Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-11-23
2004-12-14
Yao, Kwang Bin (Department: 2667)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S468000
Reexamination Certificate
active
06831894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a method and system for reserving transmission capacity required by the acknowledgement and/or response messages in bi-directional transmission systems.
2. Discussion of Related Art
Many modern transmission systems use time division multiple access technology utilizing one available resource in order to transmit information which is obtained from several different sources. Such systems often include a so called point-to-multipoint architecture, a possibility to transmit packets in the form of bursts, and a centralized management of the transmission resource, such as a transmission channel. For instance transmission systems using the the Transmission Control Protocol (TCP) can be realized as systems of the mentioned type.
FIG. 1
shows a prior art solution based on the so-called reservation contest method for reserving transmission capacity in systems of the above-described kind. The transmission system
10
according to
FIG. 1
a
consists of a transmission network
11
and four transmission units
12
,
13
,
14
and
15
connected to the network
11
. When an information packet
16
shall be transmitted from the first unit
12
to the second unit
13
the information packet
16
is transmitted directly to the transmission network
11
. If the transmission capacity of the network
11
is available the information packet
16
is conveyed from the first unit
12
to the second unit
13
, as shown in
FIG. 1
a
. If for instance the third unit
14
simultaneously tries to transmit another information packet
17
, there occurs a so-called collision between the packets, as shown in
FIG. 1
b
. In such a situation neither transmitted packet
16
and
17
will reach its destination.
When the first and third transmission units
12
and
14
detect the collisions, for instance by listening to the traffic in the network
11
, they both wait a period of a random length, and then they try to re-transmit the packets
16
and
17
. This is continued until the transmission of the packets succeeds without collisions.
When the above described reservation contest method is used it is natural that also the probability of collisions increases when the number of information packets moving in the network
11
increases. For instance, the theoretical maximum efficiency, or the throughput probability of the transmission, in the widely used slotted ALOHA reservation contest system is 1/e≈37% [
1
] in a system with infinitely many users. This restricts the usefulness of reservation contest methods in congested networks.
FIG. 2
illustrates the use of the above described prior art reservation contest method in the transmission between the first and second transmission units
12
and
13
, when the first unit
12
transmits information
16
which requires an acknowledgement (ACK) to the second unit
13
. This is the case for instance in transmitting a simple information packet according to the TCP, because according to the TCP each received packet must be acknowledged, otherwise the transmitting unit thinks that the packet could not reach its destination and tries to re-transmit the packet.
In
FIG. 2
, as in the other diagrams in this patent application illustrating the information travel, the time axis extends from top to bottom, in other words, the events which are higher up occur before those events which are below them.
When the first transmission unit
12
has successfully transmitted the information packet
16
through the network
11
to the second unit
13
the second unit
13
tries to acknowledge that the packet
16
is received, by transmitting via the network
11
an acknowledgement signal
21
to the first unit
12
. As was noted above when the reservation contest method is used, due to the packet collisions it may become necessary that the acknowledgement signal is transmitted many times before the first unit receives the acknowledgement. This means unnecessary consumption of resources both in the second unit
13
and in the network
11
, compared to a situation where the acknowledgement signal
21
is conveyed to the first unit
12
by a single transmission.
FIG. 3
shows another prior art embodiment
30
for reserving transmission capacity in a transmission system. The embodiment is based on a resource management table maintained in the first transmission unit
12
, where the available transmission capacity is allocated to different units on the basis of request provided by them. In
FIG. 3
a message
16
is transmitted from the first unit
12
to the second unit
13
. If the message is for instance a status inquiry or any such information which requires that a response message
33
be transmitted back to the first unit
12
, then the second transmission unit
13
recognizes the need for a response message when it processes the received packet
16
.
The second transmission unit
13
transmits a capacity request
31
to the first unit
12
so that it is able to reserve the transmission capacity required to transmit the response message
33
. Because the second unit
13
is not able to control the transmission resource in use, the reservation request
31
must by transmitted with the aid of the reservation contest method described above. The first unit
12
processes the capacity request
31
and updates the granted capacity in the resource distribution table. Then the first unit
12
transmits the information about the transmission capacity reserved for the transmission of the response message
33
with the aid of a grant message
32
. The second unit
13
receives the grant message
32
and on the basis of the information contained in it the second unit transmits the response message
33
to the first unit
12
with the aid of the transmission capacity allocated to the second unit by the first unit
12
.
As such the prior art solution
30
shown in
FIG. 3
is more advanced than the system based on reservation contest presented in
FIG. 2
, but even the system
30
according to
FIG. 3
utilizes the transmission capacity at a rather low efficiency, because also the transmission of the response message
33
requires the transmission of two other messages, i.a. the request and grant messages
31
and
32
. Further the system according to the
FIG. 3
is not able to eliminate the use of the reservation contest system completely, because the reservation request message
31
is still transmitted by the reservation contest system.
SUMMARY OF THE INVENTION
The object of this invention is to provide a new method and system with which the
According to a first aspect of the invention, a method for reserving transmission capacity required by acknowledgement and/or response messages in a bi-directional transmission system, where a message is transmitted form a first unit to a second unit, a second unit receives the message transmitted by the first unit, and the second unit transmits an acknowledgement and/or response message as a response to the received message, is characterized in that a reservation of transmission capacity required by the acknowledgement and/or response message is made substantially in connection with transmission of the message transmitted from the first unit to the second unit.
Further in accord with the first aspect of the invention, the reservation of the transmission capacity required by the acknowledgement and/or response message is made before said message is transmitted from the first unit to the second unit.
Still further according to the first aspect of the invention, the reservation of the transmission capacity required by the acknowledgement and/or response message is made simultaneously when said message is transmitted from the first unit to the second unit.
Still further according to the first aspect of the invention, the reservation of the transmission capacity required by the acknowledgement and/or response message is made after said message has been transmitted from the first unit to the second unit.
Further still in accordance with the first aspect of the invention, the bi-dir
Hahtala Matti
Kokkinen Heikki
Nokia Multimedia Terminals Oy
Yao Kwang Bin
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