Operations and Management Area Working P. Fan Group L. Li Internet-Draft China Mobile Intended status: Standards Track July 9, 2012 Expires: January 10, 2013 Requirements for IP/MPLS network transmission interruption duration draft-fan-opsawg-transmission-interruption-00 Abstract The transmission performance of IP/MPLS network affects upper layer services and networks, but there is no consensus in the industry on transmission interruption for IP/MPLS network up to now. This memo studies requirements for the interruption duration criteria in several service scenarios. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as Fan & Li Expires January 10, 2013 [Page 1] Internet-Draft IP/MPLS transmission interruption July 2012 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Services and Performance Criteria . . . . . . . . . . . . . . . 3 2.1. Softswitch . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. LTE Backhaul . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. VPN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.4. IPTV . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 6. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Fan & Li Expires January 10, 2013 [Page 2] Internet-Draft IP/MPLS transmission interruption July 2012 1. Introduction Today's IP/MPLS network is widely used as a bearer network to carry diversified packet switched services. The transmission qualities of these services are closely related to the performance of bearer layers, as network failure, delay, congestion and other abnormities will inevitably bring about service interruption and user perception degradation. However, there is no consensus in the industry on transmission interruption for IP/MPLS network up to now. This memo studies relationships between service performance and transmission interruption duration in several scenarios, and is intended to reach a list of requirements for these interruption duration criteria. 2. Services and Performance Criteria Services delivered by IP/MPLS network have different transmission quality requirements, thus introduce different performance criteria for the bearing IP/MPLS network. In this section we will describe concerns on IP/MPLS network interruption duration from aspects of four kinds of service scenarios, namely Softswitch, LTE backhaul, VPN and IPTV. 2.1. Softswitch From the softswitch point of view, the IP carrying nature imposes certain influence to the service quality. Especially when speech is delivered by IP, the communication quality of voice is impaired, and in turn makes higher requirements for the transmission performance of IP. This part will mainly focus on three communication quality criteria and their influence factors to give requirements for softswitch and IP bearer networks. 2.1.1 Call Loss Call loss is used to describe the circumstance where a phone call fails to establish after initiated by a subscriber due to network faults. In the practical network, the call loss rate is mainly associated by the factors as follows: (1) Interfaces, including Nc, Mc and interface between MSS and SG. (2) State machine message timer. If a timeout takes place, the state machine releases signaling messages, producing a call loss. Typical value of BICC timer is 10~15 seconds and value of DTAP timer about 15 seconds. (3) Interface association timer. Associations breaks off at the Fan & Li Expires January 10, 2013 [Page 3] Internet-Draft IP/MPLS transmission interruption July 2012 expiration of timer. (4) Bearer network convergence time. If the configured timer duration of a state machine is shorter than the timer duration of interface association, then although interface association may not be broken off, call loss is still possible to occur due to message timer expiration. If the association timer duration is shorter than IP routing convergence time, the association is considered broken off by SCTP, hence message loss at interface between MSS and SG as well as interface Nc results in massive call loss, and new calling request cannot be satisfied because of interface Mc breakoff. In this case, the call loss rate can be calculated as Call Loss Rate = ( IP Convergence Time + Association Restoration Time ) * CAPS / BHCA. However, if the association timer duration is longer than IP routing convergence time, then the association is considered normal by SCTP, and data will be retransmitted. Although this may cause buffer overflow leading to call loss, the call loss rate is possible to achieve approximately zero if buffer is big enough. From the analysis above and practical operation experience, the requirements for softswitch and IP bearer are as follows: the duration of SCTP interface association timer should be shorter than that of the state machine message timer, and this duration is further recommended to be no longer than 6 seconds in order to maintain detection sensitivity; the interruption duration of IP bearer network should be as short as possible to avoid call loss during the IP layer interruption period, and this duration is further recommended to be no longer than 5 seconds. 2.1.2 Call Cut-off Call cut-off is referred to the abnormal release during a phone call due to reasons other than intentional release by any of the parties involved in the call. The call cut-off rate is related with: (1) Interfaces, including Nc and interface between MSS and SG. (2) Interface association timer. (3) Bearer network convergence time. If the association timer duration is shorter than IP routing convergence time, established phone calls will be released once Fan & Li Expires January 10, 2013 [Page 4] Internet-Draft IP/MPLS transmission interruption July 2012 interruption of interface Nc or interface connecting MSS and SG is detected. In the case of association breakoff, call cut-off rate can be calculated as Call Cut-off Rate = ( CAPS * Call Duration ) * Busy Hour Association Breakoffs / BHCA. While if the association is not interrupted, the call cut-off rate can be approximately zero. In conclusion, the SCTP association should be guaranteed during IP layer interruption to avoid interface breakoff alert. The requirements for softswitch and IP bearer are the same as those related to call loss. 2.1.3 Connection Delay The connection delay from a call initiation by a calling party to PLMN should be no longer than 4 seconds. This delay is affected by factors below: (1) RRC connection setup delay (irrelevant to whether service is carried by IP or not). (2) Core network signaling interaction delay. The message number at interface Nc/Nb is 6, and is 8 (calling side) or 16 (called side, in case of IP-IP) at interface Mc. Each message is with a delay of no longer than 50 milliseconds. Calling message delay at interface Nc is no longer than 300 milliseconds. If long distance call is made though CMN, the message delay is to be increased by transmission delay of 5 msec/km and CMN process delay. So the message delay is likely to be 400 milliseconds. (3) IP bearer network QoS and load. The connection delay is influenced by the delay criterion defined in the IP bearer network QoS, and is raised by delay, jitter, packet loss caused by network overload. In addition, if the configured timer duration of interface association is too long, the SCTP sensitivity to the retransmitted messages after packet loss will be decreased, which increases connection delay. Connection delay is generally expressed as Connection Delay = (IP convergence time + RRC connection setup delay + Signaling Interaction Delay), and is no longer than 4 seconds. So the IP network in normal working Fan & Li Expires January 10, 2013 [Page 5] Internet-Draft IP/MPLS transmission interruption July 2012 state should be constrained within a certain range of load to ensure that delay is shorter than 50 milliseconds, while in interruption state the IP convergence time should be no longer than 3 seconds to ensure that connection delay is shorter than 4 seconds. From the analysis of IP/MPLS performance according to the three criteria above, we suggest the transmission interruption duration of IP/MPLS network for softswitch service should be no longer than 3 seconds. 2.2. LTE Backhaul To be further analyzed. 2.3. VPN To be further analyzed. 2.4. IPTV To be further analyzed. 3. Security Considerations TBD 4. IANA Considerations This memo includes no request to IANA. 5. Acknowledgements We would like to thank Kai Li for his help in the analysis of softswitch voice communication quality. 6. Normative References Fan & Li Expires January 10, 2013 [Page 6] Internet-Draft IP/MPLS transmission interruption July 2012 Authors' Addresses Peng Fan China Mobile 32 Xuanwumen West Street, Xicheng District Beijing 100053 P.R. China Email: fanpeng@chinamobile.com Lianyuan Li China Mobile 32 Xuanwumen West Street, Xicheng District Beijing 100053 P.R. China Email: lilianyuan@chinamobile.com Fan & Li Expires January 10, 2013 [Page 7]