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TLMN 625

TLMN 625. CLASS 3 SPRING 2003 Circuit Switching Packet Switching Cell Switching. USER PERSPECTIVE INTERACTIVE COMMUNICATION. No. Yes. No. No. Yes. No. Yes. Yes. No. Maybe. Yes. Yes. Circuit Switching. Nodes function as switches Uses dedicated path Requires 3 phases

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TLMN 625

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  1. TLMN 625 CLASS 3 SPRING 2003 Circuit Switching Packet Switching Cell Switching

  2. USER PERSPECTIVE INTERACTIVE COMMUNICATION No Yes No No Yes No Yes Yes No Maybe Yes Yes

  3. Circuit Switching • Nodes function as switches • Uses dedicated path • Requires 3 phases • Establishment (set-up) • Data transfer • Termination (tear-down)

  4. Circuit-Switching • Long-haul telecom network designed for voice • Network resources dedicated to one call • Shortcomings when used for data: • Inefficient (high idle time, i.e. gaps in message) • Constant data rate

  5. Public Network Switching Hierarchy

  6. Packet Switching • Messages broken into “packets” and routed through network • Two services offered • Virtual circuit (connection oriented) • Datagram (connectionless) • Key concepts of packet networks • Routing, Traffic control, Error control • Internet (Datagram- Best effort)

  7. Hardware Utilized in Packet Switching Transmission link Packet switch “Router” Network Figure 7.9

  8. Packet switching demo http://www.pbs.org/opb/nerds2.0.1/geek_glossary/packet_switching_flash.html

  9. Packet Switching Network Access Hardware for Cable Modems, LANs CPU I/O Bus 1 NIC Card 2 NIC Card NIC Card 3 Main Memory … … N NIC Card Figure 7.11

  10. Packet Switching

  11. Advantages of Packet Network Packet Switch PACKET CLOUD LEASED LINES

  12. Advantages over Circuit-Switching • Greater line efficiency (packets from multiple sources can go over shared link) • Data rate conversions • Non-blocking under heavy traffic (but increased delays)

  13. Disadvantages Relative to Circuit-Switching • Packets incur additional delay with every node they pass through • Jitter: variation in packet delay • Data overhead in every packet for routing information, etc • Processing overhead for every packet at every node traversed

  14. Packet-Switching Characteristics • Data transmitted in short blocks, or packets • Packet length < 1000 octets • Each packet contains user data plus control info (routing) • Store and forward

  15. Elements of a packet and packet size Packet No. Addressing Message Error control Size of Message: Examples: Ethernet 1500 bytes ATM 48 bytes X.25 128 bytes

  16. Packet SizeUltimately it is the capacity of routers that determine packet size for a WAN If fragmentation of packet not allowed packet is dropped ROUTER MTU- message transport unit Source: CISCO

  17. Packet size • It is fairly common for implementations to use 576-byte packets whenever they can't verify that the entire path is able to handle larger packets

  18. Observation:Internet Packet Size Almost half of the packets are less than 44 bytes, Another 18% are either 552 or 576 bytes. Almost 18% are 1500 bytes, Note this difference in packet and byte distribution: while there are many teeny packets, they do not account for much of the overall payload: while over half of the packets are 44 bytes or less, over half of the byte volume is carried by 1500 byte packets.

  19. Figure 14-13 The McGraw-Hill Companies, Inc., 1998 WCB/McGraw-Hill

  20. Datagram (connectionless) routing Packet 1 Packet 1 Packet 2 Packet 2 Packet 2 Figure 7.15

  21. Datagrams (Connectionless) • No connection setup phase • Best effort, no guaranteed delivery • Each packet forwarded independently • Analogy: postal system • Sometimes called connectionless model • Each switch maintains a forwarding (routing) table

  22. Virtual Circuit Switching • Subsequent packets follow same circuit • Analogy: phone call • Sometimes called connection-oriented model Each switch maintains a VC table.

  23. Virtual Circuit The McGraw-Hill Companies, Inc., 1998 WCB/McGraw-Hill

  24. SUMMARY COMPARISON

  25. Alternative Switching Question: Is there some method which contains the elements of both types of switching?

  26. Cell Relay, Statistical Multiplexing Voice Data packets MUX Wasted bandwidth Images TDM 4 3 2 1 4 3 2 1 4 3 2 1 ATM ` 4 3 1 3 2 2 1 Figure 7.37

  27. Switching: How long will auser get to use a transmission segment? • For the duration of the conversation? Circuit Switching • For a tiny, variable length, portion of the conversation? Packet Switching • For a tiny, fixed length, portion of the conversation? Cell Switching

  28. Circuit vs. PacketComparison • (a)What key disadvantage of circuit switched Time Division Multiplexing (TDM) does packet switching fix? • (b) Does this create new problems?

  29. 2nd class Homework Problem Review

  30. Homework Problem to compare datagram and virtual circuit packet switching • Do problem 21 p. 539 in the text

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