Chapter 5 Network and Transport Layers

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

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

Network Layers Computer 1 Computer 2 4

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

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

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

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

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

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

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

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

TCP/IP’s 5-Layer Network Model 13

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

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

5.2.1 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

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., e-mail) 17

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

5.2.2 Application Layer Services

5.2.3 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)

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?

5.2.3.1 Setting up Virtual Connections B SYN SYN Data 1 Data 2 ACK 2 Data 3 Data 4 FIN not busy

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?

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