Internet Protocols

Internet protocols

Internet architecture

In short, a packet switching network

Figure taken from Tanenbaum

Shows the complexity of the internet

Communication protocols

Funnily enough, how we communicate over the internet

Sometimes high-level protocols are built on lower-level protocols

Example: low level protocols get messages across a LAN but a higher level, built on top of these, gets a single packet routed along multiple links to its destination

Reference to pic, lower level may get it around the token ring, higher can go anywhere

OSI

Hardly used anymore

Example protocols by layer

Data linke IEEE 802.3x

Network layer (IPv4) now some use IPv6

Transport layer- TCP, UDP

Addressing in the internet

Any computer attached to the internet should have a unique ip address

In IPv4 it is a 32-bit number but in IPv6 it is 128 bits

IPv4 commonly broken up as XXX.XXX.X.X

XXX *256 to power of 3

Plus XXX * 256 to power of two

Plus X *256

Plus X

IPv6 is different, it is instead four hex digits which then get converted

Domain names

Translation service from IP address to human readable form

So would show www.myuniwebsite.ac.uk and its address

Internet protocols

IPv4

Individual messages or packets are up to 64kb long

Ever packet contains a header and some data

Header describes the packet- source, destination, size etc

Usually short

So the packet goes from the source computer, to a router, to another router for example

Example of a packet header

IHL- internet header length

defines number of operations at end of header

header checksum is used to check headers are note corrupted

packets are not perfect, they can be lost, duplicated or even corrupt

Internet control protocols

Include

ICMP- Internet control message protocol- notifies sender of problems

DHCP- Dynamic host configuration protocol- dynamically assigns ip if host does not have one

ARP- Address resolution protocol- mapping from ip address to mac addresses on LAN

UPD and TCP

These are what most applications and high-level protocols build upon

UDP- adds concept of ports- resembles ip itself

TCP- widely used, see label for more info

Can have many connections at once

Endpoint is ip address plus port number

TCP segment header

Application level protocols

HTTP

Human readable text

e.g. HTTP get request