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Digital Circuit Switches

Digital Circuit Switches. CET 533. Communication Systems. It is all about interfacing Point-to-point is not efficient Communication networks Sharing resources to make interconnections efficient The main question is how to reserve and release resources Communication network categories

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Digital Circuit Switches

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  1. Digital Circuit Switches CET 533

  2. Communication Systems • It is all about interfacing • Point-to-point is not efficient • Communication networks • Sharing resources to make interconnections efficient • The main question is how to reserve and release resources • Communication network categories • Broadcast networks • Switching networks

  3. Switching Networks • Three basic approaches • Circuit switched networks • Telephone network • Packet switched networks • ATM; TCP/IP • Message switched networks • Telegraph; emails

  4. Digital Circuit Switches • Advent of digital technology • microprocessors and computers • Deployed in 1979 • Reliable, high capacity • Offers many different features • Small and cheap! • Vary depending on where the switch is located and what features it offers

  5. Architecture of DCS Central Processing Network Control Processor Line Module Interface Controller Switch Fabric Interface Controller Trunk Interface Module • LM: interfaces with the subscriber (analog side); check for off-hook/on-hook • IC: format the signal before going to the switch • CP: call processing, system recovery, storage, software upgrade, maintaining records, billing information, routing • NCP: transfer routing information, switch setup, line module setup Trunk Side Line Side Control plan and data plane

  6. Architecture of DCS Central Processing Network Control Processor Line Module Interface Controller Switch Fabric Interface Controller Trunk Interface Module • Reliability: 5-9s (99.999%) • Redundancy • Other features: • Optical Electrical Interface • Framing and parity check • Digital v.s. Analog • Switch Fabric • Control section Trunk Side Line Side

  7. Local Switch (class 5) • Also called End office switch • Resides in the Central Office • Most complex • Contain different line and trunk interfaces • Analog Lines, ISDN, T1, ISDN-PRI (Line/Trunk) • Provides call recording on each line • Terminates thousands of subscriber lines • Provides special features: call waiting, forwarding, blocking, etc. • Routes many calls • Local calls; 911 calls; Operator; Long distance Regional Toll SW Sectional Switch Toll Center Tandem Switch Local Switch

  8. Tandem Switch (class 4) • Switches trunks • Provides routing between class 5 switches • Resides between the toll switch (center) and the local switch • No need to have line modules (only trunk interface) – otherwise similar to the local switch • Many local switches has class 4 capabilities Regional Toll SW Sectional Switch Toll Center Tandem Switch Local Switch

  9. Toll Switch (class 3) • Resides between the international gateway switches and class 4 • Also called the long distance switch • Determines which trunk is available for the cheapest and shortest connection • Determines the route for calls between subscribers in different area codes • The call is routed to toll switch when you dial 1+ • Long distance carriers have toll switches Regional Toll SW Sectional Switch Toll Center Tandem Switch Local Switch

  10. Sectional Toll Switch (class 2) Regional Toll Switch (class 1) Regional Toll SW • Providing redundant routing through the national network • Assuming ALL Class 4 switches are busy; class 4 can be connected to Class 2 • Typically low-end fixed switch • Not expandable • Not much flexibility • Not very configurable • Affordable and simple • Not used extensively Sectional Switch Toll Center Tandem Switch Local Switch https://www.microsoft.com/technet/security/topics/networksecurity/secmod40.mspx#ESAA

  11. Other Switch Types • International Gateway Switch • Performs three basic functions: • Connect trunks between domestic and international toll networks • Performs signaling conversion • SS7C7 (out of band signaling) • Performs physical interface conversion • T1ETSI • Mobile Telephone Switch Office (MTSO) • Connecting cell phone towers together via cable • Private Branch Exchange (PBX) • Small local class 5 switch for small campuses

  12. A few issues: • Why SS-7 • Provides fast setup connection • Out-of-band signaling • Billing is a tough process in all these! • When B is in IntraLATA and the same rate center, no extra charge

  13. Switch Interfaces

  14. Local Access and Transport Area LATA IntraLATA • Switches allow call routing • Depending on where you are on the network • Following break off of AT&T • 161 LATA (Local access and transport area) • Each LATA has many rate centers • Today there are many competitive companies providing phone services • ILEC (Incumbent LECs) • CLEC (Competitive LECs) • Routing: IntraLATA and InterLATA • LATA boundaries become less significant if ILECs can provide end-to-end phone service InterLATA LATA

  15. Call Routing in Telephone Network Exchange Code NPA – NXX - XXXX Subscriber Line Number Area Code • North American Numbering Plan (NPAN) • International Direct Distance Dialing (IDDD) • Each country has a country code • To access the country code you need a notification code (0 or 011) • Local Number Portability (LNP) • Your telephone number is not tied to a switch • According to 1996 Telecom Act: You can maintain your number even if you change the carrier

  16. Interconnection Between Different Switch Types Intern SW IST Featured Group Long Distance Long Distance ISP IMT Digital ISDN PRI Featured Group IST: Interswitch Trunk/T1 IMT: Intermachine Trunk PSAP: Public Safety Answer Position Access Tandem 911 Trunk 911 PSAP Featured Group IST End Office IST End Office IST Operator Services Switch Sub scriber POT Line Operator Services Trunk Analog Trunk PBX PBX

  17. Making an Intra Switch Call Central Processing Network Control Processor Line Module Interface Controller Switch Fabric Interface Controller Line Module A B • A is off-hook • The switch sends a tone • A dials a number • NCP checks the number Number belongs to the subscriber on the sw • NCP can route the number • NCP checks B if it is busy • If B is idle, NCP establishes a route • NCP sends a ringing voltage (ring back) • If B picks up, connection is maintained and circuit is marked as busy • When on-hook, connection is released all tables are updates • Lines is idle! • A Calling B; A & B are connected to the same end-office End Office SW

  18. Making an IntraLATA Call A B • A is off-hook • The switch sends a tone • A dials a number • NCP checks the number Number does not belongs to the subscriber on the sw • NCP pass the number to local Tandem (via SS-7 signaling) • SS-7 tells SA to seize trunk 10 between SA & T • SS-7 tells T to setup trunk 8 between T & SB • SS-7 tells SB to seize trunk 8 • SB receives the request and check B if idle • If B is idle, trunk 8 is setup; ring back is provided • SA receives the ring back B is idle; sends the ring back to A • same as before • A Calling B; A & B are services by different end-offices both belong to the same ILEC Tandem SW (T) End Office SW (SA) End Office SW (SB)

  19. Making an IntraLATA Call A B • A Calling B; A & B are services by different end-offices belonging to different carriers Class 5 SW LNP Tandem SW (T) Collocation Q & C End Office SW (SA) End Office SW (SB) Carriers: Note: ILEC owns all The copper lines! Qwest Facility (ILEC) Chapar Facility (CLEC) LNP: Local Number Portability

  20. Making an IntraLATA Call • A is off-hook • ChaparCom sees a call request and send a dial tone to A • A dials a number • NCP of ChaparCom checks the number Number does not belongs to the subscriber on ChaparCom • ChaparCom check the data base for number (query on the number to see whose subscriber it is and where located) – via SS-7 • LNP dB indicates B is a subscriber of Qwest and connected to SB • Chapar notifies T SW for a a call request to B • The tandem makes a connection as described before A B LNP LNP: Local Number Portability Class 5 SW Tandem SW (T) Collocation Q & C End Office SW (SA) End Office SW (SB) Carriers: Note: ILEC owns all The copper lines! Qwest Facility (ILEC) Chapar Facility (CLEC)

  21. Cell Phone Switches

  22. 911 Trunks

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