There are two ways to verify the delivery of SMS messages.
When a message is send using the SMPP protocol, the provider returns a message reference. Using this reference, we can query the provider for the delivery status of this message. This is done by sending a 'query_sm' packet to the provider. If the message reference is known by the provider, it responds with a 'query_sm_resp' packet. This packet holds the status of the message. This can be one of the following values:
|0||SCHEDULED||The message is scheduled for later sending.|
|1||ENROUTE||The message is enroute.|
|2||DELIVERED||The message was successfully delivered.|
|3||EXPIRED||The SMSC was unable to deliver the message in a specified amount of time.For instance when the phone was turned off.|
|4||DELETED||The message was deleted.|
|5||UNDELIVERABLE||The SMS was unable to deliver the message.For instance, when the number does not exist.|
|6||ACCEPTED||The SMS was accepted and will be send.|
|7||UNKNOWN||Unknown error occured.|
|8||REJECTED||The message was rejected.The provider could have blocked phonenumbers in this range.|
|9||SKIPPED||The message was skipped.|
The disadvantage of this method is, that you have to poll once in a while to get the current message status. When a lot of messages are enroute for a couple of hours, this will cause heavy data traffic. Most providers recommend you to request delivery reports instead of querying, because there is only data sent by the provider when the status of a message has changed.
The best way to check the status of each message sent, is to ask for delivery reports. This can be done by setting the 'registered_delivery' value of the 'submit_sm' packet. This parameter can have one of the following values:
|0||Do not send delivery reports|
|1||Always send delivery reports|
|2||Send delivery report in case of an error||3||Send delivery report only when message is delivered|
By setting this value to '1', the provider will send a delivery report to the client every time the status of this message changes. You can set this value per message.
The delivery reports are sent to the client using the 'deliver_sm' packet. This is the same packet as used to deliver incoming messages. To detect whether a 'deliver_sm' is a delivery report or a message, you have to check the 'esm_class' field. If bit 2 of this byte is set ( 0x04 ), it is a delivery report. To use delivery reports, you have to setup a transceiver connection to the SMPP provider, because you are going to send and receive messages. The delivery status is encoded in the 'short_message' field as an ASCII text message. This format is product specific, but the following format is used by most SMPP providers:
id:c449ab9744f47b6af1879e49e75e4f40 sub:001 dlvrd:0 submit date:0610191018 done date:0610191018 stat:ACCEPTD err:0 text:This is an Acti id:7220bb6bd0be98fa628de66590f80070 sub:001 dlvrd:1 submit date:0610190851 done date:0610190951 stat:DELIVRD err:0 text:This is an Acti id:b756c4f97aa2e1e67377dffc5e2f7d9b sub:001 dlvrd:0 submit date:0610191211 done date:0610191211 stat:REJECTD err:1 text:This is an Acti id:bd778cd76ae9e79da2ddc8188c68f8c1 sub:001 dlvrd:0 submit date:0610191533 done date:0610191539 stat:UNDELIV err:1 text:This is an Acti
|id||The message reference of the message.|
|sub||Sub-ID, not used.|
|dlvrd||Value '1' when the message has been delivered, if the message is still pending '0'.|
|submit date||Submission date and time.|
|done date||Date and time the status has changed, or message delivery time when stat is set to 'DELIVRD'.|
|stat||Current status of the message.|
|err||Additional error code, provider specific.|
|text||Part of the original message text.|
When using SMPP version 3.4, sometimes the message has some optional parameters (TLV's) attached containing the message state, message reference and a network error code. Please refer to the SMPP version 3.4 documentation on how to use these TLV's.