mirror of
https://github.com/moparisthebest/xeps
synced 2024-11-27 03:32:16 -05:00
276 lines
12 KiB
XML
276 lines
12 KiB
XML
<?xml version='1.0' encoding='UTF-8'?>
|
|
<!DOCTYPE xep SYSTEM 'xep.dtd' [
|
|
<!ENTITY % ents SYSTEM 'xep.ent'>
|
|
%ents;
|
|
<!ENTITY nokia11 "<note>LTE Smartphone measurements <<link url='https://web.archive.org/web/20160624043050/http://networks.nokia.com/system/files/document/lte_measurements_final.pdf'>http://networks.nokia.com/system/files/document/lte_measurements_final.pdf</link>></note>">
|
|
<!ENTITY huang12 "<note>A Close Examination of Performance and Power Characteristics of 4G LTE Networks <<link url='https://doi.org/10.1145/2307636.2307658'>doi:2307636.2307658</link>></note>">
|
|
]>
|
|
<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
|
|
<xep>
|
|
<header>
|
|
<title>Mobile Considerations on LTE Networks</title>
|
|
<abstract>
|
|
This document provides background information for XMPP implementors
|
|
concerned with mobile devices operating on an LTE cellular network.
|
|
</abstract>
|
|
&LEGALNOTICE;
|
|
<number>0286</number>
|
|
<status>Active</status>
|
|
<lastcall>2017-11-15</lastcall>
|
|
<type>Informational</type>
|
|
<sig>Standards</sig>
|
|
<approver>Council</approver>
|
|
<dependencies>
|
|
<spec>XMPP Core</spec>
|
|
</dependencies>
|
|
<supersedes/>
|
|
<supersededby/>
|
|
<shortname>NOT_YET_ASSIGNED</shortname>
|
|
&dcridland;
|
|
&sam;
|
|
<revision>
|
|
<version>1.0.0</version>
|
|
<date>2018-01-25</date>
|
|
<initials>XEP Editor (jwi)</initials>
|
|
<remark><p>Advance to Active as per Council vote on 2018-01-10.</p></remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.4.1</version>
|
|
<date>2017-09-17</date>
|
|
<initials>ssw</initials>
|
|
<remark>
|
|
<ul>
|
|
<li>Minor editorial fixes.</li>
|
|
<li>Remove reference to EXI which has no implementations.</li>
|
|
</ul>
|
|
</remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.4.0</version>
|
|
<date>2017-01-17</date>
|
|
<initials>ssw</initials>
|
|
<remark>
|
|
<ul>
|
|
<li>Attempt to fix some confusing paragraphs.</li>
|
|
<li>Add Client State Indication to Notable Extensions.</li>
|
|
</ul>
|
|
</remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.3</version>
|
|
<date>2015-07-24</date>
|
|
<initials>ssw</initials>
|
|
<remark>
|
|
<p>
|
|
Include real world compression numbers and additional recommended
|
|
reading.
|
|
</p>
|
|
</remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.2</version>
|
|
<date>2015-07-22</date>
|
|
<initials>ssw</initials>
|
|
<remark><p>Overhaul to include LTE.</p></remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.1</version>
|
|
<date>2010-09-15</date>
|
|
<initials>psa</initials>
|
|
<remark><p>Initial published version.</p></remark>
|
|
</revision>
|
|
<revision>
|
|
<version>0.0.1</version>
|
|
<date>2010-07-13</date>
|
|
<initials>dwd</initials>
|
|
<remark><p>First draft. Also John's birthday.</p></remark>
|
|
</revision>
|
|
</header>
|
|
<section1 topic='Introduction' anchor='intro'>
|
|
<p>
|
|
XMPP as a protocol was designed before the wide spread adoption of mobile
|
|
devices, and is often cited as not being very mobile friendly as a result.
|
|
However, this mostly stems from undocumented lore and outdated notions of
|
|
how XMPP works. As the Internet and protocol design have changed to be
|
|
more accommodating for mobile, so has XMPP.
|
|
</p>
|
|
<p>
|
|
This XEP aims to provide useful background knowledge of mobile handset
|
|
behavior, and those considerations that client and server designers can
|
|
take to ensure that bandwidth and battery are used efficiently.
|
|
</p>
|
|
</section1>
|
|
<section1 topic='Overview' anchor='overview'>
|
|
<p>
|
|
The two major constraints on mobile devices are power and bandwidth.
|
|
With the wide spread proliferation of 3G and LTE technologies, mobile
|
|
bandwidth and speeds have become broadly comparable to broadband.
|
|
However, they are still relatively expensive compared to traditional wired
|
|
networks, and therefore conserving them is still desirable.
|
|
This XEP mostly focuses on LTE as it already has a very wide deployment
|
|
and will only continue to further replace 3G technologies.
|
|
</p>
|
|
</section1>
|
|
|
|
<section1 topic='Compression' anchor='compression'>
|
|
<p>
|
|
XML, and by extension XMPP, is known to be highly compressible.
|
|
Compression of XMPP data can be achieved with the DEFLATE algorithm
|
|
(&rfc1951;) via TLS compression (&rfc3749;) or &xep0138; (which also
|
|
supports other compression algorithms).
|
|
A description of the security implications of stream compression is beyond
|
|
the scope of this document (See &rfc3749; or &xep0138; for more
|
|
information), but the author does not recommend using TLS compression with
|
|
XMPP (or in general).
|
|
If compression must be used, stream level compression should be
|
|
implemented instead, and the compressed stream should have a full flush
|
|
performed on stanza boundaries to help prevent chosen plaintext attacks.
|
|
While this may mitigate some of the benefits of compression by raising
|
|
compression ratios, in a large, real world deployment, network traffic was
|
|
still observed to decrease by a factor of 0.58 when enabling &xep0138;
|
|
with ZLIB compression.
|
|
</p>
|
|
<p>
|
|
While the CPU cost of compression may directly translate to higher power
|
|
usage, it is vastly outweighed by the benefits of reduced network
|
|
utilization, especially on modern LTE networks which use a great deal more
|
|
power per bit than 3G networks as will be seen later in this document.
|
|
However, CPU usage is also not guaranteed to rise due to compression.
|
|
In the aforementioned deployment of stream compression, a
|
|
<em>decrease</em> in CPU utilization by a factor of 0.60 was observed,
|
|
presumably due to reductions in TLS and packet handling overhead.
|
|
Therefore CPU time spent on compression (for ZLIB, at least; other
|
|
algorithms were not tested) can be considered negligable.
|
|
</p>
|
|
<p>
|
|
Supporting compression and performming a full flush on stanza boundaries
|
|
is recommended for mobile devices.
|
|
</p>
|
|
</section1>
|
|
<section1 topic='Power Consumption' anchor='power'>
|
|
<p>
|
|
While the wide spread adoption of LTE has dramatically increased available
|
|
bandwidth on mobile devices, it has also increased power consumption.
|
|
According to one study, early LTE devices consumed 5–20% more power
|
|
than their 3G counterparts &nokia11;.
|
|
On some networks that support the legacy SVLTE (Simultaneous Voice and
|
|
LTE) or CSFB (Circuit-switched fallback) instead of the more modern VoLTE
|
|
(Voice Over LTE) standard, this number would (presumably) be even higher.
|
|
</p>
|
|
<p>
|
|
XMPP server and client implementers, bearing this increased power usage in
|
|
mind, and knowing a bit about how LTE radios work, can optimize their
|
|
traffic to minimize network usage.
|
|
For the downlink, LTE user equipment
|
|
(UE) utilizes Orthogonal Frequency Division Multiplexing (OFDM), which is
|
|
somewhat inefficient &huang12;.
|
|
On the uplink side a different technology, Single-carrier frequency
|
|
division multiple access (SC-FDMA) is used, which is slightly more
|
|
efficient than traditional OFDM, slightly offsetting the fact that
|
|
broadcasting requires more power than receiving.
|
|
LTE UE also implements a Discontinuous reception (DRX) mode in which the
|
|
hardware can sleep until it is woken by a paging message or is needed to
|
|
perform some task.
|
|
LTE radios have two power modes: RRC_CONNECTED and RRC_IDLE.
|
|
DRX is supported in both of these power modes.
|
|
By attempting to minimize the time which the LTE UE state machine spends
|
|
in the RCC_CONNECTED state, and maximize the time it stays in the DRX
|
|
state (for RCC_CONNECTED and RRC_IDLE), we can increase battery life
|
|
without degrading the XMPP experience.
|
|
To do so, the following rules should be observed:
|
|
</p>
|
|
<section2 topic='Transmit no data'>
|
|
<p>
|
|
Whenever possible, data that is not strictly needed should not be
|
|
transmitted (by the server or client).
|
|
Supporting &xep0352; is recommended.
|
|
Most importantly, XMPP pings should be kept as far apart as possible and
|
|
only used when necessary.
|
|
Server operators are encouraged to set high ping timeouts, and client
|
|
implementors are advised to only send pings when absolutely necessary to
|
|
prevent the server from closing the socket.
|
|
</p>
|
|
</section2>
|
|
<section2 topic='When transmitting, transmit as much as you can'>
|
|
<p>
|
|
If one is on 3G, transmitting a small amount of data will cause the
|
|
radio to enter FACH mode which is significantly cheaper than its high
|
|
power mode.
|
|
On LTE radios, however, transmitting small amounts of data is vastly
|
|
more expensive per bit due to the higher tail-time (the time it takes
|
|
for the radio to change state) of approximately 11 seconds&huang12;.
|
|
On LTE radios, one should transmit as much data from the client as
|
|
possible when the radio is already on (eg. by placing messages in a send
|
|
queue and executing the queue as a batch when the radio is on).
|
|
Similarly, when data is being received from the server, the mobile
|
|
devices radio is already in a high power state and therefore any data
|
|
that needs to be sent to the server should be transmitted.
|
|
</p>
|
|
<p>
|
|
These rules also apply to server operators: If the server receives data,
|
|
the phones radio is already on, therefore you should flush any pending
|
|
data as soon as possible after receiving data from a client.
|
|
</p>
|
|
</section2>
|
|
</section1>
|
|
<section1 topic='Notable Extensions' anchor='xeps'>
|
|
<p>
|
|
This section provides pointers to other documents which may be of interest
|
|
to those developing mobile clients, or considering implementing
|
|
optimizations for them in servers.
|
|
</p>
|
|
<p>&xep0138; provides stream level compression.</p>
|
|
<p>
|
|
&xep0115; provides a mechanism for caching, and hence eliding, the
|
|
disco#info requests needed to negotiate optional features.
|
|
</p>
|
|
<p>
|
|
&xep0237; provides a relatively widely deployed extension for reducing
|
|
roster fetch sizes.
|
|
</p>
|
|
<p>
|
|
&xep0198; allows the client to send and receive smaller keep-alive
|
|
messages, and resume existing sessions without the full handshake.
|
|
This is useful on unstable connections.
|
|
</p>
|
|
<p>
|
|
&xep0352; allows clients to indicate to the server that they are inactive,
|
|
allowing the server to optimize and reduce unnecessary traffic.
|
|
</p>
|
|
<p>
|
|
&xep0357; implements push notifications (third party message delivery),
|
|
which are often used on mobile devices and highly optimized to conserve
|
|
battery.
|
|
Push notifications also allow delivery of notifications to mobile clients
|
|
that are currently offline (eg. in an XEP-0198 "zombie" state).
|
|
</p>
|
|
<p>
|
|
&xep0313; lets clients fetch messages which they missed (eg. due to poor
|
|
mobile coverage and a flaky network connection).
|
|
</p>
|
|
</section1>
|
|
<section1 topic='Acknowledgements' anchor='acks'>
|
|
<p>
|
|
This XEP was originally written by Dave Cridland, and parts of his
|
|
original work were used in this rewrite.
|
|
Thanks to Atlassian (HipChat) for allowing me to release numbers from
|
|
their XMPP compression deployment.
|
|
</p>
|
|
</section1>
|
|
<section1 topic='Security Considerations' anchor='security'>
|
|
<p>This document introduces no new security considerations.</p>
|
|
</section1>
|
|
<section1 topic='IANA Considerations' anchor='iana'>
|
|
<p>
|
|
This document requires no interaction with the Internet Assigned Numbers
|
|
Authority (IANA).
|
|
</p>
|
|
</section1>
|
|
<section1 topic='XMPP Registrar Considerations' anchor='registrar'>
|
|
<p>
|
|
No namespaces or parameters need to be registered with the XMPP Registrar
|
|
as a result of this document.
|
|
</p>
|
|
</section1>
|
|
</xep>
|