Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-12-16
2004-05-04
Ton, Dang (Department: 2666)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S241100, C370S395100, C370S399000, C370S409000, C370S474000
Reexamination Certificate
active
06731641
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns transmission and reception of signalling cells in the node, especially an ATM node, of a broad-band telecommunications network.
BACKGROUND OF THE INVENTION
As is known, ATM (Asynchronous Transfer Mode) is a connection-oriented packet switching technique chosen by the ITU-T, the international standardisation organisation in the telecommunications field, as the “target solution” for a broad-band multiservice network (B-ISDN). Information is transferred in the cells shown in
FIG. 1
, which include a 5-bit heading and a 48-bit information part. The heading fields include the VPI (Virtual Path Indicator) and the VCI (Virtual Channel Indicator), the Payload Type, the CLP (Cell Loss Priority) and the HEC heading error check with which errors of one bit can be corrected and errors of two bits can be detected.
The standard dimensions of cells allow their swift connection. Cells belonging to different connections are separated from each other with the aid of the VPI and VCI indicators. When setting up a connection, a fixed route or virtual connection is determined through the network along which the cells of the connection will be routed. In network nodes, the cells are connected according to their VPI/VCI values. The VPI/VCI values of cells are connection space specific and will thus generally change together with the connection of the VP or VC level. When the information transfer ends, the connection is disconnected.
FIG. 2
illustrates a reference model of B-ISDN connection practices, wherein the functions are divided on the one hand into layers and on the other hand into levels.
The physical layer PHY includes two partial layers, of which partial layer PM contains transfer system specific bit level tasks while the transfer system convergence layer TC attends to adapting of cells into each transfer system and to cell bounding, to heading error check of the cell and to equalisation of the cell rate.
The ATM layer offers a cell transfer service to the AAL layer. It deals only with the cell heading and its tasks are cell connection, multiplexing and de-multiplexing, cell heading generation and removal and flow control (GFC) at the UNI (User Network Interface).
The AAL (ATM Adaptation Layer) segments the frames of upper layers, places the segments in cells and again assembles the frames at the opposite end.
The user plane attends to data transfer of user applications and to the control required therein. In principle, processing of the data of this level takes place in the user's terminal equipment only. The control plane includes telephone and connection control functions and functions related to processing of the related signalling. This level is present in those network elements only which provide connection-related services or take part otherwise in the processing of signalling.
Of the management plane divided into two parts the tasks of layer management include management of the resources and parameters of the connection practice items of its own layer as well as management of the OAM cells relating to the structural use and maintenance of the ATM layer. It is the task of plane management to co-ordinate between different levels and to manage the system as a whole.
The interface between the integrated circuits performing functions of the physical layer PHY and the ATM layer has been standardised by the ATM Forum under the names of UTOPIA, An ATM-PHY. Interface Specification, Level 1, hereinafter the abbreviation UTOPIA
1
will be used, and UTOPIA, An ATM-PHY Interface Specification, Level 2, hereinafter UTOPIA
2
. In practice, the ATM equipment must be implemented with commercially available ATM micro circuits, which implement an interface in accordance with the UTOPIA specification. The interface has become a de facto industrial standard which is complied with by all component suppliers making integrated ATM circuits. In the UTOPIA interface, the data is defined as 8-bit or 16-bit data depending on the actual bit rate (UTOPIA level 1 and level 2). Only ATM data is transferred in the interface and it contains the control or so-called handshaking required in two-way transfer. Circuit manufacturers implement the functions of the ATM layer as masters of their circuits, because the UTOPIA specification defines the ATM layer circuits as masters and because the manufacturers can not know in what kind of environment their customers will use the circuits. Correspondingly, the circuits of the physical layer are slaves. Slaves connected to a UTOPIA bus may communicate with the master equipment only, but not with one another.
In an ATM network, OAM cells relating to the operation and maintenance of the ATM layer are transferred from one node to another and inside the node. In addition, signalling messages may be sent over lines in the same way as is also done in a narrow-band ISDN network, although due to packet switching there is less need for signalling. Signalling on ATM lines is a rather new matter and is only now beginning to be a feature of products. Signalling may end at the node, whereby the signalling cell comes and remains in the node, or of the transit type, whereby it is relayed through the node. Performance of signalling requires implementation of the so-called SAR (Segmentation and Reassembly) function belonging to the ATM adaptation layer, which makes it possible to add signalling cells to the cell flow and to separate them from the cell flow. The SAR functions used and the ATM adaptation layer are controlled by a processor.
It is a problem with processing of signalling cells how the processor will have access to the cell flow of ATM lines in practice. If one SAR card is used, how it will be able to send signalling messages to any line and to receive messages from any line.
One way of solving the problem of signalling messages exchange between the subscriber equipment and the ATM node is presented in Patent Application EP-0355797, applicant Hitachi Ltd. The principle of this solution is shown in FIG.
3
. Optical subscriber lines are connected to the ATM switchswitch through subscriber line interfaces. They perform the conversion between the optical and electric signals and also add/remove cell headings. Corresponding trunk line interfaces are located on the other side of the ATM switchswitch. One bus on the trunk line side of the switchswitch, bus
41
, is reserved solely for signalling channels. This line is connected to line signalling apparatus
42
, which performs assembling of the payload data of ATM cells into a signalling message data frame and, correspondingly, segmentation of the data frame and its locating in the ATM cells, that is, the function of layer
3
in FIG.
2
. The function corresponds to the SAR function. Processor
43
attends to processing of the message. The function is such that when a signalling cell arrives from the subscriber line, the subscriber line interface identifies the signalling cell, modifies its heading to address bus
41
, that is, line signalling apparatus
42
, and adds such information to the heading which indicates from which subscriber line the cell has come. In the opposite direction, the line signalling apparatus segments the data frame into cells, adds such information to cell headings which indicates for which subscriber line and for which subscriber equipment the cell is intended. The subscriber line interface receives the signalling cell and also performs an address modification for it before it is sent to the subscriber line.
The described patent application also presents an embodiment carrying out transmission of signalling messages to trunk lines and reception from them. The embodiment is shown in FIG.
4
. By adding the trunk line signalling apparatus
43
on the subscriber line side of the ATM switchswitch it is possible to receive signalling cells from trunk lines and to send them to trunk lines. The solution is practicable, because signalling on a subscriber line is different from signalling on a trunk line as regards protocol stacks.
The described known method is charact
Seppänen Juha
Tossavainen Tero
Tuomisto Janne
Ylönen Timo
Hom Shick
Nokia Corporation
Squire Sanders & Dempsey L.L.P.
Ton Dang
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