RTPS locator port calculation

#network/dds

Locator used for discovery traffic

Discovery traffic is the traffic generated by the Participant and Endpoint Discovery Protocols(SPDP and SEDP). Discovery traffic is the traffic exchanged between the built-in topics. ^[1]^[2]^[3]

Ports used by the built-in endpoints

traffic type	default port number expression
Multicast	$P B + D G \times d o m a i n I D + d 0$
Unicast	$P B + D G \times d o m a i n I D + d 1 + P G \times p a r t i c i p a n t I d$
where:

domain_id: domain identifier
participant_id: participant identifier
PB, DG, d0 and d1: tunable parameters
- PB: port base number (default: 7400)
- DG: domain gain (default: 250)
- d0: additional offsets (default: 0)
- d1: additional offsets (default: 10)

The domain_id and participant_id are used to avoid conflicts among Participants on the same node. Each Participant on the same node and in the same domain must use a unique participant_id.

Locator used for user traffic

User traffic is the traffic exchanged between user-defined endpoints (e.g. non built-in endpoints).

Ports used by the user-defined endpoints

traffic type	default port number expression
Multicast	$P B + D G \times d o m a i n I D + d 2$
Unicast	$P B + D G \times d o m a i n I D + d 3 + P G \times p a r t i c i p a n t I d$
where:

domain_id: domain identifier
participant_id: participant identifier
PB, DG, d0 and d1: tunable parameters
- PB: port base number (default: 7400)
- DG: domain gain (default: 250)
- d1: additional offsets (default: 1)
- d3: additional offsets (default: 11)

Given UDP port numbers are limited to 64K, the above default enables the use of about 230 domains with up to 120 participants per node per domain.