collision remains) if the channel was idle for a longer time (min. for a duration of 1700 bit) a terminal can send at once without using EY-NPMA synchronization using the last data transmission Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - DT-HCPDU/AK-HCPDU
Freie Universität Berlin Institut of Computer Science HIPERLAN 1 - DT-HCPDU/AK-HCPDU Mobile Communications 2002 1 2 3 4 5 6 7 bit LBR 1 1 1 1 1 2 3 4 5 6 7 bit 1 HI AID LBR 1 1 1 1 AID AIDCS 1 HI HDA Acknowledgement HCPDU HDA HDACS BLIR = n BL- HI: HBR-part Indicator HDA: Hashed Destination HCSAP Address HDACS: HDA CheckSum BLIR: Block Length Indicator BLIRCS: BLIR CheckSum TI: Type Indicator BLI: Block Length Indicator HID: HIPERLAN IDentifier DA: Destination Address SA: Source Address UD: User Data ( byte) PAD: PADding CS: CheckSum AID: Acknowledgement IDentifier AIDS: AID CheckSum IRCS 1 bit 1 2 3 4 5 6 7 byte HBR TI BLI = n 1 PLI = m 2 HID 3 - 6 DA 7 - 12 SA UD 19 - (52n-m-4) PAD (52n-m-3) - (52n-4) CS (52n-3) - 52n Data HCPDU Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - MAC layer Mobile Communications 2002 Compatible to ISO MAC Supports time-bounded services via a priority scheme Packet forwarding support of directed (point-to-point) forwarding and broadcast forwarding (if no path information is available) support of QoS while forwarding Encryption mechanisms mechanisms integrated, but without key management Power conservation mechanisms mobile terminals can agree upon awake patterns (e.g., periodic wake-ups to receive data) additionally, some nodes in the networks must be able to buffer data for sleeping terminals and to forward them at the right time (so called stores) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

HIPERLAN 1 - DT-HMPDU Mobile Communications 2002 LI: Length Indicator TI: Type Indicator RL: Residual Lifetime PSN: Sequence Number DA: Destination Address SA: Source Address ADA: Alias Destination Address ASA: Alias Source Address UP: User Priority ML: MSDU Lifetime KID: Key Identifier IV: Initialization Vector UD: User Data, 1–2383 byte SC: Sanity Check (for the unencrypted PDU) bit 1 2 3 4 5 6 7 byte LI = n 1 - 2 TI = 1 3 RL 4 - 5 PSN 6 - 7 DA 8 - 13 SA ADA ASA UP ML 32 ML 33 KID IV 34 IV UD 38 - (n-2) SC (n-1) - n n= 40–2422 Data HMPDU Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Information bases Mobile Communications 2002 Route Information Base (RIB) - how to reach a destination [destination, next hop, distance] Neighbor Information Base (NIB) - status of direct neighbors [neighbor, status] Hello Information Base (HIB) - status of destination (via next hop) [destination, status, next hop] Alias Information Base (AIB) - address of nodes outside the net [original MSAP address, alias MSAP address] Source Multipoint Relay Information Base (SMRIB) - current MP status [local multipoint forwarder, multipoint relay set] Topology Information Base (TIB) - current HIPERLAN topology [destination, forwarder, sequence] Duplicate Detection Information Base (DDIB) - remove duplicates [source, sequence] Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Ad-hoc networks using HIPERLAN 1
Freie Universität Berlin Institut of Computer Science Ad-hoc networks using HIPERLAN 1 Mobile Communications 2002 Information Bases (IB): RIB: Route NIB: Neighbor HIB: Hello AIB: Alias SMRIB: Source Multipoint Relay TIB: Topology DDIB: Duplicate Detection RIB NIB HIB AIB DDIB 2 1 Forwarder RIB NIB HIB AIB SMRIB TIB DDIB 4 3 Forwarder RIB NIB HIB AIB DDIB 5 RIB NIB HIB AIB DDIB RIB NIB HIB AIB SMRIB TIB DDIB RIB NIB HIB AIB SMRIB TIB DDIB 6 Forwarder neighborhood (i.e., within radio range) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Some history: Why wireless ATM?
seamless connection to wired ATM, a integrated services high-performance network supporting different types a traffic streams ATM networks scale well: private and corporate LANs, WAN B-ISDN uses ATM as backbone infrastructure and integrates several different services in one universal system mobile phones and mobile communications have an ever increasing importance in everyday life current wireless LANs do not offer adequate support for multimedia data streams merging mobile communication and ATM leads to wireless ATM from a telecommunication provider point of view goal: seamless integration of mobility into B-ISDN Problem: very high complexity of the system – never reached products Prof. Dr.-Ing. Jochen Schiller, MC SS

ATM - basic principle Mobile Communications 2002 favored by the telecommunication industry for advanced high-performance networks, e.g., B-ISDN, as transport mechanism statistical (asynchronous, on demand) TDM (ATDM, STDM) cell header determines the connection the user data belongs to mixing of different cell-rates is possible different bit-rates, constant or variable, feasible interesting for data sources with varying bit-rate: e.g., guaranteed minimum bit-rate additionally bursty traffic if allowed by the network ATM cell: [byte] cell header user data connection identifier, checksum etc. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Cell-based transmission
Freie Universität Berlin Institut of Computer Science Cell-based transmission Mobile Communications 2002 asynchronous, cell-based transmission as basis for ATM continuous cell-stream additional cells necessary for operation and maintenance of the network (OAM cells; Operation and Maintenance) OAM cells can be inserted after fixed intervals to create a logical frame structure if a station has no data to send it automatically inserts idle cells that can be discarded at every intermediate system without further notice if no synchronous frame is available for the transport of cells (e.g., SDH or Sonet) cell boundaries have to be detected separately (e.g., via the checksum in the cell header) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

B-ISDN protocol reference model
Freie Universität Berlin Institut of Computer Science B-ISDN protocol reference model Mobile Communications 2002 3 dimensional reference model three vertical planes (columns) user plane control plane management plane three hierarchical layers physical layer ATM layer ATM adaptation layer Out-of-Band-Signaling: user data is transmitted separately from control information management plane control user plane plane higher higher layers layers plane management layer management ATM adaptation layer ATM layer physical layer layers planes Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

ATM layers Physical layer, consisting of two sub-layers ATM layer
physical medium dependent sub-layer coding bit timing transmission transmission convergence sub-layer HEC (Header Error Correction) sequence generation and verification transmission frame adaptation, generation, and recovery cell delineation, cell rate decoupling ATM layer cell multiplexing/demultiplexing VPI/VCI translation cell header generation and verification GFC (Generic Flow Control) ATM adaptation layer (AAL) Prof. Dr.-Ing. Jochen Schiller, MC SS

ATM adaptation layer (AAL)
Provides different service classes on top of ATM based on: bit rate: constant bit rate: e.g. traditional telephone line variable bit rate: e.g. data communication, compressed video time constraints between sender and receiver: with time constraints: e.g. real-time applications, interactive voice and video without time constraints: e.g. mail, file transfer mode of connection: connection oriented or connectionless AAL consists of two sub-layers: Convergence Sublayer (CS): service dependent adaptation Common Part Convergence Sublayer (CPCS) Service Specific Convergence Sublayer (SSCS) Segmentation and Reassembly Sublayer (SAR) sub-layers can be empty Prof. Dr.-Ing. Jochen Schiller, MC SS

ATM and AAL connections
Freie Universität Berlin Institut of Computer Science ATM and AAL connections Mobile Communications 2002 ATM layer: service independent transport of ATM cells multiplex and demultiplex functionality AAL layer: support of different services end-system A end-system B service dependent AAL connections AAL AAL service independent ATM connections ATM ATM physical layer physical layer ATM network application Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

ATM Forum Wireless ATM Working Group
ATM Forum founded the Wireless ATM Working Group June 1996 Task: development of specifications to enable the use of ATM technology also for wireless networks with a large coverage of current network scenarios (private and public, local and global) compatibility to existing ATM Forum standards important it should be possible to easily upgrade existing ATM networks with mobility functions and radio access two sub-groups of work items Radio Access Layer (RAL) Protocols radio access layer wireless media access control wireless data link control radio resource control handover issues Mobile ATM Protocol Extensions handover signaling location management mobile routing traffic and QoS Control network management Prof. Dr.-Ing. Jochen Schiller, MC SS

WATM services Office environment
multimedia conferencing, online multimedia database access Universities, schools, training centers distance learning, teaching Industry database connection, surveillance, real-time factory management Hospitals reliable, high-bandwidth network, medical images, remote monitoring Home high-bandwidth interconnect of devices (TV, CD, PC, ...) Networked vehicles trucks, aircraft etc. interconnect, platooning, intelligent roads Prof. Dr.-Ing. Jochen Schiller, MC SS

WATM components WMT (Wireless Mobile ATM Terminal)
RAS (Radio Access System) EMAS-E (End-user Mobility-supporting ATM Switch - Edge) EMAS-N (End-user Mobility-supporting ATM Switch - Network) M-NNI (Network-to-Network Interface with Mobility support) LS (Location Server) AUS (Authentication Server) Prof. Dr.-Ing. Jochen Schiller, MC SS

Reference model EMAS-N WMT RAS EMAS-E M-NNI LS AUS

User plane protocol layers
WATM terminal adapter MATM terminal RAS EMAS -E -N ATM- Switch fixed end system radio segment fixed network segment user process user process AAL AAL ATM ATM RAL PHY ATM- CL ATM PHY ATM PHY ATM PHY ATM ATM- CL RAL PHY Prof. Dr.-Ing. Jochen Schiller, MC SS

Control plane protocol layers
WATM terminal adapter MATM terminal RAS EMAS -E -N ATM- Switch fixed end system radio segment fixed network segment RAL M-ATM SAAL SIG, M-UNI ATM- CL ATM PHY SAAL SIG, M-UNI, M-PNNI ATM PHY SAAL SIG, M-PNNI ATM PHY SAAL SIG, PNNI, UNI ATM PHY SAAL SIG, UNI ATM RAL PHY ATM- CL Prof. Dr.-Ing. Jochen Schiller, MC SS

Reference model with further access scenarios I
1: wireless ad-hoc ATM network 2: wireless mobile ATM terminals 3: mobile ATM terminals 4: mobile ATM switches 5: fixed ATM terminals 6: fixed wireless ATM terminals WMT: wireless mobile terminal WT: wireless terminal MT: mobile terminal T: terminal AP: access point EMAS: end-user mobility supporting ATM switch (-E: edge, -N: network) NMAS: network mobility supporting ATM switch MS: mobile ATM switch Prof. Dr.-Ing. Jochen Schiller, MC SS

Reference model with further access scenarios II
WMT 1 ACT WMT RAS 2 EMAS -E EMAS -N T 5 WMT RAS EMAS -E 6 MT WT 3 RAS NMAS MS RAS RAS T 4 Prof. Dr.-Ing. Jochen Schiller, MC SS

BRAN – Broadband Radio Access Networks
Motivation deregulation, privatization, new companies, new services How to reach the customer? alternatives: xDSL, cable, satellite, radio Radio access flexible (supports traffic mix, multiplexing for higher efficiency, can be asymmetrical) quick installation economic (incremental growth possible) Market private customers (Internet access, tele-xy...) small and medium sized business (Internet, MM conferencing, VPN) Scope of standardization access networks, indoor/campus mobility, Mbit/s, 50 m-5 km coordination with ATM Forum, IETF, ETSI, IEEE, .... Prof. Dr.-Ing. Jochen Schiller, MC SS

Broadband network types
Common characteristics ATM QoS (CBR, VBR, UBR, ABR) HIPERLAN/2 short range (< 200 m), indoor/campus, 25 Mbit/s user data rate access to telecommunication systems, multimedia applications, mobility (<10 m/s) HIPERACCESS wider range (< 5 km), outdoor, 25 Mbit/s user data rate fixed radio links to customers (“last mile”), alternative to xDSL or cable modem, quick installation Several (proprietary) products exist with 155 Mbit/s plus QoS HIPERLINK – currently no activities intermediate link, 155 Mbit/s connection of HIPERLAN access points or connection between HIPERACCESS nodes Prof. Dr.-Ing. Jochen Schiller, MC SS

BRAN and legacy networks
Independence BRAN as access network independent from the fixed network Interworking of TCP/IP and ATM under study Layered model Network Convergence Sub-layer as superset of all requirements for IP and ATM Coordination IETF (TCP/IP) ATM forum (ATM) ETSI (UMTS) CEPT, ITU-R, (radio frequencies) core network ATM core network IP network convergence sublayer BRAN data link control BRAN PHY-1 BRAN PHY-2 ... Prof. Dr.-Ing. Jochen Schiller, MC SS

HiperLAN2 Official name: BRAN HIPERLAN Type 2
H/2, HIPERLAN/2 also used High data rates for users More efficient than a Connection oriented QoS support Dynamic frequency selection Security support Strong encryption/authentication Mobility support Network and application independent convergence layers for Ethernet, IEEE 1394, ATM, 3G Power save modes Plug and Play Prof. Dr.-Ing. Jochen Schiller, MC SS

HiperLAN2 architecture and handover scenarios
AP MT1 Core Network (Ethernet, Firewire, ATM, UMTS) APT APC 1 MT2 3 AP MT3 APT APC 2 MT4 APT Prof. Dr.-Ing. Jochen Schiller, MC SS

Centralized vs. direct mode
AP AP/CC control control control data MT1 MT2 MT1 MT2 MT1 data MT2 +CC data control Centralized Direct Prof. Dr.-Ing. Jochen Schiller, MC SS

HiperLAN2 protocol stack
Higher layers Convergence layer DLC control SAP DLC user SAP Data link control - basic data transport function Radio link control sublayer Radio resource control Assoc. control DLC conn. control Scope of HiperLAN2 standards Error control Radio link control Medium access control Physical layer Prof. Dr.-Ing. Jochen Schiller, MC SS

Physical layer reference configuration
PDU train from DLC (PSDU) scrambling FEC coding interleaving mapping OFDM PHY bursts (PPDU) radio transmitter Prof. Dr.-Ing. Jochen Schiller, MC SS

Operating channels of HiperLAN2 in Europe
36 40 44 48 52 56 60 64 channel 5150 5180 5200 5220 5240 5260 5280 5300 5320 5350 [MHz] 16.6 MHz 100 104 108 112 116 120 124 128 132 136 140 channel 5470 5500 5520 5540 5560 5580 5600 5620 5640 5660 5680 5700 5725 16.6 MHz [MHz] center frequency = *channel number [MHz] Prof. Dr.-Ing. Jochen Schiller, MC SS

Basic structure of HiperLAN2 MAC frames
2 ms 2 ms 2 ms 2 ms TDD, 500 OFDM symbols per frame MAC frame MAC frame MAC frame MAC frame . . . broadcast phase downlink phase uplink phase random access phase variable variable variable 2 406 24 bit LCH PDU type payload CRC LCH transfer syntax 2 10 396 24 bit LCH PDU type sequence number payload CRC UDCH transfer syntax (long PDU) 54 byte Prof. Dr.-Ing. Jochen Schiller, MC SS

Valid configurations of HiperLAN2 MAC frames
2 ms 2 ms 2 ms 2 ms MAC frame MAC frame MAC frame MAC frame . . . random access broadcast downlink uplink BCH FCH ACH DL phase DiL phase UL phase RCHs Valid combinations of MAC frames for a single sector AP BCH FCH ACH DiL phase UL phase RCHs BCH FCH ACH DL phase UL phase RCHs BCH FCH ACH UL phase RCHs BCH FCH ACH DL phase DiL phase RCHs BCH FCH ACH DiL phase RCHs BCH FCH ACH DL phase RCHs BCH FCH ACH RCHs Prof. Dr.-Ing. Jochen Schiller, MC SS

Mapping of logical and transport channels
BCCH FCCH RFCH LCCH RBCH DCCH UDCH UBCH UMCH downlink BCH FCH ACH SCH LCH UDCH DCCH LCCH ASCH UDCH UBCH UMCH DCCH RBCH LCCH LCH SCH RCH LCH SCH uplink direct link Prof. Dr.-Ing. Jochen Schiller, MC SS

Bluetooth Mobile Communications 2002 Idea Universal radio interface for ad-hoc wireless connectivity Interconnecting computer and peripherals, handheld devices, PDAs, cell phones – replacement of IrDA Embedded in other devices, goal: 5€/device (2002: 50€/USB bluetooth) Short range (10 m), low power consumption, license-free 2.45 GHz ISM Voice and data transmission, approx. 1 Mbit/s gross data rate One of the first modules (Ericsson). Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Bluetooth Mobile Communications 2002 History 1994: Ericsson (Mattison/Haartsen), “MC-link” project Renaming of the project: Bluetooth according to Harald “Blåtand” Gormsen [son of Gorm], King of Denmark in the 10th century 1998: foundation of Bluetooth SIG, 1999: erection of a rune stone at Ercisson/Lund ;-) 2001: first consumer products for mass market, spec. version 1.1 released Special Interest Group Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola > 2500 members Common specification and certification of products (was: ) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

History and hi-tech… Mobile Communications 2002 1999: Ericsson mobile communications AB reste denna sten till minne av Harald Blåtand, som fick ge sitt namn åt en ny teknologi för trådlös, mobil kommunikation. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

…and the real rune stone
Freie Universität Berlin Institut of Computer Science …and the real rune stone Mobile Communications 2002 Located in Jelling, Denmark, erected by King Harald “Blåtand” in memory of his parents. The stone has three sides – one side showing a picture of Christ. Inscription: "Harald king executes these sepulchral monuments after Gorm, his father and Thyra, his mother. The Harald who won the whole of Denmark and Norway and turned the Danes to Christianity." This could be the “original” colors of the stone. Inscription: “auk tani karthi kristna” (and made the Danes Christians) Btw: Blåtand means “of dark complexion” (not having a blue tooth…) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Characteristics Mobile Communications 2002 2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing Channel 0: 2402 MHz … channel 78: 2480 MHz G-FSK modulation, mW transmit power FHSS and TDD Frequency hopping with 1600 hops/s Hopping sequence in a pseudo random fashion, determined by a master Time division duplex for send/receive separation Voice link – SCO (Synchronous Connection Oriented) FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, circuit switched Data link – ACL (Asynchronous ConnectionLess) Asynchronous, fast acknowledge, point-to-multipoint, up to kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched Topology Overlapping piconets (stars) forming a scatternet Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Piconet Mobile Communications 2002 Collection of devices connected in an ad hoc fashion One unit acts as master and the others as slaves for the lifetime of the piconet Master determines hopping pattern, slaves have to synchronize Each piconet has a unique hopping pattern Participation in a piconet = synchronization to hopping sequence Each piconet has one master and up to 7 simultaneous slaves (> 200 could be parked) P S S M P SB S P SB M=Master S=Slave P=Parked SB=Standby Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Forming a piconet Mobile Communications 2002 All devices in a piconet hop together Master gives slaves its clock and device ID Hopping pattern: determined by device ID (48 bit, unique worldwide) Phase in hopping pattern determined by clock Addressing Active Member Address (AMA, 3 bit) Parked Member Address (PMA, 8 bit)    P  S SB  SB  S   SB   M P SB SB    SB  S   SB SB  P  SB SB SB Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Scatternet Mobile Communications 2002 Linking of multiple co-located piconets through the sharing of common master or slave devices Devices can be slave in one piconet and master of another Communication between piconets Devices jumping back and forth between the piconets Piconets (each with a capacity of < 1 Mbit/s) P S S S P P M M SB S M=Master S=Slave P=Parked SB=Standby P SB SB S Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Bluetooth protocol stack
Freie Universität Berlin Institut of Computer Science Bluetooth protocol stack Mobile Communications 2002 audio apps. NW apps. vCal/vCard telephony apps. mgmnt. apps. TCP/UDP OBEX AT modem commands TCS BIN SDP Control IP BNEP PPP Audio RFCOMM (serial line interface) Logical Link Control and Adaptation Protocol (L2CAP) Host Controller Interface Link Manager Baseband Radio AT: attention sequence OBEX: object exchange TCS BIN: telephony control protocol specification – binary BNEP: Bluetooth network encapsulation protocol SDP: service discovery protocol RFCOMM: radio frequency comm. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Frequency selection during data transmission
fk fk+1 fk+2 fk+3 fk+4 fk+5 fk+6 M S M S M S M t fk fk+3 fk+4 fk+5 fk+6 M S M S M t fk fk+1 fk+6 M S M t Prof. Dr.-Ing. Jochen Schiller, MC SS

Baseband Mobile Communications 2002 Piconet/channel definition Low-level packet definition Access code Channel, device access, e.g., derived from master Packet header 1/3-FEC, active member address (broadcast + 7 slaves), link type, alternating bit ARQ/SEQ, checksum 68(72) 54 0-2745 bits access code packet header payload 4 64 (4) 3 4 1 1 1 8 bits preamble sync. (trailer) AM address type flow ARQN SEQN HEC Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

SCO payload types payload (30) HV1 audio (10) FEC (20) HV2 audio (20)
DV audio (10) header (1) payload (0-9) 2/3 FEC CRC (2) (bytes) Prof. Dr.-Ing. Jochen Schiller, MC SS

ACL Payload types payload (0-343) header (1/2) payload (0-339) CRC (2)
DM1 header (1) payload (0-17) 2/3 FEC CRC (2) DH1 header (1) payload (0-27) CRC (2) (bytes) DM3 header (2) payload (0-121) 2/3 FEC CRC (2) DH3 header (2) payload (0-183) CRC (2) DM5 header (2) payload (0-224) 2/3 FEC CRC (2) DH5 header (2) payload (0-339) CRC (2) AUX1 header (1) payload (0-29) Prof. Dr.-Ing. Jochen Schiller, MC SS

Baseband data rates Mobile Communications 2002 Payload User Symmetric Asymmetric Header Payload max. Rate max. Rate [kbit/s] Type [byte] [byte] FEC CRC [kbit/s] Forward Reverse DM /3 yes DH no yes DM /3 yes DH no yes DM /3 yes DH no yes AUX no no HV1 na 10 1/3 no 64.0 HV2 na 20 2/3 no 64.0 HV3 na 30 no no 64.0 DV 1 D 10+(0-9) D 2/3 D yes D D ACL 1 slot 3 slot 5 slot SCO Data Medium/High rate, High-quality Voice, Data and Voice Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Baseband link types Mobile Communications 2002 Polling-based TDD packet transmission 625µs slots, master polls slaves SCO (Synchronous Connection Oriented) – Voice Periodic single slot packet assignment, 64 kbit/s full-duplex, point-to-point ACL (Asynchronous ConnectionLess) – Data Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint SCO ACL SCO ACL SCO ACL SCO ACL MASTER f0 f4 f6 f8 f12 f14 f18 f20 SLAVE 1 f1 f7 f9 f13 f19 SLAVE 2 f5 f17 f21 Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Robustness Mobile Communications 2002 Slow frequency hopping with hopping patterns determined by a master Protection from interference on certain frequencies Separation from other piconets (FH-CDMA) Retransmission ACL only, very fast Forward Error Correction SCO and ACL Error in payload (not header!) NAK ACK MASTER A C C F H SLAVE 1 B D E SLAVE 2 G G Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Baseband states of a Bluetooth device
Freie Universität Berlin Institut of Computer Science Baseband states of a Bluetooth device Mobile Communications 2002 standby unconnected inquiry page connecting detach transmit AMA connected AMA active park PMA hold AMA sniff AMA low power Standby: do nothing Inquire: search for other devices Page: connect to a specific device Connected: participate in a piconet Park: release AMA, get PMA Sniff: listen periodically, not each slot Hold: stop ACL, SCO still possible, possibly participate in another piconet Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Example: Power consumption/CSR BlueCore2
Freie Universität Berlin Institut of Computer Science Example: Power consumption/CSR BlueCore2 Mobile Communications 2002 Typical Average Current Consumption (1) VDD=1.8V Temperature = 20°C Mode SCO connection HV3 (1s interval Sniff Mode) (Slave) mA SCO connection HV3 (1s interval Sniff Mode) (Master) 26.0 mA SCO connection HV1 (Slave) mA SCO connection HV1 (Master) mA ACL data transfer 115.2kbps UART (Master) mA ACL data transfer 720kbps USB (Slave) mA ACL data transfer 720kbps USB (Master) mA ACL connection, Sniff Mode 40ms interval, 38.4kbps UART 4.0 mA ACL connection, Sniff Mode 1.28s interval, 38.4kbps UART 0.5 mA Parked Slave, 1.28s beacon interval, 38.4kbps UART 0.6 mA Standby Mode (Connected to host, no RF activity) 47.0 µA Deep Sleep Mode(2) µA Notes: (1) Current consumption is the sum of both BC212015A and the flash. (2) Current consumption is for the BC212015A device only. (More: ) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Example: Bluetooth/USB adapter (2002: 50€)

L2CAP - Logical Link Control and Adaptation Protocol
Freie Universität Berlin Institut of Computer Science L2CAP - Logical Link Control and Adaptation Protocol Mobile Communications 2002 Simple data link protocol on top of baseband Connection oriented, connectionless, and signalling channels Protocol multiplexing RFCOMM, SDP, telephony control Segmentation & reassembly Up to 64kbyte user data, 16 bit CRC used from baseband QoS flow specification per channel Follows RFC 1363, specifies delay, jitter, bursts, bandwidth Group abstraction Create/close group, add/remove member Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

L2CAP logical channels Master Slave Slave L2CAP L2CAP L2CAP baseband
1 1 d d d d 1 1 d d 2 baseband baseband baseband signalling ACL connectionless connection-oriented Prof. Dr.-Ing. Jochen Schiller, MC SS

L2CAP packet formats Connectionless PDU 2 2 2 0-65533 bytes length
CID=2 PSM payload Connection-oriented PDU 2 2 bytes length CID payload Signalling command PDU 2 2 bytes length CID=1 One or more commands 1 1 2 0 code ID length data Prof. Dr.-Ing. Jochen Schiller, MC SS

Security Mobile Communications 2002 User input (initialization) PIN (1-16 byte) Pairing PIN (1-16 byte) Authentication key generation (possibly permanent storage) E2 E2 link key (128 bit) Authentication link key (128 bit) Encryption key generation (temporary storage) E3 E3 encryption key (128 bit) Encryption encryption key (128 bit) Keystream generator Keystream generator Ciphering payload key payload key Cipher data Data Data Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

SDP – Service Discovery Protocol
Freie Universität Berlin Institut of Computer Science SDP – Service Discovery Protocol Mobile Communications 2002 Inquiry/response protocol for discovering services Searching for and browsing services in radio proximity Adapted to the highly dynamic environment Can be complemented by others like SLP, Jini, Salutation, … Defines discovery only, not the usage of services Caching of discovered services Gradual discovery Service record format Information about services provided by attributes Attributes are composed of an 16 bit ID (name) and a value values may be derived from 128 bit Universally Unique Identifiers (UUID) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Additional protocols to support legacy protocols/apps.
Freie Universität Berlin Institut of Computer Science Additional protocols to support legacy protocols/apps. Mobile Communications 2002 RFCOMM Emulation of a serial port (supports a large base of legacy applications) Allows multiple ports over a single physical channel Telephony Control Protocol Specification (TCS) Call control (setup, release) Group management OBEX Exchange of objects, IrDA replacement WAP Interacting with applications on cellular phones Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Profiles Mobile Communications 2002 Represent default solutions for a certain usage model Vertical slice through the protocol stack Basis for interoperability Generic Access Profile Service Discovery Application Profile Cordless Telephony Profile Intercom Profile Serial Port Profile Headset Profile Dial-up Networking Profile Fax Profile LAN Access Profile Generic Object Exchange Profile Object Push Profile File Transfer Profile Synchronization Profile Applications Protocols Profiles Additional Profiles Advanced Audio Distribution PAN Audio Video Remote Control Basic Printing Basic Imaging Extended Service Discovery Generic Audio Video Distribution Hands Free Hardcopy Cable Replacement Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

WPAN: IEEE 802.15-1 – Bluetooth
Freie Universität Berlin Institut of Computer Science WPAN: IEEE – Bluetooth Mobile Communications 2002 Data rate Synchronous, connection-oriented: 64 kbit/s Asynchronous, connectionless 433.9 kbit/s symmetric 723.2 / 57.6 kbit/s asymmetric Transmission range POS (Personal Operating Space) up to 10 m with special transceivers up to 100 m Frequency Free 2.4 GHz ISM-band Security Challenge/response (SAFER+), hopping sequence Cost 50€ adapter, drop to 5€ if integrated Availability Integrated into some products, several vendors Connection set-up time Depends on power-mode Max. 2.56s, avg. 0.64s Quality of Service Guarantees, ARQ/FEC Manageability Public/private keys needed, key management not specified, simple system integration Special Advantages/Disadvantages Advantage: already integrated into several products, available worldwide, free ISM-band, several vendors, simple system, simple ad-hoc networking, peer to peer, scatternets Disadvantage: interference on ISM-band, limited range, max. 8 devices/network&master, high set-up latency Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

WPAN: IEEE 802.15 – future developments 1
Freie Universität Berlin Institut of Computer Science WPAN: IEEE – future developments 1 Mobile Communications 2002 : Coexistance Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local Area Networks (802.11), quantify the mutual interference : High-Rate Standard for high-rate (20Mbit/s or greater) WPANs, while still low-power/low-cost Data Rates: 11, 22, 33, 44, 55 Mbit/s Quality of Service isochronous protocol Ad hoc peer-to-peer networking Security Low power consumption Low cost Designed to meet the demanding requirements of portable consumer imaging and multimedia applications Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

WPAN: IEEE 802.15 – future developments 2
Freie Universität Berlin Institut of Computer Science WPAN: IEEE – future developments 2 Mobile Communications 2002 : Low-Rate, Very Low-Power Low data rate solution with multi-month to multi-year battery life and very low complexity Potential applications are sensors, interactive toys, smart badges, remote controls, and home automation Data rates of kbit/s, latency down to 15 ms Master-Slave or Peer-to-Peer operation Support for critical latency devices, such as joysticks CSMA/CA channel access (data centric), slotted (beacon) or unslotted Automatic network establishment by the PAN coordinator Dynamic device addressing, flexible addressing format Fully handshaked protocol for transfer reliability Power management to ensure low power consumption 16 channels in the 2.4 GHz ISM band, 10 channels in the 915 MHz US ISM band and one channel in the European 868 MHz band Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

WLAN: Home RF Mobile Communications 2002 Data rate 0.8, 1.6, 5, 10 Mbit/s Transmission range 300m outdoor, 30m indoor Frequency 2.4 GHz ISM Security Strong encryption, no open access Cost Adapter 130€, base station 230€ Availability Several products from different vendors Connection set-up time 10 ms bounded latency Quality of Service Up to 8 streams A/V, up to 8 voice streams, priorities, best-effort Manageability Like DECT & 802-LANs Special Advantages/Disadvantages Advantage: extended QoS support, host/client and peer/peer, power saving, security Disadvantage: future uncertain due to DECT-only devices plus a/b for data Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

RF Controllers – ISM bands
Freie Universität Berlin Institut of Computer Science RF Controllers – ISM bands Mobile Communications 2002 Data rate Typ. up to 115 kbit/s (serial interface) Transmission range 5-100 m, depending on power (typ mW) Frequency Typ. 27 (EU, US), 315 (US), 418 (EU), 426 (Japan), 433 (EU), 868 (EU), 915 (US) MHz (depending on regulations) Security Some products with added processors Cost Cheap: 10€-50€ Availability Many products, many vendors Connection set-up time N/A Quality of Service none Manageability Very simple, same as serial interface Special Advantages/Disadvantages Advantage: very low cost, large experience, high volume available Disadvantage: no QoS, crowded ISM bands (particularly 27 and 433 MHz), typ. no Medium Access Control, 418 MHz experiences interference with TETRA Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

RFID – Radio Frequency Identification (1)
Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (1) Mobile Communications 2002 Data rate Transmission of ID only (e.g., 48 bit, 64kbit, 1 Mbit) 9.6 – 115 kbit/s Transmission range Passive: up to 3 m Active: up to m Simultaneous detection of up to, e.g., 256 tags, scanning of, e.g., 40 tags/s Frequency 125 kHz, MHz, 433 MHz, 2.4 GHz, 5.8 GHz and many others Security Application dependent, typ. no crypt. on RFID device Cost Very cheap tags, down to 1€ (passive) Availability Many products, many vendors Connection set-up time Depends on product/medium access scheme (typ. 2 ms per device) Quality of Service none Manageability Very simple, same as serial interface Special Advantages/Disadvantages Advantage: extremely low cost, large experience, high volume available, no power for passive RFIDs needed, large variety of products, relative speeds up to 300 km/h, broad temp. range Disadvantage: no QoS, simple denial of service, crowded ISM bands, typ. one-way (activation/ transmission of ID) Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (2) Mobile Communications 2002 Function Standard: In response to a radio interrogation signal from a reader (base station) the RFID tags transmit their ID Enhanced: additionally data can be sent to the tags, different media access schemes (collision avoidance) Features No line-of sight required (compared to, e.g., laser scanners) RFID tags withstand difficult environmental conditions (sunlight, cold, frost, dirt etc.) Products available with read/write memory, smart-card capabilities Categories Passive RFID: operating power comes from the reader over the air which is feasible up to distances of 3 m, low price (1€) Active RFID: battery powered, distances up to 100 m Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (3) Mobile Communications 2002 Applications Total asset visibility: tracking of goods during manufacturing, localization of pallets, goods etc. Loyalty cards: customers use RFID tags for payment at, e.g., gas stations, collection of buying patterns Automated toll collection: RFIDs mounted in windshields allow commuters to drive through toll plazas without stopping Others: access control, animal identification, tracking of hazardous material, inventory control, warehouse management, ... Local Positioning Systems GPS useless indoors or underground, problematic in cities with high buildings RFID tags transmit signals, receivers estimate the tag location by measuring the signal‘s time of flight Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (4) Mobile Communications 2002 Security Denial-of-Service attacks are always possible Interference of the wireless transmission, shielding of transceivers IDs via manufacturing or one time programming Key exchange via, e.g., RSA possible, encryption via, e.g., AES Future Trends RTLS: Real-Time Locating System – big efforts to make total asset visibility come true Integration of RFID technology into the manufacturing, distribution and logistics chain Creation of „electronic manifests“ at item or package level (embedded inexpensive passive RFID tags) 3D tracking of children, patients Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (5) Mobile Communications 2002 Devices and Companies AXCESS Inc., Checkpoint Systems Group, GEMPLUS, Intermec/Intellitag, I-Ray Technologies, RF Code, Texas Instruments, WhereNet, Wireless Mountain, XCI, Only a very small selection… Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (6) Mobile Communications 2002 Example Product: Intermec RFID UHF OEM Reader Read range up to 7m Anticollision algorithm allows for scanning of 40 tags per second regardless of the number of tags within the reading zone US: unlicensed 915 MHz, Frequency Hopping Read: 8 byte < 32 ms Write: 1 byte < 100ms Example Product: Wireless Mountain Spider Proprietary sparse code anti-collision algorithm Detection range 15 m indoor, 100 m line-of-sight > 1 billion distinct codes Read rate > 75 tags/s Operates at 308 MHz Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (7) Mobile Communications 2002 Relevant Standards American National Standards Institute ANSI, Automatic Identification and Data Capture Techniques JTC 1/SC 31, European Radiocommunications Office ERO, European Telecommunications Standards Institute ETSI, Identification Cards and related devices JTC 1/SC 17, Identification and communication ISO TC 104 / SC 4, Road Transport and Traffic Telematics CEN TC 278, Transport Information and Control Systems ISO/TC204, Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science RFID – Radio Frequency Identification (8) Mobile Communications 2002 ISO Standards ISO 15418 MH Data Identifiers EAN.UCC Application Identifiers ISO Syntax for High Capacity ADC Media ISO Transfer Syntax ISO 18000 Part 2, kHz Part 3, MHz Part 4, 2.45 GHz Part 5, 5.8 GHz Part 6, UHF ( MHz, 433 MHz) ISO RFID Device Conformance Test Methods ISO RF Tag and Interrogator Performance Test Methods Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

ISM band interference Mobile Communications 2002 Many sources of interference Microwave ovens, microwave lightning 802.11, b, g, , Home RF Even analog TV transmission, surveillance Unlicensed metropolitan area networks … Levels of interference Physical layer: interference acts like noise Spread spectrum tries to minimize this FEC/interleaving tries to correct MAC layer: algorithms not harmonized E.g., Bluetooth might confuse OLD NEW © Fusion Lighting, Inc. Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

vs.(?) /Bluetooth Mobile Communications 2002 Bluetooth may act like a rogue member of the network Does not know anything about gaps, inter frame spacing etc. IEEE discusses these problems Proposal: Adaptive Frequency Hopping a non-collaborative Coexistence Mechanism Real effects? Many different opinions, publications, tests, formulae, … Results from complete breakdown to almost no effect Bluetooth (FHSS) seems more robust than b (DSSS) f [MHz] 2480 802.11b 3 channels (separated by installation) 1000 byte ACK 79 channels (separated by hopping pattern) DIFS SIFS DIFS 500 byte ACK 500 byte ACK 500 byte DIFS SIFS DIFS SIFS DIFS 100 byte ACK 100 byte ACK 100 byte ACK 100 byte ACK 100 byte ACK DIFS SIFS DIFS SIFS DIFS SIFS DIFS SIFS DIFS SIFS 2402 t Prof. Dr.-Ing. Jochen Schiller, MC SS Prof. Dr.-Ing. Jochen Schiller

Mobile Communications Chapter 7: Wireless LANs

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Mobile Communications Chapter 7: Wireless LANs

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