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.