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DC 8 - 1 DATACOMM John Abbott College JPC Data Transport Networks M. E. Kabay, PhD, CISSP Director of Education, ICSA President, JINBU Corp Copyright ©

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Presentation on theme: "DC 8 - 1 DATACOMM John Abbott College JPC Data Transport Networks M. E. Kabay, PhD, CISSP Director of Education, ICSA President, JINBU Corp Copyright ©"— Presentation transcript:

1 DC 8 - 1 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

2 DC 8 - 2 Data Transport Networks l OSI lower-level functions – Physical layer (1) – Data link layer (2) – Network layer (3) l Key technologies – Local Area Networks (LANs) – Wide-Area Networks / Internetworking (WANs) – Metropolitan Area Networks (MANs) – Packet-Switching Networks (PSN)

3 DC 8 - 3 Local Area Networks l Definition l LAN Topologies l Baseband vs Broadband Transmission l LAN Access Methods l Priority and Random Backoff l LAN Standards l Widely-Used LANs l Higher-Speed LANs

4 DC 8 - 4 Local Area Networks l A local area network (LAN) is a user-owned communications mechanism linking information- processing and -storage equipment within one building or a cluster of buildings within a circumscribed geographical area. l No absolute distinction between a LAN and a WAN (wide-area network) l LANs evolved because of desire to – share expensive resources – share information l Networks linking dumb terminals to hosts are not considered LANs

5 DC 8 - 5 Local Area Networks Features l Continuous connection l Interconnectivity l Variety of hardware permitted l Relatively inexpensive l High speeds (2.5-100 Mbps)

6 DC 8 - 6 Local Area Networks LAN Topologies STAR RING NET/MESH BUS/TREE

7 DC 8 - 7 Local Area Networks Star topology l Failure of CPU / Hub downs entire network l Performance is function of node at centre l Costs largely due to central node

8 DC 8 - 8 Local Area Networks Ring topology l Failure of any one node downs entire network l Performance declines as # nodes increases n – P{network failure} = 1 - (1-p) l Relatively low cost

9 DC 8 - 9 Local Area Networks Net/Mesh topology l Network survives node failure l Performance declines as # nodes increases l Higher cost

10 DC 8 - 10 Local Area Networks Bus/Tree topology l Network survives node failure l Performance declines as nodes increase l Medium cost

11 DC 8 - 11 Local Area Networks Baseband vs Broadband Transmission l Baseband lower installation cost l Broadband higher bandwidth « « « « « « « « « « BasebandBroadband

12 DC 8 - 12 Local Area Networks LAN Access Methods l Devices may accidentally transmit at same time: collision l Most access methods use CSMA (Carrier Sense Multiple Access) – Will not begin transmitting while another node is transmitting l CSMA/CA (Collision Avoidance) – If acknowledgement of message not received, node retransmits – But both nodes wait fairly long

13 DC 8 - 13 Local Area Networks LAN Access Methods l CSMA/CD (Collision Detection) – Nodes can detect collision quickly – Both nodes immediately stop transmitting when collision occurs l Wait a certain amount of time before starting again

14 DC 8 - 14 Local Area Networks Priority Backoff and Random Backoff l In CSMA/CD, what determines when node starts transmitting again? l Priority backoff – each node waits a fixed amount of time before retransmitting – short-wait nodes have priority over long- wait nodes l Random backoff – each node waits a random time – equalizes access to network

15 DC 8 - 15 Local Area Networks l Token Passing (1)

16 DC 8 - 16 Local Area Networks l Token Passing (2)

17 DC 8 - 17 Local Area Networks l Token Passing (3)

18 DC 8 - 18 Local Area Networks l Token Passing (4)

19 DC 8 - 19 Local Area Networks l Token Passing (5)

20 DC 8 - 20 Local Area Networks l Token Passing (6)

21 DC 8 - 21 Local Area Networks IEEE LAN Standards l 802.1: Encapsulation standards for CSMA/CD l 802.2: Logical link protocols l 802.3: Broadband & baseband bus using CSMA/CD l 802.4: Broadband and baseband bus using token passing l 802.5: Token-passing rings l 802.6: Metropolitan-area networks using cable TV facilities l 802.7: Other broadband systems l 802.8: Fibre optics

22 DC 8 - 22 Local Area Networks Widely-Used LANs l Ethernet (IEEE 802.3) – 10 Mbps commonplace (10Base-T) – twisted pair – 100 m max distance between nodes l IBM Token Ring (IEEE 802.5) – 4 or 16 Mbps l Banyan VINES (IEEE 802.5)

23 DC 8 - 23 Local Area Networks Higher-Speed LANs l ANSI Fiber Distributed Data Interface (FDDI) – Fibre optics – 100 Mbps – Similar to IEEE 802.5 – Double rings for increased robustness l 100Base-T (IEEE 802.3) l 100VG-Any-LAN – IEEE 802.12 – Demand priority scheme

24 DC 8 - 24 Wide-Area Networks (WANs): Internetworking l Definition: an internet is a collection of linked LANs l Ordinary internets are built of – LANs – Repeaters – Bridges – Routers – Gateways l A WAN is an extension of an internet: the connection of LANs not physically co-located l THE Internet is something else….

25 DC 8 - 25 WANs Repeaters 7-Applications 6-Presentation 5-Session 4-Transport 3-Network 2-Link 1-Physical Repeaters on each floor ThickLAN backbone risers Fibre optic link under roadway LANs on each floor »

26 DC 8 - 26 WANs Bridges » 10Base-T Local bridge 100Base-T Remote bridge Digital Leased Line Remote bridge 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

27 DC 8 - 27 WANs Bridges l Protocol insensitive l Learning – modify routing table automatically as devices are added l Filtering – discard packets staying on local bus l Forwarding – send packets to right network » 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

28 DC 8 - 28 WANs Routers & Brouters l Intelligence: can be addressed l Requires protocol agreement l Can select alternate routes l Bridges becoming smarter – now called brouters » Montreal Québec Halifax 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

29 DC 8 - 29 WANs Gateways l Sometimes called protocol converters l Can link LANs with different protocols l Especially important in multi-vendor internetworks; e.g., linking OSI system with SNA network l Multiprotocol switches are hardware l Software protocol conversion also common » 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

30 DC 8 - 30 WANs Internetworking Transmission Options l Commercial services make internetworking possible at low cost l Switched Multi-Megabit Data Service (SMDS) – offered by many carriers in Canada / US – connectionless: simply routes packets or frames l Connectionless Broadband Data Service (CBDS) – popular in Europe

31 DC 8 - 31 WANs Internetworking Transmission Options: T-carriers (leased lines) l T1: 1.544 Mbps 24 voice l T1C: 3.152 Mbps 48 voice l T2: 6.312 Mbps96 voice4 T1 l T3:44 Mbps672 voice28 T1 l T4:274 Mbps4032 voice168 T1

32 DC 8 - 32 WANs The Internet l TCP/IP based internetworking l Store-and-forward technology l Began as DARPA project in late 1960s l Steady expansion during 1970s-80s l Explosive growth late 1980s and in 90s l Now thought to have several million hosts l NOT the Information Superhighway l More details in Hot Topics course

33 DC 8 - 33 WANs Wireless Data Transport l Wireless LANs – radio – infrared l Broadcast – beepers – stock quotes l Two-way – cellular modems – Cellular Digital Packet Data (CDPD)

34 DC 8 - 34 Packet-Switching Networks l Public Packet-Switching Networks l X.25 l PSN Services l Routing Data in PSNs l Frame Relay Networks

35 DC 8 - 35 Packet-Switching Networks l Cost of leased lines can be prohibitive for sporadic use l Virtual circuits established for sessions at low cost l Packet Assembler-Disassembler (PAD) – Links devices to PSN cloud – Data disassembled into packets – Packets routed through PSN cloud – Packets reassembled into data stream

36 DC 8 - 36 Packet-Switching Networks DATA DATA I/O PAD PACKET DATACOMM OVERHEAD Destination Sequence ID CRC Route ID

37 DC 8 - 37 Packet-Switching Networks » « » « » « » Montreal Node Halifax Node Vancouver Node Buffers Processor Circuits Packets »

38 DC 8 - 38 Packet-Switching Networks » « » « » « » Montreal Node Halifax Node Vancouver Node Buffers Processor Circuits Packets »

39 DC 8 - 39 Packet-Switching Networks Public PSNs l Widely-available public nodes l Charge by kilopacket l Datapac (Stentor / Bell Canada) l Telenet (SPRINT) l Tymnet (MCI) l ARPANET (US govt)

40 DC 8 - 40 Packet-Switching Networks CCITT X.25 (X-and-a-quarter) l Most common standard for PSN l Functions divided into 3 levels that correspond to OSI stacks lower layers – Physical level: CCITT V.24/V.28 like RS- 232-C – Frame level: LAP-B data link like SDLC – Packet level: network addressing and routing l PAD used to convert asynch to X.25 flow

41 DC 8 - 41 Packet-Switching Networks PSN Services l Closed user group l Incoming calls only l Outgoing calls only l Flow-control negotiation – define packet size, other parms l Throughput class negotiation – define allowable use of bandwidth l Reverse charging = collect calls – like 800 number for datacomm

42 DC 8 - 42 Packet-Switching Networks l Routing Data in PSNs l Virtual circuit unlike telephone call circuit – Applies to one packet at a time – No user control over how individual packets reach destination l Packets often arrive at destination nodes out of sequence l Destination nodes therefore buffer and resequence the packets to reconstitute original data stream

43 DC 8 - 43 Packet-Switching Networks Frame Relay Networks l X.25 and other PSN have heavy overhead – designed for analog phone circuits – extensive error correction l Digital circuits much higher reliability, lower noise l Frame Relay drops node-based error checking l Functions at OSI layers 1 & 2 (application & presentation) l User systems do their own error-checking and recovery

44 DC 8 - 44 Homework l Read Chapter 8 of your textbook in detail, adding to your workbook notes as appropriate. l 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) l 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) l Scan Chapters 9 and 10 of your textbook before coming to class on Day 4.


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