CPA Documentation: technical part

Structure of simple subscription [legend]:

       [HTTP connection]                [SMS conversation]
[CP] ...................... [CPA] <===== content request ====== [DC]

[CP] <== content-request == [CPA] ............................. [DC]
[CP] ------ Accepted -----> [CPA] ............................. [DC]

[CP] ====== content ======> [CPA] ............................. [DC]   \
[CP] <----- Accepted ------ [CPA] ............................. [DC]    \
                                                                         \    repeated 
[CP] ...................... [CPA] ========== content =========> [DC]      *——— during 
                                                                         /   subscription
[CP] <== delivery report == [CPA] ............................. [DC]    /
[CP] ------ Accepted -----> [CPA] ............................. [DC]   /

[CP] ===== invitation ====> [CPA] ............................. [DC]
[CP] <----- Accepted ------ [CPA] ............................. [DC]

[CP] ...................... [CPA] ========== content =========> [DC]

[CP] <== delivery report == [CPA] ............................. [DC]
[CP] ------ Accepted -----> [CPA] ............................. [DC]

Note: SMPP gateway messages (passed back to CPA after sending something to subscriber) aren't shown here as more low-level, but that's how CPA gets the message status for e.g. delivery reports.

Note 2: the separated items are repeated during the subscription; there's a CPA side limit on the number of content-carrying messages with identical RID, so the last message could be an invitation to continue the subscription.

In sample responses these are substituted by "XXX+n" for sequential content messages and "XXX+N" for free message with an invitation to resubscribe to the service. Generally, this should be satisfied:

0 <= n <= N <= N_max

where

XXX: is some base value chosen by CP;
n: is a "counter" running with each new piece of content sent during the subscription;
N: is a total number of messages being passed to the subscriber during the subscription;
N_max: is a hard limit on the number of messages with identical RID (and thus responses to a single request); it is enforced by CPA.