Telephonic communications – Telephone line or system combined with diverse electrical... – Having transmission of a digital message signal over a...
Reexamination Certificate
1999-08-16
2003-04-08
Woo, Stella (Department: 2643)
Telephonic communications
Telephone line or system combined with diverse electrical...
Having transmission of a digital message signal over a...
Reexamination Certificate
active
06546090
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to system for communicating both voice and data over modems, and more particularly to high speed modems offering robust communication between a central office and a customer premises.
BACKGROUND OF THE INVENTION
High speed digital modems, such as Rate Adaptive Digital Subscriber Loop (“RADSL”) modems, are able to transfer data at high rates over the local loop, because they use frequencies which are significantly higher than the voice band frequencies used in Plain Old Telephone Service (“POTS”). By way of example, speech on a POTS system generally occurs in the frequency spectrum between about 0 Hz (“DC”) and about 4 kHz, whereas RADSL modems use the frequency spectrum of between about 20 kHz to about 1 MHz. High speed digital modems generally include error detection circuitry which measures the errors which occur during communications. By making such measurements, they are then able to update their statistical knowledge of the wire pair which extends between the subscriber's location and the central office. Using that statistical knowledge, the modems can select optimal operating speeds. These modems were originally proposed when it was thought that services, such as video-on-demand, would be desirable.
As modem technology has developed, another need has arisen, in that the Internet has become a popular medium for both personal and work related use.
While the high speeds of RADSL modems seem to be quite desirable, their use of high frequencies mean that they also need to be protected from high frequency noise, such as cross-talk from adjacent channels or adjacent loops in the loop cable binder, as such noise causes them to downwardly adjust their operating speeds. In order to avoid certain types of noise, RADSL modems typically require the use of filters, called POTS filters, together with splitters for isolating Public Switched Telephone Network (“PSTN”) equipment from the RADSL modems. Indeed, without POTS filters and POTS splitters, POTS signals directly interfere with the RADSL spectrum below about 20 kilohertz and the RADSL spectrum directly interferes with the POTS. POTS filters and POTS splitters reduce POTS signaling transients from interfering with RADSL data transmission. In addition, the use of the high RADSL bandwidth demands relatively high transmit power, which can cause distortions and dynamic range overload to POTS equipment.
Unfortunately, the manufacture and installation of POTS filters and splitters are expensive, and their use sometimes requires rewiring of the customer premises to ensure that all PSTN equipment is properly isolated from the RADSL modems and computing equipment. Consequently, it would be desirable to avoid the use of POTS splitters and filters, in order to avoid the expense they impose (e.g., purchase cost and possible rewiring of customer premises).
Accordingly, there appears to be a need for a mass market modem which has data transfer rates greater than the 33.6 Kbps attainable by PSTN modems, yet under the rate that requires the addition of POTS filters, splitters, etc. to address noise and deleterious transmission line effects often encountered in high speed DSL modems.
Yet another problem which is manifest in increased Internet access and data communications is the increasingly limited availability to the customer phone line or local loop for its original purpose, i.e., voice communications. Of course, one solution is for a customer to purchase an additional phone line. This, however, imposes an additional cost on the customer. Moreover, unless the line is dedicated by the customer for a specific purpose (which is poor utilization), the second line may not always be available when needed.
Accordingly, there is a need to provide an improved modem that accommodates data transmissions, while simultaneously allowing traditional voice operation of a telephone attached to the same line at the customer premise. It is particularly desirable to have such a modem that does not require the use of costly POTS filters and splitters.
SUMMARY OF THE INVENTION
Certain objects, advantages and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the advantages and novel features, the present invention is generally directed to a method and apparatus for communicating data across a local loop, in a manner that senses and dynamically adapts to the simultaneous transmission of POTS (e.g., voice or PSTN modem) information across the local loop. In accordance with one aspect of the invention, a method is provided for dynamically communicating data over a local loop using a modem comprising the steps of transmitting data in a full-band transmission state, sensing a band-limiting condition, and adjusting the transmission of data from the full-band transmission state to a band-limited transmission state, in response to the sensing step. The step of sensing a band-limiting condition includes both the detection of the onset of a condition indicating that the method should enter the band-limited transmission state, as well as the detection of the cessation of that condition, indicating that the method should enter the full-band transmission state from the band-limited transmission state.
In accordance with the method of the present invention, data may be transmitted by the modem across the local loop at the same time that POTS (e.g., voice or PSTN modem data) information is communicated across the same local loop. A significant aspect of the present invention is the dynamic allocation of the data transmission bandwidth, whereby the invention senses a condition indicative of whether POTS information is being communicated. If so, then the system shifts and/or narrows the data transmission bandwidth to allow for voice communications without interference from or with the data transmission. However, when no POTS information is being communicated, the invention dynamically allocates the data transmission bandwidth to utilize at least a portion, if not all, of the frequency band otherwise used for communicating voice information.
In accordance with the preferred embodiment, the method senses an off-hook condition of a telephone handset of a telephone electrically connected to the local loop. In use, a local loop extending between a customer premises and a central office branches, at the customer premise, to support multiple connections to the local loop. In this regard, the various branches or connections are typically routed throughout a customer premises to phone jacks, such as RJ-11 jacks. Multiple telephones may be plugged directly into these jacks for voice communication across the local loop. Similarly, a modem constructed in accordance with the present invention may be plugged directly into one of these jacks. The off-hook condition is preferably sensed by detecting either a change in impedance in the telephone line, or alternatively, a drop in line voltage across the telephone line.
In accordance with one embodiment of the invention, the full-band transmission state is defined by a transmission frequency bandwidth having a lower frequency boundary of less than about 15-20 kilohertz (and preferably less than 4 kilohertz). In the band-limited transmission state, the transmission frequency bandwidth has a lower frequency boundary of greater than 4 kilohertz. The significance of these values, for purposes of the invention, is that when no voice information is being communicated across the local loop, the transmission frequency bandwidth invades that frequency band generally dedicated to the transmission of voice information (i.e., the 0-4 kilohertz POTS frequency band). When, however, the invention senses that POTS information is being
Bingel Thomas
Bremer Gordon
Paradyne Corporation
Thomas Kayden Horstemeyer & Risley LLP
Woo Stella
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