Computer Science 302 Presentation bUSINESS DATA AND COMMUNICATION

Chapter 5

Network and Transport Layers

Business Data Communications & Networking

FitzGerald ● Dennis ● Durcikova

Prepared by Taylor M. Wells: College of Business Administration, California State University, Sacramento

Outline

Transport Layer Protocols

Network Layer Protocols

Transport Layer Functions

Linking to the application layer

Segmenting

Session Management

Network Layer Functions

Addressing

Routing

TCP/IP Examples

Implications for Management

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

Network Layer

Data Link Layer

Application Layer

Transport Layer

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Network and Transport Layers

Transport Layer

Layer 4 in the Internet model

Links application and network layers

Responsible for segmentation and reassembly

Session management

Responsible for end-to-end delivery of messages

Network Layer

Layer 3 in the Internet model

Responsible for addressing and routing of messages

Internet Model

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

Transport Layer

Application Layer

Network Layer

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Introduction – Network Layer

Responsible for addressing and routing of messages

Selects the best path from computer to computer

until the message reaches destination

Performs encapsulation on sending end

Adds network layer header to message segments

Performs de-capsulation on receiving end

Removes the network layer header at receiving end and passes them up to the transport layer

Network Layer

Transport Layer

Data Link Layer

6

Transport/Network Layer Protocols

TCP/IP (Transmission Control Protocol / Internet Protocol)

Most common, used by all Internet equipment

IPX/SPX

Similar to TCP/IP

Mainly used by Novell networks (Novell has since replaced it with TCP/IP)

X.25

Used mainly in Europe

SNA (System Network Architecture)

IBM’s protocol suite

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TCP/IP Protocol

Developed in ‘74 by V. Cerf and B. Kahn

As part of Arpanet (U.S. Department of Defense)

Most common protocol suite

Used by the Internet.

Almost 70% of all backbone, metropolitan, and wide area networks use TCP/IP

Most common protocol on LANs (surpassed IPX/SPX in ‘98)

Reasonably efficient and error free transmission

Performs error checking

Transmits large files with end-to-end delivery assurance

Compatible with a variety of data link layer protocols

Transport Layer Protocols

Transmission Control Protocol (TCP)

Most common transport layer protocol

PDU called a segment

Breaking up a large message into smaller packets

Numbering the packets and

Reassembling them at the destination end

Used for reliable transmission of data

160 - 192 bits (20 -24 bytes) of overhead

Options field is not required

Destination Port

(16 bits)

Unused

(6 bits)

Source Port

(16 bits)

Sequence Number

(32 bits)

ACK number

(32 bits)

Header Length

(4 bits)

Flags

(6 bits)

Flow Control

(16 bits)

CRC-16

(16 bits)

Urgent Pointer

(16 bits)

Options

(32 bits)

User Data

(varies)

The header length field is used to tell the receiver how long the TCP packet is

used in message reassembly

how much data it can accept and then wait for further instructions

mark a segment of data as 'urgent'

TCP Header: 192 bits (24 bytes)

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Transport Layer Protocols

User Datagram Protocol (UDP)

Operates at the transport layer

 Used when the sender needs to send a single small packet to the receiver

No need to worry about segmenting or reassembling

Faster transmission

PDU called a segment

Used in time-sensitive situations, for control messages, or when reliability is handled by the application layer

32-64 bits (4-8 bytes) of overhead

Source port is optional in IPv4 and IPv6, Checksum is optional in IPv4

Destination Port

(16 bits)

Source Port

(16 bits)

Length

(16 bits)

Checksum

(16 bits)

User Data

(varies)

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Network Layer Protocols

Internet Protocol (IP)

Responsible for addressing and routing of packets

IP version 4 (IPv4)

Most common version of IP used

a 192 bit (24 byte) header, uses 32 bit addresses

32-bit addresses (232 or ~4.29 billion possible)

Exhaustion of address space

IP version 6 (IPv6)

Mainly developed to increase IP address space due to the huge growth in Internet usage (128 bit addresses)

128-bit addresses (2128 or ~3.4 × 1038 possible)

Slowly being adopted due to IPv4 exhaustion

Both versions have a variable length data field

Max size depends on the data link layer protocol.

e.g., Ethernet’s max message size is 1,492 bytes, so max size of TCP message field:

1492 – 24 – 24 = 1444 bytes

TCP header

IPv4 header

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Network Protocols

IPv4 Packet

160-192 bits (20-24 bytes) of overhead

Options field rarely used

Header length

(4 bits)

Packet Offset

(13 bits)

Version number

(4 bits)

Type of service

(8 bits)

Total length

(16 bits)

IDs

(16 bits)

Flags

(3 bits)

Time to Live /

Hop Limit

(8 bits)

CRC-16

(16 bits)

Protocol

(8 bits)

Options

(32 bits)

User Data

(varies)

Source Address

(32 bits)

Destination Address

(32 bits)

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Network Protocols

IPv6 Packet

Fixed Header

320 bits (40 bytes) of overhead

Traffic Class / Priority

(8 bits)

Version number

(4 bits)

Flow Label

(20 bits)

Payload length

(16 bits)

Next Header

(8 bits)

Hop Limit

(8 bits)

User Data

(varies)

Source Address

(128 bits)

Destination Address

(128 bits)

Optional Headers

Optional Headers

Hop-by hop options

Destination options (with routing options)

Routing

Fragment

Authentication

Encapsulation Security Payload

Destination options

Mobility

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Transport Layer Functions

Linking to Application Layer

Packetization and Reassembly

Establishing connection (virtual)

Connection Oriented

Connectionless

Quality of Service (QoS)

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Linking to Application Layer

TCP may serve several Application Layer protocols at the same time

Problem: Which application layer program to send a message to?

Solution: Port numbers located in TCP header fields; 2-byte each (source, destination)

Standard port numbers

Usual practice

Nonstandard port numbers

Possible, but requires configuration of TCP

TCP

HTTP

FTP

SMTP

…

80

21

25

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Transport Layer Functions

Linking to the application layer

TCP/UDP may serve multiple application layer protocols

Ports used to identify application (2-byte numbers)

Many source/destination ports follow standards

Common port standards

HTTP: TCP port 80

HTTPS: TCP port 443

FTP: TCP ports 20 and 21

SMTP: TCP port 25

IMAP: TCP port 143

POP3: TCP port 110 (more commonly TCP port 995 secure version)

DNS: TCP or UDP port 53 (most commonly UDP)

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Transport Layer Functions