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