Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-12-14
2003-12-02
Marcelo, Melvin (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S449000
Reexamination Certificate
active
06658009
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a band allocation method in a system for dividing a variable-length packet into cells, superimposing the cells on a time slot and transmitting the time slot and a transmission system realizing the method.
2. Description of Related Art
A transmission system is widely known in which a plurality of terminal units are connected to a network unit using branched optical transmission lines, etc., polling information is transmitted according to polling request information sent from a terminal unit and information divided into cells is transmitted from a terminal unit designated by the polling information. In this system, a band can be allocated to a terminal unit using polling information from a network unit. Such a band allocation is strongly desired.
FIG. 1
shows the rough configuration of a conventional transmission system, and in
FIG. 1
, a plurality of terminal units
52
-
1
through
52
-n are connected to a network unit
51
via an optical transmission line
53
. Specifically, this system comprises a multiplexer/demultiplexer
54
for connecting an optical transmission line
53
from the network unit
51
and optical transmission lines from the plurality of terminal units
52
-
1
through
52
-n, and has a so-called PON (Passive Optical Network) or PDS (Passive Double Star) configuration. The terminal units
52
-
1
through
52
-n correspond to subscriber line terminating units on the subscriber side, and a telephone set, facsimile transmitter/receiver, personal computer, etc., are connected to the terminal units
52
-
1
through
52
-n.
The network unit
51
comprises an identification unit
55
for identifying polling request information, a control unit
56
and a creation unit
57
for creating polling information. The terminal units
52
-
1
through
52
-n comprise a buffer
58
for temporarily storing transmission information and a request creation unit
59
for creating polling request information. A transmitter/receiver unit, optical/electrical (O/E) converter unit, etc., possessed by both the network unit
51
and terminal units
52
-
1
through
52
-n, are not shown in
FIG. 1
for simplicity.
When transmission information is stored in the buffer
58
, the terminal units
52
-
1
through
52
-n create polling request information using the request creation unit
59
, and the polling request information is transmitted to the network unit
51
. The network unit
51
receives the polling request information from a terminal unit, identifies the terminal unit which has transmitted the polling information using the identification unit
55
, creates polling information using the creation unit
57
under the control of the control unit
56
and transmits the polling information to the terminal unit which has transmitted the polling request information.
The terminal units
52
-
1
through
52
-n superimposes an information cell on the prescribed time slot of the polling information from the network unit
51
and transmits the information cell to the network unit
51
. In this case, the network unit
51
can allocate a wide band to a prescribed terminal unit, for example, by repeatedly transmitting polling information to the terminal unit in response to the polling request information from a plurality of terminal units.
A method in which the network unit
51
sets an individual management time slot, makes the terminal units
52
-
1
through
52
-n transmit information about the amount of transmission information stored in the buffer
58
, executes the allocation process of a time slot in the next frame based on information about the amount of storage of a buffer and transmits polling information to the terminal units
52
-
1
through
52
-n corresponding to the time slot allocation, is widely known (for example, see Japanese Patent Laid-open No. 10-107755).
A method for executing the time slot allocation process according to the amount of storage (amount of information queued) of a buffer, by comparing the amount of storage with a threshold value or according to the priority among the terminal units
52
-
1
through
52
-n, and transmitting polling information to the terminal units
52
-
1
through
52
-n accordingly, is also known (for example, Japanese Patent Laid-open No. 10-242981).
As described earlier, according to the conventional method, the network unit
51
transmits polling information based on band allocation carried out based on the amount of storage of a buffer of the terminal units
52
-
1
through
52
-n, and each of the terminal units
52
-
1
through
52
-n divides a frame or packet into cells and transmits the cells according to polling information from the network unit
51
. Therefore, the network unit
51
can receive and process cells from the plurality of terminal units
52
-
1
through
52
-n without collision.
According to a system for dividing a frame or packet into a plurality of cells and transmitting the cells, whether all the cells can be received is judged by assembling received cells into the frame or packet. During this time, cells composing the next frame or packet arrive. Therefore, if even one of the cells composing a frame or packet is lost, the frame or packet must be transmitted again. However, since cells composing the next frame or packet have already arrived, the re-transmission process becomes complicated, which was one problem. If a band is allocated based on only the amount of storage of a buffer, as in the conventional method and, for example, if the amount of storage of a buffer of a packet with a short packet length and the amount of storage of a buffer of a packet with a long packet length are the same, the same band is allocated to both the long and short packets, and cells are allocated to time slots in the same way in both cases. Therefore, in a system for transmitting data in units of packets, a packet cannot be efficiently divided into cells, multiplexed and transmitted, which was another problem.
SUMMARY OF THE INVENTION
The objective of the present invention is to carry out an efficient band allocation and to improve transmission efficiency when a variable-length packet is transmitted.
A method for allocating a band to transmit a variable-length packet, which is one of the aspects of the present invention, assumes a method for allocating a band to transmit a variable-length packet in a system where a plurality of terminal units connected to a network unit divide a variable-length packet into cells and transmit the cells according to polling information from the network unit.
According to this aspect of the present invention, the terminal units transmit polling request information including information about the number of cells composing a variable-length packet stored in a buffer, to a network unit, whereas the network unit allocates in order a time slot to the plurality of terminal units in units of variable-length packets according to the polling information and transmits polling information based on the allocated time slot.
The terminal units can also be designed so as to transmit polling request information including information about both the number of cells remaining in a buffer, composing a variable-length packet being read from the buffers by the terminal units and the number of cells composing the next variable-length packet to be transmitted.
The network unit can also be designed so as to allocate in order a time slot to a terminal unit in which a cell remains, so as to allocate in order a time slot to the terminal unit in units of cells of the next variable-length packet to be transmitted when the number of remaining cells becomes zero.
The system can also be configured in such a way that the polling request information further includes information indicating the service class of a variable-length packet stored in a buffer and that the network unit carries out with priority the time slot allocation based on the number of cells corresponding to the service class of a variable-length packet.
Alternatively, the network unit can
Kasa Masamichi
Miyabe Masatake
Shinomiya Tomohiro
Tajima Kazuyuki
Yamashita Haruo
Do Nhat
Fujitsu Limited
Katten Muchin Zavis & Rosenman
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