Broadband networks

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The ideal telecommunication network would have the following characteristics: broadband, multi-media, multi-point, multi-rate and economical implementation for a diversity of services (multi-services) [1][2]. The Broadband Integrated Services Digital Network (B-ISDN) provides these characteristics in today's networks. Asynchronous Transfer Mode (ATM) is a target technology for meeting these requirements and is widely deployed as a broadband network [2].

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[edit] Modern communication services

Society is becoming more informationally and visually oriented. Personal computing facilitates easy access, manipulation, storage, and exchange of information. These processes require reliable transmission of data. The means or media for communicating data are becoming more diverse. Communicating documents by images and the use of high-resolution graphics terminals provide a more natural and informative mode of human interaction than just voice and data. Video teleconferencing enhances group interaction at a distance. High-definition entertainment video improves the quality of pictures but requires much higher transmission rates.

These new data transmission requirements may require new transmission means other than the present overcrowded radio spectrum [3][4]. A modern telecommunications network (such as the broadband network) must provide all these different services (multi-services) to the user.

[edit] Differences between traditional (telephony) and modern communication services

Conventional telephony communicates using:

  • the voice medium only,
  • connects only two telephones per call, and
  • uses circuits of fixed bit-rates.

In contrast, modern communication services depart from the conventional telephony service in these three essential aspects. Modern communication services can be:

  • multi-media,
  • multi-point, and
  • multi-rate.

These aspects are examined individually in the following three sub-sections [5].

[edit] Multi-media

A multi-media call may communicate audio, data, still images, or full-motion video, or any combination of these media. Each medium has different demands for communication qualities, such as:

  • bandwidth requirement,
  • signal latency within the network, and
  • signal fidelity upon delivery by the network.

The information content of each medium may affect the information generated by other media. For example, voice could be transcribed into data via voice recognition and data commands may control the way voice and video are presented. These interactions most often occur at the communication terminals, but may also occur within the network [2][3].

[edit] Multi-point

A few examples will be used to contrast point-to-point communications versus multi-point communications. Traditional voice calls are predominantly two party calls, requiring a point-to-point connection using only the voice medium. To access pictorial information in a remote database would require a point-to-point connection that sends low bit-rate queries to the database, and high bit-rate video from the database. Entertainment video applications are largely point-to-multi-point connections, requiring one way communication of full motion video and audio from the program source to the viewers. Video teleconferencing involves connections among many parties, communicating voice, video, as well as data. Thus offering future services requires flexible management of the connection and media requests of a multi-point, multi-media communication call [3][4].

[edit] Multi-rate

A multi-rate service network is one which allocates transmission capacity flexibly to connections. A multi-media network has to support a broad range of bit-rates demanded by connections, not only because there are many communication media, but also because a communication medium may be encoded by algorithms with different bit-rates. For example, audio signals can be encoded with bit-rates ranging from less than 1 kbit/s to hundreds of kbit/s, using different encoding algorithms with a wide range of complexity and quality of audio reproduction. Similarly, full motion video signals may be encoded with bit-rates ranging from less than 1 Mbit/s to hundreds of Mbit/s. Thus a network transporting both video and audio signals may have to integrate traffic with a very broad range of bit-rates [3][5].

[edit] A single network for multiple services

[edit] Traditional networks

Traditionally, the various services mentioned above were carried via separate networks – voice on the telephone network, data on computer networks or local area networks (LANs), video teleconferencing on private corporate networks, and television on broadcast radio or cable networks.

These networks are largely engineered for a specific application and are not suited for other applications. For example, the traditional telephone network is too noisy and inefficient for bursty data communication. On the other hand, data networks which store and forward messages using computers have very limited connectivity, usually do not have sufficient bandwidth for digitised voice and video signals, and suffer from unacceptable delays for the real-time signals. Television networks using the radio or the cable medium are largely broadcast networks with minimum switching facilities [2][3].

[edit] Benefits of a single network for multiple services

It is desirable to have a single network for providing all these communication services in order to achieve the economy of sharing. This economy motivates the general idea of an integrated services network. Integration avoids the need for many overlaying networks, which complicate network management and reduce the flexibility in the introduction and evolution of services. This integration is made possible with the advances in broadband technologies and high speed information processing [2][3].

[edit] Fiber optics for broadband networks and MSO

While there are multiple network structures capable of supporting broadband services, an ever increasing percentage of broadband and MSO providers are opting for fiber optic network structures to support both present and future bandwidth requirements.

CATV (cable television), HDTV (high definition television), VoIP (voice over internet protocol), and broadband internet are some of the most common applications now being supported by fiber optic networks, in some cases directly to the home (FTTh – Fiber To The Home). These types of fiber networks incorporate a wide variety of products to support and distribute the signal from the central office to an optic node, and ultimately to the subscriber (end-user).

[edit] Broadband Traffic

[edit] Types of traffic carried by the network

Modern networks have to carry integrated traffic consisting of voice, video and data. The Broadband Integrated Services Digital Network (B-ISDN) satisfies these needs [7]. The types of traffic supported by a broadband network can be classified according to three characteristics [6]:

  • Bandwidth: is the amount of network capacity required to support a connection
  • Latency: is the amount of delay associated with a connection. Requesting low latency in the Quality of Service (QoS) profile means that the cells need to travel quickly from one point in the network to another.
  • Cell-delay variation (CDV): is the range of delays experienced by each group of associated cells. Low cell-delay variation means a group of cells must travel through the network without getting too far apart from one another.

[edit] Requirements of the different types of traffic

The different types of traffic found in a broadband network (with examples) and their respective requirements are summarized in Table 1.

Table 1: Network traffic types and their requirements [6]
TRAFFIC TYPE EXAMPLE REQUIRED BANDWIDTH CELL-DELAY VARIATION LATENCY
Constant Voice, Guaranteed circuit emulation Minimal Low
Variable Compressed Video Guaranteed Variable Low
Available Data Not guaranteed Widely variable Variable

[edit] See also

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References

[1] ATM Congestion Control, Fang Lu, http://www.cse.ohio-state.edu/~jain/cis788-95/ftp/atm_cong/index.html, Last accessed 1 March 2005.

[2] Saito, H., Teletraffic Technologies in ATM Networks, Artech House, 1993. ISBN 0-89006-622-1.

[3] Hui J., “Switching and traffic theory for integrated broadband networks”, Kluwer Academic Publishers, 1990. ISBN 0-7923-9061-X.

[4] Sexton M., Reid A., “Broadband Networking: ATM, SDH and SONET”, Artech House Inc., Boston, London, 1997. ISBN 0-89006-578-0.

[5] Ferguson P., Huston G., “Quality of Service: Delivering QoS on the Internet and in Corporate Networks”, John Wiley & Sons, Inc., 1998. ISBN 0-471-24358-2.

[6] ATM Traffic Control, Mark Juliano, http://www.byte.com/art/9412/sec10/art5.htm, Last accessed 3 March 2005.

[7] Congestion Control and Traffic Management in ATM Networks, Invited submission to Computer Networks and ISDN Systems, Vol 28 (1996), 1723-1738, Raj Jain, http://www.cse.ohio-state.edu/~jain/papers/ftp/cnis/index.html, Last accessed 7 March 2005.

[edit] External links