| name | rfc-sip-lookup |
| description | Look up SIP/RTP/SDP protocol details across RFC text files using parallel agents. Use when researching protocol specs, debugging SIP compliance, or checking RFC requirements. |
| user-invocable | true |
RFC SIP/RTP/SDP Lookup
You are looking up protocol details from RFC text files vendored in rfcs/.
Step 1: Consult the Index
Read .claude/skills/rfc-sip-lookup/rfc-index.md to identify which RFC sections are relevant to the user's query. The index maps topic areas (registration, INVITE, SDP, RTP, timers, etc.) to specific files and line ranges.
Step 2: Dispatch Parallel Explore Agents
Launch 2–3 Explore agents via the Task tool (subagent_type: "Explore") to read the relevant RFC sections in parallel. Each agent should:
- Read the specific line range(s) from the index using the Read tool with
offset and limit parameters
- Search for specific keywords within the identified sections using Grep
- Extract the precise normative text (MUST, SHOULD, MAY statements), protocol rules, or message format details relevant to the query
Structure each agent prompt like:
Read rfcs/rfc3261.txt lines 7471–7633 (§17.2.1 INVITE Server Transaction).
Find details about: [user's specific question].
Return the exact normative requirements, relevant ABNF, and any examples.
Dispatch agents for different RFC files in parallel. If the query spans multiple topics (e.g., "INVITE with SDP offer"), send one agent for the SIP sections and another for the SDP sections.
Step 3: Synthesize
Combine the agents' findings into a concise answer:
- Lead with the direct answer to the user's question
- Include exact RFC section references (e.g., "RFC 3261 §17.2.1, line 7520")
- Quote key normative language verbatim when precision matters
- Note any cross-references between RFCs (e.g., SIP→SDP, SIP→Digest Auth)
- If the query is about implementation, connect the RFC requirements to what the code should do
ITU-T Recommendations
Some topics reference ITU-T recs instead of IETF RFCs. These are not vendored locally but can be fetched on demand as PDFs from ITU's free access program:
| Rec | Topic | Direct PDF URL |
|---|
| G.711 | μ-law / A-law PCM codec (8kHz, 8-bit), 9 pages | https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.711-198811-I!!PDF-E&type=items |
| G.712 | Telephony passband (0–3.4kHz) | https://www.itu.int/rec/T-REC-G.712/en (landing page — find PDF link via WebFetch) |
| G.114 | One-way delay budget (<150ms good, <400ms limit), 18 pages | https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-G.114-200305-I!!PDF-E&type=items |
To look up an ITU-T rec:
- Download the PDF with curl:
curl -fsSL -o /tmp/g711.pdf "<url>"
- Read it with the Read tool using the
pages parameter (e.g., pages: "1-9")
- Delete the PDF after use — do not vendor it:
rm /tmp/g711.pdf
The landing page URLs (/rec/T-REC-G.xxx/en) list versions but don't expose direct download links. Use WebFetch on the version-specific page (e.g., /rec/T-REC-G.711-198811-I/en) to find the dologin_pub.asp PDF URL if you need a rec not listed above.
Tips
- For broad queries ("how does INVITE work?"), focus on the primary sections and summarize rather than reading everything
- For narrow queries ("what's Timer G's default value?"), target the exact line range and quote the text
- RFC 3665 (call flow examples) is the best companion to RFC 3261 — check it for annotated message exchanges
- The smaller RFCs (2617, 3264, 3389, 3551, 3581) can often be read in their entirety by a single agent
