BANDWIDTH-ON-DEMAND PROTOCOL
At the protocol level, C-cation is developing a
patented bandwidth-on-demand protocol for guaranteed response
time in a multi-access media and for a flexible bandwidth-on-demand scheme. The
patent covering this protocol is entitled “Dynamic Channel Management and
Signaling Method and Apparatus” and bears US Patent No. 5,563,883. The
designed protocol has universal applicability to all transmission media, such
as CATV, fiber, ethernet, wireless, etc. This technology overcomes the
probabilistic nature of IP services and provides unprecedented quality of
service (QoS) from the following key features, among others:
- Controlled polling scheme: The bandwidth-on-demand
protocol provides a robust and yet simple add-on protocol layer that
guarantees response time in a multiple access system. In a broadband
communication system, a central controller (similarly situated at the
CMTS) periodically sends ‘general’ polling messages, which are also used
for synchronization, to the remote terminals (CMs). When a remote
terminal is ready to transmit, it should transmit within a set time
interval, which is used to accommodate the different propagation delays
from different remote terminals, after receiving the poll message from the
central controller. If there is no contention, the protocol achieves
optimal response time. In case of contention, a binary decision
process is deployed to identify the contending parties by progressively
halving the ranges of terminal IDs (similar to SID in DOCSIS). This
process identifies the first party in the contention within T*log2N
time in the worst case, where T is the round trip transmission delay and N
is the number of possible terminal IDs. As a result, the contention
is resolved within a deterministic timeframe. To further improve the
system performance, the central controller may use a strategy based on
past behaviors of the remote terminals to poll them selectively.
- Bandwidth management:
Bandwidth is set aside as a pool of resources, which may be dynamically
adjusted and/or assigned according to system requirements. The
number of links to the wide area network, the broadband channels, and the
remote terminals, are denoted respectively as L, M, and N. Normally,
the configuration used to take advantage of statistical savings is
L<M<N. The broadband communication resources between the
central controller and the remote terminals are classified as downstream
signaling data (FD), downstream data bearing (FB), upstream signaling data
(RD), upstream data bearing (RB) as shown in the diagram below.
These channels comprise the pool of resources. The numbers, location
and/or size of FD, FB, RD, and RB channels may be dynamically adjusted to
meet system requirements. The number of broadband channels, M, is to
be allocated from this pool. This scheme affords flexibility to meet
the a/symmetrical traffic requirements of the communication system.
This scheme also affords system failure and/or communication channel
anomaly recovery.
- Subscriber grouping:
A flexible management scheme is possible for channel arrangement and
remote terminals grouping. Multiple access of the remote terminals
for the upstream traffic are mitigated by separating remote terminals in
groups via the terminal assignment process. This grouping helps to
establish various services offering and/or to improve system performance.
- Overlapping polling cycle:
The central controller may initiate another polling cycle before receiving
a response from the remote terminals to the previous poll. The
resulting overlapping polling cycle doubles system performance when
contention is unlikely. The remote terminals require no change and behave
the same way as before by responding to the poll within a set
timeframe. If there is contention, the central controller performs a
rollback procedure with the remote terminals and engages the binary
determination process described above to resolve the contention.
- Parallel operation:
Parallel operation in different communication channels may be used to
improve system performance. Taking advantage of the availability of
multiple channels in a broadband communication system, contention
resolution processes may be dispatched in parallel to a number of
communication channels. This scheme helps improve system performance
while adding flexibility in organizing different service classes. A
US patent pending application covers this feature.