1. Chapter 5 Network and Transport Layers

2. Chapter 5 Outline Transport & Network Layer Protocols
TCP/IP
Transport Layer Functions
Linking to the Application Layer
Segmenting
Session management
Addressing
Assigning addresses and address resolution
Routing
Types of routing, routing protocols, and multicasting
TCP/IP Examples
Copyright 2010
John Wiley & Sons, Inc

3. Network Layer
Computer 1
Computer 2

4. 5.4 Routing
Process of identifying what path to have a packet take through a network from sender to receiver
Routing Tables
Used to make routing decisions
Shows which path to send packets on to reach a given destination
Kept by computers making routing decisions
Routers
Special purpose devices used to handle routing decisions on the Internet
Maintain their own routing tables
Dest. B C D E F G
Next

5. 5.4.1 Simple Routing Example
Possible paths from A to G:
ABCG
ABEFCG
ADEFCG
ADEBCG A
Routing Table for A
Dest. B C D E F G
Next
Each node has its own routing table

6. 5.4.1 Routing Example – LAN with Routers

7. 5.4 Routing

8. 5.5.1 TCP/IP Network Example

9. Types of Routing
Centralized routing
Decentralized routing

10. 5.4.2 Routing Protocols – how tables are set up
Static routing:
Uses fixed routing tables developed by network managers
Each node has its own routing table
Changes when computers added or removed
Dynamic routing or Adaptive routing:
Uses routing tables at each node that are updated dynamically
Based on routing condition information exchanged between routing devices
Types

11. 5.4.2 Dynamic Routing Algorithms
Distance Vector
Uses the least number of hops to
decide how to route a packet
Link State
Uses a variety of information types to decide how to route a packet (more sophisticated)
e.g., number of hops, congestion, speed of circuit
Links state info exchanged periodically by each node to keep every node in the network up to date
Provides more reliable, up to date paths to destinations

12. 5.4.2.1 Routing Information Protocol (RIP)
A dynamic distance vector interior routing protocol
Operations:
Manager builds a routing table by using RIP
Routing tables broadcast periodically (every minute or so) by all nodes
When a new node added, RIP counts number of hops between computers and updates routing tables

13. 5.4.2.1 Open Shortest Path First (OSPF)
A dynamic link state interior routing protocol
Became more popular on Internet
More reliable paths
Less burdensome to the network

14. 5.5.1 Sending Messages using TCP/IP
Required Network layer addressing information
Address information is obtained from a configuration file or provided by a DHCP server
What additional information is needed for servers?

15. 5.5.1 TCP/IP Configuration Information

16. Subnet Masks
Tells the computer what part of an Internet Protocol address to be used to determine whether the destination is on the same subnet or on a different subnet
Example
Subnet: x
Subnet mask:
Subnets: ,
Subnet mask

17. 5.5.1 TCP/IP Network Example

18. 5.5.1 Moving Messages - TCP/IP and Layers
How layers are handled in a LAN:
Host Computers
Packets move through all layers
Gateways, Routers
Packet moves from Physical layer to Data Link Layer through the network Layer
At each stop along the way (e.g. from router to router):
Ethernet packets is removed and a new one is created for the next node
IP and above packets never change in transit (created by the original sender and destroyed by the final receiver)

19. 5.5.1 Message Moving Through Layers

20. Known IP Address
Transmit from A => E (A knows E’s IP Address) How many Hops will it take?
PATH IP
Source
Destination
Ethernet

21. Unknown IP Address
Transmit from A => E (A doesn’t know E’s IP address)
How do we do this?
PATH IP
Source
Destination
Ethernet
DNS
Request
PATH IP
Source
Destination
Ethernet
DNS
Response

22. 5.5.4 Unknown Data Link Address
Transmit from A => E (doesn’t know E’s Ethernet address)
An ARP request from D will occur once the message sent by A is received by D.
PATH IP
Source
Destination
Ethernet

23. 5.5.2 Known IP Address and Ethernet Address
Transmit from B => F (B knows F’s IP Address)
PATH IP
Source
Destination
Ethernet

24. Unknown IP Address
Transmit from B => F (B doesn’t know F’s IP address)
PATH IP
Source
Destination
Ethernet

25. 5.5.4 Unknown Ethernet Address
Transmit from B => F (doesn’t know F’s Ethernet address)
PATH IP
Source
Destination
Ethernet

26. Implications for Management
Most organizations moving toward a single standard based on TCP/IP
Decreased cost of buying and maintaining network equipment
Decreased cost of training networking staff
Telephone companies with non-TCP/IP networks are also moving toward TCP/IP
Significant financial implications for telcos
Significant financial implications for networking equipment manufacturers