Inter-network connecting device

Details Inter-network connecting device Inter-network connecting device

2000-03-22

2003-09-23

Maung, Zarni (Department: 2154)

Electrical computers and digital processing systems: multicomput

Network-to-computer interfacing

C709S249000, C370S392000

Reexamination Certificate

active

06625662

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an inter-network connecting devise.which transmits a message having a protocol according to a plurality of protocol layers respectively defined as a physical layer to upper layers. The inter-network connecting device is disposed between plural networks and has a function of connecting these networks to each other at a specific protocol layer, and which is used for transmitting a message including its destination address data from a sender to its destination which are in different networks. The invention relates particularly to a network connecting apparatus which makes it possible to efficiently perform such processes as a transmission path determining process and the like in a network connecting apparatus by reducing looping processes or replacing them with comparatively simple processes mainly with regard to such processes which have been up to now complicated and time-consuming as a process of extracting a network address or a subnetwork address from the destination address of a received message (received frame) and the like, and thereby makes it possible to improve the processing speed and make a cost reduction by simplification of the hardware to be used, and be formed into hardware as a whole.
BACKGROUND ART
Such a telephone-network built for the purpose of intercommunication by voice as a public line of telephone communication, a leased line, and the like is restricted in transmission quality and transmission speed when being used in data communication. Therefore, public digital data networks more adaptive in such characteristics specific to data communication as data traffic characteristics and the like are being built up in various countries including Japan. The public digital data network uses transmission paths and switching systems for digital signals, and some services by circuit switching networks or packet switching networks are provided in Japan. For international connection also, international standardization is promoted by the International Telegraph and Telephone Consultative Committee (CCITT), and at present has been almost provided as recommendations (X-series Recommendations) related to such new data networks as circuit switching systems, packet switching systems, leased digital lines, and the like.
In recent years, a network called a Local Area Network (LAN) has been widely used for the purpose of sharing such information (data) as a database or the like and peripheral apparatuses. The LAN is a network for connecting digital apparatuses such as computers, communication terminals and the like distributed in such a limited specific area as an office, a factory, a laboratory, a university and the like, and has a kind of switching function. In such a LAN also, standardization of protocols and the like has been performed by Committee 802 of the Institute of Electrical and Electronic Engineers (IEEE), the International Standardization Organization (ISO) and the like.
The reference model for the Open Systems Interconnection (OSI) being applied to a public digital data network and the above-mentioned LAN protocol standardized by IEEE are defined by plural protocol layers which are defined as a physical layer to upper layers. Protocols used widely in Wide Area Networks (WAN) or other LANs and the like also are generally defined according to plural protocol layers. In such a way, most network protocols are defined according to plural protocol layers.
Plural networks such as LANS, WANs, public digital networks, or the like have been connected with one another up to now. For example, even networks which have at least a few protocol layers different from one another out of a plurality of protocol layers to define a protocol for a message to be transmitted have been connected with one another up to now.
Hereupon, an inter-network connecting device for connecting with each other through the second layer two networks which have the same Media Access Control (MAC) layer which is the second layer for OSI is called a bridge or the like. An inter-network connecting device for connecting to one another a plurality of networks which are different from one another in the first to seventh layers for OSI is called a gateway or the like. And an inter-network connecting device, as referred to as an embodiment described later in this application, for connecting to one another through the third layer a plurality of networks which are different from one another in the first to third layers for OSI is called a router or the like.
An inter-network connecting device which the present invention considers as an object is not limited to a router in an embodiment described later, but can be applied also to a bridge and a gateway described above for example. And also networks which an inter-network connecting device according to the present invention connects to one another are not limited to the above-mentioned specific LANS, but may be various LANS, WANs, public digital data networks.
Hereupon, an inter-network connecting device used up to now for connecting LANs to one another, particularly an Interment Protocol (IP) router is described in detail with regard to the present invention.
An IP router performs a process for determining a transmission path of a received frame (hereinafter referred to as an IP routing process) on the basis of the destination IP address in the IP header contained in the received frame. Such an IP routing process is performed as extracting various address components, particularly the network address of the destination IP address.
However, a general inter-network connecting device also performs a series of processes (called a routing process) for transferring a received message to an appropriate network at the destination side to be connected to the said inter-network connecting device as extracting various address components from the destination address in the received message and performing a control according to the various address components.
The destination IP address of 32 bits is composed of a total of three fields, namely, a class bit field, a network address bit field and a host address bit field, as shown in FIG.
1
. Each of the fields is composed in this order from the most significant bit (MSB) side to the least significant bit (LSB) side of the IP address of 32 bits. As shown in
FIG. 1
, the number of bits of a network address bit field, the number of bits of a host address bit field as well as the number of bits of a class bit field are determined according to the address classes A to C indicated by the class bits.
As shown in
FIG. 1
, first, in case that the MSB of an IP address of 32 bits is “0”, an address class of “A” (hereinafter referred to as class A) is shown in the class bit field. In this case the network address bit field becomes 7 bits and the host address bit field becomes 24 bits. In case that the first two bits from the MSB of an IP address are “10”, an address class of “B” (referred to as class B) is shown in the class bit field. In this case the network address bit field becomes 14 bits and the host address bit field becomes 16 bits. And in the first three bits from the MSB of an IP address are “110”, an address class of “C” (referred to as class C) is shown in the class bit field. In this case the network address bit field becomes 21 bits and the host address bit field becomes 8 bits.
Said network address indicates the address of a network on the Internet. The network address is represented with said class bits and said network address bits. A host address indicates the address of an individual host in a network indicated by said network addresses. The host address is represented with said host address bits.
Said IP router is disposed between plural networks and checks the destination IP address in the IP header contained in a received frame received from a network. The IP router checks particularly the network address in a destination IP address and when the IP network address is a network connected to a port of that IP router (its own port), the IP router extracts the MAC address

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