1. Chapter 5 Network and Transport Layers

2. Announcements and Outline
Recap
4 Data Link Layer
4.1 Media Access Control
4.2 Error Control
4.3 Data Link Protocols
Outline
5 Network and Transport Layers
5.1 Protocol
5.2 Transport Layer Functions
5.3 Addressing
5.4 Routing
5.5 TCP/IP Example
Copyright 2010
John Wiley & Sons, Inc 2

3. Chapter 5 Outline Transport & Network Layer Protocols
TCP/IP
Transport Layer Functions
Segmenting
Linking to the Application Layer
Session management
Addressing
Assigning addresses and address resolution
Routing
Types of routing, routing protocols, and multicasting
TCP/IP Examples 3

4. Network Layers
Computer 1
Computer 2 4

5. Introduction Transport and Network layers
Responsible for moving messages from end-to-end in a network
Closely tied together
TCP/IP: most commonly used protocol
Used in Internet
Compatible with a variety of Application
Layer protocols as well as with many
Data Link Layer protocols
Application Layer
Transport Layer
Network Layer
Data Link Layer 5

6. Transport/Network Layer Protocols
TCP/IP (Transmission Control Protocol / Internet Protocol)
Most common, used by all Internet equipment
Developed in 1974 by V. Cerf and B. Kahn
As part of Arpanet (U.S. Department of Defense)
Most common protocol suite
Used by the Internet
Largest percentage of all backbone, metropolitan, and wide area networks use TCP/IP
Most commonly used protocol on LANs 6

7. Introduction - Transport layer
Responsible for end-to-end delivery of messages
Responsible for segmentation and
reassembly
Breaking the message into several smaller
pieces at the sending end
Reconstructing the original message into a single whole at the receiving end
Interacts with Application Layer
Application Layer
Transport Layer
Network Layer 7

8. Transmission Control Protocol (TCP)
TCP Header: 192 bits (24 bytes)
used in message reassembly

9. Introduction – Network Layer
Responsible for addressing and routing of messages
Selects best path from computer to computer
until the message reaches destination
Performs encapsulation on sending end
Adds network layer header to
message segments
Performs decapsulation on receiving end
Removes the network layer header at receiving end and passes them up to the transport layer
Transport Layer
Network Layer
Data Link Layer 9

10. Internet Protocol (IP)
Two versions in current in use 10

11. IP Packet Formats: IPv4 (24 bytes) vs. IPv6 (40 bytes)
IPv4 Header: 192 bits (24 bytes)
IPv6 Header: 320 bits (40 bytes)

12. Student Questions
What goes in the data field of an IP Packet in the Network Layer? What about the previous layer’s packet? 12

13. TCP/IP’s 5-Layer Network Model13

14. Efficiency
You want to transmit a 500 byte message. What would be the efficiency in transmitting this message?
Overhead:
SMTP:
TCP:
IP:
Ethernet:
What about an HTTP file of 4000 bytes? 14

15. Transport Layer Functions
Segmenting
Linking to the Application Layer
Session management
Application Layer
Transport Layer
Network Layer 15

16. Segmenting
Breaking outgoing messages from the application layer into a set of smaller segments for transmission through network. When the transport layer is set up, it determines what size segments will make best use of its data link protocols. 16

17. Packetization and Reassembly
FTP
FTP
TCP
TCP IP IP
sender
receiver
What size packet to use?
Delivers incoming packets
as they arrive (e.g., Web pages) or
to wait until entire message arrives (e.g., ) 17

18. 5.2.2 Linking to Application Layer
TCP may serve several Application Layer protocols at the same time
Problem
Solution
How do we know what number
the server uses?
What would be the other type of number used and why?
TCP
HTTP
FTP
SMTP … 80 21 25

19. 5.2.2 Application Layer Services

20. Session Management
A session can be thought of as a conversation between two computers.
Types of Session Management
Connection Oriented
Connectionless Routing
Quality of Service (QoS)

21. 5.2.3.1 Session Management - Connection Oriented
Setting up a virtual circuit, or a TCP connection
Packet deliveries are acknowledged
For which application layer packets does the transport layer use a connection oriented session for?

22. 5.2.3.1 Setting up Virtual ConnectionsB
SYN
SYN
Data 1
Data 2
ACK 2
Data 3
Data 4
FIN
not busy

23. 5.2.3.2 Session Management - Connectionless Routing
Provided by UDP
Sending packets individually without a virtual circuit
Each packet is sent independently of one another, and will be routed separately, following different routes and arriving at different times
For which application layer packets does the transport layer use a connection oriented session for?

24. 5.2.3.2 UDP - User Datagram Protocol
Protocol used for connectionless routing in TCP/IP suite that uses no acks, no flow control
Uses only a small packet header
Only 8 bytes containing only 4 fields:
Source port
Destination port
Message length
Header checksum
Can also be used for applications where a packet can be lost, such as information rich video