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© Copyright 1997, The University of New Mexico 4-1 LAN Technologies Ethernet Token Ring FDDI Gigabit Ethernet.

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Presentation on theme: "© Copyright 1997, The University of New Mexico 4-1 LAN Technologies Ethernet Token Ring FDDI Gigabit Ethernet."— Presentation transcript:

1 © Copyright 1997, The University of New Mexico 4-1 LAN Technologies Ethernet Token Ring FDDI Gigabit Ethernet

2 © Copyright 1997, The University of New Mexico 4-2 IEEE/ISO Protocol Set Deal with Physical and Data Link layers only 3 medium access control (MAC) standards –IEEE CSMA/CD; ISO –IEEE Token bus; ISO –IEEE Token ring; ISO Physical Logical Link Control (LLC) Medium Access Control (MAC) Layer 1 Layer 2

3 © Copyright 1997, The University of New Mexico 4-3 Ethernet Developed in early 1970’s Xerox PARC Standardized as IEEE Provides data communications for LAN systems Baseband technology developed by Xerox, Intel, Dec Broadband version developed by Mitre Frame based transmission Most commonly used medium access control

4 © Copyright 1997, The University of New Mexico 4-4 Ethernet CSMA/CD –Carrier Sense Multiple Access with Collision Detection Nodes listen before transmitting Nodes may transmit at any time Collisions result in back-off and retransmission –random access contention based media access stations contend for access to the medium

5 © Copyright 1997, The University of New Mexico 4-5 CSMA/CD If too many collisions or other errors (CRC alignment, Jabber, Giant frames) occur on a given port, hubs will auto partition that port to prevent it from repeating on the entire segment.

6 © Copyright 1997, The University of New Mexico 4-6 Ethernet MAC frame: 64 bytes min PreambleSDFDASALengthLLC dataPadFCS 712 or 6 >/ 02 4 bytes PreambleSDFDASATypeLLC dataPadFCS 712 or 6 >/ 02 4 bytes IEEE Ethernet

7 © Copyright 1997, The University of New Mexico 4-7 Ethernet IEEE MAC frame –Preamble: 7 byte pattern of alternating 0s and 1s used by the receiver to establish bit synchronization –Start frame delimiter (SDF): sequence indicating start of frame, enables receiver to establish first bit of frame –Destination address (DA): specifies the stations for which the frame is intended ( 2 or 6 bytes, implementation decision, usually 6 bytes) it may be one of the following –a unique physical address –a group address –a global address

8 © Copyright 1997, The University of New Mexico 4-8 Ethernet Source address (SA): specifies the station that sent the frame (2 or 6 bytes, usually 6 bytes) Length: length of the LLC data field LLC data: data unit supplied by LLC, less than 1518 bytes Pad: octets added to ensure the frame is long enough for the proper collision detection operation (optional) Frame check sequence (FCS): 32-bit cyclic redundancy check (CRC); except preamble, SDF and FCS

9 © Copyright 1997, The University of New Mexico 4-9 Ethernet Ethernet v2 –Type: deals with protocols IP protocol, Type = 0800 No two machines should have the same physical address LSB of first octet –if 0 then unique address –if 1 then multicast address

10 © Copyright 1997, The University of New Mexico 4-10 Ethernet 10Mbps transmission –Manchester Encoding Baseband 20MHz Network Interface Cards –Each node has a NIC –NIC is responsible for transmitting & receiving data frames –Each NIC has a different address MAC address

11 © Copyright 1997, The University of New Mexico 4-11 Ethernet- Network Interface Card PLX9032 or PLX Meg Flash 82556BIG MAC 100 Mbps Thunder Module 16 K SRAM FIFO RJ45 Relay Mags

12 © Copyright 1997, The University of New Mexico 4-12 MAC Address Media Access Control Address OSI Layer 2 6 Bytes –1st 3 Bytes- Manufacturer ID –2nd 3 Bytes- Random a3-4b –Vendor Specific 10-a3-4b

13 © Copyright 1997, The University of New Mexico 4-13 Ethernet Thick Coax (Thicknet) –IEEE 10Base-5 –Maximum distance of 500m –Nodes “tap” into cable with transceivers –Supports up to 250 nodes per cable segment –Must be terminated at both ends –Bus topology –50 ohm coaxial cable

14 © Copyright 1997, The University of New Mexico 4-14 Ethernet- Thick Coax

15 © Copyright 1997, The University of New Mexico 4-15 Ethernet Thin Coax (Thinnet) –IEEE 10Base-2 –Maximum distance 180m –Supports up to 30 nodes per cable segment –Nodes connect via BNC connectors –Must be terminated at both ends –Bus topology –50 ohm coaxial cable

16 © Copyright 1997, The University of New Mexico 4-16 Ethernet- Thinwire

17 © Copyright 1997, The University of New Mexico 4-17 Ethernet Unshielded Twisted Pair (UTP) –IEEE 10Base-T –Star topology from hub –EIA/TIA category 3, 4, 5 supported –Uses RJ-45 connectors –Maximum distance 100m (500 m with fiber) –Supports 1 node per cable segment

18 © Copyright 1997, The University of New Mexico 4-18 Ethernet- UTP

19 © Copyright 1997, The University of New Mexico BaseT Pinout RJ45 Connector TX+TX-RX+RX- Note that TX and RX are going to be reversed on the hub side, Thus when connecting hub to hub, the need for MDI/MDIX. MDIX looks for a NIC, MDI looks for a repeater port

20 © Copyright 1997, The University of New Mexico 4-20 Ethernet 10BROAD36 –75 ohm coaxial cable, CTV –Bus/tree topology –Maximum segment length is 1800 m –Signaling technique is broadband (DPSK)

21 © Copyright 1997, The University of New Mexico 4-21 Ethernet Fiber Optic –IEEE 10Base-F, 10Base-FL, 10Base-FOIRL –Star topology from hub –Multi Mode Fiber supported –MMF supports up to 2km distance –Point-to-Point –Secure

22 © Copyright 1997, The University of New Mexico 4-22 Fast Ethernet Set of specifications developed by IEEE committee to provide Ethernet compatible LAN operating at 100Mbps Specifications are: –100Base-TX: 2 CAT 5 UTP –100Base-FX: 2 optical fiber –100Base-T4: 4 CAT 3 or CAT 5 UTP

23 © Copyright 1997, The University of New Mexico 4-23 Ethernet- Repeaters 500 meters between repeaters for 10Base5 - Thicknet 2 repeater limit between any two stations any more and you need to insert a bridge/switch or a router

24 © Copyright 1997, The University of New Mexico 4-24 Ethernet- Equipment Hubs –Commonly referred to as concentrators or multiport repeaters –Used to connect multiple cable segments –Retimes & Regenerates signal –May support multiple cable types

25 © Copyright 1997, The University of New Mexico 4-25 Ethernet- Hubs If too many collisions or other errors (CRC alignment, Jabber, Giant frames) occur on a given port, many Bay Networks hubs will auto partition that port to prevent it from repeating on the entire segment.

26 © Copyright 1997, The University of New Mexico 4-26 Token Ring Logical Operation Control token concept by IBM and GM Deterministic access method, no contention Two main standards: IEEE MAC protocol, FDDI Where Ethernet uses CSMA/CD, Token Ring uses a token passing mechanism where one station is allowed to talk at a time Traffic moves in a logical circle, going from station to station, until the appropriate station receives it and holds on to it

27 © Copyright 1997, The University of New Mexico 4-27 Token Ring Physical Operation Ring is emulated through TR hub by passing frames from station to station (1, 4 or 16Mbps). When a station has a problem or is pulled from the ring, that port is “wrapped” to allow the ring to continue An active hub retimes and regenerates the signal, a passive hub connects the ring When a station inserts at the wrong speed or loses track of its neighbor, a beacon condition is created on the ring

28 © Copyright 1997, The University of New Mexico 4-28 Token Ring Pros and Cons Light load: TR is not very efficient. Stations must wait for the token to arrive Heavy load: TR operates in a round robin fashion Priority and reservation schemes can be implemented Bandwidth can be guaranteed High overhead for token maintenance Loss of token prevents further use or TR Duplication of token disrupts operation A monitor station is need to manage the TR network

29 © Copyright 1997, The University of New Mexico 4-29 FDDI Defined by four separate specifications Logical Link Control Media Access Control (MAC) Physical Layer Control (PHY) Physical Layer Medium (PMD) Station Management (SMT) Fiber Distributed Data Interface (FDDI) Standards Layer 2 Layer 1

30 © Copyright 1997, The University of New Mexico 4-30 FDDI MAC: how medium is accessed, frame format, token handling, addressing, CRC check, error recovery PHY: defines data encoding/decoding, clocking requirements, and framing PMD: defines characteristics of transmission medium, power levels, bit error rates, optical components, connectors

31 © Copyright 1997, The University of New Mexico 4-31 FDDI SMT: defines FDDI station configuration, ring configuration, ring control features, station insertion and removal, initialization, fault isolation and recovery, scheduling, and collection of statistics

32 © Copyright 1997, The University of New Mexico 4-32 FDDI Follows the token ring scheme Similar to IEEE Has no priority or reservation bits Designed for LANs and MANs Accommodates higher data rates of 100Mbps

33 © Copyright 1997, The University of New Mexico 4-33 FDDI FDDI operation Primary Ring Secondary Ring Single Attach Station Dual Attach Station

34 © Copyright 1997, The University of New Mexico 4-34 Primary and Secondary Rings –normal traffic is on primary ring –secondary “counter-rotating” ring is redundant - for primary failure Three Paths –primary - normal conditions –secondary - backup –local - intelligent insertion and removal

35 © Copyright 1997, The University of New Mexico 4-35 FDDI Stations Dual Attached Stations (DAS) –connected to both rings Single Attached Stations (SAS) –attached only to the primary ring through a hub/concentrator port SAS ConcentratorDAS Primary Ring Secondary Ring

36 © Copyright 1997, The University of New Mexico 4-36 FDDI Token Frame Preamble: 64 bits Starting Delimiter (SD): 8 bits Frame Control (FC): 8 bits –bit format of or to indicate that it is a token Ending Delimiter (ED): 4 bits –contains a pair of non-data symbols (T) that terminate token frame PreambleSDFCED

37 © Copyright 1997, The University of New Mexico 4-37 FDDI Frame Preamble: 64 bits –synchronize frame with each station’s clock –repeating stations may change length of the field as per clocking requirements Starting Delimiter (SD): 8 bits –indicates beginning of a frame; –coded as JK where J and K are non-data symbols; J same polarity as preceding symbol, K opposite polarity PreambleSDFCEDDASADATAFCSFS

38 © Copyright 1997, The University of New Mexico 4-38 FDDI Frame Frame Control (FC): 8 bits –has bit format CLFFZZZZ –C indicates synchronous or asynchronous frame –L indicates use of 16 or 48 bit addresses –FF indicates whether it is a LLC, MAC control or reserved frame –in a control frame ZZZZ indicates the type of control Destination Address (DA): 16 or 48 bits –specifies station for which the frame is intended Source Address (SA): 16 or 48 bits –specifies station that sent the frame

39 © Copyright 1997, The University of New Mexico 4-39 FDDI Frame Data: bytes –contains an LLC data unit or information related to a control operation Frame Check Sequence (FCS): 32 bits –cyclic redundancy check based on FC, DA, SA and Data fields Ending Delimiter (ED): 4 bits –contains a non-data symbol T; T=0 token frame, T=1 normal frame Frame Status (FS): 1 bit –contains one of the following: E: error detected A: address recognized F: frame copied

40 © Copyright 1997, The University of New Mexico 4-40 FDDI Limitations STP, UTP, Single and Multimode Fiber implementation over copper is known as CDDI 500 stations per ring 200 km or 124 miles total length 10 km between station and concentrator single mode 2 km between station and concentrator multimode

41 © Copyright 1997, The University of New Mexico 4-41 FDDI Ports DAS A - Primary In, Secondary Out DAS B - Primary Out, Secondary In Master - concentrator port only Slave - SAS only primary in and out Primary Secondary Port B Port A FDDI DAS

42 © Copyright 1997, The University of New Mexico 4-42 Optical Bypass Switch When a station is off this goes into by-pass mode Prevents Ring-Wrap A B MAC Station Ring Wrap

43 © Copyright 1997, The University of New Mexico 4-43 FDDI Architecture Use only concentrators on the FDDI dual ring –Minimize chance of ring segmentation by reducing number of components on dual ring –Enhance scalability by allowing stations to be added and removed without disrupting the dual ring –Do not use ring wiring unless forced to do so by existing cable plant Place all equipment attached to the FDDI dual-ring in one or two physically secure locations

44 © Copyright 1997, The University of New Mexico 4-44 FDDI Architecture Dual home critical bridges, routers and servers – provide physical layer redundancy –Connect remote locations to the FDDI backbone via dual- homed routers and/or concentrators Single attach non-critical desktop connections Use star wiring wherever possible

45 © Copyright 1997, The University of New Mexico 4-45 What is Gigabit Ethernet? Speed Cost IEEE Standard Media Access Protocol Frame Format Topology Cable support Network diameter (max) UTP link distance (max) Media independent interface Full duplex capable? Broad multivendor support.. Multivendor Availability Mbps X CSMA/CD IEEE Bus or star Coax, UTP, fiber 2,500 meters 100 meters Yes (AUI) Yes Now 100 Mbps 2X 10BT 802.3u CSMA/CD IEEE Star UTP, fiber 210 meters 100 meters Yes (MII) Yes Now EthernetFast Ethernet 1000 Mbps 2-4X 100BT 802.3z CSMA/CD IEEE Star UTP, fiber 200 meters 100 meters Yes (G-MII) Yes 1998 Gigabit Ethernet

46 © Copyright 1997, The University of New Mexico 4-46 Gigabit Ethernet Technology 10 Mbps Ethernet CSMA/CD MAC Thick Coax (10Base5) Thin Coax (10Base2) Fiber (10Base- F) Twisted Pair (10Base-T) 100 Mbps Ethernet CSMA/CD MAC Four Pair UTP (100Base-T4) Fiber (100Base-FX) Two Pair UTP, STP (100Base-TX) No change AUIMII 1000 Mbps Ethernet CSMA/CD MAC Four Pair UTP (TBD) MM Fiber CD Laser 1300nm Laser SM Fiber 1300nm Laser G-MII Minor change

47 © Copyright 1997, The University of New Mexico 4-47 Gigabit Ethernet Topology CSMA/CD Topology –Supports 100 Meter distance for CSMA/CD protocol over all media options. Full Duplex Topology –Supports variable distance dependent on media capabilities –Supports server, switch and router DTE applications.

48 © Copyright 1997, The University of New Mexico 4-48 Gigabit Ethernet vs. ATM Link Speed Standards Shared Access Protocol Switched Access Protocol..... Frame Format Transmission Control Redundancy VLAN support Network diameter (max) UTP link distance (max) Priority Full duplex switching Broad multivendor support.. Multivendor Availability , 100, 1000 Mb/s IEEE CSMA/CD N/A IEEE Frame Connectionless Spanning Tree 802.1Q (?) 200 meters 100 meters 802.1P (?) Yes 1998 Ethernet(Gigabit) 25, 155, 622, 1.2 Gb/s ATM Forum N/A SVC/CMS ATM Cell Connection Oriented ATM Mesh LANE 2,500 meters 100 meters ATM QoS Yes Now ATM

49 © Copyright 1997, The University of New Mexico 4-49 Three generations of LANs Apple, Bellcore, Sun and Xerox identified the three generations of LANs in their document [ABSX92].

50 © Copyright 1997, The University of New Mexico 4-50 First Generation LANs Typified by CSMA/CD and Token ring LANs. Provided terminal to host connectivity at moderate data rates. Supported client server architecture at moderate data rates.

51 © Copyright 1997, The University of New Mexico 4-51 Second Generation LANs Typified by FDDI. Supported backbone LANs. Supported high performance work stations.

52 © Copyright 1997, The University of New Mexico 4-52 Third Generation LANs Typified by ATM LANs. Provide aggregate throughputs and real time transport guarantees for multimedia applications.

53 © Copyright 1997, The University of New Mexico 4-53 Further Criteria For Third Generation LANs Support multiple, guaranteed classes of service. –examples: a live video application requires 2 Mbps guaranteed. a file transfer uses background class of service. Provide scaleable throughput in terms of per host capacity. –enabling applications requiring large volumes of data in and out of a single host. Provide scaleable throughput in terms of aggregate capacity. –enabling installations to grow from a few to several hundred high performance hosts. Internetwork between LAN and WAN technology.

54 © Copyright 1997, The University of New Mexico 4-54 ATM - A Third Generation LAN Multiple classes of service provided by virtual paths and virtual channels. Permanent connections provide pre-configured service. Switched connections provide on demand service. ATM is scaleable –more switching nodes can be added. –higher data rates can be used for attached devices. Cell based data transport at high rates allow wide area networking and local area networking, with seamless connectivity between the two.

55 © Copyright 1997, The University of New Mexico 4-55 Types of ATM LANs Gateway to ATM WAN –ATM switch acts as a router and traffic concentrator, linking premises networks to an ATM WAN. Backbone ATM switch –Single ATM switch interconnects LANs. –Network of ATM switches interconnects LANs. Workgroup ATM –End systems(high performance multimedia workstations) connect directly to an ATM switch.

56 © Copyright 1997, The University of New Mexico 4-56 Data Communications With Processors Two types –Input/Output channel –Network communications

57 © Copyright 1997, The University of New Mexico 4-57 I/O Channel Features Direct point to point or multipoint high speed communications link over very short distances. Hardware based link. Data is transferred between a buffer at source device and a buffer at destination device. No special formatting is used, data is transferred in raw form. Transfer control and error detection is implemented in hardware. I/O channel links processors with peripheral devices.

58 © Copyright 1997, The University of New Mexico 4-58 Network Communications Features Collection of interconnected access points. Software protocol structure enables communication. Many different types of data transfer are allowed. Network protocols that provide flow control, error detection and error recovery are implemented in software. Data transfer, between end systems in the local, metropolitan and wide area distances, is managed.

59 © Copyright 1997, The University of New Mexico 4-59 Fiber Channel Features Has simplicity and speed of channel communications. Implements communications oriented protocols as in network communications. Provides interconnectivity between end systems like in the network communications and also short distance connectivity as in the case of channel communications. One multiprotocol interface is used to provide: –Peripheral connectivity. –Host to host internetworking. –Connected processor clusters. –Multimedia capabilities.

60 © Copyright 1997, The University of New Mexico 4-60 Channel Oriented Features of Fiber Channel Architecture Data-type qualifiers for routing frame payload into particular interface buffers. Link-level constructs associated with individual I/O operations. Protocol interface specifications to allow support of existing I/O channel architectures, such as the small computer interface (SCSI).

61 © Copyright 1997, The University of New Mexico 4-61 Network Oriented Features of Fiber Channel Architecture Full multiplexing of traffic between multiple destinations. Peer-to-peer connectivity between any pair of ports on a Fiber channel network. Capabilities of internetworking with other technologies.

62 © Copyright 1997, The University of New Mexico 4-62 Fiber Channel Requirements as per Fiber Channel Association Full duplex links with two fibers per link. Performance from 100 Mbps to 800 Mbps on a single link(200 Mbps to 1600 Mbps per link). Support for distances upto 10 kms. Small concentrators. High capacity utilization with distance insensitivity.

63 © Copyright 1997, The University of New Mexico 4-63 Fiber Channel Requirements as per Fiber Channel Association Greater connectivity than existing multidrop channels. Broad availability. Support for multiple cost/performance levels, from small systems to super-computers. Ability to carry multiple existing interface command sets for existing channel and network protocols.

64 © Copyright 1997, The University of New Mexico 4-64 Fiber Channel Elements (Slide 1) Nodes –These are the end systems Fabric –Collection of switching elements –Fabric connects nodes and switches by point to point links –Routes frames between nodes connected to the fabric –May buffer frames to enable connections at different data rates –Can be a single fabric element or can be a collection of fabric elements networked together

65 © Copyright 1997, The University of New Mexico 4-65 Fiber Channel Elements (Slide 2) N_port –Port on a node which participates in a point to point link. Frames –Data units used for communications on the point to point links. F_port –Port on a switching fabric which participates in a point to point link.

66 © Copyright 1997, The University of New Mexico 4-66 Fiber Channel Vs. Other LANs Circuit switched or packet switched as opposed to shared medium LAN. No medium access control issues. Scales easily in : –Number of N_ports –Data rate –Distance covered New transmission media, technology and data rates can be accommodated by adding new switches and F_ports to existing fabrics.

67 © Copyright 1997, The University of New Mexico 4-67 Fiber Channel Protocol Architecture (Slide 1) FC-O physical media –Optical cable with laser or LED transmitters for long distance transmissions. –Copper coaxial cable for highest speeds over short distances. –Shielded twisted pair for low speeds over short distances. –Rates of 100 Mbps, 200Mbps, 400Mbps, 800Mbps

68 © Copyright 1997, The University of New Mexico 4-68 Fiber Channel Protocol Architecture (Slide 2) FC-1: Transmission protocol –Byte synchronization and encoding –8B/10B encoding/decoding scheme Balanced scheme Simple to implement Has useful error detection capability –Special code character maintains byte and word alignment

69 © Copyright 1997, The University of New Mexico 4-69 Fiber Channel Protocol Architecture (slide 3) FC-2: Signaling protocol –Transport mechanism –Framing protocol and flow control between N_ports –Three classes of service between ports FC-3: Common Services –Port related services –Services that appear across two or more ports in a node

70 © Copyright 1997, The University of New Mexico 4-70 Fiber Channel Protocol Architecture (slide 4) FC-4: Upper layer protocols –Supports a variety of channel and network protocols. –Channel: SCSI, HIPPI,IPI-3, SBCS

71 © Copyright 1997, The University of New Mexico 4-71 Fiber Channel Physical Interface and Media Specified by fiber channel FC-0 Several data rate allowed : –100 Mbps to 800 Mbps Several mediums allowed : –Optical fiber –Coaxial cable –Shielded twisted pair Maximum distances for point-to-point links range from 50 meters to 10 Km.

72 © Copyright 1997, The University of New Mexico 4-72 Fiber Channel Transmission Protocol Specified by fiber channel FC-1 Defines: –Signal encoding technique for transmission 8B/10B encoding scheme is used. 8 bits of data from level FC-2 is converted into 10 bits for transmission. –Signal encoding technique for synchronization

73 © Copyright 1997, The University of New Mexico 4-73 Fiber Channel Common Services (Slide 1) Specified by fiber channel FC-3. Striping –Transmit a single information unit across multiple links simultaneously. –Good for transferring large data sets in real time. –Good for video-imaging applications.

74 © Copyright 1997, The University of New Mexico 4-74 Fiber Channel Common Services (Slide 2) Hunt groups –Set of associated N_ports at a single node identified by an alias. –Any frame sent to the alias is processed by an available N_port within the set. –Good for decreasing latency.

75 © Copyright 1997, The University of New Mexico 4-75 Fiber Channel Common Services (Slide 3) Multicast –Sends to all N_ports on a fabric. –Sends to a subset of the N_ports on a fabric.

76 © Copyright 1997, The University of New Mexico 4-76 Fiber Channel Mapping Specified by FC-4 I/O channels mapped by FC-PH –Small Computer System Interfaces (SCSI) supports. High capacity devices like disks. High data rate devices like graphics and video equipment. –High Performance Parallel Interface (HIPPI). Used for mainframe/supercomputer environments. –Network protocols mapped by FC-PH. IEEE802 Mac frames to FC frames. ATM IP

77 © Copyright 1997, The University of New Mexico 4-77 Fiber Channel Transmission Media (Slide 1) Single mode fiber –10Km at 800Mbps, 10Km at 400Mbps, 10Km at 200Mbps 50 um multimode fiber –0.5Km at 800Mbps, 1Km at 400Mbps, 1500m at 200Mbps, 1500m at 100Mbps um multimode fiber –175m at 800Mbps, 350m at 400Mbps, 1500m at 200Mbps, 1500m at 100Mbps.

78 © Copyright 1997, The University of New Mexico 4-78 Fiber Channel Transmission Media (Slide 2) Video coaxial cable –25m at 800Mbps, 50m at 400Mbps, 75m at 200Mbps, 100m at 100Mbps. Miniature coaxial cable –10m at 800Mbps, 15m at 400Mbps, 25m at 200Mbps, 35m at 100Mbps. Shielded twisted pair –50m at 200Mbps, 100m at 100Mbps.

79 © Copyright 1997, The University of New Mexico 4-79 Fiber Channel Topologies(Slide 1) Fabric or switched topology –An arbitrary topology requiring at least one switch to interconnect a number of N_ports. –The fabric may be a switched network of a number of switches, with or without end nodes. –Each port in fabric has a unique address. –Destination address of data from a node is examined by an edge switch and is appropriately forwarded to a node or another switch enroute to the node.

80 © Copyright 1997, The University of New Mexico 4-80 Fiber Channel Topologies(Slide 2) Point to point topology –Only two N_ports directly connected. Arbitrated loop topology –Connects up to 126 nodes in a loop. –Ports on loop must support N_port and F_port functionalities. –Ports are called NL_ports –Operation is roughly equal to token ring protocols. –Each port sees all frames and passes them along, keeping the ones it needs and ignoring the ones not addressed to it. –A token access protocol is used to get loop access by a port

81 © Copyright 1997, The University of New Mexico 4-81 Wireless LANs Terminology Standards defined by IEEE committee. Basic services set: –Contains stations executing the same MAC protocol. –Stations compete to use the shared wireless medium. Access point –Allows a basic set to connect to a backbone distribution system. –Access point acts as a bridge.

82 © Copyright 1997, The University of New Mexico 4-82 Wireless LANs Terminology (Cont.) Distribution system –Connects two or more basic sets together. –Typically it is a wired backbone LAN. Extended service set –Collection of BSSs connected by a distribution system.

83 © Copyright 1997, The University of New Mexico 4-83 Types of Wireless Stations Definitions specified in IEEE , based on mobility. Three types of stations are specified: –No transition Usually stationary. May be mobile in direct communication range of communicating stations within the BSS. –BSS transition Station moves from one BSS to another within the same ESS –ESS transition Station moves from one BSS in one ESS to a BSS in another ESS.

84 © Copyright 1997, The University of New Mexico 4-84 Wireless Physical Medium Specification defines 3 physical media –Infrared 1Mbps using range 850nm to 950nm. 2Mbps using range 850nm to 950nm. –Direct sequence spread spectrum 7 channels, each with a data rate of 1Mbps or 2 Mbps can be used. Operates in 2.4GHz ISM band. –Frequency hopping spread spectrum Operates in 2.4GHz ISM band. Details are still being worked on.

85 © Copyright 1997, The University of New Mexico 4-85 Wireless Media Access Control (Slide 1) Two types of MAC algorithms were considered: –Distributed access protocols Decision to transmit was distributed over all nodes using a carrier sense mechanism. Makes more sense for the adhoc peer station networks. Good for networks whose traffic is busy. –Centralized access protocols Access is managed by a central management station. Makes more sense in wireless networks including base stations attached to backbone networks. Good for networks whose traffic is time sensitive and high priority.

86 © Copyright 1997, The University of New Mexico 4-86 Wireless Media Access Control (Slide 2) Distributed Foundation Wireless MAC (DAFWMAC) was the final product of committee’s efforts to come up with a wireless MAC protocol. Allows distributed access control mechanisms. Allows central control of access as an optimal feature Contains 3 layers: –Physical layer –Distrbuted coordination function (DCF) –Point coordination function (PCF)

87 © Copyright 1997, The University of New Mexico 4-87 Wireless Media Access Control (Slide 3) Distributed coordination function –Uses CSMA algorithm. –No collision detection function is used. –A priority scheme based on a set of delays is used. –A single delay is known as an interframe space (IFS)

88 © Copyright 1997, The University of New Mexico 4-88 Wireless Media Access Control (Slide 4) The rules of CSMA algorithm –Transmitting station senses the medium and may transmit if it finds the medium to be idle for one IFS. –In case the medium is found busy, transmitting station defers transmission and continues to sense the medium until current transmission ends. –If the medium is found busy over another IFS, transmitting station backs of for a random period of time and tries again later using a binary exponential backoff algorithm.

89 © Copyright 1997, The University of New Mexico 4-89 Wireless Media Access Control (Slide 5) Three values of IFS are used: –SIFS Short IFS is used for all immediate response actions. Upon reception of a frame ack frames are sent after a SIFS delay. –PIFS Point coordination function IFS is used for central access control. –DIFS Distributed coordination function IFS is used as a minimum delay for asynchronous frames contending for access.

90 © Copyright 1997, The University of New Mexico 4-90 Wireless Media Access Control (Slide 6) Point coordination function –Built on top of DCF. –A central point coordinator issues polls in a round robin fashion to stations and offers each one the medium as required by it. –The central point coordinator gains control of the channel through the CSMA mechanism described above. –The central point coordinator has to relinquish control of the medium after it has controlled it to some pre set time.


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