Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2001-01-12
2003-04-08
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S449000
Reexamination Certificate
active
06546014
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to access networks, and more particularly to a passive optical access network.
BACKGROUND OF THE INVENTION
The explosion of the Internet and the desire to provide multiple communications and entertainment services to end users have created a need for a broadband network architecture that improves access to end users. Although the bandwidth of backbone networks has experienced a substantial growth in recent years, the bandwidth provided by access networks has remained relatively unchanged. Thus, the “last mile” still remains a bottleneck between a high capacity LAN or Home network and the backbone network infrastructure.
Digital Subscriber Line (DSL) and Cable Modem (CM) technologies offer some improvements over more conventional last mile solutions. However, these technologies still do not provide enough bandwidth to support emerging services such as Video-On-Demand (VoD) or two-way video conferencing. In addition, not all customers can be covered by DSL and CM technologies due to distance limitations.
One broadband access network architecture that offers a solution to the “last mile” problem is a point-to-multipoint passive optical network (PON). A point-to-multipoint PON is an optical access network architecture that facilitates broadband communications between an optical line terminal (OLT) and multiple remote optical network units (ONUs) over a purely passive optical distribution network. A point-to-multipoint PON utilizes passive fiber optic splitters and combiners to passively distribute optical signals between the OLT and the remote ONUs.
FIGS. 1A and 1B
illustrate the management of network traffic in a point-to-multipoint PON. As an example, the PON is shown to include an OLT
102
and three ONUs
104
,
106
and
108
, although the PON may include additional ONUs. Referring to
FIG. 1A
, the OLT includes an optical transmitter
110
that sends downstream traffic containing ONU-specific information blocks
1
,
2
and
3
to the ONUs. The downstream traffic is optically broadcasted by a passive optical splitter/combiner
112
into three separate signals that each carries all of the ONU-specific information blocks. The ONUs
104
,
106
and
108
include optical receivers
114
,
116
and
118
, respectively, that receive all the information blocks transmitted by the OLT. Each ONU then processes the information blocks that are intended for that ONU and discards the information blocks that are intended for the other ONUs. For example, ONU-
1
receives information blocks
1
,
2
, and
3
. However, ONU-
1
only delivers information block
1
to end user
1
. Likewise, ONU-
2
only delivers information block
2
to end user
2
and ONU-
3
only delivers information block
3
to end user
3
.
Referring to
FIG. 1B
, the ONUs
104
,
106
and
108
also include optical transmitters
120
,
122
and
124
, respectively, to transmit upstream traffic to OLT
102
. The upstream traffic is managed utilizing a time division multiplex access (TDMA) protocol, in which specific transmission time slots are dedicated to individual ONUs. The ONU-specific time slots are synchronized so that upstream information blocks from the ONUs do not interfere with each other once the information blocks are combined onto the common fiber. For example, ONU-
1
transmits information block
1
in a first ONU-specific time slot, ONU-
2
transmits information block
2
in a second ONU-specific time slot, and ONU-
3
transmits information block
3
in a third ONU-specific time slot. The time division multiplexed upstream traffic is then received by an optical receiver
126
of the OLT.
A concern with a TDMA PON is that the bandwidth of the PON is not always efficiently utilized for data transmission because network traffic typically exhibits a high degree of burstiness. The bursty network traffic results in some transmission time slots that consistently overflow even under a very light traffic load. In addition, the bursty network traffic results in some transmission time slots that are not completely filled even when the overall traffic load is very high.
In view of the above concern, there is a need for an access network based on PON technology that efficiently utilizes the available bandwidth by reducing the amount of bandwidth wasted because transmission time slots are not filled to the maximum capacity.
SUMMARY OF THE INVENTION
An optical access network and method for transmitting optical data in the network utilizes an interleaved polling scheme to efficiently use the available bandwidth of the network. The use of the interleaved polling scheme allows a central terminal of the network to dynamically allocate upstream bandwidth from remote terminals of the network to the central terminal in response to the amount of data that is waiting at the remote terminals to be transmitted to the OLT. In one embodiment, the optical access network is based on Passive Optical Network (PON) technology. In another embodiment, the optical access network utilizes Ethernet protocol to encapsulate data in Ethernet frames for transmission. Thus, in these embodiments the optical access network includes all of the advantages associated with the PON technology and/or the Ethernet protocol. In addition, since the allocation of upstream bandwidth is on an as needed basis, loss of bandwidth due to unfilled time slots is substantially eliminated.
A method of transmitting optical data in an optical network in accordance with the invention includes the steps of generating a table that includes information about the current sizes of data waiting to be transmitted from a plurality of remote terminals to a central terminal, selectively transmitting grant messages to the remote terminals, receiving authorized amounts of the data from the remote terminals and request messages containing updated information about the current sizes of the data waiting to be transmitted at the remote terminals in response to the grant messages, and updating the table using the updated information contained in the request messages received from the remote terminals. Each grant message is indicative of a permission for a targeted remote terminal to transmit an authorized amount of data waiting at the targeted remote terminal, which is dependent on the information included in the table with regard to the targeted remote terminal. In an embodiment, the optical network is a passive optical network (PON), which may be an Ethernet-based PON.
In an embodiment, the table that-includes information about the current sizes of data waiting to be transmitted from the plurality of remote terminals further includes information about round trip times of data transmission between the central terminal and the remote terminals. In this embodiment, the method may include steps of computing current round trip times for the remote terminals, including monitoring transmission times associated with the grant messages from the central terminal and reception times associated with the authorized amounts of the data from the remote terminals, and updating the information about round trip times of data transmission using the computed current round trip times.
In an embodiment, the step of updating the table includes subtracting a value from a new entry for the targeted remote terminal. The value corresponds to the actual amount of data transmitted from said targeted remote terminal, while the new entry corresponds to the updated information contained in a request message from the targeted remote terminal.
In an embodiment, the method may further include a step of scheduling transmission times for the grant messages such that the data and the updated information from the remote terminals do not overlap during transmission. The transmission times for the grant messages substantially define receptions times for the request messages at the central terminal. The step of scheduling transmission times may include rescheduling an original transmission time for a grant message to a rescheduled transmission time when the original transmi
Kramer Glen
Pesavento Gerry
Alloptic, Inc.
Ham Thomas
Wilson & Ham
Yao Kwang Bin
LandOfFree
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