cunicu/docs/Signalling.md

Session signalling

Lets assume two Wireguard peers Pa & Pb are seeking to establish a ICE session.

The smaller public key (PK) of the two peers takes the role of the controlling agent. In this example PA is the controlling agent: PK(PA) < PK(PB).

PA                         PB

  --- initial offer     -->        id=SID_Pa, version=0, candidates=[], eoc=false
  <-- initial offer     ---        id=SID_Pb, version=0, candidates=[], eoc=false

  --- subsequent offers -->        id=SID_Pa, version=1, candidates=[C1_Pa], eoc=false
  <-- subsequent offers ---        id=SID_Pb, version=1, candidates=[C1_Pb], eoc=false

  --- subsequent offers -->        id=SID_Pa, version=2, candidates=[C1_Pa, C2_Pa], eoc=false
  <-- subsequent offers ---        id=SID_Pb, version=2, candidates=[C1_Pb, C2_Pb], eoc=false

  ---  eoc. offer       -->        id=SID_Pa, version=3, candidates=[C1_Pa, C2_Pa], eoc=true
  <--  eoc. offer       ---        id=SID_Pb, version=3, candidates=[C1_Pb, C2_Pb], eoc=true

Restart

Agent will restart

• if

  • last_recv.id has been set
  • recv.id!=last_recv.id
  • recv.version==0

• then

  • set
    • local.id=rand()
    • local.version=0
    • local.candidates=[]
  • publish new offer
  • wait for first offer including candidates from remote
  • (re)start agent
  • add first received
  • start gathering candidates
    • send an offers for each candidate c:
      • candidates=local.candidates.append(c)
      • id=local.id
      • rid=local.rid
      • version=local.version++

Offer

Offers are encoded as JSON:

{
  "id": 1232353452,                                     // Unique session id
  "version": 0,                                         // Session version, incremented with each updated offer
  "cands": [                                            // List of ICE candidates
    {
      "type": "host",
      "foundation": "1742129347",
      "component": 1,
      "network": "udp4",
      "priority": 2130706431,
      "address": "10.2.0.11",
      "port": 37518
    }
  ],
  "eoc": false                                          // Flag to indicate that all candidates have been gathered (ICE trickle)
}