Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-08-29
2001-10-02
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S433000
Reexamination Certificate
active
06298065
ABSTRACT:
TECHNICAL FIELD
This invention relates to telecommunications systems, and more particularly, to providing subscriber line cards deployed in such telecommunications systems.
BACKGROUND OF THE INVENTION
Telecommunications has evolved from transmitting only voice to a multimedia vehicle for communication. Modern users of telecommunications services are supported by subscriber lines which not only transmit voice but also send data transmissions generated by facsimiles and Internet access. A common implementation of a modem subscriber line interconnects a twisted cable pair from a subscriber's customer premises equipment to a subscriber line card associated with a digital switching system. The line card provides functions of battery, overvoltage protection, ringing, supervision, hybrid and testing (commonly referred to as the BORSHT functions) and converts analog voice band frequencies into a stream of pulse code modulation octets carried at 64 kilobits per second across the digital switching system and the rest of the public-switched telecommunications network (PSTN).
Current line card implementations operate in a mode for optimizing voice transmission. The transmission of data signals requires use of modulator/demodulator devices (modems) for transforming digital data signals into analog signals which are carried within the standard voice band frequency limitations of the telecommunications network. Current voice band frequency limitations of the PSTN hold the per subscriber line modem data transmission rate to approximately 56 kilobits per second. Unfortunately, the 56 kilobits per second transmission rate is unacceptably slow for many telecommunications service subscribers who routinely send data via the PSTN. To obtain higher transmission rates, it is common for these subscribers to bind two or more analog subscriber lines together through special modems working in the role of inverse multiplexers. Special modems, or any increase in the number of lines used per subscriber, are problematic because of the increase in average holding time of all telephone calls served by the switch. Further, increased subscriber line usage invalidates current standards for concentration of subscriber lines per switch and the provisioning of intraswitch time slot facilities.
The real-life impact of an increase in concentration of subscriber lines per switch is the more frequent denial of dial tone or the receipt of busy signals by subscribers who are accustomed to consistent and reliable access to the PSTN. The current state of subscriber line concentration is especially troubling since switch resources are unnecessarily occupied. This is because a significant amount of data transmissions between a subscriber line and the PSTN carry idle data (that is, non-useful packets of information) which is a well known and common phenomenon of data connections. Therefore there is a need in the art for decreasing the occurrence of blocked access to the telecommunications network while efficiently accommodating prolonged data transmissions.
SUMMARY OF THE INVENTION
This need is addressed and a technological advance is achieved in the telecommunications art by a multi-mode line card for determining and establishing a mode of operation consistent with subscriber needs. More particularly, a multi-mode subscriber line card operates in a packet transmission mode (hereinafter referred to as “mode
2
”) for allowing a faster bit rate transmission from a line card to a digital switching system but can be automatically switched to a voice only transmission mode (hereinafter referred to as “mode
1
”). Other modes of operation may accommodate new voice companding techniques or packet transmission of compressed voice signals.
In the preferred embodiment, the multi-mode line card serves a plurality of subscribers in a local telecommunications system. When off-hook status is detected by a subscriber line interface circuit, a determination is made as to whether a distinct packet mode initiation signal is received within a predetermined time period. If no such signal is received, the subscriber line operates in mode
1
in which well-established filtering, sampling and companding standards are used for voice transmissions.
If a packet mode initiation signal is received, the multi-mode line card establishes filters, analog-to-digital (A/D) sampling and line coder/decoders for receiving and decoding packet transmissions in mode
2
. The parameters of the filters, A/D sampling and coding are established in an exchange with customer premises equipment initiating the packet call. A packet protocol exchange, which occurs between the line card and the customer equipment for the duration of the packet mode state, allows the removal and insertion of packets to and from the subscriber line via a packet queue. The packet queue is shared across multiple subscriber line interface circuits and reduces the number of circuit resources which must be held active during packet mode calls. A shared transmission capacity (hereinafter referred to as a “packet link”) is used for reading and writing packets of data into and out subscriber line associated queues. Advantageously, prolonged periods of non-useful data transmission, such as when a user is simply viewing information received on a personal computer but not actively sending data, are not transmitted to the digital switch. The transmission of only meaningful data decreases the inefficient use of intraswitch time slot facilities and minimizes the prevention of other users from transmitting useful data In this manner, subscriber line congestion is reduced by effectively allocating switch resources.
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B. S. Bosik, “Time-compression Multiplexing, Squeezing Digits Through Loops”,At&T Bell Laboratories Record, Feb. 1984, pp. 22-25.
Computer Networks—Protocols, Standards and Interfaces, Prentice-Hall, Inc., 1987, pp. 298-301.
Dombkowski Kevin Eugene
Witschorik Charles Arthur
Ghose Mony
Lucent Technologies - Inc.
Mac Intyre John B.
Nguyen Chau
Nguyen Phuongchau Ba
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