1. Network layer Accepts messages from the application layer Prepares messages for the data link layer Packetising Addressing Routing

2. Many protocols TCP/IP Used by the internet IPX/SPX Mostly used in LANs X25 Popular WAN protocol. SNA Used on IBM mainframes

3. Parts of the network layer TCP like part –Packetising, Numbering –Reliable delivery IP like part –Routing –Addressing IP everywhere along the route, TCP only at sender and receiver.

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

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

6. Future of the network layer TCP/IP only? Running out of addresses, IPv6

7. Addresing Application layer: www.eit.ac.nz Network layer: 202.50.252.20 Data link layer: 00-0C-00-F5-03-5A Data link in hardware Network in software: Uses a DNS

8. Routing Centralised or decentralised routing Static or dynamic routing –Routing Information Protocol

9. Introduction to TCP/IP Military origins Address classes, Subnetting Static or Dynamic addressing, BOOTP Ports Routing: DNS or Data link layer Firewalls, Gateways Next year