1.3. IP Service Model

“IP provide deliberately simple, dumb, minimal service”

I. Network Layer:

is responsible send IP datagram to the other end: IP Datagram = IP Data + IP Header

IP(Internet Protocol) is only one protocol must used by Network Layer

II. IP Service’s Property

1. Datagram: self-contained, individual hop-by-hop routing

2. Unreliable: no promise delivered to destination, that is it is not registered mail

3. Best effort: only makes errors, certain conditions happened

4. Connectionless: communication doesn’t start by establishing connection to end

III. IP Service is simple and minimal: WHY?

1. To keep network simple:

packet delivered quickly at low cost maintenance

2. End-to-End principle:

network can become easier to evolve if complicated feature implemented at end host(software). Not in hardware of the Internet

3. Allow a reliable / unreliable choice on top layer

let application choose the reliability(i.e. TCP / UDP) for performance reasons

4. Can work over any link layer:

IP makes a very little expectation of the link layer below. So any of link layer technologies(i.e. wired, wireless) can be implemented

IV. Other services provided by IP

1. TTL(Times To Live: Hop Count): prevent packet looping forever

2. Fragment packets if they are too long to send as itself:

each link layer has maximum bandwidth to send a frame at a time

3. Use header checksum to reduce chance of wrong destination on delivery

4. Allow compatible with new version of IP: IPv6

5. Allow new fields added to datagram header:

pros: new service can be added using new fields

cons: break the goal of simple and minimal design of IP

V. IP Datagram Detail…



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