Switching 2-Data Communication and Computer Networks-Lecture Slides, Slides of Data Communication Systems and Computer Networks

Download Switching 2-Data Communication and Computer Networks-Lecture Slides and more Slides Data Communication Systems and Computer Networks in PDF only on Docsity!

Switching

 A Network is set of connected devices. When we have multiple devices, we have the problem of how to connect them to make one-to-one communication possible.

 Solution can be

• Point to point connection between devices.
• Bus, star, mesh or other topologies.
• Other solution is Switching.

 A switched network consist of series of interlinked nodes, called switches.

 Switches are devices capable of creating connections between two or more devices linked to the switch.

 In switched network, some of these nodes are connected to the end systems computer or telephone).

1. Setup Phase

 The end systems are connected through dedicated lines to the switches, connection setup means creating a dedicated channels between the switches.

 If System A connects with system M.

 System A send a setup request that includes the address of system M , to switch I.

 Switch I then sends request to switch IV for dedicated channel.

 Switch IV then finds the dedicated channel between itself and switch III.

 Switch III informs the end system M the system A ’s intention.

 After making a connection, an Acknowledgment from system M sent to system A in opposite direction.

2. Data Transfer Phase

After the establishment of the dedicated circuit channel), the two parties can transfer data.

3. Teardown Phase

When one of the parties needs to disconnect, a signal is sent to each switch to release the resources.

Efficiency

 In circuit switched network the resource of network are allocated during the entire connection.

 These resources are unavailable to other connection at that time.

Delay

The total delay is the time to

• Create connection (propagation time of the source request, request signal transfer time , propagation time of the acknowledgment from the destination , the second transfer time of the acknowledgment),
• Transfer data,
• Disconnect the circuit.

Example

A message consist of four packets or data grams delivered from station A to station X.

 Each switch maintains Routing table which is based on destination address.

 Destination address and corresponding output ports are recorded in the table.

Efficiency

Its efficiency is better than circuit-switched network; resources are allocated only when there are packets to be transferred.

Delay

 There is no setup or tear down time.

 The delay is not uniform for the packets of a message.

 Packet travels through two switches.

 Three transmission times(3T), three propagation delays (slopes 3τ of the lines), and two waiting times (w1,w2).

 Total delay =3T + 3τ + w1 + w

Virtual Circuit Identifier

 The identifier is used for data transfer is called the virtual–circuit identifier (VCI).

 VCI is a small number that has only switch scope; it used by a frame between two switches.

 When a frame arrives at a switch, it has a VCI, when it has a different VCI.

Switch and tables in a Virtual-Circuit Network

Three phases of Virtual Circuit

1. Setup Phase
2. Data transfer
3. Teardown phase 1. Setup Phase

1. Setup Request
2. Setup Acknowledgment

Setup Request

Setup Acknowledgment

Delay in a virtual-circuit network

Total Delay= 3T (transmission time) + 3τ (propagation time) + Setup delay + Teardown delay

Structure of Packet Switch