GNIOT GIRLS INSTITUTE OF TECHNOLOGY(A Unit of Vinayak Education Society)

Approved by AICTE, Ministry of H.R.D.(Govt. of India)(Affiliated to U.P. Technical University Lucknow)

PRESENTED BY

AANCHAL SAXENA

1141631001

EC-1

CONTENTS:

INTRODUCTION WHY SWITCHING? BASIC SWITCHING BLOCK CLASSIFICATION OF SWITCHING TECHNOLOGY CIRCUIT SWITCHING ADVANTAGES OF CIRCUIT SWITCHING DISADVANTAGES OF CIRCUIT SWITCHING PACKET SWITCHING DATAGRAM VIRTUAL CIRCUIT VIRTUAL CIRCUIT v/s DATAGRAM ADVANTAGES OF PACKET SWITCHING DISADVANTAGES OF PACKET SWITCHING MESSAGE SWITCHING

INTRODUCTION

Switching is a process which involves the control consisiting of a mechanical

or elctrical or electronic device for making or breaking or changing the

connections in a circuit.

The switching centers receives the conytrol signals,messages or

conversations and forwards to the required destination,after necessary

modification(link amplifications) if necesssary .

A switching system is a collection of switching elements arranged and

controlled in such a way as to setup a communication path between any two

distant points.

Why Switching?

A

B change

Calling

subscribersCalled

subscribers

P

Fig. A

Called

subscribers

Calling

subscribers

A

B

Fig. B

P

Q

• In Fig. A , the no. of calling subscribers > no. of called subscribers , whereas

• In Fig. B , the no. of calling subscribers = no. of called subscribers.

• Fig. A depicts a practical & real situation , and Fig. B is an ideal situation which is not possible.

We always deal with the former situation , where no. of calling subcribers are more & the resources are less and we cannot provide 1 : 1 service , therefore switching is required.

BASIC SWITCHING BLOCK

UMB

MAU

Exchange

CP ‘A’ CP ‘B’

visible

audible

Alarm Panel

Fig. C Switching Block

Fig. C shows a switching block & its functioning in a telephone exchnge. The block diagram consists of :

• two CP’s (Control Processors), namely CP ‘A’ which is the ‘Executive CP’ & CP ‘B’ is the ‘Hot Standby CP’,

• an UMB(Update & Matching Bus) - updates & matches the data of both the CP’s,

• a MAU(Maintenance Unit) - observes & maintains both the CP’s,and

• an Alarm Panel – in case of any failure gives an alert.

• If CP ‘A’ fails, MAU will sense and send a message to Alarm Panel,and if a fault is acknowledged at CP ‘A’ , the MAU smoothly changes control to CP ‘B’.

• The change is so very seamless & a hot standby is used to make it available alongwith mains.

CLASSIFICATION OF SWITCHING

TECHNOLOGY

Switching technology can be classified as follows :

CIRCUIT SWITCHING PACKET SWITCHING MESSAGE SWITCHING

CIRCUIT SWITCHING

Dedicated communication path between two stations Used in Landline communications Three phases :

• Circuit Establishment• Data Transfer

• Circuit Disconnection Must have switching capacity and channel capacity to

establish connection

Must have intelligence to work out routing

Fig. C Circuit Switching

CIRCUIT ESTABLISHMENT :

• Sub. ‘A’ goes OFF hook-receives a ring back tone.

• Sub. ‘A’ dials telephone no. of Sub. ‘B’ which is received by switching unit.

• If any path is available switching unit connects Sub. ‘A’ to Sub. ‘B’ – Sub. ‘B’ receives a ringing current otherwise Sub. ‘A’ receives an acknowledgement message that the connection has not been established.

• In the former case, Sub. ‘B’ goes OFF hook- a dedicated path has been established.

DATA TRANSFER :

• Now, a dedicated path has been established b/w Sub. ‘A’ & Sub. ‘B’.

• Full duplex(both ways) communication is accounted.

• A counter keeps track of the communication timings in order to generate a bill

• If Sub. ‘B’ goes ON hook-there is a delayed disconnection(usually 1 min).

• If Sub. ‘A’ goes ON hook-immediate disconnection takes place.

CIRCUIT DISCONNECTION :

• NOW, Sub. ‘A’ is ON hook- deallocation of resources takes place.

• The counter stops immediately.• Dedicated path has been diconnected.

ADVANTAGES OF CIRCUIT

SWITCHING

Fixed Bandwidth Dedicated path Lack of buffers in the data path Possibility of all-optical data paths

Higher switching capacity

DISADVANTAGES OF CIRCUIT

SWITCHING

Inefficient• Channel capacity dedicated for duration of connection

• If no data, capacity wasted Set up (connection) takes time Once connected, transfer is transparent

Developed for voice traffic (phone)

PACKET SWITCHING

Digital networking communications method that groups all transmitted data – regardless of content, type, or structure –into suitably sized blocks, called packets

Used in mobile communication Station breaks long message into packets Packets sent one at a time to the network Packets handled in two ways:• DATAGRAM (Connectionless Approach)• VIRTUAL CIRCUIT (Connection-oriented Approach)

Fig. D Packet Switching

DATAGRAM

Each packet treated independently

Packets can take any practical route

Packets may arrive out of order

Packets may go missing

Up to receiver to re-order packets and recover from missing packets

VIRTUAL CIRCUIT

Preplanned route established before any packets sent

Call request and call accept packets establish connection (handshake)

Each packet contains a virtual circuit identifier instead of destination address

No routing decisions required for each packet

Clear request to drop circuit

Not a dedicated path

DATAGRAM v/s VIRTUAL CIRCUIT

Datagram• Circuit setup is not needed• Each packet contains the address of source and destination• Router do not hold state information about connections• Congestion control is difficult

Virtual circuits• Circuit setup is needed• Each packet contains a short VC no.• Each VC requires router table space per connection• Congestion control is easy

ADVANTAGES OF PACKET

SWITCHING

Line efficiency• Single node to node link can be shared by many packets

over time

• Packets queued and transmitted as fast as possible Data rate conversion

• Each station connects to the local node at its own speed

• Nodes buffer data if required to equalize rates Packets are accepted even when network is busy

• Delivery may slow down Priorities can be used

DISADVANTAGES OF PACKET

SWITCHING

Packets may be lost on their route, so sequence numbers are required to identify missing packets

Switching nodes requires more processing power as the packet switching protocols are more complex

Switching nodes for packet switching require large amount of RAM to handle large quantities of packets

A significant data transmission delay occurs - Use of store and forward method causes a significant data transmission.

MESSAGE SWITCHING It was the precursor of packet switching messages were routed in their entirety, one hop at a time

nowadays mostly implemented over packet-switched or circuit-switched data networks

also known as a 'store-and-forward' network-each message is

stored (usually on hard drive due to RAM limitations) before being transmitted to the next switch

Email is a common application for Message Switching

Fig. E Message Switching

THANK YOU