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Network Working GroupP. Saint-Andre
Internet-DraftXMPP Standards Foundation
Intended status: InformationalOctober 4, 2007
Expires: April 6, 2008 


Interdomain Presence Scaling Analysis for the Extensible Messaging and Presence Protocol (XMPP)
draft-saintandre-xmpp-presence-analysis-02

Status of this Memo

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Copyright Notice

Copyright © The IETF Trust (2007).

Abstract

This document analyzes the scalability of presence sharing between domains that federate using the Extensible Messaging and Presence Protocol (XMPP). This analysis is provided as a source of comparison with a similar analysis being performed regarding the presence extensions to the Session Initiation Protocol (SIP).



Table of Contents

1.  Introduction
2.  Assumptions
3.  Protocol Flows
4.  Analysis
    4.1.  Constants
    4.2.  Initial Messages
    4.3.  Steady State Messages
    4.4.  Termination Messages
    4.5.  Bottom Line
5.  Scenarios
    5.1.  Basic
    5.2.  Widely Distributed Inter-Domain Presence
    5.3.  Very Large Network Peering
    5.4.  Intra-Domain Peering
6.  Conclusion
7.  Security Considerations
8.  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 over 1,500 contacts in his list of presence subscribers). The volume is increased by communication of information beyond basic on-off 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. Such traffic may be a concern even in a standalone presence domain. However, when presence is shared across domain boundaries then such traffic may introduce a more significant impact on the functioning of the Internet as a whole. Therefore it is important to analyze the traffic generated during interdomain communication of presence information.

There are several standardized technologies for sharing presence information. One is a set of extensions (commonly called "SIMPLE") 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., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 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 particular, this document focuses on traffic load exclusively since bandwidth usage has the greatest potential impact on the Internet. By contrast, issues such as state management and server processing of presence information are implementation-specific. This document also briefly mentions existing methods for improving the scalability of XMPP presence (and presence-like) communications.



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2.  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., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 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., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.) assumes that presence notification packets will typically be on the order of 3.5 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 for basic on-off presence. However, some XMPP applications may include additional information in a presence notification packet, such as entity capabilities as described in [XEP‑0115] (Hildebrand, J., Saint-Andre, P., and R. Tronçon, “Entity Capabilities,” August 2007.).

Both [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.) strongly recommend that XMPP presence notifications should include only information that is relevant to a user's willingness or ability to communicate using real-time methods such as instant messaging. However, some XMPP applications include information that is not communications-relevant, such as the hash of a user's avatar icon (see [XEP‑0153] (Saint-Andre, P., “vCard-Based Avatars,” August 2006.) and even metadata about the music to which a user is listening (see [XEP‑0118] (Saint-Andre, P., “User Tune,” June 2007.)). Although it is recommended to communicate such information using the XMPP publish-subscribe extension (see [XEP‑0060] (Millard, P., Saint-Andre, P., and R. Meijer, “Publish-Subscribe,” September 2007.)) and appropriate profiles thereof (e.g., [XEP‑0163] (Saint-Andre, P. and K. Smith, “Personal Eventing via Pubsub,” September 2007.)), some existing XMPP clients send non-communications-relevant information using presence notifications instead of dedicated publish-subscribe nodes. Such behavior marginally increases notification size but can drastically increase the number of notifications sent (e.g., one notification every 3 or 4 minutes when the user begins listening to a new music track). This document does not discuss such usage, since it is actively discouraged and borders on abusive.

This document does not discuss various optimizations for SIMPLE (for which see [PROBLEM] (Houri, A., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.)) or XMPP. The primary deployed optimization for XMPP is stream compression, implemented either at the TLS level via native TLS compression or at the XMPP level where TLS compression is not available (see [XEP‑0138] (Hildebrand, J. and P. Saint-Andre, “Stream Compression,” September 2007.)). Because XMPP communications occur over long-lived TCP connections and associated long-lived XML streams, such compression has been found to yield significant bandwidth savings, up to 90% or even 95%. Stream compression is therefore the recommended method for reducing bandwidth consumption in XMPP systems.



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3.  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 (82 bytes):

<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 (170 bytes):

<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 (160 bytes):

<presence
    from='juliet@example.com/balcony'
    to='romeo@example.net/orchard'
    xml:lang='en'>
  <show>xa</show>
  <status>bbiab</status>
  <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 (96 bytes):

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

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



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4.  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., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.), with 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., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.) and the terminology is adjusted to conform to XMPP.



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4.1.  Constants



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4.2.  Initial Messages



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4.3.  Steady State Messages



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4.4.  Termination Messages



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4.5.  Bottom Line



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5.  Scenarios



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5.1.  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 during an 8-hour presence session. The calculations are as follows.

CONSTANTS
(C01) Presence session lifetime (hours) ....................... 8
(C02) Presence state changes per hour ......................... 3
(C03) Subscription refresh interval per hour ................ N/A
(C04) Total federated contacts per user ....................... 4
(C05) Number of dialogs to maintain per watcher ............... 4
(C06) Number of federated users .......................... 40,000
(C07) Subscription request size in bytes .................... 100
(C08) Subscription approval size in bytes ................... 100
(C09) Presence notification size in bytes ................... 200
(C10) Presence notification ack size in bytes ............... N/A
(C11) Presence document size in bytes ....................... N/A

INITIAL MESSAGES
(I01) Initial subscribe requests per presence session ......... 4
(I02) Initial subscription approvals per presence session ..... 0
(I03) Number of initial presence notifications ................ 4
(I04) Number of initial presence acks ......................... 0
(I05) Total number and bytes of initial subscribe messages
            Number ...................................... 160,000
            Bytes  ................................... 16,000,000
(I06) Total number and bytes of initial subscribe acks
            Number ............................................ 0
            Bytes ............................................. 0
(I07) Total number and bytes of initial notifications
            Number ...................................... 160,000
            Bytes  ................................... 32,000,000
(I08) Total number and bytes of initial notification acks
            Number ............................................ 0
            Bytes ............................................. 0
(I09) Total number and bytes of initial messages
            Number ...................................... 320,000
            Bytes  ................................... 48,000,000

STEADY STATE MESSAGES
(S01) Presence notifications caused by state changes ......... 22
(S02) Notification acks for state change notifications ........ 0
(S03) Number and size of steady-state presence notifications
            Number .................................... 3,520,000
            Bytes ................................... 704,000,000
(S04) Subscription refreshes .................................. 0
(S05) Acks for subscription refreshes ......................... 0
(S06) Notify messages caused by refreshes ..................... 0
(S07) Acks for notify messages caused by refreshes ............ 0
(S08) Number and size of messages caused by refreshes ......... 0
(S09) Total number and bytes of steady-state messages
            Number .................................... 3,520,000
            Bytes ................................... 704,000,000

TERMINATION MESSAGES
(T01) Number of terminating subscribe messages ................ 0
(T02) Number of acks for terminating subscribe messages ....... 0
(T03) Number of terminating notifications ..................... 4
(T04) Number of acks for terminating notifications ............ 0
(T05) Total number and size of terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T06) Total number and size of acks for terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T07) Total number and size of terminating notifications
            Number ...................................... 160,000
            Bytes  ................................... 16,000,000
(T08) Total number and size of acks for terminating notifications
            Number ............................................ 0
            Bytes ............................................. 0
(T09) Total number and size of terminating messages per session
            Number ...................................... 160,000
            Bytes  ................................... 16,000,000

BOTTOM LINE
(B01) Total number and bytes per presence session
            Number .................................... 4,000,000
            Bytes  .................................. 768,000,000
(B02) Total number and bytes per second
            Number .......................................... 139
            Bytes  ....................................... 26,667

For the bottom-line figures, the comparable numbers for SIMPLE in a non-optimized state (see [PROBLEM] (Houri, A., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.)) are 12,800,000 total messages, 20,376,000,000 bytes, 444 messages per second, and 707,500 bytes per second; thus for this scenario XMPP uses 31% of the messages and 3.8% of the bytes used by SIMPLE.



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5.2.  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 during an 8-hour presence session. The calculations are as follows.

CONSTANTS
(C01) Presence session lifetime (hours) ....................... 8
(C02) Presence state changes per hour ......................... 3
(C03) Subscription refresh interval per hour ................ N/A
(C04) Total federated contacts per user ...................... 20
(C05) Number of dialogs to maintain per watcher .............. 20
(C06) Number of federated users .......................... 40,000
(C07) Subscription request size in bytes .................... 100
(C08) Subscription approval size in bytes ................... 100
(C09) Presence notification size in bytes ................... 200
(C09) Presence notification ack size in bytes ............... N/A
(C11) Presence document size in bytes ....................... N/A

INITIAL MESSAGES
(I01) Initial subscribe requests per presence session ........ 20
(I02) Initial subscription approvals per presence session ..... 0
(I03) Number of initial presence notifications ............... 20
(I04) Number of initial presence acks ......................... 0
(I05) Total number and bytes of initial subscribe messages
            Number ...................................... 800,000
            Bytes  ................................... 80,000,000
(I06) Total number and bytes of initial subscribe acks
            Number ............................................ 0
            Bytes ............................................. 0
(I07) Total number and bytes of initial notifications
            Number ...................................... 800,000
            Bytes  .................................. 160,000,000
(I08) Total number and bytes of initial notification acks
            Number ............................................ 0
            Bytes ............................................. 0
(I09) Total number and bytes of initial messages
            Number .................................... 1,600,000
            Bytes  .................................. 240,000,000

STEADY STATE MESSAGES
(S01) Presence notifications caused by state changes ......... 22
(S02) Notification acks for state change notifications ........ 0
(S03) Number and size of steady-state presence notifications
            Number ................................... 17,600,000
            Bytes ................................. 3,520,000,000
(S04) Subscription refreshes .................................. 0
(S05) Acks for subscription refreshes ......................... 0
(S06) Notify messages caused by refreshes ..................... 0
(S07) Acks for notify messages caused by refreshes ............ 0
(S08) Number and size of messages caused by refreshes ......... 0
(S09) Total number and bytes of steady-state messages
            Number ................................... 17,600,000
            Bytes ................................. 3,520,000,000

TERMINATION MESSAGES
(T01) Number of terminating subscribe messages ................ 0
(T02) Number of acks for terminating subscribe messages ....... 0
(T03) Number of terminating notifications .................... 20
(T04) Number of acks for terminating notifications ............ 0
(T05) Total number and size of terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T06) Total number and size of acks for terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T07) Total number and size of terminating notifications
            Number ...................................... 800,000
            Bytes  .................................. 160,000,000
(T08) Total number and size of acks for terminating notifications
            Number ............................................ 0
            Bytes ............................................. 0
(T09) Total number and size of terminating messages per session
            Number ...................................... 800,000
            Bytes  .................................. 160,000,000

BOTTOM LINE
(B01) Total number and bytes per presence session
            Number ................................... 20,000,000
            Bytes  ................................ 3,920,000,000
(B02) Total number and bytes per second
            Number .......................................... 694
            Bytes  ...................................... 136,111

For the bottom-line figures, the comparable numbers for SIMPLE in a non-optimized state (see [PROBLEM] (Houri, A., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.)) are 65,000,000 total messages, 101,880,000,000 bytes, 2,222 messages per second, and 3,537,500 bytes per second; thus for this scenario XMPP uses 31% of the messages and 3.8% of the bytes used by SIMPLE.



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5.3.  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 during an 8-hour presence session. The calculations are as follows.

CONSTANTS
(C01) Presence session lifetime (hours) ....................... 8
(C02) Presence state changes per hour ......................... 6
(C03) Subscription refresh interval per hour ................ N/A
(C04) Total federated contacts per user ...................... 10
(C05) Number of dialogs to maintain per watcher .............. 10
(C06) Number of federated users ...................... 20,000,000
(C07) Subscription request size in bytes .................... 100
(C08) Subscription approval size in bytes ................... 100
(C09) Presence notification size in bytes ................... 200
(C09) Presence notification ack size in bytes ............... N/A
(C11) Presence document size in bytes ....................... N/A

INITIAL MESSAGES
(I01) Initial subscribe requests per presence session ........ 10
(I02) Initial subscription approvals per presence session ..... 0
(I03) Number of initial presence notifications ............... 10
(I04) Number of initial presence acks ......................... 0
(I05) Total number and bytes of initial subscribe messages
            Number .................................. 200,000,000
            Bytes  ............................... 20,000,000,000
(I06) Total number and bytes of initial subscribe acks
            Number ............................................ 0
            Bytes ............................................. 0
(I07) Total number and bytes of initial notifications
            Number .................................. 200,000,000
            Bytes  ............................... 40,000,000,000
(I08) Total number and bytes of initial notification acks
            Number ............................................ 0
            Bytes ............................................. 0
(I09) Total number and bytes of initial messages
            Number .................................. 400,000,000
            Bytes  ............................... 60,000,000,000

STEADY STATE MESSAGES
(S01) Presence notifications caused by state changes ......... 46
(S02) Notification acks for state change notifications ........ 0
(S03) Number and size of steady-state presence notifications
            Number ...............................  9,200,000,000
            Bytes ............................  1,840,000,000,000
(S04) Subscription refreshes .................................. 0
(S05) Acks for subscription refreshes ......................... 0
(S06) Notify messages caused by refreshes ..................... 0
(S07) Acks for notify messages caused by refreshes ............ 0
(S08) Number and size of messages caused by refreshes ......... 0
(S09) Total number and bytes of steady-state messages
            Number ...............................  9,200,000,000
            Bytes ............................  1,840,000,000,000

TERMINATION MESSAGES
(T01) Number of terminating subscribe messages ................ 0
(T02) Number of acks for terminating subscribe messages ....... 0
(T03) Number of terminating notifications .................... 10
(T04) Number of acks for terminating notifications ............ 0
(T05) Total number and size of terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T06) Total number and size of acks for terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T07) Total number and size of terminating notifications
            Number .................................. 200,000,000
            Bytes  ............................... 20,000,000,000
(T08) Total number and size of acks for terminating notifications
            Number ............................................ 0
            Bytes ............................................. 0
(T09) Total number and size of terminating messages per session
            Number .................................. 200,000,000
            Bytes  ............................... 20,000,000,000

BOTTOM LINE
(B01) Total number and bytes per presence session
            Number ................................ 9,800,000,000
            Bytes ............................. 1,920,000,000,000
(B02) Total number and bytes per second
            Number ...................................... 340,278
            Bytes  ................................... 66,666,667

For the bottom-line figures, the comparable numbers for SIMPLE in a non-optimized state (see [PROBLEM] (Houri, A., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.)) are 25,600,000,000 total messages, 44,046,000,000,000 bytes, 888,889 messages per second, and 1,529,375,333 bytes per second; thus for this scenario XMPP uses 38% of the messages and 4.4% of the bytes used by SIMPLE.



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5.4.  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 during an 8-hour presence session. The calculations are as follows.

CONSTANTS
(C01) Presence session lifetime (hours) ....................... 8
(C02) Presence state changes per hour ......................... 3
(C03) Subscription refresh interval per hour ................ N/A
(C04) Total federated contacts per user ...................... 10
(C05) Number of dialogs to maintain per watcher .............. 10
(C06) Number of federated users ......................... 120,000
(C07) Subscription request size in bytes .................... 100
(C08) Subscription approval size in bytes ................... 100
(C09) Presence notification size in bytes ................... 200
(C09) Presence notification ack size in bytes ............... N/A
(C11) Presence document size in bytes ....................... N/A

INITIAL MESSAGES
(I01) Initial subscribe requests per presence session ........ 10
(I02) Initial subscription approvals per presence session ..... 0
(I03) Number of initial presence notifications ............... 10
(I04) Number of initial presence acks ......................... 0
(I05) Total number and bytes of initial subscribe messages
            Number .................................... 1,200,000
            Bytes  .................................. 120,000,000
(I06) Total number and bytes of initial subscribe acks
            Number ............................................ 0
            Bytes ............................................. 0
(I07) Total number and bytes of initial notifications
            Number .................................... 1,200,000
            Bytes  .................................. 240,000,000
(I08) Total number and bytes of initial notification acks
            Number ............................................ 0
            Bytes ............................................. 0
(I09) Total number and bytes of initial messages
            Number .................................... 2,400,000
            Bytes  .................................. 360,000,000

STEADY STATE MESSAGES
(S01) Presence notifications caused by state changes ......... 22
(S02) Notification acks for state change notifications ........ 0
(S03) Number and size of steady-state presence notifications
            Number ................................... 26,400,000
            Bytes ................................. 5,280,000,000
(S04) Subscription refreshes .................................. 0
(S05) Acks for subscription refreshes ......................... 0
(S06) Notify messages caused by refreshes ..................... 0
(S07) Acks for notify messages caused by refreshes ............ 0
(S08) Number and size of messages caused by refreshes ......... 0
(S09) Total number and bytes of steady-state messages
            Number ................................... 26,400,000
            Bytes ................................. 5,280,000,000

TERMINATION MESSAGES
(T01) Number of terminating subscribe messages ................ 0
(T02) Number of acks for terminating subscribe messages ....... 0
(T03) Number of terminating notifications .................... 10
(T04) Number of acks for terminating notifications ............ 0
(T05) Total number and size of terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T06) Total number and size of acks for terminates
            Number ............................................ 0
            Bytes ............................................. 0
(T07) Total number and size of terminating notifications
            Number .................................... 1,200,000
            Bytes  .................................. 240,000,000
(T08) Total number and size of acks for terminating notifications
            Number ............................................ 0
            Bytes ............................................. 0
(T09) Total number and size of terminating messages per session
            Number .................................... 1,200,000
            Bytes  .................................. 240,000,000

BOTTOM LINE
(B01) Total number and bytes per presence session
            Number ................................... 30,000,000
            Bytes ................................. 5,880,000,000
(B02) Total number and bytes per second
            Number ......................................... 1042
            Bytes  ...................................... 204,167

For the bottom-line figures, the comparable numbers for SIMPLE in a non-optimized state (see [PROBLEM] (Houri, A., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” July 2007.)) are 96,000,000 total messages, 152,820,000,000 bytes, 3,333 messages per second, and 5,306,250 bytes per second; thus for this scenario XMPP uses 31% of the messages and 3.8% of the bytes used by SIMPLE.



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6.  Conclusion

With respect to presence scaling, the differences between XMPP systems and SIP-based systems are startling. In particular, this analysis indicates that XMPP requires only about 1.5% of the bandwidth required by SIMPLE. There are two primary causes for this disparity: (1) XMPP requires only about 25% of the packets required by SIMPLE and (2) XMPP packets are about 5% of the size of SIMPLE packets for presence notifications and 20% of the size for subscribe packets. Together, these two factors appear to result in a significant disparity with respect to the scalability of presence technologies. Naturally, real-world studies of deployed systems will be necessary to determine if these theorized differences occur in reality.



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7.  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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8. Informative References

[PROBLEM] Houri, A., “Presence Interdomain Scaling Analysis for SIP/SIMPLE,” draft-ietf-simple-interdomain-scaling-analysis-01 (work in progress), July 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.
[XEP-0060] Millard, P., Saint-Andre, P., and R. Meijer, “Publish-Subscribe,” XSF XEP 0060, September 2007.
[XEP-0115] Hildebrand, J., Saint-Andre, P., and R. Tronçon, “Entity Capabilities,” XSF XEP 0115, August 2007.
[XEP-0118] Saint-Andre, P., “User Tune,” XSF XEP 0118, June 2007.
[XEP-0138] Hildebrand, J. and P. Saint-Andre, “Stream Compression,” XSF XEP 0138, September 2007.
[XEP-0153] Saint-Andre, P., “vCard-Based Avatars,” XSF XEP 0153, August 2006.
[XEP-0163] Saint-Andre, P. and K. Smith, “Personal Eventing via Pubsub,” XSF XEP 0163, September 2007.
[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:  https://stpeter.im/


 TOC 

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Acknowledgment