Communications networks propagate information signals through a complex array of apparatus. Such information signals include voice and data, with the latter originating from a virtually limitless number of information sources, such as facsimile, text, video, etc. The communications media used in such networks can be homogeneous or diversified and presently include wire, optical fiber, radio, satellite and submarine cable.
The different types of information signals conducted through the network combined with the myriad of dissimilar types of network apparatus give rise to situations in which system performance is impaired. Such situations, in the main, arise in the context of the transmission of data as opposed to voice signals and, in particular, to the transmission of high-speed data signals. For example, the telecommunications networks include echo suppressors and cancellers necessary for long-haul voice communications which are incompatible with certain types of data communications. Or, for example, the network includes certain digital coding and decoding devices (codecs) which do not operate harmoniously with data transmission above a certain rate. Or, in still another example, digital networks include apparatus which rearranges incoming groups of digital channels carrying voice and data information into different outgoing groups and such apparatus requires complex signal conditioning applied to the digital channels conveying data when such channels constitute more than a predetermined percentage of the incoming digital channels.
One solution to the problem of incompatibility between certain information signals and specific types of communications apparatus is to route the troublesome information signals through segregated networks, also known as private-line networks, which are especially reserved and "conditioned" for such signals. Conditioning is a term which denotes that a communication facility has been engineered to assure no more than some preselected amount of signal impairment. While such segregation provides a satisfactory solution, the cost of such networks, especially the cost of conditioning, can exceed the objectives of certain system applications.
Another solution for certain forms of the referenced incompatibility problem is to transmit a tone to identify data signals. For example, a 2100 Hertz tone, as presently defined in the CCITT V.25 standard, is presently transmitted to identify a data signal and, depending on the phase characteristic of this tone, to disable echo suppressors or to disable both echo suppressors and echo cancellers. While this technique also works satisfactorily for certain system applications, the tone must be transmitted for a minimum time period so as to be able to distinguish between the tone and a naturally occurring speech harmonic. This minimum time interval makes the use of tones incompatible for use with fast start-up modem procedures. In addition, use of the tone as an information signal identifier with many present "standard" transmission schemes requires a revision of such schemes to accommodate the transmission of a tone in an already occupied time span. Such revision is difficult, if not impossible, to obtain.
In light of the foregoing, it can be seen that the problem of incompatibility between certain types of information signals and network apparatus has not been optimally solved and a variety of solutions have been developed which are not acceptable for all system applications. With the burgeoning growth of data carried by communications networks, it would be extremely desirable if a universally applicable technique could be devised which could improve the present situation.