The History Of Asynchronus Transfer Mode

Published Date: 02 Nov 2017

Asynchronus Transfer Mode is a very important packet switched network widely used in today’s technology. If we look back to present technologies we find that it has got several limitations first coming is the frame size which is variable size. Considering that for complex networks we need to carry more header which causes inefficiency transmission. In order to increase the efficiency we have choices either to increase the data field or use variable data field. If we uses variable lengths for data fields. We can’t ensure the data will deliver exactly to appropriate destination due to traffic. Because the transmission media uses higher bandwidths for supporting higher bandwidths which makes use of Broadband technology called Time Division Multiplexing(TDM) this technique is commonly used in Asynchrnous Transfer Mode to ensure higher data rates. By considering all above points the ATM has been developed.

DEVELOPING STEPS:

Most of the earlier protocols like X.25 and Frame relay uses transmission medium of lesser bandwidth (for example twisted pair and coaxial cable). On the other hand ATM uses optical fiber which is the most powerful transmission media using in present days. It has got higher bandwidth and the possibility of errors is less which means the frames sending through transmission media got less prompt to errors. We have to design ATM such that which can interface to any existing and earlier systems with the low cost and which also must support telecommunication industry services such as T1,T2…. Most of the circuits are circuit switched for example PSTN is a circuit switched network which got several limitations so we moved to packet switching networks. Hence the Asynchronous Transfer Mode uses virtual packet switched network to get accuracy and high speed which can’t be done by Datagram. Most of the functionalities are implemented in hardware rather in software, so that it can be fast and implemented in lower cost.

CELL FORMAT

Frames are generally carries user and control information along the transmission medium in case of the Asynchronous Transfer Mode the data will be sent through Cells. A cell is a basic unit which conveys the user information to communicating devices usually the length of the cells are fixed. Which is about 53 bits per cell each cell is having fixed length. In ATM the TDM technology is used which is generally a Asynchronous TDM. Because of high speed and smaller fame size the cells reach the destination much more quickly. The ATM is simple to implement cost is effective and faster because of used Asynchronous TDM and virtual switching. ATM cell got greater percentage of header which are in 53 bits.

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Figure 1 : ATM Cell format

GEC: termed as Generic Flow Control is used in user to network side which gives the cells from user to the network

VPI: termed as Virtual Path Identifier which are generally 8 and 12 bit length in terms used for identification of routing and control information

VCI: termed as Virtual Channel Identifier used for identifying the channel

PTI: termed as Payload Type Indicator which generally carries various types of information

CLP: termed as Cell Loss Priority

HEC: termed as Header Error Control which is used of error correction generally contains a error control field of 8 bit and corrects on remaining 32 bits

ARCHITECTURE OF ATM :

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Figure 2 : Architecture of Asynchronous Transfer Mode

This is a basic architecture used for communication between user end to network end.

The physical layer in the basic architecture is for choosing type of encoding system and transmission medium. The data rates are chosen at this layer (25.6 Mbps to 62.2Mbps) and the ATM layer is used for switching virtual circuits setup and termination and also used for sizing the cells, routing information. The ATM adaption layer (AAL) which is used to interface user and network and provides information for the higher levels. User plane provides the user information, flow control and error control Control plane is used for all connection control fields Management plane provides coordination to all planes by managing them

CONNECTIOS IN ATM:

The connections in Asynchronous Transfer Mode are logical

C:\Users\mamathareddy\Desktop\ATm picz\logcl conctn.PNG

Figure 3: Logical Connections

Virtual channel connections(VCC) which are most basic unit of switched network to communicate with the end users. In ATM the VCC’s are logical connections which was very similar to virtual circuit switches in X.25 technology the full duplex transmission is possible between either user to network or network to network at a variable data rates usually the frames here are in fixed lengnth

Virtual path connections(VPC) are used in logical connection such that which will provide some control information to the data usually these are the secondary sublayers for the VCC’s having the same end points. Generally the connections are at high speed Data rates with lower possibility of errors hence the VPC’s came to support to share the medium of VCC’s in order to reduce the overall cost

CONCLUSION:

Hence for ever increasing communication models we require a higher performance protocols for transmission at higher data rate, lower probability of errors at lower cost. The Asynchronous Transfer Mode provides transmission of video and audio data at higher data rates successfully.

FIBER CHANNEL

PREFACE:

For ever increasing communication models we required higher range of data transfers. Fiber Channel is developed to cope up with present technologies such that which provides higher range of data transfers and provides storage of data on networks which also provides backup data.

DEVELOPING STEPS :

The Fiber channel was developed using optical fiber which is the most efficient transmission media in nowadays. The frames sending through these type of transmission media lesser prompts to errors and it has got higher bandwidth supports up to 100Mbps data rate. Developed such that which can interface to any existing and earlier systems with the low cost and topologies with flexible nature. Most of the functionalities are implemented in hardware rather than in software to support higher data rates over smaller distances and small amount of data over longer distances. Which was developed to support several protocols fiber channel carries these type of protocols along with it such as IP and SCSI. The data transmission usually between two switching nodes in a packet switched network

LAYERS IN FC:

There are five layers in Fiber channel i) Fiber channel layer 0 ii) Fiber channel layer 1 iii) Fiber channel layer 2 iv) Fiber channel layer 3 v) Fiber channel layer 4 which are like seven layers in OSI-ISO system in which each layer functions for data transmission in which Fiber channel layer 0 to 2 deals with the physical description and Fiber channel layer 3 and 4 deals with the user interface applications these are the higher level layers in stack of layers

Fiber channel layer 0 : which is the lower layer in stack of layers deals with the physical connection establishments like type of connector usually there are two types of cable connector optical and copper and which sets the variable data rates , lower noise probability. Established links must connect to two ports of optical fiber.

Fiber channel layer 1 : this layer describes to choose transmission layer protocol and type of encoding and decoding technique is used which also perform error detection and correction. The user data is encoded in 8 bits per time on the 10 bit stream.

Fiber channel layer 2: which defines the mechanism to transport the required data to higher levels which forms the frames by choosing data correctly and provides encapsulation, flow control for data at higher rates.

Fiber channel layer 3: this layer of fiber channel provides the basic and advanced features like group ports if one request is generated more number of ports are responded.

Fiber channel layer 4: which defines the user application interfaces between the higher level protocols that are exist in this layer and user using lower level protocols at lower levels.

TOPOLOGY :

http://hsi.web.cern.ch/HSI/fcs/spec/ov1.gif

Figure: Topologies in Fiber channel

The Topolgies in Fiber channel are i) Fabric ii) point to point iii) Loop

Fabric: Fabric topology is defined in fiber channel such that which will connects to N number of ports via uni directional path one is for receiver and another is for transmitter. When Fabric is in middle F-port of node is connected to fabric and N-port is for another end of node.

Point to Point : which describes a direct connection between two nodes.

Loop : which defines a circular connection between all switching nodes.

CONCLUSION:

Fiber channel supports higher data rates using higher bandwidth with low probability of errors at lower cost on the other hand Asynchronous Transfer Mode also provides same type of functionalities apart from these the Fiber Channel provides network solution and input/output and data storage backup.