ATM transmission system

Details ATM transmission system ATM transmission system

1999-03-04

2003-01-28

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Communication over free space

Using atm as a wireles protocol

C370S395600

Reexamination Certificate

active

06512747

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an ATM (Asynchronous Transfer mode) transmission system for transmitting an ATM cell through a radio channel or a wired channel, in particular, relates to such a system which uses a communication channel with high efficiency and suppresses useless traffic.
In an ATM transmission system, a data is transmitted by using an ATM cell which has a fixed length of data. An ATM cell has generally 53 bytes data including a cell header having 5 bytes followed by an information field having 48 bytes, as shown in FIG.
5
.
Since an ATM cell has fixed length, high speed data transmission is possible by repetition of relatively simple process.
In an ATM transmission system, an ATM cell is repeated by a node which is called an ATM switch so that the ATM cell is transmitted from a source terminal equipment to a destination terminal equipment. Assuming that an ATM switch has the function to discard a wrong ATM cell (as shown in Japanese patent laid open publication 163141/1996), when there is something wrong in an ATM cell, such as a queue of an ATM cell and/or overflow of a buffer memory, a useless traffic may be suppressed for a transmission line at an output side of the ATM switch, however, no transmission is suppressed in a transmission line at an input side of the ATM switch.
Further, in a prior art, the discard of an ATM cell is triggered by a long queue of an ATM cell in an ATM switch and an overflow of a buffer memory, but not by a transmission error of an ATM cell. A transmission error occurs with high probability in case of a wireless transmission line.
FIG. 11
shows a basic system structure of a wireless ATM system. In
FIG. 11
, the numeral
11
shows a base station,
12
,
13
and
14
are a radio module,
15
,
16
and
17
are a terminal equipment, and
18
shows a network.
In
FIG. 11
, the base station
11
is coupled with radio modules
12
-
14
through a wireless channel. Each of radio modules
12
-
14
is connected to a related terminal equipment
15
-
17
. Further, the base station
11
is coupled with the network
18
through an optical fiber, or a metal cable.
The terminal equipment
15
-
17
and the network
18
carry out transmission and reception of data by using an ATM cell, which is the minimum unit of data to be transmitted.
FIG. 12
shows a protocol stack concerning a user plane (U plane) of a wireless ATM system of FIG.
11
. The base station
11
is coupled with the network
18
through a node
19
.
As shown in
FIG. 12
, the protocol of the terminal equipment
15
-
17
comprises a physical layer (PHY), an ATM layer (ATM), an ATM adaptation layer (AAL), and an application layer (AP). Each of the radio modules
12
-
14
and the base station
11
has the protocol comprising a physical layer (PHY), an ATM layer (ATM), a wireless layer (Wireless), a data link layer (DLC), and a media access control layer (MAC). The node
19
has a physical layer (PHY) and an ATM layer (ATM).
As for a U plane of the base station
11
and the radio modules
12
-
14
, a layer higher than an ATM adaptation layer (AAL) is not terminated. The terminal equipment
15
-
17
are seamlessly coupled with the node
19
in the network
18
through the ATM layer (ATM). In a wireless channel between the base station
11
and the radio modules
12
-
14
, a plurality of virtual paths (VP) and virtual channels (VC) which are a logical link of an ATM layer may exist.
FIG. 13
shows a flow of an ATM cell C
1
-C
8
when a terminal equipment
15
transmits a network
18
a data, in a wireless ATM system in FIG.
11
. In the embodiment of
FIG. 13
, a radio module
12
is a transmitter, a base station
11
is a receiver, and the terminal
15
is sending an ATM cell.
As shown in
FIG. 13
, it is assumed that the terminal
15
sends ATM cells C
1
through C
8
sequentially to the radio module
12
, and that the second ATM cell C
2
is erroneous in the wireless section between the radio module
12
and the base station
11
, so that the base station
11
receives the first ATM cell C
1
and the ATM cells C
3
through C
8
. Then, the base station
11
sends the first ATM cell C
1
and the cells C
3
through C
8
to the network
18
.
A base station
11
and a radio module
12
have a transmitting station and a receiving station as shown in
FIG. 14. A
transmitting station comprises an input means for accepting an ATM cell, a transmit buffer, and a transmit means. The transmit buffer stores temporarily an ATM cell which is in the queue for transmission. A receiving station comprises a receive means, a receive buffer, and an output means. An ATM cell received by the receive means is stored temporarily in the receive buffer. An ATM cell is read out of the receive buffer when requested, and is transmitted through the output means.
FIG. 15
shows the transfer sequence of the ATM cells C
1
through C
8
in the wireless section in case of FIG.
13
. In
FIG. 15
, a TDMA (Time Division Multiple Access) system is used in wireless data communication between a radio module
12
and a base station
11
, and each TDMA frame includes three ATM cells.
In
FIG. 15
, when cells in a first TDMA frame are transmitted, a first through third ATM cells C
1
-C
3
are transmitted. It is assumed that a second ATM cell C
2
is erroneous in a wireless section. Therefore, the base station
11
receives only the first ATM cell C
1
and the third ATM cell C
3
.
When the ATM cell in the first TDMA frame has been transmitted, the radio module
12
has five ATM cells C
4
, C
5
, C
6
, C
7
and C
8
in the transmit buffer. The fourth through sixth ATM cells C
4
-C
6
are transmitted when the cells in the second TDMA frame is transmitted. Then, the base station
11
has five ATM cells C
1
, C
3
, C
4
, C
5
and C
6
in the receive buffer.
When the ATM cells in the second TDMA frame has been transmitted, the radio module
12
has two ATM cells C
7
and C
8
in the transmit buffer. Those two cells C
7
and C
8
are transmitted when the ATM cells in the third TDMA frame are transmitted.
As a result, the base station
11
receives seven ATM cells C
1
, C
3
, C
4
, C
5
, C
6
, C
7
and C
8
. Then, the base station transmits the network
18
seven ATM cells C
1
, C
3
, C
4
, C
5
, C
6
, C
7
and C
8
.
By the way, the recent network which uses an ATM communication system, can provide a variety of services. And, for instance, it is requested that a user terminal is seamlessly coupled with an ATM network including wireless means, in other words, it is requested that a user terminal is coupled with a network only through an ATM layer.
However, it should be noted that an ATM cell is erroneous with relatively high probability in a wireless communication section.
In a data communication service which uses an ATM system, a TCP/IP protocol is used in a higher layer. The communication using the TCP/IP protocol is implemented for instance by a standardized specification (IP over ATM; RFC 1483). In this case, AAL type
5
is used as an ATM adaptation layer (AAL).
In a data communication system using the AAL type
5
as the ATM adaptation layer, the size of a packet in a higher layer is generally larger than the data size (48 bytes) of an information field of an ATM cell, therefore, a packet in a higher layer is segmented to a plurality of ATM cells for transmission.
If an ATM cell or a plurality of ATM cells are in error in transmission, and an error correction by a destination terminal (forward error correction; FEC) can not recover a packet data, when a packet is transmitted in a plurality of ATM cells, then, a packet itself is in error, and it is dealt as a useless packet.
When re-transmission is carried out in a higher layer, the re-transmission of a whole packet must be carried out when only one ATM cell is erroneous. In this case, when a wireless section exists in a network, the probability of a non-useful packet might be relatively high, since the probability of an error of an ATM cell in a wireless section is high.
As described above, when an erroneous ATM cell is included in a packet which ha

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