Telecommunication Switching Network

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1 Telecommunication Switching Network Tuhina Samanta

2 IT-602: TELECOMMUNICATION SYSTEMS Introduction, elements of Tele traffic, Erlang's formula. Switching techniques - Electronics switching, generic switch and Engset formula, SD/TD/STS networks. Hybrid time and space division switching Telephone networks- Signaling, DTMF techniques, transmission, digital transmission requirements. Cellular Mobile Telephone System- Cell concepts, architecture, hardware procedures, GSM and CDMA standard, Data networks, Packet/Circuit Switching, LAN, MAN, WAN, ISDN, Broadband network, ATM concept and functionality. Services- FAX, Cable TV, Video on demand. 2

3 Telecommunication Switching Network

4 Basic Terms Calling subscriber initiates the call Called subscriber call is destined to Setting up connection to required destination information sent to serving exchange. May pass through several exchanges (all exchanges on route). Signaling required to draw attention of the called subscriber 4

5 Modes of Communication Simplex One way communication involving two entities Half-duplex An entity is capable of both transmitting and receiving but not simultaneously Full-duplex Information transfer takes place in both the directions 5

6 A Network with a Point-to-point Link N entities, Number of links (L) = (n-1) + (n -2) = n (n-1)/2 6

7 Communication Network 7

8 A Telecommunication Network Subscriber Lines Subscriber Lines SS1 SS2 Trunks Trunks SS4 Subscriber Lines SS= Switching System SS3 Subscriber Lines 8

9 Switching Network Configurations N inlets Switching Network M Outlets Symmetric Network (M= N) Incoming Trunks Subscriber inlets Switching Network Inlet-Outlet Connection Outgoing Trunks Subscriber outlets N Incoming Trunks Switching Network M Outgoing Trunks N subscriber Lines Switching Network Nonfolded Network Folded Network 9

10 Tele-traffic Nonblocking network networks with N subscribers has N/2 simultaneous switching paths Blocking Network number of simultaneous switching paths is less than number of simultaneous conversation that can take place Erlang(E) internationally accepted standard for traffic intensity A switching resource is said to carry one Erlang of traffic if it is continuously occupied throughout a given period of observation 10

11 Evolution of Switching System Space Switch 11

12 Manual System Obtain the number to connect from caller Connect the call of the called line (inserting plug of cord circuit) Alerts the called customer Monitoring process called supervision 12

13 Strowger Step-by-Step Connections are set up in stages called progressive control. The uniselectors act as concentrator at each customer premise. The final is the expander. 13

14 Crossbar Switching Strowger switches require regular maintenance. Replace manual operated switch by matrix telephone relays called Matrix Crosspoints. The switch retains a set of contacts at each crosspoint. Contacts are multiplied together. Uneconomic as N inlets and N outlets requires N 2 relays. 14

15 Electronic Switching Facilities controlled by customers Call barring, Repeat last call, Reminder calls, Call diversion, Three way calls, Charge advice Multiplex System FDM TDM Space Division (SD) System Connection is made over a different path in. Time Division (TD) System connection made over the same path but different instant in time. 15

16 Speech Digitization and Transmission Speech digitization PCM DPCM Line Coding Properties Types of coding 16

17 Time Division Multiplexing Subdivide the capacity of a digital transmission system into parts in time. STDM Synchronous TDM Time slots are assigned in repetitive manner ATDM Asynchronous TDM Assign capacity as and when needed 17

18 Four Channel TDM Frame Structure Frame Bit Interleaving Frame 4-bit word Interleaving 18

19 Frame Synchronization Extra frame bit is added, or some data bit treated as frame bits to ensure resume of new frame. For T1 channel structure, 24 channels are multiplexed having frame length of 193bits ( )bits. Average frame acquisition time F t is important for frame synchronization 19

20 Frame Synchronization Assume F t uses 1 framing bit per frame with alternating ones and zeros F t = avg. time required to examine the required number of bits before a framing bit is hit upon F t = avg. time required to test and ensure that chosen bit is a frame bit F t = F t F t This implies bits are chosen one by one and tested sequentially 20

21 Frame Synchronization p = prob. of finding a 1 in a bit position q = p -1 = prob. of finding a 0 in a bit position If the first bit observed is a 1, then the probability that a mismatch occurs at the end of, One frame = p Two frame = q.q = q 2 Three frames = q.p.p = qp 2 Four frames = q.p.q.q = q 3 p Five frames = q.p.q.p.p = q 2 p 3 Six frames = q.p.q.p.q.q = q 4 p 2 Hence F t = p + 2q 2 + 3qp 2 + 4q 3 p + 5q 2 p 3 + 6q 4 p 2 21

22 Frame Synchronization Assume, p = q Then, F t = p/(1-p) 2 frame times Setting p =1/2, F t = 2 frame times = 2N bit times Average number of bits that must be tested before the framing bit is encountered is N/2, i.e.f t = (N/2) F t = (2N)(N/2) = N 2 bit times 22

23 Added Channel Framing Recent technique use dedicated separate channel for framing Framing digits are added in a group CCITT multiplexing standard 32 channels per frame with one channel carrying framing information, one channel signalling information, and 30 channels for data 2 N N For multibit frame code, F t 2(2 L 1) 2 bits N = length of the frame L = length of the frame code Assumption: 1 and 0 occurs with equal probability 23

24 Books 1. B.P. Lathi, Modern Digital and Analog Communication Systems, Oxford University Press 2. Thiagarajan Viswanathan, Telecommunication Switching Systems and Networks, Prentice Hall India, Taub, Schilling, Principle of Communication Systems, Tata Mcgraw Hill 4. J. E. Flood, Telecommunications, Switching, Traffic and Networks, Prentice Hall,

DE62 TELECOMMUNICATION SWITCHING SYSTEMS DEC 2013

DE62 TELECOMMUNICATION SWITCHING SYSTEMS DEC 2013 Q.2 a. A 00 line exchange is to be designed using uniselectors and two motion selectors that provide a switching capacity of 20. Give your requirement of components and explain how you will implement this