Presentation on theme: "Debrecen, 2012. Train IT - Networks 1 Train IT – Computer Networks University of Debrecen."— Presentation transcript:
Debrecen, Train IT - Networks 1 Train IT – Computer Networks University of Debrecen
Debrecen, Train IT - Networks 2 I. – Basics of Computer Networks
Debrecen, Train IT - Networks 3 Computer Networks Computer Networks : Two or more computers linked together with some software and hardware tools for an information transmission related purpose. Objectives: Sharing resources. Increasing reliability. Increasing speed. Human communication.
Debrecen, Train IT - Networks 4 Classification of Computer Networks Based on their Sizes Name Multicomputer Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Range < 1m 1 km 10 km 100 km <
Debrecen, Train IT - Networks 5 Components of LANs Computers Network cards Peripherals Network transmission lines Network devices
Debrecen, Train IT - Networks 6 Functions of WANs Covering large geographical area Providing (real-time) communication between users Nonstop access to remote resources that can be connected to local services Providing , internet, file transfer, and e-commerce services
Debrecen, Train IT - Networks 7 Accessibility of Networks Public Network: A network that is accessible for everyone (eg. Internet). Private Network: A network that is accessible only for the owner organization (expensive for large networks). Virtual Private Network(VPN): A private network that provides private type access and data transfer via public infrastructure (eg. Internet).
Debrecen, Train IT - Networks 8 Computer Network Node Node: Device with own network address. It can communicate independently (eg. computer, printer, router). In a communication a node can act either as a transmitter (sender, source) or as a receiver (destination). Categories of network devices and tools: End user node: computer, printer, scanner, and any other devices that provide services directly to the user Network linking/connecting tools: devices that enable communication between end user nodes by connecting them to each other
Debrecen, Train IT - Networks 9 Signal, Signal Coding, Modulation Signal: Physical quantities, depending on place and time, and carrying information. Information carrier on the communication chanel, it could be analog or digital. Signal Coding: Mapping the (digital) information onto the (digital) carrier signal (eg. voltage levels, changing of voltage levels). Modulation: Mapping onto analog carrier signal. The process of creating the (modulated) signal to be transmitted through the chanel from the modulating signal coming from the source and the analog carrier signal. The inverse process is the demodulation. A modem performs modulation and demodulation, as well.
Debrecen, Train IT - Networks 10 Transmission Media, Chanel, Collision Transmission media: Device or material on which the transmission of information (signal) is performed. (Eg. twisted-pair cable, coaxial cable, fiber-optic cable, or air). Transmission chanel: Data path, frequency band for transmitting signals. Usually, in a transmission media multiple chanels (data path) are formed. Collision: A collision occurs when two (or more) nodes transmit information at the same time on a common transmission chanel.
Debrecen, Train IT - Networks 11 Transmission Speed Transmission speed (network speed, bandwidth, bit rate): Amount of information transmitted during a time unit. Measure of unit: bit/sec, b/s, bps. The throughput measured in applications is always lower than the physical bandwidth. Larger units: 1 Kbps = 1000 bps 1 Mbps = 1000 Kbps 1 Gbps = 1000 Mbps
Debrecen, Train IT - Networks 12 Connections of Data Transmission Peer-to-peer (Point-To-Point) connection: The propagation of information performed between two points (a transmitter and a receiver) is called a peer-to-peer connection. Multipoint connection, broadcasting: A transmitter provided information to multiple receivers is called a multiple nodes connection. Broadcasting is a multiple nodes connection, where all receivers get the information inside a given range (eg. radio broadcasting).
Debrecen, Train IT - Networks 13 Directions of Information Transmission One way (simplex) connection: The transmission of information allowed only one way is called a one way (simplex) connection (eg. radio broadcasting). Alternate way (half duplex) connection: The transmission allowed both directions, but only one direction at a time is called a half duplex connection (eg. CB radio). Two way (full duplex) connection: The traffic allowed in both directions simultaneously is called a full duplex connection (eg. telephone).
Debrecen, Train IT - Networks 14 Basics of Addressing Unicast (Unique) address: An identifier, assigned to a network interface of a node. Broadcast address: An address, identifying all nodes (and interfaces of nodes) in a so called broadcast domain.
Debrecen, Train IT - Networks 15 Computer Network Protocol Protocol: The formal description of all rules and conventions which determines the communication of the network devices (nodes) (set of communication rules).
Debrecen, Train IT - Networks 16 Server-Client Architecture Server: A network node (and software) which provides services for other nodes. The service of a server is ensured by a server- software (eg. a web-server). Client: A network node (and software) which has some kind of network service demand. For recourse to the service the client uses a client-software (eg. web browser). The communication between the server and the client is described by a high level protocol (eg. http).
Debrecen, Train IT - Networks 17 Layered Network Architecture
Debrecen, Train IT - Networks 19 Layered Network Architecture - Concepts Layer N protocol: A protocol which describes the specifications of layer (level) N. Peers: Entities which located on the same level of the two communication endpoints (nodes). In some logical way the peers communicate each other by the help of the corresponding layer protocol. Layer N/N+1 interface: Connection of boundary surface of layers N and N+1. Service of Layer N: Set of actions (services) which are provided to layer N+1 by layer N (through the interface).
Debrecen, Train IT - Networks 20 Scheme of Network Communication 4 Layer 5 protocol Layer 4 protocol Layer 3protocol Layer 2 pr DestinationLayerSource M H3 H4 M2 H4 M H2 H3 H4 M2 T2 H3 H4 M1 H2 H3 H4 M1 T2 M H3 H4 M2 H4 M H2 H3 H4 M2 T2 H3 H4 M1 H2 H3 H4 M1 T2
Debrecen, Train IT - Networks 21 Network Communication - Concepts Encapsulation: Packaging the information arrived from a higher level with a header of a specific protocol (it is similar when a surface mail letter is put in an envelope and the envelope is addressed). Protocol Data Unit (PDU): Entity (contains header and data) handled by the considered protocol. (It is frequently mentioned as packet.)
Debrecen, Train IT - Networks 22 Encapsulation - Example Pictures and text are transformed into data. Data are packaged into segments. The data segment is encapsulated into a packet containing the addresses (IP addreses) of the source and destination nodes. The packet is encapsulated into a frame containing the physical address (Ethernet address) of the next device connected directly. The frame is transformed into series of bits (ones and zeros) which can be transferred through the transmission media.
Debrecen, Train IT - Networks 23 OSI Reference Model Physical Layer Data Link Layer Network Layer Transport Layer Session Layer 1 Presentation Layer Application Layer LayerName of PDU Packet APDU PPDU SPDU Frame Bit TPDU, Segment
Debrecen, Train IT - Networks 24 Mapping of TCP/IP - OSI Model Physical Layer Transport Layer Session Layer 1 Presentation Layer Application Layer TCP/IP LayerOSI Layers Host-to-Network Layer Network Layer Transport Layer Application Layer Data Link Layer Network Layer 2 Not present in the TCP/IP model
Debrecen, Train IT - Networks 25 Hybrid Reference Model Physical Layer Transport Layer 1 Application Layer Data Link Layer Network Layer 2
Debrecen, Train IT - Networks 26 Network Interconnection Devices
Debrecen, Train IT - Networks 27 Network Interconnection Devices - Basics Collision domain; Bandwidth domain: Part of a network, where collisions can be detected (a common communication channel that is shared by multiple nodes). In a collision domain only one information transmission can be performed at a time. Broadcast domain: Part of a network, where information transmitted with a broadcast destination address can be detected.
Debrecen, Train IT - Networks 28 Network Interconnection Devices Subnetworks – based on the functionality of network interconnection devices – can be connected in different OSI Layers: Repeater Bridge Router Gateway Physical Layer Data Link Layer Network Layer Above Transport Layer Connector itemOSI layer
Debrecen, Train IT - Networks 29 Repeater: Amplifies and repeats the signals sent on transmission media. Does not separate the connected subnetworks. Repeater with multiple ports is called a HUB. Bridge: Working in Data Link Layer it performs selective connection. The interconnected subnets form separate collision domains. Usually transmits the broadcast messages towards all interconnected subnets. Network Interconnection Devices
Debrecen, Train IT - Networks 30 Switch: A multiple port device with bridge functionality between any two ports. Router: Working in Network Layer it performs selective connection, routing, and traffic control. The interconnected subnets form separate collision domains and separate broadcast domains. It is a node with own IP address. It is also called a gateway in the Network Layer (default gateway). Network Interconnection Devices
Debrecen, Train IT - Networks 31 Topologies
Debrecen, Train IT - Networks 32 Physical topology: Investigates the placement of nodes and their connection possibilities. (Cable topologies, Physical topologies). Logical topology: Investigates the logical sequence and order of nodes. Topologies
Debrecen, Train IT - Networks 33 Star (extended star) Ring Host (workstation or server) Center Physical Topologies
Debrecen, Train IT - Networks 34 Repeater Bus Physical Topologies
Debrecen, Train IT - Networks 35 Tree Physical Topologies
Debrecen, Train IT - Networks 36 II. – Physical Layer
Debrecen, Train IT - Networks 37 Electricity is the free flow of electrons. Materials highly restraining the flow of electrons are called insulators. Materials slightly restraining the flow of electrons (free of resistance) are called conductors. Semiconductors are able to control accurately the conducted electricity. The resistance is denoted by R, the measure of unit is ohm, (Ω) The current is the quantity of electric charge through a circuit in a second. It is denoted by I, the measure of unit is ampere (A) The voltage is an electronic force or pressure which arises at separation of electrons and protons. It is denoted by U, the measure of unit is volt (V) Ohm’s Law: U=I*R Electricity - Basics
Debrecen, Train IT - Networks 38 The amplitude of a signal is decreasing during its way in a transmission media. The length of a transmission media is determined such a way that the signal should be interpreted securely by the receiver. If large distance has to be covered, the signal has to be restored by the help of amplifiers (repeaters). The attenuation depends on frequency, thus the amplifiers have to compensate this with frequency dependent amplification. The quantity of attenuation and amplification is expressed in decibels (dB) on a logarithmic scale. Attenuation
Debrecen, Train IT - Networks 39 Optical fiber 3/8” coaxial cable Twisted pair 1 kHz 1 MHz1 GHz1 THz1000 THz Frequency Attenuation (dB/km) 0, Attenuation of Guided Media
Debrecen, Train IT - Networks 40 Four pairs are typically grouped in a plastic sheath. The grouped pairs can be shielded (Shielded Twisted Pair, STP) or unshielded (UTP). Twisted Pair
Debrecen, Train IT - Networks 41 The cheapest and most commonly used transmission media. Two insulated copper conductors are twisted according to a regular pattern. Usually several pairs are grouped (UTP has 4 pairs) and protected with a plastic sheath. Number of twists decreases crosstalk between pairs and ensures noise protection. The length of twists might be different in pairs in order to decrease crosstalk. The diameter of conductor is mm. It is the cheapest media, easy to use but the data transmission speed and the distance to be covered are highly limitated. Twisted Pair– Physical Characteristics
Debrecen, Train IT - Networks 42 Transmission characteristics The attenuation of twisted pairs is highly dependent on frequency. It is sensitive to interference and noise. For example easily takes the 50Hz energy from the parallel AC network. A shield can be used against disturbance (STP, FTP). Crosstalk between neighbour pairs can be decreased by variable twist length. With a point-point analog signals a frequency bandwidth of cca. 100KHz can be obtained (transmission of multiple voice channels). For short distance over 100 Mbps speed can be achieved. Twisted Pair– Transmission Characteristics
Debrecen, Train IT - Networks 43 Category 5. UTP cable and connector for 100 MHz transmission. For limited distance (100 meters) it provides 100 Mbps speed transmission. Cabling of new buildings usually is done with this cable. New standards: Cat5e – enables simultaneous use of the 4 pairs, Cat6: ~250MHz; Cat7 STP: ~600MHz.) STP: Twisted pairs are shielded separately. FTP: Twisted pairs has a common shield cover (foil). (It is cheaper than STP, and better than UTP.) Types of Twisted Pairs
Debrecen, Train IT - Networks 45 Straight RJ-45 female (PC, Router): Tx+Tx-Rv+Rv Cross RJ-45 female (Switch, Hub): Rv+Rv-Tx+Tx RJ-45 females with same assignment (eg. pc-pc, hub-hub) are connected with a crossover cable (568A – 568B). The different RJ-45 females (eg. pc-hub, pc-switch, router-switch) are connected with a straight-through cable (568A – 568A or 568B – 568B). Certain devices can detect the assignment of RJ-45 female on the other side, and are able to handle it automatically (auto sense). Assignment of Contacts of RJ-45 Connectors
Debrecen, Train IT - Networks 46 Physical Characteristics Cross section of a coaxial cable Inner conductor Outer cover Insulation Outer conductor Diameter of the cable: mm. Due to the concentric structure, it is less sensitive for interference and crosstalk, than the twisted pair. It can be used for larger distance and in multipoint application supports more stations, than the twisted pair. Coaxial Cable– Physical Characteristics
Debrecen, Train IT - Networks 47 Applications Transmission of television broadcasting. Large distant telephone transmission. Connection of computers Local networks. Transmission characteristics In case of analog transmission, amplifiers are required in every several km. It can be used up to 400 MHz. In case of digital transmission amplifiers are required in every km. Coaxial Cable
Debrecen, Train IT - Networks 49 Physical Characteristics Optical fiber Cladding Core Protecting cover Angle of incidence Angle of reflection A light ray incident below the critical angle is absorbed in the cladding Optical Fiber– Physical Characteristics
Debrecen, Train IT - Networks 50 Physical Characteristics A floppy optical fiber with μm of diameter is able to transmit light ray. Optical fiber is made of glass or plastic. The cladding is also made of glass or plastic, but it has different optical characteristics than the core. The outer plastic cover protects against impurities, wearing, and other outer effects. Optical Fiber– Physical Characteristics
Debrecen, Train IT - Networks 51 Applications (benefits): Larger capacity High transmission speed can be achieved (2 Gbps in10x km). Smaller size and weight Smaller attenuation The attenuation is smaller, and it is constant at a wide frequency range. Electromagnetic isolation Not sensitive for outer electromagnetic effects, there is no crosstalk. Does not emit energy, thus it can not be intercepted. It is difficult to tap an optical fiber. Larger repeating distance Smaller the number of repeaters is, smaller the possibilities of errors and the costs are. Technology keeps developing. Eg. 3.5 Gbps transmission speed over 318 km without any amplifier (AT&T, 1990). Optical fiber- Advantages
Debrecen, Train IT - Networks 52 Applications Big city trunks Long-haul country trunks Telephone center trunks Subscriber loops Local area networks Transmission characteristics Works in Hz (infrared) domain. 3 versions are used: multi mode single mode multi mode graded index Possible light sources: LED Laser diode. Optical Fiber
Debrecen, Train IT - Networks 53 Transmission characteristics Multi mode fiber Light rays coming with different angles from light source are reflecting in different angles at the boundary of the two materials, thus they travels different distances during different time. So light impulses will be distorted. Consequently, the data transmission speed is decreasing. Single mode fiber Decreasing the diameter of core, only rays paralell with fiber axis will pass through the fiber. Light impulses will not be distorted, higher data transmission speed can be achieved. Multi mode graded index fiber The refractive index of core material is increasing when the radial distance from the fiber axis become larger. Due to this property the light rays will be focused. The characteristics of this type can be placed between the two other types. Types of Optical Fibers
Debrecen, Train IT - Networks 54 Types of Optical Fibers Single mode Multi mode graded index fiber Multi mode Wavelength and diameter of fiber 3 – 10 μm Optical detector Optical source
Debrecen, Train IT - Networks 55 Propagation and detection of electromagnetic signals are performed by antennas. The two ways of broadcasting: Directed Omnidirectional (not directed) In directed case the antenna radiates a focused electromagnetic ray. The receiver antenna should be positioned very precisely. The omnidirectional radiation can be received with multiple antennas. Signals with higher frequency can be focused better. Three frequency ranges can be used for wireless transmission: GHz (microwave transmission) (directed) 30 MHz - 1 GHz (radio frequency) (omnidirectional) Hz (infrared) Wireless Transmission
Debrecen, Train IT - Networks 56 WAN Technologies
Debrecen, Train IT - Networks 57 WAN Cabling Technologies Serial connections: provide reliable, long-distance communications ISDN: For dial-based on demand services or spare connections DSL: For achieving a T1/E1 (1, ,048 Mbit/s) speed via telephone line Cable modem connection: Cable providers use the coaxial TV-cables. The coaxial cables are appropriate for achieving high-speed connections. These speeds can even be higher, than the speed of the DSL-accesses These technologies require specific transmission media and connectors.
Debrecen, Train IT - Networks 58 Technical Structure of ADSL Subscriber sideNetwork side CPE Filter ADSL NT Computer POTS or ISDN Phone ATM Backbone DSLAM Telephone center Data network Phone network PTSN
Debrecen, Train IT - Networks 59 WAN Technologies WAN connection Serial or smart-serial ports of router can be used. Connection based on clock signal: Data Communication Equipment (DCE, provides clock signal eg. modem, CSU/DSU). Data Terminal Equipment (DTE, eg. router) ISDN concepts, equipements TE1Terminal Equipment 1 ISDN compatible device, connecting to NT1 or NT2. TE2Non ISDN compatible device, connecting to TA. TATerminal Adapter Connects a non ISDN device to an ISDN network. NT1Connects a 4-wire ISDN to a 2-wire ISDN (2-wire connects to CO). NT2Connects different „subscriber devices” to NT1 (switching and connectivity)
Debrecen, Train IT - Networks 60 III. – Data Link Layer LAN Data Link Layer Solutions
Debrecen, Train IT - Networks 61 IEEE 802 Logical Link Control Medium Access Control Physical Network Layer Transmission media Physical Layer Data link Layer ISO reference model = Logical Link Control Protocol = CSMA/CD = Token bus = Token ring Media access protocols The IEEE 802 protocol family IEEE LAN Standards
Debrecen, Train IT - Networks 62 Ethernet (CSMA/CD)
Debrecen, Train IT - Networks 63 10BASE-T: transmission speed 10 Mbit/s, type of transmission is digital, T refers to using a twisted pair). Maximum cable length is 100m. 10BASE-2: transmission speed 10 Mbit/s, type of transmission is digital, no. 2 refers to the maximum 200 of segment size. A 10BASE2 segment contains up to 30 station. 10BASE-5: transmission speed 10 Mbit/s, type of transmission is digital, no. 5 refers to the 500 meters maximum distance of signals transmitted to rule: Five segments of transmission media (max meter). Four repeater or hub. Three segments for connecting stations. Two connector segment without any station. One large collision domain. Ethernet – Physical Technologies
Debrecen, Train IT - Networks 64 Destination address Preamble Source address Start of Frame Pad (if necessary) Data CRC Length/Type 7 bytes: 7 x ‘ ’ (Synchronization) 1 byte: ‘ ’ 6 bytes: 1-3 bytes ID of manufacturer, 4-6 bytes offset 6 bytes: 1-3 oktet ID of manufacturer, 4-6 offset 2 bytes bytes 4 bytes Direction of transmission IEEE / Ethernet frame format bytes: minimum frame length is 64 bytes Ethernet Frame Format
Debrecen, Train IT - Networks 65 Parameters of functionality Transmission speed10 Mbps (Manchester kódolás) Slot time512 bit-time Gap time9,6 s Max. no. of transmission frames16 Jam size32 bits Maximum frame lenght1518 byte Minimum frame length512 bits (64 bytes) Destination address can be Exact address of a station All bits are ‘1’ : broadcast, message is sent for all stations. Source address must not be a multiple address! Ethernet
Debrecen, Train IT - Networks 66 Waiting for frame to be transmitted. Formatting the frame. Is the chanel busy? Waiting the gap time. Starting transmission Is there a collision? Complete transmission.. Indicating of reaching the maximum numbers of trials Sending JAM signals. Increasing the number of trials. Max. number of trials is reached (16)? Computing the delay and waiting a random time period. I N I I N N Functionality of MAC sublayer: transmitting frames Ethernet Frame Transmission (CSMA/CD)
Debrecen, Train IT - Networks 67 Determining the time of repeated transmission of a frame: The slot time or round-trip delay is twice the time it takes for the first bit of frame to travel the length of the maximum distance between two nodes. During this time tne nodes detect the collisions almost surely. (Cable delay: ~5 μ s/1000m.) Slot time = 2 * (cable delay + repeaters delay)+ reserve time Slot time = 51.2 μs (2 * (2.5 km + delay of 4 repeaters), transmission time of 512 bits) Waiting time is the multiplication of slot time with a random integer, which depends on the number of transmission trials: 1 collision 1Waiting randomly 0 or 1 slot time 2 collisions Waiting randomly 0, 1, 2 or 3 slot times 3 collisions Waiting randomly 0, 1, 2 …7 slot times. 10 collisions Waiting randomly 0 – ( ) slot times 11 collisions - ” -.- “ - 15 collisions- “ - After 16 collisions the interface card does not try any more time. It indicates that the transmission failed. Ethernet Frame Transmission
Debrecen, Train IT - Networks 68 Is there any incoming signal? Indicating the busy state of chanel. Bit synchronization, waiting for the frame delimiter. Reading the frame. CRC and frame lengt are OK? Forwarding the frame to a higher protocol layer for processing Discarding the frame. N I N Functionality of MAC sublayer: receiving frames Dest. addr = own addr. or a broadcast addr.? I I N Receiving an Ethernet Frame
Debrecen, Train IT - Networks 69 Goal of developement: For 10 Base T Ethernet(IEEE 802.3) 10 times transmission speed, Preserve the cabling system, Keep the MAC method and the frame format. Major part of 10 Base T networks were connetcted to repeater with cables less than 100m. So the distance between two stations is at most 200m. In case of 100 Mbps transmission speed the outermost stations can detect collision, too during the time of 512 bits data transmission. Thus, shortening the maximum lenghts the method of CSMA/CD MAC can be retained. The standard: 100BASE-TX can reach 100 Mbit/s transmission speed in half-duplex mode, and 200 Mbit/s in full-duplex mode. 100BASE-FX separate transmit (Tx) and receive (Rx) lines together ensure 200 Mbit/s transmission speed. Fast Ethernet (802.3u)
Debrecen, Train IT - Networks Base X (100BaseTX, 100BaseFX) It was designed for divverent media (X): Category 5 unshielded (UTP) cable, Category 5 shielded (STP) cable, Optical fiber The 4B5B (4B/5B) binary coding developed for FDDI networks was adapted for 100 Base X. Every 4 bits of data (nibble) is coded on 5 bits. Only those 5-bit symbols are used, where exist at most two adjacent ‘0’ bits. The guaranteed 2 bit signal transmit ensures a good bit synchronizing. The 100BASE-TX version performs first 4B/5B coding, then performs shuffling and multi-level transmit, (MLT-3) coding. Fast Ethernet (802.3u)
Debrecen, Train IT - Networks 71 Data symbolsControl symbols IDLE11111 J11000 K10001 T01101 R00111 S11001 QUIET00000 HALT bit data group 5-bit symbol 4B5B codes 4B/5B binary coding
Debrecen, Train IT - Networks BASE-TX: – for Cat5e UTP cable(802.3ab). A Cat5e cables can reliably reach up to 125 Mbit/s transmission speed. For Gigabit bandwidth all of 4 wires is used. Hybrid cirtuits are required, which enable duplex transmission on a single pair. Thus the bandwidth increased up to 250 Mbit/s. The required 1000 Mbit/s speed can be achieved by applying the four pairs. 1000BASE-SX: 850 nm laser or LED sources on a multi mode optical fiber. It is not so expensive and suitable for short distances. 1000BASE-LX: 1310 nm laser sources on a single or multi mode optical fiber. Using laser on a single mode optical fiber the signals can be transferred even a distance of 5000 m. Separate optical fibers are set for transmitting (transmit, Tx) and for receiving (receive, Rx). The connection originally has duplex characteristics. Gigabit Ethernet (802.3ab, 802.3z)
Debrecen, Train IT - Networks 73 At Ethernet transmisson, each transmission has to be at least the length of slot time. The slot times can be calculated by the largest regular network architecture and the longest allowed cable parts. For a 10 and 100 Mbit/s speed Ethernet the slot time is 512 bit ie. 64 byte For a 1000 Mbit/s speed Ethernet the slot time is 4096 bit, ie.512 byte In case of collision detection a32 bit congestion signal has to be used The minimum gap between two non-colliding frames is called Frame gap On a10 Mbit/s speed Ethernet network after sending a frame each node has to be wait at least the time of 96 bits (9.6 microsecundum) In case of collision, each node – waiting the time of frame gap– leaves the cable idle Ethernet - Timing
Debrecen, Train IT - Networks 74 Ethernet Switching
Debrecen, Train IT - Networks 75 A collision domain occurs when multiple computers are connected to the single, shared transmisson media (line). Devices in second layer divide the collision domains. These devices control the transmission of frames by Mac-addresses assigned to the Ethernet devices. Second layer devices are the bridges and switches. The devices in second and third layers do not transmit collisions. The collision domains are divided smaller domains by the third level devices, as well. Ethernet - Segmentation
Debrecen, Train IT - Networks 76 A switch is essentially a fast speed bridge (in 2. layer) with multiple ports. Each port forms a separate collision domain. (Eg. A 24-port switch forms 24 separate collision domains.). Switches for each port stores the Ethernet addresses (Mac addresses) of the accessible devices from that port in a table (switching table). Switches upload and maintain their switching tables dynamically (based on the source addresses of incomingframes). The switching table is stored in a content-addressable memory (CAM). A CAM memory works reverse way compared to a common memory: if you enter a data (Ethernet address), the output will be the corresponding memory address. By the help of CAM, switches are able to find the port corresponding to a given MAC address without using any search algorythm. Ethernet – Switches
Debrecen, Train IT - Networks 77 The switch looks for the destination address of the incoming Ethernet frames in its switching table: If the destination address is a broadcast address (48 times ‘1’ bit value), then the frame will be transmitted on each port (except the incoming port). If the destination address can not be found in the switching table, then the frame will be transmitted on each port (except the incoming port). If the destination address can be found in the switching table, then the frame will be transmitted on the corresponding port (assuming, that this port is not identical with the incoming port of the frame). Ethernet Switching
Debrecen, Train IT - Networks 78 Switching methods: Store-and-forward: Transmission of the frame will start after the whole frame has been arrived. The switch recomputes the frame checksum (FCS). If the frame is corrupted, it is discarded. Cut-through switching: After arriving the destination address (6 bytes), the transmission of frame starts immediately on the outgoing port. Fragment free switching: After arriving a minimum frame length (64 bytes), the transmission of frame starts on the outgoing port. (Collided frames will not be transmitted.) Ethernet Switching
Debrecen, Train IT - Networks 79 IV. – Network Layer
Debrecen, Train IT - Networks 80 The IP Network Protocol IP (Internet Protocol) RFC 791 The network layer protocol of TCP/IP reference model. Widely used, it is the basic element of Internet. Most important characteristics: –Structure of IP header. »Consists of 32-bit words. »Length: Minimum 5, maximum 15 words. –IP addressing, address classes. –Fragment supporting. –Datagram services towards Transport Layer. –Ethernet frame type value: 0x0800.
Debrecen, Train IT - Networks 81 Structure of Internet Protocol Whole lengthVersionIHL Type of service Fragment offsetIdentifier MFMF DFDF Header checksum Upper Layer protocol TTL Optional field(s) Sender (Source) IP address Receiver (Destination) IP address
Debrecen, Train IT - Networks 82 IP Addresses Identifies the node in Network Layer. Dotted decimal notation eg Managing identifiers – InterNIC, IANA. For organisations not unique addresses but address domains (network identifiers) are assigned. The first part on an IP address identifies the network, the second part identifies the node (inside the network). The IP routing based on the network identifiers. How many bits should be in network IDs? –If too small, the large domains will be unused. –Il too large, only small subnetworks can be handled.
Debrecen, Train IT - Networks 83 Classes of IP Addresses Class C1Host #Network # Bit#1218 Class A0Host #Network # Bit# Class B0Host #Network # Bit#
Debrecen, Train IT - Networks 84 The Rule of the first byte 110 Leading bit(s) C Class Value of 1st byte 0A B
Debrecen, Train IT - Networks 85 Network mask Network mask (netmask): A 32 bit mask, which contains bits with values of 1 in place of network and subnetwork identifiers, and bits with values of 0 in place of host identifiers. By the help of netmask the boundary of network-machine can be modified, which boundary originally was determined (static way) by the classes. Prefix length: The number of value 1 in the netmask (number of network identifier bits in the netmask).
Debrecen, Train IT - Networks 86 Default Network Masks Network masks belonging to each classes: Class A : Network mask: Prefix lenght: 8. Class B : Network mask : Prefix lenght: 16. Class C: Network mask : Prefix lenght: 24.
Debrecen, Train IT - Networks 87 Special IP addresses Broadcast on actual network ID of the specific networkNetwork … AnythingLoopback Non specificated host Broadcast on the specific networkNetwork …
Debrecen, Train IT - Networks 88 Data Link and Network Addressing Problems
Debrecen, Train IT - Networks 89 In Network and Data Link Layers two independent address classes (IP addresses and Ethernet addresses) are considered. For encapsulation of Data Link Layer (forming an Ethernet frame) the physical address (MAC address) belonging to the IP address has to be determined. In certain cases (eg. Network boot, central IP address assignment) it could be necessary to determine the IP address by the help of Ethernet address. Problems of Dual Address Classes
Debrecen, Train IT - Networks 90 Network Address > Physical Address (ARP) ARP (Address Resolution Protocol) RFC 826 Each node records physical addresses belonging to the network addresses in a table (ARP table). How get a new data (pair of addresses) into the table? 1. Broadcasted ARP question: Who knows the physical address of the network address X? 2. Each node of of subnet receives and processes the frame of the question by a broadcast message. 3. If a node ‘identifies itself’ with network address X, sends an answer to the ARP question with own physical address.
Debrecen, Train IT - Networks 91 Structure of ARP Frame Type of protocol Action code Type of hardware Lenght of net. add. Physical address of destination Physical address of sender IP address of sender Length of ph. add. IP address of destination Words 1 - 2: General ARP header. Words : IPv4/Ethernet-specific data segment. Ethernet frame type value: 0x0806 Physical address of sender Physical address of destination
Debrecen, Train IT - Networks 92 Physical Address > Network Address (RARP) RARP (Reverse Address Resolution Protocol) RFC 903 It is needed only in special cases (eg. network boot). The RARP server(s) records the network addresses belongig to physical addresses in a table (RARP table). The table is maintained by the system administrator. The assignment of physical address – network address is static. In case of more RARP servers, the same network address has to be assigned to a physical address on each RARP server (the assignment must not depend on servers).
Debrecen, Train IT - Networks 93 Physical Address > Network Address (RARP) RARP (Reverse Address Resolution Protocol) RFC 903 Scheme of functioning: 1. RARP question: Who knows the network address of the physical address X? 2. Each node of of subnet receives the frame of the question by a broadcast message. 3. The RARP servers process the question: If the physical address X is found in their tables, send an answer for RARP question with the network address found in tables.
Debrecen, Train IT - Networks 94 Physical Address > Network Address (BOOTP) BOOTP (BOOTstrap Protocol) RFC 951 The RARP works within only one broadcast domain. The BOOTP is an IP/UDP-based protocol, where the client and the server could be in different broadcast domain. Phases of boot based on BOOTP: –Determine IP address. –Download Boot file (not investigated). Working scheme is the same as RARP. BOOTP agent – boot support through a router.
Debrecen, Train IT - Networks 95 Physical Address > Network Address (DHCP) DHCP (Dynamic Host Configuration Protocol) RFC 1531 Allows assignment of IP address domain. In case of more DHCP servers, the handled address domains should not overlep (in default). Packet structure similar to BOOTP. Clients get the IP address for a (renewable) time period.
Debrecen, Train IT - Networks 96 Physical Address > Network Address (DHCP) DHCP (Dynamic Host Configuration Protocol) scheme of functioning : 1. DHCP question: Who can give me an IP address? (DHCPDISCOVER) 2. Each node of of subnet receives the frame of the question by a broadcast message (DHCP relay agent). 3. A DHCP servers process the question: If there is a free IP address in the handled address domain, then send an answer to DHCP question with that IP address. (DHCPOFFER) 4. The client chooses one from the received DHCP answers, and sends a feedback of its choice to the corresponding DHCP server. (DHCPREQUEST) 5. The DHCP server „books” the choice of address (the address became occupied), and confirms client on booking. (DHCPACK/DHCPNAK) DHCPDECLINE: The assigned IP address by the server is invalid (in use). DHCPRELEASE: The client does not need for an IP address any more.
Debrecen, Train IT - Networks 97 IP Subnets
Debrecen, Train IT - Networks 98 IP Subnets Why is it necessary to create subnets? The logical functionality of the institute can be a reason. On an IP network more than one broadcast domains (usually with the same size) have to be created. How can we create a subnet? Some of the higher position bits of the host ID of the IP address will be used identifying the subnet. The new network-node boundary is denoted with the network mask (longer prefix is used).
Debrecen, Train IT - Networks 99 Subnets - Example Example: IP address of network: Default subnet mask: bits are used identifying the subnet. Network mask: subnets can be created.
Debrecen, Train IT - Networks 100 Subnets - Example Addresses of the subnets: No.Network IDHost Addresses
Debrecen, Train IT - Networks 101 Subnet Routing Destination IP address: E2 E1E0 Routing table: Destination Netmask Int. Next hop Metric E E E
Debrecen, Train IT - Networks 102 Subnet Routing Destination IP address : & Network mask:
Debrecen, Train IT - Networks 103 IP Network Problems in ‘90s
Debrecen, Train IT - Networks 104 The growth of Internet 90 January 90 April 90 July 90 October 91 January 91 April 91 July 91 October 92 January Routing table sizes of IP backbones
Debrecen, Train IT - Networks 105 Depletion of Internet Addresses Assignment status of classful addresses in 1992 (RFC 1466): Total Assigned Assigned (%) Class A % Class B % Class C %
Short Time solution: CIDR Debrecen, Train IT - Networks 106
Debrecen, Train IT - Networks 107 Problems of Classful IP Addressing- CIDR The solution: CIDR (Classless Inter-Domain Routing) RFC Assigning continuous class C addresses (instead of class B). By the help of a network mask with a variable length the network-machine boundary can be shifted with arbitrary number of bits (supernetting) or right (subnetting). Forming address domain zones based on locations. Joined routing informations by the help of network masks. Giving the mask representation of network addresses is mandatory:
Debrecen, Train IT - Networks 108 IP Address Domains of Continents The class C IP addresses are assigned based on the continents (sizes of routing tables can be reduced significantly) RFC 1366,1466: Asia, Australia Address domainContinent Europe North America Middle & South America
Debrecen, Train IT - Networks 109 Long Time solution: NAT
Debrecen, Train IT - Networks 110 NAT The major part of nodes take part „only” as clients in communication. It is sufficient to provide for clients possibilities of access to services for clients. Application dependent solutions: Proxy, ALG. Non application dependent solutions : NAT, PAT RFC , 2766, 3022.
Debrecen, Train IT - Networks 111 NAT Basics Address realm: Part of a network, where the uniqueness of IP addresses has to be ensured. Public/Global/External Network: Address realm with address domain managed by IANA. Private/Local Network: Address realm with local, organizational addressing / / /16
Debrecen, Train IT - Networks 112 NAT, Address Realms – Principle of Function Global address realm Local (private) address realm Private IP addresses: / / /8 Local (private) address realm Addressing informations
Debrecen, Train IT - Networks 113 Server NAT, Address Realms – Sending Packets Global address realm Local (private) address realm NAT Box Sender Data Client Sender Data Client private adr Client glob. adr NAT table
Debrecen, Train IT - Networks 114 Server NAT, Address Realms – Sending Packets Global address realm Local (private) address realm NAT Box Cél Answer Client Destin. Answer Client private adr Client glob. adr NAT table IP address IP addr + Port no.
Debrecen, Train IT - Networks 115 NAT Resources NAT solutions require resources (processor). Searching address transformation tables. Address exchange (port number exchange). Recompute checksums. There is no need to perform the computations for the whole PDU: –„Substracting” the old addresses from the old checksums. –„Adding” new addresses to the obtained result.
Debrecen, Train IT - Networks 116 IP - Routing
Debrecen, Train IT - Networks 117 Routing Basics Routing: Make decisions on the directions of transmitting packets (IP datagrams). Routing table: A table containing necessary informations for routing. Typical (most important) fields: Destination net Netmask Outgoing int. Next hop Metric
Debrecen, Train IT - Networks 118 Routing Basics Routed protocol: A general data transmission protocol belonging to Network Layer, which can be controlled by the router (eg. IP). Routing protocol: A protocol describing the propagation of necessary informations (exchange between routers) for building up routing table(s) (eg. RIP, OSPF, BGP).
Debrecen, Train IT - Networks 119 Routing Basics Autonomous System (AS): The routing administration unit of a network, where a common routing strategy (routing protocol) works. Metric: Measuring method of the quality of a path resulted by a given routing process. Basically there are two categories (can be transformed into each other): –Metric based on distance (cost). –Metric based on goodness.
Debrecen, Train IT - Networks 120 Basic Operations of Routers – Fitting IP Addresses 1./ The rows of the routing table is ordered descending by prefix length. N=1. This ensures, that in case of more than one matching lines the one with the longest prefix will be the result. 2./ If the line N does not exist in the table, then there is no matching line. The router discards the packet. The algorythm is terminated. 3./ A Bitwise AND operation is performed on every bit of the destination address of the packet and the network mask of line N. 4./ If the result of this AND operation is identical with the address of destination network in line N, then the address matches line N. The router transmits the packet towards the direction in line N. End of algorythm. 5./ N=N+1, continue with Step 2.
Debrecen, Train IT - Networks 121 Classification of Routing Configurations Minimal routing: Fully isolated (without router) network configuration (eg. giving IP address and network mask). Static routing: The routing table is maintained by the system administrator (eg. giving default gateway). Dynamic routing: The routing tables are maintained by some routing protocol. –Interior routing protocols (IGP - eg. RIP, OSPF). »The main principle is to determine the „best path” with a method of distance vector or link state. –Exterior routing protocols(EGP - eg. EGP, BGP). »The aim is not necessarily to determine the best path (policy based routing - BGP).
Debrecen, Train IT - Networks 122 Distance Vector Routing
Debrecen, Train IT - Networks 123 Distance Vector Routing Basic principle of operation: The routers keep records for all accessible destinations (machine or network) how can a given destination be reached on the best path (direction and distance – distance vector). The routers exchange these information in a certain time period. Concerning the new information, the routers check whether there is any necessary modification regarding the previously known best path.
Debrecen, Train IT - Networks 124 Distance Vector – Routing Table Problems Problem of too small initial value: If the optimal path is„corrupted” a path with larger cost (longer) can not replace it. Solution: Larger cost from the direction of optimal path overrides the (lower) cost. Problem of counting to infinity: In certain cases the procedure responds very slow to changing of topology.
Debrecen, Train IT - Networks 125 Count to Infinity- Example Consider the routing towards D. Starting routing entries (optimal paths to D): A: B,2 B: D,1 C: B, C B D A
Debrecen, Train IT - Networks 126 Count to Infinity- Example Consider changing of routing tables in case of corruption of link B-D: A B,2C,3C,4C,5…C,10C,11C,11 B ---C,3C,4C,5…C,10C,11C,11 C B,2A,3A,4A,5…A,10D,10D, C B D A
Debrecen, Train IT - Networks 127 Routing Information Protocol - RFC 1058 Characteristics of Routing Information Protocol (RIP): Distance vector based IGP protocol. Old, but continuously developed and enhanced. Metric: Number of hops (16=infinite distance). It can be used in cases of optimal paths with maximum length of 15 routers. Propagate routing informations in every 30 seconds. „Triggered update” for reducing the time of count to infinity. RIP V2 (RFC 1723) CIDR compatible.
Debrecen, Train IT - Networks 128 Enhanced Interior Gateway Routing Protocol (EIGRP) It is the own distance vector based routing protocol of Cisco. Multiple goals, flexible, scaleable. Metric: compound (computed from 5 variables, can be weighted): –bandwidth –delay –load –reliability –MTU
Debrecen, Train IT - Networks 129 Enhanced Interior Gateway Routing Protocol (EIGRP) Most important characteristics: CIDR compatible. The metric based on „Bandwith” in default. Mechanism of exploring neighbours (avoid broadcast). Handling count to infinity: –Split Horizon, Holddown Timer, Triggered update. –Recording potential substitute paths. Propagating updates (not the whole table). Integrated routing (can be used for multiple directed protocol).
Debrecen, Train IT - Networks 130 Link State Routing
Debrecen, Train IT - Networks 131 Link State Routing Scheme of functioning of Link State Routing: 1./ Exploring neighbours 2./ Measuring the costs (length) of the link to the neighbours. 3./ Creating packets containing the measurement results. 4./ Propagate the packets to all routers of the network unit. 5./ All routers know the topology of the network and can compute (eg. with Dijkstra algorythm) the optimal paths (spanning tree) to the other routers.
Debrecen, Train IT - Networks 132 Link State Routing– Processes (IS-IS)
Debrecen, Train IT - Networks 133 Open Shortest Path First - RFC 1131 Characteristics of Open Shortest Path First (OSPF): Link State Routng IGP protocol. New, recommended as default protocol since 90er years. Using smaller network unit (area) than AS. (Non disjunct) classification of routers: –Routers working inside the area. –Routers working on boundaries of areas. –Routers working on backbones. –Routers working on AS boundary. Able to perform equal cost, multiple paths routing. Using the „Service type” field of IP header. Recent version: OSPF V2 (RFC 2328).
Debrecen, Train IT - Networks 134 OSPF Areas The base of the decision process (Dijkstra algorythm) is the area. The areas form a „star pattern” with a special area – the backbone – in the center connecting the areas. Tasks of routers on area boundaries are complex: Separate decision process for all areas. Summarizing informations get from areas. Propagating the summarized informations to other areas. Inter area routing: Routing in source area as far as the boundary router. Routing on backbone as far as the boundary router of the destination area. Routing in destination area to destination network.
Debrecen, Train IT - Networks 135 Administration of OSPF Data Most important items of an OSPF router table: Type of destination (network, area boundary router, AS boundary router). Id. of destination (IP address). Type of service. Giving the path/paths towards destination: –Type of path (intra-area, inter-area, AS-external). –Cost of path. –Next router (IP address, interface of access).
Debrecen, Train IT - Networks 136 Transport Layer
Debrecen, Train IT - Networks 137 Transport Layer Protocols UDP - User Datagram Protocol RFC 768 Connection free, non-reliable Transport Layer protocol. TCP - Transmisson Control Protocol RFC 793 Connection based, Összeköttetés alapú, reliable Transport Layer protocol.
Debrecen, Train IT - Networks 138 UDP The UDP (User Datagram Protocol) is the connection free transport protocol of the TCP/IP protocol set. Transmission of datagrams without any guarantee (without confirmation). Failure management is to higher level (applications) protocols. The UDP protocol is suitable applications which do not need to concatenate sequences of segments. Eg. TFTP, SNMP, DHCP, DNS.
Debrecen, Train IT - Networks 139 Structure of UDP header Destination port numberSource port number ChecksumLength (byte)
Debrecen, Train IT - Networks 140 PORT Numbers- Protocols (RFC 1700) echo7/tcpecho echo7/udp echo ftp-data 20/tcp # File Transfer [Default D] ftp-data 20/udp # File Transfer [Default D] ftp 21/tcp # File Transfer [Control] telnet 23/tcp telnet telnet 23/udp telnet smtp 25/tcp mail # Simple Mail Trans smtp 25/udp mail # Simple Mail Trans http 80/tcp # World Wide Web HTTP http 80/udp # World Wide Web HTTP
Debrecen, Train IT - Networks 141 TCP The TCP (Transmission Control Protocol) is the connection based transfer protocol of the TCP/IP protocol set. It provides a reliable (receipted) bit stream for applications. Before starting data transmission, the two nodes build up a TCP connection (TCP session) by the help of the so called three-way handshake. Information to be submitted is divided into segments (64KB). Before transmission each segment gets a number. The sender keeps record on each transmitted TCP segments, and requires a receipt. The destination node reverts the original message from the segments, and receipts the segment(s). If a segment is missing, the TCP protocol ensures re-transmission of the missing segment.
Debrecen, Train IT - Networks 142 Structure of TCP Header Source port number No. of sequence (SEQ No.) No. of acknowledgement(ACK No.) Filling Data Offset URG pointer Destination port number ACKACK PSHPSH RSTRST SYNSYN FINFIN URGURG Window sizeBusy Checksum Options
Debrecen, Train IT - Networks 143 TCP – Three-Way Handshake TCP Client TCP Server 0. CLOSED LISTEN 1. SYN-SENT --> --> SYN-RECEIVED 2. ESTABLISHED <-- SYN-RECEIVED 3. ESTABLISHED --> --> ESTABLISHED 4. ESTABLISHED <-- ESTABLISHED
Debrecen, Train IT - Networks 144 Application Layer
Debrecen, Train IT - Networks 145 Application Layer Protocol The highest level protocol which ensures the communication required by the users via applications typically with client-server architecture). The most common protocols: Name-IP address assignment – dns Web, www – http File transfer – ftp, sftp Remote login – telnet, ssh – smtp; pop3, imap4
Debrecen, Train IT - Networks 146 HTTP Protocol The HTTP (HyperText Transfer Protocol) is the protocol of web, which is the most quickly spreading and most widely used part of internet. It provides easy information access We can navigate on World Wide Web by the help of hyperlinks. (A hyperlink is an object on a web page pointing to an other web page.) The URL address (Uniform Resource Locator) necessary for this is contained by the web page, usually embedded in the HTML code.
Debrecen, Train IT - Networks 147 HTTP Protocol The HTTP protocol is based on a client-server architecture. The web browser is a client application. A web browser requires components with client and server functionality, as well. At first the web browser examines the protocol, from which it determines whether an other program should be called or launched. It determines the IP address of web server via DNS. It builds up a session with web server via TCP. The data sent to HTTP server give the name of the folder (and the HTML file) containing the web page. The server responds the request by sending to client the text, voices, clips, and graphics defined on the HTML page. The client-side browser composes files, displays the web page, and closes the session.
Debrecen, Train IT - Networks 148 Traffic Filtering – Access Control Lists Without filtering the whole traffic is enabled. With traffic filtering you can control the traffic on a specified interface of the firewall (router): what kind of traffic is enabled or disabled. The control is described with a list (ACL): –Condition 1 specification / enable –Condition 2 specification / disable –… In the control list conditions can be stated for IP addresses, protocols (TCP/UDP), and port numbers (80=http, 25=smtp). If a packet does not match any list items, the packet is discarded (implicit deny). The traffic filtering works independently of routing.
Debrecen, Train IT - Networks 149 Wireless Network Technologies
Debrecen, Train IT - Networks 150 Wireless Network Technologies Local network technologies (WLAN, Wi-Fi): Wireless extension of an organizational LAN. Free frequencies for use (2.4 GHz, 5 GHz). –Spreading as the light. –2.4 GHz is near to resonance frequency of water! Ensures mobility on the organizational data communication network. Provides long distance connection (GPRS, EDGE, UMTS). Enables global network access. Extension of mobile phone technology to data transmission. Data (transmission) charges.
Debrecen, Train IT - Networks 151 Bases of Wireless Communication Wave: A kind of changing, which results point-to-point (cyclic) energy transfer. Amplitude: Distance between the zero and the maximum signal height. Frequency (F): Number of cycles in one second. Time of period (T): The time of one cycle T = 1/F. Wave length Distance between two identical signal height values. C = F = km/s (light speed)
Debrecen, Train IT - Networks 152 WLAN Devices Access Point, AP: Provides the access to a wired network (Internet) for clients (mobile devices). Bridge: A device for connecting two wired LAN. The connection can be done in Data Link Layer. Client adapter: Network card for wireless networks. RF devices: antennas, cables, connectors. Wi-Fi Certification!
Debrecen, Train IT - Networks 153 Antennas Antenna: A device developed for transmitting and receiving RF signals. The strength of signal transmission of an antenna can be controlled or uncontrolled. Antenna gain: Changing the strength of signal (power) compared to isotropic antenna (theoretical point source of waves). The gain measures how efficiently the antenna focuses the radiated RF energy. (measure of unit: dBi)
Debrecen, Train IT - Networks 154 Omnidirectional Antennas Isotropic antenna: A theoretical point source of waves (0 dBi). Dipol antenna: Rod shaped circle source of waves (2.2 dBi).
Debrecen, Train IT - Networks 155 Directional Antennas Yagi antenna: An antenna equipped with RF Mirrors and elements providing direction for waves (12 dBi).
Debrecen, Train IT - Networks 156 Directional Antennas Yagi antenna: An antenna equipped with RF Mirrors and elements providing direction for waves (12 dBi). Parabolic antenna: An antenna equipped with a parabolic mirror and a head positioned in the point of focus (22 dBi).
Debrecen, Train IT - Networks 157 WLAN Modes Infrastructure: The mobile devices are connected to the (wired) organizational network via a radio access point (AP). The mobile devices do not perform direct radio communication. Ad-hoc: The mobile devices are connected directly each other via their own radio interface. In case of large numbers of machines it is not efficient.
Debrecen, Train IT - Networks 158 WLAN Logical Architectures BSS (Basic Service Set): Network environment working within a coverage of a radio interface (AP). Identifying the network environment a text identifier (SSID) is used. IBSS (Independent BSS): Several independent BSS. It is used typically in Ad-hoc networks. DS (Distributed Systam): Several BSS connected via radio or wired infrastructure. ESS (Extended Service Set): Several BSS (with DS connection). The transit between BSSs is possible without any loss of network connections (Roaming).
Debrecen, Train IT - Networks 159 Scheme of WLAN Transmission Client AP 1. --> --> 2. < > --> 4. <-- The measured throughput is significantly less, than the theoretical bandwidth!
Debrecen, Train IT - Networks b 13 (overlapping) channels (EU) with 5 MHz bandwidth on 2.4 GHz. Four different data transmission speeds with four different coding and modulating technologies: 11 Mbps (least coverage) 5.5 Mbps 2 Mbps 1 Mbps (largest coverage)
Debrecen, Train IT - Networks g and a g: New coding and modulating technology on 2.4 GHz (PBCC, OFDM). 54 Mbps data transmission speed. Retain frequency (2.4 GHz) provides a backward compatibility for b systems a: Technology working on 5 GHz (light-like propagation). 54 Mbps data transmission speed. Requires a separate RF unit (5 GHz).
Debrecen, Train IT - Networks 162 Wireless Security SSID: Not a protective factor (it is only an identifier, can be intercepted). WEP (Wired Equivalent Privacy): RC4 encryption, tha standard specifies a 64-bit key, or in some manufacturer implementation a 128-bit key. Nowdays it is not safe, using free softwares for analyzing the trafic the key (even the 128-bit key) can be „obtained”. MAC address filtering: Based on the MAC addresses of clients the connection can be enabled or disabled. Not specified in WPA (Wi-Fi Protected Access): A system, (partly) containing the (second generation) security elements of i (Extensible Authentication Protocol, EAP; Temporary Key Integrity Protocol, TKIP).
Debrecen, Train IT - Networks 163 XP – The Most Important Network Commands
Debrecen, Train IT - Networks 164 Writing and Renewing the IP Configuration ipconfig – Writes the IP address, netmask, and the default gateway (for all network cards). ipconfig /all – Writes the whole configuration (MAC address, address of DNS server, expiration dates). ipconfig /release – „Releases” the IP address (previously assigned by DHCP). ipconfig /renew – Renew (asking again) the IP address assigned by DHCP. Before this one submitting an ipconfig /release command is recommended.
Debrecen, Train IT - Networks 165 Testing the Accessibility of a Node ping machine – Tests the accessibility of the given (by name or IP address) machine with 4 packets. ping –t machine – Tests the accessibility of the given machine with continuous packet sending (until pressing Ctrl+C). ping –a IP address – Beside testing it writes the DNS name belongigng to the IP address (Fully Qualified Domain Name).
Debrecen, Train IT - Networks 166 Testing the Accessibility of a Node ping –l size machine – Tests the accessibility of the machine with packets containing bytes given with parameter of size. ping –i ttl machine – Adjust the TTL field of IP packets to ttl during testing. (Investigates, wheter the machine can be accessed through routers max. number of ttl.)
Debrecen, Train IT - Networks 167 Exploring a Path to a Destination tracert machine – Writes the sequence of routers (hops) on a path leading to the machine (given with name or IP address). The DNS names of routers are displayed in the list (DNS names are backtracked from IP addresses). tracert –d machine – The IP addresses of routers are displayed in the list (faster, because DNS names are not backtracked from IP addresses).
Debrecen, Train IT - Networks 168 Displaying and Modifying the Routing Table route print – Displays the routing table: destination network, netmask, gateway, connection (interface), metric. netstat -nr – Identical with the route print command. route ADD destination MASK mask gateway METRIC metric – Inserts a new row into the routing table for the given destination network with the specified parameters ( mask, gateway, metric ). Despite of the occasionally displayed „Network database can not be open” error message the command can be executed normally (can be verified with the route print command). route DELETE destination MASK maszk – Deletes the given row (specified with the destination, mask parameters) of the routing table. Despite of the occasionally displayed „Network database can not be open” error message the command can be executed normally (can be verified with the route print command).
Debrecen, Train IT - Networks 169 Displaying and Modifying the ARP Table arp –a – Displays the ARP table (a table, containing the IP address – MAC address assignment). arp –s IP address Eth. address – Assigns the given IP address with the Eth. Address inserting a new entry in the ARP table (creates a static ARP entry). arp –d IP address – Deletes the row belonging to the given IP address from the ARP table.
Debrecen, Train IT - Networks 170 Writing NetBIOS Network Configuration nbtstat -n – Writes NetBIOS names of local machine. nbtstat –a machine – Lists the NetBIOS nametable of remote machine. Displays the Mac address of the given machine, as well. nbtstat –A IP address – Lists the NetBIOS nametable of remote machine with IP address. Displays the Mac address of the given IP address. nbtstat -r – Lists the names resolved by broadcasting or WINS. nbtstat -R – Deletes the list of resolved names by broadcasting.
Bibliography Andrew S. Tanenbaum, David J. Wetherall: Computer Networks, 5th edition, , Prentice Hall, Fred Halsall: Computer Networking and the Internet, 5th edition, , Addison Wesley, William Stallings: Data and Computer Communications, 8th edition, , Prentice Hall, RFC Documents: Debrecen, Train IT - Networks 171