Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-07-23
2003-10-28
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S310100, C370S389000, C370S401000
Reexamination Certificate
active
06639916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of communicating in Asynchronous Transfer Mode (hereinafter, referred to as “ATM”) and, in particular, to a method of communicating by using an AAL (ATM Adaptation Layer) receiving circuit.
2. Description of the Related Art
In the past, a technology about an ATM network has been enthusiastically developed as the Internet has been broadly spread. Information which is transferred in the ATM network is divided into a plurality of ATM cells each of which has 53 bytes of data, and the ATM cells are actually transferred through the ATM network. Each of the ATM cells is constructed of 48 bytes of “payload” which includes a part of the information and 5 bytes of “header” which includes a destination address and etc. Furthermore, in the destination address of the header, a VPI (Virtual Path Identifier) and a VCI (Virtual Channel Identifier) are included.
The ATM cells are transferred to the corresponding destination address through a plurality of ATM exchanges located in the ATM network. However, information about a VPI and a VCI is individually defined between a terminal and an ATM exchange, and between ATM exchanges. Therefore, each of the ATM exchanges, to transfer the ATM cells, should convert a VPI and a VCI in the ATM cell to another VPI and VCI that correspond to the next ATM exchange. Such conversion of the VPI and the VCI at the ATM exchanges is referred to as “header conversion”.
A previous technique of the header conversion uses a header conversion table as disclosed in Japanese Laying-Open Publication No. H09-181728 (namely, 181728/1997). In this case, VPIs and VCIs of the outgoing ATM cells are previously stored into the header conversion table in correspondence with VPIs and VCIs of the incoming ATM cells, and the VPIs and the VCIs of the incoming ATM cells are replaced by the corresponding VCIs and VPIs in the header conversion table when the incoming cells arrived.
Therefore, when a header of an ATM cell is converted by using a header conversion table, a large amount of header conversion table is required to store possible ATM cell header information, and a circuit for retrieving the large table and a circuit for conversion are required. As a result, a scale of a circuit for the header conversion on a transmission line interface becomes huge.
Also, the ATM cells may include voice, images, and the other kinds of data. Then, to treat each type of the data, the ATM cells are defined in a plurality of types of protocols (AAL type 1 through type 5). The AAL type of the ATM cells can be identified by referring to a value of a VCI included in the ATM cells.
It often happens that there may be a large amount of vacant area in the payload when an ATM cell is used for sending data of a single user, and when the amount of the data is much less than a payload in the ATM cell.
To avoid such occurrence of the large amount of vacant area, a type of ATM cell has been proposed which can collectively include data which are to be transmitted from a plurality of users and which have different destinations. The type is referred to as AAL type 2 (hereinafter, called as “AAL2”) and the type is defined by ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) recommendation I.363.2.
Therefore, an AAL2 cell is normally used when voice information, which has a small size and a short allowable delay time, is transferred. On the other hand, a standard cell is often used on transferring the other information, which has a large size and a long allowable delay time.
In the past, in an AAL receiving circuit, for example, in a radio base station, provision has been made to receive both the standard cell and the AAL2 cell. However, since the earlier AAL receiving circuit must produce an individual header of the standard ATM cell from the AAL2 cell which collects data of a plurality of users, the AAL receiving circuit must include AAL terminating units for the AAL2 cell and AAL terminating units for the standard ATM cell, individually. Further, since it can not be known in advance that either type of the cells is mainly transferred, a large number of both types of the AAL terminating units are needed even if all the units are not fully used. Therefore, the scale of the AAL receiving circuit becomes large, and as a result, the scale of a radio base station including the AAL receiving circuit also becomes large.
In recent years, attention has been focused on a radio communication system employing CDMA (Code Division Multiple Access) as next generation radio communication system. Using a W-CDMA (wide band-CDMA), which is one of the techniques employing CDMA, information between a radio base station and an exchange is transferred in the form of ATM cells. Therefore, in the radio base station including previous AAL receiving circuit as described above, enhancing the number of the communication lines leads to increasing a scale of the circuit, as a result, efficient usage of frequency band, which is advantage of CDMA, is degraded.
More detail description is made about the previous AAL receiving circuit.
Eight bits of a field are assigned to a VPI based on the UNI (User Node Interface), and 12 bits of field are assigned based on the NNI (Network Node Interface). A field of sixteen (16) bits is assigned to a VCI based on UNI and NNI.
FIG. 1
shows a header format of an ATM cell based on UNI.
The header also includes three bits of PT (Payload Type), a single (8) bit of CLP (Cell Loss Priority), and an eight bits of HEC (Header Error Control).
Next, description is made about the case where messages of users A, B, and C shown in
FIG. 2A
will be sent through the same path until they reach an intermediate portion located on the way to their destinations. Here, the message of the user A has twelve (12) bytes length, the message of the user B has eighteen (18) bytes length, and the message of the user C has six (6) bytes length. When these messages are sent through an ATM cell other than AAL2 type cell (hereinafter, referred to as “standard cell”), each of the messages is included in a ATM cell different from each other as shown in FIG.
2
(
b
). In
FIG. 2B
, an ATM cell containing the message of the user A has 36 bytes of vacant space out of 48 bytes payload. The vacant space is shown as a shaded portion. Similarly, an ATM cell containing the message of the user B has a 30 bytes of vacant space, and an ATM cell containing the message of the user C has a 42 bytes of vacant space.
FIG. 2C
shows format of an ATM cell when the above messages are sent in AAL2 cell.
As shown in
FIG. 2C
, the AAL2 cell includes short cells (also called “CPS (Common Part Sub-layer) packet”) containing the messages of users A, B. and C, and STF (start field)
111
. Each of the short cells includes the message of the user (short cell payload) and the short cell header (
110
a
,
110
b
, or
110
c
). The STF
111
has 1 byte length and each of the short cells (
110
a
,
110
b
, and
110
c
) has 3 bytes length. Therefore, the 48 bytes of payload of the ATM cell shown in
FIG. 2C
is occupied by 46 bytes of data (1 (STF
111
) +3 (short cell header)×3+12+18+6=46), and the only 2 bytes of area is unused.
Here, more detail description is made about the above AAL2 cell with reference to FIG.
3
.
As described above, the 48 bytes of payload in the AAL2 cell includes the 1 byte of STF
111
and a plurality of short cells.
The STF
111
further includes 6 bits of OSF (offset field), a 1 bit of SN (sequence number), and a 1 bit of P (odd parity of the STF). In
FIG. 3
, each of the numbers in parentheses indicates the number of bits of the corresponding data. The OSF indicates a boundary of a first short cell.
Also, each of the short cells includes 3 bytes of short cell header and a short cell payload which has a variable length. The short cell header includes 8 bits of CID (Channel Identifier), 6 bits of LI (Length Indicator), 5 bits of UUI (User-to-User Indication), and 5 bits of HEC (Header Erro
NEC Corporation
Nguyen Brian
Vanderpuye Kenneth
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