Browse Prior Art Database

Time Switch

IP.com Disclosure Number: IPCOM000043131D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 76K

Publishing Venue

IBM

Related People

Poret, M: AUTHOR

Abstract

The time switch is a part of a test tool which allows telephone line interface modules (LIM) to be tested. The time switch is necessary to establish voice links between different modules. The test station is built around a microprocessor with associated memory. As shown in Fig. 1, two adapters are driven by the microprocessor, one is the signalling adapter and the other one is the time switch. Both work in memory mapped I/O mode; that is, their address space is a part of the microprocessor memory space. The time switch is shown in Fig. 2. It is based on voice digitization. Voice is sampled every 125 ms and samples are coded as 8-bit bytes or slots. This digitization is performed inside the LIM.

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Time Switch

The time switch is a part of a test tool which allows telephone line interface modules (LIM) to be tested. The time switch is necessary to establish voice links between different modules. The test station is built around a microprocessor with associated memory.

As shown in Fig. 1, two adapters are driven by the microprocessor, one is the signalling adapter and the other one is the time switch.

Both work in memory mapped I/O mode; that is, their address space is a part of the microprocessor memory space. The time switch is shown in Fig. 2. It is based on voice digitization. Voice is sampled every 125 ms and samples are coded as 8-bit bytes or slots. This digitization is performed inside the LIM. Between the LIM and the time switch where slots are switched, slots are organized in serial channels at the rate of 2 megabits per second (32 slots per channel). The time switch can handle two voice channels or 64 slots. It is organized around three buffers: - The voice buffer (VB) on which voice samples are stored during the time between their input to and output from the switch. - The pointer input buffer (PIB) in which is stored the address of VB at which the voice sample will be stored in. - The pointer output buffer (POB) in which is stored the address of VB from which the voice sample will be read out. The voice buffer can be addressed by the microprocessor for diagnostic purposes. Before input to the voice buffer, the two channels are deserialized and multiplexed. At the voice buffer output, the two channels are demultiplexed and serialized. Any communication between the two stations called A and B needs two half-paths: the half-path A T B and and the half-path B E A Each station is strictly related to a slot number respectively called X and Y. Channels are full-duplex; that is: - voice samples issued from A are put into slot X in, - voice samples sent to A are put into slot X out,

- voice samples issued from B are put into slot Y in, and

- voice samples sent to B are put in slot Y out. The input and output of each slot in the time-switch is synchronous. Maximum internal delay is one frame. After multiplexing, all slots are serially considered. Fig. 3 shows the time diagram of a talk between A and B. Half-path A T B:

Input: Slot X is stored in VB at time TOX.

Output: Slot X is read out from VB at time TOY and put

into slot Y.

Half-path B T A: At the same time TOY, slot Y is stored in VB. This slot will be read out from VB at time T1X and put into slot
X. Voice samples sent from A towards B are stored in VB during time TOX to TOY, T1X to T1Y, T2X to T2Y. Voice samples send from B towards A are stored during time T...