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Multiplexing and Routing in Telecommunications

Learn about the concepts of multiplexing, circuit switching, frequency domain multiplexing, synchronous time domain multiplexing, packet switching, connectionless and connection-oriented communication, virtual circuits, side-tracks routing, and network coding.

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Multiplexing and Routing in Telecommunications

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  1. Chapter 1.6 Multiplexing & Routing TelecommunicationsConcepts

  2. Multiplexing Circuit switching Frequency domain multiplexing Synchronous time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  3. Multiplexing Circuit switching Frequency domain multiplexing Synchronous time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  4. Circuit vs. Packet SwitchingA resource multiplexing issue !!! Main shared resource in networks = transmission capacity between nodes How to share such resource optimally? Fixed transmission capacity Shared resource examples

  5. Multiplexing Circuit switching Frequency domain multiplexing Synchronous time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  6. Circuit Switching The preferred multiplexing technique in the traditional telephony world. Fixed transmission capacity • A predefined share is allocated to each user. • The allocation remains valid until revocation, • whether it is used or not. • Charges are duration based.

  7. Multiplexing Circuit switching Frequency domain multiplexing Synchronous time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  8. cos(( t sin(t) 2 cos(( t ~ / 2 X ~ cos(( t sin(t) + 2 Frequency Domain Multiplexing Modulation allows shifting the frequency spectrum: Example: amplitude modulation of carrier at frequency Ω by signal at frequency ω power 0 Ω frequency Other modulation techniques have a similar effect

  9. Baseband signal Mod Mod Mod Ω3 Ω1 Ω2 Carrier Baseband signal Mod Mod Mod Local Oscillator Ω3 Ω1 Ω1 FDM in broadcasting

  10. FM radio: 50 KHz StuBru Premiere Nostalgie Campus 105.50 87.60 frequency FDM in broadcasting Cable TV: 7-8 MHz TF1 VTM RTBF VRT RTL frequency

  11. Multiplexing Circuit switching Frequency domain multiplexing Synchronous time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  12. 0 1 0 1 Time Domain MultiplexingSynchronous 1 0 0 1 1 0 0 1 XX 0 1 0 1 Unique bit pattern to delimit frames

  13. Multiplexing Circuit switching Frequency domain multiplexing Synchronous time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  14. Packet Switching(Invented by Paul Baran, 1960) The preferred multiplexing technique in the data world. Fixed transmission capacity • Data streams are separated in data packets. • Packets belonging to different streams are • intermixed for transmission over the shared link. • Packets are eventually queued while waiting for • access to the shared resource. • Charges can be volume based.

  15. Peak data rate / Average data rate Voice : ~2 (both speakers talk 50% of time) Data : >> 2 (think and processing times > transmission times) Circuit vs. Packet Switching Typical voice traffic Typical data traffic t

  16. Circuit Switching peak data rates <= transmission capacity Acceptable for voice and image transmission wasteful of resources for data transmission Fixed total delay Packet Switching average data rates <= transmission capacity Optimal use of transmission capacity Congestion control to handle traffic peaks Variable total delay caused by queuing in front of shared resource problematic for transmission of voice or images Circuit vs. Packet Switching

  17. Multiplexing Circuit switching Frequency domain multiplexing Synchronous Time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  18. Circuit Switching Intrinsically connection oriented Packet Switching Connectionless Each packet carries the destination address Routing decisions to be made for each packet Typical example : Internet Protocol Connection oriented : Virtual Circuits Each packet carries a local identifier (VCN) of the data flow it belongs to Routing decisions at virtual circuit set-up. Typical examples : X25, Frame Relay, ATM Connection oriented vs. Connectionless

  19. Internal vs. External Policies Network services (NUI) Connection oriented Connectionless Network operation (NNI) Connection oriented Connectionless

  20. Multiplexing Circuit switching Frequency domain multiplexing Synchronous Time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  21. c a d b Datagram RoutingBased upon routing tables 3 1 3 3 1 1 2 2 2 1 4 4 3 2 a:3 b:3 c:1 d:2 a:1 b:2 c:3 d:3 a:3 b:3 c:2 d:2 a:3 b:3 c:1 d:1

  22. Multiplexing Circuit switching Frequency domain multiplexing Synchronous Time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  23. Routing table gives next hop on best route to all destination nodes Best route is application dependant Shortest latency Highest throughput Lowest cost Best route can change Nodes can go down or can become congested Links can be interrupted Routing tables maintained by exploring periodically the network Routing

  24. VUB, 5 VUB, 10 B A 1 4 E 1 C ? VUB, 7 3 D What is E’s shortest path to VUB ? VUB, 20 Finding the best routeExample : Distance Vector Routing

  25. VUB, 5 VUB, 10 B A 1 4 E 1 C VUB, 8 VUB, 7 3 D VUB, 20 Finding the best route Example : Distance Vector Routing Known as Old ARPANET routing Based on Bellman-Ford algorithm Base of Routing Information Protocol

  26. c a d b Best route consequence 1 1 1 Idle 1 1 Risk of congestion

  27. Complete routing tables impossible in large networks Hierarchical routing is the solution Routing table restricted to one level of hierarchy Routing in large networks

  28. Multiplexing Circuit switching Frequency domain multiplexing Synchronous Time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  29. a>b a>c a>d b>c b>d a>b d>c a>d b>d b>c a>c d>c a>c a>d b>c b>d 10 11 12 11 12 21 11 20 21 10 11 12 13 20 21 22 Virtual Circuit Number c a d b Each virtual circuit is identified by a specific number on each physical link

  30. Forwarding Tables 11 21 c a 10 1 3 1 3 2 2 1.11>3.10 1.10>3.21 d b

  31. a>c a>c 21 11 a Permanent Virtual CircuitForwarding tables set-up and cleared by network manager through “separate” network c 1 3 1 3 2 2 1.11>3.10 1.10>3.21 “Separate” signaling network d b Signaling and data packets travel through different (virtual) circuits

  32. Multiplexing Circuit switching Frequency domain multiplexing Synchronous Time domain multiplexing Packet switching Connectionless = datagrams Connection oriented = Virtual circuit Side-tracks routing Network coding Contents

  33. c a d b Network CodingClassical packet routing m1: a > d m2: c > b 3 3 Bottleneck:2t b/s needed All links : t b/s

  34. + + + + + c a d b m1 m2 m1 Network CodingMessage merging m1: a > d m2: c > b 3 3 m1 m2 t b/s needed m2 m1 m2 All links : t b/s

  35. Circuit switching for uniform traffic Fixed bandwidth multiplexing FDM vs. TDM Connection oriented Packet switching for bursty traffic Statistical multiplexing Connectionless : datagrams Connection oriented : Virtual circuits Switched vs. permanent virtual circuits Routing Centralized vs. decentralized Best route, but risk for unbalanced loads Introduced concepts

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