Multiplex communications – Channel assignment techniques – Using a separate control line or bus for access control
Reexamination Certificate
1998-11-30
2003-11-11
Vincent, David (Department: 2661)
Multiplex communications
Channel assignment techniques
Using a separate control line or bus for access control
C370S458000, C370S236000
Reexamination Certificate
active
06647021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an interface protocol for digital communications, and more particularly, to an interface protocol for an asymmetrical digital subscriber line (ADSL) subscriber bus interface (SBI).
2. Background
The telecommunications industry has developed schemes for transmitting telephony signals in digital formats, for example, in the form of time division multiplexed (TDM) signals for transmission over a physical layer interface, such as a subscriber bus interface (SBI). The SBI receives data signals divided into frames. Each SBI frame includes time slots which are assigned payload data representing digitized telephony signals for conventional telephone services.
An example of a conventional telephone service is a plain old telephone service (POTS), which uses a digital format that is known to a person skilled in the art. An example of an SBI frame format for upstream transmission used in Litespan line cards made by DSC corporation of Plano, Tex. is shown in FIG.
1
. The SBI frame format of
FIG. 1
includes 32 time slots numbered consecutively from 0 to 31. Each of the slots within the conventional SBI frame includes 16 bits. As shown in
FIG. 1
, for time slot #
0
, abbreviated as “TS
0
”, bits are interleaved with reserved bits denoted by “R”, which are not assigned to carry information in the upstream SBI protocol.
POTS digital signal 0 bytes, abbreviated as “DS
0
”, are assigned to time slots #
1
-
3
,
5
-
15
,
17
-
23
, and
25
-
31
within the SBI frame. Each of the DS
0
signals has a format similar to that of the TS
0
cell. Each DS
0
byte includes 8 bits which are interleaved with eight reserved bits similar to the interleaving of the TS
0
byte with the eight reserved bits within time slot #
0
as shown in FIG.
1
.
In the SBI frame as shown in
FIG. 1
, time slot #
4
is assigned to carry a “SIG” byte which identifies a signaling channel. The SIG byte in time slot #
4
is required in the conventional SBI protocol and is known to a person skilled in the art. Time slot #
16
is assigned a “SRQ” byte which identifies a SBI service request channel. The SRQ byte in time slot #
16
is required in the SBI communication protocol and is known to a person skilled in the art. Time slot #
24
includes an SBI data link channel which is abbreviated as “DL” in FIG.
1
. The DL byte in time slot #
24
which is assigned to carry the SBI data link channel is required in the SBI communication protocol and is known to a person skilled in the art.
FIG. 2
shows a diagram of a conventional POTS channel bank where POTS line cards
102
a
,
102
b
, . . .
102
n
are connected to the backplane conventional bank control unit (BCU)
110
through a backplane interface such as a conventional SBI
106
. In the conventional POTS SBI channel bank, each of the line cards
102
a
,
102
b
, . . .
102
n
is capable of supporting up to 24 conventional POTS DS
0
channels and 4 conventional POTS control channels. A DS
0
channel is 64 kilobits per second (kbps) digital channel each having a transmission rate of 8,000 bytes per second, each byte including 8 bits. Each of the DS
0
channels supports one conventional POTS interface or its equivalent. SBI
106
, which is on the backplane of the BCU
110
, allows the BCU to process upstream DS
0
signals from one or more POTS line cards
102
a
,
102
b
, . . .
102
n
. A conventional SBI channel bank system is capable of carrying upstream and downstream traffic separately, with the upstream traffic defined as transmission in the direction from one of the POTS line cards
102
a
,
102
b
, . . .
102
n
to the BCU
110
, and the downstream traffic defined as transmission in the direction from the BCU to the POTS line card. The direction of the upstream traffic is indicated by arrows
104
a
,
104
b
, . . .
104
n
leading from the POTS line cards
102
a
,
102
b
, . . .
102
n
to the BCU
110
, respectively.
For the upstream traffic, each of the line cards
102
a
,
102
b
, . . .
102
n
has a serial backplane traced to the BCU
110
through the SBI
106
, which is physically provided on the backplane of the BCU
110
. The conventional SBI frame format allows each of the line cards
102
a
,
102
b
, . . .
102
n
to support 32 channels each capable of providing a transmission rate of 64 kbps. The 32 channels may include 24 conventional DS
0
channels, 4 control channels, 2 data link channels, a framing channel and a reserved channel. The DS
0
channels, the control channels, the data link channel, the framing channel and the reserved channel are multiplexed in the time domain by using a conventional time division multiplexing (TDM) technique, which is known to a person skilled in the art. A clock
108
is provided for the BCU
110
and operates at a clock rate of 4.096 MHZ. In the conventional POTS SBI channel bank system, every other bit time on the clock
108
is unused, thereby producing an affective data rate of 2.048 MHZ, which is one half of the clock rate of 4.096 MHZ, on the backplane trace of the BCU
110
. The effective data rate of 2.048 MHZ is sufficient to support 32 time slots, with each time slot sufficient for supporting a conventional 64 kbps channel. As shown in
FIG. 1
, a conventional SBI frame which has a duration of 125 &mgr;s is long enough to carry one 8-byte per SBI time slot for each of the 32 channels each having a data rate of 64 kbps.
Broadband traffic of data in an asynchronous transfer mode (ATM) format is carried by conventional asymmetrical digital subscriber lines (ADSL). The ATM data are transmitted in the form of ATM cells assigned to the respective time slots in the SBI frames, each frame having a duration of 125 &mgr;s. The transmission of the ATM cells over the ADSL is called “ATM over ADSL.” Examples of digital signals which are carried in the ATM format include digital video signals and computer data signals. On the other hand, telephony signals are usually carried over the conventional DS
0
channels which are time division multiplexed and assigned to the SBI time slots according to the SBI frame format as shown in FIG.
1
. It is desirable to be able to transmit the conventional POTS DS
0
channels and the ATM data within the same SBI frame. It is also desirable to be able to convey both ATM and POTS traffic over existing conventional channel bank backplanes.
However, the conventional SBI frame format as shown in FIG.
1
and described above is not capable of supporting both the POTS DS
0
channels and the broadband ATM traffic with a desirable data rate, when each bit in the DS
0
cells is interleaved with a reserved bit. Therefore, there is a need for an upstream subscriber bus interface protocol which allows an SBI frame to carry both POTS and ATM traffic. Furthermore, there is a need for an upstream SBI data format which allows an SBI frame to be processed by either a conventional narrowband BCU or a broadband ADSL bank control unit (ABCU). There is yet a further need for an upstream SBI protocol which allows mixed connections between the line cards and the control unit, for example, a mixed connection between a conventional POTS line card and a broadband ABCU, or a mixed connection between an ADSL line card and a conventional narrowband BCU.
SUMMARY OF THE INVENTION
The present invention satisfies these needs. In accordance with the present invention, a method of formatting an SBI frame comprises the steps of:
assigning asynchronous transfer mode (ATM) payload bytes to some SBI time slots within the SBI frame; and
assigning plain old telephone service (POTS) digital signal bytes to some of the SBI time slots within the SBI frame, wherein the SBI frame is configured for transmission from a line card selected from the group including an asymmetrical digital subscriber line (ADSL) line card and a POTS line card to a control unit selected from the group including an ADSL bank control unit (ABCU) and a narrowband bank control unit (BCU).
In one embodiment, the SBI frame includes an overhead byte. The
Appanna Prakash
Baradaran Hamid
Huang Tony
Koai Tom
Lee Jensheng
Alcatel USA Sourcing L.P.
Sewell V. Lawrence
Vincent David
LandOfFree
Asymmetrical digital subscriber line (ADSL) upstream... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Asymmetrical digital subscriber line (ADSL) upstream..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Asymmetrical digital subscriber line (ADSL) upstream... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3174351