Fiber Channel Protocol Architecture

Published Date: 02 Nov 2017

Introduction:

Asynchronous Transfer Mode (ATM) is developed to carry a range of user data that includes voice signals, video signals along with user data. The main purpose of developing ATM is to merge telecommunications with Computer Networks.

ATM works on the Data Link Layer model using Fiber cable or twisted pair cable. ATM is completely different from other data link layer technologies, it do not use routing techniques as many data link technologies like Ethernet do. ATM switches are used to establish connections between two points and makes the communication possible. ATM uses fixed length packets called cells instead of using packets of different length in Ethernet. Each ATM cell is of 53 bytes length in which 5 bytes are used for the header information and the remaining 48 bytes for user data.

ATM performance can be expressed in Optical Carrier levels (OC). OC-192 can be used over ATM for faster data transfer as it supports 10 Gbps data rate. Other levels like OC-155 and OC-12 are also used over ATMs whose speeds are 155 and 622 Mbps respectively. The main motto behind development of ATM is to improve the quality for high traffic networks.

It is a connection oriented protocol, before communicating; a virtual connection is established between source and destination to make data communication possible. As ATM uses fixed size cells and no routing is implemented, the bandwidth can be effectively used in ATM. But ATM is more costly than Ethernet which lags ATM behind Ethernet in popularity.

Protocol Architecture:

Unlike OSI model or TCP/IP model which have 2-dimentional protocol stack, ATM protocol architecture is little complex as it is a 3-dimentional model unlike other architectures.

As shown in the figure, ATM protocol reference model involves 3 separate planes, they are:

1. User plane

2. Control plane

3. Management plane

FIG:1 PROTOCOL ARCHITECTURE OF ATM NETWORKC:\Users\Arun\Desktop\Capture.JPG

1. User plane:

This plane is responsible for transferring user information. This is associated with controls like error control and flow control.

2. Control plane:

This plane is responsible for establishing connections that is control functions and call functions.

3. Management plane:

The whole system is under the control of this plane, as it coordinates all the planes by using management functions. These management functions works on resources and parameters that residing in protocol entities.

The main layers related to ATM protocol are ATM Adaption layer(AAL) and ATM layer.

ATM Adaption layer:

The ATM adaption layer (AAL) describes how to segment the data and reassemble the packets coming from higher layers into ATM packets. It also deals with different transmission aspects of the ATM layer.

ATM Adaption layer is sub divided into two sub layers Convergence sub layer and Segmentation and reassembly sub layer.

The major services provided by ATM adaption layer are:

Segmenting and reassembling the packets

Error handling during transmission

Flow control between fast sender and slow receiver.

Some of the services that require ATM Adaption Layer are IP, Frame relay, Gigabit Ethernet etc.

ATM Layer:

ATM layer resides just above the physical layer as you can see in the figure. It handles multiplexing and switching to maintain Quality of service. Whenever a connection is established, an agreement is made between sender and the receiver. It checks the type of data to be transferred and it allocates the resources like bandwidth to make sure that data transfer is possible.

The major functions of ATM layer are:

It generates the cell header

It makes cells to flow in and order by using sequencing

It also handles the dropped cells.

ATM cells:

There are many uses of using ATM cells.By making use of small ATM cells, we can reduce the queuing delay for a cell with high priority.

Fixed size cells can be switched more effectively by which we can achieve high data rates.

Every ATM cell comprises of 53 bytes, out of which 5 bytes are used for header and the remaining 48 bytes to carry the user information. Two different types of headers are used for ATM cells, they are UNI header and NNI header.

Fig:2 ATM Cell format

C:\Users\Arun\Desktop\lightspeed1000-atm-analyzer-web-uni-nni-format.gif

Two different kinds of ATM headers are:

User -Network Interface Header (UNI)

Network-network Interface header (NNI)

The fields in the above heads are explained below:

Generic flow control (GFI):

This field is used to control the flow of traffic to improve the Quality of service.

4 bits are allocated for this field.

End to end user functions can be performed using this field.

Used for control of cell flow at User-Network header only and it is not present in Network-Network interface header.

The details of its applications are not yet defined and retained for further study.

Virtual path Identifier (VPI):

Virtual path identifier is an 8 bit field for User-Network Interface and 12 bit field for Network-Network Interface.

A virtual path identifier (VPI) uniquely finds a network path for an (ATM) cell packet to reach its destination node.

Virtual channel Identifier is used for routing the packets to and from the end user. It is a 4 bit field.

PTI (payload type) is a 3 bit field that indicates the type of information present in the information field.

C:\Users\Arun\Desktop\pti.JPG

Cell loss priority (CLP):

Whenever congestion occurs, this bit is used guiding to the network. A ‘0’ I this field indicates that the packet is of comparatively high priority, and a ‘1’ in this field indicated that the packet can be discarded.

Header error control (HEC):

It is an 8-bit header generally used for error control. It is calculated on the remaining 32 bits of the header. Polynomial X8+X2+X+1 is used to generate the code. It is useful in correction of errors.

Advantages of ATM:

ATM supports voice, video and data which allows multimedia over a single network.

It works with the existing and even on older technologies.

Quality of service can be achieved using ATM networks

Bandwidth can be effectively utilised as it uses statistical multiplexing

It provides communication with high data rates which are in Gbps.

It is highly scalable, as it operates on any of LAN, WAN, MAN.

FIBER CHANNEL

Introduction:

The requirement for more speed in delivering the data to the processor has grown because of the growth in Graphic applications that use video and Audio which resulted in development of Fiber channel.

Fiber channel is an interconnect technology for high performance computer networks . It enables data rates that are two and half times faster than the High end Interfaces.It also carries Audio, Video, Voice signals and even it is easy to integrate with the already existing systems.

Fiber channel is nothing but a group of physical layer networking standards. It handles disk storage with high performance for different applications on corporate networks. Fiber channel supports Data backups, replication and clustering.Similar to Ethernet, its competitor, Fiber channel makes use of copper wiring. Fiber Channel operates in 1 Gbps or 2 Gbps and even 10 Gbps is under the development.

Fibre Channel networks have a bad fame for being costlier to build, difficult to manage, and not flexible to upgrade due to compatibility issues raised with other products.

Fiber channel protocol architecture:

The Architecture of Fiber Channel consists of the following layers:

Fiber Channel 0 (FC 0):It is the lower level layer in the stack of 5 layers. This layer tells about the establishment of physical connection. It specifies the type of connection used like Optical fiber or copper cable.

Fiber Channel 1 (FC 1):This layer tells about the transmission protocol that is to be used. It also specifies which encoding technique needs to be used. Data is encoded 8 bits at a time. This layer performs error detection and error correction.

Fiber channel 2 (FC 2):It provides various mechanisms to send the data to its upper layers. Flow control is maintained in order to maintain synchronization between fast sender and slow receiver.

Fiber Channel 3 (FC 3): This layer provides advanced features like grouping ports. By using grouping ports, ports can be grouped so that for one request a set (group) of ports get responded.

Fiber Channel 4 (FC 4):This layer specifies the application user interfaces.

FIG 4: MAXIMUM DISTANCE FOR FIBER CHANNEL MEDIA TYPES:

C:\Users\Arun\Desktop\adf.JPG

Topologies in Fiber Channel:

Fabric topology:

Fabric topology connects N number of ports through uni-directional path one for receiver and another for transmitter as shown in the figure below:

Fig 5.1:Fabric Topology :

C:\Users\Arun\Desktop\fab.JPG

Loop topology:

In loop topology, a circular connection is established in between all the existing nodes.

Fig 5.2: Loop topology:

C:\Users\Arun\Desktop\loop.JPG

Point-Point topology:

In this topology, direct connection is established between the two nodes as shown below:

Fig 5.3:point-point topology:

C:\Users\Arun\Desktop\pp.JPG