Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-09-28
2001-04-17
Ton, Dang (Department: 2732)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06219349
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to broadband switching networks using ATM (Asynchronous Transfer Mode) technics.
2. Description of the Related Art
Efforts for integrating individual service networks such as telephone networks, data networks, FAX networks, and so forth which have been developed and constructed over 100 years of history into one network system with ISDN (Integrated Services Digital Network) have been made throughout the world.
As the first step for constructing the ISDN system, narrow band ISDN systems have been operated in advanced countries including Japan since 1988. In addition, besides integration with a broadcasting network by using a broadband ISDN based on the ATM technics, the engineering developments of the ISDN network have been initiated by CCITT (International Telegraph and Telephone Consultative Committee) and promoted in major laboratories in the world.
The broadband ISDN network is provided with an ultra high speed user-network interface with a transmission speed of 155.52 Mbps or 622.08 Mbps. Thus, through the same interface, the conventional telephones, facsimile machines, and so forth can be treated as a constant speed service CBR (Continuous Bit Rate), while computer data with large capacity and ultra high speed including motion pictures, such as, high definition TV pictures, CAD (Computer Aided Design) data, and computer graphics data, and so forth can be treated as a variable speed service VBR (Variable Bit Rate). Thus, with the CBR and the VBR services, various data can be flexibly transmitted through the same interface.
However, thus far, before making a communication, the user had to declare call attribute data such as peak traffic, mean traffic, burstiness, terminal equipment type, service quality (for example, cell loss rate, cell transmission delay), and the like upon the network. In accordance with the call attribute data that the user has declared, the network estimates a required communication resource necessary for making the communication with respect to the call, checks the use state of the resource in the network, and determines whether or not to accept the call request. As the result of the determination, when the call request is accepted, the information to be transmitted is divided into packets which have a constant length (53 octets) (the packets are named cells) and then sent to the network. However, occasionally, cells which do not conform with the attribute data being declared may be sent to the network.
Thus, when unexpectedly excessive cells are sent to the network and they are concentrated in one path (as the burstiness is strong, this tendency becomes remarkable), they reside in the network. To prevent that, ATM switches, each of which is a constructional key element of the broadband ISDN network, are provided with a cell buffer with a large storage capacity. However, if such a cell buffer cannot store the cells which stay in the network, they will be lost. This situation is named a cell discard. When the network receives cells and then marks those which exceeds the range of attribute data declared by so-called polling function as violation cells, they are discarded. In addition, when a terminal equipment sends cells as non-priority cells in VBR such as class B (variable bit rate picture communication) (for example, in hierarchical picture coding system, a method where cells are divided into priority cells and non-priority cells depending on their importance is being considered), they are discarded. If the buffer does not fully store the cells even after the marked cells are discarded, cells in class A (circuit emulation communication) or the like will be also discarded.
Generally, a bit error due to noise or the like over the transmission path is checked with a CRC code disposed at the last position of information to be transmitted. When necessary, by issuing a retransmission request to the sender side, the information with respect to a bit error can be restored. However, when the cell discard is performed, since the receiver side cannot know the transmission of cells, it cannot request the retransmission of the cells to the sender side.
Since the cell discard will become a critical problem in data communication with respect to class C (connection oriented) and class D (support of transmission of connection-less data), a sequence number is provided for the information field of each cell (48 octets) as an ATM adaptation layer function. In addition, a mechanism for detecting the cell discard and for issuing a retransmission request on the receiver side is additionally provided.
On the other hand, for calls in the classes A and B, which should be transmitted in real time, CCITT has recommended a coding system which can withstand the cell discard.
Major problems with respect to the broadband ISDN switching networks which have been studied mainly by CCITT are summarized as follows.
(1) Service quality
(a) Cell discard
As was described earlier, by assigning a sequence number, it is possible to detect a cell loss on the receiver side. However, since calls in the classes A and B should be transmitted in real time, it is substantially difficult to restore cells which are lost by the retransmission. By the coding method, which is a future study subject, it may be possible to reduce the adverse effect of the discard of non-priority cells. However, besides the discard of the normal cells (those which are neither violation cells nor non-priority cells), the discard of violation cells will result in critical problems.
In other words, when a honest (innocent) user unconsciously violates the range of the attribute data being declared, cells that the user has transmitted will be discarded regardless of whether they are priority cells or non-priority cells. In other words, the information received by the network may be lost. In addition, the sender side cannot know what and how much information is lost. To prevent that, a prudent and honest user will always have to declare the attribute data with an allowance although he or she knows that the communication fee will becomes expensive.
On the other hand, a user who wants to save the communication fee will declare the attribute data which is rather small while observing the traffic condition of the network although he or she knows that violation cells may take place. In other words, each user will haggle with the network about the negotiation of the attribute data like playing a game therewith. Whenever the user repeats success and failure in the negotiations with the network, his or her action will escalate.
The increase of such users causes the traffic in the network to be abnormally increased and thereby loosing ordinal cells transmitted by prudent and honest users. Thus, the users have suspicion and apprehension about the network. It is inevitable that the essential purpose of the public communication network, which is “correct, fast, and impartial communication transmission”, is discarded.
Moreover, even in the classes C and D, the same situation will take place. Particularly, in data communication, as was described above, since the loss of information is never permitted, the retransmission of cells which were lost will be performed in a high rank layer.
As the traffic is heavy, probability of occurrence of a cell discard will become high. When the retransmission of cells which were lost is repeated, the traffic will become much higher. Thus, the network will become congested. In other words, the cell discard will result in deteriorating the stability of the network.
(b) Variation of cell delay
As was described above, in high traffic conditions, cells will reside in the network. In other words, the cells will be transmitted with a delay. As the capacity of the switch (the scale of ATM switch) becomes large and/or the number of relays in the network increases, the amount of delay increases. In addition, the amount of delay varies depending on the traffic condition in the network. This variation of the amount of delay is named the
Aida Kazuo
Hidaka Yoshiharu
Ikeda Takashi
Kamura Kouichirou
Kobayashi Hiroshi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Ton Dang
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