Advances in digital voice communications over packet channels such as the Internet and Local Area Networks have made it necessary to create a transmission standard for IP (Internet Protocol) Telephony systems. The term coined for these IP Telephony systems is “Voice Gateway” (VG), which is the equivalent to the term PBX as used for traditional time-division-multiplexed (TDM) systems. PBX requirements are specified in ANSI/TIA-464-C.
This standard establishes performance and technical criteria for interfacing and connecting with the various elements of public and private telecommunications networks. Compliance with these requirements should assure quality service.
ANSI T1.508 and to fully comply with the regulatory requirements of TIA-968-A with the addendum TIA-968-A-1.
Voice quality-of-service issues such as the impact of transmission delay, speech compression and packet loss are addressed in TIA/EIA/TSB32-A and TIA/EIA/TSB116.
This standard was also developed in conjunction with ETSI TC STQ, who generated an equivalent half-channel loss plan standard, ETSI ES 202 020, for voice gateways that is harmonized with this standard.
1.3Categories of Performance Criteria
Four types of requirements are specified in this standard: Mandatory, Recommended, Permissive and Advisory:
Mandatory requirements are designated by the terms “shall” and “shall not”. These requirements are used to indicate conformity in which no deviation is permitted.
Recommended requirements are designated by the terms “should” and “should not”. These requirements generally relate to compatibility or performance advantages toward which future designs should strive.
Permissive requirements are designated by the terms “may” and “may not”. These requirements are used to indicate an action that is permitted within the limits of the standard.
Advisoryrequirements are designated by the term “desirable”. Advisory criteria represent product goals or are included in an effort to ensure universal product compatibility and may be used instead of a Recommended requirement. If both a mandatory and an advisory level are specified for the same criterion, the advisory level represents a goal currently identifiable as having distinct compatibility or performance advantages toward which future designs should strive.
This standard covers the transmission requirements for voice gateways. For the purposes of this standard, a voice gateway is considered to be a device that performs voice routing functions between:
Voice over Cable Multimedia Terminal Adaptor (MTA)
Telephones considered in this standard consist of two different types:
Analog telephones assumed to be compatible with the parameters specified in ANSI/TIA-470.110-C.
Digital telephones assumed to be compatible with the parameters specified in ANSI/TIA/EIA-810-A.
2.1Compliance Reference Point
The reference point for this standard is determined at the voice gateway interface boundaries and is not to be construed as a constraint on the internal coding or switching techniques of the voice gateway.
A voice gateway complies with this standard when it conforms to the requirements applicable to the interfaces with which it is equipped.
This standard is intended to be in conformity with TIA-968-A plus TIA-968-A-1 (an addendum to TIA-968-A) regarding network harm, but is not limited to the scope of this standard. In the event that the TIA-968-A plus TIA-968-A-1 requirements are more stringent than those contained in this standard, the provisions of TIA-968-A plus TIA-968-A-1 apply.
2.4Changes Relative to TIA-912
Numerous technical changes were made in this revision of the VG loss plan standard. The following list is provided to assist loss planners in understanding these changes:
Separated Enterprise VGs from MTAs and IADs. Created new packet port, PAL, for MTAs and IADs.
In Table 1, changed ONS-to-DAL from 3 to 0 dB to send at SLR = 8 dB (now that TIA-968-A-1 relaxed this connection to 0 dB).
In Table 1, changed OPS-to-DGS and OPS-to-WAN from -3 to 0 dB to harmonize with OPS-to-DAL.
In Table 1, changed DAL-to-FXO from 3 to 0 dB to harmonize with “everything else”-to-FXO.
In Table 1, changed FXO-to-DGS from -9 to -6 dB to harmonize with FXO-to-WAN.
In Table 1, changed FXO-to-DAL from -3 to -6 dB to harmonize with FXO-to-WAN.
In Table 1, changed FXD-to-DGS from -6 to -3 dB to harmonize with FXO-to-WAN and FXO-to-DAL.
In Table 1, changed ATT-to-DAL from -3 to 0 dB because TIA-968-A-1 tightened this connection to 0 dB. Changed ATT-to-DGS and ATT-to-WAN to harmonize with ATT-to-DAL.
In clause 6.4 (2) and Table 3 (ESLR and ERLR for FXO and FXD), changed the DEO loss for nominal loss planning purposes from 3 to 6 dB to harmonize with the latest revision of the DEO loss plan, T1.508.
Changed sub-clause 18.104.22.168 to reflect the significant changes made to TIA-968-A by the recent Addendum, TIA-968-A-1. Corrected Table 5 (used to be Table 3a in TIA-912) to the values specified in TIA-968-A-1 (Table 4.6). Deleted the former Tables 3b, 4 and 5 as they are no longer relevant given the changes in TIA-968-A-1, the corresponding changes in Table 1 and the new appreciation for the implications of Note 4 to Table 4.6 in TIA-968-A.