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Chapter 4 Circuit-Switching Networks

Chapter 4 Circuit-Switching Networks. Multiplexing SONET. Circuit Switching Networks. End-to-end dedicated circuits between clients Client can be a person or equipment (router or switch) Circuit can take different forms Dedicated path for the transfer of electrical current

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Chapter 4 Circuit-Switching Networks

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  1. Chapter 4 Circuit-Switching Networks Multiplexing SONET

  2. Circuit Switching Networks • End-to-end dedicated circuits between clients • Client can be a person or equipment (router or switch) • Circuit can take different forms • Dedicated path for the transfer of electrical current • Dedicated time slots for transfer of voice samples • Dedicated frames for transfer of Nx51.84 Mbps signals • Dedicated wavelengths for transfer of optical signals • Circuit switching networks require: • Multiplexing & switching of circuits • Signaling & control for establishing circuits • These are the subjects covered in this chapter

  3. How a network grows • A switch provides the network to a cluster of users, e.g. a telephone switch connects a local community Network Access network (b) A multiplexer connects two access networks, e.g. a high speed line connects two switches

  4. a b A d c Network of Access Subnetworks A Network Keeps Growing 1* b a 2 4 (a) Metropolitan network A viewed as Network A of Access Subnetworks 3 A c d Metropolitan (b) National network viewed as Network of Regional Subnetworks (including A) A • Very high-speed lines  Network of Regional Subnetworks National & International

  5. Chapter 4Circuit-Switching Networks Multiplexing

  6. (a) (b) A A A A B B MUX MUX B B C C C C Multiplexing • Multiplexing involves the sharing of a transmission channel (resource) by several connections or information flows • Channel = 1 wire, 1 optical fiber, or 1 frequency band • Significant economies of scale can be achieved by combining many signals into one • Fewer wires/pole; fiber replaces thousands of cables • Implicit or explicit information is required to demultiplex the information flows. Shared Channel

  7. Channel divided into frequency slots Guard bands required AM or FM radio stations TV stations in air or cable Analog telephone systems B f A f 0 Wu C C 0 Wu f 0 Wu B A f W 0 Frequency-Division Multiplexing (a) Individual signals occupy Wu Hz (b) Combined signal fits into channel bandwidth

  8. A1 A2 … t 0T 6T 3T B1 B2 … t 6T 3T 0T C1 C2 … t 0T 6T 3T C2 A2 B2 … A1 C1 B1 t 0T 1T 2T 3T 4T 5T 6T Time-Division Multiplexing (a) Each signal transmits 1 unit every 3T seconds • High-speed digital channel divided into time slots • Framing required • Telephone digital transmission • Digital transmission in backbone network (b) Combined signal transmits 1 unit every T seconds

  9. 1 DS1 signal, 1.544Mbps . . Mux 24 1 DS2 signal, 6.312Mbps . 24 DS0 . 4 DS1 Mux 4 1 DS3 signal, 44.736Mpbs . . 7 DS2 Mux 7 1 . . 6 DS3 Mux 6 DS4 signal 274.176Mbps North American Digital Multiplexing Hierarchy • DS0, 64 Kbps channel • DS1, 1.544 Mbps channel • DS2, 6.312 Mbps channel • DS3, 44.736 Mbps channel • DS4, 274.176 Mbps channel

  10. 1 2.048 Mbps . . Mux 30 1 8.448 Mbps . 64 Kbps . Mux 4 1 34.368 Mpbs . . Mux 139.264 Mbps 1 . . Mux 4 CCITT Digital Hierarchy • CCITT digital hierarchy based on 30 PCM channels • E1, 2.048 Mbps channel • E2, 8.448 Mbps channel • E3, 34.368 Mbps channel • E4, 139.264 Mbps channel

  11. Optical fiber link carries several wavelengths From few (4-8) to many (64-160) wavelengths per fiber Imagine prism combining different colors into single beam Each wavelength carries a high-speed stream Each wavelength can carry different format signal e.g. 1 Gbps, 2.5 Gbps, or 10 Gbps Optical deMUX Optical MUX 1 1 2 1 2 2. m Optical fiber m m Wavelength-Division Multiplexing

  12. Typical U.S. Optical Long-Haul Network

  13. Chapter 4Circuit-Switching Networks SONET

  14. SONET: Overview • SynchronousOptical NETwork • North American TDM physical layer standard for optical fiber communications • 8000 frames/sec. (Tframe = 125 sec) • compatible with North American digital hierarchy • Greatly simplifies multiplexing in network backbone • Protection & restoration

  15. MUX MUX DEMUX DEMUX Insert tributary Remove tributary MUX DEMUX ADM Insert tributary Remove tributary SONET simplifies multiplexing Pre-SONET multiplexing SONET Add-Drop Multiplexing: Allows taking individual channels in and out without full demultiplexing

  16. SONET Specifications • Defines electrical & optical signal interfaces • Electrical • Multiplexing, Regeneration performed in electrical domain • STS – Synchronous Transport Signals defined • Very short range (e.g., within a switch) • Optical • Transmission carried out in optical domain • Optical transmitter & receiver • OC – Optical Carrier

  17. SONET & SDH Hierarchy

  18. MUX DEMUX ADM Insert tributary Remove tributary SONET ADM Networks • SONET ADMs: the heart of existing transport networks • ADMs interconnected in linear and ring topologies • SONET signaling enables fast restoration (within 50 ms) of transport connections

  19. (a) (b) a a OC-3n OC-3n b c b c OC-3n Logical fully connected topology Three ADMs connected in physical ring topology SONET Rings • ADMs can be connected in ring topology • Clients see logical topology created by tributaries

  20. SONET Ring Options • 2 vs. 4 Fiber Ring Network • Unidirectional vs. bidirectional transmission • Path vs. Link protection • Spatial capacity re-use & bandwidth efficiency • Signaling requirements

  21. Two-Fiber Unidirectional Path Switched Ring Two fibers transmit in opposite directions • Unidirectional • Working traffic flows clockwise • Protection traffic flows counter-clockwise • 1+1 like • Selector at receiver does path protection switching

  22. UPSR 1 W 2 4 P W = Working Paths P = Protection Paths Each path uses 2x bw 3

  23. UPSR path recovery 1 W 2 4 P W = Working line P = Protection line 3

  24. UPSR Properties • Low complexity • Fast path protection • 2 TX, 2 RX • Suitable for lower-speed access networks • Different delay between W and P path

  25. Four-Fiber Bidirectional Line Switched Ring • 1 working fiber pair; 1 protection fiber pair • Bidirectional • Working traffic & protection traffic use same route in working pair • 1:N like • Line restoration provided by either: • Restoring a failed span • Switching the line around the ring

  26. 4-BLSR 1 Equal delay W P Standby bandwidth is shared 2 4 Spatial Reuse 3

  27. BLSR Span Switching 1 W Equal delay P • Span Switching restores failed line 2 4 Fault on working links 3

  28. BLSR Span Switching 1 W Equal delay P • Line Switching restores failed lines 2 4 Fault on working and protection links 3

  29. 4-BLSR Properties • High complexity: signalling required • Fast line protection for restricted distance (1200 km) and number of nodes (16) • 4 TX, 4 RX • Spatial re-use; higher bandwidth efficiency • Good for uniform traffic pattern • Suitable for high-speed backbone networks • Multiple simultaneous faults can be handled

  30. Regional ring Metro ring Interoffice rings Backbone Networks consist of Interconnected Rings UPSR OC-12 BLSR OC-48, OC-192 UPSR or BLSR OC-12, OC-48

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