LAN Protocols LAN Protocols CSE  Fall  Instructor N

LAN Protocols LAN Protocols CSE Fall Instructor N - Description

Vlajic Required reading Garcia 67 68 brPage 2br How to allow station to place groups of bits on the medium Aloha CSMA Scheduling Schemes How to transmit data bits over a medium ASK FSK PSK Line Coding How to reliably transmit groups of bits frames o ID: 27755 Download Pdf

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LAN Protocols LAN Protocols CSE Fall Instructor N

Vlajic Required reading Garcia 67 68 brPage 2br How to allow station to place groups of bits on the medium Aloha CSMA Scheduling Schemes How to transmit data bits over a medium ASK FSK PSK Line Coding How to reliably transmit groups of bits frames o

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LAN Protocols LAN Protocols CSE Fall Instructor N




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Page 1
LAN Protocols LAN Protocols CSE 3213, Fall 2010 Instructor: N. Vlajic Required reading: Garcia 6.7, 6.8
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How to allow station to place groups of bits on the medium? Aloha, CSMA, Scheduling Schemes How to transmit data (bits) over a medium? ASK, FSK, PSK, Line Coding How to reliably transmit groups of bits (frames) over the medium? Forward Error Correct ion (e.g. Internet Checksum, CRC) Flow & Error Control (e.g. Go-Back-N, Selective Repeat) 2.1 2.2 0100101111
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What is LAN? Local Area Network Local Area Network (LAN) (LAN) properties private

ownership private ownership freedom from regulatory constraints of WANs low cost low cost single broadcast medium relatively small number of stations complex and expensive switching equipment NOT necessary high speed high speed short distance ~ 1 km between computers relatively error free (high-speed) communication possible complex error control unnecessary
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What is LAN? (cont.) computers computers and network devices network devices (e.g. printers) connected to broadcast cabling system broadcast cabling system through network interfac e card (NIC) network interfac e card (NIC)

computers connected via a LAN to the Internet need all 5 layers of the Internet model 3 upper layers (network, transpor t, application) are common to all LANs physical layer can be considerably different data link layer is divided into 2 sublayer: medium access control MAC ) – coordinates access to shared medium; provides connectionless transfer of datagr ams – several standards !!! logical link control LLC may be needed to provid e extra flow and error control to upper layers (in reality, only IP exi sts, and IP doe s not need additional flow and error control) – single IEEE 802.2 standard

Typical LAN Typical LAN Structure Structure
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Ethernet Ethernet (IEEE 802.3) (IEEE 802.3)
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MAC Protocols: Ethernet Ethernet Ethernet History History set of protocols at the physical and data link layer (MAC sublayer) developed by Robert Metcal fe, at Xerox, in 1970s promoted and used by Dec, IBM and Xerox in 1980s 10 Mbps Ethernet became an IEEE standard in 1985 IEEE 802.3 IEEE 802.3 high-speed versions: 100 Mbps Fast Ethernet (1995) 1000 Mbps - Gigabit Ethernet (1998) 10 Gbps 10 Gigabit Ethernet (2002) 100 Gbps 100 Gigabit Ethernet (2007 / 2010) currently used

in about 80-90 % of all LANs
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MAC Protocols: Ethernet (cont.) IEEE 802.3 IEEE 802.3 (10 Mbps) (10 Mbps) MAC Features MAC Features backoff : 1-persistent CSMA/CD CSMA/CD with truncated binary exponential backoff algorithm if medium idle – transmit; if medium busy, wait until idle then transmit with p=1; in case of retransmission, re-tr ansmission time is determined by selecting an integer in range: 0 < r < 2 , where k=min(n,10) give up after 16 retransmissions frame size : original IEEE 802.3 was designed to operate at 10 Mbps over max distance of 2500 [m] with 4 repeaters

(additional delay!!!) 2*10 [m/sec] 2*t prop + delays on repeaters 51.2 P 512 [bits] min frame size = 512 bits = 64 bytes = 46 + 18 max frame size = 1518 bytes = 1500 + 18 (prevents one station from monopolizing the medium) for the given min frame size, each 10x increase in bit-rate is accompanied with 10x decrease in max distance min frame time = 2*max segment / c = min frame size / data rate
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MAC Protocols: Ethernet (cont.) IEEE 802.3 IEEE 802.3 (10 Mbps) (10 Mbps) MAC Frame MAC Frame – 7 bytes / 56 bits of alternating 0s and 1s alerts receiving stations of the coming frame

and enables them to synchronize – 56 bits long , to allow stations to synchronize even if they miss some bits at the beginning added at the physical layer, no t (formally) part of the frame –1 byte ( 10101011 signals the beginning of a frame; last chance for synchronization two consecutive 1-bits indicate that the next bit is the first bit of the destination address –6 bytes contains the physical address of the station to receive the frame –6 bytes contains the physical address of the sending station 64 to 1518 bytes
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10 MAC Protocols: Ethernet (cont.) IEEE 802.3 IEEE 802.3

MAC Frame MAC Frame (cont.) (cont.) –2 bytes indicates the number of bytes in ‘data’ (information) field min allowable frame size 64 bytes, with 18 bytes of overhead min data length = 46 bytes max allowable frame size 1518 bytes, with 18 bytes of overhead max data length = 1500 bytes – 46 to 1500 bytes data from upper-layer protocols ensures that the frame size is always at least 64 bytes –4 bytes CCITT 32-bit CRC check that covers addresses, length and data 64 to 1518 bytes
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11 MAC Protocols: Ethernet (cont.) IEEE 802.3 IEEE 802.3 10 Mbps 10 Mbps Physical Layer Physical Layer

10 Mbps Mthernet uses Manchester signaling – additional bandwidth to achieve better synchronization, not a big issue thick (10 mm) coaxial cable Ethernet – awkward to handle and install thin (5 mm) coaxial cable Ethernet – cheaper and easier to handle, but the length of each segment cannot exceed 200 m , due to high level of attenuation in thin coaxial cable unshielded twisted pair Ethernet – low-cost and prevalent in offices, but due to poor transmission qualitie s of twisted pair the length of individual links is limited to 100 m hub – multiport repeater baseband
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Ethernet vs. Telephone Cable MAC Protocols: Ethernet (cont.) Ethernet Coaxial Cable Ethernet Coaxial Cable Ethernet Twisted Pair Ethernet Twisted Pair
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13 IEEE 802.3 IEEE 802.3 100 Mbps 100 Mbps Physical Layer Physical Layer MAC Protocols: Ethernet (cont.) 100 Mbps Ethernet uses a combination of 4B/5B block coding MLT-3 linear coding (instead of Manchester coding) to minimize the demand on bandwidth
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14 Token Ring Token Ring (IEEE 802.5) (IEEE 802.5)
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15 MAC Protocols: Token Ring History History set of protocols at the phy sical and data link

layer (MAC sublayer) developed by IBM in 1980s IEEE 802.5 IEEE 802.5 standard modeled after IBM Token Ring in 1990s IBM and IEEE specifications differ in minor ways: IBM’s Token Ring specifies a star; IEEE 802.5 does not specify a topology, but most IEEE 802.5 impl ementations are based on a star IBM’s Token Ring uses twisted-pair wire; IEEE 802.5 does not specify a media type speed : 4 Mbps and 16 Mbps signalling : Differential Manchester size : max 250 stations
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16 Wiring Center MAC Protocols: Token Ring (cont.) Token Ring Token Ring Advantages Advantages fairness and

stability Token Ring Token Ring Disadvantages Disadvantages entire network fails if any link, station or mechanism for token passing fails Token Ring with Token Ring with Star Topology Star Topology stations connected to a hub ( Multistation Access Unit ) in ‘star’ fashion physical star, logical ring hub performs token passing management and network diagnostics advantage : failed wires or stations can be easily bypassed disadvantage : hub – single point of failure
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17 MAC Protocols: Token Ring (cont.) IEEE 802.5 IEEE 802.5 MAC Frame MAC Frame two basic frame formats supported:

data / control frame format: 21-byte overhead + data token frame format: 3-byte – alerts arrival of a token / data / control frame – determines the frame type – token or data/control – indicates whether frame contains data or control info – CCITT-32 CRC checksum – signals the end of token / data frame – tells the sending device whether the destination device is on the ring and, if it is, whethe r it copied the frame primitive ACK Max frame size = 4500 bytes. Token frame format SD FC AC Destination address Source address Information FCS 14 ED FS Data frame format SD AC ED
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(1) Cost Cost Ethernet is generally less expensi ve and easier to install than Token Ring . (2) Stability Stability Token Ring is generally more secu re and more stable than Ethernet. (3) Scalability Scalability It is usually more difficult to add more computers on a Token Ring LAN than it is to an Ethernet LAN. However, as additional computers are added, performance degradatio n will be less pr onounced on the Token Ring LAN than it will be on the Ethernet LAN. (4) QoS QoS Ethernet uses CSMA/CD media ac cess control and Token Ring uses token passing. This makes Ethernet better suited in a

situation where there are a large number of computers sending fewer, larger data frames. Token Ring is better suited for small to medium size LANs sending many, smaller data frames. Performance Comparison Ethernet vs. Token Ring Ethernet vs. Token Ring Wiring Center