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16-HighSpeedLANs - Data and Computer Communications...

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Unformatted text preview: Data and Computer Communications Communications Chapter 16 – High Speed LANs Chapter LAN Eighth Edition by William Stallings Lecture slides by Lawrie Brown High Speed LANs LAN Congratulations. I knew the record would stand until it was broken. Yogi Berra Yogi Introduction Introduction range of technologies Fast and Gigabit Ethernet Fibre Channel High Speed Wireless LANs Why High Speed LANs? Why speed and power of PCs has risen has graphics-intensive applications and GUIs for client/server computing centralized server farms power workgroups high-speed local backbone see LANs as essential to organizations now have requirements for Ethernet (CSMA/CD) Ethernet most widely used LAN standard developed by Xerox - original Ethernet IEEE 802.3 Carrier Sense Multiple Access with Carrier Collision Detection (CSMA/CD) Collision random / contention access to media ALOHA ALOHA developed for packet radio nets when station has frame, it sends then listens for a bit over max round trip time if receive ACK then fine if not, retransmit if no ACK after repeated transmissions, give up uses a frame check sequence (as in HDLC) frame may be damaged by noise or by another frame station transmitting at the same time (collision) station any overlap of frames causes collision max utilization 18% Slotted ALOHA Slotted time on channel based on uniform slots equal to time frame transmission time frame need central clock (or other sync mechanism) transmission begins at slot boundary frames either miss or overlap totally max utilization 37% both have poor utilization fail to use fact that propagation time is much less fail than frame transmission time than CSMA CSMA stations soon know transmission has started so first listen for clear medium (carrier sense) if medium idle, transmit if two stations start at the same instant, collision wait reasonable time wait if no ACK then retransmit collisions occur occur at leading edge of frame max utilization depends on propagation time max (medium length) and frame length (medium Nonpersistent CSMA Nonpersistent Nonpersistent CSMA rules: 1. 2. if medium idle, transmit iif medium busy, wait amount of time drawn from f probability distribution (retransmission delay) & retry probability random delays reduces probability of collisions capacity is wasted because medium will remain idle following end of transmission idle nonpersistent stations are deferential 1-persistent CSMA 1-persistent 1-persistent CSMA avoids idle channel time 1-persistent CSMA rules: 1-persistent rules: 1. 1. 2. 2. iif medium idle, transmit; f iif medium busy, listen until idle; then transmit f immediately immediately 1-persistent stations are selfish if two or more stations waiting, a collision is guaranteed guaranteed P-persistent CSMA P-persistent a compromise to try and reduce collisions and idle time idle p-persistent CSMA rules: p-persistent rules: 1. 1. 2. 3. if medium idle, transmit with probability p, and delay one time unit with probability (1–p) one if medium busy, listen until idle and repeat step 1 if transmission is delayed one time unit, repeat step 1 issue of choosing effective value of p to avoid instability under heavy load instability Value of p? Value have n stations waiting to send have waiting at end of tx, expected no of stations is np is if np>1 on average there will be a collision >1 on repeated tx attempts mean collisions likely repeated tx eventually when all stations trying to send have eventually continuous collisions hence zero throughput ontinuous collisions thus want np<1 for expected peaks of n thus np if heavy load expected, p small but smaller p means stations wait longer CSMA/CD Description CSMA/CD with CSMA, collision occupies medium with for duration of transmission for better if stations listen whilst transmitting CSMA/CD rules: 1. 2. 3. 4. if medium idle, transmit if busy, listen for idle, then transmit iif collision detected, jam and then cease f transmission transmission after jam, wait random time then retry CSMA/CD CSMA/CD Operation Which Persistence Algorithm? Algorithm? IEEE 802.3 uses 1-persistent IEEE uses both nonpersistent and p-persistent have both performance problems performance 1-persistent seems more unstable than ppersistent persistent because of greed of the stations but wasted time due to collisions is short with random backoff unlikely to collide on next attempt to send attempt Binary Exponential Backoff Binary for backoff stability, IEEE 802.3 and Ethernet for both use binary exponential backoff both stations repeatedly resend when collide stations when on first 10 attempts, mean random delay doubled value then remains same for 6 further attempts attempts after 16 unsuccessful attempts, station gives up and after reports error reports 1-persistent algorithm with binary exponential 1-persistent backoff efficient over wide range of loads backoff but backoff algorithm has last-in, first-out effect has Collision Detection Collision on baseband bus collision produces higher signal voltage collision detected if cable signal greater than collision single station signal single signal is attenuated over distance limit to 500m (10Base5) or 200m (10Base2) activity on more than one port is collision use special collision presence signal on twisted pair (star-topology) IEEE 802.3 Frame Format IEEE 10Mbps Specification (Ethernet) (Ethernet) 10BASE5 Transmission medium Signaling technique Topology Coaxial cable (50 ohm) Baseband (Manchester) Bus 10BASE2 Coaxial cable (50 ohm) Baseband (Manchester) Bus 185 30 5 10BASE-T Unshielded twisted pair Baseband (Manchester) Star 100 Ñ 0 . 4 to 0 . 6 10BASE-FP 850-nm optical fiber pair Manchester/on-off Star 500 33 62.5/125 µm Maximum segment 500 length (m) Nodes per segment 100 Cable diameter (mm) 10 100Mbps Fast Ethernet 100Mbps 100BASE-TX Transmission medium Signaling technique Data rate Maximum segment length Network span 2 pair, STP MLT-3 100 Mbps 100 m 200 m 2 pair, Category 5 UTP MLT-3 100 Mbps 100 m 200 m 100BASE-FX 2 optical fibers 4B5B, NRZI 100 Mbps 100 m 400 m 100BASE-T4 4 pair, Category 3, 4, or 5 UTP 8B6T, NRZ 100 Mbps 100 m 200 m 100BASE-X 100BASE-X uses a unidirectional data rate 100 Mbps over single twisted pair or optical fiber link single encoding scheme same as FDDI same 4B/5B-NRZI 100BASE-TX 100BASE-TX • uses two pairs of twisted-pair cable for tx & rx • STP and Category 5 UTP allowed • MTL-3 signaling scheme is used two physical medium specifications 100BASE-FX • uses two optical fiber cables for tx & rx • convert 4B/5B-NRZI code group into optical signals 100BASE-T4 100BASE-T4 100-Mbps over lower-quality Cat 3 UTP 100-Mbps UTP takes advantage of large installed base takes does not transmit continuous signal between packets useful in battery-powered applications so data stream split into three separate streams four twisted pairs used data transmitted and received using three pairs two pairs configured for bidirectional transmission two pairs can not get 100 Mbps on single twisted pair can 100 use ternary signaling scheme (8B6T) 100BASE-T Options 100BASE-T Full Duplex Operation Full traditional Ethernet half duplex using full-duplex, station can transmit and receive simultaneously receive 100-Mbps Ethernet in full-duplex mode, giving a 100-Mbps theoretical transfer rate of 200 Mbps theoretical stations must have full-duplex adapter cards and must use switching hub each station constitutes separate collision domain CSMA/CD algorithm no longer needed 802.3 MAC frame format used Mixed Configurations Mixed Fast Ethernet supports mixture of existing 10Mbps LANs and newer 100-Mbps LANs supporting older and newer technologies e.g. 100-Mbps backbone LAN supports 10-Mbps hubs e.g. 100-Mbps • • • stations attach to 10-Mbps hubs using 10BASE-T hubs connected to switching hubs using 100BASE-T high-capacity workstations and servers attach directly to -capacity 10/100 switches 10/100 • switches connected to 100-Mbps hubs use 100-Mbps links • 100-Mbps hubs provide building backbone • connected to router providing connection to WAN connected to connection Gigabit Ethernet Configuration Configuration Gigabit Ethernet - Differences Gigabit carrier extension at least 4096 bit-times long (512 for 10/100) frame bursting not needed if using a switched hub to not provide dedicated media access provide Gigabit Ethernet – Physical Gigabit 10Gbps Ethernet 10Gbps growing interest in 10Gbps Ethernet for high-speed backbone use with future wider deployment alternative to ATM and other WAN technologies alternative WAN uniform technology for LAN, MAN, or WAN advantages of 10Gbps Ethernet no expensive, bandwidth-consuming conversion no between Ethernet packets and ATM cells IP and Ethernet together offers QoS and traffic IP QoS policing approach ATM policing have a variety of standard optical interfaces 10Gbps Ethernet Configurations Configurations 10Gbps Ethernet Options 10Gbps Fibre Channel - Background Fibre I/O channel direct point to point or multipoint comms link hardware based, high speed, very short hardware distances distances based on interconnected access points software based protocol with flow control, software error detection & recovery error for end systems connections network connection Fibre Channel Fibre combines best of both technologies channel oriented data type qualifiers for routing frame payload link level constructs associated with I/O ops protocol interface specifications to support existing I/O protocol architectures architectures full multiplexing between multiple destinations peer to peer connectivity internetworking to other connection technologies network oriented Fibre Channel Requirements Fibre full duplex links with two fibers per link 100 Mbps to 800 Mbps on single line 100 support distances up to 10 km support to small connectors high-capacity utilization, distance insensitivity greater connectivity than existing multidrop channels broad availability multiple cost/performance levels carry multiple existing interface command sets for carry existing channel and network protocols Fibre Channel Network Fibre Fibre Channel Protocol Architecture Architecture FC-0 Physical Media FC-1 Transmission Protocol FC-2 Framing Protocol FC-3 Common Services FC-4 Mapping Fibre Channel Physical Media Fibre 800 Mbps Single mode fiber 50-µm multimode fiber 62.5-µm multimode fiber Video coaxial cable Miniature coaxial cable Shielded twisted pair 10 km 0.5 km 175 m 50 m 14 m 28 m 400 Mbps 10 km 1 km 1 km 71 m 19 m 46 m 200 Mbps 10 km 2 km 1 km 100 m 28 m 57 m 100 Mbps Ñ Ñ Ñ 100 m 42 m 80 m Fibre Channel Fabric Fibre most general supported topology is fabric or switched topology switched arbitrary topology with at least one switch to interconnect number of end systems interconnect may also consist of switched network may also when data transmitted into fabric, edge switch uses when destination port address to determine location destination either deliver frame to node attached to same switch or transfers frame to adjacent switch or routing transparent to nodes Fabric Advantages Fabric scalability of capacity protocol independent distance insensitive distance insensitive switch and transmission link technologies switch and may change without affecting overall configuration configuration burden on nodes minimized Alternative Topologies Alternative Point-to-point topology only two ports directly connected, so no routing needed simple, low-cost topology up to 126 nodes in loop operates roughly equivalent to token ring Arbitrated loop topology topologies, transmission media, and data topologies, rates may be combined rates Fibre Channel Applications Fibre Fibre Channel Prospects Fibre backed by Fibre Channel Association various interface cards available widely accepted as peripheral device widely interconnect interconnect technically attractive to general high-speed LAN requirements requirements must compete with Ethernet and ATM LANs cost and performance issues will dominate cost consideration of competing technologies Summary Summary High speed LANs emergence Ethernet technologies CSMA & CSMA/CD media access 10Mbps ethernet 100Mbps ethernet 1Gbps ethernet 10Gbps ethernet Fibre Channel ...
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