Stream Control Transmission Protocol
_____________ _____________ | SCTP User | | SCTP User | | Application | | Application | |-------------| |-------------| | SCTP | | SCTP | | Transport | | Transport | | Service | | Service | |-------------| |-------------| | |One or more ---- One or more| | | IP Network |IP address \/ IP address| IP Network | | Service |appearances /\ appearances| Service | |_____________| ---- |_____________| SCTP Node A |<-------- Network transport ------->| SCTP Node B Figure 1: An SCTP Association
Acknowledgement and Congestion Avoidance
SCTP assigns a Transmission Sequence Number (TSN) to each user data fragment or unfragmented message. The TSN is independent of any Stream Sequence Number assigned at the stream level.
The receiving end acknowledges all TSNs received, even if there are gaps in the sequence. In this way, reliable delivery is kept functionally separate from sequenced stream delivery.
SCTP Common Header Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port Number | Destination Port Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Verification Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
----- -------- (from any state) / \ / rcv ABORT [ABORT] rcv INIT | | | ---------- or ---------- --------------- | v v delete TCB snd ABORT generate Cookie \ +---------+ delete TCB snd INIT ACK ---| CLOSED | +---------+ / \ [ASSOCIATE] / \ --------------- | | create TCB | | snd INIT | | strt init timer rcv valid | | COOKIE ECHO | v (1) ---------------- | +------------+ create TCB | | COOKIE-WAIT| (2) snd COOKIE ACK | +------------+ | | | | rcv INIT ACK | | ----------------- | | snd COOKIE ECHO | | stop init timer | | strt cookie timer | v | +--------------+ | | COOKIE-ECHOED| (3) | +--------------+ | | | | rcv COOKIE ACK | | ----------------- | | stop cookie timer v v +---------------+ | ESTABLISHED | +---------------+Multi-Homed SCTP Endpoints
An SCTP endpoint is considered multi-homed if there are more than one
transport address that can be used as a destination address to reach
that endpoint.
Moreover, the ULP of an endpoint shall select one of the multiple
destination addresses of a multi-homed peer endpoint as the primary
path
unless the SCTP user explicitly specifies the destination transport
address (and possibly source transport address) to use.
for more info RFC4960
