1. Computer Networks Chapter 4: Transmission systems and the telephone network

2. B B C C A A B C A B C A MUX (a) (b) Trunk group Multiplexing

3. A C B f C f B f A f W W W 0 0 0 (a) Individual signals occupy W Hz (b) Combined signal fits into channel bandwidth FDM ● Original multiplexing systems used it for voice comm. ● Group=12*4kHz (60-108kHz), Supergroup=5 groups ● Mastergroups=10 supergroups ● Currently used in radio and TV comms: ● AM channels(10kHz), FM (200kHz), TV(6MHz)

4. (b) Combined signal transmits 1 unit every T seconds t A1A1 A2A2 t B1B1 B2B2 t C1C1 C2C2 3T3T 0T0T 6T6T 3T3T 0T0T 6T6T 3T3T 0T0T 6T6T t B1B1 C1C1 A2A2 C2C2 B2B2 A1A1 0T 1T 2T 3T 4T 5T 6T (a) Each signal transmits 1 signal every 3T TDM ● Obviously the outgoing line has n times the rate of an incoming line ● Practically the outgoing rate is slightly higher: make up sync. defficiencies ● Most existing multiplexing hierarchies based on TDM ● Ex: T1= (1+24*8)bits/frame*8000frames/s=1.544Mbps

5. Primary Multiplex Eg. Digital Switch 30 chan PCM 4th order Multiplex x4 2nd order Multiplex x4 3rd order Multiplex x4 34.368 Mbps 2.048 Mbps 8.448 Mbps 139.264 Mbps CEPT 1 CEPT 4 North American Digital Hierarchy European Digital Hierarchy 28 M13 Multiplex M23 Multiplex x7 Primary Multiplex Eg. Digital Switch 24 chan PCM M12 Multiplex x4 1 DS3 44.736 Mbps DS1 1.544 Mbps DS2 6.312 MbpsDS3 44.736 Mbps Existing digital multiplexing hierarchies

6. Low-Speed Mapping Function Medium Speed Mapping Function High- Speed Mapping Function DS3 44.736 DS1 DS2 CEPT-1 CEPT-4 139.264 ATM 150 Mbps STS-1 STS-3c OC-n Scrambler E/O 51.84 Mbps High- Speed Mapping Function Mux STS-n SONET multiplexing ● Interconnection of cities/networks

7. MUX DEMUX MUX DEMUX MUX DEMUX (a) pre-SONET multiplexing remove tributary insert tributary ADM remove tributary insert tributary (b) SONET Add-Drop multiplexing Add/drop in multiplexing

8. a b c logical fully-connected net (a) a b c 3 ADMs connected in physical ring topology OC-3n (b) Ring topology in SONET

9. Inter-Office Rings Metro Ring Regional Ring Ring structures: Local Metropolitan, regional networks

10. BBB 87B Information Payload 9 Rows 125  s Transport overhead 90 bytes Section Overhead 3 rows 6 rows Line Overhead Sonet ST-1 frame structure ● Data bit rate 8x9x90x8000=51.84Mbps ● Information bit rate 8x9x87x8000=50.122Mbps ● Efficiency =96.7%

11. 1 2 m Optical MUX 1 2 m Optical deMUX 1 2. m Optical fiber Wavelength-division multiplexing: The present and future (a) WDM chain network a b c d (b) WDM ring network a b c 3 ADMs

12. User 1 Switch Link User n User n-1 (a) Network (b) Switch Control 1 2 3 N 1 2 3 N Connection of inputs to outputs Circuit switching ● Switchs: non-blocking or blocking, complexity is limiting factor

13. N 1 2 1 N 2  N-1 nxknxk nxknxk nxknxk nxknxk N/n x N/n kxnkxn 1 2 N/n N inputs 1 2 3 3 N/n N outputs 1 2 k 2(N/n)nk + k (N/n) 2 crosspoints kxnkxn kxnkxn kxnkxn Space-division and multistage switch Crossbar: Non-blocking Multistage: If k<n can be blocking

14. 1 2 24 1 2 From TDM DeMUX To TDM MUX 24 23 1 2 2 24123 Read slots in permuted order

15. nxknxk nxknxk nxknxk nxknxk N/n x N/n kxnkxn 1 2 N/n N inputs 1 3 1 1 2 n input TDM frame with n slots output TDM frame with k slots

16. nxknxk nxknxk nxknxk nxknxk N/n x N/n Time-Shared Space Switch kxnkxn 1 2 N/n N inputs 1 2 3 3 N/n N outputs TDM n slots kxnkxn kxnkxn kxnkxn TDM k slots TDM k slots TSI Stage Space Stage ● We will skip the study of the telephone system, and its signaling schemes

17. N(t) t 1 2 3 4 5 6 7 all trunks busy trunk #

18. # trunks Blocking Probability 1 234 5 6 7 8 9 10 offered load

19. Tandem Switch 2 Tandem Switch 1 B C A (b) Trunk group 10 Erlangs between each pair 90 Erlangs E F D B C A (a) E F D Routing control 1%blocking prob., 10Erl=>18trunks 18*9=162trunks 106 trunks

20. High Usage Route B-E Tandem Switch 1 Alternate Routes for B-E, C-F High Usage Route C-F Switch A Switch B Switch C Switch E Switch D Switch F Tandem Switch 2

21. High Usage Route Alternate Routes Tandem Switch 3 Tandem Switch 1 Tandem Switch 2 Switch A Switch B

22. Carried Load Offered Load Network Capacity We will skip cellular telephone networks and satellite cellular networks