Combined Use of Collision-Resolution and Collision-Avoidance Media-Access Communication Protocols
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Gopal, IS: AUTHOR [+3]
Disclosed is method of combining two media-access protocols: using a collision-resolution protocol like ALOHA in a control channel for providing efficient access to a data channel for a large number of users, and using a collision-avoidance protocol like polling in the data channels for reliable real-time transmission.
Combined Use of Collision-Resolution and
method of combining two media-access protocols:
using a collision-resolution protocol like ALOHA in a control channel
for providing efficient access to a data channel for a large number
of users, and using a collision-avoidance protocol like polling in
the data channels for reliable real-time transmission.
point-to-multipoint data communication problem.
example is communication between the set-top-boxes at the homes and
the associated headend in a traditional CATV coax plant. Another is
communication between the base-site and the mobile users in a single
cell of a wireless (cellular) system. In such a system, the total
number of (active and inactive) users can be large while the number
of active users is small. Typical protocols used in such cases are
ALOHA and Carrier Sense Multiple Access (CSMA or ethernet) which can
result in collisions among data packets and consequently are not
suitable for real-time traffic like video and voice. In addition,
these protocols do not use the available bandwidth efficiently since
they involve retransmissions. We would like to devise a protocol (or
protocols) for packet-switched communication by which the users in
the system can have collision-free transmission and reception of
(user) data packets. This implies that the users are allocated the
available bandwidth in some fashion. One method would be to allocate
bandwidth to both active and inactive users but this would be very
inefficient if the total number of users is large.
invention is described combines the use of a
collision-resolution protocol like ALOHA which can support a large
number of users with a bandwidth allocation (collision-avoidance)
protocol like polling that is suitable for real-time traffic.
invention is described in the context of last-mile
communication in a traditional tree-shaped CATV network. The
available bandwidth is divided into two bands: one for downstream
communications (from the head of the CATV coax tree to the users) and
the other for upstream communication (from the users to the head of
the CATV coax tree). Each band is further divided into a number of
channels (e.g., each having a bandwidth of 6 MHz) but the number of
active users is typically much larger than the number of channels so
that each data channel must still be shared by multiple users.
data channels by users is controlled by means of a
connection establishment procedure. This procedure is carried over
dedicated control channels. There are two control channels: a
forward control channel located in the downstream band and a reverse
control channel located in the upstream band. Control channels are
at fixed locations in a given system, and user receiver and
transmitter are tuned to these pre-assigned frequencies upon powering