1. The Network Layer

2. Network Performance Measures
Two Performance Measures
Quantity of Service (Throughput)
How much data travels across the net?
How long does it take to transfer long files?
Quality of Service (Average packet delay)
How long does it take for a packet to arrive at its destination?
How responsive is the system to user commands?
Can the network support real-time delivery such as audio and video?

3. Types of Routing Algorithms
Nonadaptive (static)
Do not use measurements of current conditions
Static routes are downloaded at boot time
Adaptive Algorithms
Change routes dynamically
Gather information at runtime
locally
from adjacent routers
from all other routers
Change routes
Every delta T seconds
When load changes
When topology changes

4. Network Layer Design Issues
Store-and-forward packet switching
Services provided to transport layer
Implementation of connectionless service
Implementation of connection-oriented service
Comparison of virtual-circuit and datagram networks

5. Store-and-Forward Packet Switching
ISP’s equipment
The environment of the network layer protocols.

6. Services Provided to the Transport Layer
Services independent of router technology.
Transport layer shielded from number, type, topology of routers.
Network addresses available to transport layer use uniform numbering plan
even across LANs and WANs

7. Implementation of Connectionless Service
ISP’s equipment
A’s table (initially) A’s table (later) C’s Table E’s Table
Routing within a datagram network

8. Implementation of Connection-Oriented Service
ISP’s equipment
A’s table C’s Table E’s Table
Routing within a virtual-circuit network

9. Comparison of datagram and virtual-circuit networks

10. 1.Distance Vector Routing 2.Link State Routing
Routing Algorithms
1.Distance Vector Routing
2.Link State Routing

11. The Concept of Distance
Vector Routing

12. Distance Vector Routing Table

13. Routing Table Distribution

14. Updating Routing Table for Router A

15. Final Routing Tables

16. Example 21.1

17. Concept of Link State Routing

18. Cost in Link State Routing

19. Link State Packet

20. Flooding of A’s LSP

21. Link State Database

22. Dijkstra algorithm

23. Shortest Path Algorithm (1)
The first five steps used in computing the shortest path from A to D. The arrows indicate the working node

24. Hierarchical Routing
Hierarchical routing.

25. Broadcast Routing
Reverse path forwarding. (a) A network. (b) A sink tree. (c) The tree built by reverse path forwarding.

26. Flooding
Flooding is a simple routing algorithm in which every incoming packet is sent through every outgoing link except the one it arrived on.
Algorithm
Each node acts as both a transmitter and a receiver.
Each node tries to forward every message to every one of its neighbors except the source node.

27. Flooding
Advantages:
If a packet can be delivered, it will (probably multiple times).
Since flooding naturally utilizes every path through the network, it will also use the shortest path.
This algorithm is very simple to implement

28. Flooding