Glossary — SIP and SIPp terms

Read this before touching engine or scenario code if you’re not fluent in SIP. Confusing these terms causes real bugs (especially transaction vs dialog vs call).

SIP protocol

• UAC / UAS — User Agent Client (sends a request) / Server (answers it). Roles are per transaction: the callee becomes a UAC when it sends BYE. In sipp/sipr CLI terms, uac = caller scenario, uas = callee scenario.
• Transaction — one request + its responses (+ retransmissions). INVITE transactions end at a final response (ACK for non-2xx is part of it; ACK for 2xx is a separate transaction per RFC 3261). Identified by the Via branch.
• Dialog — a peer-to-peer relationship spanning transactions, identified by Call-ID + local tag + remote tag. Established by INVITE/2xx (or early via 1xx with tag). Holds CSeq counters both directions, route set, remote target.
• Call — in sipp/sipr: one execution of the scenario (one line in the call table), which usually maps to one dialog but needn’t (e.g. REGISTER scenarios have no dialog).
• Via / branch — routing breadcrumb header; branch (must start with magic cookie z9hG4bK) identifies the transaction.
• CSeq — per-dialog, per-direction request sequence number + method.
• Tags — random tokens in From/To identifying dialog ends. UAS adds the To tag; [peer_tag_param] in SIPp exposes the remote one.
• Record-Route / Route / route set — proxies inserting themselves into the dialog path; rrs="true" on a recv captures them, [routes] replays them.
• T1 / T2 — RFC 3261 retransmission timers for unreliable transport: T1=500ms initial, doubling per retransmit, capped at T2=4s.
• REGISTER / OPTIONS / INFO / UPDATE / NOTIFY — non-INVITE methods that show up in test scenarios; -aa auto-answers the in-dialog ones with 200.
• Digest auth — 401 (UAS) / 407 (proxy) challenge → request re-sent with Authorization/Proxy-Authorization. RFC 2617 (MD5) / RFC 7616 (SHA-256, qop).
• SDP — session description carried as the body of INVITE/200; for signaling-only v1 it is opaque template bytes (only [len] cares).
• 3PCC — third-party call control: an external controller coordinates two scenario halves; SIPp implements it as sendCmd/recvCmd between instances.
• B2BUA — back-to-back user agent (two dialogs bridged); relevant only as the kind of DUT sipr often tests.
• DUT / SUT — device/system under test.

SIPp-specific

• Scenario — the XML file: an ordered list of send/recv/pause/nop steps the call must follow. Compiled in sipr to a flat step IR (“message index” order).
• Keyword — [call_id]-style placeholder substituted into message templates at send time.
• Action — per-step operation (<action> on recv/nop): regex capture (ereg), variable math, branching (test+next), logging, exec.
• Call variables — per-call named values ([$1], [$name]) written by actions, read by keywords/conditions.
• Injection file (-inf) — CSV whose rows feed [field0..N] keywords; sequential/random/user modes. (v1.x)
• Open loop vs closed loop — SIPp default is open loop: -r new calls per period regardless of completions (models real traffic, can overload DUT). -users mode is closed loop: fixed population, new call only when one ends.
• cps — calls per second (the -r rate).
• RTD (response time duration) — stopwatch between start_rtd and rtd markers in the scenario; reported in percentiles/histograms.
• Repartition — SIPp’s term for histogram bucket tables (ResponseTimeRepartition, CallLengthRepartition).
• Unexpected message — inbound that matches no pending recv (incl. optional window); increments counters and by default kills the call.
• Retrans — either the protocol-level UDP retransmission (timer-driven) or the retrans attribute overriding its base interval. Context matters.
• Timewait — post-scenario linger absorbing late retransmissions before the call slot is freed (SIPp timewait element / deadcall handling).
• OOC (out-of-call) — messages not attributable to any live call.
• PCAP play / rtp_stream — media features (later; out of v1).