NETWORK DESIGNTIJ3053

Chapter 1 – Overview of Computer Network

Data Communications, Data Networks, and the Internet

The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point - The Mathematical Theory of Communication, Claude Shannon

Contemporary Data Comms trends

traffic growth at a high & steady rate development of new services advances in technology

significant change in requirements emergence of high-speed LANs corporate WAN needs digital electronics

A Communications Model

Communications TasksTransmission system utilization Addressing

Interfacing Routing

Signal generation Recovery

Synchronization Message formatting

Exchange management Security

Error detection and correction Network management

Flow control

Data Communications Model

Transmission Medium selection is a basic choice

internal use entirely up to business long-distance links made by carrier

rapid technology advances change mix fiber optic wireless

transmission costs still high hence interest in efficiency improvements

Networking growth of number & power of computers is

driving need for interconnection also seeing rapid integration of voice,

data, image & video technologies two broad categories of communications

networks: Local Area Network (LAN) Wide Area Network (WAN)

Wide Area Networks span a large geographical area cross public rights of way rely in part on common carrier circuits alternative technologies used include:

circuit switching packet switching frame relay Asynchronous Transfer Mode (ATM)

Circuit Switching uses a dedicated communications path

established for duration of conversation comprising a sequence of physical links with a dedicated logical channel eg. telephone network

Packet Switching data sent out of sequence small chunks (packets) of data at a time packets passed from node to node

between source and destination used for terminal to computer and

computer to computer communications

Frame Relay packet switching systems have large

overheads to compensate for errors modern systems are more reliable errors can be caught in end system Frame Relay provides higher speeds with most error control overhead removed

Asynchronous Transfer Mode ATM evolution of frame relay fixed packet (called cell) length with little overhead for error control anything from 10Mbps to Gbps constant data rate using packet switching

technique with multiple virtual circuits

Local Area Networks smaller scope

Building or small campus usually owned by same organization as

attached devices data rates much higher switched LANs, eg Ethernet wireless LANs

Metropolitan Area Networks MAN middle ground between LAN and WAN private or public network high speed large area

The Internet Internet evolved from ARPANET

first operational packet network applied to tactical radio & satellite nets also had a need for interoperability led to standardized TCP/IP protocols

Internet Elements

Internet Architecture

Example Configuration

OSI Reference Model & TCP/IP (Comparison)

How many layers that OSI & TCP/IP Model?

What are differences between OSI & TCP/IP Model?

What are similarities among OSI & TCP/IP Model?

Applications – The Interface Between Human and Data Networks

Most applications such as web browsers or e-mail clients, incorporate functionality of the OSI layer 5, 6, and 7.

Most TCP/IP applications layer protocols were developed before the emergence of personal computer, GUIs and multimedia objects.

A comparison of the OSI and TCP/IP model

Applications – The Interface Between Human

and Data Networks There are six steps OSI encapsulation process.

1. People create the communication

2. The app layer prepares human comm for transmission over the data network

3. Software and hardware convert comm to a digital format

4. App layer services initiate the data transfer

5. Each layer plays its role

6. The app layer receives data from the network and prepares it for human use.

Roles of Transport Layer Provide services to the adjacent layers Prepare application data for transport over network Process network data for use by applications

Transport Layer Functions Primary Functions:

1. Tracking individual communication between applications on sender and receiver

2. Segmenting data and managing each piece

3. Reassembling segments into streams of application data

4. Identifying the different applications

5. Performing flow control between end users

6. Enabling error recovery7. Initiating a session

OSI network layer

OSI model layer 3 TCP/IP model Internet layer

ApplicationPresentationSessionTransportNetworkData linkPhysical

Application

TransportInternet

Network Access

TCP, UDP

IPEthernet, WAN technologies

HTTP, FTP, TFTP, SMTP etc

Segment

PacketFrame

Bits

Data stream

Layer 3 protocol

A layer 3 protocol such as IP version 4 must: Provide an addressing scheme to identify

networks and individual hosts Encapsulate a segment from layer 4 into a

packet and include addresses Direct the packet across one or many

networks to the destination host Decapsulate (remove the packet header)

and give the segment to layer 4.

Data Link Layer – Accessing the Media

It provides a means for exchanging data over a common local media. Also links many upper layer services responsible for packaging the data

for communication between hosts. Data Link layer to prepare Network layer packets for transmission and to

control access to the physical media.

Physical Layer Protocols & Services

The role of the OSI Physical layer is to encode the binary digits that represent Data Link layer frames into signals and to transmit and receive these signals across the physical media - copper wires, optical fiber, and wireless - that connect network devices.

Physical Layer Protocols & Services The delivery of frames across the local media requires the following Physical layer

elements: a. The physical media and associated connectors b. A representation of bits on the media c. Encoding of data and control information d. Transmitter and receiver circuitry on the network devices

Physical Layer Protocols & Services

There are three basic forms of network media on which data is represented: - Copper cable - Fiber - Wireless

The representation of the bits - that is, the type of signal - depends on the type of media. Copper cable media, the signals

are patterns of electrical pulses. Fiber, the signals are patterns of

light. Wireless media, the signals are

patterns of radio transmissions..

The TCP/IP Concept Use existing network hardware Interconnect networks Add abstractions to hide heterogeneity

TCP/IPTCP/IP is designed to use all types of

networks Connection-oriented Connectionless Local Area Network (LAN) Wide Area Network (WAN) Point-to-point link Set of bridged networks

Examples Of PacketSwitched Networks

Wide Area Nets ARPANET, NSFNET, ANSNET Common carrier services

Leased line services Point-to-point connections

Local Area Nets Ethernet Wi-Fi

Summary introduced data communications needs communications model defined data communications overview of networks introduce Internet OSI Reference Model & TCP/IP