DLR (Delivery Reporting)
Delivery reporting or DLR is an attribute for every sent message of SMS MT that reports back if the SMS message has been delivered. It is sourced directly from the handset.
Basically, DLRs are URL call-backs for Delivery Reports. Instead of the gateway logging the activity, it will call-back the provided URL using a query string (at the end) with the criterions of the delivery statement itself.