Local area network with a header converter

Details Local area network with a header converter Local area network with a header converter

1998-04-16

2003-03-04

Ton, Dang (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395100

Reexamination Certificate

active

06529511

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a local area network operating in the asynchronous transfer mode (ATM), more particularly, a one-way or two-way ring network, comprising a plurality of stations and network interfaces (ATM transceivers) assigned to these stations and/or further networks comprising further stations, which network interfaces have each a send and a receive ring connection, the exchange of information being effected digitally via ATM cells in whose headers are stored address data, more particularly, trunk identifiers (VPI virtual path identifiers) and link identifiers (VCI virtual channel identifiers). In addition, the invention relates to an ATM cell suitable for use in such a network and a network interface for such a local area network and, finally, a stackable ATM unit comprising a plurality of network interfaces for constructing a switching point (switch).
In a local area network operating in the asynchronous transfer mode (ATM), fixed-length blocks are formed from the information to be transmitted (messages). An additional control indication bit completes each block form to a transmission unit called an ATM cell. An ATM cell is thus formed by a header and a payload which contains the information to be transmitted.
The ATM technique is used in different switching services such as data transmission services, speech transmission services, video services (for example, video conferences, video data bases), or when multimedia information in which speech, data and video information is combined is to be transmitted. An ATM network may then be a private network as well as a public network. A public ATM network is, for example, the B-ISDN network (broadband integrated services digital network). Private or public ATM networks may be connected based on the predefined ATM standard.
With ATM, cells are uninterruptedly transmitted on each transmission section. If no payload is to be sent at a certain time, specially marked idle cells are sent. In this manner, the ATM payload cells are transmitted independently of each other, because the distances in time on the line between neighboring payload cells are generally different. This type of transmission is therefore referenced asynchronous. Thus ATM represents an asynchronous transmission of payload cells of fixed length.
A distinction is made in payload cells between user cells containing, for example, messages or data of the user of a previously set-up connection in their information field, and signaling cells containing overhead bytes in their information field, for example, for the control unit of a network interface.
In ATM networks, the available transmission capacity (bandwidth) of a broadband channel is subdivided into so-called virtual paths. A virtual path represents in its turn a group of virtual channels. When a virtual channel is set up between a transmitter and a receiver, first the suitable virtual path is selected. Subsequently, a part of the bandwidth is occupied as a virtual channel of this path. For the identification of the virtual channel is used the identifier VCI (virtual channel identifier). For the identification of the paths is used the identifier VPI (virtual path identifier). This allows each transmitted cell to be allocated unambiguously because the combination VPI&VCI (virtual path and virtual channel identifiers) represents the logic identifier for the defined connection.
In addition, a distinction is made between a unicast connection set up between a single user of a first station and a user of a second station. When the connection is set up between a first user and a plurality of further users, the connection is referenced a multicast connection. When there are an arbitrary number of further users with such a multicast connection, this is called a broadcast connection.
From EP 0 614 296 A2 is known a local area ATM network of the type defined in the opening paragraph in which both user cells and signaling cells are processed as payload cells. Each network interface is then assigned a station. The user cells then contain the actual information, for example, messages or data of the user of this connection. When a virtual link is used, for example, for transmitting speech signals (telephone call), the information field of the user cell contains speech data. On the other hand, a signaling cell contains in its information field overhead bytes which are necessary for example, for coordination of the switching function in the ring, and more particularly, for setting up a connection or clearing the connection after the information has been transmitted. On the other hand, signaling cells are also used for transmitting overhead bytes between a station and the network. In such a case, the signaling cell has a standardized structure prescribed by UNI/NNI.
In such a known network, the connection is set up in the following manner: in the case of a connection request from a transmitter station to at least one receiver station, first a signaling cell is generated containing a query about the state of the receiver station. The at least one receiver station sends at least one signaling cell in response to the query which signalling cell contains the information about its status. Upon reception of the status information, the transmitter station forms at least one signaling cell for setting up the connection if the status of the at least one receiver station allows a connection. Subsequently, the connection is set up and the information is transmitted. The connection is cleared in reverse order.
From U.S. Pat. No. 5,600,795 is known a local area network operating in the asynchronous transfer mode (ATM), in which a connection is set up in similar manner in that first a control arrangement assigned to a transmitter station receives a signaling cell coming from the transmitter station which cell contains a realizable request for a unicast or multi-cast/broadcast connection of a user of the transmitter station. Subsequently, the signaling cell is sent to a user of at least one receiver station while the signaling cell contains in its payload at least one data about the user, the address of the transmitter station and a user-related identification for the return link. Upon reception of the signaling cell originating from the transmitter station, a control arrangement assigned to the receiver station generates a signaling cell to be sent to the transmitter station, which signaling cell contains in its payload at least an indication about the address of the assigned receiver station and a user-related identifier for the down link. Also in this network, each station has its own assigned network interface.
From “Telekommunikation aktuell, ATM Anwendungen, Multimediakommunikation über Datenautobahnen, VDE Verlag GmbH 1995”, pp. 11-16 is known the basic structure of ATM cells according to the prescribed ATM standard. Hence, the ATM cell comprises a payload part having a length of 48 bytes and a header having a length of 5 bytes. The header is then structured differently depending on whether it is an ATM cell which is transmitted via an interface between a station and the network (UNI, user network interface) or between two different networks (NNI, network network interface).
When a UNI payload cell is concerned, the first 4 bits of the header form the GFC function (generic flow control). This makes it possible to avoid overload situations in the network due to a transgression of predefined bandwidths. Subsequently, a bit sequence of 8 bits VPI and 16 bits VCI follows for defining the virtual path and virtual channel, respectively. The next information of the header cell relates to the type of cell (PT, payload type) with which a distinction is made in this state of the art between user cells and signaling cells. Further information is given by the cell loss priority (CLP) and the header error control (HEC). The above structures PT, CLP, HEC are identical in UNI/NNI cells. In contrast, the NNI cell distinguishes itself from the UNI cell in that in lieu of the GFC structure occurring in the UNI cell, the st

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