Transport Area Working Group M. Suznjevic Internet-Draft University of Zagreb Intended status: Informational J. Saldana Expires: December 15, 2015 University of Zaragoza June 13, 2015 Delay Limits and Multiplexing Policies to be employed with Tunneling Compressing and Multiplexing Traffic Flows draft-suznjevic-tsvwg-mtd-tcmtf-05 Abstract This document contains recommendations to be taken into account when using methods which optimize bandwidth utilization through Tunneling Compressing and Multiplexing (TCM) traffic flows over a network path. Different multiplexing policies and implementation issues which are service and link specific are discussed. Additionally, this document describes policies which can be used for detecting, classifying, and choosing the network flows suitable for optimization by using TCM. Finally, recommendations of maximum tolerable delays to be added by optimization techniques are reported. Recommendations are presented only for network services for which such bandwidth optimization techniques are applicable (i.e., services with low payload to header size ratio, which will also be denoted as "small-packet flows"). Status of This Memo This Internet-Draft is submitted to IETF 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/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 15, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. Suznjevic & Saldana Expires December 15, 2015 [Page 1] Internet-Draft Delay Limits and Policies for TCM June 2015 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Considered services . . . . . . . . . . . . . . . . . . . . . 4 3.1. Real-time services . . . . . . . . . . . . . . . . . . . 4 3.2. Non real-time services . . . . . . . . . . . . . . . . . 5 4. Multiplexing policies in TCM . . . . . . . . . . . . . . . . 5 5. Detecting, classifying, and choosing network flows to be optimized . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Optimization within an administrative domain . . . . . . 6 5.2. Optimization based on statistics . . . . . . . . . . . . 7 6. Delay recommendations . . . . . . . . . . . . . . . . . . . . 8 6.1. VoIP . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.2. Online games . . . . . . . . . . . . . . . . . . . . . . 12 6.3. Remote desktop access . . . . . . . . . . . . . . . . . . 13 6.4. Non real-time service . . . . . . . . . . . . . . . . . . 13 6.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction This document extends the draft [TCM] with a set of recommendations regarding the processes of traffic optimization, which may include compressing, multiplexing, and/or tunneling a number of packets. These recommendations are needed because these traffic optimization techniques, while saving bandwidth and reducing overhead, may cause network impairments if packets are delayed before being sent together. These techniques are also proposed at layer 2. For example, in [IEEE.802-11N.2009], a number of Protocol Data Units can be grouped and transmitted together. Network delay is one of the main factors which can degrade the Quality of Experience (QoE) of real-time network services RFC 6390 Suznjevic & Saldana Expires December 15, 2015 [Page 2] Internet-Draft Delay Limits and Policies for TCM June 2015 [RFC6390] [TGPP_TR26.944]. In order to prevent the perceived quality degradation of the services when using TCM, a policy defining a multiplexing period can be employed. First, the document describes different multiplexing policies which can be employed for defining which native packets are multiplexed together. A policy combining a multiplexing period and a packet size limit is proposed in order to put an upper bound on the added delay. Additionally, this document describes the policies that can be employed for detecting, classifying, and choosing the network flows suitable for TCM optimization. Finally, values for maximum tolerable delays presented here from the base of the proposed multiplexing policy. The recommendations are presented for both real-time and non real-time network services in which TCM bandwidth optimization is applicable (i.e., services which have low payload-to-header-size ratio, which results in high protocol overhead, which will also be denoted as small-packet flows). 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. Terminology This document uses a number of terms to refer to the roles played by participants in, and objects of, the TCM sessions. TCM optimizer The host where TCM optimization is deployed. If that hosts corresponds to the ingress of the tunnel where native packets are included it is called TCM-ingress optimizer (TCM-IO). The host where TCM multiplexed packets are received and rebuilt to their native form is called TCM-egress optimizer (TCM-IO). It corresponds to the tunnel egress. policy manager A network entity which makes the decisions about TCM parameters: multiplexing period; flows to be multiplexed together, depending on their IP addresses, ports, etc. It is connected with a number of TCM optimizers, and orchestrates the optimization that takes place between them. Suznjevic & Saldana Expires December 15, 2015 [Page 3] Internet-Draft Delay Limits and Policies for TCM June 2015 native packet A packet sent by an application, belonging to a flow that can be optimized by means of TCM. TCM-optimized packet A packet including a number of multiplexed and header-compressed native ones, and also a tunneling header shared by all the packets, as detailed by TCM. 3. Considered services The services considered suitable for being optimized by TCM are those that generate long-term flows of small packets, with a low payload to header size ratio. Some real-time and some non real-time services are suitable for optimization by means of TCM. 3.1. 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 with low payload to header size ratio as candidates for the bandwidth optimization techniques presented in TCM: o Voice over IP o Online games o Remote desktop services While video services are considered real-time, they are not suitable for bandwidth optimization techniques proposed in [TCM], due to their high payload to header size ratio. Due to the same reason, we do not take into account cloud gaming services. In such gaming services all the calculations of the game state are deployed at the server and a real-time video stream is sent to the client. In these cases, TCM optimization is neither interesting nor applicable. Suznjevic & Saldana Expires December 15, 2015 [Page 4] Internet-Draft Delay Limits and Policies for TCM June 2015 3.2. Non real-time services On the other hand, TCM can be applied for some non real-time services such as streaming audio, and instant messaging. These applications are suitable for TCM in terms of payload to header size ratio, but different studies have shown that acceptable delays for these services are up to several seconds [ITU-T_G.1010]. Also, some types of machine to machine (M2M) traffic (e.g., metering messages from various sensors) may have traffic properties suitable for TCM. Acceptable delays for these services can be go up to an hour [Liu_M2M]. We list limitations for these services as well, although in the practical application TCM should not introduce delays which would be noticeable in comparison with delays of such magnitude (i.e., seconds and more). 4. Multiplexing policies in TCM A multiplexing policy defines the decision process for determining which native packet goes in which multiplexed packet. The policies proposed for TCM are: o Fixed number of packets - once a fixed number of packets (N) has arrived, a multiplexed packet is created and sent. o Size limit - once a size limit is reached (e.g., next to the MTU of the underlying network), a multiplexed packet is sent. o Period - a multiplexed packet is sent every time period T. o Timeout - sends a multiplexed packet if a native one arrives and the time since the last multiplexed packet departure is above a defined timeout value. Only the two latter policies are able to control the additional delay introduced by multiplexing. In addition, different policies can be combined. In this document we focus on the combination of "size limit" and "period" policies, as shown in Figure 1. A multiplexed packet is sent at the end of each "period". However, if the size limit is reached, then a multiplexed packet is sent immediately, and the period is "reset". Thus, the added delay is for the worst case scenario equal to the defined period. Suznjevic & Saldana Expires December 15, 2015 [Page 5] Internet-Draft Delay Limits and Policies for TCM June 2015 native traffic: |<--P-->|<--P-->|<--P-->|<--P-->|<-t*->|<--P-->| | | | | | | | |# # | # # | | # #|######| # #| -------------------------------------------------------> t multiplexed traffic: | | | | | | | | |# |# | |# |## |# | |# |# | |# |## |# -------------------------------------------------------> t * period reset (t
R ^ |
| | | |
| |transac. total RTT
| | | |
| -------S v |
| ------- | ^ |
| ------- | | |
| ------- |transf. |
| ------- | | |
R<------ | v v
| |
S: Packet sent
R: Packet received
Figure 2
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Figure 2 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.
The use of TCM requires the addition of TCM optimizers in the
scenario. A number of flows are multiplexed together before being
sent through the network. The packets are demultiplexed and rebuilt
before being forwarded to the application server. A scheme of TCM is
included in Figure 3:
+--------+
|client 1|___
+--------+ \
\ _ _
+--------+ +--------+ ( ` )_ +--------+ +------+
|client 2|--->| TCM-IO |--> ( ) `) --->| TCM-EO |-->|server|
+--------+ +--------+ (_ (_ . _) _) +--------+ +------+
/ Internet
/
+--------+ / <--------------TCM----------->
|client n|_/
+--------+
Figure 3
This technique groups packets in order to build a multiplexed one.
As previously stated, the focus of this document is on "multiplexing
period" policy for creating the multiplexed packet combined with size
limit policy. Multiplexing period is a time frame in which the TCM
optimizer waits for native packets to arrive in order to send them as
one multiplexed packet. If the multiplexed packet size limit is
reached before the multiplexing period has run out (i.e., if enough
native packets arrive to fill the limit), the multiplexed packet is
sent right away. In this way a certain amount of delay caused by the
TCM optimization is added in the communication. It is important to
emphasize that multiplexing delay can't exceed the multiplexing
period, and that it will only reach the value of multiplexing period
on a link with a low traffic load. Multiplexing delay can be
classified as caused by the middlebox presence as defined in RFC 6390
RFC 6390 [RFC6390]. The delay in the TCM-IO includes the time during
which the packets are retained until the bundled packet is sent, plus
processing time. In the TCM-EO however, the packets are not
retained, so only the processing time is considered.
Figure 4 shows the total delay, when a TCM optimizers are added. It
should be noted that multiplexing can be deployed independently in
both directions, or only in one of them.
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+---------+ +----------+ +---------+ +---------+
| Host 1 | | TCM-IO | | TCM-EO | | Host 2 |
+---------+ +----------+ +---------+ +---------+
S------- | | | ^ ^
| ------- | | | | |
| --R ^ | | | |
| | | | | | |
| | mux | | | |
| | | | | | |
| | | | | transf. |
| S---- v | | (& mux) |
| | ------- | | | |
| ------R ^ | | |
| | demux | | total
| | | | | RTT
| S--- v | v |
| | --------->R ^ |
| | | |
| |transac. |
| | | |
| --------S v |
| -------- | ^ |
| -------- | | |
| -------- | transf. |
| ------- | | |
R<-------- | v v
| |
S: Packet sent
R: Packet received
Figure 4
With respect to efficiency in terms of use of the bandwidth, a
tradeoff appears: the longer the multiplexing period, the higher the
number of packets which can be grouped, thus obtaining better
bandwidth savings. So in order to calculate the maximum multiplexing
period, the rest of the delays have to be considered: if the sum of
transaction, and transfer delays is under the maximum tolerable
delay, then multiplexing will be possible without harming the user
experience. The overall delay may be calculated according to the
ITU-T Y.1541 recommendation [ITU-T_Y.1541]. Subtracting propagation,
processing, and transmission delay from the tolerable delay for
specific service results in the maximum value of the multiplexing
period.
Next, we will report the maximum tolerable latency for the previously
listed real-time network services.
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6.1. 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]. Tunneling
Multiplexed Compressed RTP (TCRTP) [RFC4170] already considers
tunneling, compressing and multiplexing VoIP packets.
6.2. 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:
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.
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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].
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].
6.3. 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].
6.4. Non real-time service
Traffic flows of several types of non real-time services can be
optimized using TCM. Under this category we include services for M2M
metering information, streaming audio, and instant messaging. M2M
metering services are suitable for TCM optimization not only due to
their very loose delay requirements, but also because of the one way
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nature of the 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], work over UDP and send small
packets. 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].
6.5. 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).
+--------------------------+--------------------------+-------------+
| 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
7. Acknowledgements
Jose Saldana was funded by the EU H2020 Wi-5 project (Grant Agreement
no: 644262).
8. IANA Considerations
This memo includes no request to IANA.
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9. Security Considerations
No relevant security considerations have been identified
10. References
10.1. 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,