PWE3 Working Group Yaakov (Jonathan) Stein Internet Draft Ronen Shashoua draft-stein-tdm-as-00.txt Ron Insler Expires: December 2002 RAD Data Communications June 2002 TDM Applicability Statement draft-stein-tdm-as-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. TDMoIP [PAGE 1] TDM Applicability Statement June, 2002 Abstract This document is an applicability statement for emulation of time division multiplexed (TDM) digital voice and data signals over Pseudo Wires. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. Table of Contents 1. Introduction .................................................2 2. Applicability Statement ......................................2 3. References ...................................................5 4. Contact Information ..........................................5 1. Introduction Telephony traffic is conventionally carried over connection- oriented synchronous or plesiosynchronous networks (which will be loosely called TDM networks herein). With the proliferation of packet-switched networks (PSNs), telephony carriers desire integration of TDM services into a unified PSN infrastructure. This integration requires emulation of TDM circuits within the PSN, a function that can be carried out using Pseudo Wires (PWs), as described in the PWE3 requirements [PWE-REQ] and framework [PWE-FR] documents. This emulation must ensure QoS and voice quality similar to those of existing circuit-based networks as well as preserving signaling features. 2. Applicability Statement 2.1 Reliability A method of transporting TDM traffic over PWs must take into account a customer's expectations regarding end-to-end behavior of TDM services. Customers have become accustomed to "five nine" reliability, meaning that the infrastructure functions correctly 99.999 percent of the time. Due to the limitations of packet switched networks (PSNs), it will not be possible to maintain this level of service reliability in PW emulations of TDM services. Instead we suggest requiring "three nines" reliability. This means in particular, that no more than Stein et al. [PAGE 2] TDM Applicability Statement June, 2002 one in a thousand calls will be disconnected prematurely, no more than one in a thousand initiations will be misrouted, etc. When transporting SS7 signaling, the availability and dependability performance objectives of [Q.766] are not expected to be met unless further mechanisms are put in place. 2.2 TDM traffic types A method for transporting TDM traffic over PWs MUST be able to handle all of the following types of TDM traffic [G.703,G.704,G.751,T1.107] n*64K unstructured T1 unstructured E1 structured T1 without CAS structured E1 without CAS structured T1 with CAS structured E1 with CAS T3 E3 The traffic may consist of any combination of multiplexed voice, voice-band data, or leased-line services. 2.3 Timing transport TDM circuits need to maintain jitter and wander to within limits specified by the relevant standards [G.823,G.824]. In all cases a jitter buffer will be required to be supplied by the edge devices, in order to allow compensation for the packet delay variation of the underlying PSN. If a reliable local source of timing is not available, clock information MUST be transferred edge to edge. Although some degradation in the stratum level is to be expected, the recovered clock must conform to the standards. 2.4 TDM Alarms Standard TDM alarms MUST be both transferred edge to edge and MUST be generated when required. 2.5 Latency Latency and hence round trip delay may increase when transporting over a PW. Since round-trip delay may not conform to what is termed "acceptable for most user applications" in [G.114], mechanisms for reducing latency (such as trading off reduced efficiency for reduced latency) SHOULD be provided. Stein et al. [PAGE 3] TDM Applicability Statement June, 2002 2.6 Audio Quality For voice traffic the voice quality MUST be similar to those of existing circuit-based networks, but may suffer minor degradation due to increased delay and jitter. [P.800] Non-voice, in-band signals required for the proper operation of the public switched telephone network MUST be transported sufficiently accurately as to enable their detection and disallow their false-alarms, in order to maintain proper operation according to their normative standards. Such signals include dual tone multifrequency (DTMF) tones, the 2100 Hz tone including any associated phase reversals and amplitude modulations, multifrequency tones incorporated in the various signaling systems of the PSTN, and tones used in national signaling systems for ring-back, busy and congestions indication. Voice-band modem transmissions MUST be transported sufficiently accurately as to enable their essentially unimpaired operation. 2.7 Echo cancellation Echo cancellation conforming to [G.168] MUST be provided whenever the emulated service would have provided it. In addition, due to latency often exceeding that of the emulated service, echo cancellation MUST be provided whenever the latency exceeds 30 milliseconds and echo cancellation is not otherwise provided. 2.8 CAS signaling When present, CAS signaling MUST be transparently transferred edge to edge. The precise phase of signaling bits inside multiframes need not always be retained. Since CAS signaling bits can be used to transport hooking, hook- flash, and pulse dialing indications, CAS transition timings and durations MUST be maintained. 2.9 CCS signaling Trunk associated CCS signaling (e.g. [Q.700]) MUST be transferred edge to edge. For HDLC type payloads the precise number of idle flags may not be preserved, and to conserve bandwidth, unnecessary flags SHOULD be removed. 2.10 PSN Bandwidth Conservation In order to conserve PSN bandwidth the encapsulation overhead SHOULD be kept to a minimum. Whenever possible, PSN bandwidth conservation techniques such as dynamic bandwidth allocation (whereby only active timeslots are transported), SHOULD be employed. Stein et al. [PAGE 4] TDM Applicability Statement June, 2002 3. References [G.114] ITU-T Recommendation G.114 (05/00) One-way transmission time [G.168] ITU-T Recommendation G.168 (04/00) Digital network echo cancellers [G.703] ITU-T Recommendation G.703 (10/98) Physical/electrical characteristics of hierarchical digital interfaces [G.704] ITU-T Recommendation G.704 (10/98) Synchronous frame structures used at 1544, 6312, 2048, 8448 and 44736 Kbit/s hierarchical levels [G.751] ITU-T Recommendation G.751 (11/88) Digital multiplex equipments operating at the third order bit rate of 34 368 Kbit/s and the fourth order bit rate of 139 264 Kbit/s and using positive justification [G.823] ITU-T Recommendation G.823 (03/00) The control of jitter and wander within digital networks which are based on the 2048 Kbit/s hierarchy [G.824] ITU-T Recommendation G.824 (03/00) The control of jitter and wander within digital networks which are based on the 1544 Kbit/s hierarchy [P.800] ITU-T Recommendation P.800 (08/96) Methods for Subjective Determnation of Transmission Quality [Q.700] ITU-T Recommendation Q.700 (03/93) Introduction to CCITT Signalling System No. 7 [Q.766] ITU-T Recommendation Q.766 (03/93) Performance Objectives in the Integrated Services Digital Network Application (SS7 ISUP) [T1.107] ANS - I T1.107 1995 (07/95) Digital Hierarchy - Formats Specifications 4. Contact Information Yaakov (Jonathan) Stein RAD Data Communications 24 Raoul Wallenburg St., Bldg C Tel-Aviv 69719 ISRAEL Phone: +972 3 645-5389 Email: yaakov_s@rad.co.il Stein et al. [PAGE 5] TDM Applicability Statement June, 2002 Ronen Shashoua RAD Data Communications 24 Raoul Wallenburg St., Bldg C Tel-Aviv 69719 ISRAEL Phone: +972 3 645-5447 Email: ronen_s@rad.co.il Ron Insler RAD Data Communications 24 Raoul Wallenburg St., Bldg C Tel-Aviv 69719 ISRAEL Phone: +972 3 645-5445 Email: ron_i@rad.co.il Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." Stein et al. [PAGE 6]