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 Broadcast networks Switching networks

Switching Networks Three basic approaches Circuit switched networks Telephone network Packet switched networks ATM; TCP/IP Message switched networks Telegraph; s

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

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

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

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

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

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

Sectional Toll Switch (class 2) Regional Toll Switch (class 1) Regional Toll SW Sectional Switch Toll Center Tandem Switch Local Switch 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

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

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

Switch Interfaces

Local Access and Transport Area LATA 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 LATA IntraLATA InterLATA

Call Routing in Telephone Network 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 NPA – NXX - XXXX Area Code Exchange Code Subscriber Line Number

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

Making an Intra Switch Call A Calling B; A & B are connected to the same end-office End Office SW AB 1.A is off-hook 2.The switch sends a tone 3.A dials a number 4.NCP checks the number Number belongs to the subscriber on the sw 5.NCP can route the number 6.NCP checks B if it is busy 7.If B is idle, NCP establishes a route 8.NCP sends a ringing voltage (ring back) 9.If B picks up, connection is maintained and circuit is marked as busy 10.When on-hook, connection is released all tables are updates 11.Lines is idle! Line Module Interface Controller Switch Fabric Interface Controller Line Module Network Control Processor Central Processing

Making an IntraLATA Call A Calling B; A & B are services by different end-offices both belong to the same ILEC End Office SW (SA) AB 1.A is off-hook 2.The switch sends a tone 3.A dials a number 4.NCP checks the number Number does not belongs to the subscriber on the sw 5.NCP pass the number to local Tandem (via SS- 7 signaling) 6.SS-7 tells SA to seize trunk 10 between SA & T 7.SS-7 tells T to setup trunk 8 between T & SB 8.SS-7 tells SB to seize trunk 8 9.SB receives the request and check B if idle 10.If B is idle, trunk 8 is setup; ring back is provided 11.SA receives the ring back B is idle; sends the ring back to A 12.same as before End Office SW (SB) Tandem SW (T)

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

Making an IntraLATA Call LNP: Local Number Portability End Office SW (SA) AB End Office SW (SB) Tandem SW (T) Class 5 SW Qwest Facility (ILEC) Chapar Facility (CLEC) Carriers: Collocation Q & C Note: ILEC owns all The copper lines! 1.A is off-hook 2.ChaparCom sees a call request and send a dial tone to A 3.A dials a number 4.NCP of ChaparCom checks the number Number does not belongs to the subscriber on ChaparCom 5.ChaparCom check the data base for number (query on the number to see whose subscriber it is and where located) – via SS- 7 6.LNP dB indicates B is a subscriber of Qwest and connected to SB 7.Chapar notifies T SW for a a call request to B 8.The tandem makes a connection as described before LNP

Cell Phone Switches

911 Trunks