[erlang-questions] question re. message delivery

[Matthias Lang]

On 27. September 2017, Richard A. O'Keefe wrote:

> (3) I also told them that it is the nature of
>     the physical world that when you send someone
>     a message (texting on a mobile phone is a
>     great example) you can know that you SENT it
>     but you can never know they RECEIVED it
>     unless they tell you and gave the example of
>     my daughter wanting a ride home but my phone's
>     extremely limited mailbox filling up so I did
>     not get her message until hours later.

SMS is a good example, and there's a detail you omitted. Your daughter
could most likely have seen that the message had not been delivered.

SMS has a mechanism for telling the sender that a particular message
was delivered to the phone. Exactly how that information is displayed
is different on different phones and it's often disabled by default.

This is an interesting detail because it illustrates the difference
between ACKs in different layers.

Matthias

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Note 1: On the Android phone I have, it's enabled in the SMS app by
selecting settings/advanced/'get SMS delivery reports'. The word
'delivered' appears each SMS when the receiving phone has it.

Note 2: In the old GSM standards, e.g. 03.40 (from the 1990s), the
'status report capabilities' are listed as optional. I haven't noticed
any mobile networks that don't have it.