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ICE candidate types

ICE is RFC 8445, which obsoletes RFC 5245. Candidates are host, srflx, prflx, and relay.

Learn in 5 minutes

  1. Name the four candidate types
  2. State that RFC 8445 obsoletes RFC 5245 and where status is decided
  3. Let connectivity checks choose the pair

Visual

Gather, offer, check, nominate · study drawing · cyphermonkeylabs.com AliceSTUN/TURNCarrier Gather INVITE 200 Check

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prflx is discovered during checks. It is not usually in the first offer.

Worked example

Read the candidate types Negotiate the offer. Then read the a=candidate lines yourself. The negotiator matches codecs. You match the types.

  1. Press Negotiate.
  2. Find typ host, typ srflx, and typ relay.
  3. Confirm the answer still has one m-line.

Fault

The offer had host, srflx, and relay candidates. The forwarded offer has only c= and no a=candidate lines, and media fails.

RFC 8445 selects a working pair by checks. Without candidates there is nothing to check.

Quiz

ICE is


The four candidate types are


srflx comes from


relay comes from


prflx is


ICE does not cancel the rule that


Ecosystem

Glossary, sister systems, and the integration seam for this room.

CRM Screen pop uses data the contact center already has: ANI, DNIS, case id. Those values may arrive in SIP headers or in a CTI event after the call is up. The CRM is not a SIP element.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper