Describe the ISDN? Explain the types of ISDN Service.

ISDN stands for (Integrated Services Digital Network) is a system of digital phone connections. This system allows voice and data to be transmitted simultaneously across the world using End-to-End digital connectivity. The ISDN is a method used to bridge b/w the central office and the premise connection home.
ISDN uses the existing wiring so no new cabling is required with ISDN voice and data are carried by bearer channel. Occupying a bandwidth of (64Kb/s).  Some switches limit B channels to the capacity 56Kb/s. A data D channel handles signaling at 16Kb/s or 64Kb/s depending the service type.
There are Two types of ISDN service:
1. Basic Rate Interface (BRI)
2. Primary Rate Interface (PRI)

Basic Rate Interface:

BRI consists of 2B+D channels, which stands for 2 bearer channel of 64Kb/s each for data and 1D channel of 16Kb/s for handshaking and control. Having separate channels for handshaking and control is called Out of “band signaling”. The 2B channel can be bonded together for single data with a 128Kb/s transfer rate.

Primary Rate Interface:

PRI consists of 23B+d channels, which stands for 23 bearer channel of 64Kb/s each for data and 1D channel of 64Kb/s for handshaking and control. The bearer channel can be bonded in any combination as required PRI consists of two 64Kb/s B channels and one 16Kb/s for a total of one 44Kb/s. This basic service is intended to meet the needs of most individual user.
PRI intended for user with greater capacity requirement typically the channels structure 23B channels plus one 64Kb/s D channels for a total of 1536Kb/s.
In Europe PRI consists of 30B channels plus one 64Kb/s D channels for total of 1984Kb/s. it is also possible to supports multiple lines with one 64Kb/s D channel using (Non Facility Associated Signaling) NFAS.
ISDN lines can be dedicated lines that always up and connected or they can be dial on demand (DOD) lines. When the line is required the connection is dialed up and made. The connection for an ISDN line is very quick in the order 0.5second or so, this can result in a substations cost saving if used over long distance or paying by the minutes.
The lines charges are only for when data is being transferred and not when it is sitting idle.

Describes the ATM?

ATM is a high-speed networking standard designed to support both voice and data communications. ATM is normally utilized by Internet service providers on their private long-distance networks. ATM operates at the data link layer (Layer 2 in the OSI model) over either fiber or twisted-pair cable.
Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line.

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Switching: Explained with its types

Definition of Switching:

Switching is important technique that determines how connections are made and how data move over WAN. Switching sends data along different in the same way as train can be sending or switched on multiple tracks.

Types of Switching:

1.     Packet Switching

2.     Circuit Switching

3.     Message Switching

Circuit Switching :

In circuit Switching, a dedicated physical connection is established b/w the sender and the receiver and maintain for the entire conversation, for example the PSTN ( Public switch telephone network) uses a circuit switching system.

When you make a call a physical link b/w the two phones is dedicated during the entire conversation when one hangs up, the connection is terminated and the circuit is released.

Routing Methods in circuit switched networks:

Before any two computers can transfer data, a dedicated circuit must be established b/w the two. The sending machine requests a connections to the destination, after which the destination machine signals that it is ready to accept data, the data in then sent the source to the destination, and the destination sends acknowledgement back to the source.

When the conversation is finished the source sends a signal to the destination, indicating that the connection is no longer needed, and disconnects itself.

Advantages:

Ø  This is important for time critical application such as audio and video.

Ø  The communication channel (once established) is dedicated.

Ø  Also once  the circuit a established , there is virtually no channel access delay; since the channel is always available, it does not need to be requested again.

Disadvantages:

Ø  Circuit switching does have its disadvantages. One is that it is often an inefficient use of the transmission media.

Ø  Possible long wait to establish a connection, (10 seconds,   more on long- distance or international calls.) during which  no data can be transmitted.

Ø  More expensive than any other switching techniques, because a dedicated path is required for each connection.

Ø  Because the connection is dedicated even when it is idle, no other devices can use the channel.

Message Switching:

Message switching is unlike circuit switching in that it does not establish dedicated path b/w two communication devices; instead, each message treated as an independent unit and includes its own destination and source address. Each complete message is then transmitted from device to device through the inter-network. Each intermediate device receives the message, stores it until the next device is ready to receive it and then forwards it to the next device. For this reason a message-switching network is sometimes referred to as a store and forward network.

Packet switching:

In packet switching messages are  broken up into packets, each of which includes a header with source, destination and intermediate node address information. Individual packets don’t always follow the same route, the is called independent routing, from source to destination and can follow multiple routes to reach to the destination unlike message switching, packet switching restrict packets maximum length packet switching work more quickly and efficiency than message switching. There are two method of packet switching.

       I.        Data Grame packet switching

    II.       2. Virtual circuit packet switching

Data gram packet switching:

Datagram packet switching is similar to message switching in that each packet is a self-contained unit with complete  addressing information attached.

In it a message is divided into a stream of packet, each packet is separating address and independent.

It is possible for a packet to be destroyed if one of the nodes on  its way is crashed momentarily. Thus all its queued packets may lost.

Virtual packet switching:

•          In the virtual circuit approach, a preplanned route is established  before any data packets are sent.

•            A logical connection is established when

Ø        a sender send a "call  request packet" to the receiver and

Ø        the receiver send back an acknowledge packet "call accepted

         packet" to the sender if the  receiver agrees on conversational parameters.

Advantages of packet switching:

v  Packet switching is cost effective, because switching  devices do not need massivamountof secondary   storage.

v  Packet can be rerouted if there is any problem, such as,  busy or  disabled links.

v  The advantage of packet switching is that many  network users can share the samechannel at the same   time. Packet switching can maximize link efficiency by  making optimal use of link bandwidth.

 Disadvantages:

v     Protocols for packet switching are typically more complex.

v     It can add some initial costs in implementation.

v     If packet is lost, sender needs to retransmit the data

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Server: Explained with its types

Definition:

A server is a computer that provides data to other computers. It may serve data to systems on a local area network (LAN) or a wide area network (WAN) over the Internet.

Types of server:

There are four types of server:

1.     Mail server

2.     File server

3.     Print server

4.     Application server

File server: 

A file server is a server that store files on the network for user. A user at a client machine can save a file to a hard disk located on a file server.

If the user wants to access files later, it can access the file from the client machine to a network connection to the file server.

Maintaining a central location for file storage on the server makes it easier to provide a back up copy of important files and implement of a fault tolerance system such as “RAIT” (Redundant array in expensive disk).

Print Server:

A print server manages access to network printing resources, thus enabling several client machine to use the same printer.

Because file and printers are so basic and so important to most network file and print services are very basic components of most network operating system.

Application Server:

Application  server is the server that actually run in application for the client.

 An application server is typically used for complex transaction-based applications. To support high-end needs, an application server has to have built-in redundancy, monitor for high-availability, high-performance distributed application services and support for complex database access.

Mail server:

A mail server is a server that is responsible for sending and receiving Text, E-mail and E-mail with attachments towards other users.

It keeps the record of all the mail which has to sent and received by different users, member of that specific users.

It accept all mail request from the client user and forward them using some port such as (8080, 81,83,86) which is defined during installation of main server.

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What is Data Flow Control?

Definition:

 Flow control is the process of controlling the amount of data sent to a device so that it does not exceed the capabilities of the receiving system.

It enables a receiver to regulate the flow of data from sender so that the receivers’ buffers do not overflow. Flow control is technique of assuring that a transmitting entry does not over flow a receiving entity with data. The receiving entity typically all allocates a data buffer of some maximum length for a transfer. When data are received, the receiver must do a certain amount of processing before passing the data to the higher level software.

Describe Sliding Window Flow Control:

In communication system the transfer of data takes place in the form of frames when one frame reach their destination the next frame allowed to the transmitter to send, if we are using such a link which can support several frames in same times then transmitter will send a group of frames in same time and after reaching these frames to their destination the acknowledgement will come to send the next group of frames both source and destination maintain a lest of frame that has been send and received and also that frames which will be transmit and will be received and this type of flow control is called sliding window control.

Illustrate sliding window control:

The essence of the problem describe so for is that only one frame at a time can be in transit. In situations where the bit length of link I greater than the frame length (a>1) serious inefficiencies result. Efficiency can be greatly improved by allowing multiple frames to be in transit at the same time.

Let us examine how this might of work for two stations, A and B, connected via a full duplex link station B allocates buffer space for W frame. Thus, B can accept W frame and A is allowed to send W frame without waiting for any acknowledgement. To keep track of which frames have been acknowledged, each is labeled with a sequence number B acknowledges a frame by sending an acknowledgement that include the sequence number of the next frame excepted.

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What is Ethernet? Describe the types of cabling system used for this type.

Definition:

The Ethernet "access method" is used to connect computers in a company or home network as well as to connect a single computer to a cable modem or DSL modem for Internet access.

Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet was invented by engineer Robert Metcalfe.

It is most popular network architecture. Ethernet is a bus or star bus based technique that uses base band signaling and CSMA/CD (Carrier sense multiple access with collision detection).

v  Sense the medium.

v  If the medium is busy then random wait and go to 1.

v  If the medium is idle then transmit data.

v  Sense the medium again.

v  If collision then go to 1.

1.    10Mbps Ethernet (Slow)

Its speed range is 10Mbps. It is less frequently uses in market.

There are Four types of cabling system used for this type[10Mbps].

v  10 Base 5

Ø  Speed = 10Mbps

Ø  Signaling mode = Base band

Ø  Maximum Segment length = 500 meter

Ø  Cable type = RG-8, RG-11 etc

Ø  Node capacity = 100 nodes per second

Ø  Physical Topology = Bus Topology

Ø  Maximum length of office transceiver cable is 12.5 meters.

Ø  Maximum of 2 repeaters may be used between devices.

v  10 Base 2

Ø  Speed = 10Mbps

Ø  Signaling mode =  Base band

Ø  Maximum Segment length = 185 to 200 meter

Ø  Cable type = Coaxial cable

Ø  Node capacity = 30 nodes per segment

Ø  Physical Topology =  Bus Topology

v  10 Base T (Twisted pair)

Ø  Speed = 10Mbps

Ø  Maximum length = 300 meter

Ø  Signaling mode = Base band

Ø  Cable type = UTP category 3,4 & 5

Ø  Node capacity = 2 nodes per segment

Ø  Physical Topology = Star Topology

v  10 Base FL (Fiber link)

Ø  Speed = 10Mbps

Ø  Signaling mode = Base band

Ø  Maximum segment length = 2000 meter

Ø  Cable type = Fiber optic cable                                 

Ø  Physical Topology = Star Topology

2. 10Mbps or Fast Ethernet:

Speed = 100Mbps

Use = Most frequently used in market

Physical Topology = Star Topology

Cabling system = There are three cabling systems

v  100 Base T4 use  4pair category (3,4&5)UTP or STP

v  10 Base TX use  2pair category 5 UTP or STP

v  10 Base FX use 2pair standard fiber optic cable

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