1. Copyright 1998, S.D. Personick. All Rights Reserved. Telecommunications Networking I Lecture 16 & 17 Switching Fundamentals

2. Copyright 1998, S.D. Personick. All Rights Reserved. Switching Fundamentals The Classical Switching Opportunity # of links: N(N-1)/2 End system e.g., Telephone End system

3. Copyright 1998, S.D. Personick. All Rights Reserved. The Classical Switching Opportunity # of links: N Switch

4. Copyright 1998, S.D. Personick. All Rights Reserved. What’s a Switch? Crossbar switch wires closed crosspoint Signal path # of crosspoints:

5. Copyright 1998, S.D. Personick. All Rights Reserved. Mechanical Crosspoint:Reed Relay Coil Glass tube Reeds Control Signal Apply a current to the coil, and the resulting magnetic field forces the reeds to touch

6. Copyright 1998, S.D. Personick. All Rights Reserved. Multi-stage Switching Fabric 3x3 #1 3x3 #2 3x3 #3 3x3 #1 3x3 #2 3x3 #3 1 9 1 9 9x9 crosspoints vs 9x6 crosspoints (with blocking) # of crosspoints: ~

7. Copyright 1998, S.D. Personick. All Rights Reserved. Blocking Blocking occurs when a input cannot reach an idle output Previous example: Blocking on group 1 occurs if: 2 or 3 inputs try to reach the same output group Probability of blocking = [1/3 + 1/3] - 1/9 =5/9 Switching theory: how to design switches with an acceptable # of crosspoints, and an acceptable level of blocking

8. Copyright 1998, S.D. Personick. All Rights Reserved. Banyon Switching Fabric 2x2 # of crosspoints = 1 8 1 8

9. Copyright 1998, S.D. Personick. All Rights Reserved. Time Division Switching TSI Space Switch Time-Space-Time Digital Switch TSI= Time Slot Interchanger Input and output streams are time-division multiplexed 7 19 Channel bank

10. Copyright 1998, S.D. Personick. All Rights Reserved. There’s More to Switching than Switches For example: -On-hook/Off-hook detection -Providing dial tone -Signaling (e.g., tones or dial pulses) -Call processing -Advanced services (e.g., caller ID) -Routing (finding a path to the destination) -Automatic Message Accounting (AMA)

11. Copyright 1998, S.D. Personick. All Rights Reserved. On-Hook/Off-Hook Detection Line Interface Circuit Hook switch inductor Specification: “Off hook” = 20-120 ma of “loop” current Telephone Line Card in Central Office

12. Copyright 1998, S.D. Personick. All Rights Reserved. Signaling 1 2 3 4 5 6 7 8 9 * 0 # DTMF*=Dual tone multi- frequency Send two tones… Choose: 1 of {a,b,c} and 1 of {d,e,f,g} Total of 12 combinations *Also known as: TouchTone(R) a b c d e f g

13. Copyright 1998, S.D. Personick. All Rights Reserved. Signaling STP Trunk Group Switch STP=Signaling Transfer Point SS7= Signaling System Number 7 SS7

14. Copyright 1998, S.D. Personick. All Rights Reserved. Call Processing Call State: Idle (on hook) Active (off hook) Dial tone Dialing (digit collection) Post Dial (waiting) Active/Busy (talking) Idle (on hook) Call State: Idle (on hook) Ringing Active/Busy Idle (on hook) Bill’sJanet’s Time

15. Copyright 1998, S.D. Personick. All Rights Reserved. Advanced Services: Example “Calling Party Name” SW LIDB Incoming call Query/response Bill Janet Bill dials Janet. Bill’s switch queries the line information data base (LIDB) for the name associated with Bill’s line. This information is passed to Janet’s switch using SS7. Janet’s switch delivers this information between the first and second ring of Janet’s phone, using a modem-like signal.

16. Copyright 1998, S.D. Personick. All Rights Reserved. “Calling Party Name” Bill dials Janet. Bill’s switch queries the line information data base (LIDB) for the name associated with Bill’s line. This information is passed to Janet’s switch using SS7. Janet’s switch delivers this information between the first and second ring of Janet’s phone, using a modem-like signal. It is also possible to implement this functionality by having Janet’s switch send a query to Bill’s LIDB only if Janet subscribes to the calling name delivery service (rather than sending the information for every call).

17. Copyright 1998, S.D. Personick. All Rights Reserved. Finding a route to the Destination Telephone switches are uploaded with “translation tables” which map dialed telephone numbers to predetermined output ports on the switch. Thus, when I dial 1-215-895-6208 from home in NJ, my local switch “translates” the first six numbers (plus the “1”), and knows that this is a call that must be passed to an “access tandem” switch…for routing on to my chosen long distance carrier.

18. Copyright 1998, S.D. Personick. All Rights Reserved. Mobility Management Switch Bill Janet’s HLR Janet’s current VLR Radio port controller Switch Janet HLR=Home Location Register VLR=Visited Location Register Radio port

19. Copyright 1998, S.D. Personick. All Rights Reserved. Mobility Management When Janet turns on her cell/PCS phone, her signal is detected by a nearby radio port in her current (visited) location. The radio port controller associated with this radio port exchanges information with Janet’s phone. The radio port controller communicates with its VLR, to register Janet. This VLR communicates with Janet’s HLR to register her current location and her temporary telephone #

20. Copyright 1998, S.D. Personick. All Rights Reserved. Automatic Message Accounting Telephone switches collect “automatic message accounting” (AMA) information: called number, calling number, start time, end time, special features used; and store it on a disk. This information is periodically downloaded by a billing center for offline processing into telephone bills. A telephone company’s billing system is a strategic competitive asset.