Path setting method, communication unit and storage medium

Details Path setting method, communication unit and storage medium Path setting method, communication unit and storage medium

1999-04-13

2003-12-02

Cangialosi, Salvatore (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395540

Reexamination Certificate

active

06658001

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to path setting methods, communication units and storage mediums, and more particularly to a path setting method which sets a short-cut path in an internetwork having a connection oriented network as an infrastructure, a communication unit which sets such a short-cut path, and a computer-readable storage medium which stores a program for causing a computer to set such a short-cut path.
Recently, much attention is drawn to the interworking of a Local Area Network (LAN) and an Asynchronous Transfer Mode (ATM) which is a switching system that provides high-speed switching by use of high-speed transmission line and hardware processing. The LAN was developed to realize a communication between computers in a relatively limited range. However, there are demands to connect distributed LANs by the ATM which provides a switching technique by use of the high-speed hardware processing, a high-speed interface and a long-distance transmission.
In addition, according to the ATM, it is possible to logically multiplex data types such as LAN data and audio data in one connection, and for this reason, it is possible to simplify the network itself. Such a simplified network enables a facilitated network management.
In order to realize the connection between the LANs by the ATM, it is necessary to provide a LAN service on an ATM network. Hence, standard protocols such as LAN Emulation Over ATM (LANE) and Multi-Protocol Over ATM (MPOA) have been prescribed. The LANE is used to set a connection within a sub network (hereinafter simply referred to as a subnet) which is logically defined in the ATM. On the other hand, the MPOA is used to set a connection spanning a plurality of subnets.
The LANE itself is described in Y. Hariguchi, “NETWORK TECHNOLOGY, ATM: LAN Emulation (LANE)”, UNIX MAGAZINE 1998, 1, pp.29-40, and “Introduction to LAN, How to Avoid Bottleneck”, NIKKEI COMMUNICATIONS 1997, 6.2, pp.72-80, for example. In addition, the MPOA itself is described in the latter article, that is, “Introduction to LAN, How to Avoid Bottleneck”, NIKKEI COMMUNICATIONS 1997, 6.2, pp.72-80, for example. Accordingly, a detailed description on the LANE itself and the MPOA itself will be omitted in this specification.
As will be described later, the present invention provides a means for setting a connection at a high speed in a simple manner when communicating among a plurality of subnets using the MPOA, and the present invention is applicable to both private networks and public networks.
2. Description of the Related Art
A host unit connected to a LAN generates a frame when data is generated, and sends the frame on a shared media. The frame indicates address information such as an Internet Protocol (IP) address of a destination host unit and a Media Access Control (MAC) address. A host unit which is connected to the same shared media receives the frame if a destination address within the frame is the address of this host unit or, if this host unit judges that this host unit must forward the frame. Otherwise, this host unit discards the frame.
On the other hand, in the connection oriented network such as the ATM network, an ATM device sets a logical connection with a destination ATM device when the data is generated, and sends the data on the connection in the form of cells. As a result, it is possible to transmit the data only with respect to the device which is to receive the data, and it is unnecessary to carry out a process of checking the destination address at the receiving end, as is necessary in the case of the LAN.
Accordingly, in order to mutually connect two networks having different characteristics, it is necessary to use a special protocol such as the LANE and the MPOA described above.
The LANE, which is logically defined on the ATM network, provides the LAN services on a broadcast domain called Emulated LAN (ELAN). Hence, the LANE provides a protocol which enables a host unit on the LAN to make a communication without being aware of the ATM network. The LAN services provided on the broadcast domain include unicast, multicast, broadcast and the like. However, when making a communication between edge devices in an ATM network, the edge devices may belong to different ELANs although the edge devices are connected in the same ATM network. In other words, even though a direct connection can be set between the edge devices via an ATM switch, it is necessary to connect the ELANs via a router, similarly to the case where a router is required to connect the subnets on the LAN. For this reason, in a communication spanning a plurality of ELANs, the performance of the router through which the connection is made forms the bottleneck, thereby making it difficult to sufficiently utilize the performance of the ATM network.
The MPOA is a protocol which was standardized to eliminate the above described problems. According to the MPOA, an address resolution message defined by the MPOA is transmitted on the connection which is once set via the router using the LANE, so as to receive the ATM address from a device which becomes the final destination within the ATM network. By setting the connection directly to the destination device using this ATM address, it is possible to make a high-speed communication which is independent of the performance of the router.
FIG. 1
is a diagram showing the physical construction of an example of an ATM-LAN network. The ATM-LAN network includes an ATM switch
500
, edge devices
501
and
502
, routers
503
and
504
, and ATM host units
506
and
507
which are connected as shown in FIG.
1
. The edge device
501
is connected to a device
512
, such as a work station, via a LAN
511
. The edge device
502
is connected to a device, such as a work station, via a LAN
521
. In the physical layer, the devices such as the edge devices
501
and
502
, the routers
503
and
504
, and the ATM host units
506
and
507
are connected to the ATM switch
50
by use of a physical medium such as an optical fiber cable and an Unshielded Twisted Pair (UTP) cable.
For example, the edge device
501
at the transmitting source (or request source) transmits a connection set request to the ATM switch
500
by use of a SETUP message of a signaling protocol for transmitting the cells. For example, the edge device
502
at the destination is specified by the ATM address. The ATM switch
500
transfers the SETUP message to the destination edge device
502
, and in the process of transferring a CONNECT message from the destination edge device
502
to the transmitting source edge device
501
, the ATM switch
500
assigns a connection identifier to each of the edge devices
501
and
502
which is unique in each physical medium, that is, a Virtual Path Identifier/Virtual Channel Identifier (VPI/VCI). By use of this connection identifier, it becomes possible to set a plurality of logical connections on one physical medium. The edge device
501
which transmits the cells indicates this connection identifier within a header of the cell. The ATM switch
500
recognizes the connection identifier of the received cell by hardware, and sends the cell via an appropriate path.
On the other hand, an internetwork protocol such as the IP operates in a layer in a higher level, and a logical subnet is formed by allocating an internetwork address such as the IP address to each device. In
FIG. 1
, the ATM switch
500
, the edge device
501
, the router
503
and the ATM host unit
506
form a subnet
511
. In addition, the ATM switch
500
, the routers
503
and
504
, and the ATM host unit
507
form a subnet
512
. Furthermore, the ATM switch
500
, the edge device
502
and the router
504
form a subnet
513
.
FIG. 2
is a diagram logically showing the physical construction of
FIG. 1
from the internetwork point of view. In
FIG. 2
, those parts which are the same as those corresponding parts in
FIG. 1
are designated by the same reference numerals, and a description thereof will be omitted. In
FIG. 2
, the subnets
511
t

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