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DATACOMM John Abbott College JPC Data Transport Networks M. E. Kabay, PhD, CISSP Director of Education, ICSA President, JINBU Corp Copyright © 1998 JINBU Corp. All rights reserved DC 8 - 1 Data Transport Networks DC 8 - 2 OSI lower-level functions – Physical layer (1) – Data link layer (2) – Network layer (3) Key technologies – Local Area Networks (LANs) – Wide-Area Networks / Internetworking (WANs) – Metropolitan Area Networks (MANs) – Packet-Switching Networks (PSN) Local Area Networks DC 8 - 3 Definition LAN Topologies Baseband vs Broadband Transmission LAN Access Methods Priority and Random Backoff LAN Standards Widely-Used LANs Higher-Speed LANs Local Area Networks DC 8 - 4 A local area network (LAN) is a user-owned communications mechanism linking informationprocessing and -storage equipment within one building or a cluster of buildings within a circumscribed geographical area. No absolute distinction between a LAN and a WAN (wide-area network) LANs evolved because of desire to – share expensive resources – share information Networks linking dumb terminals to hosts are not considered LANs Local Area Networks Features Continuous connection Interconnectivity Variety of hardware permitted Relatively inexpensive High speeds (2.5-100 Mbps) DC 8 - 5 Local Area Networks LAN Topologies STAR DC 8 - 6 RING NET/MESH BUS/TREE Local Area Networks Star topology Failure of CPU / Hub downs entire network Performance is function of node at centre Costs largely due to central node DC 8 - 7 Local Area Networks Ring topology Failure of any one node downs entire network Performance declines as # nodes increases n – P{network failure} = 1 - (1-p) Relatively low cost DC 8 - 8 Local Area Networks Net/Mesh topology Network survives node failure Performance declines as # nodes increases Higher cost DC 8 - 9 Local Area Networks Bus/Tree topology Network survives node failure Performance declines as nodes increase Medium cost DC 8 - 10 Local Area Networks Baseband vs Broadband Transmission Baseband lower installation cost Broadband higher bandwidth Baseband Broadband « « « « « « « « « DC 8 - 11 « Local Area Networks LAN Access Methods Devices may accidentally transmit at same time: collision Most access methods use CSMA (Carrier Sense Multiple Access) – Will not begin transmitting while another node is transmitting CSMA/CA (Collision Avoidance) – If acknowledgement of message not received, node retransmits – But both nodes wait fairly long DC 8 - 12 Local Area Networks LAN Access Methods CSMA/CD (Collision Detection) – Nodes can detect collision quickly – Both nodes immediately stop transmitting when collision occurs Wait a certain amount of time before starting again DC 8 - 13 Local Area Networks Priority Backoff and Random Backoff In CSMA/CD, what determines when node starts transmitting again? Priority backoff – each node waits a fixed amount of time before retransmitting – short-wait nodes have priority over longwait nodes Random backoff – each node waits a random time – equalizes access to network DC 8 - 14 Local Area Networks DC 8 - 15 Token Passing (1) Local Area Networks DC 8 - 16 Token Passing (2) Local Area Networks DC 8 - 17 Token Passing (3) Local Area Networks DC 8 - 18 Token Passing (4) Local Area Networks DC 8 - 19 Token Passing (5) Local Area Networks DC 8 - 20 Token Passing (6) Local Area Networks IEEE LAN Standards 802.1: Encapsulation standards for CSMA/CD 802.2: Logical link protocols 802.3: Broadband & baseband bus using CSMA/CD 802.4: Broadband and baseband bus using token passing 802.5: Token-passing rings 802.6: Metropolitan-area networks using cable TV facilities 802.7: Other broadband systems 802.8: Fibre optics DC 8 - 21 Local Area Networks Widely-Used LANs Ethernet (IEEE 802.3) – 10 Mbps commonplace (10Base-T) – twisted pair – 100 m max distance between nodes IBM Token Ring (IEEE 802.5) – 4 or 16 Mbps Banyan VINES (IEEE 802.5) DC 8 - 22 Local Area Networks Higher-Speed LANs ANSI Fiber Distributed Data Interface (FDDI) – Fibre optics – 100 Mbps – Similar to IEEE 802.5 – Double rings for increased robustness 100Base-T (IEEE 802.3) 100VG-Any-LAN – IEEE 802.12 – Demand priority scheme DC 8 - 23 Wide-Area Networks (WANs): Internetworking DC 8 - 24 Definition: an internet is a collection of linked LANs Ordinary internets are built of – LANs – Repeaters – Bridges – Routers – Gateways A WAN is an extension of an internet: the connection of LANs not physically co-located THE Internet is something else…. WANs Repeaters » LANs on each floor Repeaters on each floor Fibre optic link under roadway ThickLAN backbone risers DC 8 - 25 7-Applications 6-Presentation 5-Session 4-Transport 3-Network 2-Link 1-Physical 7-Applications 6-Presentation 5-Session 4-Transport 3-Network 2-Link 1-Physical WANs Bridges » 10Base-T Local bridge 100Base-T Remote bridge Digital Leased Line Remote bridge DC 8 - 26 WANs » Bridges Protocol insensitive Learning – modify routing table automatically as devices are added Filtering – discard packets staying on local bus Forwarding – send packets to right network DC 8 - 27 7-Applications 6-Presentation 5-Session 4-Transport 3-Network 2-Link 1-Physical WANs Routers & Brouters » Intelligence: can be addressed Requires protocol agreement Montreal Can select alternate routes Bridges becoming smarter – now called brouters 7-Applications 6-Presentation 5-Session 4-Transport 3-Network 2-Link 1-Physical Québec Halifax DC 8 - 28 WANs Gateways DC 8 - 29 » 7-Applications 6-Presentation 5-Session 4-Transport 3-Network 2-Link 1-Physical Sometimes called protocol converters Can link LANs with different protocols Especially important in multi-vendor internetworks; e.g., linking OSI system with SNA network Multiprotocol switches are hardware Software protocol conversion also common WANs Internetworking Transmission Options Commercial services make internetworking possible at low cost Switched Multi-Megabit Data Service (SMDS) – offered by many carriers in Canada / US – connectionless: simply routes packets or frames Connectionless Broadband Data Service (CBDS) – popular in Europe DC 8 - 30 WANs Internetworking Transmission Options: T-carriers (leased lines) T1: 1.544 Mbps 24 voice T1C: 3.152 Mbps 48 voice T2: 6.312 Mbps 96 voice 4 T1 T3: 44 Mbps 672 voice 28 T1 T4: 274 Mbps 4032 voice 168 T1 DC 8 - 31 WANs The Internet TCP/IP based internetworking Store-and-forward technology Began as DARPA project in late 1960s Steady expansion during 1970s-80s Explosive growth late 1980s and in 90s Now thought to have several million hosts NOT the “Information Superhighway” More details in Hot Topics course DC 8 - 32 WANs Wireless Data Transport Wireless LANs – radio – infrared Broadcast – beepers – stock quotes Two-way – cellular modems – Cellular Digital Packet Data (CDPD) DC 8 - 33 Packet-Switching Networks DC 8 - 34 Public Packet-Switching Networks X.25 PSN Services Routing Data in PSNs Frame Relay Networks Packet-Switching Networks DC 8 - 35 Cost of leased lines can be prohibitive for sporadic use Virtual circuits established for sessions at low cost Packet Assembler-Disassembler (PAD) – Links devices to PSN cloud – Data disassembled into packets – Packets routed through PSN cloud – Packets reassembled into data stream Packet-Switching Networks DATACOMM OVERHEAD Destination DATA I/O Sequence ID DATA CRC PAD Route ID PACKET DC 8 - 36 Packet-Switching Networks Montreal Node « « » » » » » « « » » » » » » » » « « » » » » » » » » » » « « » » » » DC 8 - 37 Circuits » » » » « « » » Vancouver Node Processor » » » » » » « « » » Buffers « « » » Halifax Node Packets Packet-Switching Networks Montreal Node « « » » » » » « « » » » » » » » » « « » » » » » » » » » » « « » » » » DC 8 - 38 Circuits » » » » « « » » Vancouver Node Processor » » » » » » « « » » Buffers « « » » Halifax Node Packets Packet-Switching Networks Public PSNs Widely-available public nodes Charge by kilopacket Datapac (Stentor / Bell Canada) Telenet (SPRINT) Tymnet (MCI) ARPANET (US govt) DC 8 - 39 Packet-Switching Networks CCITT X.25 (“X-and-a-quarter”) Most common standard for PSN Functions divided into 3 levels that correspond to OSI stack’s lower layers – Physical level: CCITT V.24/V.28 like RS232-C – Frame level: LAP-B data link like SDLC – Packet level: network addressing and routing PAD used to convert asynch to X.25 flow DC 8 - 40 Packet-Switching Networks PSN Services Closed user group Incoming calls only Outgoing calls only Flow-control negotiation – define packet size, other parms Throughput class negotiation – define allowable use of bandwidth Reverse charging = collect calls – like 800 number for datacomm DC 8 - 41 Packet-Switching Networks DC 8 - 42 Routing Data in PSNs Virtual circuit unlike telephone call circuit – Applies to one packet at a time – No user control over how individual packets reach destination Packets often arrive at destination nodes out of sequence Destination nodes therefore buffer and resequence the packets to reconstitute original data stream Packet-Switching Networks Frame Relay Networks X.25 and other PSN have heavy overhead – designed for analog phone circuits – extensive error correction Digital circuits much higher reliability, lower noise Frame Relay drops node-based error checking Functions at OSI layers 1 & 2 (application & presentation) User systems do their own error-checking and recovery DC 8 - 43 Homework DC 8 - 44 Read Chapter 8 of your textbook in detail, adding to your workbook notes as appropriate. Review and be prepared to define or expand all the terms listed at the end of Chapter 8 of your textbook (no hand-in required) Answer all the exercises on page 187 of the textbook using a computer word-processing program or absolutely legible handwriting (hand in after quiz Monday morning) Scan Chapters 9 and 10 of your textbook before coming to class on Day 4.