ERROR REPORTING MECHANISM (ICMP)

INTRODUCTION:

 IP gives best-effort delivery. Delivery causes can be ignored; datagrams may be 'dropped on the ground'. Internet Control Message Protocol gives error-reporting mechanism.

BEST-EFFORT ERROR AND SEMANTICS DETECTION:

Internet layer can check a variety of errors: e.g.

• Checksum
• TTL expires
• No route to receiver network.
• Can't deliver to receiver host.

Internet layer discards datagrams with causes.

INTERNET CONTROL MESSAGE PROTOCOL:

Some errors can be noticed.  Router transmits message back to host in datagram. Message has information about problem. It is included in IP datagram.

TYPES OF MESSAGES:

Internet control Message Protocol (ICMP) describes error and informational messages. These are shown as follows:

1. ERROR MESSAGES:

These are as given:

• Source quench
• Time exceeded
• Destination unreachable
• Redirect
• Fragmentation required

2. INFORMATIONAL MESSAGES:

These are as given:

• Echo request/reply
• Address mask request /reply
• Router discovery

ICMP MESSAGE TRANSPORT:

 ICMP message transport is performed upon by getting ICMP included in IP. This is given in the figure below: