Network layerNetwork layer

Accepts messages from the application layer

Prepares messages for the data link layer

PacketisingAddressingRouting

Many protocolsMany protocols

TCP/IPUsed by the internet

IPX/SPXMostly used in LANs

X25Popular WAN protocol.

SNAUsed on IBM mainframes

Parts of the network Parts of the network layerlayerTCP like part

– Packetising, Numbering– Reliable delivery

IP like part– Routing– Addressing

IP everywhere along the route, TCP only at sender and receiver.

Typical network packet Typical network packet (TCP)(TCP) Source and Destination ID Sequence number ACK number Header length Flags, Urgency, Options Flow control CRC16 User data

Typical network packet Typical network packet IPIP Version header and total length Type of service and protocol Identifiers, Flags, options hop limit CRC Source and destination address User data

Future of the network Future of the network layerlayerTCP/IP only?Running out of addresses, IPv6

AddresingAddresing

Application layer: www.eit.ac.nzNetwork layer: 202.50.252.20Data link layer: 00-0C-00-F5-03-5AData link in hardwareNetwork in software: Uses a DNS

RoutingRouting

Centralised or decentralised routing

Static or dynamic routing– Routing Information Protocol

Introduction to TCP/IPIntroduction to TCP/IP

Military origins Address classes, Subnetting Static or Dynamic addressing, BOOTP Ports Routing: DNS or Data link layer Firewalls, Gateways Next year