Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1999-11-29
2004-01-06
Nguyen, Steven (Department: 2697)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S535000, C370S537000, C370S540000, C370S541000, C370S907000
Reexamination Certificate
active
06674771
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a transmission method and apparatus which transmits low-speed SDH (synchronous digital hierarchy) signals using a high-speed SDH frame.
(2) Description of the Related Art
In order to exploit the immense bandwidth available for transmission in an optical fiber, research in wavelength-division multiplexing (WDM) technology is driven. However, the bandwidth utilized by the WDM cannot be directly utilized by time-division multiplexed (TDM) systems due to the speed limitations posed by fiber dispersion. The WDM offers a practical solution of multiplexing many high-speed channels at different optical carrier frequencies and transmitting them over the same fiber. WDM systems are beginning to be deployed more widely in the field and are expected to play a greater role in the near future.
There has been rapid advances in the Internet technology in recent years. The demand for increasing the per-fiber transmission capacity of telecommunications networks continues to grow and the need for economical capacity upgrades becomes compelling. The existing TDM systems are not suitable to meet the higher-capacity demand due to the speed limitations. The WDM systems offer a practical solution of increasing the network transmission capacity and are suited for supporting the high-capacity demand. Recent developments of add-drop multiplexers and digital cross-connect systems have made possible a tremendous increase in the per-fiber transmission capacity.
However, there are at least two problems which relate to the WDM technology. The first is that the dispersion shifted fiber (DSF), widely deployed in the field, is generally suitable for long-haul transmissions of high-speed signals but is not suited for the WDM systems. For this reason, when deploying the DSF, a high-speed TDM system is needed. The second problem of the WDM technology is that the WDM technology offers a bit-rate-free transmission but the efficiency of transmission attained by the WDM is higher when many high-speed signals (e.g., 10 Gbps) are transmitted than when low-speed signals (e.g., 2.4 Gbps) in the same number are transmitted. In order to meet the high-capacity demand, the higher transmission efficiency is preferred.
By taking account of the above-mentioned matters, currently available upgrade options are: use of higher speed electrically-multiplexed systems; use of additional fibers; and use of wavelength multiplexing. Although a mix of three approaches will most likely be used in different parts of the network depending on the need and the economics, a transmission technology which utilizes high-speed electrically-multiplexed systems that operate in a transparent manner similar to the WDM systems is especially attractive. Since cost saving is made possible through fiber and amplifier sharing, the demand for such a technology becomes more compelling.
FIG. 13
shows a configuration of high-speed WDM systems which are connected to low-speed electrically-multiplexed systems via working and protection optical-fiber cables.
In the configuration of
FIG. 13
, reference numerals
1
(
1
) through
1
(
4
) denote 2.4-Gbps electrically-multiplexed systems which includes four working channels #
1
through #
4
and one protection channel, both having a data rate of 2.4 Gbps. Reference numerals
2
(
1
) through
2
(
5
) denote high-speed WDM systems which use the wavelength multiplexing. Various optical-fiber cables accommodating the working and protection channels are connected between the 2.4-Gbps systems and the WDM systems. For example, an optical signal sent from one (the working channel #
1
) of the working channels #
1
-#
4
of the 2.4-Gbps system
1
(
1
) reaches the WDM system
2
(
1
), and the WDM system
2
(
1
) outputs a wavelength-multiplexed optical signal. Optical signals sent from the protection channels of the 2.4-Gbps systems
1
(
1
) and
1
(
4
) reach the WDM system
2
(
5
), and the WDM system
2
(
5
) outputs a wavelength-multiplexed signal.
The WDM configuration of
FIG. 13
offers a bit-rate-free transmission and makes the signal processing simple. When a failure of any of the WDM systems
2
(
1
) through
2
(
4
) occurs, the faulty WDM system is substituted for by the WDM system
2
(
5
) by suitably switching the optical-fiber cables.
In the WDM systems
2
(
1
) through
2
(
5
) of
FIG. 13
, the failure recover capability of
1
protection channel to
4
working channels is provided since all the optical signals of the working channels #
1
-#
4
and the protection channel are transported to these WDM systems.
FIG. 14
shows a configuration of a high-speed electrically-multiplexed system which is connected to a low-speed electrically-multiplexed system.
In the configuration of
FIG. 14
, reference numerals
1
denote 2.4-Gbps electrically-multiplexed systems which include four working channels #
1
through #
4
and one protection channel, both having a data rate of 2.4 Gbps. The two low-speed systems
1
are connected by an optical-fiber cable containing the working channels #
1
through #
4
and the protection channel. Reference numeral
3
denotes a 10-Gbps electrically-multiplexed system which has a data rate of 10 Gbps. In the high-speed system
3
, the four 2.4-Gbps signals sent by the low-speed system
1
are electrically multiplexed into a 10-Gbps high-speed signal, and then the high-speed multiplexed signal is converted into an optical signal. The high-speed system
3
transmits the optical signal on a first optical-fiber cable as the working channel, and regenerates an optical signal on a second optical-fiber cable as the protection channel.
In the high-speed electrically-multiplexed system
3
of
FIG. 14
, only the failure recover capability of
1
protection channel to
1
working channel can be provided since the low-speed signals of the working channels #
1
-#
4
sent by the low-speed system
1
are terminated at the input of the system
3
.
In the configuration of
FIG. 14
, the low-speed system
1
which includes the four working channels #
1
through #
4
and one protection channel has a failure recovery capability of 80%, but the high-speed system
3
has only the failure recovery capability of 50%. That is, there is a problem in that the use of the high-speed electrically-multiplexed system
3
will lower the failure recovery capability. Further, when the vender of the low-speed systems
1
is different from the vendor of the high-speed system
3
, the configuration of
FIG. 14
does not necessarily assure the compatibility between the low-speed systems
1
and the high-speed system
3
.
By taking account of the above-mentioned matters, the demand for a transmission technology which utilizes high-speed electrically-multiplexed systems that operate in a transparent manner similar to the WDM systems becomes more compelling than before.
The fundamental concept to meet the above-mentioned demand for the WDM-like transmission technology is that four low-speed signals are simply multiplexed into a high-speed signal at a transmit-side network element and the high-speed signal is demultiplexed at a receive-side network element. For example,
FIG. 12
shows a multiplexing of four 2.4-Gbps signals into a 10-Gbps signal and demultiplexing of the 10-Gbps signal.
As shown in
FIG. 12
, a parallel-to-serial conversion (P/S) of 4 inputs to 1 output is provided at a transmit-side network element to multiplex the 2.4-Gbps signals #
1
through #
4
of the four channels into a 10-Gbps signal. This 10-Gbps signal is serially transported on an optical-fiber cable to a receive-side network element. A serial-to-parallel conversion (S/P) of 1 input to 4 outputs is provided at the receive-side network element to demultiplex the 10-Gbps signal into the reconstructed 2.4-Gbps signals #
1
through #
4
.
The correspondence between the reconstructed low-speed signals and their channels is unknown to the receive side of the network, and it is necessary that the n
Katten Muchin Zavis & Rosenman
Nguyen Steven
Volper Thomas E.
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