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Transmission Systems and the Telephone Networks

Transmission Systems and the Telephone Networks. Transmission Systems and the Telephone Networks. Multiplexing. Multiplexing. Multiplexing involves the sharing of network resources by several connections or information flows. The primary shared network resources is bandwidth.

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Transmission Systems and the Telephone Networks

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  1. Transmission Systems and the Telephone Networks

  2. Transmission Systems and the Telephone Networks Multiplexing

  3. Multiplexing • Multiplexing involves the sharing of network resources by several connections or information flows. • The primary shared network resources is bandwidth. • measured in Hz for analog transmission. • measured in bps for digital transmission. (a) (b) A A A A Trunk group B B B B MUX DEMUX C C C C

  4. A f W 0 B f 0 W C f 0 W Frequency-division multiplexing (a) Individual signals occupy W Hz • Combined signal fits into • channel bandwidth B A C f

  5. Uses of FDM • In FDM the user information can be analog or digital form and that the information from all users flows simultaneously. • Applications: • Broadcast radio • FM: 200 kHz band • AM: 10 kHz band • Broadcast and cable TV • Cellular telephony • 25 to 30 kHz frequency slot

  6. The L-carrier

  7. A1 A2 t 0T 6T 3T B1 B2 t 6T 3T 0T C1 C2 t 0T 6T 3T 0T 1T 2T 3T 4T 5T 6T A2 B2 B1 C1 C2 A1 t Time-division multiplexing Each signal transmits 1 unit every 3T seconds • Combined signal transmits 1 unit every T seconds

  8. T-1 carrier system 1 1 2 DEMUX MUX 2 . . . . . . b 24 1 22 24 2 23 b . . . 24 frame 24 (1+248) bits/frame8000 frames/second = 1.544 Mbps

  9. Primary Multiplex Eg. Digital Switch 24 chan PCM M23 Multiplex x7 M12 Multiplex x4 DS2 6.312 Mbps DS3 44.736 Mbps DS1 1.544 Mbps 1 M13 Multiplex DS3 44.736 Mbps    28 North American digital hierarchies DS 1, which corresponds to the output of a T-1 multiplexer, became the basic building block.

  10. CEPT 1 Primary Multiplex Eg. Digital Switch 30 chan PCM 3rd order Multiplex x4 CEPT 4 2nd order Multiplex x4 4th order Multiplex x4 34.368 Mbps 8.448 Mbps 2.048 Mbps 139.264 Mbps European Digital Hierarchy

  11. Timing in a TDM multiplexer t 5 4 3 2 1 5 4 3 2 1

  12. Bit slip • Bit slip: the slow input will fail to produce its input bit. • The late bit will be viewed as an early arrival in the next interval. • The slow stream will alternate between being late, undergoing a bit slip, and then being early. • Bits that are arriving faster than they can be sent out, will accumulate at the multiplexer and eventually be dropped.

  13. Asynchronous multiplexer • Time-division multiplexers have traditionally been designed to operate at a speed higher than the combined speed of the inputs. • The frame structure of the multiplexer output signal contains bits that are used to indicate to the receiving multiplexer that a slip has occurred. • The introduction of these extra bits implies that the frame structure of the output stream is not exactly synchronized to the frame structure of all the input streams. • Before we extract an individual input stream, we need to demultiplex the entire combined signal and make the adjustment for slips.

  14. Transmission Systems and the Telephone Networks SONET

  15. SONET/SDH • To meet the need for standards to interconnect optical transmission systems, the Synchronous Optical Network (SONET) standard was developed in North America. • The CCITT has developed a corresponding set of standards called Synchronous Digital Hierarchy (SDH). • SONET and SDH form the basis for current high-speed backbone networks.

  16. SONET • The basic building block of the SONET hierarchy is the synchronous transport signal level-1 (STS-1) and has a bit rate of 51.84 Mbps. • Each STS-n electrical signal has a corresponding optical carrier level-n (OC-n) signal. • The bit format of STS-n and OC-n signal is the same except for the use of scrambling in the optical signal. • A higher-level signal is obtained through the interleaving of bytes from the lower-level component signals.

  17. SDH • The SDH standard refers to synchronous transfer modules-n (STM-n) signals and begins at a bit rate of 155.52 Mbps. • The SDH STM-1 signal is equivalent to the SONET STS-3 signal. • The STM-1 signal accommodates the CEPT-4 signal in the CCITT digital hierarchy.

  18. SONET digital hierarchy

  19. SONET multiplexing DS1 Low-Speed Mapping Function DS2 STS-1 CEPT-1 51.84 Mbps Medium Speed Mapping Function STS-1 DS3 44.736       OC-n STS-n STS-3c MUX Scrambler E/O STS-1 High- Speed Mapping Function CEPT-4 STS-1 STS-1 139.264 STS-3c STS-1 High- Speed Mapping Function STS-1 Tributary : the component streams that are multiplexed together. ATM STS-1 150 Mbps

  20. SONET add-drop multiplexing (a) pre-SONET multiplexing DEMUX DEMUX MUX MUX insert tributary remove tributary (b) SONET Add-Drop multiplexing ADM DEMUX MUX insert tributary remove tributary

  21. SONET ring network a ADM OC-3n OC-3n b c STS-n STS-n ADM ADM OC-3n physical loop net

  22. a c b logical fully-connected net Configuration of logical networks a OC-3n OC-3n b c OC-3n 3 ADMs connected in physical ring topology

  23. Survivability in a SONET ring a a b d b d c c Loop-around in response to fault Dual ring In normal operation, one fiber is in working mode, while another is in a protect mode.

  24. SONET ring structure The capability to manage bandwidth flexibly and to respond quickly to faults has altered the topology of long-distance and metropolitan area networks from a mesh of point-to-point links to interconnected ring networks. Regional Ring Metro Ring Inter-Office Rings

  25. STS PTE STS PTE LTE LTE SONET Terminal SONET Terminal STE STE STE Mux Mux reg reg reg Section Section STS Line STS-1 Path section optical Section, line, and path layers (a) STE: Section Terminating Equipment, e.g. a repeater LTE: Line Terminating Equipment, e.g. a STS-1 to STS-3 multiplexer PTE: Path Terminating Equipment, e.g. an STS-1 multiplexer (b) path path line line line line section section section section section section optical optical optical optical optical optical

  26. SONET STS-1 frame format 90 bytes 87B B B B Section Overhead 3rows Information Payload 9 Rows Line Overhead 6rows 125 s Transport overhead 8  9  90  8000 = 51.84 Mbps

  27. The synchronous payload envelope first octet Pointer Frame k 87 columns Synchronous Payload Envelope 9 rows Pointer last octet Frame k+1 first column is path overhead

  28. Byte Interleave Synchronous multiplexing in SONET STS-1 STS-1 STS-1 STS-1 Map STS-1 STS-1 STS-3 STS-1 STS-1 Map STS-1 STS-1 STS-1 STS-1 Map Incoming STS-1 Frames Synchronized New STS-1 Frames

  29. Virtual tributary • Various mapping have been defined to combine lower-speed tributaries of various formats into standard SONET stream. • A STS-1 signal can be divided into virtual tributary signals. • In each SPE, 84 columns are set aside and divided into seven groups of 12 columns. • Each group constitutes a virtual tributary and has a bit rate of 12988000=6.912 Mbps. • A virtual tributary can accommodate four T-1 carrier signals, or three CEPT-1 signals.

  30. Concatenation • Several STS-1 frames can be concatenated to accommodate signals with bit rates that cannot be handled by a single STS-1. • The suffix c is appended to the signal designation when concatenation is used. • Concatenated STS frames carry only one column of path overhead. • The SPE in an STS-3 frames has 86  3 = 258 columns of user data, whereas the SPE in an STS-3c frame carries 87  3 – 1 = 260 columns of user data.

  31. Transmission Systems and the Telephone Networks Wavelength-Division Multiplexing

  32. Wavelength-division multiplexing • Multiple information signals modulate optical signals at different optical wavelengths. • The resulting signals are combined and transmitted simultaneously over the same optical fiber. • Prisms and diffraction gratings can be used to combine and split color signals. 1 1 2 2 1 2 , m Optical fiber Optical MUX Optical deMUX m m

  33. Optical signal in a WDM system

  34. WDM network configuration • Optical add-drop multiplexers have been designed for WDM systems. • The assignments in various multiplexer configuration can then be used to create networks with various logical topologies. • In these topologies a light path between two nodes is created by inserting information at an assigned wavelength at the source node, bypassing intermediate nodes, and removing the information at the destination node.

  35. WDM chain network c b d a

  36. WDM ring network Through the assignment of wavelengths, it is possible to obtain logical topologies that differ from the physical topology. a 3 ADMs b c

  37. Transmission Systems and the Telephone Networks Circuit Switches

  38. Link Switch User n User n-1 User 1 Networks = links + switches Control 1 1 Network 2 2 Connection of inputs to outputs 3 3       N N

  39. 1 2    N N-1 2 N  1 Crossbar switch • The crossbar switch is nonblocking. • Connection requests are never denied because of lack of connectivity of resources.

  40. Multistage switch 2(N/n)nk + k (N/n)2 crosspoints kxn nxk N/n x N/n 1 1 1 kxn nxk N inputs 2 2 N outputs N/n x N/n kxn nxk 2 3 3          kxn nxk N/n N/n N/n x N/n k

  41. It is nonblocking if k = 2n - 1 kxn nxk N/n x N/n 1 1 1       n-1 busy N/n x N/n Desired input n-1 Desired output nxk kxn j n-1 busy m N/n x N/n n+1       N/n x N/n 2n-2 nxk kxn N/n x N/n N/n free path free path N/n 2n-1

  42. Time-slot interchange 1 From TDM DeMUX 2 24    24 1 23 2    Read slots in permuted order 2 1 24 23       1 To TDM MUX 2 24 125 sec Maximum number of slots = 2 x memory cycle time

  43. Hybrid switches kxn nxk N/n x N/n 1 1 1 nxk input TDM frame with n slots N inputs 2 nxk n 3 2 1       nxk    N/n output TDM frame with k slots

  44. Flow of slots between switches first slot first slot kxn nxk N/n x N/n 1 1 1 kxn nxk 2 2 N/n x N/n 2       kxn nxk N/n x N/n N/n N/n k kth slot kth slot

  45. Time-space-time switches Space Stage TSI Stage TSI Stage kxn TDM n slots nxk TDM k slots TDM k slots 1 1 kxn nxk n slots N/n x N/n Time-Shared Space Switch 2 2 N outputs N inputs kxn nxk n slots 3 3       kxn nxk n slots N/n N/n

  46. Example of a TST switch B2 A2 B1 A1 B1 A1 A1 A1 C1 C1 3x2 2x3 1 1 B1 D1 D1 B1 3x2 C2 D1 C1 C1 D2 D1 2x3 2 2 (A, B, C, D) to (C, A, D, B)

  47. Transmission Systems and the Telephone Networks The Telephone Network

  48. Circuit switching

  49. Telephone call setup • Three phases of connection-oriented communications • call setup • message transfer • call release Source Signal Go Ahead Signal Message Release Signal Destination

  50. Routing in a local area 4 C D 2 3 5 B A 1

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