Multiplex communications – Pathfinding or routing – Through a circuit switch
Utility Patent
1998-03-06
2001-01-02
Vu, Huy D. (Department: 2733)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S375000, C370S360000, C370S357000
Utility Patent
active
06169737
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to switching of user data through a switch or a switch stage. In particular, the invention relates to a method and device for switching user data, belonging to a connection, between different time slots in the switch or switch stage.
BACKGROUND OF THE INVENTION
User data switched through a digital switch belong to channels, so called connections. In the switch, user data originating from each connection from a respective input in the switch are switched to a respective selectable output in the switch. A technique used in connection thereto is circuit switching. A common switch structure in circuit switching is called “Time Space Time” (TST). In switches having this structure, a plurality of time switch stages are connected to a space switch stage. User data is first switched through an incoming time switch stage, then through a space switch stage and finally through an outgoing time switch stage.
User data from several connections that are to be switched through a switch of TST-structure are multiplexed by means of time multiplexing. In time multiplexing, the user data is placed in time slots that are arranged in frames. In switching the user data through the switch, it is moved between different time slots and frames. This is accomplished by delaying the user data in memories, so called speech memories, in the time switch stages of the switch. A speech memory comprises storage positions for storing user data. Each storage position corresponds to a time slot and stores, during a certain time, a data word of the user data, such as a byte. In addition to the speech memories, the time switch stages also include control memories and time slot counters by means of which writing of the user data into, and reading of the user data out of the speech memories are performed in different time slots. A control memory also includes storage positions, each of which corresponds to a time slot. A time slot counter cyclically addresses storage positions in the control memory as well as in the speech memory. For each time slot, a storage position in the control memory is addressed for reading control information stored in the control memory. The control information in the control memories in turn addresses the speech memories for reading the user data from the incoming time switch stages on one hand, and for writing the user data into the outgoing time switch stages on the other hand.
User data arriving to an incoming time switch stage appears in incoming time slots. In the space switch stage, the user data is placed by the incoming time switch stage in so called internal time slots. The user data going out from an outgoing time switch stage is placed by the outgoing time switch stage in outgoing time slots. Conflict in the space switch stage is avoided by means of the internal time slots.
Control information is generated in a control system, such as a computer program-controlled control system, being part of the telecommunication system. The control system is connected to the switch. Writing of control information into the control memories is instructed from the control system for assigning time slots used in the switching of the user data through the switch.
In one type of connection, a so called narrowband connection, user data arrives in a single incoming time slot each frame. User data are delayed differently for different narrowband connections. For each narrowband connection, the delay depends on in which incoming time slots that user data arrives to the switch, and in which internal time slots and outgoing time slots that user data for the narrowband connection are switched through the switch. The reciprocal timing relations between the incoming time slots, the internal time slots and the outgoing time slots for a narrowband connection determines the delay of the user data belonging to the narrowband connection.
Another type of connection, a so called wideband connection, occupies several time slots in each frame. User data belonging to a wideband connection arrives in several incoming time slots in each frame, and is switched through the switch in several internal time slots and in several outgoing time slots, in a sense as several separate narrowband connections. Thus, a wideband connection may be considered as an association of several narrowband connections. User data belonging to a wideband connection will consequently be switched through the switch in several narrowband connections with different delays.
A problem in connection thereto is to obtain sequence integrity, so called Time Slot Sequence Integrity (TSSI), and frame integrity, so called Time Slot Frame Integrity (TSFI), for wideband connections, i.e. to assure that data words constituting user data for a wideband connection maintain one and the same reciprocal time order through the switch on one hand, and that those data words that arrive in incoming time slots in one and the same frame are placed in the same frame in outgoing time slots on the other hand.
If as an example frame integrity (TSFI) is not preserved through the switch, then the user terminals in some telecommunication applications have to be equipped with frame analysis and frame regeneration equipment. This means an undesirable increased cost for the users.
SUMMARY OF THE INVENTION
An object of the invention is to find a simple way of obtaining sequence integrity (TSSI) and frame integrity (TSFI) in switching connections through a switch or a switch stage.
In particular, a main object of the invention is to provide a method and device for switching user data, belonging to a connection, between different time slots in a switch or a switch stage such that sequence and frame integrity are preserved.
A further object of the invention is the provision of a simple and effective algorithm for determining information that controls the distribution of user data between different time slots such that the reciprocal time order for user data (sequence integrity) is preserved through the switch or switch stage. It is also desirable that the time delay through the switch stage or stages becomes as small as possible.
Yet another object of the invention is to extend the algorithm such that it also determines control information, in form of delay values, that controls the delay of the user data through the switch or switch stage so that frame integrity is preserved.
These objects are met by the invention as defined by the accompanying patent claims.
User data belonging to a connection, preferably of wideband type, is distributed among the internal time slots in each frame that have been assigned to the wideband connection for switching the user data through the switch on one hand, and among the outgoing time slots in each frame that have been assigned to the wideband connection for switching the user data through the switch on the other hand.
According to the invention, an algorithm is used for determining information utilized in connection with the preservation of sequence and frame integrity. The algorithm includes two parts. The first part of the algorithm is associated with the preservation of sequence integrity through a time switch stage. The first part in combination with the second part of the algorithm is associated with the preservation of both sequence and frame integrity through the switch.
In particular, the first part of the algorithm is used for determining distribution information, in form of storage positions in a control memory in the switch. Data words that constitute user data are caused to be switched according to the distribution information from the first part of the algorithm through a time switch stage such that the data words maintain one and the same reciprocal time order through the switch stage. The distribution information determined by the first part of the algorithm assures sequence integrity and at the same time minimizes the delay of user data through the switch stage.
In a TST-switch as an example, the first part of the algorithm can be applied to the incoming time stage for preserving
Hansson Ulf
Lindberg Mikeal
Olsson Fredrik
Burns Doane Swecker & Mathis L.L.P.
Telefonaktiebolaget LM Ericsson (publ)
Trinh Dung
Vu Huy D.
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