Frame Relay versus Asynchronous Transfer Mode: A Comparative Study and Simulation

Published Online October 2017 in MECS DOI: 10.5815/ijcnis.2017.10.04

There are many techniques and protocols of the wide area communication for transferring data between remotely networks and devices. But, to carry out the realtime data with high accuracy and with minimum delay in high-speed network needs high-speed technologies. The Frame Relay and ATM are two well-known technologies that are used in these days.

They are considered as the variations of the legacy X.25 protocol to eliminate the data transmitted overhead and to provide best controlling of signals by carrying the signals on different channels and paths using the virtual connections[1].

Both Frame Relay and ATM are connection oriented protocols, support switching and multiplexing of multiple logical connections on the single physical link and they provide dynamic bandwidth allocation for efficient traffic management, but there is no processing of an error correction .

In addition, Frame Relay has the characteristics of packet switching network, variable packet size, more cheap cost than the ATM and other network's types like leased lines. It appeared in the early 1990s as the successful technique for X.25 by overcoming physical errors (e.g. noise lines) that were found in X.25. Hence it is taken as better controlled congestion, high performance, throughput and high speed compared to X.25 for the lowest two layers of OSI model (Link-layer and the physical layer)[1][2].

Whereas, ATM is known as cell relay, it was designed in the 1980s, and fit to standardize in ITU-T at 1987. ATM combines the circuit switching and packet switching of small size. It is designed for low latency in real-time applications like video and voice and high throughput like file transfer. But in this method there is minimum flow control and error control capabilities. The ATM’s virtual circuits are established for both the source and the destination devices [1][2].The data is transferred as fixed cell of 53 bytes long of both header (5 bytes) and data payload (48 bytes) [3].

Moreover, in the ATM a virtual channel is a logical connection similar to virtual circuit. The virtual channels which have the same end points can be grouped into virtual paths. Hence, all the circuits in virtual paths are switched together. This offers increased efficiency, architectural simplicity, and the ability to offer enhanced network services.

In general, the real-time applications such as voice over IP and video on demands need high data rate and throughput for data transmission from source to destination. The Frame Relay has less data rate than the ATM and it provides low quality for communication of those applications. Hence, this paper provides and analyses the comparative study between the Frame Relay and ATM to understand the overview and the nature of these technologies in Wide Area Network (WAN) for real-time applications. The analysis of voice application was done using the OPNET simulation tool based on the various parameters(traffic sent, traffic received, delay, Jitter and the end-to-end delay) to compare the performance of the ATM and Frame Relay in high-speed networks.

• II.    Frame Relay

  Frame Relay appeared in early 1990s. it is the backbone of a communication network for more companies and it is also provided by Internet Service Provider (ISP) for the remote intranet branches on different remote cities.

Moreover, it is an enhanced network of X.25 for reducing the End-to-end delay, equipment cost, and overhead of X.25. At the beginning, Frame Relay is developed to work on ISDN and now it is expanded to other public and private non-ISDN network interfaces. It is also considered as the backbone to provide services to upper layer protocols that have the network layer like IP. Furthermore, it has typical data rate from 64Kbps reach to 45Mbps (or T3).There are three types of frames show in table 1.

Table 1. The Frames Type

SN	Type	Description
1	Information Frames	Carry data as well as Next Send (NS) and Next Receive (NR) counts
2	Supervisory Frames	Controls flow of data with Receiver Ready (RR), Receiver Not Ready (RNR), and Reject (REJ) frames
3	Unnumbered Frames	Establish and maintain communications with Set Asynchronous Balanced Mode (SABM), Unnumbered Acknowledgment (UA), Disconnect (DISC), Disconnect Mode (DM) and Frame Reject (FRMR)

The data transfer in Frame Relay, which works typically on the data link layer, occurs in packets that are named frames. The virtual connections are recognized by the unique identifier that is called Data link connection identifier (DLCI). The DLCI connections in Frame Relay devices are called 'ports'. All Data Terminal Equipment’s (DTEs) devices that connected to frame relay network need a port that is unique for every remote device. However, there are 10 bits for DLCI's field value in the Frame Relay header that provides 1,024 different virtual connections or DLCIs.

Furthermore, the data terminal equipment (DTE) that connected to Frame Relay network needs a port that is unique for every remote device. There are two types of connections in Frame Relay such as the Switched Virtual Circuit (SVC) and the Permanent Virtual Circuit (PVC) which are defined by ANSI and ITU-T. The PVC has two stages of operational states as data transfer and idle. Whereas, the SVC has four operational states as call setup, data transfer, idle, and call-termination. The DTE’s devices establish the virtual connections via call setup and then they transfer the data between DTE’s devices. The idle stage means that the connection is active, but there is no data transferring. The call-termination, as the last stage, is tearing the virtual connection off [1][2][3][4].

There are two types of establishing connection between devices in frame relay which are the point to point and point to multipoint sub-interfaces connection. It is considered as the Non-Broadcast Multi-Access (NBMA) network that does not provide broadcast between its virtual channels by default and it provides multi access across PVC or SVC channels [4].

However, there are some limitations such as the function of Frame Relay is just to detect errors at the data link layer and there is neither error control nor hop to hop flow control of data. Furthermore, the Frame Relay is weak in control and administration of the congestion for the data traffic (e.g. drop packets when congestion occurs).Whereas, the upper layers are responsible for the error correction and flow control of an entire payload [1].

The author of paper[5] showed such limitations by comparing the Frame Relay with other networks like MPLS which has low latency and a labeling feature of packets instead of the huge process of routing that is based on IP addresses. He used OPNET simulator tool according to certain parameters as latency, Ethernet delay and traffic received.

• III.    ATM

ATM is a node or a switching device which routes cells. The cell is a basic transmission unit that is always fix length. Therefore, an ATM is also known as a cell relay.

The ATM has features of both circuit switching and packet switching techniques. Such ATM is implemented as controlled hardware and it is designed for using realtime applications with low latency, and also for using high throughput in case of file transfer. The same ATM uses an external or isochronous clocking for transferring data faster[3], and it can be deployed in private, public or hybrid networks either Local Area Network (LAN), Campus Area Network (CAN) or WAN.

The ATM header has two types of formats such as: User-Network Interface (UNI) and Network-Network

Interface (NNI) formats. Each type has two fields in each ATM cell header as Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI) that are reserved for the virtual connections.

The VPI field works as routing and it uses the virtual values for switching the cells between ATM’s networks. In UNI interface the VPI field has 8-bits value to permit up to 256 virtual path identifiers (i.e. from 0 to 255 values). While, in NNI interface format the VPI field has 12-bits value to allow for 4,096 virtual path identifiers (from 0 up to 4,095).

Whereas, the VCI field is used as switching for the end users. This field has 16-bits value for both UNI and NNI interface formats which can allow to get 65,536 virtual channels. The actual values of such range from 32 to 65,535 are used for virtual circuit connections in ATM network, whereas the other VCIs values are reserved by ATM Forum and ITU-T. The combining of both VPI and VCI is referred to as virtual channel connection (VCC).The VCC is defined as allocating connection of VPI and VCI known as the connection identifier (CI) [1][6][7].

There are some previous studies in the area of the Frame Relay and ATM networks that are summarized and conducted as follows: