Advantages Of Fibre Optics

Published Date: 02 Nov 2017

ATM provides high speed communication in the wide area network(WAN).  ATM is connection oriented with cell -switching , where data is transfers in the form of packets in fixed size. For video and audio (voice) communication ATM is used . Data which requires high speed of communication ATM is the best choice. Communication takes place in form of fixed size packets of 53 byte ,where 48 byte is used for user data and 5 bytes for the header. As the size of each cell is small ,it can transmit large amount of data . And the bandwidth can given in limited for user by the Internet service provider ,in result over all connection speed becomes faster.

REF : http://www.techterms.com/definition/atm

ATM requires less number of bits for the overhead, which increases the data transfer rate. It contains three different layers they are

ATM Physical layer : It deals with the bit timing ,framing on the physical medium.

It contains two sub layers physical medium and transmission convergence

Physical Medium : The PM sub layer provides the bit transmission and it also converts electrical and optical conversions. Transmission Medium :It performs some task .

a) Frame is generated and recovered . Which makes the cells in the correct format .

b) The data which is received by the user must be adapted according to ATM cell flow .

c) The next task is cell delineation which makes the ATM receiver to recover the cell boundaries.

d) Error control on header . CRC is performed and compared by receiver with respective to the transmitter . If it matches, the process is continued . Due to this mechanism data congestion can be reduced . If any errors are occurred then the source must re transmit the data as per the destination acknowledgment.

e)Data rate of the ATM is matched with the payload capacity of the system.

ATM Layer : Quality of service is provided in this layer as it provides multiplexing in this layer, through which virtual circuits can be shared . It also provides frame relay . Different VC's and VP's can be transmitted in one cell in one direction by using multiplexing

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Virtual Channel: By considering virtual channel identifier(VCI) , ATM cells are transmitted with unique id. This id is encrypted in the header . The main task of the virtual channel is to provide the communication between the end to end points .

Virtual path : ATM cells are transmitted , with same id on the virtual channel .This path is called as virtual path . It can also say as combining of virtual channels with same identifier. They are four types if AAL to satisfy different needs, between the source and destination Virtual channel and virtual path improves the performance.

ATM Adaption Layer : This layer provides segmentation and reassemble the packets . Which also provides error transmission and flow control during transmission. There are four different AAL classes

Class A: It is for constant bit rate, with timing voice is an example. It corresponds to AAL 1 and supports connection-oriented service.

Class B: It is for variable bit rate, with timing video is an example. It corresponds to AAL 2 and supports connection-oriented service.

Class c : It is for variable bit rate,1 without timing X.25 is an example. It corresponds to AAL 3/4. and supports connection-oriented service.

Class D: It is variable bit rate without timing LAN is an example. It corresponds to AAL 5. and supports connection-less service.

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Generic Flow control :

four bits are allocated. This is used for flow control, and it is presented n user- network header and not present Network -Network interface header

Virtual path Identifier(VPI): It is 8-bit field for user network Interface and 12 bit for Network- Network Interface .Packets can be reached for destination on the path identified by the VPI.

Virtual Channel Identifier : Packets are routed from source to destination.(routing)

Payload Type Identifier : we can know the type of data present in information field.

Cell lose priority: During transmission there is a chance of data congestion ,as network don't know which data should be omitted . This bit helps in doing so . If the data bit is shows 0 the priority is given to the data, and if the data is 1 packet can be neglected.

Header error control: This is used for error control. The polynomial equation X8+x2+X+1 is used to generate the code.

Advantages of ATM:

1) High speed communication.

2) Flexibility and scalability is provided .

3)Quality of service is provided as it works on both older and existing.

Conclusion: ATM is a connection oriented, provides reliable communication. As the overhead is less , it provides good data transfer rate. Through, ATM video and audio transmission is done over network is done in WAN network

Ref :http://lyle.smu.edu/~levine/ee8304/cmoore.pdf

FIBRE CHANNEL

Introduction: To increase the data transfer rate for the storage and network device. Back up is possible up to 10 km .It can handle more connections at a time . By using arbitrated loop we can connect 126 connection. Different cables can be mixed with the single topology. Fibre channel is the main source in the industry for communcation . As Ethernet and SCSI gives the limited performance to solve this problem fibre channel came into existence . It can transfer large amount of data .

Fibre Channel Works: selecting the cable type depends on the signal passing

1) If electrical signal to be passed ,t hen Twin-ax copper wire is used .

2)optical signal is to be passed on Multimode fibre ,short wave laser.

Data in communication transfers bit at a time .because, it is a serial data protocol.

It provides three topologies.

point -to-point

Arbitrated loop

fabric

Point to Point :The connection will be in between the two devices. It can be between the user and peripheral.

Arbitrated loop: The connection will be in a closed loop. The data is transfer to next device. Thus data is reached to destination from source. It provide connection up 126 devices. One request is done at a time. By using hub in the center ,devices are no need to connect each other, they are connected to the hub. If any device is failed in the circuit data circulation is not stopped because hub provides the data for all the devices

Fabric : It requires one switch in the middle and all the devices are attached to that switch . It is a full duplex communication can be done between the transmitter and receiver

http://benjr.tw/files/images/other/fc_topologies.png

Ref: http://benjr.tw/node/511

REF:http://www.unylogix.com/data_storage/raid_san/PDFs/White_Paper_Fibre_Channel_Fundamentals.pdf

Levels in fibre channel:

Fibre channel 0(FC 0):This is the physical layer with connecters and cables. Hubs are operated in this layers.

Fibre channel 0(FC 1): This is data link layer ,where encoding and decoding is done.

Fibre channel 2(FC 2): This is network layer, framing and addressing and control is done protocols.

Fibre channel 3(FC 3): This provides the service like encryption and RAID.

Fibre channel 4(FC 4): Mapping is done between the protocols.

http://www.hill2dot0.com/wiki/images/f/ff/Fibre_Channel_Protocol_Stack.JPG

Ref: http://www.hill2dot0.com/wiki/index.php?title=Image:Fibre_Channel_Protocol_Stack.JPG.

Storage Area Network (SAN):

It connects different types of storage devices together , it also supports disk mirroring and restore. SAN can be implemented in many methods. But generally switch is used for implementation of storage area network. when a fibre channel is connected to fibre channel switch, then the communication parameters can be exchanged. As it supports 16 million devices, it's better to register in Simple Name Server. Which acts as database for all the devices . When SAN increases SNS also increased, as the information is exchanged between the switches. In SAN data can be stored and retrieved at any point of time.SAN is sometimes also refereed as System Area Network.

Advantages of fibre optics

1)Data is more secured as no magnetic field is generated to tap the data.

2)Bandwidth is high over a long distance.

3)It is non conductive.

4)Less expensive.

Conclusion:

Communication is done with high reliability with low cost, where many connections can be provided through which it provides service to the users.. Data transfer rate is very high, it also provides flow control and error checking.