6 encoded using a variety of alphabets: the default GSM 7-bit alphabet see GSM
03.38 for details, the 8-bit data alphabet, and the 16-bit UTF-16 alphabet. [3]
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,
[28]
but characters in languages such as Arabic, Chinese, Korean, Japanese or Cyrillic alphabet languages e.g. Russian, Serbian, Bulgarian, etc
must be encoded using the 16-bit UTF-16 character encoding see Unicode. Routing data and other metadata is additional to the payload size. [3]
Larger content Concatenated SMS, multipart or segmented SMS or long sms can be sent using multiple messages, in which case each message will start
with a user data header UDH containing segmentation information. Since UDH is inside the payload, the number of characters per segment is lower: 153 for 7-
bit encoding, 133 for 8-bit encoding and 67 for 16-bit encoding. The receiving handset is then responsible for reassembling the message and presenting it to the
user as one long message. While the standard theoretically permits up to 255 segments,
[29]
6 to 8 segment messages are the practical maximum, and long messages are often billed as equivalent to multiple SMS messages. See
Concatenated SMS for more information. Some providers have offered length- oriented pricing schemes for SMSs; however, the phenomenon is disappearing.
[4]
2.2.2 Short message service technical realization SMSC
The Short Message Service – Point to Point SMS-PP is defined in GSM recommendation 03.40,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.
7 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.
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 request delivery reports to confirm that messages reach the intended recipients, either via the SMS settings of most modern
phones, or by prefixing each message with 0 or N. [5]
2.2.3 Interconnectivity with other networks
Message Service Centres communicate with the Public Land Mobile Network PLMN or PSTN via Interworking and Gateway MSCs.Subscriber-
originated messages are transported from a handset to a Service Centre, and may be destined for mobile users, subscribers on a fixed network, or Value-Added
Service Providers VASPs, also known as application-terminated. A subscriber-terminated message are transported from the Service Centre
to the destination handset, and may originate from mobile users, from fixed network subscribers, or from other sources such as VASPs.It is also possible, on
some carriers, for non-subscribers to send messages to a subscribers phone using an E-Mail to SMS gateway. Additionally, many carriers, including ATT,
T-Mobile, Sprint, and Verizon Wireless, offer the ability to do this through their respective websites.
Sending a message this way is free but subject to the normal length limit. Text enabled fixed-line handsets are required to receive messages in text format.
However, messages can be delivered to non-enabled phones using conversion. Short messages can also be used to send binary content such as ringtones or
