Internet DRAFT - draft-suznjevic-dispatch-delay-limits
draft-suznjevic-dispatch-delay-limits
Dispatch M. Suznjevic
Internet-Draft University of Zagreb
Intended status: Informational J. Saldana
Expires: June 13, 2016 University of Zaragoza
December 11, 2015
Delay Limits for Real-Time Services
draft-suznjevic-dispatch-delay-limits-00
Abstract
Network delay is one of the main factors which can degrade the
Quality of Experience (QoE) of network services. This document
surveys a set of recommendations about the maximum latency tolerated
by the users of services with delay constraints. Some
recommendations already exist for e.g. VoIP, but emerging services
as e.g. online gaming, have different requirements. Different papers
in the literature reporting these constraints are surveyed, and a
summary of the latency limits for each service is provided.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Considered services . . . . . . . . . . . . . . . . . . . . . 3
2.1. Real-time services . . . . . . . . . . . . . . . . . . . 3
2.2. Non real-time services . . . . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Delay recommendations . . . . . . . . . . . . . . . . . . . . 5
4.1. VoIP . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. Online games . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Remote desktop access . . . . . . . . . . . . . . . . . . 7
4.4. Non real-time service . . . . . . . . . . . . . . . . . . 7
4.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The "Workshop on Reducing Internet Latency" [Workshop], sponsored by
the Internet Society and some research projects, discussed different
ways for reducing Internet latency, stating that "For Internet
applications, reducing the latency impact of sharing the
communications medium with other users and applications is key."
Network delay is one of the main factors which can degrade the
Quality of Experience (QoE) of network services [RFC6390]
[TGPP_TR26.944]. In order to prevent the degradation of the
perceived quality of the services with delay constraints, a maximum
limit can be defined. This "latency budget" has to be taken into
account when considering the possibility of adding new network
functions (e.g. through middleboxes), since every optimization adds
some delay as a counterpart. These new functions not only exist at
upper layers, but they can also be found in Layer 2. For example, in
[IEEE.802-11N.2009], a number of Protocol Data Units can be grouped
and transmitted together, but this will add a new delay required to
gather a number of frames together.
This document surveys a set of recommendations about the maximum
latency tolerated by the users of services with delay constraints.
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Some recommendations already exist for e.g. VoIP [ITU-T_G.114], but
emerging services as e.g. online gaming, have different requirements,
which may also vary with the game genre.
1.1. Requirements Language
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 [RFC2119].
2. Considered services
2.1. Real-time services
Under the term "real-time network services" we consider both
conversational and streaming service classes as defined in [TGPP_TS].
Interactive and background services are considered non real-time.
Fundamental requirements of real-time network services include
conversational pattern (stringent and low delay) and preservation of
the time relation (variation) between the information entities of the
stream.
We identify the following real-time network services, as those with
the most stringent real-time constraints:
o Voice over IP
o Online games
o Remote desktop services
2.2. Non real-time services
Non real-time services such as streaming audio or video, and instant
messaging also have delay limits, but different studies have shown
that acceptable delays for these services are up to several seconds
[ITU-T_G.1010].
Some types of machine to machine (M2M) traffic (e.g., metering
messages from various sensors) for these services can be go up to an
hour [Liu_M2M].
3. Definitions
The three normally considered network impairments in the studies
related to subjective quality in delay-constrained services are:
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o delay - can be reported as one-way-delay (OWD) [RFC2679] and two-
way-delay (Round Trip Time) [RFC2681]. In this document, under
the term latency, one way end-to-end delay is considered.
o delay variation - which is a statistical variance of the data
packet inter-arrival time, in other words the variation of the
delay as defined in RFC 3393 [RFC3393].
o packet loss - more important for certain services, while other
include very good algorithms for concealing it (e.g. some game
genres receive accumulative updates, so packet loss is not
important).
In this document we give recommendations for overall tolerable delays
to be taken into account when adding new middleboxes or
functionalities in the network. In an interactive service, the total
delay is composed by the addition of delays as defined in 3GPP TR
26.944 [TGPP_TR26.944]. The overall delay may be calculated
according to the ITU-T Y.1541 recommendation [ITU-T_Y.1541].
o Transfer delay - from Host1 to Host2 at time T is defined by the
statement: Host1 sent the first bit of a unit data to Host2 at
wire-time T and that Host2 received the last bit of that packet at
wire-time T+dT. Thus, it includes the transmission delay (the
amount of time Host1 requires to push all of the packet's bits
into the wire) and the propagation delay in the network (the
amount of time it takes for the head of the packet to travel from
Host1 to Host2).
o Transaction delay - the sum of the time for a data packet to wait
in queue and receive the service during the server transaction.
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+-----------+ +-----------+
| Host1 | | Host 2 |
+-----------+ +-----------+
S------- | ^ ^
| ------- | | |
| ------- |transf. |
| ------- | | |
| ------- | v |
| ------>R ^ |
| | | |
| |transac. total RTT
| | | |
| -------S v |
| ------- | ^ |
| ------- | | |
| ------- |transf. |
| ------- | | |
R<------ | v v
| |
S: Packet sent
R: Packet received
Figure 1
Figure 1 illustrates these delays. The labeled times (S and R)
designate the times in which the packet is sent and received,
respectively, by the network card interface.
4. Delay recommendations
4.1. VoIP
For conversational audio, the International Telecommunication Union
recommends [ITU-T_G.114] less than 150 millisecond one-way end-to-end
delay for high-quality real time traffic, but delays between 150 ms
and 400 ms are acceptable. When considering conversational audio it
should be noted that this delay limits include jitter buffers and
codec processing. For streaming audio, delay constraints are much
looser, the delay should be less than 10 s [ITU-T_G.1010].
4.2. Online games
Online games comprise game genres which have different latency
requirements. This draft focuses on real-time online games and
endorses the general game categorization proposed in
[Claypool_Latency] in which online games have been divided into:
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o Omnipresent, with the threshold of acceptable latency (i.e.,
latency in which performance is above 75% of the unimpaired
performance) of 1000 ms. The most representative genre of
omnipresent games are Real-Time Strategies.
o Third Person Avatar, with the threshold of acceptable latency of
500 ms. These games include Role Playing Games (RPG) and
Massively Multiplayer Online Role-Playing Games (MMORPG).
o First Person Avatar, in which threshold of acceptable latency is
100 ms. The most popular subgenre of them are First Person
Shooters, such as "Call of Duty" or "Halo" series.
As remarked in [Bernier_Latency] and [Oliveira_online], different
methods can be employed to combat delay in online games. The so-
called "client-side prediction" has been largely used in First Person
Shooters. It can be divided into "input prediction" and "dead
reckoning," where input prediction hides the latency for the client-
controlled actions while dead reckoning hides the latency of other
participating players.
The study [Claypool_Latency] evaluated players' performance in
certain tasks, while increasing latency, and reported values at which
the performance dropped below 75% of the performance under unimpaired
network conditions. While measuring objective performance metrics,
this method highly underestimates the impact of delays on players'
QoE. Further studies accessing a particular game genre reported much
lower latency thresholds for unimpaired gameplay.
Other approach some studies have taken is to perform "objective
measurements" [Kaiser_objective] a number of identical "bots", i.e.
virtual avatars controlled by Artificial Intelligence, are placed in
the same virtual scenario and a number of parties between them are
performed. If the number of parties if high enough, then the score
will be the same for all the bots. Then, different network
impairments (latency, jitter, packet loss) are added to one of the
bots, and another set of tests is performed. The performance
degradation of the network-impaired bot can then be statistically
characterized.
A survey using a large number of First Person Shooter games has been
carried out in [Dick_Analysis]. They state that latency about 80 ms
could be considered as acceptable, since the games have been rated as
"unimpaired". Besides service QoE, it has been shown that delay has
great impact on the user's decision to join a game, but significantly
less on the decision to leave the game [Henderson_QoS].
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A study on Mean Opinion Score (MOS) evaluation, based on variation of
delay and jitter for MMORPGs, suggested that MOS drops below 4 for
delays greater than 120 ms [Ries_QoEMMORPG]. The MOS score of 5
indicates excellent quality, while MOS score of 1 indicates bad
quality. Another study focused on extracting the duration of play
sessions for MMORPGs from the network traffic traces showed that the
session durations start to decline sharply when round trip time is
between 150 ms and 200 ms [Chen_HowSensitive].
While original classification work [Claypool_Latency] states that
latency up to 1 second is tolerated by omnipresent games, other
studies argued that only latency up to 200 ms is tolerated by players
of RTS games [Cajada_RTS].
4.3. Remote desktop access
For the remote computer access services, the delays are dependent on
the task performed through the remote desktop. Tasks may include
operations with audio, video and data (e.g., reading, web browsing,
document creation). A QoE study indicates that for audio latency
below 225 ms and for data latency below 200 ms is tolerated
[Dusi_Thin].
4.4. Non real-time service
Under this category we include services for M2M metering information,
streaming audio, and instant messaging. M2M metering services
present a one way communication (i.e., most information travels from
sensors to the central server) [Liu_M2M]. The signalling information
related to M2M can also be optimized. Internet of Things application
layer protocols such as CoAP RFC 7252 [RFC7252], used in Constrained
RESTful Environments (CoRE)[RFC6690]. The ACK_TIMEOUT period in CoAP
is set to 2 seconds. Instant messaging (despite "instant" in its
name) has been categorized as data service by the ITU-T, and it has
been designated with acceptable delays of up to a few seconds
[ITU-T_G.1010].
4.5. Summary
We group all the results in the Table 1 indicating the maximum
allowed latency and proposed multiplexing periods. Proposed
multiplexing periods are guidelines, since the exact values are
dependant of the existing delay in the network. It should be noted
that reported tolerable latency is based on values of preferred
delays, and delays in which QoE estimation is not significantly
degraded. Multiplexing periods of about 1 second can be considered
as sufficient for non real-time services (e.g., streaming audio).
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+--------------------------+--------------------------+-------------+
| Service | Tolerable latency (OWD) | Mux. period |
+--------------------------+--------------------------+-------------+
| Voice communication | < 150ms | < 30ms |
| Omnipresent games | < 200ms | < 40ms |
| First person avatar | < 80ms | < 15ms |
| games | | |
| Third person avatar | < 120ms | < 25ms |
| games | | |
| Remote desktop | < 200ms | < 40ms |
| Instant messaging | < 5s | < 1s |
| M2M (metering) | < 1hour | < 1s |
+--------------------------+--------------------------+-------------+
Table 1: Final recommendations
5. Acknowledgements
Jose Saldana was funded by the EU H2020 Wi-5 project (Grant Agreement
no: 644262).
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
No relevant security considerations have been identified
8. References
8.1. Normative References
[IEEE.802-11N.2009]
"Information technology - Telecommunications and
information exchange between systems - Local and
metropolitan area networks - Specific requirements - Part
11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications - Amendment 5: Enhancements for
higher throughput", IEEE Standard 802.11n, Oct 2009,
<http://standards.ieee.org/getieee802/
download/802.11n-2009.pdf>.
[ITU-T_G.1010]
International Telecommunication Union-Telecommunication,
"End-user multimedia QoS categories", SERIES G:
TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND
NETWORKS; Quality of service and performance , 2001.
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[ITU-T_G.114]
ITU-T, "ITU-T Recommendation G.114 One-way transmission
time", ITU G.114, 2003.
[ITU-T_Y.1541]
International Telecommunication Union-Telecommunication,
"; Network performance objectives for IP-based services",
SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET
PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS; Internet
protocol aspects - Quality of service and network
performance , 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, September 1999.
[RFC3393] Demichelis, C., Chimento, S., and P. Zekauskas, "IP Packet
Delay Variation Metric for IP Performance Metrics (IPPM)",
RFC 3393, November 2002.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", RFC 6390, October 2011.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, August 2012.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
8.2. Informative References
[Bernier_Latency]
Bernier, Y., "Latency Compensating Methods in Client/
Server In-Game Protocol Design and Optimization", Proc.
Game Developers Conference, San Jose Vol. 98033. No. 425.,
2001.
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[Cajada_RTS]
Cajada, M., "VFC-RTS: Vector-Field Consistency para Real-
Time-Strategy Multiplayer Games", Master of Science
Disertation , 2012.
[Chen_HowSensitive]
Chen, K., Huang, P., and L. Chin-Luang, "How sensitive are
online gamers to network quality?", Communications of the
ACM 49, 2006.
[Claypool_Latency]
Claypool, M. and K. Claypool, "Latency and player actions
in online games", Communications of the ACM 49, 2006.
[Dick_Analysis]
Dick, M., Wellnitz, O., and L. Wolf, "Analysis of factors
affecting players' performance and perception in
multiplayer games", Proceedings of 4th ACM SIGCOMM
workshop on Network and system support for games, pp. 1 -
7 , 2005.
[Dusi_Thin]
Dusi, M., Napolitano, S., Niccolini, S., and S. Longo, "A
Closer Look at Thin-Client Connections: Statistical
Application Identification for QoE Detection", IEEE
Communications Magazine, pp. 195 - 202 , 2012.
[Henderson_QoS]
Henderson, T. and S. Bhatti, "Networked games: a QoS-
sensitive application for QoS-insensitive users?",
Proceedings of the ACM SIGCOMM workshop on Revisiting IP
QoS: What have we learned, why do we care?, pp. 141-147 ,
2003.
[Kaiser_objective]
Kaiser, A., Maggiorini, D., Boussetta , K., and N. Achir,
"On the Objective Evaluation of Real-Time Networked
Games", Proc. IEEE Global Telecommunications Conference
(GLOBECOM 2009) , 2009.
[Liu_M2M] Liu, R., Wu, W., Zao, H., and D. Yang, "M2M-Oriented QoS
Categorization in Cellular Network", Master of Science
Disertation , 2012.
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[Oliveira_online]
Oliveira, M. and T. Henderson, "What online gamers really
think of the Internet?", Proceedings of the 2nd workshop
on Network and system support for games (NetGames '03).
ACM, New York, NY, USA pp. 185-193, 2003.
[Ries_QoEMMORPG]
Ries, M., Svoboda, P., and M. Rupp, "Empirical Study of
Subjective Quality for Massive Multiplayer Games",
Proceedings of the 15th International Conference on
Systems, Signals and Image Processing, pp.181 - 184 ,
2008.
[TGPP_TR26.944]
3rd Generation Partnership Project;, "Technical
Specification Group Services and System Aspects; End-to-
end multimedia services performance metrics", 3GPP TR
26.944 version 9.0.0 , 2012.
[TGPP_TS] 3rd Generation Partnership Project, European
Telecommunications Standards Institute, "Quality of
Service (QoS) concept and architecture", 3GPP TS 23.107
version 11.0.0 Release 11 , 2012.
[Workshop]
Ford, M., "Workshop report: reducing internet latency",
SIGCOMM Comput. Commun. Rev. 44, 2 (April 2014), 80-86. ,
2013.
Authors' Addresses
Mirko Suznjevic
University of Zagreb
Faculty of Electrical Engineering and Computing, Unska 3
Zagreb 10000
Croatia
Phone: +385 1 6129 755
Email: mirko.suznjevic@fer.hr
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Jose Saldana
University of Zaragoza
Dpt. IEC Ada Byron Building
Zaragoza 50018
Spain
Phone: +34 976 762 698
Email: jsaldana@unizar.es
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