Network access method and network access server therefor

Details Network access method and network access server therefor Network access method and network access server therefor

1999-06-14

2003-10-21

Jung, Min (Department: 2663)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S466000, C379S093010

Reexamination Certificate

active

06636519

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to modems for enabling data communication between multiple data signal sources over a combination of analog and digital telephone company lines, and more particularly relates to techniques for processing signals at the inputs and outputs of such modems.
DESCRIPTION OF THE PRIOR ART
FIG. 1
describes prior art for enabling communication between computers connected to analog telephone lines and computers coupled together over a digital network. Digital computers C
1
-C
12
communicate with a telephone company network TC
1
via conventional modems M
1
-M
12
, respectively. Each of computers C
1
-C
12
is a separate source of digital data signals representing digital data. In a well known manner, modems M
1
-M
12
convert the digital data signals into corresponding analog telephone signals for transmission over conventional pairs of analog telephone wires A
1
-A
12
, respectively. The analog telephone wires typically extend to a telephone company central station at which the analog telephone signals are converted to digital telephone signals for transmission and switching through the telephone company digital network. The telephone company typically uses a digital conversion called CODEC which samples the analog telephone signals at 8,000 samples per second using 8 digital bits per sample. The resulting digital telephone signals typically are transmitted over a four wire digital telephone span line commonly called a T1 line. Each T1 telephone line carries 24 digital channels that are multiplexed onto the T1 lines by a well known time division multiplex technique. For each of the digital channels, the telephone company adds layers of call set-up information according to the conventions established by the International Standards Organization (ISO). The call set-up information typically includes the telephone number being called.
Assuming the twelve digital channels of information representing data from computers C
1
-C
12
are directed to a single user location, they typically will be switched to digital telephone line T1 which is terminated by a PBX box P
1
at the user's location. PBX box P
1
demultiplexes the 24 channels of digital telephone signals on line T1 and converts each digital signal to a corresponding analog telephone signal. Thus, the 24 channels of multiplexed digital telephone signals on line T1 are divided into 24 separate analog telephone signals on 24 separate pairs of analog telephone lines. Twelve pairs of the analog telephone lines A
13
-A
24
are represented in
FIG. 1
as inputs to conventional modems M
13
-M
24
. Modems M
13
-M
24
are identical to modems M
1
-M
12
.
For incoming calls on line T1 from computers C
1
-C
12
, modems M
13
-M
24
demodulate the analog telephone signals and covert them into digital data signals. The digital data signals typically are in a serial digital form suitable for transmission through an RS-232 digital port. Each of the twelve channels for modems M
13
-M
24
may be connected to a terminal server TS
1
. Such servers have software and an output port which distribute data on a local area network, such as token ring network TRN
1
, among computers, such as computers C
13
-C
24
.
As shown in
FIG. 1
, analog telephone signals are used to represent digital data at two different points in the system, i.e., analog conductors A
1
-A
12
and analog conductors A
13
-A
24
. Conversion between digital and analog signals occurs twice irrespective of whether a telephone call is incoming or outgoing.
For an incoming call from computers C
1
-C
12
, modems M
1
-M
12
convert the digital data signals from the computers to analog telephone signals that are transmitted to the telephone company network TC
1
. Network TC
1
converts the analog telephone signals to corresponding digital telephone signals. At the receiving station, PBX unit P
1
converts the digital telephone signals to analog telephone signals that are demodulated by modems M
13
-M
24
to generate network digital data signals suitable for use by server TS
1
and computers C
13
-C
24
.
For outgoing calls from computers C
13
-C
24
, the network digital data signals generated by the computers are converted to corresponding analog telephone signals by modems M
13
-M
24
. The analog telephone signals are converted by PBX unit P
1
to digital telephone signals suitable for transmission on the T1 line. After transmission in digital form, network TC
1
converts the digital telephone signals into analog telephone signals that are transmitted over analog telephone lines A
1
-A
12
. The analog telephone signals are demodulated by modems M
1
-M
12
and are converted to digital form for use by computers C
1
-C
12
.
The data from computers C
1
-C
24
appears in RS-232 form at two points in the system, i.e., on one set of conductors connected to modems M
1
-M
12
and on another set of conductors connected to modems M
13
-M
24
. Before signals originating at computers C
1
-C
12
can be used on network TRN
1
, the RS-232 form of the signals at modems M
13
-M
24
must be converted to blocks of digital data suitable for transmission on network TRN
1
.
The applicant has found that the prior art requirement for twice converting signals between digital and analog form and twice converting signals to and from RS-232 form in order to allow digital data sources to communicate via telephone company networks is inefficient and expensive. In addition, the need for separate busses for the distribution of data from modems M
13
-M
24
to terminal server TS
1
creates time delays and requires substantial duplication of circuitry.
In Hugh E. White, “A T1-Based DSP Modem For Interfacing Voice And Packet Networks” (IEEE 1988), an all digital system converts PCM samples on a T1 trunk to and from data bits on a virtual circuit of an X25 trunk. However, the described structure of the system is insufficient to enable the high speed transfer of data between multiple modems with sufficient flexibility to provide efficient utilization of the modems for different applications.
In Paul Desmond, “Primary Access adds PAD To Network Access System,” (
Nework World,
p. 17, Mar. 4, 1991), certain functions of a network access system are identified. Output from DSP cards which perform a modem function is said to route to DCP cards over an RS-232 interface. The DCP cards are said to perform a packetizing function. This arrangement also is not sufficiently flexible or fast enough to properly utilize the capabilities of the DSP cards.
SUMMARY OF THE INVENTION
In order to overcome the deficiencies of the prior art, a primary object of the invention is to create a bus structure that increases the efficiency of data communication between one group of computers connected to analog telephone lines and a second group of computers connected to a local area network.
Another object of the invention is to demodulate telephone signals to form packets of signals that can be stored and analyzed to facilitate the demodulation of the telephone signals.
Still another object of the invention is to reduce the number of conversions between digital and analog form required for communication by digital data sources via telephone company networks employing both analog and digital telephone lines.
Still another object of the invention is to provide an improved bus for transmitting signals between a single digital telephone line and a plurality of modems.
Yet another object of the invention is to provide a bus of the foregoing type which employs a switch enabling bidirectional transmission of either (1) data from or to a telephone line; or (2) control signals under the control of a processing unit.
Still another object of the invention is to provide an improved bus for transmitting signals between a single local area network and a plurality of modems.
Yet another object of the invention is to provide a modem system in which communication channels are coupled from a telephone line to the modems over a circuit switched time division miltiplex bus and in which data is coupled from the modems to a network ov

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