Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-03-27
2001-10-16
Ton, Dang (Department: 2932)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S220000
Reexamination Certificate
active
06304569
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for routing message cells from connections having respectively different priorities particularly in the reception of message cells from low-priority connections, such as non-real time (NRT) traffic, of the type wherein redundant message cells are respectively transmitted via redundant transmission paths, and only one of the received redundant message cells is selected for further processing.
2. Description of the Prior Art
In ATM (Asynchronous Transfer Mode) transmission, the sequence of message cells belonging to a virtual connection should be maintained. In order to meet a prescribed loss probability, parallel routing or forwarding, via through-connections along redundant transmission paths may be necessary. Among the redundantly transmitted message cells, only one message cell is selected at the reception location as the next message expected in the sequence. To designate the sequence, each message cell carries a series number, allocated to it in a cyclically progressing fashion in a field for the series number. The individually distinguishable series numbers of a virtual connection define a message cell sequence cycle.
The redundant transmission paths can each include a statistical multiplexer unit which is intended to form the traffic of low-priority connections during the activity of large buffer memories in such a way that the total traffic loads the output line optimally, i.e. to nearly 100 percent.
The statistical multiplexer units of the coupling field slices operate independently of each other, so that message cell streams with different contents can arise.
If a simple recombination algorithm is applied at the receiving location at the end of the redundant transmission paths, then the message cells which were rejected on one transmission path for reasons of overload are replaced by redundant message cells transmitted on another transmission path, which leads to a load of greater than 100% and thus to an overflow of the RPC buffer at the exit of the output unit.
A selection identification character could be entered in the receiving unit for the connections of lower priority, this selection identification character determining the transmission path by which message cells of the relevant connection are exclusively received for further processing. Given the failure of a transmission path, the board controller would have to rewrite all the affected entries which would last several seconds, given up to 8192 connections, and which would have to be followed by a message cell sequence cycle in order to avoid an undesired mixing of the message cell streams of the low-priority connections of the transmission paths participating in the switchover. During such a cycle the transmission paths participating in the switchover do not receive any message cells for further processing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for a transmission system in which message cells transmitted redundantly via redundant transmission paths are rejected independently of each other on the transmission paths. It is a further object to provide such a method wherein a switchover from reception of only a first transmission path to reception of only a second transmission path takes place with a considerably reduced time requirement.
The above object is achieved in accordance with the principles of the present invention in a method for routing message cells received from connections having different priority via redundant transmission paths, wherein redundant message cells are respectively transmitted via redundant transmission paths with only one of the received redundant message cells being selected for further processing, wherein connections having low ranking priority are assigned an identification bit, with a number of such connections designated by the same identification bit forming a class, and wherein the identification bit is evaluated upon reception of a message cell, and the message cell contains a selection condition character which defines the transmission path by which the message cells belonging to the class are accepted for further processing.
Besides a simplification of the switchover, the method according to the invention offers a considerable abbreviation of the time requirement for the switchover which correspondingly lowers the loss of message cells due to the switchover, because for a number of connections, only the selection identification character has to be changed.
In an embodiment of the inventive method the identification bit is carried in each message cell of a connection of low priority. This measure offers a low-outlay distinguishability between message cells of different priority.
In another embodiment, an identification bit identifying the connections is evaluated in the reception of a message cell. Besides the advantage that no modifications to the message cells of a priority class are necessary, this measure, whereby an entry ensues in the output unit in the course of the buildup of a connection, offers the advantage that the entry is valid for all the message cells of the relevant connection.
The selection condition character in the method can be switched into an active mode or an inactive mode. This measure offers a simple possibility for exchange between an operation via only one transmission path and an operation via redundant transmission paths.
With the switchover from one transmission path to another transmission path, the receipt of message cells is interrupted for a strictly prescribed time-span. This measure prevents repetitions of message cells or overload at the exit due to the switchover.
In order to prevent cell repetition, with the switchover from a transmission path the reception of message cells ensues corresponding to an algorithm with blocking windows, as described in the United States Patent No. patent application by the present applicant entitled “Redundant Transmission System That Avoids Cell Repetitions” filed simultaneously herewith Ser. No. 09/049,815.
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Sam Phirin
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
Ton Dang
LandOfFree
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