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Network Working GroupP. Saint-Andre
Internet-DraftXSF
Expires: October 13, 2007April 11, 2007


Interdomain Presence Scaling Analysis for the Extensible Messaging and Presence Protocol (XMPP)
draft-saintandre-xmpp-presence-analysis-00

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Copyright Notice

Copyright © The IETF Trust (2007).

Abstract

This document analyzes the traffic that is generated as a result of presence subscriptions between users of federated domains that support the Extensible Messaging and Presence Protocol (XMPP). This analysis is provided as a source of comparison with a similar analysis being performed regarding domains that support federated presence using Session Initiation Protocol (SIP) for Instant Messaging and Presence Leveraging Extensions (SIMPLE).



Table of Contents

1.  Introduction
2.  Traffic Load
    2.1.  Assumptions
    2.2.  Protocol Flows
    2.3.  Analysis
    2.4.  Scenarios
        2.4.1.  Basic
        2.4.2.  Widely Distributed Inter-Domain Presence
        2.4.3.  Very Large Network Peering
        2.4.4.  Intra-Domain Peering
3.  Security Considerations
4.  Informative References
§  Author's Address
§  Intellectual Property and Copyright Statements




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1.  Introduction

Presence is information about the network availability of an individual (or, more precisely, of a presence address of the kind that is often but not necessarily associated with an individual). As typically designed and deployed, presence is shared only with authorized entities, where the authorization takes the form of a subscription. (In this document, we employ the term "user" to signify an account that generates presence information and the term "contact" to signify an annount that is subscribed to the user's presence.)

The sharing of presence information can result in a large volume of traffic as users log on or off throughout the life of a presence session, especially for users with large numbers of contacts (e.g., the author of this document has approximately 1,500 contacts in his list of presence subscribers). The volume is increased by communication of information beyond boolean network availability, such as availability substates (e.g., "away" and "do not disturb"). The volume is further increased if the presence "transport" is used to communicate information such as geolocation, mood, activity, even the music to which an individual is listening. While such traffic may not be a concern in a standalone presence domain, interdomain communications may introduce a more significant impact on the functioning of the Internet as a whole.

There are several standardized technologies for sharing presence information. One is a set of extensions to the Session Initiation Protocol (SIP), where the base protocol is defined in [SIP] (Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” June 2002.) and the extensions are defined in [SIP‑EVENT] (Roach, A., “Session Initiation Protocol (SIP)-Specific Event Notification,” June 2002.) and [SIP‑PRES] (Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” August 2004.). Another is the Extensible Messaging and Presence Protocol (XMPP) as defined in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.) and [XMPP‑IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.).

[PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.) analyzes several factors regarding the scalability of interdomain communication of presence information using SIP/SIMPLE technologies. For the sake of comparison, this document aims to provide a similar analysis regarding XMPP technologies; in its first iteration, it discusses traffic load exclusively since bandwidth usage has the greatest potential impact on the Internet (whereas issues such as state management and server processing of presence information are implementation-specific).



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2.  Traffic Load



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2.1.  Assumptions

The model for XMPP presence subscriptions is different from that of SIP. In particular, XMPP presence subscriptions are long-lived, and once established last until cancelled. Thus XMPP does not have subscription timeouts and refresh periods as SIP presence does. In addition, this document does not include presence subscriptions in its protocol flows since in XMPP they are preconditions for the exchange of presence notifications (in any case, the number of XML stanzas exchanged in the process of establishing a presence subscription is negligible compared to the volume of presence notifications).

XMPP presence subscriptions are typically bidirectional (i.e., the contact has a subscription to the user's presence and the user has a subscription to the contact's presence). However, because [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.) assumes that subscriptions are uni-directional (i.e., the contact has a subscription to the user's presence but not vice-versa), the same assumption is made herein.

Although an XMPP user or contact may have multiple connected "resources" (e.g., client or device) at any one time, for the sake of simplification this document assumes that each entity has only one simultaneous resource.

Note that, unlike in SIP, XMPP packets are not typically acknowledged with the equivalent of a 200/OK message.

[PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.) assumes that presence notification packets will typically be on the order of 4 kilobytes in size (not including TCP or UDP overhead). XMPP presence notification packets tend to be much smaller than SIP presence notification packets; in this document we assume (based on deployment experience) that they are typically 200 bytes in size.



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2.2.  Protocol Flows

When a contact (in these examples romeo@example.net) becomes available, the contact's server sends an XMPP presence stanza of type "probe" to the user (in these examples juliet@example.com) on behalf of the contact, as shown in the following example (this can be seen as similar to the initial SUBSCRIBE in SIP presence):

Contact's server sends presence probe to user:

<presence
    from='romeo@example.net/orchard'
    to='juliet@example.com'
    type='probe'/>

If the user's server determines that the contact is authorized to see the user's presence, the user's server return's the user's current presence state to the contact (this is equivalent to the "Initial NOTIFY" in SIP presence).

User's server sends presence to contact:

<presence
    from='juliet@example.com/balcony'
    to='romeo@example.net/orchard'
    xml:lang='en'>
  <show>away</show>
  <status>be right back</status>
  <priority>0</priority>
</presence>

If the user subsequently changes her presence, the user's server sends an updated presence notification to the contact.

User's server sends updated presence to contact:

<presence
    from='juliet@example.com/balcony'
    to='romeo@example.net/orchard'
    xml:lang='en'>
  <priority>0</priority>
</presence>

A presence session can include any number of presence changes.

When the user goes offline, the user's server sends a presence stanza of type "unavailable" to the contact.

User's server sends unavailable presence to contact:

<presence
    from='juliet@example.com/balcony'
    to='romeo@example.net/orchard'
    type='unavailable'
    xml:lang='en'/>

Naturally, similar protocol flows are generated by the contact during the life of his presence session.



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2.3.  Analysis

To enable valid comparison between SIMPLE and XMPP with regard to interdomain presence scaling, this document adheres as closely as possible to the analysis presented in [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.), witih appropriate modifications given differences between the two technologies. In particular, traffic calculations are based on the following inputs and formulae, where the numbering follows that in [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.) and the terminology is adjusted to conform to XMPP:



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2.4.  Scenarios



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2.4.1.  Basic

This scenario assumes two domains, each with 20,000 users, where each user has 4 contacts in the other domain and changes presence 3 times per hour. The calculations are as follows:

For the last three factors, the comparable numbers for SIMPLE (from [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.)) are 14,080,000 total messages, 489 messages per second, and 830 kilobytes per second.



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2.4.2.  Widely Distributed Inter-Domain Presence

This scenario assumes two domains, each with 20,000 users, where each user has 20 contacts in the other domain and changes presence 3 times per hour. The calculations are as follows:

For the last three factors, the comparable numbers for SIMPLE (from [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.)) are 70,400,000 total messages, 2,444 messages per second, and 1,968 kilobytes per second.



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2.4.3.  Very Large Network Peering

This scenario assumes two domains, each with 10,000,000 users, where each user has 10 contacts in the other domain and changes presence 6 times per hour. The calculations are as follows:

For the last three factors, the comparable numbers for SIMPLE (from [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.)) are 27,200,000,000 total messages, 944,444 messages per second, and 880,555 kilobytes per second.



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2.4.4.  Intra-Domain Peering

This scenario assumes two domains, each with 60,000 users, where each user has 10 contacts in the other domain and changes presence 3 times per hour. The calculations are as follows:

For the last three factors, the comparable numbers for SIMPLE (from [PROBLEM] (Houri, A., “Problem Statement for SIP/SIMPLE,” February 2007.)) are 105,600,000 total messages, 3,667 messages per second, and 3,683 kilobytes per second.



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3.  Security Considerations

This document introduces and addresses no security concerns above and beyond those already defined in [XMPP‑CORE] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” October 2004.) and [XMPP‑IM] (Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” October 2004.).



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4. Informative References

[PROBLEM] Houri, A., “Problem Statement for SIP/SIMPLE,” draft-ietf-simple-interdomain-scaling-analysis-00 (work in progress), February 2007.
[SIP] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, “SIP: Session Initiation Protocol,” RFC 3261, June 2002.
[SIP-EVENT] Roach, A., “Session Initiation Protocol (SIP)-Specific Event Notification,” RFC 3265, June 2002.
[SIP-PRES] Rosenberg, J., “A Presence Event Package for the Session Initiation Protocol (SIP),” RFC 3856, August 2004.
[XMPP-CORE] Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Core,” RFC 3920, October 2004.
[XMPP-IM] Saint-Andre, P., “Extensible Messaging and Presence Protocol (XMPP): Instant Messaging and Presence,” RFC 3921, October 2004.


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Author's Address

  Peter Saint-Andre
  XMPP Standards Foundation
  P.O. Box 1641
  Denver, CO 80201
  USA
Email:  stpeter@jabber.org
URI:  xmpp:stpeter@jabber.org


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Full Copyright Statement

Intellectual Property

Acknowledgment