TEKNIK PENYAMBUNGAN IT-041246

1. TEKNIK PENYAMBUNGANIT-041246 P2-7 | Evolusi dan Jenis-Jenis Sistem Switching

2. Switching • (definition) “The establishment on demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information.”

3. Intro to Switching • A switch routes a call based on a number system • e.g 1 302 369 6923 • access code • area code • exchange code • subscriber code

4. Intro to Switching • Local (line-to-line) switching • Transit (tandem) • Call distribution End Office Transit Concentrator Transit End Office Local Transit TrunkGroup TandemSwitch

5. Switching System Control Switching Matrix Trunks Signaling Subscriber Lines

6. Interconnection Control Alerting Attending Information receiving Information sending Busy Testing Supervising Essential Switch Functions

7. Functions of Switching Systems • Signaling • monitor line activity • send incoming information to control function • send control signals to outgoing lines • Control • process signaling and set-up/knock down connections • Switching • make connections between input and output lines

8. Basic Switch Requirements • A switch must be able to connect any incoming call to one of a multitude of outgoing calls • A switch must have the ability to hold and terminate calls • A switch has to prevent new calls from intruding into circuits already in use

9. General Switch Requirements • Speed of call setup should be kept short relative to the call holding time • Grade of service should be high • .99 overall • .95 busy-hour • HIGH availability!

10. Switching Methods • Connectivity • Full: any input to any output • Blocking • Blocking: Possibility exists that call setup may fail due to insufficient switching resources • Non-blocking: If any input Ij and output Oj are free, they can be connected

11. Time Division Switching • Time mapping of inputs and outputs I1 I2 . . . . . . In O1 O2 . . . . . . O36 . . . . . .

12. Space Division Switching • Spatial mapping of inputs and outputs • Used primarily in analog switching systems Space O1 I1 ... ... Om In

13. Space-Time-Space Switching I1 I2 . . . . . . In O1 O2 . . . . . . O36 . . . . . .

14. Single Stage Switches • Crosspoint switches • Complex - many crosspoints ( i × j ) • Poor utilization of crosspoints • Not fault tolerant

15. Multiple Stage Switches • Input connected to output via two or more smaller switches • Crosspoints shared by several possible connections (potential for blocking) • Possible to provide multiple paths between any 2 ports

16. Three Stage Switch Matrix(Multiple Stage Switch example)

17. Reducing Cross-point Complexity • Increase number of stages • Allow some blocking • Switch in more than one dimension

18. Number of Cross-pointsNon-blocking Switch

19. Principal of Crossbar Switching The basic idea of crossbar switching is to provide a matrix of n×m sets of contacts with only n+m activators or less to select one of the n×m sets of contacts. This type of switching is also known as coordinate switching as the switching contacts are arranged in a xy-plane.

20. Components of Crossbar switch • A set of horizontal and vertical wires (shown by solid lines) • A set of horizontal and vertical contact points connected to these wires. The contact point form pairs, each pair consisting of a bank of three or four horizontal and a corresponding bank of vertical contact points. A contact point pair acts as a crosspoint switch. • The contact points are mechanically mounted and electrically insulated on a set of horizontal and vertical bars shown as dotted lines. • The bars, in turns are connected to a set of electromagnets.

21. Working of Crossbar Switch The crosspoint switches remains separated or open when not in use. When an electromagnetic, say in the horizontal direction, is energized, the bar attached to it slightly rotates in such a way that the contact points attached to the bar move closer to its facing contact points make do not actually make any contact. Now if an electromagnetic in the vertical direction is energized, the corresponding bar rotates causing the contact points at the intersection of the two bars to close. This happens because the contact points move towards each other.

22. Cont. • As an example, if electromagnets M2 and M3/ are energized, a contact is established at the crosspoint 6 such that the subscriber B is connected the subscriber C.

23. Energizing sequence for latching the crosspoints Let us consider a 6×6 crossbar schematic shown below.

24. Cont. • Let us consider the establishment of the following connections in sequence: A to C and B to E. • First the horizontal bar A is energized. • Then the vertical bar B is energized • The crosspoint AC is latched and the conversation between A and C can now proceed. • Suppose we now energize the horizontal bar of B to establish the connection B-E, the crosspoint BC may latch and B will be brought into the circuit of A-C. This is prevented by an energizing sequence for latching the crosspoints. • A crosspoint latches only if the horizontal bar is energized first and then the vertical bar.

25. Cont. • In order to establish the connection B-E, the vertical bar E need to be energized after the horizontal bar is energized. • In this case the crosspoint AE may latch as the horizontal bar A has already been energized for establishing the the connection A-C. • This should also be avoided and is done by de-energizing the horizontal bar A after the crosspoint is latched and making a suitable arrangement such that the latch is maintained even though the energisation in the horizontal direction is withdrawn. • The crosspoint remains latched as long as the vertical bar E remains energized.

26. Cont. • The complete procedure for establishing a connection in a crossbar switch: • energize horizontal bar • energize vertical bar • de-energize horizontal bar

27. Design parameters In a non-blocking crossbar configurations, there are N2 switching elements for N subscribers. When all the subscribers are engaged, only N/2 switches are actually used for connections.

28. Crossbar switch configurations Different switch points are used to establish a connection between two given subscribers depending upon who initiate the call. For example when the subscriber C wishes to call subscriber B, crosspoint CB is energized. On the other hand when B initiates the call to contact C, the switch BC is used. By designing a suitable control mechanism, only one switch may be used to establish a connection between two subscribers, irrespective of which of them initiates the call. The crosspoints in the diagonal connect the inlets and the outlets of the same subscriber. Hence they can also be eliminated.

29. Cont.

30. Cont. The crosspoints in the diagonal connect the inlets and the outlets of the same subscriber. Hence they can also be eliminated.

31. Class work Calculate the number of switches in a diagonal crosspoint matrix if the number of Subscribers is N.

32. Blocking Crossbar switch The diagonal crosspoint matrix is a nonblocking configuration. The number of crosspoint switches can be reduced significantly by designing blocking configurations. • The number of vertical bars is less than the number of subscribers. • The vertical bars determines the number of simultaneous calls that can be out through the switch.

33. Cont. Let a connection be required to be established between the subscriber A and B. The sequence to be followed in establishing the A-B circuit may be summarized as: • Energize horizontal bar A • Energize free vertical bar P • De-energize horizontal bar A • Energize horizontal bar B • Energize vertical bar P’ • De-energize horizontal bar B

34. Cont. Alternative Energizing sequence: Energize horizontal A and B Energize vertical P De-energize horizontal A and B The number of switches required is 2NK, where N is the number of subscribers and K is the number of vertical bars that are used to establish the connections.

35. Definition:space-division switching Space division switching was originally developed for the analog environment and has been carried over into the digital realm. A space division switching is one in which the signal paths are physically separate from one another (divided in space).

36. Limitations of crossbar switch The basic building block of the switch is crossbar switch in which a metallic cross-point or semiconductor gate is enabled or disabled by a control unit for the establishment of a physical path. But the crossbar switch has a no. of limitations: • The no. of cross-points grows with the square of the no. of attached stations. This is costly for a large switch. • The loss of a cross-point prevents connection between the two devices whose lines intersect at that cross-point. • Cross-points are inefficiently utilized. Only a small fraction of cross-points are engaged even when all devices are active.

37. Cont’d. • To overcome these limitations of crossbar switch, multiple stage switches are employed. Although a multistage network requires a more complex control scheme, it has several advantages over a single stage switch.

38. Single stage vs Multistage networks

39. Single stage vs Multistage networks

40. Two stage representation of N X N network Theorem: For any single stage network there exists an equivalent multistage network. So, N X N single stage network with capacity k can be realized by a two stage network of N X K and K X N stages.

41. Cont. • Any of the N inlets can be connected to any of the K outputs of 1st stage. • Similarly, Any of the K inputs can be connected to any of the N outputs of 2nd stage. • So, there are K alternative paths and 2NK switching elements. Any of the N inlets can be connected to any of the N outlets.

42. Cont. • Each stage has NK switching elements • Assume only a fraction of the subscribers to be active on an average • K can be equal to N/16 • So, no. of switching elements, S = 2NK = N2/8 --- (1) Example: N = 1024, K = 64 S = 131,027 So, for large N, the switching matrix NxK may still be difficult to realize practically.

43. Two stage network with multiple switching matrices • M inlets are divided into r blocks of p inlets. M = pr • N inlets are divided into s blocks of q outlets. N = qs

44. Cont. • For full connectivity there must be at least one outlet from each block in the 1st stage terminating as inlet on every block of the 2nd stage. • So, block sizes are p x s and r x q respectively • So, S = psr + qrs --- (2) • Putting values for M, N • S = Ms + Nr --- (3) • The number simultaneous calls in the network, switching capacity, SC = rs --- (4)

45. Cont. • For rs connections to be simultaneously active, the s active inputs in one block of the 1st stage must be uniformly distributed across all the s blocks in the 2nd stage at the rate of one per block. • Blocking may occur in two conditions: • Calls are uniformly distributed (there are rs calls in progress and (rs + 1)th calls arrives) • Calls are not uniformly distributed, there is a call in progress from I-th block from the first stage to the J-th block in the 2nd stage and another call originates in the I-th block destined to J-th block.

46. The blocking probability Let αbe the probability the a given inlet is active. Now, probability that an outlet at the I-th block is active is, β = (pα)/s The probability that another inlet becomes active and seeks an outlet other than the one which already active is given by (p - 1)α/(s - 1) Now, Probability that an ready active outlet is sought PB = ((pα)/s)[1 – (p-1)α/(s-1)] Substituting, p = M/r, we have PB = ((Mα)/rs)[1 – ((M/r)-1)α/(s-1)] --- (5)

47. Discussion. • If s and r decrease then S can be minimized • But if we decrease s and r we are increasing blocking probability! • So, we have to choose values for s and r as small as possible but giving sufficient links to provide a reasonable grade of service.

48. Cont. • If N > M, network is expanding traffic • If M > N, concentrating the traffic • If N = M, matrix size is uniform i.e. r=s, p=q So, S = 2Nr --- (6) SC = r2 --- (7)

49. Cont. • For square switching matrices as in standard ICs. • p=r=s=q = √N Thus the network has √N blocks each in the 1st and 2nd stages and each block is a square matrix of √N X √N inlets and outlets. So, S= N √N + N √N = 2N √N --- (8) SC = √N X √N = N --- (9)

50. Cont. • In the two stage network discussed so far, there is only one link between a block in the 1st stage and a block in the 2nd stage. • What will happen if this particular link failure? • Rise of severe blocking in the network!! • How can we improve this performance?