1. Mobile Communication
The SMS implies of several additional elements in the network architecture <GSM GPRS, or UMTS>
There is also another Element called the SME <Short Message Entity> usually in the form as a software application in the mobile device.
Elements that can send or receive SMS are called SME’s, whether a mobile device, software, facsimile device, telex equipment or even a remote internet server.
An SME can be a server that interconnects to SMSC directly or via gateway. Such an SME is also known as ESME <external>

2. Mobile Communication SMSC
The main function of the SMSC is to relay the Short messages between SME’s and the store-and-forward.
This device can be either integrated with the MSC or an independent entity.
It can also be located outside the network and be managed by a third party.

3. Mobile Communication Email Gateway
This enables -SMS interoperatorbility by interconnecting the SMSC with the internet.
The role of the GW is to convert message format and to relay between SMS and domains

4. Mobile Communication Message Sending.
Mobile-originated messages are msgs which are submitted from a MS to an SMSC, which are addressed to other SME’s,
This feature is known as SM-MO
Message Delivery
Mobile terminated messages are msg delivered by the SMSC to the MS.
This feature is known as SM-MT
Msg can be sent or received over GSM signalling channels.

5. Mobile Communication Addressing Modes.
Several addressing modes are possible for message originating SME
However the most common are MSISDN number format and less common are address.
An option addressing feature of SMS consists of conveying a Sub-address information as a part of the message.
This is appended at the end of the recipient address by the O-SME

6. Mobile Communication Addressing Modes.
When the Sub-addressing scheme is applied the SMSC extracts the sub-addressing info from the address and appends it to the originator address.
This is useful to maintain session identifications for exchange of messages by identifying a specific code to which a message relates.
This sub-addressing info is separated from the regular addressing by the “#” delimiter
For example “64” may stand for a Weather update SMS service therefore for the SMSC to acknowledge the service it must relay according to the service code, entity.
The serving ESME also has option to reply to another address if required.

7. Mobile Communication SMS protocol stack is composed of FOUR LAYERS:
Application Layer
Transfer Layer
Relay Layer
Link Layer
SMS-based applications are directly based on the transfer layer. Any engineer willing to develop application for which SMS is the building block needs to master the “Transfer Layer”.
The Application Layer:
This layer is implemented in SME in the form of software applications that send, receive and interpret the content of messages. The application layer is also known as SM-AL

8. Mobile Communication SMS protocol stack is composed of FOUR LAYERS:
Application Layer
Transfer Layer
Relay Layer
Link Layer
Transfer Layer.
The message is consdidered as a sequence of octets containing information such as message lenth, message originator or recipient. Date of reception etc.
The Transfer layer is also known as SM-TL
The Relay layer
This layer allows the transport of messages between various networks elements, the MSC handles two functions in addition to usually switching, SMS-GMSC includes interrogating with HLR for location info, and SMS interworking SMS-IWMSC, submitting to serving MSC.

9. Mobile Communication SMS protocol stack is composed of FOUR LAYERS:
Application Layer
Transfer Layer
Relay Layer
Link Layer
Link Layer
This allows the transmission of the message at physical level. For this the message is protected to cope with low-level channel errors.
This layer is known as SM-TL.

10. Mobile Communication SMS protocol stack is composed of FOUR LAYERS:
Application Layer
Transfer Layer
Relay Layer
Link Layer
For transport purposes, an application maps the message content and associated delievery instructions onto a TPDU <transfer protocol data unit> at the transfer layer.
A TPDU is composed of various parameters indicating the type of message, specifiying whether or not a status report is requested, containing the text part of the message etc.
E.g. Each parameter os prefixed by an abbreviation TP-MTI, <message type indicator> TP-SRI, <status report indicator> or TP-UD <user data>

11. Mobile Communication SMS protocol stack is composed of FOUR LAYERS:
Application Layer
Transfer Layer
Relay Layer
Link Layer
At the Transfer layer, the exchange of messages from the O-SME to the R-SME consists of two to three steps.
The Three steps are shown in the Fig, after the creation by the O-SME, the message is submitted to the SMSC <step 1>.
The SMSC may varify with elements if the O-SME is allowed to send messages. The SMSC delivers the message to the recipient.<Step 2>
If the recipient is not available the SMSC stores for a set period.
Upon delivery of the message or the deletion from the network, a status report may be delivered back to the O-SME <step 3>