telecom switching network basic ppt

BEIT, 6th Semester

Telecommunication Switching Network

Tuhina Samanta

2BEIT, 6th Semester

IT-602: TELECOMMUNICATION SYSTEMS • Introduction, elements of Tele traffic, Erlang's formula.• Switching techniques - Electronics switching, generic

switch and Engset formula, SD/TD/STS networks. Hybrid time and space division switching

• Telephone networks- Signaling, DTMF techniques, transmission, digital transmission requirements.

• Cellular Mobile Telephone System- Cell concepts, architecture, hardware procedures, GSM and CDMA standard,

• Data networks, Packet/Circuit Switching, LAN, MAN, WAN, ISDN, Broadband network, ATM concept and functionality.

• Services- FAX, Cable TV, Video on demand.

BEIT, 6th Semester

Telecommunication Switching Network

4BEIT, 6th Semester

Basic Terms

• Calling subscriber – initiates the call• Called subscriber – call is destined to• Setting up connection to required destination

– information sent to serving exchange.– May pass through several exchanges (all

exchanges on route).

• Signaling— required to draw attention of the called subscriber

5BEIT, 6th Semester

Modes of Communication

• Simplex– One way communication involving two entities

• Half-duplex– An entity is capable of both transmitting and

receiving but not simultaneously

• Full-duplex– Information transfer takes place in both the

directions

6BEIT, 6th Semester

A Network with a Point-to-point Link

N entities,Number of links (L) = (n-1) + (n -2) + 1 + 0 = n (n-1)/2

7BEIT, 6th Semester

Communication Network

8BEIT, 6th Semester

A Telecommunication Network

SS1

SS4 SS3

SS2

Trunks

Trunks

SS=Switching

System Subscriber LinesSubscriber Lines

Subscriber LinesSubscriber Lines

9BEIT, 6th Semester

Switching Network Configurations

Switching Network Switching

Network

Ninlets

MOutlets

Symmetric Network (M= N)

Incoming Trunks

Outgoing Trunks

Subscriberinlets

Subscriberoutlets

Switching Network

Folded Network

Inlet-Outlet Connection

Switching Network

NIncomingTrunks

MOutgoingTrunks

Nonfolded Network

N subscriber

Lines

10BEIT, 6th Semester

Tele-traffic• Nonblocking network

– networks with N subscribers has N/2 simultaneous switching paths

• Blocking Network– number of simultaneous switching paths is less than

number of simultaneous conversation that can take place

• Erlang(E) – internationally accepted standard for traffic intensity– A switching resource is said to carry one Erlang of traffic

if it is continuously occupied throughout a given period of observation


Evolution of Switching System

Space Switch


Manual System

• Obtain the number to connect from caller• Connect the call of the called line

(inserting plug of cord circuit)• Alerts the called customer• Monitoring process called supervision


Strowger Step-by-Step

• Connections are set up in stages called progressive control.

• The uniselectors act as concentrator at each customer premise.

• The final is the expander.


Crossbar Switching• Strowger switches require regular

maintenance.• Replace manual operated switch by matrix

telephone relays called Matrix Crosspoints.• The switch retains a set of contacts at each

crosspoint.• Contacts are multiplied together.• Uneconomic as N inlets and N outlets

requires N2 relays.


Electronic Switching• Facilities controlled by customers

– Call barring, Repeat last call, Reminder calls, Call diversion, Three way calls, Charge advice

• Multiplex System– FDM– TDM

• Space Division (SD) System– Connection is made over a different path in.

• Time Division (TD) System– connection made over the same path but different

instant in time.


Speech Digitization and Transmission

• Speech digitization– PCM– DPCM

• Line Coding– Properties– Types of coding


Time Division Multiplexing

• Subdivide the capacity of a digital transmission system into parts in time.

• STDM– Synchronous TDM– Time slots are assigned in repetitive manner

• ATDM – Asynchronous TDM– Assign capacity as and when needed


Four Channel TDM Frame Structure

1 2 3 4 1 2 3 4 1

Frame

4 4 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 1 1 1 1

Frame

Bit Interleaving

4-bit word Interleaving


Frame Synchronization

• Extra frame bit is added, or some data bit treated as frame bits to ensure resume of new frame.

• For T1 channel structure, 24 channels are multiplexed having frame length of 193bits (24 8 + 1)bits.

• Average frame acquisition time Ft is important for frame synchronization


Frame Synchronization

• Assume Ft uses 1 framing bit per frame with alternating ones and zeros

• Ft’ = avg. time required to examine the required

number of bits before a framing bit is hit upon• Ft

’’ = avg. time required to test and ensure that chosen bit is a frame bit

• Ft = Ft’ Ft

’’

• This implies bits are chosen one by one and tested sequentially


Frame Synchronization• p = prob. of finding a 1 in a bit position• q = p -1 = prob. of finding a 0 in a bit position• If the first bit observed is a 1, then the probability

that a mismatch occurs at the end of,– One frame = p– Two frame = q.q = q2

– Three frames = q.p.p = qp2

– Four frames = q.p.q.q = q3p– Five frames = q.p.q.p.p = q2p3

– Six frames = q.p.q.p.q.q = q4p2

• Hence Ft’’ = p + 2q2 + 3qp2 + 4q3p + 5q2p3 + 6q4p2


Frame Synchronization• Assume, p = q• Then, Ft

’’ = p/(1-p)2 frame times• Setting p =1/2 , Ft

’’ = 2 frame times = 2N bit times

• Average number of bits that must be tested before the framing bit is encountered is N/2, i.e.Ft

’ = (N/2)• Ft = (2N)(N/2) = N2 bit times


Added Channel Framing • Recent technique use dedicated separate

channel for framing • Framing digits are added in a group• CCITT multiplexing standard – 32 channels per

frame with one channel carrying framing information, one channel signalling information, and 30 channels for data

• For multibit frame code, bitsNN

F Lt 2)12(2

2

N = length of the frameL = length of the frame codeAssumption: 1 and 0 occurs with equal probability


Books

1. B.P. Lathi, “Modern Digital and Analog Communication Systems”, Oxford University Press

2. Thiagarajan Viswanathan, “Telecommunication Switching Systems and Networks”, Prentice Hall India, 2007

3. Taub, Schilling, “Principle of Communication Systems”, Tata Mcgraw Hill

4. J. E. Flood, “Telecommunications, Switching, Traffic and Networks”, Prentice Hall, 1999.

telecom switching network basic ppt

Documents

switching resource

semestera network

broadband network

n subscribers

n outlets

n inlets

telephone networks

data networks