Net Protocols pt2

ICMP message header format type4 code 0 is know as source quench and was designed to add a kind of flow and congestion control to the IP it informs the source that a datagram has been discarded due to congestion in a router or the destination host, the source must slow donw the sending of datagrams until the congestion is relieved

• 1)When datagram visits a router the value of this field is decrementd by 1 until it reaches 0 the router discards it
• 2)When the destination host doesns't recive the frame withing a set time it discards it and sends a time exceeded message to the original source

• To communicate with a remote host a mobile host goes through 3 phases
• 1)Agent Discovery
• 2)Registration
• 3)Data Transfer

Agent Discovery: A mobile host must discover (learn the address of) a home agent before it leaves its home network. A mobile host must also discover a foreign agent after it has moved to foreign network. This discovery consists of learning the care of address as well as the foreign agent's address. The discovery involves 2 types of messages: advertisement and solicitation, when a mobile host has moved to a new network and has not received agent advertisements, it can initiate an agent soliciation

Registration:After a mobile host has moved to a foreign network and discovered the foreign agent it must register. To register with the foreign agent and the home agent, themobile host uses a registration request and registration reply

Data Transfer: After agent discovery and registration a mobile host can communicate with a remote host

• Persistance connection:
• The server keeps a TCP conneciton open for more requests after sending a response. The server can close the connection at the request of a client or if a time-out has been reached

• Nonpersistent connection:
• One TCP connection is made for each request/response
• Every connection requires 1 handshake
• Is not instantaneous
• Imposes high overhead on the server becuase the server needs N + 1 different buffers and requires a slow start procedure each time a connection is opened