|Processing of general expenses||increased||decrease|
|Data transfer||Implemented in more than one geographical network.||It takes place within a LAN|
|Cost||cheap||The highest cost|
|QoS||Quantifiable QoS not provided.||It offers quantifiable QoS.|
|Error checking||No support for errors and flow control is provided||The error and flow control is provided.|
|Data rate||64 Kbps up to 45 Mbps.||155, 5 Mbps or 622 Mbps.|
Definition of Frame Relay
The Frame Relay a packet broadcasting service designed to manage the updated WAN type. X.25 was the previous technology used instead of frame relay, but there are some shortcomings of use such as low data transmission speed, an unnecessary increase in flow speed and error control.
The Frame Relay service uses a permanent or switched virtual circuit to set up the connection and enable the transfer of the bit from the source to the destination at an adequate speed at an affordable cost. Before the advent of Frame Relay and X.25, slow phone lines were used for the intended purpose. In the previous technology, the main delays were network delays, general protocol costs and equipment costs.
Frame Relay features
- Frame relay operates at the speed of 1.544 Mbps and 44.376 Mbps.
- It involves only two levels: physical and data link levels. Therefore, it could be used as a backbone network with protocols with network layer protocol to provide services.
- Bursty data has no negative effect on frame relay.
- The frame size allowed in the 9000 byte frame relay to carry entire dimensions of the local network frame.
- Frame relay reduces the cost of WAN technology.
- It only supports error detection in the data link layer but no flow control and error control mechanism. Therefore, if a frame is damaged, there is no retransmission policy and the frame is automatically discarded.
Frame Relay operation
Frame relay it is used to transfer data in the form of packets, with the help of the data link layer. Here, a unique identifier DLCI (connection data identifier) identifies the virtual connection that is referred to as ports. The frame relay basically connects two DTE devices using a DCE device. DTE devices connected to the frame relay are assigned with a port to make each remote connection unique. It can create two types of circuits, PVC (permanent virtual circuit) is SVC (switched virtual circuit) .
The first type of virtual circuit, PVC composed of two operational states, data transfer and inactivity. In the data transfer state, data transfer takes place within the DTE devices via the virtual circuit. in waiting state, data transfer does not occur even if the connection within DTE devices is active.
The second type of SVC establishes the transient connection that could prevail until the data is transferred. It includes various operations such as call setup, data transfer, inactivity and call termination. In the call setup, termination operation, the connection is established and terminated between the two DTE devices and other operations are similar to PVC operation.
Layers of the Frame Relay
There are only two levels in the frame relay which are the physical level and the data link level.
Definition of ATM
ATM stands for asynchronous transmission mode ; a switching technique developed by integrating the characteristics of telecommunications and computer networks. ATM uses cells to transfer information about many forms of service such as voice, data and video. These cells are encoded using asynchronous time division multiplexing. It also allows communication between devices to work at variable speed by combining multiplexing and switching, and appropriate for bursty traffic. These cells are nothing more than the collection of fixed-size packages.
ATM networks need ATM switches and ATM endpoints for its operation. The ATM switch transits on a cell transmitted by a ATM endpoint to an ATM network. Before transmitting the cell, first scan the frame header and, if necessary, update it, then switch to the output interface to deliver it to the destination. ATM endpoints also include the network interface adapter.
The ATM reference model consists of levels and planes as shown in the diagram. There are three basic levels in the physical AAL level, ATM and ATM.
- Physical level : this ATM layer manages the transmissions dependent on the medium.
- ATM level : the ATM layer similar to the data connection level that allows the sharing of virtual circuits between different users and the transmission of cells on the virtual circuit.
- Application Adaptation Layer (AAL) : the AAL responsible for hiding the ATM implementation details of the upper layers. It also transforms data into 48-bit cell payloads.
The different plans included in the ATM reference model are control, user and management.
- Control : the main function of this plan to produce and manage the reporting request.
- User : this plan manages data transfer.
- Management : level functions, such as fault detection, protocol problems are governed by this plan. It also involves the functions related to the complete system.
The ATM header includes two types of format UNI (User network interface) is NNI (Network network interface) . These formats contain two fields in the named ATM header VPI (Virtual Path Identifier) is VCI (Virtual Circuit Identifier) .
Now let's see first the concept of connection to the virtual channel and connection to the virtual path. The virtual channel is the most fundamental unit in the ATM network, while the connection to the virtual path is a collection of virtual channel connections. Furthermore, a set of connections to virtual paths constitutes a transmission path.
The VPI field uses virtual values to switch cells between ATM networks such as routing. The UNI interface contains 8 bits for the VPI field which allows 256 virtual path identifiers. While the NNI interface format can have 12 bits in the VPI fields and allows 4,095 virtual path identifiers. On the other hand, the VCI field is used to perform the switch for end users and has a 16-bit value for the UNI and NNI interface formats. This field allows to obtain 65,536 virtual channels.
Key differences between Frame Relay and ATM
- The packet size in the frame relay varies while ATM uses a fixed-size packet known as a cell.
- ATM produces less overhead than Frame Relay technology.
- Relative less expensive frame for the ATM.
- ATM faster than frame relay.
- ATM provides a flow and error control mechanism, while frame relay does not.
- The less reliable frame relay of the ATM.
- The throughput generated by the average frame relay. In contrast, ATM has a higher return.
- The delay in the frame relay of pi. By contrast, less in the case of ATM.
Advantages of Frame Relay
- Efficient communication process
- It performs fewer functions in the user-network interface.
- Even the delay has been lowered.
- Produces higher throughput.
- faster than its X.25 predecessor.
Advantages of the ATM
- It can easily interface with the existing network as a PSTN, ISDN. It can be used on SONET / SDH.
- Perfect integration with different types of networks (LAN, MAN and WAN).
- Effective use of network resources.
- less susceptible to noise degradation.
- It provides a wide bandwidth.
Disadvantages of Frame Relay
- Unreliable service
- The order of incoming packages may not be maintained.
- Incorrect packages are deleted directly.
- Frame relay offers no flow control.
- The confirmation of the received packets and the retransmission control for the frames is not provided.
Disadvantages of ATMs
- The cost of switching devices is higher.
- The overhead generated by the cell header pi.
- The rather complex ATM QoS mechanism.
Software controlled frame relay while ATM implemented for hardware, which makes it more expensive and faster. ATM can achieve greater processing and switching speed by providing flow and error control.