End equipment and router

Details End equipment and router End equipment and router

1998-12-14

2003-09-23

Sheikh, Ayaz (Department: 2155)

Electrical computers and digital processing systems: multicomput

Computer-to-computer data routing

C709S218000, C370S392000, C370S397000, C370S401000

Reexamination Certificate

active

06625658

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an end equipment and a router, and in particular to an end equipment and a router which execute a destination address resolution of a data packet.
In recent years, a Non-Broadcast Multi Access (hereinafter abbreviated as NBMA) network represented by an ATM (Asynchronous Transfer Mode) network has numerously come into use for a network environment centering around a Distance Carrier and a network provider. In the mechanism of a data transmission a connection type of the NBMA network is quite different from a connectionless type broadcast network such as an Ethernet and the like. However, in either of both networks, an address resolution protocol (hereinafter referred to as ARP protocol) is required for recognizing a data link layer address each hardware has from a network layer logical address of a destination end equipment to which a packet is transmitted.
2. Description of the Related Art
In general, an end equipment or apparatus is connected to a LAN which is a subnetwork, and LAN's are mutually connected with a router which is a relaying or repeating equipment to form an enterprise network, a campus network and the like.
When the end equipments communicate with each other within the same subnetwork, it is possible to transmit a packet directly to a destination end equipment. However, the end equipments in different subnetworks transmit the packet to a router at the boundary of the subnetworks for the direct transmission. The router which has received the packet determines to which router the packet should be transmitted in order to deliver the packet to the destination end equipment and transfers the packet to the next router. In this way, it also becomes possible to communicate with the end equipments in the different subnetworks.
It is to be noted that the end equipment transmits the packet by a transmission processor in an OS (operating system). The OS has an address list of the network, which can be reached from itself, as a routing table. In each of table entries, a destination IP address, its own output interface, a gateway address and the like are written.
The gateway address indicates the IP address of the router to which the packet is to be sent next, in order to send the packet to a destination end equipment in a subnetwork other than the home subnetwork. When the destination is for the same subnetwork, not the IP address of the router but that of the destination end equipment or its own IP address is set for the gateway address.
In addition, the OS holds an ARP table for a data link layer whereby a network layer address corresponds to a data link layer address.
When the packet is inputted including the destination address designated by the network layer address, for instance, the IP address (hereinafter referred only to the IP address), the transmission processor retrieves the routing table with the destination IP address as a key, and obtains the output interface and the gateway address.
When the destination end equipment is in the same subnetwork, the transmission processor retrieves the ARP table corresponding to the output interface to obtain a hardware address corresponding to the IP address for the communication. When the destination end equipment is in another subnetwork, the transmission processor retrieves the ARP table with the address of a gateway router obtained from the routing table as a key.
When no entry is found in the ARP table, the OS makes a MAC address demand for the destination IP address to all of the end equipments within the same subnetwork by using an ARP protocol. The MAC address having been obtained, it becomes possible to make the end equipment communicate with the router.
For instance, the ARP table which the end equipment in a conventional Ethernet in the broadcast network holds, where the IP address corresponds to the MAC address, enables the recognition of the MAC address from the IP address of the end equipment or the gateway which can be reached directly, as well as the communication between the end equipment and the router by using this MAC address.
In addition, the ARP protocol inquires the MAC address which is the data link layer address of all of the end equipments in the network by broadcast to obtain the same.
FIGS. 15 and 16
show examples of a conventional ARP protocol. In these examples, protocols on an ATM network which has been often used especially in recent years as an example of an NBMA network are shown. Over an ATM network
10
, subnetworks
20
_
1
-
20
_
3
(hereinafter occasionally referred to as “
20
” in general) are provided, and the subnetworks
20
_
1
,
20
_
2
are mutually connected with a router
30
_
1
and the subnetworks
20
_
2
,
20
_
3
are mutually connected with a router
30
_
2
. Also, the subnetworks
20
_
1
,
20
_
3
are connected to end equipments
40
_
1
,
40
_
2
(hereinafter occasionally referred to as “
40
” in general).
FIG. 15A
shows an example of an ATM_ARP (ATM Address Resolution Protocol; hereinafter referred to as ATM_ARP protocol). In this example, the subnetwork
20
is a logical subnetwork (LIS: Logical IP Subnetwork) in a network layer. To the subnetwork
20
_
1
is further connected an end equipment
40
_
3
and to each logical subnetwork
20
are connected ATM_ARP servers
31
_
1
-
3
(hereinafter occasionally referred to as “
31
” in general).
The ATM_ARP protocol is designed to achieve an equal function to an ARP protocol on an ATM-LAN. Namely, it is the ARP protocol in an IPoverATM which carries out the transfer of an IP packet by using an ATM connection, provided between the end equipments by an ATM address instead of the MAC address, especially an SVC (Switched Virtual Connection).
In operation, first of all, each of the end equipments
40
registers its own IP address and ATM address in the ATM_ARP server which manages itself.
Sending a data packet addressed to the end equipment
40
_
2
of a different logical subnetwork
20
_
3
where no connection is established, the end equipment
40
_
1
sends an ARP request packet in which the destination IP address is added to the ATM_ARP server
31
_
1
.
The ATM_ARP server
31
_
1
returns an ARP response packet including the ATM address of a next hop router
30
_
1
to the end equipment
40
_
1
. The end equipment
40
_
1
transfers the packet to the router
30
_
1
, which executes the address resolution by the ATM_ARP server
31
_
2
to transfer the packet to the router
30
_
2
.
The router
30
_
2
recognizes the ATM address of the end equipment
40
_
2
by sending the ARP request packet to the ATM_ARP server
31
_
3
, and completes the communication by sending the data packet to the end equipment
40
_
2
.
Since there is originally no concept of broadcast in the NBMA network
10
, it is impossible to make any inquiry by broadcast. Therefore, by preparing the ATM_ARP server
31
, the ATM_ARP protocol executes a registering management of the ATM address for the end equipment within each of the logical subnetworks
20
to execute the address resolution. Each of the logical subnetworks
20
corresponds to an area, on the NBMA network
10
of the end equipment, of which each of the ATM_ARP servers
31
is in charge.
Namely, the logical subnetwork
20
is logically made over the ATM network
10
which can be communicated only with the. ATM address which is the address of the data link layer. Therefore, if only the ATM address of the end equipment
40
_
2
of the destination is recognized even when the communication is provided over the different logical subnetworks
20
, using this address enables a source end equipment
40
_
1
to set up a VC (Virtual Connection) which is a direct path to the destination end equipment and to directly transmit the packet.
However, since the ATM_ARP protocol has to provide the packet communication over the logical subnetworks
20
through the router, the direct path connection between the end equipments which the original ATM network can provide cannot be set up.
As a protocol which provides a mechanism o

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