Digital Circuit Switches CET 533. Communication Systems It is all about interfacing Point-to-point is not efficient Communication networks Sharing resources.

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; emails

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

TrunkInterface Module

InterfaceController

SwitchFabric

InterfaceController

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

TrunkInterface Module

InterfaceController

SwitchFabric

InterfaceController

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

https://www.microsoft.com/technet/security/topics/networksecurity/secmod40.mspx#ESAA

Other Switch Types International Gateway Switch

Performs three basic functions: Connect trunks between domestic and international toll

networks Performs signaling conversion

SS7C7 (out of band signaling) Performs physical interface conversion

T1ETSI

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

InternSW

Long Distance

Long Distance

Access Tandem

EndOffice

End Office

911 PSAP

Operator ServicesSwitch

ISP

PBXPBX

Interconnection Between Different Switch Types

Subscribe

r

911 Trunk

Operator ServicesTrunk

Analog Trunk

Featured Group IST: Interswitch Trunk/T1IMT: Intermachine TrunkPSAP: Public Safety Answer Position

IST

ISTIST

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 OfficeSW

A B

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 sw5. 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

InterfaceController

SwitchFabric

InterfaceController

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 OfficeSW (SA)

A B

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 sw5. NCP pass the number to local Tandem

(via SS-7 signaling)6. SS-7 tells SA to seize trunk 10 between

SA & T7. SS-7 tells T to setup trunk 8 between T &

SB8. SS-7 tells SB to seize trunk 89. SB receives the request and check B if

idle10.If B is idle, trunk 8 is setup; ring back is

provided11.SA receives the ring back B is idle;

sends the ring back to A12.same as before

End OfficeSW (SB)

TandemSW (T)

Making an IntraLATA Call

A Calling B; A & B are services by different end-offices belonging to different carriers

End OfficeSW (SA)

A B

End OfficeSW (SB)

TandemSW (T)

Class 5 SW

Qwest Facility (ILEC)

Chapar Facility (CLEC)

Carriers:

Collocation

Q & C

Note: ILEC owns allThe copper lines!

LNP

LNP: Local Number Portability

Making an IntraLATA Call

LNP: Local Number Portability

End OfficeSW (SA)

A B

End OfficeSW (SB)

TandemSW (T)

Class 5 SW

Qwest Facility (ILEC)

Chapar Facility (CLEC)

Carriers:

Collocation

Q & C

Note: ILEC owns allThe 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