Telephonic communications – Telephone line or system combined with diverse electrical...
Reexamination Certificate
2003-04-14
2004-06-29
Woo, Stella (Department: 2643)
Telephonic communications
Telephone line or system combined with diverse electrical...
C379S093050
Reexamination Certificate
active
06757368
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of wired communication systems, and, more specifically, to the networking of devices using telephone lines.
BACKGROUND OF THE INVENTION
FIG. 1
shows the wiring configuration for a prior-art telephone system
10
for a residence or other building, wired with a telephone line
5
. Residence telephone line
5
consists of single wire pair which connects to a junction-box
16
, which in turn connects to a Public Switched Telephone Network (PSTN)
18
via a cable
17
, terminating in a public switch
19
, apparatus which establishes and enables telephony from one telephone to another. The term “analog telephony” herein denotes traditional analog low-frequency audio voice signals typically under 3 KHz, sometimes referred to as “POTS” (“plain old telephone service”), whereas the term “telephony” in general denotes any kind of telephone service, including digital service such as Integrated Services Digital Network (ISDN). The term “high-frequency” herein denotes any frequency substantially above such analog telephony audio frequencies, such as that used for data. ISDN typically uses frequencies not exceeding 100 Khz (typically the energy is concentrated around 40 Khz). The term “telephone line” herein denotes electrically-conducting lines which are intended primarily for the carrying and distribution of analog telephony, and includes, but is not limited to, such lines which may be pre-existing within a building and which may currently provide analog telephony service. The term “telephone device” herein denotes, without limitation, any apparatus for telephony (including both analog telephony and ISDN), as well as any device using telephony signals, such as fax, voice-modem, and so forth.
Junction box
16
is used to separate the in-home circuitry from the PSTN and is used as a test facility for troubleshooting as well as for wiring new telephone outlets in the home. A plurality of telephones
13
a
,
13
b
, and
13
c
connects to telephone line
5
via a plurality of telephone outlets
11
a
,
11
b
,
11
c
, and
11
d
. Each telephone outlet has a connector (often referred to as a “jack”), denoted in
FIG. 1
as
12
a
,
12
b
,
12
c
, and
12
d
, respectively. Each telephone outlet may be connected to a telephone via a connector (often referred to as a “plug”), denoted in
FIG. 1
(for the three telephone illustrated) as
14
a
,
14
b
, and
14
c
, respectively. It is also important to note that lines
5
a
,
5
b
,
5
c
,
5
d
, and
5
e
are electrically the same paired conductors.
There is a requirement for using the existing telephone infrastructure for both telephone and data networking. In this way, the task of establishing a new local area network in a home or other building is simplified, because there would be no additional wires to install. U.S. Pat. No. 4,766,402 to Crane (hereinafter referred to as “Crane”) teaches a way to form LAN over two-wire telephone lines, but without the telephone service.
The concept of frequency domain/division multiplexing (FDM) is well-known in the art, and provides means of splitting the bandwidth carried by a wire into a low-frequency band capable of carrying an analog telephony signal and a high-frequency band capable of carrying data communication or other signals. Such a mechanism is described for example in U.S. Pat. No. 4,785,448 to Reichert et al. (hereinafter referred to as “Reichert”). Also is widely used are xDSL systems, primarily Asymmetric Digital Subscriber Loop (ADSL) systems.
Relevant prior art in this field is also disclosed in U.S. Pat. No. 5,896,443 to Dichter (hereinafter referred to as “Dichter”). Dichter is the first to suggest a method and apparatus for applying such a technique for residence telephone wiring, enabling simultaneously carrying telephone and data communication signals. The Dichter network is illustrated in
FIG. 2
, which shows a network
20
serving both telephones and a local area network. Data Terminal Equipment (DTE) units
24
a
,
24
b
, and
24
c
are connected to the local area network via Data Communication Equipment (DCE) units
23
a
,
23
b
, and
23
c
, respectively. Examples of Data Communication Equipment include modems, line drivers, line receivers, and transceivers. DCE units
23
a
,
23
b
, and
23
c
are respectively connected to high pass filters (HPF)
22
a
,
22
b
, and
22
c
. The HPF's allow the DCE units access to the high-frequency band carried by telephone line
5
. In a first embodiment (not shown in FIG.
2
), telephones
13
a
,
13
b
, and
13
c
are directly connected to telephone line
5
via connectors
14
a
,
14
b
, and
14
c
, respectively. However, in order to avoid interference to the data network caused by the telephones, a second embodiment is suggested (shown in FIG.
2
), wherein low pass filters (LPF's)
21
a
,
21
b
, and
21
c
are added to isolate telephones
13
a
,
13
b
, and
13
c
from telephone line
5
. Furthermore, a low pass filter must also be connected to Junction-Box
16
, in order to filter noises induced from or to the PSTN wiring
17
. As is the case in
FIG. 1
, it is important to note that lines
5
a
,
5
b
,
5
c
,
5
d
, and
5
e
are electrically the same paired conductors.
However, the Dichter network suffers from degraded data communication performance, because of the following drawbacks:
1. Induced noise in the band used by the data communication network is distributed throughout the network. The telephone line within a building serves as a long antenna, receiving electromagnetic noise produced from outside the building or by local equipment such as air-conditioning systems, appliances, and so forth. Electrical noise in the frequency band used by the data communication network can be induced in the extremities of telephone line
5
(line
5
c
or
5
a
in
FIG. 2
) and propagated via telephone line
5
throughout the whole system. This is liable to cause errors in the data transportation.
2. The wiring media consists of a single long wire (telephone line
5
). In order to ensure a proper impedance match to this transmission-line, it is necessary to install terminators at each end of telephone line
5
. One of the advantages of using the telephone infrastructure for a data network, however, is to avoid replacing the internal wiring. Thus, either such terminators must be installed at additional cost, or suffer the performance problems associated with an impedance mismatch.
3. In the case where LPF
21
is not fitted to the telephones
13
, each connected telephone appears as a non-terminated stub, and this is liable to cause undesirable signal reflections.
4. In one embodiment, LPF
21
is to be attached to each telephone
13
. In such a configuration, an additional modification to the telephone itself is required. This further makes the implementation of such system complex and costly, and defeats the purpose of using an existing telephone line and telephone sets ‘as is’ for a data network.
5. The data communication network used in the Dichter network supports only the ‘bus’ type of data communication network, wherein all devices share the same physical media. Such topology suffers from a number of drawbacks, as described in U.S. Pat. No. 5,841,360 to the present inventor, which is incorporated by reference for all purposes as if filly set forth herein. Dichter also discloses drawbacks of the bus topology, including the need for bus mastering and logic to contend with the data packet collision problem. Topologies that are preferable to the bus topology include the Token-Ring (IEEE 803), the PSIC network according to U.S. Pat. No. 5,841,360, and other point-to-point networks known in the art (such as a serial point-to-point ‘daisy chain’ network). Such networks are in most cases superior to ‘bus’ topology systems.
The above drawbacks affect the data communication performance of the Dichter network, and therefore limit the total distance and the maximum data rate such a network can support. In addition, the Dichter network typically requires a complex and therefore cos
Browdy and Neimark
Serconet Ltd.
Woo Stella
LandOfFree
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