Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2000-01-10
2004-06-08
Sam, Phirin (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S432000, C370S437000, C370S412000
Reexamination Certificate
active
06747990
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a packet communication system, a network-side apparatus to be used therein, and a time slot allocation control method wherein plural terminal-side apparatus are connected with a network-side apparatus sharing physical media, and the network-side apparatus allocates time slots dynamically according to the varying traffic of each terminal-side apparatus.
BACKGROUND OF THE INVENTION
As a prospective system for realizing access network at a low cost, there is a media-shared type one-to-plural communication system wherein plural terminal-side apparatus are connected with one network-side apparatus sharing physical media. As an example of such media-shared type one-to-plural communication system, an ATM-PON (Asynchronous Transfer Mode-Passive Optical Network) system with 4 terminal-side apparatus is shown in FIG.
1
. In the ATM-PON system, as shown in
FIG. 1
, the terminal-side apparatus
800
~
830
are connected with one network-side apparatus
840
via the optical branch/merger device
860
. In such an ATM-PON system, so as to avoid collisions of data (henceforth described as cells) on the transmission line (henceforth described as shared transmission line)
870
between the optical branch/merger device and the network-side apparatus
840
, shared by all the terminal-side apparatus connected to the network-side apparatus
840
, each of the terminal-side apparatus
800
~
830
use time slots allocated by the network-side apparatus
840
to transmit cells to the network-side
840
. If the network-side apparatus
840
allocates fixed time slots to each of the terminal-side apparatus
800
~
830
, and one accommodates the Best Effort traffic having strong burst characteristics such as Internet service, the transmission capacity of the shared transmission line
870
may not be effectively utilized, because a certain amount of time slots are allocated fixedly in spite of the varying input traffic. Thus, in order to utilize the shared transmission line
870
effectively, the network-side apparatus
840
is required to change the time slot allocation dynamically according to the input state of the traffic to each of the terminal-side apparatus
800
~
830
.
A prior art in which the network-side apparatus changes dynamically the time slot allocation to each of the terminal-side apparatus
800
~
830
as stated above, is described, for example, in JPAH
10
-242981, “Dynamic time slot allocation system”. With reference to
FIG. 1
, the time slot allocation control system described in the application above and a media shared type one-to-plural communication system to realize it will be described.
The terminal-side apparatus
800
comprises the Queue length (stored cell number, and hence forth described as Queue length) report function
802
, which monitors the buffer
801
for storing input cells from each of terminals
880
,
881
and the stored cell numbers in the buffer
801
, and reports the Queue length information to the network-side apparatus
840
, and to the output control function
803
which controls the output of cells in the buffer
801
. Also the terminal-side apparatus
810
,
820
, and
830
are assumed to have a similar structure. And the network-side apparatus
840
is provided with the Queue length proportional time slot allocation control function
841
which calculates the time slot allocation for each of the terminal-side apparatus
800
~
830
. The terminal-side apparatus
800
~
830
and the network-side apparatus
840
are connected by the separate transmission lines
850
~
853
connecting the terminal-side apparatus
800
~
830
with the optical branch/merger device
860
, and by the shared transmission line
870
connecting the optical branch/merger device
860
with the network-side apparatus
840
.
In such a structure, cells are transferred from the terminal-side apparatus
800
~
830
to the network-side apparatus
840
in the operation as will be described below. Cells input from the terminals
880
,
881
, are stored in the buffer
801
, and then transferred to the network-side apparatus
840
by the output control function
803
. The output control function
803
uses the time slots allocated by the Queue length proportional time slot allocation control function
841
of the network-side apparatus
840
to output cells to the network-side apparatus
840
. The Queue length of the buffer
801
is also monitored by the Queue length report function
802
, and the Queue length information is reported to the network-side apparatus
840
by the Queue length report function
802
. Cells output from the terminal-side apparatus
800
~
830
and the Queue length information of the buffer
801
are input to the Queue length proportional time slot allocation control function
841
of the network-side apparatus
840
via the separate transmission lines
850
~
853
, the optical branch/merger device
860
, and the shared transmission line
870
.
The Queue length proportional time slot allocation control function
841
of the network-side apparatus
840
allocates time slots to each of the terminal-side apparatus
800
~
830
according to the proportion based on the Queue length information of the buffer
801
reported from the Queue length report function
802
. And the information about the allocated time slots is reported to each of the terminal-side apparatus
800
~
830
by the control signal
890
.
As an example, in case Queue lengths of the buffer for each of the terminal-side apparatus are 20, 50, 40, and 10 respectively, and the total time slots allocated to each of the terminal-side apparatus
800
~
830
is 60, time slot allocation will be described with reference to FIG.
2
. In
FIG. 2
, Queue lengths and allocated time slot numbers in the buffer
801
are shown for each of the terminal-side apparatus
800
~
830
. In this case, the Queue length proportional time slot allocation control circuit
841
allocates the total time slots of
60
to each of the terminal-side apparatus
800
~
830
, according to the Queue length ratio 20:50:40:10 in the buffer
801
for each of the terminal-side apparatus
800
~
830
. Thus the time slot numbers allocated to each of the terminal-side apparatus
800
~
830
, turn out to be 10, 25, 20, 5.
As described as above, in a conventional time slot allocation control system where the time slot is allocated in proportion to the Queue length of each of the terminal-side apparatus, time slot allocation is based on the input state of the traffic to each of the terminal-side apparatus. Thus, transmission capacity of the shared transmission line
870
is effectively utilized.
In a system of the prior-art, when the time slot allocation is changed, the total time slots are allocated to each terminal-side apparatus, according to the proportion of the Queue length of each terminal-side apparatus. Thus, time slots are allocated even to terminal-side apparatus having buffer of short Queue length, and sufficient time slots may not be allocated to terminal-side apparatus having buffer of long Queue length. As a result, there is a problem where buffer capacity necessary may increase so as to satisfy a certain cell loss rate, as the Queue length of buffer having long Queue length increases.
In the conventional allocation methods according to the ratio of Queue lengths, since the ratio of Queue lengths is that of values of the Queue length minus the time slot number allocated, the variance of Queue lengths among each of the terminal-side apparatus is large even in a steady state. The buffer capacity necessary is determined by the longest Queue length of the buffer of all the terminal-side apparatus, and the larger the variance of Queue lengths among terminal-side apparatus, the larger the buffer capacity necessary.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a time slot allocation control method wherein the buffer capacity necessary for the buffer of each terminal-side apparatus may be reduced in a dynamic time slot allocation control, and provide a one-to-plural media shared type communicat
Takagi Kazuo
Umayabashi Masaki
Dickstein Shapiro Morin & Oshinsky LLP.
NEC Corporation
Sam Phirin
LandOfFree
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