1. ECS 152A 9. Local Area Networks

2. LAN Applications (1) Personal computer LANs —Low cost —Limited data rate Back end networks —Interconnecting large systems (mainframes and large storage devices) High data rate High speed interface Distributed access Limited distance Limited number of devices

3. LAN Applications (2) Storage Area Networks —Separate network handling storage needs —Detaches storage tasks from specific servers —Shared storage facility across high-speed network —Hard disks, tape libraries, CD arrays —Improved client-server storage access —Direct storage to storage communication for backup High speed office networks —Desktop image processing —High capacity local storage Backbone LANs —Interconnect low speed local LANs —Reliability —Capacity —Cost

4. Storage Area Networks

5. LAN Architecture Topologies Transmission medium Layout Medium access control

6. Topologies Tree Bus —Special case of tree One trunk, no branches Ring Star

7. LAN Topologies

8. Bus and Tree Multipoint medium Transmission propagates throughout medium Heard by all stations —Need to identify target station Each station has unique address Full duplex connection between station and tap —Allows for transmission and reception Need to regulate transmission —To avoid collisions —To avoid hogging Data in small blocks - frames Terminator absorbs frames at end of medium

9. Frame Transmission on Bus LAN

10. Ring Topology Repeaters joined by point to point links in closed loop —Receive data on one link and retransmit on another —Links unidirectional —Stations attach to repeaters Data in frames —Circulate past all stations —Destination recognizes address and copies frame —Frame circulates back to source where it is removed Media access control determines when station can insert frame

11. Frame Transmission Ring LAN

12. Star Topology Each station connected directly to central node —Usually via two point to point links Central node can broadcast —Physical star, logical bus —Only one station can transmit at a time Central node can act as frame switch

13. Choice of Topology Reliability Expandability Performance Needs considering in context of: —Medium —Wiring layout —Access control

14. Bus LAN Transmission Media (1) Twisted pair —Early LANs used voice grade cable —Didn’t scale for fast LANs —Not used in bus LANs now Baseband coaxial cable —Uses digital signalling —Original Ethernet

15. Bus LAN Transmission Media (2) Broadband coaxial cable —As in cable TV systems —Analog signals at radio frequencies —Expensive, hard to install and maintain —No longer used in LANs Optical fiber —Expensive taps —Better alternatives available —Not used in bus LANs All hard to work with compared with star topology twisted pair Coaxial baseband still used but not often in new installations

16. Ring and Star Usage Ring —Very high speed links over long distances —Single link or repeater failure disables network Star —Uses natural layout of wiring in building —Best for short distances —High data rates for small number of devices

17. Choice of Medium Constrained by LAN topology Capacity Reliability Types of data supported Environmental scope

18. Media Available (1) Voice grade unshielded twisted pair (UTP) —Cat 3 —Cheap —Well understood —Use existing telephone wiring in office building —Low data rates Shielded twisted pair and baseband coaxial —More expensive than UTP but higher data rates Broadband cable —Still more expensive and higher data rate

19. Media Available (2) High performance UTP —Cat 5 and above —High data rate for small number of devices —Switched star topology for large installations Optical fiber —Electromagnetic isolation —High capacity —Small size —High cost of components —High skill needed to install and maintain Prices are coming down as demand and product range increases

20. Protocol Architecture Lower layers of OSI model IEEE 802 reference model Physical Logical link control (LLC) Media access control (MAC)

21. IEEE 802 v OSI

22. 802 Layers - Physical Encoding/decoding Preamble generation/removal Bit transmission/reception Transmission medium and topology

23. 802 Layers - Logical Link Control Interface to higher levels Flow and error control

24. Logical Link Control Transmission of link level PDUs between two stations Must support multiaccess, shared medium Relieved of some link access details by MAC layer Addressing involves specifying source and destination LLC users —Referred to as service access points (SAP) —Typically higher level protocol

25. LLC Services Based on HDLC Unacknowledged connectionless service Connection mode service Acknowledged connectionless service

26. LLC Protocol Modeled after HDLC Asynchronous balanced mode to support connection mode LLC service (type 2 operation) Unnumbered information PDUs to support Acknowledged connectionless service (type 1) Multiplexing using LSAPs

27. Media Access Control Assembly of data into frame with address and error detection fields Disassembly of frame —Address recognition —Error detection Govern access to transmission medium —Not found in traditional layer 2 data link control For the same LLC, several MAC options may be available

28. LAN Protocols in Context

29. Media Access Control Where —Central Greater control Simple access logic at station Avoids problems of co-ordination Single point of failure Potential bottleneck —Distributed How —Synchronous Specific capacity dedicated to connection —Asynchronous In response to demand

30. Asynchronous Systems Round robin —Good if many stations have data to transmit over extended period Reservation —Good for stream traffic Contention —Good for bursty traffic —All stations contend for time —Distributed —Simple to implement —Efficient under moderate load —Tend to collapse under heavy load

31. MAC Frame Format MAC layer receives data from LLC layer MAC control Destination MAC address Source MAC address LLS CRC MAC layer detects errors and discards frames LLC optionally retransmits unsuccessful frames

32. Generic MAC Frame Format

33. Bridges Ability to expand beyond single LAN Provide interconnection to other LANs/WANs Use Bridge or router Bridge is simpler —Connects similar LANs —Identical protocols for physical and link layers —Minimal processing Router more general purpose —Interconnect various LANs and WANs —see later

34. Why Bridge? Reliability Performance Security Geography

35. Functions of a Bridge Read all frames transmitted on one LAN and accept those address to any station on the other LAN Using MAC protocol for second LAN, retransmit each frame Do the same the other way round

36. Bridge Operation

37. Bridge Design Aspects No modification to content or format of frame No encapsulation Exact bitwise copy of frame Minimal buffering to meet peak demand Contains routing and address intelligence —Must be able to tell which frames to pass —May be more than one bridge to cross May connect more than two LANs Bridging is transparent to stations —Appears to all stations on multiple LANs as if they are on one single LAN

38. Bridge Protocol Architecture IEEE 802.1D MAC level —Station address is at this level Bridge does not need LLC layer —It is relaying MAC frames Can pass frame over external comms system —e.g. WAN link —Capture frame —Encapsulate it —Forward it across link —Remove encapsulation and forward over LAN link

39. Connection of Two LANs

40. Fixed Routing Complex large LANs need alternative routes —Load balancing —Fault tolerance Bridge must decide whether to forward frame Bridge must decide which LAN to forward frame on Routing selected for each source-destination pair of LANs —Done in configuration —Usually least hop route —Only changed when topology changes

41. Bridges and LANs with Alternative Routes

42. Spanning Tree Bridge automatically develops routing table Automatically update in response to changes Frame forwarding Address learning Loop resolution

43. Frame forwarding Maintain forwarding database for each port —List station addresses reached through each port For a frame arriving on port X: —Search forwarding database to see if MAC address is listed for any port except X —If address not found, forward to all ports except X —If address listed for port Y, check port Y for blocking or forwarding state Blocking prevents port from receiving or transmitting —If not blocked, transmit frame through port Y

44. Address Learning Can preload forwarding database Can be learned When frame arrives at port X, it has come form the LAN attached to port X Use the source address to update forwarding database for port X to include that address Timer on each entry in database Each time frame arrives, source address checked against forwarding database

45. Spanning Tree Algorithm Address learning works for tree layout —i.e. no closed loops For any connected graph there is a spanning tree that maintains connectivity but contains no closed loops Each bridge assigned unique identifier Exchange between bridges to establish spanning tree

46. Loop of Bridges

47. Layer 2 and Layer 3 Switches Now many types of devices for interconnecting LANs Beyond bridges and routers Layer 2 switches Layer 3 switches

48. Hubs Active central element of star layout Each station connected to hub by two lines —Transmit and receive Hub acts as a repeater When single station transmits, hub repeats signal on outgoing line to each station Line consists of two unshielded twisted pairs Limited to about 100 m —High data rate and poor transmission qualities of UTP Optical fiber may be used —Max about 500 m Physically star, logically bus Transmission from any station received by all other stations If two stations transmit at the same time, collision

49. Hub Layouts Multiple levels of hubs cascaded Each hub may have a mixture of stations and other hubs attached to from below Fits well with building wiring practices —Wiring closet on each floor —Hub can be placed in each one —Each hub services stations on its floor

50. Two Level Star Topology

51. Buses and Hubs Bus configuration —All stations share capacity of bus (e.g. 10Mbps) —Only one station transmitting at a time Hub uses star wiring to attach stations to hub —Transmission from any station received by hub and retransmitted on all outgoing lines —Only one station can transmit at a time —Total capacity of LAN is 10 Mbps Improve performance with layer 2 switch

52. Shared Medium Bus and Hub

53. Shared Medium Hub and Layer 2 Switch

54. Layer 2 Switches Central hub acts as switch Incoming frame from particular station switched to appropriate output line Unused lines can switch other traffic More than one station transmitting at a time Multiplying capacity of LAN

55. Layer 2 Switch Benefits No change to attached devices to convert bus LAN or hub LAN to switched LAN For Ethernet LAN, each device uses Ethernet MAC protocol Device has dedicated capacity equal to original LAN —Assuming switch has sufficient capacity to keep up with all devices —For example if switch can sustain throughput of 20 Mbps, each device appears to have dedicated capacity for either input or output of 10 Mbps Layer 2 switch scales easily —Additional devices attached to switch by increasing capacity of layer 2

56. Types of Layer 2 Switch Store-and-forward switch —Accepts frame on input line —Buffers it briefly, —Then routes it to appropriate output line —Delay between sender and receiver —Boosts integrity of network Cut-through switch —Takes advantage of destination address appearing at beginning of frame —Switch begins repeating frame onto output line as soon as it recognizes destination address —Highest possible throughput —Risk of propagating bad frames Switch unable to check CRC prior to retransmission

57. Layer 2 Switch v Bridge Layer 2 switch can be viewed as full-duplex hub Can incorporate logic to function as multiport bridge Bridge frame handling done in software Switch performs address recognition and frame forwarding in hardware Bridge only analyzes and forwards one frame at a time Switch has multiple parallel data paths —Can handle multiple frames at a time Bridge uses store-and-forward operation Switch can have cut-through operation Bridge suffered commercially —New installations typically include layer 2 switches with bridge functionality rather than bridges

58. Problems with Layer 2 Switches (1) As number of devices in building grows, layer 2 switches reveal some inadequacies Broadcast overload Lack of multiple links Set of devices and LANs connected by layer 2 switches have flat address space —Allusers share common MAC broadcast address —If any device issues broadcast frame, that frame is delivered to all devices attached to network connected by layer 2 switches and/or bridges —In large network, broadcast frames can create big overhead —Malfunctioning device can create broadcast storm Numerous broadcast frames clog network

59. Problems with Layer 2 Switches (2) Current standards for bridge protocols dictate no closed loops —Only one path between any two devices —Impossible in standards-based implementation to provide multiple paths through multiple switches between devices Limits both performance and reliability. Solution: break up network into subnetworks connected by routers MAC broadcast frame limited to devices and switches contained in single subnetwork IP-based routers employ sophisticated routing algorithms —Allow use of multiple paths between subnetworks going through different routers

60. Problems with Routers Routers do all IP-level processing in software —High-speed LANs and high-performance layer 2 switches pump millions of packets per second —Software-based router only able to handle well under a million packets per second Solution: layer 3 switches —Implementpacket-forwarding logic of router in hardware Two categories —Packet by packet —Flow based

61. Packet by Packet or Flow Based Operates insame way as traditional router Order of magnitude increase in performance compared to software-based router Flow-based switch tries to enhance performance by identifying flows of IP packets —Same source and destination —Done by observing ongoing traffic or using a special flow label in packet header (IPv6) —Once flow is identified, predefined route can be established

62. Typical Large LAN Organization Thousands to tens of thousands of devices Desktop systems links 10 Mbps to 100 Mbps —Into layer 2 switch Wireless LAN connectivity available for mobile users Layer 3 switches at local network's core —Form local backbone —Interconnected at 1 Gbps —Connect to layer 2 switches at 100 Mbps to 1 Gbps Servers connect directly to layer 2 or layer 3 switches at 1 Gbps Lower-cost software-based router provides WAN connection Circles in diagram identify separate LAN subnetworks MAC broadcast frame limited to own subnetwork

63. Typical Large LAN Organization Diagram

64. High Speed LANs Range of technologies —Fast and Gigabit Ethernet —Fibre Channel —High Speed Wireless LANs

65. Why High Speed LANs? Office LANs used to provide basic connectivity —Connecting PCs and terminals to mainframes and midrange systems that ran corporate applications —Providing workgroup connectivity at departmental level —Traffic patterns light Emphasis on file transfer and electronic mail Speed and power of PCs has risen —Graphics-intensive applications and GUIs MIS organizations recognize LANs as essential —Began with client/server computing Now dominant architecture in business environment Intranetworks Frequent transfer of large volumes of data

66. Applications Requiring High Speed LANs Centralized server farms —User needs to draw huge amounts of data from multiple centralized servers —E.g. Color publishing Servers contain tens of gigabytes of image data Downloaded to imaging workstations Power workgroups Small number of cooperating users —Draw massive data files across network —E.g. Software development group testing new software version or computer-aided design (CAD) running simulations High-speed local backbone —Processing demand grows —LANs proliferate at site —High-speed interconnection is necessary

67. Ethernet (CSMA/CD) Carriers Sense Multiple Access with Collision Detection Xerox - Ethernet IEEE 802.3

68. IEEE802.3 Medium Access Control Random Access — Stations access medium randomly Contention —Stations content for time on medium

69. ALOHA Packet Radio When station has frame, it sends Station listens (for max round trip time)plus small increment If ACK, fine. If not, retransmit If no ACK after repeated transmissions, give up Frame check sequence (as in HDLC) If frame OK and address matches receiver, send ACK Frame may be damaged by noise or by another station transmitting at the same time (collision) Any overlap of frames causes collision Max utilization 18%

70. Slotted ALOHA Time in uniform slots equal to frame transmission time Need central clock (or other sync mechanism) Transmission begins at slot boundary Frames either miss or overlap totally Max utilization 37%

71. CSMA Propagation time is much less than transmission time All stations know that a transmission has started almost immediately First listen for clear medium (carrier sense) If medium idle, transmit If two stations start at the same instant, collision Wait reasonable time (round trip plus ACK contention) No ACK then retransmit Max utilization depends on propagation time (medium length) and frame length —Longer frame and shorter propagation gives better utilization

72. Nonpersistent CSMA 1.If medium is idle, transmit; otherwise, go to 2 2.If medium is busy, wait amount of time drawn from probability distribution (retransmission delay) and repeat 1 Random delays reduces probability of collisions —Consider two stations become ready to transmit at same time While another transmission is in progress —If both stations delay same time before retrying, both will attempt to transmit at same time Capacity is wasted because medium will remain idle following end of transmission —Even if one or more stations waiting Nonpersistent stations deferential

73. 1-persistent CSMA To avoid idle channel time, 1-persistent protocol used Station wishing to transmit listens and obeys following: 1.If medium idle, transmit; otherwise, go to step 2 2.If medium busy, listen until idle; then transmit immediately 1-persistent stations selfish If two or more stations waiting, collision guaranteed —Gets sorted out after collision

74. P-persistent CSMA Compromise that attempts to reduce collisions —Like nonpersistent And reduce idle time —Like1-persistent Rules: 1.If medium idle, transmit with probability p, and delay one time unit with probability (1 – p) —Time unit typically maximum propagation delay 2.If medium busy, listen until idle and repeat step 1 3.If transmission is delayed one time unit, repeat step 1 What is an effective value of p?

75. Value of p? Avoid instability under heavy load n stations waiting to send End of transmission, expected number of stations attempting to transmit is number of stations ready times probability of transmitting —np If np > 1on average there will be a collision Repeated attempts to transmit almost guaranteeing more collisions Retries compete with new transmissions Eventually, all stations trying to send —Continuous collisions; zero throughput So np < 1 for expected peaks of n If heavy load expected, p small However, as p made smaller, stations wait longer At low loads, this gives very long delays

76. CSMA/CD With CSMA, collision occupies medium for duration of transmission Stations listen whilst transmitting 1.If medium idle, transmit, otherwise, step 2 2.If busy, listen for idle, then transmit 3.If collision detected, jam then cease transmission 4.After jam, wait random time then start from step 1

77. CSMA/CD Operation

78. Which Persistence Algorithm? IEEE 802.3 uses 1-persistent Both nonpersistent and p-persistent have performance problems 1-persistent (p = 1) seems more unstable than p-persistent —Greed of the stations —But wasted time due to collisions is short (if frames long relative to propagation delay —With random backoff, unlikely to collide on next tries —To ensure backoff maintains stability, IEEE 802.3 and Ethernet use binary exponential backoff

79. Binary Exponential Backoff Attempt to transmit repeatedly if repeated collisions First 10 attempts, mean value of random delay doubled Value then remains same for 6 further attempts After 16 unsuccessful attempts, station gives up and reports error As congestion increases, stations back off by larger amounts to reduce the probability of collision. 1-persistent algorithm with binary exponential backoff efficient over wide range of loads —Low loads, 1-persistence guarantees station can seize channel once idle —High loads, at least as stable as other techniques Backoff algorithm gives last-in, first-out effect Stations with few collisions transmit first

80. Collision Detection On baseband bus, collision produces much higher signal voltage than signal Collision detected if cable signal greater than single station signal Signal attenuated over distance Limit distance to 500m (10Base5) or 200m (10Base2) For twisted pair (star-topology) activity on more than one port is collision Special collision presence signal

81. IEEE 802.3 Frame Format

82. 10Mbps Specification (Ethernet) 10Base510Base210Base-T10Base-F MediumCoaxialCoaxialUTP850nm fiber SignalingBasebandBasebandBasebandManchester ManchesterManchesterManchesterOn/Off TopologyBusBusStarStar Nodes10030-33

83. 100Mbps Fast Ethernet Use IEEE 802.3 MAC protocol and frame format 100BASE-X use physical medium specifications from FDDI —Two physical links between nodes Transmission and reception —100BASE-TX uses STP or Cat. 5 UTP May require new cable —100BASE-FX uses optical fiber —100BASE-T4 can use Cat. 3, voice-grade UTP Uses four twisted-pair lines between nodes Data transmission uses three pairs in one direction at a time Star-wire topology —Similar to 10BASE-T

84. 100Mbps (Fast Ethernet) 100Base-TX100Base-FX100Base-T4 2 pair, STP2 pair, Cat 5 UTP2 optical fiber4 pair, cat 3,4,5 MLT-3MLT-34B5B,NRZI8B6T,NRZ

85. 100BASE-X Data Rate and Encoding Unidirectional data rate 100 Mbps over single link —Single twisted pair, single optical fiber Encoding scheme same as FDDI —4B/5B-NRZI —Modified for each option

86. 100BASE-X Media Two physical medium specifications 100BASE-TX —Two pairs of twisted-pair cable —One pair for transmission and one for reception —STP and Category 5 UTP allowed —The MTL-3 signaling scheme is used 100BASE-FX —Two optical fiber cables —One for transmission and one for reception —Intensity modulation used to convert 4B/5B-NRZI code group stream into optical signals —1 represented by pulse of light —0 by either absence of pulse or very low intensity pulse

87. 100BASE-T4 100-Mbps over lower-quality Cat 3 UTP —Taking advantage of large installed base —Cat 5 optional —Does not transmit continuous signal between packets —Useful in battery-powered applications Can not get 100 Mbps on single twisted pair —Data stream split into three separate streams Each with an effective data rate of 33.33 Mbps —Four twisted pairs used —Data transmitted and received using three pairs —Two pairs configured for bidirectional transmission NRZ encoding not used —Would require signaling rate of 33 Mbps on each pair —Does not provide synchronization —Ternary signaling scheme (8B6T)

88. 100BASE-T Options

89. Full Duplex Operation Traditional Ethernet half duplex —Either transmit or receive but not both simultaneously With full-duplex, station can transmit and receive simultaneously 100-Mbps Ethernet in full-duplex mode, theoretical transfer rate 200 Mbps Attached stations must have full-duplex adapter cards Must use switching hub —Each station constitutes separate collision domain —In fact, no collisions —CSMA/CD algorithm no longer needed —802.3 MAC frame format used —Attached stations can continue CSMA/CD

90. Mixed Configurations Fast Ethernet supports mixture of existing 10-Mbps LANs and newer 100-Mbps LANs E.g. 100-Mbps backbone LAN to support 10-Mbps hubs —Stations attach to 10-Mbps hubs using 10BASE-T —Hubs connected to switching hubs using 100BASE-T Support 10-Mbps and 100-Mbps —High-capacity workstations and servers attach directly to 10/100 switches —Switches connected to 100-Mbps hubs using 100-Mbps links —100-Mbps hubs provide building backbone Connected to router providing connection to WAN

91. Gigabit Ethernet Configuration

92. Gigabit Ethernet - Differences Carrier extension At least 4096 bit-times long (512 for 10/100) Frame bursting

93. Gigabit Ethernet – Physical 1000Base-SX —Short wavelength, multimode fiber 1000Base-LX —Long wavelength, Multi or single mode fiber 1000Base-CX —Copper jumpers <25m, shielded twisted pair 1000Base-T —4 pairs, cat 5 UTP Signaling - 8B/10B

94. Gbit Ethernet Medium Options (log scale)

95. 10Gbps Ethernet - Uses High-speed, local backbone interconnection between large-capacity switches Server farm Campus wide connectivity Enables Internet service providers (ISPs) and network service providers (NSPs) to create very high-speed links at very low cost Allows construction of (MANs) and WANs —Connect geographically dispersed LANs between campuses or points of presence (PoPs) Ethernet competes with ATM and other WAN technologies 10-Gbps Ethernet provides substantial value over ATM

96. 10Gbps Ethernet - Advantages No expensive, bandwidth-consuming conversion between Ethernet packets and ATM cells Network is Ethernet, end to end IP and Ethernet together offers QoS and traffic policing approach ATM Advanced traffic engineering technologies available to users and providers Variety of standard optical interfaces (wavelengths and link distances) specified for 10 Gb Ethernet Optimizing operation and cost for LAN, MAN, or WAN

97. 10Gbps Ethernet - Advantages Maximum link distances cover 300 m to 40 km Full-duplex mode only 10GBASE-S (short): —850 nm on multimode fiber —Up to 300 m 10GBASE-L (long) —1310 nm on single-mode fiber —Up to 10 km 10GBASE-E (extended) —1550 nm on single-mode fiber —Up to 40 km 10GBASE-LX4: —1310 nm on single-mode or multimode fiber —Up to 10 km —Wavelength-division multiplexing (WDM) bit stream across four light waves

98. 10Gbps Ethernet Distance Options (log scale)

99. Token Ring (802.5) Developed from IBM's commercial token ring Because of IBM's presence, token ring has gained broad acceptance Never achieved popularity of Ethernet Currently, large installed base of token ring products Market share likely to decline

100. Ring Operation Each repeater connects to two others via unidirectional transmission links Single closed path Data transferred bit by bit from one repeater to the next Repeater regenerates and retransmits each bit Repeater performs data insertion, data reception, data removal Repeater acts as attachment point Packet removed by transmitter after one trip round ring

101. Listen State Functions Scan passing bit stream for patterns —Address of attached station —Token permission to transmit Copy incoming bit and send to attached station —Whilst forwarding each bit Modify bit as it passes —e.g. to indicate a packet has been copied (ACK)

102. Transmit State Functions Station has data Repeater has permission May receive incoming bits —If ring bit length shorter than packet Pass back to station for checking (ACK) —May be more than one packet on ring Buffer for retransmission later

103. Bypass State Signals propagate past repeater with no delay (other than propagation delay) Partial solution to reliability problem (see later) Improved performance

104. Ring Repeater States

105. 802.5 MAC Protocol Small frame (token) circulates when idle Station waits for token Changes one bit in token to make it SOF for data frame Append rest of data frame Frame makes round trip and is absorbed by transmitting station Station then inserts new token when transmission has finished and leading edge of returning frame arrives Under light loads, some inefficiency Under heavy loads, round robin

106. Token Ring Operation

107. Dedicated Token Ring Central hub Acts as switch Full duplex point to point link Concentrator acts as frame level repeater No token passing

108. 802.5 Physical Layer Data Rate416100 Medium UTP,STP,Fiber Signaling Differential Manchester Max Frame45501820018200 Access ControlTP or DTRTP or DTRDTR Note: 1Gbit specified in 2001 —Uses 802.3 physical layer specification

109. Fibre Channel - Background I/O channel —Direct point to point or multipoint comms link —Hardware based —High Speed —Very short distance —User data moved from source buffer to destiation buffer Network connection —Interconnected access points —Software based protocol —Flow control, error detection &recovery —End systems connections

110. Fibre Channel 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 architectures e.g. SCSI Network oriented —Full multiplexing between multiple destinations —Peer to peer connectivity —Internetworking to other connection technologies

111. Fibre Channel Requirements Full duplex links with two fibers per link 100 Mbps to 800 Mbps on single line —Full duplex 200 Mbps to 1600 Mbps per link Up to 10 km Small connectors High-capacity utilization, distance insensitivity Greater connectivity than existing multidrop channels Broad availability —i.e. standard components Multiple cost/performance levels —Small systems to supercomputers Carry multiple existing interface command sets for existing channel and network protocols Uses generic transport mechanism based on point-to-point links and a switching network Supports simple encoding and framing scheme In turn supports a variety of channel and network protocols

112. Fibre Channel Elements End systems - Nodes Switched elements - the network or fabric Communication across point to point links

113. Fibre Channel Network

114. Fibre Channel Protocol Architecture (1) FC-0 Physical Media —Optical fiber for long distance —coaxial cable for high speed short distance —STP for lower speed short distance FC-1 Transmission Protocol —8B/10B signal encoding FC-2 Framing Protocol —Topologies —Framing formats —Flow and error control —Sequences and exchanges (logical grouping of frames)

115. FC-3 Common Services —Including multicasting FC-4 Mapping —Mapping of channel and network services onto fibre channel e.g. IEEE 802, ATM, IP, SCSI Fibre Channel Protocol Architecture (2)

116. Fibre Channel Physical Media Provides range of options for physical medium, the data rate on medium, and topology of network Shielded twisted pair, video coaxial cable, and optical fiber Data rates 100 Mbps to 3.2 Gbps Point-to-point from 33 m to 10 km

117. Fibre Channel Fabric General topology called fabric or switched topology Arbitrary topology includes at least one switch to interconnect number of end systems May also consist of switched network —Some of these switches supporting end nodes Routing transparent to nodes —Each port has unique address —When data transmitted into fabric, edge switch to which node attached uses destination port address to determine location —Either deliver frame to node attached to same switch or transfers frame to adjacent switch to begin routing to remote destination

118. Fabric Advantages Scalability of capacity —As additional ports added, aggregate capacity of network increases —Minimizes congestion and contention —Increases throughput Protocol independent Distance insensitive Switch and transmission link technologies may change without affecting overall configuration Burden on nodes minimized —Fibre Channel node responsible for managing point-to-point connection between itself and fabric —Fabric responsible for routing and error detection

119. Alternative Topologies Point-to-point topology —Only two ports —Directly connected, with no intervening switches —No routing Arbitrated loop topology —Simple, low-cost topology —Up to 126 nodes in loop —Operates roughly equivalent to token ring Topologies, transmission media, and data rates may be combined

120. Five Applications of Fibre Channel

121. Fibre Channel Prospects Backed by Fibre Channel Association Interface cards for different applications available Most widely accepted as peripheral device interconnect —To replace such schemes as SCSI Technically attractive to general high-speed LAN requirements Must compete with Ethernet and ATM LANs Cost and performance issues should dominate the consideration of these competing technologies