Dynamic bandwidth allocation within a communications channel

Details Dynamic bandwidth allocation within a communications channel Dynamic bandwidth allocation within a communications channel

1999-12-23

2004-08-10

Vanderpuye, Kenneth (Department: 2661)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via time channels

C370S468000

Reexamination Certificate

active

06775303

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to multiplex communications systems, and more particularly to the field of bandwidth allocation in such a system. Specifically, this invention addresses dynamic allocation of bandwidth in the local loop environment.
BACKGROUND OF THE INVENTION
In the 1950s, telecommunications companies began to develop high bandwidth digital communications technologies in order to allow more phone calls to be simultaneously transmitted over copper wire. The first digital transmission carrier, called T
1
, was developed by AT&T in 1956 and is still in use today. A T
1
line is capable of transmitting 1.544 Megabits per second (Mbps). Originally utilized to connect telephone central offices, in the early 1980s T
1
lines began to be utilized in the local loop.
The local loop is often thought of as the connection between a local telecommunications office and an end-user. The “end-user” could be an actual customer of telephone service, a bandwidth reseller such as an Internet service provider, or even a site maintained for the convenience of a telecommunications company. Although the local loop is commonly referred to as the “last mile,” local loop lengths in the United States are more typically about 2.5 miles, and some local loop implementations having a maximum range of almost 50,000 feet.
Digital transmission carriers such as T
1
are usually “channelized” into multiple channels using Time Division Multiplex (TDM) technology. TDM channels are created by a multiplexer that divides a digital carrier into separate, individual time segments. Each time segment is allocated for the exclusive use of a single channel. The standard T
1
line is divided in this manner into
24
separate channels. Each channel transmits 8 bits of digital data before the next channel begins transmitting. Since every channel sends 8 bits down the T
1
line in turn, a series of 192 bits (8 bits times 24 channels) is created before the process can repeat. Before each series of bits, the multiplexer adds an additional bit called the framing bit. Thus, data on a T
1
line is sent in 193 bit long “frames.” These frames are transmitted about 8,000 times per second.
Each channel in a T
1
line is called a DS-0 channel. Similarly, the total T
1
line is often referred to as a DS-1 line. Thus, there are 24 DS-0 channels in a DS-1 line. Each DS-0 channel transmits at 64 k bps. This transmission speed is the ideal bandwidth for voice communication, since voice communication is generally sampled and digitally converted into 8 bit words 8,000 times per second. In addition to serving voice communication, these DS-0 channels are commonly used for digital data communication.
The individual DS-0 channels can be operated in either a “switched” or “dedicated” fashion. Switched data channels allow the communication on the channel to be switched on and off. Voice communication is an example of switched data, in that there are times when the voice channel is active or “off-hook,” and other times when a voice channel is inactive or “on-hook.” Data communication can also operate in a switched fashion, sometimes actively communicating data and other times being inactive.
In order for a switched data channel to be switched on and off, it is necessary to signal the current status of the communication. In a voice channel, for example, it is necessary to indicate when a telephone receiver is picked up to place a phone call (signaled by an off-hook status indication), and to indicate when a local line should start ringing.
In contrast, a dedicated communication channel does not transmit status information and is always active. Although a dedicated channel may only be transmitting useful information at specific times, it does not ever become inactive.
Another important aspect of channelized digital transmission carriers is the possibility of combining multiple channels to obtain a higher bandwidth digital data path. For instance, three DS-0 channels can be combined into a single 192 k bps data communications path. Techniques for combining separate channels into a single, higher bandwidth digital communications path are well-known in the prior art.
It is common to have switched and unswitched data appearing simultaneously on the same channelized communication link. For example, a T
1
to an office could be utilized to carry both voice communications over switched data channels and computer communications with the Internet over dedicated data channels. Traditionally, some DS-0 channels in the T
1
line would be dedicated to carrying the switched, voice communications, while other DS-0 channels would carry the unswitched data communications.
Unfortunately, this fixed allocation of bandwidth on a local loop T
1
line wastes bandwidth, since the switched DS-0 channels carry no data when they are idle. A better approach is to dynamically allocate the bandwidth on an as-needed basis. With dynamic bandwidth allocation, the inactive voice channels can be utilized to handle unswitched data communications when no voice calls are active, and yet would be available for voice communications when a signal to make the voice channel active is received.
The basic idea of allowing the same data channels to be used for both switched and unswitched communication is not new. One approach to doing so is implemented through Asynchronous Transfer Mode (ATM) technology. This technology is able to successfully provide and manage bandwidth for voice, video, and data applications. To accomplish this task, ATM utilizes “cell relay” techniques instead of relying on data channels created by time division multiplexing. In cell relay, each communications task, whether data, voice, or video, is divided into fixed size packets, or “cells,” that contain a small amount of data and header information to direct the cell. Each cell is then transmitted with all other cells across the same communications path, and is directed toward its destination by the header information. Once the cells arrive at their destination, the communication is then reconstructed. While ATM may be the best solution for large-scale bandwidth-management problems, it is overly complex, too resource intensive, and too expensive for handling variable bandwidth assignments on the local loop.
A better approach is to keep the DS-0 channels created via time division multiplexing, and instead develop simpler techniques of dynamic bandwidth allocation. Unfortunately, the currently known prior art methods utilizing this approach fail to provide bandwidth allocation in a simple yet effective manner.
For instance, in U.S. Pat. No. 4,763,321 issued to Rozenblit and assigned to Bell Communications Research, Inc., a method for handling variable bandwidth allocation by changing the allocation of DS-0 channels is presented. This invention relates to Distributed Burst Switching Systems (DBSS), a system that uses virtual circuits in the manner of ATM, X.25 and Frame Relay. However, DBSS passes the frames containing the data through standard DS-0 channels. In standard DBSS, no virtual circuit can utilize more than one DS-0 channel, hence limiting transmission speeds on a virtual circuit to no more than 64 k bps. The Rozenblit invention allows a single virtual circuit to utilize more than one DS-0 channel. To accomplish this, no packets are transmitted between two nodes in a link until a 32 bit header is passed to the next node identifying the virtual circuit and specifying the number of DS-0 channels to be utilized for the virtual circuit. When a transmission between two nodes is completed, the transmitting node sends a 32-bit flag concluding the communication. When the ending flag is received, the DS-0 channels that had been utilized for the communication are freed up for use in another transmission. Unfortunately, the Rozenblit invention suffers from the same basic problems as the ATM technique, in that it imposes needless complexity and overhead on the relatively straight-forward situation of dynamic bandwidth allocation on the local loop.
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