Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-10-18
2002-12-24
Vanderpuye, Ken (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S477000
Reexamination Certificate
active
06498796
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for preventing multiple stages of compression and decompression in a voice communication system, in particular, in a communication link traversing multiple networks.
2. Description of Related Art
In modern voice communication systems, a voice communication link may include one or more wide area networks (“WAN”). The inclusion of a WAN in a voice communication link normally requires equipment to convert a voice signal transmitted on the link to a format acceptable for transmission over the WAN. When a voice communication link includes a plurality of WAN, the quality of a voice signal transmitted thereon may be reduced by multiple conversions of the voice signal to a format for transmission over the WAN as explained with reference to FIG.
1
.
FIG. 1
(Prior Art) is an example of a voice communication system
10
having a voice communication link that includes a plurality of WAN
11
,
21
.
As shown in
FIG. 1
, the voice communication system
10
includes call signal equipment
12
,
22
, two WAN
11
,
21
, a digital switch
30
and a plurality of Voice Conversion Units (VCU)
14
,
24
,
34
,
44
. The call signal equipment
12
,
22
may be any equipment that may transmit and receive a voice signal, e.g., a facsimile machine, telephone, modem, or another digital switch or private switching network. The WAN
11
,
21
is any network that transmits data packets using any protocol including time division multiplex (TDM), frame relay (FR), or internet protocol (IP). The digital switch
30
is a switch that routes voice signals to one or more locations.
The VCU
14
,
24
,
34
, and
44
converts voice signals received on a subscriber side link
16
,
26
,
36
, and
46
to packet signals that may be transmitted over a WAN on a network side link
18
,
28
,
38
, and
48
. The VCU
14
,
24
,
34
, and
44
also converts packet signals received on the network side link
18
,
28
,
38
, and
48
to voice signals that may be transmitted to subscriber equipment on the subscriber side link
16
,
26
,
36
, and
46
. Prior to conversion to a packet signal, a voice signal may be a pulse code modulation (“PCM”) or other common voice format signal. The PCM voice signal is converted to a plurality of packets to enable the voice signal to traverse the WAN
11
,
21
. It is noted in order to optimize network bandwidth utilization, the PCM voice signal received on the subscriber side
16
,
26
,
36
, and
46
is compressed prior to conversion to packets for transmission across a WAN
11
,
12
. Packets signals received on the network side
18
,
28
,
38
, and
48
are decompressed by VCU
14
,
24
,
34
, and
44
.
In the voice communication system
10
shown in
FIG. 1
, the voice communication link between call signal equipment
12
and call signal equipment
22
includes four VCUs
14
,
24
,
34
, and
44
, two WAN
11
,
21
and a digital switch
30
. Thus, a voice signal transmitted from either equipment
12
,
22
to the other
22
,
12
will be: 1) compressed and converted from a voice signal to a packet signal by VCU
14
or
44
; 2) transmitted over a first WAN
11
or
21
; converted and decompressed back into a voice signal by VCU
24
or
34
; 3) transmitted or switched from one VCU
24
or
34
to another VCU
34
or
24
by digital switch
30
; 4) compressed and converted from a voice signal to a packet signal by VCU
34
or
24
; 5) transmitted over a second WAN
21
or
11
; and 6) converted and decompressed back into a voice signal by VCU
44
or
14
and transmitted to equipment
22
or
12
. Consequently, a voice signal transmitted between equipment
11
and
21
will be compressed and decompressed twice, thus, VCU
24
, switch
30
and VCU
34
form a “tandem link”, which may reduce the voice quality of the voice signal.
Ideally, when a voice signal is compressed and decompressed more than once (a tandem link occurs) in a voice communication link, the extra stages of compression and decompression should be eliminated, i.e., the tandem link should detected and bypassed. However, in order to prevent multiple compressions and decompressions in a voice communication link, the voice communication system
10
must be able to detect when a tandem link (multiple compressions and decompressions) exists in a particular voice communication link. For example, the voice communication system
20
shown in
FIG. 2
, includes a plurality of WAN
11
,
21
, but a voice communication link between call signal equipment
12
and
32
or
22
and
32
traverses only a single WAN
11
or
21
and does not include a tandem link.
Thus, a voice signal transmitted from either equipment
12
to
32
or
22
to
32
will be: 1) compressed and converted from a voice signal to a packet signal by VCU
14
or
44
; 2) transmitted over a first WAN
11
or
21
; converted and decompressed back into a voice signal by VCU
24
or
34
; and 3) transmitted or switched from one VCU
24
or
34
to call signal equipment
32
via link
31
. Thus, the voice communication link between equipment
12
or
22
and
32
includes only one stage of compression and decompression. Thus, although voice communication system
20
includes two WAN
11
,
21
, not every voice communication link includes multiple compressions and decompressions. Accordingly, a need exists for a method that detects when a tandem link or multiple compressions and decompressions occur in a voice communication link and prevents the same to improve the voice quality of a voice signal on such a link.
SUMMARY OF THE INVENTION
The present invention includes a method of determining whether a voice communication link between a first subscriber unit and a second subscriber unit in a voice communication system includes a tandem link. The first and second subscriber units transmit and receive a voice signal on the voice communication link. In addition, the voice communication system includes a plurality of voice conversion units where each of the plurality of voice conversion units has a subscriber side link and network link. Each of the plurality of voice conversion units adds a HAIL signal to the voice signal provided on the subscriber side link. They also detect a HAIL signal or an ACK signal in the voice signal received on the subscriber side link. Further, they add an ACK signal to the voice signal provided on the subscriber side link when a HAIL signal or an ACK signal is detected on the voice signal received on the subscriber side link. A tandem link is detected when the ACK signal is detected in the voice signal received on the subscriber side link.
Each of the plurality of voice conversion units may also attempt to detect the ACK signal in the voice signal received on the subscriber side link after generating a voice signal with the ACK signal. In this case, a tandem link is detected when an ACK signal is detected in the voice signal received on the subscriber side link after generating a voice signal with the ACK signal. In a preferred embodiment, the tandem link may be detected when an ACK signal is detected in the voice signal received on the subscriber side link within a predetermined period of time after generating a voice signal with the ACK signal.
In another preferred embodiment, each of the plurality of voice conversion units may attempt to determine if a notch code exists in the received voice signal and avoiding tandem link detection when the notch is detected. The method each unit employs in this case includes attempting to detect whether the voice signal generated to the subscriber side link includes a notch code. Then, removing the notch code from voice signal generated to the subscriber side link when the notch code is detected in the voice signal generated to the subscriber side link and providing the modified voice signal on the subscriber side link. This ensures that each unit generates voice signals to the subscriber without the notch code so other units receiving voice signal without the notch code will know that the sending unit is no
McNeill Scott
Wang David T. K.
Nuera Communications, Inc.
Richman, Esq. Merle W.
Vanderpuye Ken
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