2.2.  SCX160 SCxbus Adapter in a Multi-Node System

The SCX160 SCxbus Adapter converts SCbus TTL signals into SCxbus RS485 type signals, and vice-versa, for inter-node communications between SCSA devices. This adapter uses the inherent switching capabilities of SCSA products (along with the SC2000 ASIC) to perform the necessary switching functions.

For illustrative purposes, the call processing, shared resource, multi-node call switching system shown in Figure 1.  Multi-node Example is used to highlight PC host communications via the SCxbus.

Figure 1.  Multi-node Example

In the example presented in Figure 1.  Multi-node Example, the nodes are defined as follows:

• Node 1 comprises an SCX160 board, 2 MSI/80SC boards (80 time slots; 64 for conferencing and 16 for stations) and 2 D/240SC-T1 boards (96 time slots; 48 for the voice devices and another 48 for the E-1 digital time slots) for a total of 176 time slots.
• Node 2 comprises an SCX160 board and 6 VFX/40ESC boards setup in resource mode (analog devices on these boards are disabled) for a total of 48 time slots (24 for the voice/FAX devices and 24 for the disabled analog devices).
• Node 3 comprises an SCX160 board, 1 MSI/80SC board (40 time slots) and 3 D/240SC-T1 boards (72 voice time slots and 72 E-1 digital time slots) for a total of 184 time slots.
• Node 4 comprises an SCX160 board and 6 D/160SC-LS boards for a total of 192 time slots (96 for the voice devices and 96 for the analog devices).

Time slots on the SCbus and SCxbus are transmitted in bundles of 64 across each of 16 lines for a total of 1024 time slots/bus. Each bundle of time slots is handled as a data stream (DS0 through DS15) by the SCX160 SCxbus Adapter. The SCX160 SCxbus Adapter maps the SCbus transmit data streams onto corresponding numbered SCxbus data streams, and vice-versa, and then buffers the transmit data streams between the two buses. No data streams or time slots are switched by the SCX160 SCxbus Adapter.

At Dialogic service startup, the transmit time slots required to support the SCSA products installed or allocated to each node are determined and then the appropriate quantity of data streams (bundles of 64 time slots each) are assigned to each node. In our example, the configuration established could be as follows:

• Node 1 uses 176 transmit time slots, so DS0, DS1 and DS2 comprising time slots 0 through 191 are assigned to this node.
• Node 2 uses 48 time slots, so DS3 comprising time slots 192 through 255 is assigned to this node.
• Node 3 uses 184 transmit time slots, so DS4, DS5 and DS6 comprising time slots 256 through 447 are assigned to this node.
• Node 4 uses exactly 192 transmit time slots, so DS7, DS8 and DS9 comprising time slots 448 through 639 is assigned to this node.

NOTE:

DS10 through DS15 are not used on the SCxbus in this example.

In the example above, the number of data streams allocated for each node are the minimum number required. However, you can allocate more data streams than are required to leave room for future expansion.

See Table 2.  Data Stream Versus Time Slot Bundling for the time slot bundles assigned to each Data Stream (DS); these numbers are not used, nor needed, when programming your application.

Table 2.  Data Stream Versus Time Slot Bundling

Data Stream	Time Slot Bundle	Data Stream	Time Slot Bundle
DS0	0 to 63	DS8	512 to 575
DS1	64 to 127	DS9	576 to 639
DS2	128 to 191	DS10	640 to 703
DS3	192 to 255	DS11	704 to 767
DS4	256 to 319	DS12	768 to 831
DS5	320 to 383	DS13	832 to 895
DS6	384 to 447	DS14	896 to 959
DS7	448 to 511	DS15	960 to 1023

An SCSA device in any node connects to an SCSA device in any other node by listening to the transmit time slot assigned to that SCSA device. The user application is expected to know the configuration of each node in the system and to coordinate the transfer of SCbus transmit time slot information among nodes.

For example, to connect a call on channel 1 of the first D/240SC-T1 board (assume SCbus transmit time slot 0) in node 1 to channel 4 of the first VFX/40ESC fax resource board (assume SCbus transmit time slot 195) in node 2, the application would make these SCSA devices listen to each other by issuing individual SCbus routing function calls in each node. The SCbus convenience functions cannot be used in a multi-node configuration due to the need to communicate time slot information across nodes. The following example describes how to establish communications between these devices:

• At node 1, initialize the SC_TSINFO structure with the required information.
• At node 1, get the SC_TSINFO structure that contains the number of the SCbus time slot connected to digital transmit channel 1 on the first D/240SC-T1 board by issuing a dt_getxmitslot( ) call.
• Pass this SC_TSINFO structure to node 2; for example by using a socket message.
• At node 2, connect FAX receive channel 4 of the first VFX/40ESC fax resource board to digital transmit channel 1 [SCbus transmit time slot 0] on the first D/240SC-T1 board in node 1 by issuing an fx_listen( ) call. This function uses as input the information contained in the SC_TSINFO structure returned by the node 1 dt_getxmitslot( ) call and passed to node 2.
• At node 2, get the SC_TSINFO structure that contains the number of the SCbus time slot connected to FAX transmit channel 4 of the first VFX/40ESC fax resource board by issuing an fx_getxmitslot( ) call.
• Pass this SC_TSINFO structure to node 1; for example by using a socket message.
• At node 1, connect digital receive channel 1 of the first D/240SC-T1 board to FAX transmit channel 4 [SCbus transmit time slot 195] on the first VFX/40ESC fax board in node 2 by issuing a dt_listen( ) call. This function uses as input the information contained in the SC_TSINFO structure returned by the node 2 fx_getxmitslot( ) call and passed to node 1.

When these functions return, full duplex communications between the FAX and digital time slots will be established.

The SCbus convenience functions cannot be used in a multi-node configuration due to the need to communicate time slot information across nodes.

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