JP3003648B2 - LAN emulation method on ATM - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a LAN (Local Area Network) emulation system in a communication system based on an ATM (Asynchronous Transfer Mode).

[0002]

2. Description of the Related Art A LAN emulation method used on an ATM-LAN to interconnect an ATM-LAN and an existing LAN uses the same data length as that of an existing LAN such as Ethernet.

[0003] ATM is a type of protocol for performing connection-type communication between a plurality of devices using fixed-length packets called cells. 361 and widely used in recent years as public network and LAN protocols.

FIG. 3 shows an ATM cell format.
It consists of a header and data, the header part is 5 bytes long,
The data portion has a fixed length of 48 bytes each, so the total length is a fixed length of 53 bytes. When transmitting a variable-length AAL5 packet using this ATM cell,
The AAL5 packet is cut into 48-byte units from the beginning, and each strip is stored in the data section of each ATM cell. On the receiving side, the strips included in the data portion of each ATM cell are combined to restore the original AAL5 packet.

When an ATM is applied to a LAN, an ITU-T Recommendation I.T. In general, a protocol called AAL5 defined by H.363 is loaded, and a protocol called LAN emulation defined by the ATM Forum is loaded on AAL5 for use. AAL (ATM Ada
The Pt. Layer 5 is an ATM using fixed-length packets, and defines variable-length packets which are divided into a plurality of ATM cell payloads and accommodated in order to handle variable-length burst data.

FIG. 4 shows an AAL5 packet format. It takes the form of attaching a trailer that is fixed-length management information to the back of a variable-length payload. The actual user data is inserted into the payload. The overall length of the packet is variable, up to 32 kilobytes.

[0007] The packet length of AAL5 is a maximum of 32 kilobytes, and the packet format of address information and the like is a unique format. FIG. 4 shows the AAL5 packet format. By the way, in order to newly introduce an ATM-LAN, it is essential to ensure interconnectivity with an existing LAN.

[0008] That is, Ethernet (Etherne)
t) or the format of the frame used in the existing LAN using the token ring method is AAL.
The packet of 5 is completely different.

FIG. 5 is a diagram showing a frame format of Ethernet which is one of the existing LANs. Referring to FIG. 5, the frame is of variable length, up to 1.5 kilobytes. Inside the frame are DA (destination address), SA
(Source address), TYPE (upper protocol type or length information), data (stores user data),
It is composed of FCS (error detection information).

FIG. 6 is a diagram showing a frame format of a token ring which is another existing LAN. Referring to FIG. 6, the frame is of variable length and the maximum length is implementation dependent. The frame contains AC (access control information), FC
(Frame control information), DA (destination address), SA
(Source address), data (stores user data), and FCS (error detection information).

In this state, an ATM using AAL5 is used.
The LAN and the existing LAN cannot be interconnected by a protocol below the OSI data link layer. This is because LANs with different data sizes are used below the data link layer.
This is because conversion between them cannot be performed. On the other hand, an interconnecting device using an upper network layer is called a router, but has a problem that it is expensive and has a low processing speed.

Therefore, generally, a protocol called LAN emulation is mounted on the AAL5 protocol and used. LAN emulation is
As the name implies, it emulates a LAN.
It has fields in the frame that are compatible with Ethernet or Token Ring.

FIG. 7 is a diagram showing a frame format of the conventional LAN emulation. Referring to FIG. 7, the inside of the frame is composed of LEH (control header information) and a variable length payload. The frame itself has a variable length of up to 32 kilobytes, but since one Ethernet frame or token ring frame is stored in the payload, for example, when an Ethernet frame is stored, the frame length is limited to about 1.5 kilobytes.

Also, since the data size in the frame is limited to the same value as that of Ethernet or Token Ring, if the LAN emulation is used, the ATM-L
The AN and the existing LAN can be interconnected by terminating only the protocol below the data link layer. The problem here is the problem of data transfer efficiency.

Generally, the overhead required for data transfer includes a component proportional to the amount of data, such as the time required for actual data transfer, and a component irrespective of the amount of data, such as the time required for arbitration for transferring a packet. And a component proportional to the number of packets. AAL5 packet length up to 3
The Ethernet frame length is only 1.5 kilobytes, whereas it is as long as 2 kilobytes.

Therefore, in the existing LAN emulation using the same frame length as that of the Ethernet, the influence of the overhead proportional to the number of packets is too large, and the transfer efficiency is extremely low as compared with a pure ATM.

[0017]

As described above, in the conventional LAN emulation system, the data length is limited to 1.5 kilobytes, which is the same as that of Ethernet, and the overhead is larger than that of a native ATM having a maximum data length of 32 kilobytes. However, there is a problem that transfer efficiency is poor.

As an example of a conventional system in which a plurality of frames are accommodated in one frame, for example, JP-A-8-251237 discloses an STM channel and an ATM channel.
A method of accommodating TM cells in one STM frame has been proposed.

Accordingly, the present invention has been made in view of the above-described problems, and has been made in consideration of the interoperability with an existing LAN possessed by the original LAN emulation and the native AT.
It is an object of the present invention to provide a LAN emulation system having both advantages of a long data size of M and high transfer efficiency.

[0020]

In order to achieve the above object, a LAN emulation method according to the present invention comprises a plurality of L
It has a function of accommodating AN frames simultaneously in one LAN emulation frame. The present invention
Existing LAN environment such as G (registered trademark) and token ring
Application running on ATM network
LAN emulation method that can be used on PC
In the above, one frame is composed of a plurality of subframes.
Each subframe is a frame of the existing LAN.
Data, and a subframe tag of each of the subframes.
Frame format with type and length information
And the length of the entire frame is the maximum length of the AAL5 packet.
The maximum length that can be accommodated in a subframe is included in each subframe.
Data field length is compatible with existing LAN
Is limited to the length of the existing LA.
N to ensure interoperability with the
The transfer length is improved by the data length .

[0021]

Embodiments of the present invention will be described below. The LAN emulation method of the present invention, in a preferred embodiment thereof, uses one LAN.
By embedding a plurality of LAN frames in the emulation frame, it is possible to achieve both improvement of transfer efficiency and compatibility with the existing LAN.

FIG. 1 shows an example of a frame format used in the LAN emulation system according to the embodiment of the present invention. Referring to FIG. 1, one frame is composed of a plurality of subframes, and each subframe contains data of an Ethernet frame of an existing LAN.
Each subframe has a subframe type and length information at the beginning. The subframe type indicates whether the subframe is in the Ethernet format or the token ring format, and the length information indicates the position where the subframe ends, that is, the beginning of the next subframe. The length of the entire frame is the maximum length of AA
The length that can be accommodated in the L5 packet (32 kilobytes) is limited, and the length of the data field included in the subframe is limited to a length compatible with the existing LAN.

According to the embodiment of the present invention, the variable-length subframe is accommodated in the variable-length frame, and the subframe guarantees the interconnectivity with the existing LAN such as Ethernet.
The frame guarantees an improvement in transfer efficiency due to a long data length.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

[Embodiment 1] FIG. 1 is a diagram showing a frame format of a LAN emulation system according to a first embodiment of the present invention. Referring to FIG. 1, the LEH is a LAN emulation header defined by the existing LAN emulation (see FIG. 6), and an arbitrary number of subframes are connected after it. The total length of the frame is
The limit is the length that can be accommodated in the maximum length AAL5 packet (32 kilobytes). Each subframe has a T (subframe type) field indicating whether the subframe is in Ethernet or token ring format, an L (length information) field indicating the length of the subframe,
It is composed of a V (data) field into which an actual LAN frame is inserted. The length of the data field included in each subframe is limited to a length compatible with the existing LAN. For example, in the case of Ethernet format,
1.5 kilobytes.

[Embodiment 2] FIG. 2 is a diagram showing a frame format of a LAN emulation system according to a second embodiment of the present invention. Referring to FIG. 2, the second embodiment of the present invention differs from the first embodiment shown in FIG. 1 in that the subframe type and length information of each subframe are set to 1
The TL field is defined behind the LEH. Therefore, each subframe includes only an Ethernet or token ring frame.

In the second embodiment of the present invention, the subframe type and length information of each subframe included in the frame are collected at the head of the frame. There is an advantage that the entire configuration can be confirmed.

[0028]

As described above, according to the LAN emulation method of the present invention, a plurality of Ethernet frames are accommodated in one LAN emulation frame, thereby enabling interconnection with an existing LAN possessed by the original LAN emulation. This achieves the effect of realizing high transfer efficiency due to the long data size of the native ATM.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a frame format of LAN emulation according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a frame format of LAN emulation according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an ATM cell format.

FIG. 4 is a diagram showing an AAL5 packet format.

FIG. 5 is a diagram showing a frame format of Ethernet.

FIG. 6 is a diagram showing a frame format of a token ring.

FIG. 7 is a diagram showing a frame of a conventional LAN emulation.

[Explanation of symbols]

 AC access control information DA destination address FC frame control information FCS error detection information LEH LAN emulation header T subframe type field L length field V data field SA source address TYPE Upper protocol type or length information

Claims (3)

(57) [Claims] 1. An LA that enables applications running in an existing LAN environment, such as Ethernet (registered trademark) and token ring, to be used on an ATM network.
In the N emulation method, a frame format in which one frame is composed of a plurality of subframes, each subframe contains frame data of an existing LAN, and has subframe type and length information of each of the subframes The length of the entire frame is limited to a length that can be accommodated in the maximum AAL5 packet, and the length of the data field included in each subframe is limited to a length compatible with the existing LAN. The sub-frame guarantees interconnectivity with an existing LAN, and the frame guarantees an improvement in transfer efficiency due to a long data length. Wherein said each subframe, LAN emulation method according to claim 1, characterized by having the sub-frame type and length information at the head. 3. A LAN emulation method according to claim 1, wherein the said sub-frame type and length information for each sub-frame included in the frame, are summarized in the frame head.