Telecommunications Networking ISwitching FundamentalsThe Classical Switching OpportunityWhat’s a Switch?Mechanical Crosspoint:Reed RelayMulti-stage Switching FabricBlockingBanyon Switching FabricTime Division SwitchingThere’s More to Switching than SwitchesOn-Hook/Off-Hook DetectionSignalingSlide 13Call ProcessingAdvanced Services: Example “Calling Party Name”“Calling Party Name”Finding a route to the DestinationMobility ManagementSlide 19Automatic Message AccountingCopyright 1998, S.D. Personick. All Rights Reserved.Telecommunications Networking ILecture 16 & 17 Switching FundamentalsCopyright 1998, S.D. Personick. All Rights Reserved.Switching FundamentalsThe Classical Switching Opportunity# of links: N(N-1)/2End systeme.g., TelephoneEnd systemCopyright 1998, S.D. Personick. All Rights Reserved.The Classical Switching Opportunity# of links: NSwitchCopyright 1998, S.D. Personick. All Rights Reserved.What’s a Switch?Crossbar switchwires wiresclosed crosspointSignal path# of crosspoints: 2NCopyright 1998, S.D. Personick. All Rights Reserved.Mechanical Crosspoint:Reed RelayCoilGlass tubeReedsControl SignalApply a current to the coil,and the resulting magneticfield forces the reeds totouchCopyright 1998, S.D. Personick. All Rights Reserved.Multi-stage Switching Fabric3x3#13x3#23x3#33x3#13x3#23x3#319199x9 crosspoints vs 9x6 crosspoints (with blocking)# of crosspoints: ~ 2/32NCopyright 1998, S.D. Personick. All Rights Reserved.BlockingBlocking 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 groupProbability of blocking = [1/3 + 1/3] - 1/9 =5/9Switching theory: how to design switches with an acceptable # of crosspoints, and an acceptable level of blockingCopyright 1998, S.D. Personick. All Rights Reserved.Banyon Switching Fabric2x2# of crosspoints =1818NN2log2Copyright 1998, S.D. Personick. All Rights Reserved.Time Division SwitchingTSI TSISpaceSwitchTime-Space-Time Digital SwitchTSI= Time Slot InterchangerInput and output streams are time-division multiplexed7 19Channel bankCopyright 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)Copyright 1998, S.D. Personick. All Rights Reserved.On-Hook/Off-Hook DetectionLineInterfaceCircuitHookswitchinductorSpecification: “Off hook” = 20-120 ma of “loop” currentTelephoneLine Card in Central OfficeCopyright 1998, S.D. Personick. All Rights Reserved.Signaling 1 2 3 4 5 6 7 8 9 * 0 #DTMF*=Dual tone multi-frequencySend two tones…Choose: 1 of {a,b,c} and1 of {d,e,f,g}Total of 12 combinations*Also known as: TouchTone(R) a b cdefgCopyright 1998, S.D. Personick. All Rights Reserved.SignalingSTPTrunk GroupSwitchSwitchSTP=Signaling Transfer Point SS7= Signaling System Number 7SS7Copyright 1998, S.D. Personick. All Rights Reserved.Call ProcessingCall State:Idle (on hook)Active (off hook)Dial toneDialing (digit collection)Post Dial (waiting)Active/Busy (talking)Idle (on hook)Call State:Idle (on hook)RingingActive/Busy Idle (on hook)Bill’s Janet’s TimeCopyright 1998, S.D. Personick. All Rights Reserved.Advanced Services: Example“Calling Party Name” SW SWLIDBIncoming callQuery/responseBillJanet Bill dials Janet. Bill’s switch queries the line information database (LIDB) for the name associated with Bill’s line. This information is passed to Janet’s switch using SS7. Janet’sswitch delivers this information between the first and secondring of Janet’s phone, using a modem-like signal.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).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.Copyright 1998, S.D. Personick. All Rights Reserved.Mobility ManagementSwitchBillJanet’sHLRJanet’s currentVLRRadio port controllerSwitchJanetHLR=Home Location RegisterVLR=Visited Location RegisterRadio portCopyright 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 #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