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Li 4 Internet-Draft China Mobile 5 Intended status: Standards Track March 5, 2012 6 Expires: September 6, 2012 8 Requirements for IP/MPLS network transmission interruption duration 9 draft-fan-opsawg-transmission-interuption-00 11 Abstract 13 The transmission performance of IP/MPLS network affects upper layer 14 services and networks, but there is no consensus in the industry on 15 transmission interruption for IP/MPLS network up to now. This memo 16 studies requirements for the interruption duration criteria in 17 several service scenarios. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on September 6, 2012. 36 Copyright Notice 38 Copyright (c) 2012 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Services and Performance Criteria . . . . . . . . . . . . . . . 3 55 2.1. Softswitch . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2.2. LTE Backhaul . . . . . . . . . . . . . . . . . . . . . . . 6 57 2.3. VPN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 58 2.4. IPTV . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 59 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 60 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 61 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 62 6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 63 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 65 1. Introduction 67 Today's IP/MPLS network is widely used as a bearing network to carry 68 diversified packet switched services. The transmission qualities of 69 these services are closely related to the performance of bearing 70 layers, as network failure, delay, congestion and other abnormities 71 will inevitably bring about service interruption and user perception 72 degradation. However, there is no consensus in the industry on 73 transmission interruption for IP/MPLS network up to now. This memo 74 studies relationships between service performance and transmission 75 interruption duration in several scenarios, and is intended to reach 76 a list of requirements for these interruption duration criteria. 78 2. Services and Performance Criteria 80 Services delivered by IP/MPLS network have different transmission 81 quality requirements, thus introduce different performance criteria 82 for the bearing IP/MPLS network. In this section we will describe 83 concerns on IP/MPLS network interruption duration from aspects of 84 four kinds of service scenarios, namely Softswitch, LTE backhaul, VPN 85 and IPTV. 87 2.1. Softswitch 89 From the softswitch point of view, the IP bearing nature imposes 90 certain influence to the service quality. Especially when speech is 91 delivered by IP, the communication quality of voice is impaired, and 92 in turn makes higher requirements for the transmission performance of 93 IP bearing layer. There are mainly two network design principles to 94 be considered when carrying softswitch voice services: the bearing 95 network should guarantee the communication quality of voice carried 96 by IP is as good as that of voice carried by TDM, and the 97 communication quality can still be satisfied when a network failure 98 occurs, causing transmission interruption and network convergence. 99 This part will mainly focus on three communication quality criteria 100 and their influence factors and causes to give requirements for 101 softswitch and IP bearing networks. 103 2.1.1 Connection Failure 105 Connection failure is used to describe the circumstance where a phone 106 call fails to establish after initiated by a subscriber due to 107 network faults. In the practical network, the connection failure 108 rate is mainly associated by the factors as follows: 110 (1) Interfaces, including Nc, Mc and interface connecting MSS and SG. 112 (2) Message timer of state machine. If a timeout takes place, the 113 state machine releases signaling messages, producing a connection 114 failure. In China Mobile's network, the BICC timer is configured to 115 10~15 seconds and DTAP timer about 15 seconds. 117 (3) Detected duration of interface coupling interruption. 119 (4) Bearing network convergence time. 121 If the configured timing duration of a state machine is shorter than 122 the detected duration of interface coupling interruption, then 123 although interface coupling may not be broken off, connection failure 124 is still possible to occurs due to message timeout. If the coupling 125 interruption duration is shorter than IP routing convergence time, 126 the coupling is considered broken off by SCTP, hence message loss at 127 interface between MSS and SG as well as interface Nc results in 128 massive connection failure, and new calling request cannot be 129 satisfied because of interface Mc breakoff. In this case, the 130 connection failure rate can be calculated as 132 Connection Failure Rate = ( IP Convergence Time + Coupling 133 Restoration Time ) * CAPS / BHCA. 135 However, if the coupling interruption duration is longer than IP 136 routing convergence time, then the coupling is considered normal by 137 SCTP, and data will be retransmitted. Although this may cause buffer 138 overflow leading to connection failure, the connection failure rate 139 is possible to achieve approximately zero if buffer is big enough. 141 From the analysis above and practical operation experience, the 142 requirements for softswitch and IP bearer are as follows: the 143 detected duration of SCTP interface coupling interruption should be 144 shorter than the state machine message timer, and this duration is 145 further recommended to be no longer than 6 seconds in order to 146 maintain detection sensitivity; the interruption duration of IP 147 bearer network should be as short as possible to avoid softswitch 148 connection failure during the IP layer interruption period, and this 149 duration is further recommended to be no longer than 5 seconds. 151 2.1.2 Call Cut-off 153 Call cut-off is referred to the abnormal release during a phone call 154 due to reasons other than intentional release by any of the parties 155 involved in the call. The call cut-off rate is related with: 157 (1) Interfaces, including Nc and interface connecting MSS and SG. 159 (2) Detected duration of interface coupling interruption. 161 (3) Bearing network convergence time. 163 If the detected duration of interface coupling interruption is 164 shorter than IP routing convergence time, established phone calls 165 will be released once interruption of interface Nc or interface 166 connecting MSS and SG is detected. In the case of coupling breakoff, 167 call cut-off rate can be calculated as 169 Call Cut-off Rate = ( CAPS * Call Duration ) * Busy Hour Coupling 170 Breakoffs / BHCA. 172 While if the coupling is not interrupted, the call cut-off rate can 173 be approximately zero. 175 In conclusion, the SCTP coupling should be guaranteed during IP layer 176 interruption to avoid interface breakoff alert. The requirements for 177 softswitch and IP bearer are the same as those related to connection 178 failure. 180 2.1.3 Connection Delay 182 The connection delay from a call initiation by a calling party to 183 PLMN should be no longer than 4 seconds. This delay is affected by 184 factors below: 186 (1) RRC connection setup delay (irrelevant to whether service is 187 carried by IP or not). 189 (2) Core network signaling interaction delay. The message number at 190 interface Nc/Nb is 6, and is 8 (calling side) or 16 (called side, in 191 case of IP-IP) at interface Mc. Each message is with a delay of no 192 longer than 50 milliseconds. Calling message delay at interface Nc 193 is no longer than 300 milliseconds. If long distance call is made 194 though CMN, the message delay is to be increased by transmission 195 delay of 5 msec/km and CMN process delay. So the message delay is 196 likely to be 400 milliseconds. 198 (3) IP bearing network QoS and load. 200 The connection delay is influenced by the delay criterion defined in 201 the IP bearing network QoS, and is raised by delay, jitter, packet 202 loss caused by network overload. In addition, if the configured 203 detected duration of interface coupling interruption is too long, the 204 SCTP sensitivity to the retransmitted messages after packet loss will 205 be decreased, which increases connection delay. 207 Connection delay is generally expressed as 208 Connection Delay = (IP convergence time + RRC connection setup delay 209 + Signaling Interaction Delay), 211 and is no longer than 4 seconds. So the IP network in normal working 212 state should be constrained within a certain range of load to ensure 213 that delay is shorter than 50 milliseconds, while in interruption 214 state the IP convergence time should be no longer than 3 seconds to 215 ensure that connection delay is shorter than 4 seconds. 217 From the analysis of IP/MPLS performance according to the three 218 criteria above, we suggest the transmission interruption duration of 219 IP/MPLS network for softswitch service should be no longer than 3 220 seconds. 222 2.2. LTE Backhaul 224 It is to be further analyzed. 226 2.3. VPN 228 It is to be further analyzed. 230 2.4. IPTV 232 It is to be further analyzed. 234 3. Security Considerations 236 TBD 238 4. IANA Considerations 240 It is no necessary to request new IANA code in the draft. 242 5. Acknowledgements 244 We would like to thank Kai Li for his help in the analysis of 245 softswitch voice communication quality. 247 6. Normative References 248 Authors' Addresses 250 Peng Fan 251 China Mobile 252 No.32 Xuanwumen West Street, Xicheng District 253 Beijing 100053 254 P.R. China 256 Email: fanpeng@chinamobile.com 258 Lianyuan Li 259 China Mobile 260 No.32 Xuanwumen West Street, Xicheng District 261 Beijing 100053 262 P.R. China 264 Email: lilianyuan@chinamobile.com