Method and apparatus for network transmission capacity enhancement for the telephone circuit switched network

Abstract

Adjunct apparatus for increasing network transmission capacity provides a low-cost, efficient solution for increasing the network transmission capacity of the existing telephone circuit switched network, while keeping the current network equipment unchanged. A Local Switch Network (LSN) Adjunct (LSNA) and a Tandem / Toll Switch Network (TSN) Adjunct (TSNA) interface with standard network elements, such as switches and cross connect equipment. These network adjuncts, comprising a set of low-bit rate speech coders, a dynamic timeslot manager and other supporting functions, advantageously transmit to and receive from a T1 / T3 / OC3 / E1 trunk. More than one channel of voice is carried on one 64 Kbps DS0 timeslot, while still maintaining the voice at toll quality. A sub-timeslot and sub-timeslot bundling are introduced in the standard T1 or E1 frame where each sub-timeslot is analogous to a single bit of the typical eight bit word to provide more than 24 or 30 voice channels respectively. Inband control information is generated for carrying over a T1 or E1 trunk, for example, for mapping sub-timeslot bundles to channels. Conventional out-of-band signaling is provided via SS-7 or other out-of-band signaling system.

Description

BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] The present invention relates generally to the field of voice signal compression in telecommunications networks to enhance transmission capacity and, more particularly, to the field of providing voice compression in existing telephone circuit switched networks that employ T1 and E1 frame formats while keeping the network infrastructure unchanged. [0003] 2. Description of the Relevant Art [0004] Pulse code modulation for sampling voice signals and modulating a pulse coded data stream for transmission has been known since the 1960's. Two forms of pulse code modulation are the so-called μ-Law and the A-law modulation formats of T1 and E1 frames respectively. Both share the common principle that 8 bit pulse code words describe a speech signal or, alternatively, carry data or facsimile. In the T1 frame, 24 such eight bit words and a framing bit comprise a 193 bit frame. Each eight bit word describes a voice signal sample of a d...

AI Technical Summary

Benefits of technology

[0012] The present invention creates a tremendous advantage in the existing telephone circuit switched network by increasing the network transmission capacity up to seven fold. Local and toll network adjuncts are provided in the public switched telephone network which interface to standard network elements and provide for voice compression within T1 and E1 frames. In keeping with the present invention, each channel or timeslot, normally comprising an 8 bit word is regarded, not as comprising 8 bit words, but as comprising individual bits or sub-timeslots such that a frame comprises eight times as many sub-timeslots as timeslots or channels. For example, referring briefly to FIG. 2(a) in a T1 frame there are, according to the present invention, 192 sub-timeslots which are dynamically allocated to voice / data / fax communications according to whether there is speech activity or tone / data is recognized. A 193rd timeslot 101 is still reserved for framing. A decrease in bandwidth is achieved by coding the voice so that it occupies 1, 2, 3, 4 or more bits or sub-timeslots within a conventional timeslot or channel and so the traditional channel is shared among voice communications. Any time fewer than 8 sub-timeslots are utilized for a voice communication, transmission capacity is saved.

[0014] In the case of a T1 or E1 network, instead of transmitting a voice channel in one 64 Kbps DS0 timeslot, the present invention utilizes the emerging technologies of low-bit rate speech coders and high-speed Digital Signal Processors (DSPs) to increase the network transmission capacity by effectively reducing the bandwidth required of each voice channel, while still maintaining the voice at toll quality. Therefore, this invention provides a method and apparatus to increase the network transmission capacity without increasing the network cross-connect equipment and the transmission trunk facilities.

Problems solved by technology

A minor disadvantage is that the decompression and reassembly of the original voice communications carried over such a channel may take some time and so result in some delay, but the delay is not significant.

These are minor disadvantages in comparison to the enhancement in transmission capacity obtained.

Moreover, practically none of the original speech content of the voice communication is lost.

The T carrier channel or timeslot is inherently inefficient, for example, timeslot 102, because the timeslot frequently carries periods of silence, silence that could be filled by voice segments of other voice communications.

The E1 frame format is inefficient for the same reasons.

Nevertheless, with either kind of caller, there is considerable inefficiency in communication.

To be competitive in today's telephony business, reducing the cost of handling telephone calls and increasing the existing network capacity have become crucial issues.

However, this is a very expensive venture.

Dedication of a whole timeslot or 8 bit word as described above to voice is very expensive in terms of bandwidth utilization.

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