A Performance Comparison of X.25, Frame Relay and ATM in High Speed Networks-A Review
A Performance Comparison of X.25, Frame Relay and ATM in High Speed Networks-A Review
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ABSTRACT: To carry out the real time data with high accuracy and with minimum delay between a set of
communication devices high speed network is used, which is based up on the optical fiber technology. It is not
sufficient to use the high speed data rate alone, unless there is efficient utilization of the bandwidth of the medium. This
paper presents the comparative study of three high speed technologies viz. X.25, Frame relay and ATM. Frame relay
and ATM are the variations of basic X.25 technology. Based on the various performance metrics, the comparative
study demonstrates that ATM has less delay compared to the X.25 and Frame relay and thus is efficient for
transmission of the real time data.
I. INTRODUCTION
Today's communication networks are built using digital trunks that are inherently reliable, while providing a high
throughput and minimal delay. The traditional approach to packet switching (X.25), used in-band signaling, and
includes end-to-end and well as per-hop flow control and error control. This approach results in considerable overhead
and has historically been too slow - primarily supporting low-speed terminals at 19.2 kbs and lower.
Frame relay is a packet-mode transmission service that exploits characteristics of modern networks by minimizing the
amount of error detection and recovery performed inside the network. Thus, by streamlining the communications
process, lower delay and higher throughput is achieved. Besides, it can handle multiple data sessions on a single access
line, which means that hardware and circuit requirements are reduced. Frame relay is also scalable - implementations
are available from low bandwidths (eg, 56 kbps), all the way up to T1 (1.544 Mbps) or even T3 (45 Mbps ) speeds.
ATM was designed for a network that must handle both traditional high-throughput data traffic (e.g., file transfers), and
real-time, low-latency content such as voice and video. ATM uses fixed packet lengths of 53 bytes (5 bytes of overhead
and 48 bytes of user data), which is more suitable for voice transmissions. This differs from approaches such as the
Internet Protocol or Ethernet or frame relay that use variable sized packets and frames.ATM provides extensive quality
of service information that enables the setting of very precise priorities among different types of transmissions (i.e.
voice, video & email; services include CBR, VBR, ABR and UBR).ATM is scalable ATM uses a connection-oriented
model in which a virtual circuit must be established between two endpoints before the actual data exchange[1]
II. X.25
X.25 was developed in 1970s by CCITT (Consultative Committee for International Telegraph and Telephone) for
providing an interface between public packet-switched network and their customers. The packet switching networks
use X.25 protocol. The X.25 recommendations were first prepared in 1976 and then revised in 1978, 1980 and 1984.
X.25 is a standard suite of protocols used for packet switching across computer networks. The X.25 protocols works at
the physical, data link, and network layers (Layers 1 to 3) of the Open Systems Interconnection (OSI) communication
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Vol. 5, Issue 3, March 2017
model.X.25 is one of the oldest packet-switched services available. Each X.25 packets contains up to 128 bytes of data.
The X.25 network handles packet assembly at the source device, delivery, and then dis-assembly at the destination.
X.25 packet delivery technology includes not only switching and network-layer routing, but also error checking and re-
transmission logic should delivery failures occur.X.25 supports multiple simultaneous conversations by multiplexing
packets and using virtual communication channels.X.25 was originally designed more than 25 years ago to carry voice
over analog telephone lines (dialup networks). Typical applications of X.25 today include automatic teller machine
networks and credit card verification networks. With the widespread acceptance of Internet Protocol (IP) as a standard
for corporate networks, many X.25 applications are now being migrated to cheaper solutions using IP as the network
layer protocol and replacing the lower layers of X.25 with Ethernet or ATM hardware.X.25 is a connection oriented
service. It supports switched virtual circuits as well as the permanent circuits. A switched virtual circuit is established
between a computer and network when the computer sends a packet to the network requesting to make a call to other
computer. Packets can then be sent over this connection from sender to receiver. X.25 provides the flow control, to
avoid a fast sender overriding a slow or busy receiver. A permanent virtual circuit is analogous to-a leased line. It is set
up in advance with a mutual agreement between the users. Since it is always present, no call set up is required for its
use. [1][2]
The X.25 defines the interface for exchange of packets between the user's machine (DTE) and the packet switching
node to which this DTE is attached which is called as DCE.
At the physical level X.21 physical interface is being used which is defined for circuit switched data network. At the
data link level, X.25 specifies the link access procedure-B (LAP-B) protocol which is a subset of HDLC protocol.
At the network level (3rd level), X.25 defines a protocol for an access to packet data subnetwork.
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This protocol defines the format, content and procedures for exchange of control and data transfer packets. The packet
layer provides an external virtual circuit service.
Fig. (b) Shows the relationship between the levels of x25. User data is passed down to X.25 level 3.
This data then appends the control information as a header to form a packet. This control .information is then used in
the operation of the protocol.
The entire X.25 packet formed at the packet level is then passed down to the second layer i.e. the data link layer.
The control information is appended at the front and back of the packet forming a LAP-B frame. The control
information in LAP-B frame is needed for the operation of the LAP-B protocol.
Advantages of X.25:
1. Frame delivery is more reliable
4. Flow & error control is provided at both the data link layer & the network layer.
Disadvantages of X.25:
4. X.25 is costly.
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1. Frame Relay is a virtual-circuit wide-area network that was designed in response to demands for a new type of
WAN in the late 1980s and early 1990s.
2. Frame relay has evolved from X.25 packet switching and objective is to reduce network delays, protocol overheads
and equipment cost.
3. Frame relay can support multiple users over the same line and can establish a permanent virtual circuit or a switched
virtual circuit.
4. Packet switching was developed when the long distance digital communication showed a large error rate.
5. To reduce the error rate, additional coding bits were introduced in each packet in order to introduce redundancy to
detect and recover errors.
6. But in the modem high speed telecommunication a system, this overhead is unnecessary and infect
counterproductive.
7. Frame relay was developed for taking the advantage of the high data rates and low error rates in the modem
communication system.
8. The original packet switching networks were designed with a data rate at the user end of about 64 kbps.
9. But the frame relay networks are designed to operate efficiently at the user's data rates upto 2 Mbps. This is possible
practically because most of the overhead (additional bits) are striped off.
10. Frame relay also is meant for more efficient transmission scheme than the X.25 protocol.
11. The biggest difference between Frame Relay and X.25 is that X.25 guarantees data integrity and network managed
flow control at the cost of some network delays. Frame Relay switches packets end-to-end much faster, but there is
no guarantee of data integrity at all. [5] [6]
1. Frame Relay operates at a higher speed (1.544 Mbps and recently 44.376 Mbps).This means that it can easily be
used instead of a mesh of T-I or T-3 lines.
2. Frame Relay operates in just the physical and data link layers. This means it can easily be used as a backbone
network to provide services to protocols that already have a network layer protocol, such as the Internet.
3. Frame Relay allows bursty data.
4. Frame Relay allows a frame size of 9000 bytes, which can accommodate all local area network frame sizes.
5. Frame Relay is less expensive than other traditional WANs.
6. Frame Relay has error detection at the data link layer only. There is no flow control or error control. There is not
even a retransmission policy if a frame is damaged; it is silently dropped.
7. Frame Relay was designed in this way to provide fast transmission capability for more reliable media and for those
protocols that have flow and error control at the higher layers.
Frame Relay provides permanent virtual circuits and switched virtual circuits. Figure shows an example of a Frame
Relay network connected to the Internet.
The routers are used, to connect LANs and WANs in the Internet. In the figure, the Frame Relay WAN is used as one
link in the global Internet.
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VIII. ATM
1. Asynchronous Transfer Mode (ATM) is a standard switching technique designed to unify telecommunication and
computer networks.
2. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before
the actual data exchange begins.
3. ATM is a packet network. it supports multiplexing of various signals over the same physical channel.
4. It has been design to deliver voice, data and video information.
5. Asynchronous transfer mode (ATM) is a switching technique used by telecommunication networks that uses
asynchronous time-division multiplexing to encode data into small, fixed-sized cells.
6. This is different from Ethernet or Internet, which use variable packet sizes for data or frames. ATM is the core
protocol used over the synchronous optical network (SONET) backbone of the integrated digital services network
(ISDN).
7. The ATM provides data link layer services that run on the OSI's Layer 1 physical links. It functions much like small-
packet switched and circuit-switched networks, which makes it ideal for real-rime, low-latency data such as VoIP
and video, as well as for high-throughput data traffic like file transfers.
8. A virtual circuit or connection must be established before the two end points can actually exchange data.[5] [6]
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An ATM cell header can be one of two formats: UNI or NNI. The UNI header is used for communication between
ATM endpoints and ATM switches in private ATM networks. The NNI header is used for communication between
ATM switches. Unlike the UNI, the NNI header does not include the Generic Flow Control (GFC) field. Additionally,
the NNI header has a Virtual Path Identifier (VPI) field that occupies the first 12 bits, allowing for larger trunks
between public ATM switches.
In addition to GFC and VPI header fields, several others are used in ATM cell header fields. The following descriptions
summarize the ATM cell header fields illustrated in the above figure:
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Generic Flow Control (GFC) - Provides local functions, such as identifying multiple stations that share a single
ATM interface. This field is typically not used and is set to its default value of 0 (binary 0000).
Virtual Path Identifier (VPI) - In conjunction with the VCI, identifies the next destination of a cell as it passes
through a series of ATM switches on the way to its destination.
Virtual Channel Identifier (VCI) - In conjunction with the VPI, identifies the next destination of a cell as it passes
through a series of ATM switches on the way to its destination.
Payload Type (PT) - Indicates in the first bit whether the cell contains user data or control data. If the cell contains
user data, the bit is set to 0. If it contains control data, it is set to 1. The second bit indicates congestion (0 = no
congestion, 1 = congestion), and the third bit indicates whether the cell is the last in a series of cells that represent a
single AAL5 frame (1 = last cell for the frame).
Cell Loss Priority (CLP) - Indicates whether the cell should be discarded if it encounters extreme congestion as it
moves through the network. If the CLP bit equals 1, the cell should be discarded in preference to cells with the CLP
bit equal to 0.
Header Error Control (HEC) - Calculates checksum only on the first 4 bytes of the header. HEC can correct a
single bit error in these bytes, thereby preserving the cell rather than discarding it.
Medium: ATM network is capable of supporting high data rates up to 155 Mbps (approx) so Transmission medium
used for ATM is optical Fibers instead of coaxial cables in order to support high data rates
Limitations: ATM does not provide any error control or flow control at data link layer.
Applications:
1. ATM is a core protocol used over the SONET/SDH, backbone of the public switched telephone network
(PSTN) and Integrated Services Digital Network (ISDN), but its use is declining in favour of All IP.
2. It is also used in non-ISDN systems where the data rates are very high.
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VIII. CONCLUSIONS
Although all the techniques are based on end to end delivery of quantized data, there are many differences in terms of
sizes of the data quanta, application network types, controlling techniques etc. ATM uses fixed size packets (53 bytes)
for data communication; frame relay uses variable packet sizes depending on the type of information to be sent. Frame
Relay is used to connect Local Area Networks (LAN) and it is not implemented within a single area network contrast to
ATM where data transfers are within a single LAN.ATM is designed to be convenient for hardware implementation
and therefore, cost is higher compared to frame relay, which is software controlled. Therefore frame relay is less
expensive and upgrading is easier. Frame relay has a variable packet size. Therefore it gives low overhead within the
packet which results it an efficient method for transmitting data. Although fixed packet size in ATM, can be useful for
handling video and image traffic at high speeds, it leaves a lot of overhead within the packet, particularly in short
transactions.
REFERENCES
[1] W; Stallings., “High Speed Networks: TCP/IP and ATM Design Principles”, Printice Hall, Upper Saddle River, New Jersey 07458
[2] D; Tsaih ,G; La piotis, S; Pnawar,L; Tassiulas., “A Model-Based Performance management tool for ATM and Frame Relay Networks”, journal of
network system management,vol.6,No.4.1988.
[3] E; A. Khalil., “comparative performance of high speed networks carrying multimedia”,international journal of engineering sciences & emerging
technologies, august 2012.Volume 3.
[4] C; Kalmanek, H; Kanakia., “Rate Controlled Services for very high speed networks”, AT &T Bell Laboratories, Murray Hill, NY, 07974
[5] L.Greenstein., “Frame Relay and Frame-Based ATM: A Comparison of Technologies” .June 1995
[6] Stallings, William: ISDN and broadband ISDN with Frame Relay and ATM, Fourth edition, Prentice-Hall, Inc.1999.
[7] Stallings, William: High-Speed Networks, TCP/IP and ATM Design Principles, Prentice-Hall, Inc. 1998.
[8] C. A. Heckart, “The Guide to Frame Relay Networking,” Flatiron Publishing, 1994
[9] U. Black, "ATM: Foundation for Broadband Networks," Prentice-Hall, 1995, 425 pp.
[10] R.O. Onvural, "Asynchronous Transfer Mode Networks: Performance Issues," 2nd Ed., Artech House, 1995, 535 pp.
[11] B. Kumar, "Broadband Communications: A professional's guide to ATM, Frame Relay, SMDS, SONET, and BISDN," McGraw-Hill, 1994, 513
pp.
[12] R. Handel, M.N. Huber, and S. Schroder, "ATM Networks: Concept, Protocols, Applications," 2nd Edition, Addison-Wesley, 1994, 285 pp.
BIOGRAPHY
Kiran Barapatre is currently working as an Assistant Professor in the Department of Electronics and
Telecommunication Engineering at S. B. Jain Institute of Technology, Management & Research, and Nagpur. The
author completed his graduation in Electronics and Telecommunication Engineering from University of Pune in the
year 2009 as well as his post graduation (M.Tech) from Priyadarshini college of Engineerig, Nagpur in the year 2013.
His area of specialization is VLSI and area of interest is wireless communication.