2

Scope

2.1

For the purposes of this standard, the PBX is considered to be a device that performs switching functions between station apparatus interfaces and between the station apparatus interfaces on one side and central office (CO) and special trunk interfaces on the other. Figure 1 shows two types of central of fice interfaces: communication interfaces that transmit and receive network supervisory and communication signals, and specialized interfaces, such as messge registration and AIOD, which are used for allocating billing to outgoing calls. The interface on the station side is assumed to be compatible with the parameters specified in CAN/CSA-T510, Performance and Compatibility Requirements for Telephone Sets (Ref A2) and EIA- 478, Multi-Line Key Telephone Systems for Voiceband Applications (Ref A3). The requirements in this standard are intended to assure satisfactory user voicegrade services in a high percentage of installations both initially and over some period o f time as the network grows and changes occur in telephone serving equipment.

2.2

Compliance with this standard is determined at the PBX interface bo undaries (Fig 1) and is not to be construed as a constraint on the internal coding or switching techniques of the PBX. It is recognized that a PBX using some digital encoding, digital switching, analog modulation, and analog switching techniques will not meet some of the voiceband transmission requirements in Section 4.8 of this standard. However, maintenance of the overall quality of telecommunication performance requires that each connection through a PBX meets the cate gory of transmission requirements specified in this standard with respect to the type of connection and to the PBX coding and switching technique employed.

2.3

The standard recognizes that no one PBX design or installation need be equipped with all types of interfaces contained herein. A PBX complies with this standard when it conforms to the requirements applicable to the interfaces with which it is equipped. For satisfactory service, a PBX should be capable, through the proper selection of equipment options, of satisfying the requirements applicable to its serving area. The requirements for the individual types of PBX interfaces vary between telephone companies and in some cases between central office switching machines; therefore, in some cases multiple options are stated for satisfying a particular requirement.

2.4

The criteria for supervisory and address signals sent toward the network assume that the PBX repeats or regenerates station apparatus dc signals received from the station apparatus. It is assumed that voiceband transmission from one port to a similar or different port of the PBX introduces some small amount of degradation commensurate with satisfactory overall user and end-to-end performance.

2.5

This Standard is intended to be in conformance with the requirements of CS-03, Standard for Terminal Equipment, Systems, Network Protection Devices, Connection Arrangements and Hearing Aids C ompatibility, issued by Communications Canada and mandated by various levels of Canadian regulatory authorities. However, the requirements in this Standard are not limited to those of CS-03. Where the requirements of Standard CS-03 are more stringent than those of this Standard, the requirements of Standard CS-03 shall take precedence.

2.6

It is recognized that some PBX products may not be accommodated by this standard because of nonstandard line interfaces; i.e., other than that described in 4.5. In such systems, the station apparatus must be considered as a whole with the PBX and its associated station wiring, and the overall system must be described in terms of an acoustic (user) to an electrical (network) standard.

2.7

The requirements in this document assume a ringer equivalence number (REN) of 5. If the PBX has a REN of less than 5, then the requirements designated by the parenthetical expression (REN) need to be appropriately scaled in accordance w ith Section 68.312 of the FCC Rules and Regulations. The ringer equivalence number (REN) as used in this Standard is similar to the Load Number (LN) as used in CS-03. Where a parameter in this St andard has ""(REN)"" appended to it, the value shall be appropriately scaled according to the LN determined for a particular trunk interface as specified in CS-03 Section 1. To scale a particular parameter value, the value shall be multiplied by the quotient (100/LN) for impedance parameters and by (LN/100) for dc current parameters, where LN is the Load Number as specified in CS-03.

2.8

In addition to the requirements in this standard, the safety requirements in CSA C22.2 No. 0.7 or No. 225, as applicable (Ref A17), apply. The CSA C22.2 No. 0.7 or No. 225 may be more restrictive. Environmental considerations for PBXs a re found in Ref A5.

This Standard includes Amendments.