JPH09298554A - Lan emulation method, lan emulation system and lan emulation server device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simulate an existing LAN communication at a high speed efficiently based on the 'LAN emulation-over ATM specifications' specified by the ATM forum in the case of using existing protocols such as TCP/IP in an ATM exchange network. SOLUTION: An LECa makes an IP/MAC-ARP request to a BUS to obtain a MAC address from an opposite IP address (β), the BUS searches whether or not the IP address (β) is in existence in an ARP search table, and returns a MAC address (Y) on the ARP cache table to the LECa when the corresponding address is in existence. If the corresponding IP address is not registered in the ARP search table, the IP/MAC-ARP request is transferred to all LECs by a multi-cast VCC.

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 method, a LAN emulation system, and a LAN emulation server device, for example, an ATM (Asyncron).
in a transparent transfer mode (asynchronous transfer mode) switching network, TCP (Transmissio)
n Control Protocol) / IP (Int
The present invention can be applied to control when using an existing LAN protocol such as Internet Protocol).

[0002]

2. Description of the Related Art In recent years, research and development of ATM communication systems have been actively conducted. FIG. 2 shows, in an ATM switching system, between ATM terminals (for example, workstations) 4 and 5 connected to an ATM switching network and terminals connected via bridge devices 2 and 3, between ATM terminals, And between the terminals connected via the bridge devices 2, 3, etc., the existing LAN protocol (TCP
/ IP etc.) as a means for realizing application communication on the ATM forum, "LAN emulation over (OVER) ATM specifications" (Forum
7. ATM Forum Specificatio
n, February 1995). This LAN emulation is a function that simulates the LAN protocol.

FIG. 3 shows an example of a "LAN emulation over ATM" network. "LAN emulation over ATM" is the operation of an existing LAN protocol by a client and a server.
A pseudo configuration is made on the switching network 12.

The LAN emulation client is
The interface of the existing LAN protocol is received from the upper application, the server is accessed, and
Obtain a TM address and set up an ATM connection.

The LAN emulation server 13 is L
The correspondence between the network layer address of the LAN terminal, the physical address of the terminal, and the ATM address is managed according to a request from the AN emulation client.

FIG. 4 is a model configuration diagram of LAN emulation over ATM. In FIG. 4, L
ECS (LAN Emulation Config)
is a LEC (LAN)
Emulation Client) 24,
LES (LAN Emulation Server)
26 and BUS (Broadcast and Unkn
The address of the own server) and the connection information for access are given.

The LES 26 is a MAC (Media Ac
access control: ARP (Address) that derives an ATM address from a medium access address
It has a Resolution Protocol function (address resolution procedure). The BUS 27 has a multicast function for transmitting an ARP request and a forward function for unicast data whose address is unknown.

L of the LAN emulation server of FIG.
The ECS 36 gives an address of LES or BUS and connection information for access to the LEC. L
The ES 37 has an ARP function of deriving an ATM address from a MAC address. The BUS 38 has a multicast transmission of ARP request and a forward function of unicast data whose address is unknown.

The connection management layer 39 sets and releases ATM connections. The adaptation layer 40 transfers / manages frame information for connection setting / release and disassembles / assembles cells.
The ATM layer 41 performs signal control of lines and transmission / reception of ATM cells. The layer management unit 35 sets and manages the configuration information of each layer.

FIG. 6 shows a LAN emulation over ATM communication sequence. In FIG.
First, the LAN emulation client device LEC
When the a receives the initial setting instruction from the layer management, the LECS
To request connection (step S1). Next, LAN emulation configuration server device LEC
S is the AT of the LAN emulation server device LES
L emulation configuration information such as M address
It returns to ECa (step S2). Next, LECa
Connects to LES and sends its own MAC address (X) and ATM
Register address (A) in LES, that is, LE-JO
An IN request is issued (step S3). Next, LECa
When a plurality of terminals are connected under the control such as a bridge, the MAC address thereof is also registered in the LES, that is, LE-REGISTER (step S4).

Next, when LEC receives a request for setting an IP (Internet Protocol) connection from a higher-level application,
The MAC address is set to all 1, and the BUS ATM address is requested, that is, the LE-ARP request (step S
5). Next, the LES returns the ATM address of the BUS to the LECa, that is, the LE-ARP response (step S
6). Next, LECa connects to BUS to obtain the MAC from the IP address of the communication partner (step S
7). Next, the BUS sends a multicast VCC (Virtual Channel Conn) to all LECs.
section) is set (step S8). Next, L
The ECa makes an IP / MAC-ARP request to the BUS to obtain the MAC address from the IP address (β) of the communication partner, and the BUS transfers this request on the multicast VCC (step S9).

Next, all LECs are IP / MAC-ARP
When the request is received, it is confirmed whether or not the own IP address matches the request (β), and if they match, the MAC address (Y) is returned, that is, the ARP response (step S1).
0). Next, the BUS returns the ARP response to LECa (step S11). Next, when the LECa receives the ARP response, the AT corresponding to the MAC address (Y)
Request LES to translate M address, ie LE-A
RP is requested (step S12). Next, LES is A
Return TM address (B) to LECa, ie LE
-ARP response (step S13). Next, LECa is
Connection setting is performed for LECb using the ATM address (B), that is, SETUP is performed (step S14). Next, when the LECb receives the connection setting, the LECb returns the connection completion (CONN) (step S15). Next, LECA and LECb transfer the data between the upper applications using the above connection (step S16).

FIG. 7 shows a flow of control messages for LAN emulation when the ATM switching devices are distributed in each area. ATM switching devices 47, 48
LES45 and BUS46 even if dispersed in each district
However, when there is one ATM switching network, each LEC 49 to 51 in a different area from the LES 45 registers addresses (LE-JOIN, LE-) via a relay line between switching devices.
REGISTER) and address resolution (LE-AR)
P) to LES45.

BUS46 also has LEs in different districts.
A request for setting a multicast connection for each of C49 to C51 and requesting a MAC address from the IP address in the connection (IP / MAC-AR
P) is performed.

[0015]

However, in the prior art, (1) in the address resolution procedure (ARP), in the communication between the LEC and the BUS, all LECs and multicast communication must be performed. There was a problem that it took time. (2) (a) Also,
Registration, participation (JOIN) to LES, LE-ARP when ATM exchanges are distributed in each region
(Address resolution) request message must be exchanged between the exchanges via the trunk line. (B) Furthermore, an IP / MAC-ARP request / between BUS and LEC /
The reply message must be exchanged between the exchanges via the trunk line. Therefore, the bandwidth of the relay line must be used for the above message, and there is a problem that the bandwidth of user communication is reduced.

From the above, when an existing protocol such as TCP / IP is used in the ATM switching network, it is fast and efficient based on the "LAN emulation over ATM specifications" defined by the ATM Forum. There is a demand for realization of a LAN emulation method, a LAN emulation system, and a LAN emulation server device that provide excellent LAN emulation communication that can simulate existing LAN communication.

[0017]

Accordingly, a first aspect of the present invention provides
Address resolution processing is performed to derive the physical address of the terminal of the communication partner from the address of the network layer used for LAN communication, and the packet of the network layer is transferred to the ATM.
In the LAN emulation method for transferring to a terminal on a network, the above-mentioned address resolution processing manages a network address that has a history of use and a physical address of the terminal, and responds to the address resolution request with a corresponding network address and physical address. Is managed, the multicast or broadcast communication to the terminals of the ATM network is not performed. If the corresponding network address and physical address are not managed, the multicast or broadcast communication to the terminals of the ATM network is not performed. By carrying out, the above-mentioned problems are solved.

With this configuration, the network address used once and the physical address of the terminal are managed,
When the corresponding network address and physical address are already registered for the second and subsequent address resolution requests, multicast communication or broadcast communication is not performed, so the time for address resolution in LAN emulation should be shortened. Therefore, multicast traffic or broadcast traffic can be reduced.

A second aspect of the present invention is a plurality of communication devices (for example,
ATM communication device, ATM switching device, etc.) and transfers network layer packets on an ATM network. In the LAN emulation system, each communication device includes a plurality of LAN emulation client devices, a LAN emulation server device, and a LAN emulation server device. Information (eg, broadcast, multicast, BU
A proxy client device that is connected to a communication server device under its control and relays communication with a LAN emulation client device under another communication device as a proxy for a plurality of LAN emulation client devices under one communication device. The proxy client device is interposed between communication devices, and the proxy client device is connected to the plurality of LANs via the LAN emulation server device or the broadcast communication server device.
Communicates with the emulation client device.

With this configuration, when the communication devices are distributed in different places, the LAN emulation server device managing the terminals (clients) and the broadcast communication server devices are distributed in each place. In addition,
By providing the proxy client device, it is possible to simplify the control procedure between the communication devices and reduce the communication traffic between the communication devices.

Further, a third aspect of the present invention manages a network address and a physical address of a terminal that have been used in a LAN emulation server device having an address solving means for deriving a physical address of a terminal of a communication partner from an address of a network layer. When an address search request is given from the address resolution means, the address management means for searching the requested address and outputting the search result is provided.

With this configuration, the network address used once and the physical address of the terminal can be effectively used, and the time for address resolution can be shortened.

Furthermore, a fourth aspect of the present invention is a LAN emulation server device having an address solving means for deriving a physical address of a terminal of a communication partner from an address of a network layer, under the communication device to which the own LAN emulation server device is connected. As a proxy function of multiple LAN emulation client devices, other L
Proxy client means for relaying communication with the AN emulation server device is provided.

With this configuration, the proxy client unit can be caused to proxy-process the communication control procedure between a plurality of LAN emulation client devices, so that the communication control procedure can be reduced and the communication traffic volume can be reduced. Furthermore, by providing the proxy client means in the LAN emulation server device, the system configuration can be simplified and the device functionality can be enhanced.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the drawings. In this embodiment, the AT
When using an existing protocol such as TCP / IP in the M switching network, the "L" specified by the ATM forum (a non-profit organization aiming at early use of ATM technology)
When using a protocol based on the AN emulation over ATM specifications ", in the LAN emulation server LES based on the above specifications, (1) an address resolution procedure for deriving a physical address of a terminal of a communication partner from a network layer address used for LAN communication. In this case, a means for learning the network address once used and the physical address of the terminal is provided, and when the corresponding network address and physical address are already registered for the address resolution request from the second time onward, multicast communication is performed. Means not to be provided. By this, AT
The time for address resolution in the M switching network is shortened, the multicast traffic is also reduced, and the existing LAN communication is simulated at high speed and efficiently in the ATM switching network.

(2) Further, when the ATM switching devices are distributed and installed in different areas, LAN emulation servers for managing terminals (clients) in each area are distributed and arranged in each area. By providing a proxy client function on behalf of clients in each area, it is possible to reduce the control procedure between ATM switching devices, reduce the traffic between ATM switching devices, and
The LAN emulation method and the LAN emulation server device LES are configured so that the existing LAN communication can be simulated at high speed and efficiently in the switching network.

FIG. 1 is an explanatory diagram of a communication sequence for realizing LAN emulation over ATM according to this embodiment. In FIG. 1, the LAN emulation client device LECa first requests a connection to the LECS when receiving an initial setting instruction from the layer management (step S21). Next, LECS is LES A
The LAN emulation configuration information such as the TM address is returned to LECa (step S22). Then LEC
a connects to LESa and uses its own MAC address (X) and A
Register TM address (A) in LES (LE-JOI
N request) (step S23).

Next, when a plurality of terminals are connected under the LECa such as a bridge, the MAC address of the terminal is also registered in the LESa (LE-REGISTE).
R) (step S24). Next, when the LECA receives the IP connection setting request from the higher-level application, it sends the MAC address to the LESa to all 1's.
, And make a BUS ATM address request (LE-
ARP request) (step S25). Next, LESa
Returns BUS ATM address to LECa (LE-
ARP response) (step S26).

Next, LECa connects to BUS to obtain the MAC from the IP address of the communication partner (step S27). Next, the BUS sets the multicast VCC for all LECs (step S28). next,
LECa is the MAC from the IP address (β) of the communication partner.
IP / MAC-AR to BUS to obtain address
The P request is made, and the BUS is characterized by "A shown in FIG. 9".
The RP search table is searched for an IP address (β) with a hash key or the like, and if there is a corresponding address, the MAC address (Y) on the ARP cache table is returned to LECa. If the corresponding IP address is not registered in the ARP search table, the IP / MAC-ARP request is transferred to all LECs on the multicast VCC (connection) (step S29) ".

Next, all LECs are IP / MAC-ARP
When the request is accepted, it is confirmed whether or not the own IP address matches the request (β), and if they match, the MAC address (Y) is returned (ARP response) (step S3).
0). Next, the BUS monitors the IP header shown in FIG. 8, and if the header is an ARP response, the BUS that sent the reply is sent to the ARP search table and ARP cache shown in FIG. It registers in the table and returns the ARP response to LECa (step S31). The IP header in FIG. 8 is version VE.
R, header length, service type, length (data length), identification value, flag, fragment offset, time to live, protocol (eg TCP / IP)
, Header checksum, source address, destination address, option list, padding (empty data), and data.

Next, LECa, upon receiving the ARP response, requests LESb to convert the ATM address corresponding to the MAC address (Y) (LE-ARP request) (step S32). LESb returns the ATM address (B) to LECa (LE-ARP response) (step S
33). Next, LECa is different from LECb in ATM.
Connection is set using the address (B) (SE
TUP) (step S34). Next, when the LECb accepts the connection setting, the LECb returns the connection completion (CONN) (step S35). Next, LECa, LEC
b uses the above connection to transfer the data between the upper applications (step S36).

FIG. 10 shows an LA in a LAN emulation system in which ATM switching devices are distributed in a district.
It is explanatory drawing showing the flow of the control message for N emulation. In FIG. 10, the LAN emulation system includes ATM switching devices 57 and 61 and L
AN emulation server devices LES 52 and 59,
Broadcast communication server devices BUS53, 60, proxy client device LEC58, client devices LEC54-
56 and 62-64.

(Operation): In FIG. 10, the AT
LES 52, 5 that manage clients in each district when M switching devices are distributed in the districts
9, BUS 53, 60 are arranged in a dispersed manner. At this time, the LAN emulation server is provided with an LEC 58 having a proxy function as a representative that receives requests from clients in each district.

The proxy LEC 58 displays the "proxy" on the LECs in each district in the same manner as the bridge, and registers (LE-JOIN). LES 52, 59 of each district
Is LE from LEC 54-56, 62-64 in own district
-When the ARP request is accepted, the corresponding M in your area
If the AC address does not exist, L with the "proxy" display
The LE-ARP request is transferred to the EC 58.

LEC 58 having a proxy function is LE-A
If you accept RP, L will be sent to LES 52 and 59 in your area.
Transfer E-ARP, check whether the corresponding MAC address exists in your area, and if it exists, substitute L above.
LE-ARP response via EC58
Return to ES.

Further, the BUSs 53 and 60 also set the multicast connection only to the LEC 58 having the proxy function for the LECs 54 to 56 and 62 to 64 in different areas. When the LEC 58 having the proxy function receives a request for setting a multicast connection,
Requests the connection setting from the BUS 53, 60 in the own area, and the LEs in the own area from the BUS 53, 60
A multicast connection is set for C54 to 56 and C62 to 64. Request for MAC address from IP address in the connection (IP / MAC-A
RP).

FIG. 11 is a functional block diagram of the LAN emulation server device LES. In FIG. 11,
The LAN emulation server device LES includes a layer management circuit 65, a LECS circuit 66, and a proxy LEC circuit 6.
7, LES circuit 68, BUS circuit 69, ARP cache circuit 70, connection management layer circuit 71
And an adaptation layer circuit 72 and an ATM layer circuit 73. In the configuration of FIG. 11, the function of the proxy client device LEC58 described in FIG. 10 is incorporated in the LAN emulation server device LES. This simplifies the system configuration and enhances the functionality of the server device LES.

In FIG. 11, LECS 66 is L
The addresses of the LES 68 and the BUS 69 are given to the AN emulation client device LEC, and the connection information for access is given. LES68
AR that derives ATM address from MAC address
It has a P function. The proxy LEC 67 represents the LEC of each district and registers as a “proxy” with the LES of other districts. Request from LES of other districts
It has the function of transferring to The BUS 69 has a multicast transmission of ARP request and a forward function of unicast data whose address is unknown. When forwarding the multicast data, it has a function of inquiring to the ARP cache function and confirming whether or not the corresponding IP address already exists.

The ARP cache circuit 70 has a function of monitoring the ARP response, storing the responding IP / MAC address in the ARP cache table, and searching the ARP cache table in response to the inquiry from the BUS 69. Connection management layer circuit 71
Sets and releases the ATM connection. The adaptation layer circuit 72 transfers and manages frame information for setting and releasing the connection. The ATM layer circuit 73 controls line signals and sends and receives ATM cells. The layer management circuit 65 sets and manages the configuration information of each layer.

(Operation): Signal control of the line and transmission / reception of ATM cells are performed by the ATM layer circuit 73, transfer / management of frame information for connection setting and release is performed by the adaptation layer circuit 72, and connection of ATM is performed. Connection management layer circuit 7 for setting and releasing
1 is performed, and the LECS 66 is used to give the LES and BUS addresses to the LEC and the connection information for access, and the ARP function for converting the MAC address to the ATM address is used by the LES 68.
Is registered on behalf of the LES of each district as a proxy for the LES of other districts, and the request from the LES of other districts is forwarded to the LES of the own district by the proxy LEC, and the ARP request is made. Of unicast data whose address is unknown is forwarded by BUS69, and the ARP response is monitored and there is a response IP / MAC.
Store address in ARP cache table, BUS
The ARP cache circuit 70 searches the ARP cache table for the inquiry from
The layer management circuit 65 sets and manages the configuration information of each layer.
Done in.

FIG. 12 is a functional block diagram of the LAN emulation client device LEC. In FIG. 12, the LAN emulation client device LEC
Is composed of a layer management circuit 29, an upper application circuit 30, a LAN emulation layer circuit 31, a connection management layer circuit 32, an adaptation layer circuit 33, and an ATM layer circuit 34. The twelve configurations can be similarly applied to the proxy LAN emulation client device LEC58 in FIG. 1 described above.

In FIG. 12, the upper application circuit 30 is an application circuit that operates on the existing LAN protocol. The LAN emulation layer circuit 31 performs AT operation based on the existing LAN protocol.
Simulate using M connection. The connection management layer circuit 32 sets / releases the ATM connection. The adaptation layer circuit 33 transfers and manages frame information for setting and releasing the connection. The ATM layer circuit 34 controls the line signal and
Transmits and receives TM cells. The layer management circuit 29 sets and manages the configuration information of each layer.

(Operation): Signal control of the line and transmission of ATM cells are carried out by the ATM layer circuit 34, and setting / releasing of the ATM connection is carried out by the connection management layer circuit 32 to set / release the connection. The transfer and management of frame information is performed by the adaptation layer circuit 3
3, the operation of the existing LAN protocol is simulated by using the ATM connection in the LAN emulation layer circuit 31, and the operation on the existing LAN protocol is performed in the upper application circuit 30. The layer management circuit 29 sets and manages the configuration information.

(Effects of the Embodiment of the Present Invention) According to the above-described embodiments of the present invention, "LAN emulation over AT" defined by the ATM forum is provided.
In a LAN emulation server based on "M specifications," (1) learn the network address once used and the physical address of the terminal in the address resolution procedure for deriving the physical address of the terminal of the communication partner from the network layer address used for LAN communication. Means
When the corresponding network address and physical address have already been registered for the second and subsequent address resolution requests, the means for not performing the multicast communication to the terminals of the ATM network is provided, thereby address resolution in the ATM switching network. It is possible to reduce the time required for multicast and also reduce the multicast traffic.

(2) Further, when the ATM switching devices are distributed and arranged in different areas, LAN emulation server devices for managing terminals (clients) of the respective areas are distributed and arranged as servers. By providing a proxy client function representing a client in each area, it is possible to reduce the control procedure between ATM switching devices and also reduce the traffic between ATM switching devices.

As described above, the existing LAN communication can be simulated at high speed and efficiently in the ATM switching network. Further, by providing the proxy LEC function in the LAN emulation server device, the configuration of the LAN emulation system can be simplified and the functionality of the LAN emulation server device can be enhanced.

(Other Embodiments) (1) In the above-described embodiment of FIG. 10, the proxy LAN emulation client device 58 may be provided as a router. Also, LES52, 59 and BUS53, 6
0 and 0 can be provided as routers.

(2) Further, not only the ATM switching device,
It can be applied to various communication devices as an ATM communication device.

[0049]

As described above, the first aspect of the present invention is an address resolution process for deriving the physical address of the terminal of the communication partner from the address of the network layer, and manages the network address and the physical address of the terminal that have been used. Then
If the corresponding network address and physical address are already managed for the address resolution request, A
Since multicast communication or broadcast communication is not performed to the terminals of the TM network, the time for address resolution in LAN emulation can be shortened, and the amount of broadcast traffic can also be reduced.

According to a second aspect of the present invention, each communication device in the LAN emulation system comprises a plurality of LAN emulation client devices, a LAN emulation server device, and a broadcast communication server device, and a proxy client is provided between the communication devices. A device is provided, and this device is a LAN
By communicating with a plurality of LAN emulation client devices via the emulation server device or the broadcast communication server device, it is possible to simplify the control procedure between the communication devices and reduce the communication traffic between the communication devices.

Further, the third invention manages a network address which has been used in the LAN emulation server device and a physical address of the terminal, and when an address search request is given from the address resolution means, an address for searching the requested address. By providing the management means, the time for address resolution can be shortened.

Furthermore, in the fourth invention, the LAN emulation server device is provided with proxy client means for relaying communication with other LAN emulation server devices as a proxy function of a plurality of LAN emulation client devices. It is possible to reduce the communication control procedure and the amount of communication traffic.

[Brief description of drawings]

FIG. 1 is a communication sequence diagram of LAN emulation over ATM according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional ATM communication system.

FIG. 3 LAN emulation over A of the conventional example
It is explanatory drawing of TM.

FIG. 4 LAN emulation over A in the conventional example
It is a model block diagram of TM.

FIG. 5 is a functional configuration diagram of a conventional LAN emulation server device.

FIG. 6 LAN emulation over A of the conventional example
It is a communication sequence diagram of TM.

FIG. 7 is a block diagram of a conventional LAN emulation system.

FIG. 8 is a configuration diagram of an IP header according to the embodiment.

FIG. 9 is a configuration diagram of a cache table according to the embodiment.

FIG. 10 is a configuration diagram of a LAN emulation system according to the embodiment.

FIG. 11 is a functional configuration diagram of the LAN emulation server device of the embodiment.

FIG. 12 is a functional configuration diagram of a LAN emulation client LEC according to the embodiment.

[Explanation of symbols]

BUS ... Broadcast and Unknown
Server (broadcast communication device), LEC ... LAN emulation client device, LES ... LAN emulation server device, LECS ... LAN emulation configuration server device.

Claims (4)

[Claims] 1. A LAN for performing address resolution processing for deriving a physical address of a terminal of a communication partner from an address of a network layer used for LAN communication, and transferring a packet of the network layer to a terminal on an ATM network.
In the emulation method, in the above address resolution processing, the network address and the physical address of the terminal that have been used are managed, and if the corresponding network address and physical address are already managed in response to the address resolution request, If multicast communication or broadcast communication to the terminal on the ATM network is not carried out and the corresponding network address and physical address are not managed, it is necessary to carry out the multicast communication or broadcast communication to the terminal on the ATM network. Characteristic LAN emulation method. 2. A LAN emulation system comprising a plurality of communication devices for transferring network layer packets to terminals on an ATM network, wherein each communication device comprises a plurality of LAN emulation client devices and a LAN emulation server device. , A proxy client that is connected to a broadcast communication server device under its control and relays communication with a plurality of LAN emulation client devices under another communication device on behalf of a plurality of LAN emulation client devices under one communication device. A device is interposed between communication devices, and the proxy client device communicates with the plurality of LAN emulation client devices via the LAN emulation server device or the broadcast communication server device. Simulation system. 3. A LAN emulation server device comprising address solving means for deriving a physical address of a terminal of a communication partner from an address of a network layer, managing a network address and a physical address of a terminal which have been used and managing the address. A LAN emulation server device comprising address management means for searching a requested address and outputting a search result when an address search request is given from the LAN emulation server device. 4. A LAN emulation server device comprising address resolution means for deriving a physical address of a terminal of a communication partner from an address of a network layer, wherein a plurality of LAN emulation client devices under the communication device to which the own LAN emulation server device is connected. The LAN emulation server device is provided with a proxy client unit that relays communication with another LAN emulation server device as a proxy function of the above.