LOCAL AREA N/W

LAN LAN is communication network that inter connect a variety of data

communications devices with in a small geographic area and broadcast data at high data transfer rates.

Data communication devices- pc, computer workstation , main frames computers and disk drives, printers and modems etc.

Small geographic area- Lan can be as small as one room, or extend over multiple rooms, over multiple floors within a building, or even multiple building within single campus area.

High data transfer rate – early Lan transmitted data at only 10 million bits per second , newest lan networks 10 Billion per second

Primary function of LAN

First appeared in the 1970’s It use become widespread in commercial and

academic environment . Lan provide access to h/w and s/w resources that will

allow them to perform one or more of the following activites in an office, academic or manufacturing environment:- file serving, database and application serving , print serving.

1.Share hardware and s/w. LAN perform file serving when connection to a

workstation with a large storage disk. By keeping all of the application on the s server

or part of it on server and part of it on client workstation.

Two or more users wish to share a data set. In this case the data set , like application s/w would be stored on file server. Then network provide access to those users who has the permissions

-2. provide access to one or more high quality printers.

Lan software called print server provide workstations with authorization to access a particular printer, accepts and queues print jobs , and allow users access to job queue for routine administrative function .

3. Provide service of sending and receiving e-mail. within LAN- between LAN and other network.

4. LAN can interface with other LAN and WAN. 5. provide the capabilities of transferring video images and

video streams , also teleconferencing between 2 or more users.

6. In manufacturing and industrial environments, local area often used to monitor manufacturing events and report and control their occurrence .

The lan provide process control and monitoring. 7. In addition to common activates , LAN can be an effective

tool in many application areas - word processing, spreadsheet operations, d/b functions,

internet access, electronic appointment scheduling , graphic image creation capabilities.

Adv

1.Ability to share resources in an economical and efficient manner .

h/w resources- high quality printer, tape back-up sytem, mass storage systems, and other h/w devices.

s/w end- allow the sharing of commercial applications, in- house application and data set with one or all user workstations .

Allow users to send emails, web pages send print jobs and retrieve d/b records.

Dis adv

1. LAN hardware , OS and s/w that runs on the network can be expensive.

- also require funding for network server, network OS, network cabling system including hubs, switches , network security, support and maintenance etc.

2. The management and control of LAN require many hours of dedication and service.

- a manager or network administrator of a LAN network should be properly trained .

3. finally Lan is only strong as its weakest link.

Basic LAN Topologies

Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network.

The topological structure of a network and may be in physically logically  Physical topology is the placement of the various components of a network, including device location and cable installation. logical topology illustrates how data flows within a network, regardless of its physical design.

Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two networks, yet their topologies may be identical.

1. Bus /Tree topology 2. star-wired topology 3. star-wired ring topology 4. wireless LAN.

Bus/Tree topology

Simply called bus topology It became commercially available in the 1970’s It consist of a simple cable or bus to which all device

attach. When a device transmits on the bus , all other

attached devices receive the transmission. Connecting to the cable require a simple device tap. On the workstation end of the cable is a network

interface card (NIC).

NIC :-It is an electronic device , typically in the form of computer circuit board, that perform the necessary signal conversion and protocol operation that allow the workstation to send and receive data on the network.

Two different signaling technology of LAN baseband signaling broadband signaling

Baseband signaling Baseband transmissions typically use digital signaling over a

single wire; the transmissions themselves take the form of either electrical pulses or light.

The digital signal used in baseband transmission occupies the entire bandwidth of the network media to transmit a single data signal.

Baseband communication is bidirectional, allowing computers to both send and receive data using a single cable. But , the sending and receiving cannot occur on the same wire at the same time.

Broadband signaling

broadband uses analog signals in the form of optical or electromagnetic waves over multiple transmission frequencies.

For signals to be both send and received, the transmission media must be split into two channels.

Alternatively, two cables can be used: one to send and one to receive transmissions.

Star-wired topology Star networks are one of the most common computer network

topology. In star topology, every node (computer workstation or any other

peripheral) is connected to a central node called a hub or switch. The switch is the server and the peripherals are the clients

Hub is a non intelligent device that simply receive the data from workstations and retransmit it to other devices connected to hub..

All workstation hear the transmitted data, because there is only a single transmission channel, and all workstations are using this one channel to send and receive .

Sending the data to all workstations and devices generate a lot of traffic but keeps the operation very simple.

With regard to its logical design the star-wired bus is acting as a bus, when a workstation transmits , all workstations (or devices) immediately receive the data.

Physical design , is a star because all device are connected to the hub and radiate outward in a star like pattern.

Hub at center comes in a variety of design . one of more common is the 24- port hub , which will

connect 24 workstations or device. If more than 24 workstation connection is needed ,

use 2 or more hubs. Many hub support multiple type of media- twisted pair coaxial cable fiber-optic cable

Adv

Simple installation and maintenance Low cost component (such as hub and twisted pair

wiring) High volume of compatible product due to major

market share.

Dis adv

About the amount of traffic the hubs must handle. When 2 or more hub are interconnected and a

workstation transmit data , all the workstations connected to all the hubs receive the data.

Hub is relatively non intelligent device , it does nor filter out any data framed and does not perform any routing..

Hub can be replaced with a more advanced device called switch.

Star-wired bus topology

Star-wired ring topology The star wired ring topology is a circular connection of

workstations. Star wired ring topologies support baseband signals, capable of

supporting only one channel of information. This channel of information flows in one direction around the ring,

moving from workstation to workstation . The star wired ring is a closed loop of wire, it is important for

some device to remove a circling piece of data from the ring.

The logical organization of the workstation in a star-wired ring topology is circular but the physical organization in a star wired ring is not circular.

It look like a star wired bus design , with all its workstation connected to a central device.

This central device is not a hub, but it is Multistation Access Unit(MAU).

MAU accepts the data from workstation and transmits the data to the next workstation in the ring.

MAU is different from hub that it does not send a copy of incoming data immediately out to every connection.

if a workstation is not connected to a particular port on MAU, , that port closes itself so that a continuous ring is maintained.

Adv:- advantage same as that of star-wired topology. Star wired ring also based on twisted pair wiring, which make

installing new workstation easy. Easy to maintain topology. Disadv :- slower transmission speed , higher cost, more complex

s/w.

Wireless LANs

A lan that is not based primarily on physical wiring but uses wireless transmissions between workstation is a wireless LAN.

Basic Components of WLAN:- First component is a user device such as laptop,

workstation or PDA with a special NIC that receive and transmits the wireless signals.

Second component is wired LAN. This is the conventional network component that supports standard workstation, servers and medium access control protocols. A vast majority of wireless network are connected to wired LAN.

The third component is the control module or access point(AP), which is the component that communicate with wireless user device.

AP is essentially the interface device between the wireless user device and wired LAN. Also act as a bridge and support a medium access control protocol.

Basic configurations of WLAN 1. The single cell wireless LAN. At the center of the

cell is the access point, which is connected to the WLAN.

2. multicell layout . In this multicell support by multi Access point . User device communicate with the nearest access point and may move from one cell to another .

3. peer to peer – there is no access point at the center of the cell . Each user device communicates directly with the other user device.

Local Area network system

Ethernet , IBM token Ring. Fiber Distributed data interface Wireless Ethernet .

MAN

A network that expands into a metropolitan area and exhibits high data rates, high reliability and low data loss is called a metropolitan area network..

MAN are almost exclusively fiber optic network and capable of supporting data rates in to 10 to 100 of millions of bits per second.

So it is considered as network with very low error rates and extremely high throughput.

Characteristic of MAN

1 Man cover much greater distance than LAN. 2. Man recover very quickly from a link or

switch/router failure. MAN are designed to have highly redundant

circuit so that in the time of a failure , network can quickly reroute traffic away from failed component.

3. Some MAN topology are based on ring, logically and physically.

Ability of the user to dynamically allocate more bandwidth on demand.

WAN

Is a collection of computers and computer related equipment interconnected to perform a given functions using local and long distance telecommunications systems.

Type of computers used in WAN range from microcomputers to mainframe.

Telecommunication lines can be as simple as standard telephone line or as advance as satellite systems.

WAN used to transfer bulk data b/w two endpoints and provide users with email services, access to db, and access to internet.

Used mesh topology and requires routing to transfer data across network.

To transmitted across a mesh network . The data has to be passed along a route from workstation to workstation.

In a full mesh topology, each network  node or workstation or other device) is connected directly to each of the others.

In a partial mesh topology, some nodes are connected to all the others, but others are only connected to those nodes with which they exchange the most data.

All WAN are collection of at least 2 basic type of equipment :- a station and a node

A station :- is a device that a user interacts with to access a network and it contain the s/w application that allow to use network for particular purpose.

A node is a device that allows one or more stations to access the physical network and is a transfer point for passing information through network.

When the information arrives on the proper destination , the destination node delivers it to the destination station.

The node is usually very fast and power full router with multiple ports.

A router  is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet.

Sub network

Types of sub networks

The structure of WAN is the sub network. A sub network is a collection of nodes and interconnecting telecommunication links.

The no. of interconnections between the nodes and the way network data is passed from node to node are the responsibility of the sub network.

Three basic form of sub network 1. circuit switched

2. packet switched 3. broadcast

Circuit switched

 Circuit-switched communication system involves three phases:

1. Circuit establishment (setting up dedicated links between the source and destination).

2. Data transfer (transmitting the data between the source and destination).

3. Circuit disconnect (removing the dedicated links). Examples of circuit-switched technologies include: 1• Dial-up 2• ISDN

Packet switched

Packet switching is a method for sending data whereby the data is divided in packets.

Each packet is given a header containing information of the destination.

Each packet is forwarded through the network to the destination using this information.

At the destination the data has to be reassembled from the received packages.

There are two common packet switching methods in use: Datagram Packet Switching:

Each packet is forwarded independently based on the destination address.

Routing decisions are made dynamically, so each packet may follow a different route and thus the packages may arrive out of order.

Virtual Circuit Packet Switching:A route is set up prior to packets being sent. The packets will all follow this route.

This makes the routing through the network very easy and the packages will be received in the correct order.

Broadcast network In a broadcast describes a message or data sent to more than

one person or device.  broadcasting is a method of transferring a message to all

recipients simultaneously. For example, TV shows are broadcasted to all subscribers of a

channel. With networking, the broadcast address is used to distribute a

signal across a network, commonly used for declaring devices and their information on a network. 

TCP/IP LAYERS

Protocol, in computer science, a set of rules or procedures for transmitting data between electronic devices, such as computer

Eg: TCP/IP, SMTP, HTTp,UDP In order for computers to exchange information, there

must be a preexisting agreement as to how the information will be structured and how each side will send and receive it.

TCP/IP is the first set of protocol used in internet. Allows computers to communicate/ share resources

across n/w Work on tcp/ip started in the 1970 founded by US military Advanced Research Project Ajency

The protocol that resides at the network layer in the TCP/IP protocol is called internet protocol.

IP’s primary function is to perform routing necessary to move data packet across the internet.

IP is connection less protocol . It doesn’t concern itself with the keeping track of lost,

duplicated or delayed packets of data. The sender and the receiver of these packet may not

be informed these problems have occurred.

IP is referred to as an unreliable service. So the application requires a reliable service, it

include a reliable transport service. The reliable transport service provided by software is

called transmission control protocol.(TCP) It turns the unreliable n/w into reliable, free from lost

and duplicate packets. This combined n/w is known as TCP/IP.

Internet Protocol (IP)

What does an IP do? IP transport datagram(packets) from the source to the

destination node. Responsible for routing the packets Breaks a packet into smaller pieces known as

fragments Unreliable service packet may lost packet may arrive out of order.

Internet Protocol (IP)

Internet protocol provide connectionless data transfer service over network by passing and routing IP datagrams.

All IP datagram(data packets) with IP header are passed from transport layer to network layer.

IP header contains information necessary to transfer packets from one n/w to another.

An IP datagram consists of a header part and text part

Even though the all 14 fields are important , only consider the fields that affect 3 of the primary functions of IP.

1. Fragmentation 2.datagram discard 3. addressing.

IP header

Version Which version of the protocol the datagram belongs to. The current version number is 4. Next version: 6

Identification Uniquely identifies the datagram. Usually incremented by 1 each time a datagram is sent. All fragments of a datagram contain the same

identification value. This allows the destination host to determine which

fragment belongs to which datagram.

Flags and Fragmentation Offset Used for fragmentation DF means do not fragment. It is a request to routers not

to fragment the datagram since the destination is incapable of putting the pieces back together.

MF means more fragments to follow. All fragments except the last one have this bit set. It is needed to know if all fragments of a datagram have arrived.

Fragment offset number of fragments

Time to Live Enable n/w to discard a particular datagram that has

travelling the internet for a long time. When a packet is first created , this field set to 255 Decremented 1 by each router that processes the

datagram. router discards the datagram when TTL reaches 0.

Source IP address The sender

Destination IP address the final destination

Transmission Control Protocol(TCP) TCP provide a connection –oriented reliable service for

sending messages. Split a message into packets. Reassemble packets at destination resend the packets that were lost in transmit.

Interface with IP Each packet forwarded to IP for delivery. Error control is done by TCP

TCP/IP

The primary functions of Transmission control Protocol is to turn an unreliable network into reliable network, that is free from lost and duplicate packets.

Functions of TCP : 1. Create a connection:- The TCP header include a port

address that indicates a particular application on a machine.

When TCP create a connection between sender and receiver , two ends of the connection use a port number to identify a particular application’s connection.

Port address and IP address identify a particular application of a particular machine.

2. Release connection:- The TCP dissolve a connection after all the data has been sent and received.

3. Implement the flow control:- To make sure the sending station does not overcome the receiving station with too much data.

TCP header include a field called window value , that allow the receiver to tell the sender slow down.

4. Establishing multiplexing:- Because the TCP header include a port number instead of an IP address , it is possible to multiplex multiple connections over a single IP connections.

This multiplexing can be done by creating a different connection that has a port number different from a previous connection

5. Perform error recovery:- TCP numbers each packets for transmission with sequence number. As the packets arriving at the destination site, the receiving

TCP s/w checks these sequence number for continuity . If there is a loss, the receiving TCP s/w uses an acknowledge number to inform sending TCP s/w of a possible error condition.

6. Establishing priority :- if the sender has to transmit data of a higher priority, such as

an error condition, TCP can set a value in the field (urgent pointer) that indicate the enclosed data is important.

To perform these functions , TCP places a header at the front of every data packets.

TCP datagram format

  An IP address identifies a particular computer on the Internet. The port number identifies a particular program running on that computer. 

21- FTP 55-DNS

FIELD NAME

SIZE

DESCRIPTION

Source Port 2 The 16-bit port number of the process that originated the TCP segment on the source device.

Destination Port

The 16-bit port number of the process that is the ultimate intended recipient of the message on the destination device

Sequence Number 4

That count bytes and indicates a packet’s data position within the connection. Used to reassemble the pieces at receiving end also determine any packet s are missing.

Acknowledgment

Number4 Indicate the next sequence no. that the

sending device is expect from other device

Data offset 4 bits

Specifies the number of 32-bit words of data in the TCP header.

Reserved 6 bits 6 bits reserved for future use; sent as zero.

Control Bits 6

We have seen before that TCP  is a Connection Oriented Protocol. The meaning of Connection Oriented Protocol is that, before any data can be transmitted, a reliable connection must be obtained and acknowledged.

ACK: Acknowledgement.FIN: No more data from the sender

URG: Urgent Pointer. PSH: This flag means Push function.RST: Reset the connection.SYN: This flag means synchronize sequence numbers.

Window 2

Flow control between two endpoint . If one end wants the other end of connection to stop sending data, the window value set to 0.

Cheksum 2Provide cyclic checksum of the data field that follows header.

Urgent Pointer 2

Inform receiving end that the packet of data contain urgent data.

Progression of one data packet from one network to to another:

draw the diagram and explain the flow in detail.