Multiplex communications – Communication techniques for information carried in plural... – Assembly or disassembly of messages having address headers
Reexamination Certificate
1997-11-07
2003-12-30
Ton, Dang (Department: 2666)
Multiplex communications
Communication techniques for information carried in plural...
Assembly or disassembly of messages having address headers
C370S535000, C370S395100
Reexamination Certificate
active
06671289
ABSTRACT:
TECHNICAL FIELD
The present invention relates to ATM transmission, and particularly to a short cell multiplexing for transmitting, over an ATM network, data shorter than the payload of a standard ATM cell (basically less than 48 bytes, but more than 48 bytes can be allowed) which is transmitted through a network such as an ATM network, private short cell network, STM (Synchronous Transport Module) network, radio, packet network, or FR (Frame Relay) network.
BACKGROUND ART
Forming ATM cells from low bit rate, highly real time information like voice will cause a large delay time if the information is stored fully in the payload of the standard ATM cell, resulting in the degradation in the information. To prevent this, a partial fill method is proposed which loads the information partially (into part of the ATM cell) to be transmitted.
On the other hand, in a local environment like premises, a short cell using a payload shorter than the 48-byte payload of the standard ATM cell is proposed, which is expected to match better to the low bit rate data.
FIGS. 30A and 30B
illustrate the partial fill method and short cell method.
In the partial fill method as shown in
FIG. 30A
, a partial fill cell assembler
12
forms a standard ATM cell by adding dummy data to input data, and outputs it to a B-ISDN network. A partial fill cell disassembler
13
extracts the data from the partial fill cell received from the B-ISDN network, and outputs it.
In the short cell method as shown in
FIG. 30B
, a short cell assembler
14
forms from input data a short cell matching to an intended data length, and outputs it to an exclusive network having a unique cell slot structure. A short cell disassembler
15
extracts the data from the short cell received from the exclusive network, and outputs it.
DISCLOSURE OF THE INVENTION
The partial fill method described as the conventional techniques has a problem in that it impairs efficiency of utilizing the payload of the standard ATM cell and hence the transmission efficiency accompanying that because it uses only part of the payload of the standard ATM cell.
The short cell method, on the other hand, requires the exclusive network with a unique cell slot structure, which causes a problem of bad matching with the standard ATM switching network (B-ISDN network).
In view of these, a short cell multiplex transmission method is proposed which multiplexes information from multiple users to a single ATM cell (ISS' 95 Nakajima). This method multiplexes short packets received from different users within a predetermined time period into the payload of an ATM cell. This has advantages of limiting the delay below a certain fixed amount, thereby improving the efficiency.
In connection with the transmission method, a Shinagawa patent is disclosed. Besides, a Mita patent application has been filed which increases the degree of freedom in combining the users to be multiplexed.
In handling variable length user data, the following two methods can be considered: A first method fills the variable length user data into a predetermined fixed length short cell and fills dummy information into the remainder of the cell; and a second method forms variable length short cells in accordance with the user data, thereby multiplexing/demultiplexing them into or from the ATM cell. Although the second method is superior to the first method in efficiency, it requires a technique to decide the length of the variable short cells which vary for each ATM cell to extract them. The second method has another problem in that its payload efficiency is somewhat impaired as compared with the method which transmits the payload after filling it completely, because the second method, if higher transmission efficiency is required, transmits the ATM payload after loading it with the dummy information when its occupation ratio reaches to a certain level and no new short cell can be expected to be multiplexed into the ATM cell. Thus, a cell overlapping technique is effective which allows a variable length short cell to undergo multiplexing/demultiplexing across more than one ATM cell (Docomo, ATM-F).
In connection with one of the technique of multiplexing/demultiplexing variable short cells into or from one or more ATM cells, ATT filed a letter to ITU. According to the ATT letter, each short cell is provided with length information and user identifier (LLN: logical link number) to implement the extraction of variable length short cells. The first half of a short cell extending over two ATM cells is provided with the length information indicating the entire length of the short cell, and the second half multiplexed at the initial position of the next ATM cell is provided with the length information indicating only the length of the latter part of the short cell. A receiving end, when the length information of the short cell exceeds the end of the payload of the ATM cell, decides that it continues to the next ATM cell, and combines the first half and second half of the short cell overlapping the two ATM cell when the length of the remainder of the short cell equals the length indicated by the length information of the latter half multiplexed into the initial position of the next received ATM cell.
This method, however, has the following two problems if the synchronization for the extraction processing of the short cell is lost owing to the loss of the ATM cell during its transmission. First, if the length information of the second half of the short cell multiplexed into the initial position of the ATM cell received after the cell loss disagrees with the length of the remainder expected from the previously received first half of the overlapping short cell, it is impossible to decide whether or not the short cell multiplexed at the initial position of the next received ATM cell is a complete short cell or the continued short cell from the lost ATM cell, even though the cell loss can be detected (problem
1
). Second, in spite of the cell loss, if the expected length of the remainder happens to agree with the length information of the latter half of the short cell multiplexed into the initial position of the ATM cell received after the cell loss, not only the cell loss is undetected, but also erroneous short cells are combined (problem
2
).
The present invention features the following three aspects in connection with the variable short cell multiplexed transmission system and method.
(1) A multiplex transmission method providing each short cell with information for multiplexing and demultiplexing (embodiment 1).
(2) A multiplex transmission method providing each ATM cell collectively with information for multiplexing and demultiplexing (embodiment 2).
(3) A multiplex transmission method providing no information for multiplexing and demultiplexing (embodiment 3).
Although the item (1) has a similar characteristic to that of the ATT letter in that multiplexing and demultiplexing is carried out by providing each short cell with the length information, it solves the problem
1
of the ATT letter by deciding the cell overlapping not by the length information but by proving short cell status information. Furthermore, it can add control information on the ATM transmission to the multiplexed data of the short cells to achieve more reliable detection of the cell loss for each ATM cell as an option to solve the problem
2
.
The foregoing items (2) and (3) relate to novel short cell multiplex transmission methods which have not yet been disclosed.
According to the first aspect of the present invention, a short cell multiplexing ATM transmission system comprises:
a standard ATM cell assembler (
1
) for forming short cells from various types of input information, and for multiplexing the short cells to be placed in a payload of one or more standard ATM cells to be output to an ATM switching network;
an ATM switching network (
7
) for transmitting the standard ATM cells; and
a standard ATM cell disassembler (
2
) for receiving a short cell multiplexed ATM cell, and for disassembling the short cell multiplexed ATM cell into
Kaiyama Akira
Nakajima Akihisa
Nakamura Hiroshi
Okagawa Takatoshi
Onuki Masafumi
Brown & Raysman Millstein Felder & Steiner LLP
NTT Mobile Communications Network Inc.
Ton Dang
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