Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1999-02-11
2003-04-29
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S493000
Reexamination Certificate
active
06556565
ABSTRACT:
The invention generally relates to long distance communications and more particularly to apparatus and methods for assessing whether or not a link or a path between endpoints in an internet protocol (IP) network is potentially suitable for transmission of telecommunications signals of synchronous signals origin. Examples of sources and destinations of such signals may include, but are not limited to, any of voice, data and image terminal apparatus or any combination thereof.
BACKGROUND
In telecommunications, time is an essential component in the information content of signals representing audible sounds and in the signal formats of many visibly reproducible signals, such as television signals. By contrast in data communications, preservation of the time component is not nearly so important. The field of telecommunications has long been operated on the basis of circuit switching principles for providing voice communications. In the later half of this century circuit switching networks have carried an ever increasing volume of data communications. The typical telecommunications digital network for communications of voice, digitally encoded in accordance with a pulse code modulation (PCM) standard, provides a continuous bit rate service that is concatenated as n×64 Kb/s channels. Such telecommunications facilities and networks are said to be circuit switched or synchronous networks, which by their physical natures are most suited to transporting signals between communications terminals which produce synchronous signals, for example telephone speech signals. The primary characteristic of circuit switching is that when one or more physical channels are assigned to a given communication circuit, to provide a service, that channel assignment is reserved for the exclusive use of that service continuously throughout the duration of the service provision. This characteristic of circuit switching is substantially irrelevant for data communications and is of such cost that alternatives, known as packet switched networks, have been developed for the express purpose of providing less costly data communications.
Some time ago, a packet switch, with the trademark SLl was introduced by the assignee, for improving the efficient transport of data signals. In contrast to the steady repetitive nature of PCM signals, data signals for the most part, are bursty or asynchronous in nature. Thus to accommodate the efficient transmission of data signals, a data burst is arranged into a packet of convenient length along with a header which specifies a destination. After a packet has been assembled, a high speed transmission path is allocated, only for a time sufficient to transport the packet of data toward its destination. During the packet transport, the packet is in sole possession of the transmission path. After the packet is transported, the transmission path is available for the transport of another packet, possibly from a different source. The event of transporting at least one packet of data from a point of origin to a point of destination is termed a data call, however, the number of data packets transmitted throughout the duration of a data call is generally unlimited. Packet networks operated in accordance with the internet protocol (IP) have recently become the data communications equivalent of the publicly accessible switched telephone networks (PSTNs). Users of data communications services commonly refer to the “internet” in the same fashion as users of voice communications refer to the “telephone”. If considered on a basis of bulk data transport per unit of cost, the transport of information signals using the IP is very economical as compared with the PSTN. Although digitized voice can be transported via a packet network operated in accordance with the IP, the wide variances of delay caused by the operating characteristics of an IP network tend to deteriorate, distort and occasionally even obliterate the time component. Interrupted, delayed and out of sequenced reception of voice signal packets are common occurrences from time to time in a typical packet system, particularly during higher traffic periods. In other words the IP does not provide a consistent quality of service (QOS) for voice communications and the like.
The general evolution of packet systems toward functionality as broad band carriers of information of synchronous origin is exemplified in a paper by A. Thomas et al, titled Asynchronous Time-Division Techniques: An Experimental Packet Network Integrating Video communication, which was published at the 1984 International Switching Symposium, May 7-11 in Florence Italy. Another example was published in a 1987 IEEE paper by Jean-Pierre Coudreuse and Michel Serval, titled Prelude: An Asynchronous Time-division Switched Network.
More recently, a broadband communications standard for supporting a variety of both synchronous and asynchronous communication requirements has been widely adopted by telecommunications providers, and is now referred to as the asynchronous transfer mode (ATM) of telecommunications. The recommended standards are defined by the ATM Forum and are available from several publishers including Prentice Hall of Englwood Cliffs, N.J. 07632, under the title ATM User-Network Interface Specification Version 3.0 (ISBN 0-13-2258633). One commercially available product is sold by the assignee with the trademark Magellan. Networks operable in the ATM standard are usually termed ATM systems or ATM networks. ATM systems are sophistically compromised to preserve the essence of the time component in synchronous signals yet to some extent reap the economies of packet switching. However, as the IP is strictly directed to the efficient transport of data through any packet network facility, accordingly the IP does not take advantage of the ATM potential for preserving the time component.
The quality of audible speech, reproduced from IP transport, may approach the quality of signals transmitted via the PSTN. Such is usually contingent upon all of the packet network facilities, involved with the transport of the signals, being operated at small fractions,of their capacities. Otherwise the quality may degenerate such that verbal information becomes unintelligible. Never the less, it has become commonplace for some personal computer users to link with an IP network for telephone like voice communications, as well as for data communications. Economies envisaged with utilization of IP networks for synchronous signals communications, have generated considerable development in adaptations of end terminal facilities and software. These adaptations provide degrees of compensation for the irregular delays in packet transport to improve the quality of audibly reproduced speech.
Commercial entities which depend heavily upon telecommunications usage, for their activities, spend significantly upon purchases of telephony services from PSTN and other circuit switched telephone service providers. For some time they have considereded the IP, wishing it were a practical alternative. Improvements in the adaptation of end terminal facilities and software for telephone conversations have made the IP network a potentially practical alternative to the PSTNs. Users depending heavily upon telecommunications find the potential low cost of usage of IP in comparison with the PSTN to be very attractive. Nevertheless, this attraction is tempered with the recognition that from time to time one or more links between the network endpoints related to a telephone call may provide such poor QOS as to be unacceptable. Furthermore the QOS can be unpredictably variable, changing from good to marginal to bad and to good again within an hour.
The effects of packet delays and losses as well as end terminal clocking dissimilarities are discussed in a previous U.S. patent application Ser. No. 08,982,925 assigned to Northern Telecom Ltd., the assignee of this application. The previous application teaches improvements useful in telephone facilities, terminals and personal computers which reduce the potentially deleter
Astle Ian
Cheung Cuthbert
Marshall John
Ward David P.
Kizou Hassan
Ly Anh-Vu H
Nortel Networks
Nortel Networks Limited
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