Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1998-08-20
2002-07-30
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S379000, C370S382000
Reexamination Certificate
active
06426951
ABSTRACT:
This application claims priority under 35 U.S.C. §§119 and/or 365 to 197 36 447.0 filed in Germany on Aug. 21, 1997; the entire content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The invention relates to a device and a method for switching input data frames from a plurality of input lines to output data frames on a plurality of output lines. In particular, the device and method are provided for switching data frames which comprise time slots which are divided into several sub-channels. The device and method of the invention can perform an efficient switching of such data frames at an arbitrary rate, i.e. at the normal rate of the time slots or at the sub-rate of the sub-channels.
Such normal rate or sub-rate switching is particularly advantageous in telecommunication networks, in particular in telecommunication networks using PCM-links (Pulse Code Modulation links). Furthermore, the device and method of the invention find wide application for testing and simulation equipment, where data frames need to be switched between a plurality of input lines and a plurality of output lines.
BACKGROUND OF THE INVENTION
In a given configuration of a telecommunication network, more capacity is demanded, when more subscribers are to be connected without extending the facilities of the telecommunication network. This is particularly true for mobile cellular telecommunication networks where new (mobile) subscribers are added to the network at a fast rate. Each new subscriber can be considered as using a new channel for transmission and reception of information and therefore, the obvious demand is to increase the number of channels whenever a new subscriber is added.
The physical connections in the core of a telecommunication network (e.g. between exchanges and base stations or between base transmitter stations and mobile subscribers) are usually PCM-links (Pulse Code Modulation links) for a frame-based transmission and reception of data. That is, on the PCM-links or PCM-lines data is transmitted in successive frames which are transmitted/received at a fixed frame rate of e.g. 125 &mgr;s (8 kHz) (2048 kbits/s). The frame can be subdivided into a certain number of time slots (also called channels), typically 32 or 24 time slots depending on the system type. Each time slot has a capacity to carry information data (i.e. speech data) at a rate of 8 kbit/s which is the normal telephony speech quality. For example, one time slot consists of 8 bits and corresponds to a transmission speed of 64 kbits/s (full rate) on one individual PCM-link, wherein speech is respectively coded as information data of 8 bits in each time slot.
Modern compression/decompression techniques, however, allow to compress/decompress speech data to a smaller number of bits than 8 bits, i.e. to transcode the speech to a lower data rate using a smaller number of bits. Therefore, instead of adding one more complete new channel in the mobile telecommunication system when a new subscriber station is to be connected, a more advantageous and efficient use of the resources in the network is to perform a compression/decompression of the speech data and to subdivide the time slots further into several sub-time slots or sub-channels.
A further aspect that may lead to a subdivision of the time slots into sub-time slots or sub-channels is the transmission of signalling information between modules in the system which also uses time slots on the PCM-links. This signalling information can be transmitted at a lower speed, i.e. with less bits per second, such that the usage of a full time slot for this signalling data would be a waste of resources.
When one time slot e.g. consists of 8 bits and corresponds to a transmission speed of 64 kbits/s (at full rate) on a PCM-link, then using a sub-time slot (sub-channel) of 4 bits will use a corresponding speed of 32 kbits/s (sub-rate) wherein one time slot is divided into two sub-time slots. Similarly a sub-time slot of 1 bit gives a speed of 8 kbits/s and 8 sub-time slots per time slot. If a channel has a bandwidth of n*8 kbits/s with n=1 . . . 7, then n=1 can be called a sub-rate channel with a half rate, n=2 can be called a sub-rate channel with a full rate and 2<n<8 can be called a sub-rate channel with an enhanced rate. The normal rate (a full channel) channel has 64 kbits/s. Obviously, looking at one PCM-link, the individual frames of a series of frames may each be subdivided differently into sub-channels of different sub-rates.
In the telecommunication networks many exchanges and switching devices are necessary, e.g. to switch input data frames from a plurality of input lines to output data frames on a plurality of output lines. There are well established techniques for full-rate switching, i.e. switching packets or frames having a number (32 or 24) of time slots of equal bandwidth (e.g. 64 kbits/s). However, the technique of using sub-channels with different sub-rates is a fairly recently developed new idea and has put new demands on the hardware in the switching devices, since the old full-rate switching devices in general cannot handle the switching of time slots which are further subdivided into sub-time slots or sub-channels.
Thus, there is the need for developing new switching architectures that do not only handle the normal rate switching but also the sub-rate switching.
SUB-RATE SWITCHING USING A CONVENTIONAL NORMAL RATE SWITCH
FIG. 1
shows a group switch sub-system GSS for switching data frames from one switching network terminal SNT A to a switching network terminal SNT B on input and output lines i
1
, o
1
; i
2
, o
2
using a normal rate switch NRS having an add-on sub-rate switch SRS which is to take care of the switching of the sub-channels or sub-time slots.
The sub-rate switch SRS is connected to the normal switch via one or more physical links each containing a number of time slots. The sub-rate switch SRS can connect any bit from any time slot coming from the normal rate switch to any bit in any time slot going back to the normal rate switch NRS.
FIG. 2
shows an example of one time slot in an input data frame IDF and a time slot of an output data frame ODF in a 24 kbits/s sub-rate connection. Using the sub-rate switch extension to the normal rate switch NRS, a connection of a sub-rate channel x from the switching network terminal SNT A to a sub-rate channel y at the switching network terminal SNT B can be established using the following three steps:
1. A 64 kbits/s connection in the normal rate switch from the time slot on SNT A which contains sub-channel x to any free time slot on the sub-rate switch SRS is established.
2. In the normal rate switch NRS, a connection is established from any other free time slot on the sub-rate switch SRS to the time slot on the SNT B containing the sub-channel y.
3. In the sub-rate switch SRS, the connection between the appropriate bits of the bit positions in the time slots that were selected in steps 1 and 2 is made.
FIG. 3
shows a group switch sub-system GSS with a 64 K implementation. The sub-rate switch SRS (consisting of sub-rate switch modules SRSM for each plane) is connected to the normal switch via 8 pairs of time switch modules TSMs to give 4 K multiple positions MPUs. The time switching modules TSMs have the DL2 interfaces replaced by a new interface with 512 time slots, but their switching function is unchanged. RP designates the regional processors and SPM is the space switch module, whereas CLM is the clock module providing the synchronization within the group switch sub-system GSS.
Because the sub-rate switch can connect any time slot to any time slot, the speech memories in the connecting time switching modules TSMs are not needed. For each bit of each outgoing time slot, the sub-rate switch SRS must have one memory location in a control memory. The entry of the control memory location defines a specific bit in a switch pattern memory which should be read. Hence, in order to connect a channel of more than 8 kbits/s a number of control memory locations must be written, too.
Antonsson Dan
Malmqvist Fredrik
Hyun Soon-Dong
Nguyen Chau
Telefonaktiebolaget LM Ericsson (publ)
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