JPH0292130A - Bridge method - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bridge method of a bridge device, which is one of the interconnection mechanisms of LAN (communication networks).

(Prior art) Network interconnection forms include repeaters, which are mere physical level relays, and MAC (MediaAcce).
There are bridge devices that perform relaying at the SS (Control) level, routers that perform relaying at the network layer, and gateways that perform relaying at the transport layer and above.

Figure 3 shows a typical configuration example of a LAN system using a bridge device.
2) is a bridge device, (3) is a plurality of bridge devices (2)
) is a transmission medium forming a ring-shaped main line LAN with nodes (4) being a terminal device accommodated in the branch line LAN.

Next, via the transmission medium (3) of the trunk LAN, the branch line L
Communication between the terminal devices (4) accommodated in A N (1) will be explained using the functional configuration diagram of the bridge device in FIG. 4.

The frame emitted from the terminal device (4a) is sent to the bridge device (
2a) is received by the phy part, the MAC header is decoded by the mac part, and the destination address of the frame is sent to the branch line LA.
When indicating a terminal that is not within N (la), the address filter mechanism of the bridge device (2a)
The frame is relayed to N (3). If the destination address indicates a terminal on the same branch LAN, the frame is not relayed to the main LAN.

When a frame is relayed from the branch line to the main line, the MAC header and trailer are replaced with a format according to the branch line LAN protocol. This frame flows through the main LAN and is sent to a bridge device (
In 2b), the above-mentioned inverse conversion is performed and the signal is sent to the target branch LAN.

Now, the branch LAN is set up by the International Standards Organization (ISO8802, 3).
) specified by CSMA/CD (carr
ier senseMultiple Access
With Collision Detection
) standard LAN, and the trunk LAN is also the International Standards Organization (
FDD currently being standardized under ISO/DIS9314-2)
I (Fiber Distributed Date
r Interface), each frame format is as shown in FIG. In other words, frames on the branch LAN have a preamble (Pa), a start delimiter (
Sd), destination address (Da), source address (Sa
), length field (L), information field (I), and frame check sequence (Fcs).
The frame on N has a preamble (PA), frame control (FCC start delimiter (SD), destination address (DA), source address (SA), information field (1), frame check sequence (PCS), end delimiter (ED) and frame status (FS). Among these, the branch LAN preamble (Pa
) ~ length field (L) and the main LAN preamble (PA) ~ source address (SA) form the MAC header, and the branch LAN frame check sequence (
Fcs) and the main LAN frame check sequence (FC5) to frame status (FS) are MAC
forming a trailer. In the bridge device, the contents of the destination address and information fields are saved, and other fields are generated depending on the LAN format. Branch line preamble (Pa), start delimiter (S
d), trunk preamble (PA), start delimiter (S
D) The end delimiter (HD) has a fixed bit pattern and is easy to generate. Further, the branch line frame check sequence (Fcs) and the main line frame check sequence (FC5) are error check sequences according to the bit arrangement of each frame, and can be automatically generated. The frame control (FC) and frame status (FS) of the trunk line are defined by the FDDI protocol, and are operated closed within the trunk LAN, so they do not affect communication between terminals.

The branch line length field (L) indicates the length of the information field in bytes according to international standards, but in C3MA
/CD is dropped during relaying to FDDI, but can be easily reproduced by counting the size of the information field in the bridge device. However, this is only valid if the branch length field (L) indicates the length of the information field (I).

Ethernet exists as a substantially standard protocol for CSMA/CD type LAN. In this Ethernet, the frame format is the same as the international standard, but the meaning of the length field (L) is different. In Ethernet, the length field (L) means the protocol type.

[Problem to be solved by the invention]

In the conventional bridge device described above, since the MAC header and MAC trailer are replaced, the length field (L) part is dropped when relaying from the branch line to the main line, so there is no problem in a system unified by international standards. Although there is no problem with this, there is a problem in that the actual standard cannot be accepted.

This invention was made to solve the above-mentioned problems, and it complies not only with international standards but also with the substantial standard CSMA/
The purpose of this invention is to provide a bridge method that can also be applied to CD standard LAN.

(Means for Solving the Problems) The bridge method according to the present invention is based on the C3MA/CD standard L
The length field, which is the MAC header of the AN, is regarded as part of the information field and is transparent to the bridge device.

That is, in the bridging operation from the C3MA/CDW4 quasi-LAN of the branch line to the main line, the information of the length field is saved.

[For production]

In this invention, since the length field information is not lost, the bridge device can be effective not only for CS MA/CD standard LAN but also for Ethernet, which is said to be a substantial standard.

(Example) Fig. 1 is a functional configuration diagram of a bridge device implementing the present invention, and Fig. 2 is a frame format on its branch line and trunk LAN.Here, the functions of the m80 section shown in Fig. However, the function differs from that of the mac section in FIG. 4 in that the length field (L) is regarded as part of the information field (■).

Therefore, as shown in FIG. 2, the length field (L) is preserved on both the branch and main lines.

From the above explanation, the length field (L) indicates the length of the information field (I) for the CS MA/CD standard LAN, and the length field (L) indicates the protocol type for the substantially standard Ethernet. It becomes possible to configure an effective bridge device.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, the length field, which is a part of the MAC header, is regarded as part of the information field and is relayed transparently. is no longer lost, and C5M
This has the advantage that a bridge device that is effective not only for A/CD standard LAN but also for Ethernet, which is said to be a substantial standard, can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a functional configuration diagram of a bridge device that implements the present invention, Fig. 2 is a diagram showing frame formats on branch lines and main lines of this bridge device, and Fig. 3 is a diagram of a general LAN system using the bridge device. FIG. 4 is a functional configuration diagram of a bridge device employing a conventional bridge system, and FIG. 5 is a diagram showing the frame format on the branch line and main line of this device. (1), (la), (lb)...branch line LA
N. (2), (28), (2b)...Bridge device, (3)...Transmission medium of trunk LAN, (4), (4a), (4b)...Terminal device. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A bridge system applied to a CSMA/CD standard LAN, characterized in that a length field, which is a part of the CSMA/CD MAC header, is regarded as part of an information field and is relayed transparently.