SIP and accounting Henning Schulzrinne Columbia University SIP 2003 – January 2003 Paris, France

Overview Why SIP accounting? not just billing What’s different about SIP accounting? accounting for SIP as a protocol separation of data and signaling Architecture and protocol choices Open issues

Accounting terminology (RFC 2975) Accounting: The collection of resource consumption data for the purposes of capacity and trend analysis, cost allocation, auditing, and billing. Accounting management requires that resource consumption be measured, rated, assigned, and communicated between appropriate parties. Rating: The act of determining the price to be charged for use of a resource. Billing: The act of preparing an invoice. Auditing: The act of verifying the correctness of a procedure. Real-time accounting: Real-time accounting involves the processing of information on resource usage within a defined time window. Time constraints are typically imposed in order to limit financial risk. Logging: (Not in 2975) Keeping track of activities for debugging, abuse prevention or legal reasons such as lawful intercept. Typically, does not involve money.

Why SIP accounting? Usage of (relatively) expensive resources wireless bandwidth PSTN gateways, with international calls at $3/minute translation and storage services Real-time for fraud detection and prepaid calling cards Off-line for traditional monthly billing or traffic analysis

Billing PSTN: evolution from distance/time-sensitive per- minute billing bucket of minutes flat-rate plans (“all you can eat”): Canada, AT&T Per-minute billing doesn’t fit well: SIP sessions can remain open for months, without sending a single packet voice silence suppression  unfair to charge for both directions for large conferences incremental value is non-linear thus, video unlikely bit rate utility

Billing and charging What are we billing for? infrastructure services unlikely to be able to charge for call forwarding for corporate users but Yahoo might for residential users traffic but network cost depends on peak usage, not average usage treat all traffic the same? 3G: charge more for data traffic than voice traffic? escalation of traffic cloaking and detection A simple billing model bill per-minute for calls gatewayed into the PSTN bill for services on a subscription basis (e.g., as part of ISP service) bill for traffic independent of traffic type by volume, 95 th percentile, congestion pricing

AAA = Authentication, Authorization, Accounting separate SIP protocol elements from making authentication/authorization decisions allow visited proxy to ask home proxy of visitor whether visitor is legit accounting: resource dimensioning apportionment of charges commercial billing three primary protocols: RADIUS – used for dial-up servers, popular with ISPs can lose data (UDP) DIAMETER – successor of RADIUS will be used in 3G for AAA, not widely implemented

Accounting architecture for roaming visited.net home.net accounting data authentication request challenge/response RADIUS DIAMETER SIP End systems never see AAA

Accounting in SIP Components: network resources used by SIP itself network resource consumption initiated by SIP sessions set up gateway resources services initiated and controlled by SIP voic storage media translation services Does not necessarily involve “metering” or logging SIP protocol requests! But useful to correlate byte metering to SIP sessions for usability

Resources consumed by SIP SIP is mainly signaling, but also carries user data most directly, as MESSAGE INFO messages headers such as Subject, User-Agent, From/To display field user-created header fields MIME body parts, possibly encrypted all of these are opaque to proxies can use unsuccessful call attempts to send data ISDN precedence: UU data unless all non-protocol-state fields and extensibility are removed from SIP, cannot prevent data carriage even with removal: SIP covert channel space SIP messages: long and short pauses  Morse code minor protocol variations: upper case header = 1, lower case = 0 if signaling doesn’t cost, efficiency is not a concern (for the (ab)user…)

Resources consumed by SIP Thus, sane approach is to bill for call setup and other SIP messages GPRS: $4/MB  signaling without compression ~ 4c/call with compression ~ XX c/call maybe provide monthly allowance for user

Accounting in SIP Call Detail Records (CDR) just record time/date of call start/end and source/destination cost may depend on peak bandwidth (typical 95 th percentile billing) average bandwidth compressibility (e.g., for text messages) QOS parameters, … IPDR.org: more generic format for IP services XML-based and Sun XDR-based (binary) SIP requests should only be used for session accounting: if access to the right data if no incentive or possibility for bypass (e.g., in gateway, not in proxies) e.g., send BYE with Max-Forward reaching to proxy only

Open Settlement Protocol (OSP) clearing-house model  mostly off-line settlement between different providers  CDR style

Conclusion Accounting easy for gateway services  session model fits traditional CDR model Signaling services require accounting to prevent RTP- over-SIP cloaking Open issues: RTP accounting? detail – messages? dialog? how to indicate charging preferences "I pay for audio, you pay for video" Dutch: everybody pays for bytes sent (mother-in-law mode) Preliminary requirements discussions in IETF Have done local RADIUS implementation

References H. Basilier, P. Calhoun, et al., “AAA Requirements for IP Telephony/Multimedia”, draft-calhoun-sip-aaa- reqs-04 B. Aboba, J. Arkko, D. Harrington, “Introduction to Accounting Management”, RFC 2975 J. Loughney, G. Camarillo, "Authentication, Authorization and Accounting Requirements for the Session Initiation Protocol", draft-ietf-sipping-aaa- req-01 S. Nagarayan, et al., "A Diameter accounting application for the Session Initiation Protocol", draft- narayanan-sipping-aaa-diameter-00