SMS Standards

Bruce Pinsky bep at
Fri Oct 17 01:41:59 UTC 2008

Hash: SHA1

Glen Kent wrote:
> Hi,
> Apologies in advance since this is off-topic. However, posting in on
> nanog since i am confident that we will have some experts who would be
> able to guide me here.
> I want to study the standards (RFC equivalent) for sending and
> receiving SMSs. Any ideas on what kind of protocol runs between a
> mobile phone and a SMS center (SMSC)?

Wiki_Pedia is your friend

The Short Message Service - Point to Point (SMS-PP) is defined in GSM
recommendation 03.40.[2] GSM 03.41 defines the Short Message Service - Cell
Broadcast (SMS-CB) which allows messages (advertising, public information,
etc.) to be broadcast to all mobile users in a specified geographical
area.[16] Messages are sent to a Short Message Service Centre (SMSC) which
provides a store-and-forward mechanism. It attempts to send messages to
their recipients. If a recipient is not reachable, the SMSC queues the
message for later retry.[17] Some SMSCs also provide a "forward and forget"
option where transmission is tried only once. Both Mobile Terminated (MT),
for messages sent to a mobile handset, and Mobile Originating (MO), for
those that are sent from the mobile handset, operations are supported.
Message delivery is best effort, so there are no guarantees that a message
will actually be delivered to its recipient and delay or complete loss of a
message is not uncommon, particularly when sending between networks. Users
may choose to request delivery reports (simply add *0# or *N# to the
beginning of your text message), which can provide positive confirmation
that the message has reached the intended recipient.

Transmission of short messages between the SMSC and the handset is done
using the Mobile Application Part (MAP) of the SS7 protocol. Messages are
sent with the MAP mo- and mt-ForwardSM operations, whose payload length is
limited by the constraints of the signalling protocol to precisely 140
octets (140 octets = 140 * 8 bits = 1120 bits). Short messages can be
encoded using a variety of alphabets: the default GSM 7-bit alphabet (shown
below), the 8-bit data alphabet, and the 16-bit UTF-16/UCS-2 alphabet.[18]
Depending on which alphabet the subscriber has configured in the handset,
this leads to the maximum individual Short Message sizes of 160 7-bit
characters, 140 8-bit characters, or 70 16-bit characters (including
spaces). Support of the GSM 7-bit alphabet is mandatory for GSM handsets
and network elements,[18] but characters in languages such as Arabic,
Chinese, Korean, Japanese or Cyrillic alphabet languages (e.g. Russian)
must be encoded using the 16-bit UCS-2 character encoding (see Unicode).
Routing data and other metadata is additional to the payload size.

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