1. Chapter 5 Network and Transport Layers
Part 2

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 Layers
Computer 1
Computer 2

4. Network Layer Functions
Addressing
Each device on the path between source and destination must have an address
Internet Addresses
Assignment of addresses
Translation between network layer
addresses and other addresses
(address resolution)
Routing
Process of deciding what path a packet must take to reach destination
Routing protocols
Transport Layer
Network Layer
Data Link Layer

5. Dynamic Addressing
Giving addresses to clients (automatically) only when they are logged in to a network Uses a server to supply IP addresses to computers whenever the computers connect to network

6. 5.3.2 Programs for Dynamic Addressing
Protocols:
Bootstrap Protocol (bootp)
Dynamic Host Control Protocol (DHCP)
Different approaches, but same basic operations:

7. 5.3.3 Address Resolution Server Name Resolution
Data Link Layer Address Resolution

8. 5.3.3 Server Name Resolution - DNS
Used to determine IP address for a given URL
Provided through a group of name servers
Databases containing directories of domain names and their corresponding IP addresses
Large organizations maintain their own name servers
smaller organizations rely on name servers provided by their ISPs
When a domain name is registered, IP address of the DNS server must be provided to registrar for all URLs in this domain
Example: Domain name: uncw.edu
URLs: csb.uncw.edu,

9. 5.3.3 How DNS Works – Directory Service
Where are address tables located?

10. 5.3.3 How DNS Works (Cont.) If the URL is NOT in the local DNS server
Sends DNS request packet to the next highest name server in the DNS hierarchy
Usually the DNS server at the top level domain (such as the DNS server for all .edu domains)
If the URL is NOT in the name server
Sends DNS request packet ahead to name server at the next lower level of the DNS hierarchy

11. DNS Hierarchy

12. DNS Hierarchy

13. 5.3.3 How DNS Works – Internal Request

14. 5.3.3 How DNS Works – External Request

15. 5.3.4 MAC Address Resolution
Problem: Unknown MAC address of the next node (whose IP address is known)
Solution:
Operation:

16. 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

17. 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

18. 5.4.1 Routing Example – LAN with Routers

19. 5.4 Routing

20. 5.5.1 TCP/IP Network Example

21. Types of Routing
Centralized routing
Decentralized routing

22. 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

23. 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?

24. 5.5.1 TCP/IP Configuration Information

25. 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

26. 5.5.1 TCP/IP Network Example

27. 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)

28. 5.5.1 Message Moving Through Layers

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

30. 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

31. 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

32. 5.5.2 Known IP Address and Ethernet Address
Transmit from B => F (B knows F’s IP Address)
PATH IP
Source
Destination
Ethernet

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

34. 5.5.4 Unknown Ethernet Address
Transmit from B => F (doesn’t know F’s Ethernet address)
PATH IP
Source
Destination
Ethernet