1 / 22

Chapter 4 Circuit-Switching Networks

Chapter 4 Circuit-Switching Networks. 4.1 Multiplexing 4.2 SONET Transport Networks Circuit Switches The Telephone Network Signaling Traffic and Overload Control in Telephone Networks Cellular Telephone Networks. Circuit Switching Networks.

kyrie
Télécharger la présentation

Chapter 4 Circuit-Switching Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 4 Circuit-Switching Networks 4.1 Multiplexing 4.2 SONET Transport Networks Circuit Switches The Telephone Network Signaling Traffic and Overload Control in Telephone Networks Cellular Telephone Networks

  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 4.1 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; a fiber replaces thousands of cables • Implicit or explicit information is required to demultiplex the information flows. Shared Channel

  7. A 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 1 2 MUX 2 MUX . . . . . . 22 23 24 b 24 2 1 b . . . Frame 24 24 T-Carrier System • Digital telephone system uses TDM. • PCM voice channel is basic unit for TDM • 1 channel = 8 bits/sample x 8000 samples/sec. = 64 kbps • T-1 carrier carries Digital Signal 1 (DS-1) that combines 24 voice channels into a digital stream: Framing bit • Bit Rate = 8000 frames/sec. x (1 + 8 x 24) bits/frame • = 1.544 Mbps

  10. 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

  11. 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

  12. MUX t 2 5 4 3 2 1 5 4 3 1 Clock Synch & Bit Slips • Digital streams cannot be kept perfectly synchronized • Bit slips can occur in multiplexers Slow clock results in late bit arrival and bit slip

  13. Muxing of equal-rate signals Pulse stuffing Pulse Stuffing • Pulse Stuffing: synchronization to avoid data loss due to bit slips • Output rate > R1+R2 • i.e. DS2, 6.312Mbps=4x1.544Mbps + 136 Kbps • Pulse stuffing format • Fixed-length master frames with each channel allowed to stuff or not to stuff a single bit in the master frame. • Redundant stuffing specifications • signaling or specification bits (other than data bits) are distributed across a master frame. requires perfect synch

  14. 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

  15. Example: WDM with 16 wavelengths 30 dB 1540 nm 1550 nm 1560 nm

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

  17. Chapter 4Circuit-Switching Networks 4.2 SONET

  18. 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 • SDH (Synchronous Digital Hierarchy) elsewhere • Needs to carry E1 and E3 signals • Compatible with SONET at higher speeds • Greatly simplifies multiplexing in network backbone • OA&M support to facilitate network management • Protection & restoration

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

  20. 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

  21. SONET & SDH Hierarchy

  22. DS1 Low-speed mapping function DS2 STS-1 E1 51.84 Mbps Medium speed mapping function DS3 STS-1 44.736 OC-n STS-n STS-1 STS-1 High- speed mapping function E4 STS-1 STS-1 Scrambler E/O STS-1 STS-1 139.264 . . . . . . STS-3c MUX STS-3c High- speed mapping function ATM or POS SONET Multiplexing

More Related