CP9253: High Speed Switching Architectures

LAN SWITCHING ATM SWITCHING ARCHITECTURES QUEUING STRATEGIES PACKET SWITCHING

ARCHITECTURE IP SWITCHING

Telecommunication Network Telecommunication Network Transporting

information by converting it into suitable form (electrical / optical signals) and transmitting over a distance.

Transmission subsystem Switching subsystem Signalling subsystem

Involves: Users –Subscribers Public / Private Telecommunication Operators (PTO) Service ProvidersManufacturers of equipments and components ( HW/SW)Financial Investors & Governments.

Structure of a telecommunication network

Network of links & nodes ; customer nodes, switching nodes, transmission nodes, service nodes

Network configurations mesh, bus, ring, star, tree

Area with a single exchange star

Area with several exchanges multiple stars connected by junction circuits Junction network mesh type , tandem exchange Routing via direct junctions / tandem exchange

Trunk / toll network Long-distance circuits Trunk transit exchanges

National telecommunication network

Internationalnetwork

Trunknetwork

Localnetwork

Satellite links/ submarine cables

International gateway exchange

National tandem exchanges(tertiary trunk switching centres)

Regional tandem exchanges(secondary trunk switching centres)

Local tandem exchanges(primary trunk switching centres)

Local exchanges

Customer lines, PBX, LAN

AAR

Communication Services Unidirectional Service eg. ? Multidirectional Service eg. ? Three classes of services

Voice (POTS) Data Image

Information Capacity Low speed upto 100Kbps, eg. Voice,

telemetry, videotelephony, credit card authorization, etc.

Medium speed 0.1 to 10 Mbps, eg. HI-FI sound, videoconferencing, data/images

High speed greater than 10 Mbps, eg. Interactive video, compressed video

Communication Services

Real-time services Multipoint and multimedia capability Burstiness factor average information rate/peak

rate Voice applications 30% Terminal to host communications < 1% LAN/MAN < 0.1 % Video : broadcast, interactive video

Networking Issues

Basic classification based on switching technique:

Circuit switching Message switching Packet switching

Datagram Virtual circuit

Networking Issues

Basic classification based on switching technique:

Circuit switching Message switching Packet switching

Datagram Virtual circuit

Circuit Switching

Electrical link between the transmitter and the reciever.

Link passes through different nodes or a common switching network.eg. PSTN

Resources allocated for the particular channel.

Steps in Circuit switching

1. Source and destination are identified.2. Connection is established between the

source and destination through nodes. (Routing algorithms are used to select the nodes)

3. Data transfer takes place.4. Circuit disconnection takes place by

action of either of the two stations.

Advantages of Circuit switching:

Fixed bandwidth, guaranteed capacity (no congestion).

Low variance of end-to-end delay (delay is almost constant).

Disadvantages of Circuit Switching

Channel is dedicated between the terminals leading to wastage of Bandwidth

Not suitable for small messages as more time is taken for circuit setup and circuit disconnection

As load increases,delay increases due to complexity in the routing process

More the no. of nodes higher the delay

Message Switching

The sending host parcels up data into long messages which are transferred step by step over each link between the switches and delivered to the recipient.

It is also known as STORE AND FORWARD SWITCHING

In message switching once the transmission has been initiated a message is passed in its entirety from one node to another

Illustration

The use of message switching to communicate between A and D

Drawbacks of message switching

Adequate storage in the receiving node Retransmission is required incase of any

errors which may result in large communication overheads

If a high priority short message arrives then it has to wait until the transmission of the long message ends.

These drawbacks are overcome in packet switching

Networking Issues Classification based on application:

Voice networks Basic voice communication Call waiting, call forwarding, facsimile Probability of blocking

Data networks LANs (over a radius of 1 Km) MANs WANs Internet Packet delay and packet loss

Digital Switching Systems

SD switch

PCM

PCM PCM

PCM

Incoming PCM junctions

Outgoing PCM junctions

TDswitch

Outgoing PCM junctions

Incoming PCM junctions

Evolution of Digital switching systems

TDswitch

PCM

PCM

Analog junctions

Digital junctions

Analog junctions

Digital junctions

TDswitch

CODEC

CODEC

Analog junctions

Digital junctions

Subscriber’s

line

CODEC

Digital junctions

TD

swit

ch

Digital Subscriber’s line

•MODEM•CODEC

Evolution to ISDN Analog technology – FDM and SDS Digital technology – TDM and TDS Integration of TDM & TDS => Integrated Digital Network (IDN) To better utilize communications resources Service

integration => IDN developed to ISDN (Integrated Services Digital Network)

CS N/W

PS N/W

Dedi.N/W

Segregated transport

CS N/W

PS N/W

Dedi.N/W

Sig.N/W

ISDNSw.

ISDNSw.

NB integrated access

voice voice

data

video

data

videovideo

Voicedata

Voicedata

video

ISDN ISDN stands for Integrated Services

Digital Network According to ITU-T "an ISDN is a

network, in general evolving from a telephony IDN, that provides end-to-end digital connectivity to support a wide range of services, including voice and non-voice services, to which users have addressed by a limited set of standard multi-purpose user-network interfaces."

Problem

The problem is that a uniform delay is not guaranteed; since channels do not follow the same path through the network, there is a different frame delay for each channel.

There are two solutions for the problem: The terminal solution

By using appropriate buffers at the terminals, the delays in each channel can be padded to be equal. In order to establish these delays a prior investigation should be done by the terminals

The network solution In this case the exchange processors would ensure that all channels are kept within a single time division multiplex and therefore follow a common route.

FactorsSome of the factors influencing the emergence of the B-ISDN from ITU are: Demand. Users (both commercial and

residential) are showing interest in receiving high speed, reliable services.

Technology. Advances in technology have increased demand, as well as the ability to supply it.

Service integration. There is a need to integrate both circuit switched and packet switched services into one network that can provide interactive and distribution services.

Flexibility. The resulting network must be able to satisfy the needs of the users as well as the network operators in terms of its functionality and usability.

Bandwidth Comparison

Functions

The B-ISDN needs to provide: Broadband services. Narrowband services (for backwards compatibility). User-to-network signaling, to allow the B-ISDN user

to initiate and control communication. Inter-exchange signaling within the network, to

allow the network to provide and control resources. User-to-user signaling, to allow control, operation

and maintenance information to be sent. Management facilities for controlling and operating

the network.

Problem

The problem is how services with a wide range of rates could be

efficiently multiplexed onto a common bearer. Two solutions are proposed:

Synchronous multiplexing based - this demands a format which can be configured to match the needs of the user. This is called Synchronous Digital hierarchy - SDH .

Asynchronous multiplexing - by using a very light weight protocol called Asynchronous Transfer Mode (ATM). This protocol can be implemented at high speeds due to its simplicity.

ISDN AND ATM

It is intended that the B-ISDN will offer both connection oriented (CO) and connectionless (CL).

The broadband information transfer is provided by the use of asynchronous transfer mode (ATM), in both cases, using end-to-end logical connections.