The Atm And Fiber Channels

Published Date: 02 Nov 2017

ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching with those of packet switching flexibility and efficiency for intermittent traffic –CISCO.

circuit switching provides advantages of guaranteed capacity and constant transmission delay while packet switching provides advantages of flexibility and efficiency for intermittent traffic.

It uses fixed types of cells to Carry different types of traffic like voice ,data,video.

ATM is a technology that will enable carriers to capitalize on a number of revenue opportunities through multiple ATM classes of services; high-speed local-area network (LAN) interconnection; voice, video, and future multimedia applications in business markets in the short term; and in community and residential markets in the longer term.

Technical Explaination:-

ATM is circuit switched because it established virtual circuits for communication.

It also creates virtual circuits over packet switched networks.it combines both the benefits of circuit switched and packet switched networks.

Theoratically ATM deployed from small VLAN to larger WAN. In practical world its mostly used in backbone of network because of cost issues.

In ATM network speed is scalable.

It is asynchronous technology and it uses link based on need of information to be transmitted.The cells which are used to in ATM are small compared to other wan technologies like frame relay.It uses fixed length cells which makes it easier to switch between multiple networks.

It reduces latency and delay also.

1.3 ATM Cell format

ATM uses fixed type of cells. Each cell contain 53 bytes.

5 bytes are used as cell header.

Rest 48 byte used as pay load carrying data.

ATM Cell header format

CELL NNIATMUNI

ATM cell header format consist of 2 types.

UNI cell header:- used for communication of ATM Endpoint and ATM switches .

NNI Header:- NNI used for communication between two ATM switches.

GFC(Generic flow control):-identifies multiple station that share same ATM network.

VPI(virtual path identifier):-with the help of VCI it identifies next destintion.

VCI(Virtual Channel Identifier) :- with the help of VPI ,it identifies next destination.

Payload type(PT):- 1st bit identifies whether it is control data or user data.2nd bit indicates congestion. While 3rd bit indicates the cell is the last in a series of cells that represent a single AAL5 frame (1 = last cell for the frame).

CLP(Cell Loss priority ):-indicates whether cell should be discarded or not if congestion occure.

HEC(Header error control):- calculate checksum for 1st 4 bytes.

ATM devices:-

ATM network built around these two devices.

1.ATM switch:- ATM switch can be connected to ATM switch or ATM end to end point.

2.ATM End Point:- it contain ATM end adaptor. Ex LAN switches,Video Codecs.,routers etc.

ATM Switches and interfaces:-

ATM switch support two types of interfaces

User type of interface

Network Network Interface

These both types interfaces can be again divided into two types

Private Interface

And Public Interface

1.4 ATM standards for Digital lines:-

Area of Application

Speed

Standard

T1

25 Mbps

Yes

T3/E3

155 Mbps

Yes

OC-3

622 Mbps

Y

OC-12

2.4 Gbps

Y

Fig 1.4.1 =ATM Forum

1.5 ATM reference model:-

Fig 1.5.1- ATM Model

Above Model explains functionality of that it supports.It links to the physical layer and part of the data link layer of the OSI reference model.

Following planes composed in ATM reference mode :-

Control - generate and manage signaling requests.

User - Manage the transfer of data.

Management - This plane contains two components:

Layer management manages layer-specific functions, such as the detection of failures and protocol problems.

Plane management manages and coordinates functions related to the complete system.

The ATM reference model is composed of the following ATM layers:

Physical layer –

Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission.

ATM layer - ATM layer with ATM adaption layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is accountable for the cell multiplexing and cell relay . ATM adaptation layer (AAL) -it isolates higher-layer protocols from the details of the ATM processes. It prepares user data cells and segments the data into 48-byte cell payloads.

Finally, the higher layers accept user data, arrange it into packets, and hand it to the AAL.

1.6 Conclusion:[

ATM provides unified communication between across no of upper layer traffic and administrative domain. ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching and packet switching.

2. Fiber Channels

2.1 Introduction:-

Fibre Channel is a set of advanced data transport standards that allow large amounts of data to be moved reliably at multigigabit speeds between computers, servers, disk arrays, and other devices.

It high speed technology primarily used for storage networking. It used mostly in backbone of networks.

It is a 100MB/sec, full-duplex, serial, data communication technology.

It supports several common transport protocols like Internet Protocol (IP) and SCSI.

It operates over copper and fiber optic cables at distances of up to 10 Kilometers.

It is supported by many suppliers like Compaq, Hewlett-Packard, IBM, Seagate, and Sun Microsystems.

It Provides high bandwidth utilization with distance intensitivity.

It has Ability to carry multiple existing interface command sets, including Internet Protocol (IP), SCSI, IPI, and audio and video.

Parallel Interface) are replaced by fibre channel protocol due to the fact that fibre channel is more flexible such that network devices can be placed at a distance of 10km.

2.2 Fiber channel standard:-

The T11 Committee of NCIT, a U.S. standards-development organization under the ANSI (American National Standards Institute) meets 6 times a year to develop Fibre Channel standards.

2.3 Fiber Channel topologies:-

There are mainly 3 types of Fiber channel topologies.

Point to point

Arbitrated loop

Switchd fabric

Point to Point(FC-PP):-

These is simplest type of connection. two devices are directly connected to each other.Medium is not shared between two devices so both device can utilize

Arbitrated Loop(FC-AL):-

In FC-AL all links are connected to loops and rings .The failure of one device in network will cause to fail entire network.

Switched Fabric:-

All devices are connected in loops are attached to fiber channel switch.In this connection interconnection are made in all devices so failure of one device will not affect network. Failure of one port should not affect other ports.

Fig 2.3.1- Topolgies

2.4 Fibre Channel ports:

(N_ port) Node ports are ports used in point to point topology.

(F_ port) Fabric ports are ports used in switched fabric topology.

(FL _ port) Arbitrated loop ports are ports used in arbitrated loop.

E _ port ( ports connecting switches together) .

2.5 Fiber channel protocol architecture:-

Fiber channel protocol has 5 layers.

FC-0 Physical Layer

FC-1 Encode/Decode Layer

FC-2 Flow control/Framing protocol

FC-3 Common services

FC-4 Upper level protocol services (HIPPI, SCSI)

Fig 2.5.1 FC protocol Architecture

Physical Layer:-

Its lowest layer in FC protocol architecture. It acts as physical medium between two devices for transmitting and receiving data.Copper cables and optical cables are used as physical medium. Optical cables are used for long distance communication.

Encode and decode layer:-

In this layer line coding (encoding/decoding) of signals are done so that the transmission characteristic of the information across the line is improved.It also perform functions of error detection. .

FC-2 Layer

It acts as transport mechanism in fiber channel architecture.It also perform error correction and error detection, flow control, frames formation and sequence formation.

FC-3 layer: It is a thin layer which provides the common services such as

Stripping- Multiplying bandwidth using multiple N_ ports in parallel to transmit single information in multiple links.

Hunt Groups- Ability for more than one port to respond to the same address. By doing this efficiency gets increased by decreasing the chance of reaching a busy port.

Multicast- It delivers single transmission to many destination ports.

FC-4 Layer:-

This is top notch layer in FC protocol architecture. It provides mapping for upper layer protocols(ULP).

2.6 Conclusion:-

Fiber channels are very inexpensive and reliable technology which support multiple protocols and topologies. Its application area is mostly in SAN (Storage area network). Data are transferred at very high speed than ATM.It can be employed in the many technologies when compared to Ethernet andATM. It is more reliable transmission service,It also support network,video Protocols and SCCI.