The Introduction About The Computer Networks

Published Date: 02 Nov 2017

In the world of computers, networking can be defined as the interconnection of two or more computers for the purpose of data sharing and also resource sharing these days. Both computer software and Hardware are equally necessary for building a computer network.

Computer networks can be classified into three types such as local area network, wide area network and metropolitan area network. Local area network is a network to transfer data from one system to another within a few kilometers. Wide area network is used widely to transfer the data from one system to another located at far distance like different countries. And metropolitan area networks are used for communication in between cities with in a medium distance.

In Serial communications a single bit is transferred at a time in between two computers. For this we require a single communication channel unlike 8 channels required to send a byte. By using only one channel for data transfer the costs involved are very less but the rate of data transfer is very slow. Most often we use communication channels which are wired, but sometimes we use radio and optical based. Many of the wide area network (WAN) technologies like X.25,Frame relay, Leased lines, Asynchronous transfer mode (ATM) require serial connections for data communication.

IP Address is a unique identifier for a computer or device (host) on a TCP/IP network. It is denoted as a 32-bit binary number that is usually represented as 4 decimal number separated by a period. Each and every computer should be assigned an IP address which is very important and should be done at the budding stages of designing a internetwork.

Routing information protocol is a distance vector protocol which is used for finding shortest path between source to destination over a network making use of the routing hop count algorithm. This algorithm is used to find the shortest path from the source to destination, by which faster data communication is possible making use of the shortest path.

1.0. SERIAL CONNECTIONS

1.1 INTRODUCTION:

Serial connections are a point to point connections used to connect the various devices in a network system. It is commonly used for the long distance communications such as wide area network (WAN) technologies. This serial connection is quiet opposite to the parallel connection; in which parallel connection transmit several data at a time.

Parallel communication is not best suited for communication involving long distances. By using parallel communication for long distances, we may encounter with errors by which reliable data transfer cannot be made possible.

The cables used for serial connections are less costly and they even occupy less space.

Serial connections are good for short distance communications and have good data transmission rate.

There are two serial data transmission modes. They are Synchronous mode and Asynchronous mode.

In the lab, it is required to establish a serial connection between the routers.

After establishing connections, we check the connection is established or not using PING command.

1.2 SYNCHRONOUS LINES:

Synchronous transmission mode is a commonly used mode for serial connections. This is the serial interface in which we use DB-60 connector and v.35 in the laboratory. The interface uses DB-60 connector in one end and Winchester type connector in the other end. In the synchronous transmission, entire bits of data are transmitted without start and stop bits. The control information also added in the block of the data. Every frame contains preamble, postamble and control information. The synchronous transmission frame format is shown as below 1.1 figure

8 bit flag

Control fields

Data field

Control fields

8 bit flag

The frame is generally start with the preamble bit pattern called a 8 bit flag and end with the pattern called a 8 bit flag. Usually transmission start with the preamble followed by the control fields and data fields. Then final transmission completed with the postamble. Synchronous transmission is more efficient when compared to the asynchronous transmission. The parameters of the synchronous lines are physical parameters, data link parameters and network parameters.

Source: cisco.com

1.2.1 PHYSICAL LAYER PARAMETERS:

The above figure 1.2 shows interface cable connects DB-60 male to Winchester male.

All WAN connections are made between a Data Circuit-terminating Equipment (DCE) and Data Data Terminal equipment (DTE). Before going to connect a node in Laboratory, we should check which node is on the side of DTE and which on the side of DCE.

Router# show controller serial <interface number>

The clock rate command is used to determine the bit rate of the line. This command should be used in configure-if mode. The standard serial interface supports bit rates up to 2 Mbps, which is the default rate. Other types of serial interfaces support bit rates up to 52 Mbps. Use the command to change the bit rate.

Router (config- if) # clock rate<rate in bps>

The data rate is always in bits per second.

Use the bandwidth command to obtain the appropriate bandwidth.

Router (config- if) # bandwidth<kbps>

The default data encoding scheme used in standard serial interface is non return to zero (NRZ) encoding. Non return to zero inverted (NRZI) encoding is also available. Both ends should agree to an encoding scheme, to make communication possible

Router (config-if) # nrzi-encoding

To return default condition, use command

Router (config-if) # no nrzi-encoding

1.2.2. DATA LINK LAYER PARAMETERS:

In this layer, Data can be encapsulated in various Data link protools. The data link layer protocol includes point to point protocol; high level data link control, serial data link protocol and synchronous data link control etc.

We can use the following command for the encapsulation.

Router (config-if) # encapsulation <protocol>

Example: Router(config-if) # encapsulation ppp

1.2.3. NETWORK LAYER PARAMETERS:

In the network layer, IP address can be assigned to the serial interface for the purpose of the routing. While assigning the IP address, mask address also assign with it. IP address can be assigned with the mask by using the command

Router (config-if) # ip address<address> <mask>

The mask should be 255.255.0.0

We can check the configuration and monitor the interfaces using the following command.

Router # show run

Router # show run interface serial <interface number>

The above command is used to check the running configuration of a particular interface.

1.3. FRAME ANALYSIS:

The Traffic for a particular ip address can be identified by using the following command

Router # ping<destination ip address>

Traffic analyzers can be used to check the traffic for a particular IP address.

1.4. ASYNCHRONOUS LINES:

This mode is less often used in the latest networks. In this mode a system is connected to the router using a modem. In the asynchronous mode, data cannot be sent as long to avoid timing problem. Instead, data are transmitted one character at a time, where each character is five to eight bits in length. Synchronization can be maintained within each character. Again each character can be synchronized for each character in the receiver.

Stop bit

Stop bit

Parity bit

Data bit

Data bit

Data bit

Data bit

Data bit

Data bit

Start bit

Data bit

The above shown figure represents 1.3 the asynchronous transmission format.

In this mode, start bit is one, data bits are five to eight bits and stop bits are two bits. In this parity bit will be one bit. This mode takes more time in data transmission due to the overhead bits in the each character. The data transmitted with the overhead bits so a possible error can be occurred in the receiver. A framing error also occurred due to the noise conditions. Asynchronous transmission is simple and cheap but it is inefficient entirely compare to the synchronous.

The show line command is used to list all the available asynchronous lies and their numbers

Router # show line

In the line configuration mode, hardware parameters like flow control, speed can be configured.

Router (config) # line aux 0

This command is used to enter into line configuration mode.

Router (config-line)# modem InOut

This command drops the connection on loss of DCD (Data carrier Detect) and cycles DTR (Data Terminal ready) for closing the connection.

Router (config-line)# speed 38400

This command is used to set the speed for transfer and receive.

Router (config-line)# flow control hardware

By using this command we can set the flow control either RTS or CTS flow control.

IP ADDRESSING

Introduction:

An IP address is a logical address and is used at the Network layer of the OSI reference model.

In this chapter we are going to discuss about various IP addressing schemes and Subnetting.

An IP address is an unique identifier, used to identify a computer or a device on a TCP/IP network.

There are two versions of IP addressing they are IPV4 address and IPV6 address.

The length of IPV4 address is 32 bits and length of IPV6 address is 128 bits.

In this chapter we are going to discuss only about IPV4 addresses.

It is denoted as a 32-bit binary number that is usually represented as 4 decimal numbers separated by a period in between them.

Example:

192. 127. 10. 1

11000000.01111111.00001010.00000001

A valid IP address ranges in between 0.0.0.0 to 255.255.255.255

Before going to IP addressing we must be aware of AND operations as we use AND operations frequently in IP addressing.

AND operations are defined below as:

0 AND 0 = 0

0 AND 1 = 0

1 AND 0 = 0

1 AND 1 = 1

Example:

1 0 0 1 1 1 0 0

1 1 1 1 0 0 0 0

______________________________________________ AND

1 0 0 1 0 0 0 0

We use the and operation to extract the network portion Network ID of an IP address by AND operation with an other binary number called the Mask.

Example:

192. 16. 8. 1 11000000.00010000.00001000.00000001

255. 255. 248. 0 11111111.11111111.11111000.00000000

192. 16. 8. 0 11000000.00010000.00000100.00000000

Network Classes:

For making it easier to administer with, they have divided the IP addresses into classes. The most significant bit (MSB) determines the class of the address .

The first three classes A,B,C are used for regular networks and hosts. Class D is for Multi cast addresses and Class E is used for Research purpose.

Class A – begins with 0

00000001 (110) to 01111111 (12610)

Class B – begins with 10

10000000 (12810) to 10111111 (19110)

Class C – begins with 110

11000000 (19210) to 11011111 (22310)

Class D – begins with 1110

22410 to 23910

It is reserved for multicasting.

Class E – begins with 1111

24010 to 25410

It is reserved for future use.

The addresses starting with 127 are reserved for loopback purposes.

IP address classes:

Class

1ST Octet range

Subnet mask

Network

Host

Class - A

0-126

255.0.0.0

(27-2)=126

16,777,214 (224 – 2)

Class - B

128-191

255.255.0.0

(214-2)=16,382

65,534 (216 – 2)

Class - C

191-223

255.255.255.0

(221-2)=2097160

254 (28 – 2)

Class - D

224-239

255.255.255.255

Reserved for Multicast

Reserved for Multicast

Subnet masks

The main purpose of applying a subnet mask is that it allows you to identify the Network and Host parts of the IP address.

Subnetting can be done for a variety of reasons

For a very big Organization, we can easily divide networks for separate departments. Example: Every department in our university has its own network like Library, Accounts etc

We can reserve the address space for future use.

Security can be implemented easily.

The most important reason is to control traffic in a network.

Subnetting method:

Network bits are masked as 1s

Host bits are masked as 0s

Class A – 255.0.0.0

11111111.00000000.00000000.00000000

Class B – 255.255.0.0

11111111.11111111.00000000.00000000

Class C – 255.255.255.0

_ 11111111.11111111.11111111.00000000

Example:

Here we are goig to fine the Network ID and Host ID in the IP address 172.16.130.12 whose mask is 255.255.192.0

We are using AND operation here to find Network ID and the remaining bits can be considered as Host ID.

10101100 00010000 10000010 00001100

11111111 11111111 11000000 00000000

10101100 00010000 10000000 00000000 Network ID 172.16.128.0

00000000 00000000 00000010 00001100 Host ID 0.0.2.12

Variable length subnet mask:

Variable length subnet mask is a process which is done on a subnetted network.

If a subnetted network is again subnetted, the the total number of networks will be increased drastically. So, more address space is generated which can be used for other purposes. We can also call Variable length subnet mask as subnetting the subnetted network.

Here in the figure shown above, we can clearly understand how variable length subnet mask works and a subnet is again subnetted to form more number of networks.

VLSM supports more efficient use of an organization’s assigned IP address space. The earlier limitation of supporting only a single subnet mask across a given network prefix locked the organization into a fixed number of fixed sized subnets.

2.0. ROUTING INFORMATION PROTOCOL

2.1. INTRODUCTION:

A router in the network looks at the destination address and then it finds which ports are to be selected so that the output can be sent using the best possible path.

The router selects the best path by consulting a forwarding table called is routing information table.

Routing is very important for making communication with nodes present in different sunets.

In this chapter we are going to know how router finds paths to different destinations using Routing information Protocol.

2.2. RIP V1 VERSION:

The routing information protocol v1 is used in the distance vector routing, in which 15 hops is the maximum hop count as metric to determine the shortest path. The RIP v1 uses only classful routing, that means all devices in network uses the same subnet mask. This is because RIP v1 does not send the information of the subnet mask. RIP v1 does not support the variable subnet mask.

2.3. RIP V2 VERSION:

The routing information protocol v2 is used in the distance vector protocol, in which it has a 15 maximum hop count as metric to the determine. The RIP v2 uses both classful and classless routing. By using classless routing, it sends the information of the subnet mask. Hence it supports the variable subnet mask.

2.4. STATIC ROUTING:

Static routes are manually entered by the network administrator. For this the network administrator should have the complete knowledge of the Internetwork. Then the network administrator needs to program the each router to get the routers from any node to any other node. The hosts in Static routing get the routes manually or by using Dynamic host configuration Protocol.

There are both Advantages and dis advantages by using Static routing.

The advantage of using static routing is it there is no overhead associated, so static routing is easy to implement and even the security is better in static routing. Coming to the disadvantages of static routing, It cannot adapt to the changes of networking topology.

Router (config) # ip route<destination network address> <next hop address>

Router (config) # ip route 0.0.0.0.0.0.0.0<next hop address>

2.5. DYNAMIC ROUTING:

Dynamic routing is used when protocols are used to find networks and updates the routing table on routers. It is easier routing when compare to the static and default route. But its cost is high and it is usually the preferred way to forward traffic through a network because it adapts to the change in the network topology.

Practical Implementation:

Router(config)# router rip

Router(config)#version 2

[for enabling RIP version 2 on all routers]

Router(config-router)# network

1R4(config-router)#network 192.168.12.0

1R4(config-router)#network 192.168.11.0

[for advertising all directly connected networks to router or switch]

1R4(config-router)#no auto-summary

[for disabling auto summarization of network address]

R4#show ip protocols

Routing Protocol is "rip"

Sending updates every 30 seconds, next due in 0 seconds

Invalid after 180 seconds, hold down 180, flushed after 240

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Redistributing: rip

Default version control: send version 2, receive version 2

Interface

FastEthernet1/0

FastEthernet1/1

Automatic network summarization is not in effect

Maximum path: 4

Routing for Networks:

192.168.11.0

192.168.12.0

Routing Information Sources:

Gateway

192.168.11.1

192.168.12.3

Distance: (default is 120)

Send Recv Triggered RIP Key-chain

2

2

2

2

Distance

120

120

Last Update

00:00:06

00:00:09

DEBUG IP RIP

*Mar 1 00:54:13.239: 192.168.10.0/30 via 0.0.0.0, metric 3, tag 0

*Mar 1 00:54:13.239: 192.168.12.0/24 via 0.0.0.0, metric 1, tag 0

*Mar 1 00:54:13.239: 192.168.13.0/24 via 0.0.0.0, metric 2, tag 0

*Mar 1 00:54:18.319: RIP: ignored v2 update from bad source 192.168.42.4 on FastEthernet1/0

*Mar 1 00:54:27.479: RIP: ignored v2 update from bad source 192.168.72.4 on FastEthernet1/0

*Mar 1 00:54:35.815: RIP: received v2 update from 192.168.12.3 on FastEthernet1/0

*Mar 1 00:54:35.815:

*Mar 1 00:54:35.815:

*Mar 1 00:54:37.931: RIP: ignored v2 update from bad source 192.168.42.3 on FastEthernet1/0

*Mar 1 00:54:38.691: RIP: ignored v2 update from bad source 192.168.72.3 on FastEthernet1/0

*Mar 1 00:54:38.715: RIP: received v2 request from 192.168.22.3 on FastEthernet 1/0

*Mar 1 00:54:38.715: RIP: ignore the request received from unlisted network.

*Mar 1 00:54:40.855: RIP: sending v2 update to 224.0.0.9 via FastEthernet1/0 (192.168.12.4)

*Mar 1 00:54:40.855: RIP: build update entries

*Mar 1 00:54:40.855: 192.168.10.0/24 via 0.0.0.0, metric 2, tag 0

*Mar 1 00:54:40.855: 192.168.11.0/24 via 0.0.0.0, metric 1, tag 0

*Mar 1 00:54:40.855: RIP: sending v2 update to 224.0.0.9 via FastEthernet1/1 (1

192.168.10.0/30 via 0.0.0.0 in 2 hops192.168.13.0/24 via 0.0.0.0 in 1 hops

CONCLUSION:

The report concludes that the serial connection and routing information protocols are achieved and its properties were studied. In the serial connection, synchronous serial interface and asynchronous serial interface are configured between routers. Routing information protocol is configured in the distance vector routing protocol.

REFERRENCES:

Asynchronous current mode communication by Dobkin.R, Moyal.M and kolodny.A, electrical department, Haifa, Israel, edition July 2010.

Routing information protocol by C.Hedrick, internet engineering task force, edition June 1988.

Routing information protocol version 2 – by G. Makin in edition 1998.