Electrical computers and digital processing systems: multicomput – Distributed data processing – Client/server
Reexamination Certificate
2000-07-20
2004-09-07
Thompson, Marc D. (Department: 2144)
Electrical computers and digital processing systems: multicomput
Distributed data processing
Client/server
C370S395530, C370S395540, C709S249000
Reexamination Certificate
active
06789104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communications system and method, and particularly to a communications system and method which emulate connectionless LAN environments on a connection-oriented transport network and automatically assign them to end stations.
2. Description of the Related Art
Asynchronous Transfer Mode (ATM) is a promising technology for multimedia data communications, which offers a range of transmission rates and different qualities of service to efficiently handle various types of I/O traffic over a single network medium, such as data, audio, and video. ATM, a cell-based transport mechanism, enables end stations to communicate through a pre-established path called a virtual channel, and hence is connection oriented. In contrast to this, existing local area networks (LANs) use connectionless protocols and broadcast functions, which cannot guarantee the bandwidth and quality of service required for delivery of realtime audio and video information. Since it is beneficial to combine those technologies, ATM-LAN systems have been developed. This ATM-LAN emulates LAN services across an ATM transport system, realizing more cost-effective and seamless network connections for existing and future LAN applications.
The ATM Forum's LAN Emulation (LANE) specifications Ver 1.0 and 2.0 define the mechanisms to use the vast base of existing LAN applications on an ATM transport system. The LANE emulates network services at the Media Access Control (MAC) layer.
Typically, existing LAN stations are designed to operate on the Ethernet. Because of the lack of a direct ATM access capability, most LAN stations are attached to the ATM network via appropriate ATM hubs or routers having ATM interface. In the LANE terminology, those ATM hubs and routers are referred to as the “LAN emulation clients” (LECs). LAN stations exchange messages with their local LECs, using well-known Ethernet protocols, while the LECs communicate with their peer LECs over an ATM network, according to message formats defined in the LANE specifications. Those LECs provides the LAN end stations with seamless connections, so that LAN applications can be integrated transparently with the ATM network.
FIG. 14
shows the configuration of an ATM network with LAN emulation capabilities. A group of LAN end stations (“stations” for short)
2
a
to
2
c
are connected to their nearest ATM hub
200
, while another group of stations
3
a
to
3
c
to another ATM hub
300
. The ATM hubs
200
and
300
are linked with each other via a “cloud” of switched connection services provided by ATM switching facilities (ATM-SW)
600
. This ATM connection service cloud is also coupled to the following LANE elements: a LAN Emulation Configuration Server (LECS)
100
, LAN Emulation Servers (LES)
400
-
1
and
400
-
2
, and Broadcast and Unknown Servers (BUS)
500
-
1
and
500
-
2
.
The above-listed network elements operate as follows. The ATM switching facilities
600
provide end-to-end switched connectivity for multiple users, with the ATM technologies. The LECS
100
is a server which provides LANE clients with the address of the most appropriate LES and maintains a database of the resultant associations. When joining the network, every LEC (i.e., two ATM hubs in the present case) first turns to the LECS
100
, sending a configuration request message requesting information about which LES should be used. The LECS
100
responds to this request by assigning an appropriate LES to the requesting LEC and sending back the ATM address of that LES. The LESs
400
-
1
and
400
-
2
provide address resolution services in two emulated LAN environments, which are logically defined on the same ATM network. The BUSs
500
-
1
and
500
-
2
support broadcast traffic over the emulated LAN environments. The ATM hubs
200
and
300
are multiport devices accommodating a plurality of LAN stations, the ports of which can be logically assigned to different LAN segments (or broadcast domain), each group of stations forming a separate emulated LAN (ELAN). Two LAN environments are realized in this way, independently of the physical locations of their end stations.
The illustrated system provides two ELANs, which are distinguished by their ELAN-IDs (or ELAN names), ELAN-1 and ELAN-2. Ports on the two ATM hubs
200
and
300
are assigned those ELAN-IDs as shown in the lower half of FIG.
14
. That is, the ports #
1
and #
2
on the ATM hub
200
and the same on the ATM hub
300
are for the first ELAN environment, ELAN-1. This assignment allows the stations
2
a
,
2
b
,
3
a
, and
3
b
to communicate with each other within the domain of ELAN-1. On the other hand, the ports #
3
and #
4
on the ATM hub
200
and the same on the ATM hub
300
are for the second ELAN environment, ELAN-2. This allows the stations
2
c
and
3
c
to communicate with each other within the domain of ELAN-2. The LES
400
-
1
and BUS
500
-
1
are dedicated to ELAN-1, and the LES
400
-
2
and BUS
500
-
2
to ELAN-2.
Conventional ATM hubs, however, require manual set-up operations so that appropriate ELAN-IDs will be assigned to their ports. If the port setup conflicts with the operating parameters of the station being connected, the ATM hub cannot work correctly with that station. Suppose, for example, that the user has relocated the station
2
a
from port #
1
to port #
3
on the ATM hub
200
. In this case, the station
2
a
can no longer work as a member of ELAN-1, since the port #
3
is assigned to ELAN-2. To make the station operate correctly, he/she has to modify the current setup of the ATM hub. This is indeed a burdensome task, particularly for corporate users of ATM-LAN systems. For those users, relocation of LAN stations from one office floor to another is not an unusual event because their organizations tend to change dynamically to remain competitive. In the case that a separate ELAN is deployed for each organizational unit, frequent relocation of stations could impose increased workloads on the network administrators since they have to redefine the ELAN-ID setups of ATM hubs. For this reason, there has been a need for more flexible and easy-to-use ELAN systems.
SUMMARY OF THE INVENTION
Taking the above into consideration, an object of the present invention is to provide a communications system which automatically assign an appropriate ELAN-ID to each attached end station, whichever hub port is used to physically accommodate the station.
Further, another object of the present invention is to provide a communication method which constructs emulated LAN environments on a connection-oriented network.
To accomplish the first object, according to the present invention, there is provided a communications system which constructs emulated LAN environments on a connection-oriented network. This system comprises the following elements: (a) a plurality of LAN stations each having an identifier; (b) a LAN emulation server employed in each emulated LAN environment to provide address resolution services thereon, each LAN emulation server having a network address (ATM address) on the connection-oriented network; (c) a broadcast server employed in each emulated LAN environment to support broadcast traffic thereon; (d) a LAN emulation configuration server; and (f) a LAN emulation client coupled to at least one of the LAN stations. Here, the LAN emulation configuration server comprises an ATM address manager which manages associations between the identifiers of the LAN stations and the ATM addresses of the LAN emulation servers, and when a specific identifier is given, determining which ATM address is relevant to the given identifier. Further, the LAN emulation client comprises the following elements: an ATM address requesting unit which requests the LAN emulation configuration server to provide the ATM address of the LAN emulation servers, as well as requests the LAN emulation servers to provide the ATM address of the broadcast servers associated therewith; an ELAN configuration database whi
Imanari Namiko
Iriya Katsuhisa
Kanemaki Hideyasu
Okamoto Takeshi
Yamaguchi Minoru
Fujitsu Limited
Katten Munchin Zavis Rosenman
Thompson Marc D.
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