Circuit Card Provisioning Issues

Control and service circuit cards are usually housed in designated card slots in the control carrier, although some service circuit cards may be housed in certain port carrier card slots as designated by the manufacturer. Most port circuit cards are housed in any available port circuit card slot, but there are exceptions to this generalization for certain PBX system models. A PBX system that can support any port circuit card in any open card slot is said to have a universal port circuit card slot design. If certain port circuit cards have designated port card slot assignments, the system fails to satisfy the universal port circuit card design standard.

There are several reasons port circuit card housing may have to conform to card slot mapping rules.

TDM Bus Time/Talk Slot Restrictions

This is the most prevalent card slot mapping factor for designating a PBX system a nonuniversal port circuit card slot design. PBXs that have nonblocking, segmented TDM bus designs restrict the number of active port circuits housed across contiguous card slots. For example, the NEAX2400 IPX PIM has a local TDM bus with 384 talk slots. The system software is based strictly on nonblocking access to talk slots for all potentially configured port circuit terminations. The 18-card slot PIM can house a mix of 8-port and 16-port digital line cards; each port circuit is equipped with two bearer communications channels. Although a PIM can house an 8-port digital line card in each card slot and remain within the talk slot limitations of the local TDM bus, it cannot support a 16-port digital line card (32 bearer channels, total) in each card slot. The PIM is therefore limited to twelve 8-port (12 × 8 ports × 2 channels/port = 182 channels) and six 16-port (6 × 16 ports × 2 channels/port = 192 channels) digital line cards. The maximum number of communications channels per PIM is the limiting factor for housing the higher density digital line cards. PIM card slot mapping guidelines require 16-port digital line cards to be housed in very specific card slots (ports 7 to 9 and 16 to 18). The remaining card slots are available for the 8-port cards.

Another type of talk slot limitation affecting port circuit card housing is one that requires nonblocking access to the TDM bus for a certain type of port circuit card. The Nortel Networks Meridian 1 Option 61C/81C consigns DS1 digital trunk cards to control/network carrier card slots instead of the port carrier card slot. The Meridian 1 Digital Trunk Interface (DTI) card must be housed in a network card slot to have guaranteed access to a 32 talk slot network loop. This provides nonblocking switch network access to digital trunk circuit terminations, thereby reducing the need for port carrier shelf traffic engineering.

Call Processing Limitations

Some PBX systems limit the number of port circuit card types because of system call processing limitations. Many of the early digital PBX systems supported a limited number of electronic telephones because of limited call processing capacity. When digital telephones became available, a similar limitation was made for select PBX system models. The same call processing limitation factor is in effect today with IP telephones. The processing requirements to support complex port circuit cards can limit the number of these port circuits.

Power Distribution Limitations

The internal PBX power distribution system may limit the number and type of port circuits per carrier or cabinet, based on power design limitations.

Card Slot Requirements

Some port circuit cards may require more than one card slot because of the size of the printed circuit board or the required number of talk slot connections. If two card slots have access to a limited number of talk slots and one port circuit card requires more than an average number, the contiguous card slot may have to remain open, or only a low-density port card can be housed. For example, the Fujitsu F9600 intermediate and large system models are based on segmented local TDM buses. Every two card slots per carrier has access to 32 talk slots. Although there are no hard and fast rules for port circuit card assignments, the housing of a high-density digital trunk card requiring 24 talk slots in one of two card slot pairs requires the second port circuit card to have eight or fewer port circuit terminations.