Internet DRAFT - draft-fan-opsawg-transmission-interuption

draft-fan-opsawg-transmission-interuption






Operations and Management Area Working                            P. Fan
Group                                                              L. Li
Internet-Draft                                              China Mobile
Intended status: Standards Track                           March 5, 2012
Expires: September 6, 2012


  Requirements for IP/MPLS network transmission interruption duration
              draft-fan-opsawg-transmission-interuption-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.

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   This Internet-Draft will expire on September 6, 2012.

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   Copyright (c) 2012 IETF Trust and the persons identified as the
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   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  . . . . . . . . . . . . . . . . . . . . . . . . 7



































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1.  Introduction

   Today's IP/MPLS network is widely used as a bearing network to carry
   diversified packet switched services.  The transmission qualities of
   these services are closely related to the performance of bearing
   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 bearing 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 bearing layer.  There are mainly two network design principles to
   be considered when carrying softswitch voice services: the bearing
   network should guarantee the communication quality of voice carried
   by IP is as good as that of voice carried by TDM, and the
   communication quality can still be satisfied when a network failure
   occurs, causing transmission interruption and network convergence.
   This part will mainly focus on three communication quality criteria
   and their influence factors and causes to give requirements for
   softswitch and IP bearing networks.

   2.1.1 Connection Failure

   Connection failure 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 connection failure
   rate is mainly associated by the factors as follows:

   (1) Interfaces, including Nc, Mc and interface connecting MSS and SG.




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   (2) Message timer of state machine.  If a timeout takes place, the
   state machine releases signaling messages, producing a connection
   failure.  In China Mobile's network, the BICC timer is configured to
   10~15 seconds and DTAP timer about 15 seconds.

   (3) Detected duration of interface coupling interruption.

   (4) Bearing network convergence time.

   If the configured timing duration of a state machine is shorter than
   the detected duration of interface coupling interruption, then
   although interface coupling may not be broken off, connection failure
   is still possible to occurs due to message timeout.  If the coupling
   interruption duration is shorter than IP routing convergence time,
   the coupling is considered broken off by SCTP, hence message loss at
   interface between MSS and SG as well as interface Nc results in
   massive connection failure, and new calling request cannot be
   satisfied because of interface Mc breakoff.  In this case, the
   connection failure rate can be calculated as

   Connection Failure Rate = ( IP Convergence Time + Coupling
   Restoration Time ) * CAPS / BHCA.

   However, if the coupling interruption duration is longer than IP
   routing convergence time, then the coupling is considered normal by
   SCTP, and data will be retransmitted.  Although this may cause buffer
   overflow leading to connection failure, the connection failure 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
   detected duration of SCTP interface coupling interruption should be
   shorter than 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 softswitch
   connection failure 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 connecting MSS and SG.

   (2) Detected duration of interface coupling interruption.



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   (3) Bearing network convergence time.

   If the detected duration of interface coupling interruption is
   shorter than IP routing convergence time, established phone calls
   will be released once interruption of interface Nc or interface
   connecting MSS and SG is detected.  In the case of coupling breakoff,
   call cut-off rate can be calculated as

   Call Cut-off Rate = ( CAPS * Call Duration ) * Busy Hour Coupling
   Breakoffs / BHCA.

   While if the coupling is not interrupted, the call cut-off rate can
   be approximately zero.

   In conclusion, the SCTP coupling 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 connection
   failure.

   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 bearing network QoS and load.

   The connection delay is influenced by the delay criterion defined in
   the IP bearing network QoS, and is raised by delay, jitter, packet
   loss caused by network overload.  In addition, if the configured
   detected duration of interface coupling interruption 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




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   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
   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

   It is to be further analyzed.

2.3.  VPN

   It is to be further analyzed.

2.4.  IPTV

   It is to be further analyzed.


3.  Security Considerations

   TBD


4.  IANA Considerations

   It is no necessary to request new IANA code in the draft.


5.  Acknowledgements

   We would like to thank Kai Li for his help in the analysis of
   softswitch voice communication quality.


6.  Normative References







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Authors' Addresses

   Peng Fan
   China Mobile
   No.32 Xuanwumen West Street, Xicheng District
   Beijing  100053
   P.R. China

   Email: fanpeng@chinamobile.com


   Lianyuan Li
   China Mobile
   No.32 Xuanwumen West Street, Xicheng District
   Beijing  100053
   P.R. China

   Email: lilianyuan@chinamobile.com

































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