X.25 protocol

X.25 protocol

1. Submitted by: Geetanjali Baghel M.E(ECE) X.25 PROTOCOL

2. X.25 Protocol: 1 X.25 defines how a node terminal could be interfaced to the network for communication in Packet Mode. Key terms used here are: DTE and DCE node It defines how DTE’s communicates with network and how packets are sent over that network using DCEs. It is also known as SUBSCRIBER NETWORK INTERFACE(SNI) PROTOCOL.

3. X.25 LAYERS 2 X.25 protocol specifies 3 layers:

4. Frame Layer PHASES & FRAMES 3 Communication in this layer involves 3 phases: Link Set Up Data and Control transfer Link disconnect These phases use different frames such as: U-Frames I-Frames S-Frames

5. Frame Layer and Packet Layer D omains 4

6. Virtual Circuits in X.25 5 In X.25, SVCs and PVCs both are used.

7. LCNs in X.25 6 Logical Channel Number identifies the VC at different sections of the network. A pair of LCN is defined when a VC is established between two DTE’s

8. LCN Assignment 7 The following 5 events occur : link is set up between local DTE & DCE node and also between the remote DTE and DCE. VC is established between local and remote DTE. Data is transferred between two DTEs. VC is released Link is disconnected

9. 8 Virtual Channel ID Numbers up to 4096 ( 2 12 ) multiplexed channels between each DTE and DCE the calling and called hosts use different numbers

10. Categories of PLP packets 9 Flow and Error Control used for in-band signalling(U-frame)

11. PLP Packet Format 10

12. Limitation to X.25 protocol 11 It does not explicitly define what type of addressing should be used during call set-up to access a remote DTE. It operates at low data rate of 64kbps. Links used for data and control exchange were highly erroneous. To transfer a single packet, many F&E control packets were needed. It does not support bursty nature of data.

13. 12 Thank You..