Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-05-22
2004-03-02
Rao, Seema S. (Department: 2666)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S507000, C375S354000, C375S355000, C375S357000, C375S359000, C375S360000, C714S775000, C714S789000, C714S798000
Reexamination Certificate
active
06700903
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to passive optical networks and more particularly to upstream scrambling systems for a passive optical network.
2. Description of Background Art
The use of passive optical networks (PONs) is increasing significantly as demand for additional speed and bandwidth in networks is increasing. The International Telecommunication Union (ITU) has published a standard addressing broadband optical access based upon PON. This standard, the ITU G.983.1 “Broadband optical access systems based on Passive Optical Networks (PON)” (October 1998), is incorporated by reference herein in its entirety. Another standard, the ITU-T I.432.1 “B-ISDN user-network interface—Physical layer specification: General Characteristics” (February 1999), sets forth the recommended standard for a layer
1
interface and is incorporated by reference herein in its entirety.
FIG. 1
is an illustration of a PON according to the preferred embodiment of the present invention. The PON includes an optical line termination unit (OLT)
102
, an optical distribution network (ODN)
104
, and one or more optical network units (ONUs)
106
A,
106
B. The ODN
104
offers one or more optical paths between one OLT
102
and one or more ONUs
106
. Each optical path is defined between reference points S and R in a specific wavelength window. The two directions for optical transmission in the ODN are identified as (1) the downstream direction for signals traveling from the OLT
102
to the ONU(s)
106
, and (2) the upstream direction for signals traveling from the ONU(s)
106
to the OLT
102
.
In one example, the PON architecture in
FIG. 1
is used to support asynchronous transfer mode (ATM) networking over PON. For ease of discussion, the present invention will be discussed with reference to ATM over a PON. However, it will be apparent to persons of ordinary skill in the art, that other protocols are supported by the present invention. In one embodiment, the ODN
104
is a optical fibre cable which can include conventional passive optical splitters in order to connect the OLT
102
to multiple ONUs
106
in order to share the capacity of the fiber. Because of the passive splitting, special actions are required with respect to privacy and security. Moreover, in the upstream direction a time division multiple access (TDMA) protocol is used.
The interface at the reference points S/R and R/S in
FIG. 1
is defined as IF
PON
. This is a PON-specific interface that supports all the protocol elements necessary to allow the transmission between OLT
102
and ONUs
106
and is described in more detail in the ITU G.983.1 standard, for example. Point S corresponds to a point on the optical fibre just after the OLT
102
for downstream transmissions and just after the ONU
106
for upstream transmissions. Point R corresponds to a point on the optical figure just before the ONU
106
downstream transmissions and just before the OLT
102
for upstream transmissions.
The Optical Network Unit (ONU)
106
interfaces over the IF
PON
to the OLT
102
. Together with the OLT
102
, the ONU
106
is responsible for providing transparent ATM transport service.
In this architecture, the ATM transport protocols at an IF
PON
are described as consisting of Physical Media Dependent layer, Transmission Convergence layer, and ATM layer. This architecture is only intended to address the transport of ATM, further detail is contained in ITU Recommendation I.732 which is incorporated by reference herein in its entirety. The Physical Media Dependent layer would include the modulation schemes for both the upstream and downstream channels (they may be different). It may be possible for the specification to allow for more than one type of Physical Media Dependent layer in a single direction. The Transmission Convergence layer will be responsible for managing the distributed access to the upstream PON resource across the multiple ONUs
106
. This will directly affect the resulting ATM quality of service (QoS). The ATM protocols should see no change in the way they operate over the PON. Within both the OLT
102
and the ONU
106
, the functions performed at the ATM layer at both an OLT
102
and ONU
106
would include cell relaying.
The Optical Distribution Network
104
provides the optical transmission means from the OLT
102
towards the users and vice versa. It utilizes passive optical components.
FIG. 2
is a functional illustration of an optical line termination unit
102
. The OLT
102
is connected to the switched networks via standardized interfaces, e.g., VB5.x, V5.x, NNI's. At the distribution side, it presents optical accesses according to the agreed requirements, in terms of bit rate, access latency, etc. The OLT
102
includes three parts: the service port function
202
; an ODN interface
204
; and a multiplexor (MUX)
206
for virtual circuit (VC) grooming.
The MUX
206
provides VP connections between the service port function and the ODN interface and different VPs are assigned to different services at IF
PON
. Various information such as main contents, signalling, and OAM flows are exchanged by using VCs of the VP.
The ODN interface
204
handles inserting ATM cells into the downstream PON payload and extracting ATM cells from the upstream PON payload.
In general, the ODN
104
provides the optical transmission medium for the physical connection of the ONUs
106
to the OLT
102
. Individual ODNs
104
may be combined and extended through the use of optical amplifiers as described in ITU Recommendation G.982, which is incorporated by reference herein in its entirety. However, the use of optical amplifiers are not necessary for the operation of the present invention.
The ODN
104
can include passive optical elements such as single-mode optical fibres and cables, optical fibre ribbons and ribbon cables, optical connectors, passive branching components, passive optical attenuators, and splices. More detailed information concerning passive optical components is described in ITU Recommendation G.671, which is incorporated by reference herein in its entirety. Additional information describing optical fibres and cable is described in ITU Recommendation G.652, which is incorporated by reference in its entirety.
In the context of the reference configuration illustrated in
FIG. 1
,
FIG. 3
is an illustration of a physical configuration of an optical distribution network
104
. As described above, the two directions for optical transmission in the ODN are (1) the downstream direction for signals travelling from the OLT
102
to the ONU(s)
106
and (2) the upstream direction for signals travelling from the ONU(s)
106
to the OLT
102
.
Transmission in downstream and upstream directions can take place on the same fibre and components (duplex/diplex working) or on separate fibres and components (simplex working).
The ODN
104
offers one or more optical paths between one OLT
102
and one or more ONUs
106
. Each optical path is defined between reference points in a specific wavelength window.
One aspect of PON communication as defined in the ITU G.983.1 standard is that ATM cells transmitted in the upstream direction (ONU
106
to OLT
102
) are scrambled. However, this scrambling operation is flawed. The G.983.1 standard requires scrambling of the data in the cell. If the cell is not received, the cell is resent using the same scrambling operation such that the exact same sequence of bits are resent. There are many reasons why a transmitted cell is not received. One such reason is that the data pattern (e.g., a pattern including a long string of binary zeroes or ones) is such that the receiver does not recognize the cell. In such situations, simply resending the same data will not remedy the problem at the receiver, e.g., the OLT
102
.
What is needed is a passive optical network system and method for enabling upstream data to be sent such that the receiver will recognize and receive the cell even if the data pattern of the originally sent cell cannot be recognized by the
Boyd Edward W
Perkins Barry A
Puchalski Douglas R
Fenwick & West LLP
Rao Seema S.
Scheibel Robert C.
Terawave Communications, Inc.
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