GSM Short Message Service GSM Short Message Service GSM Short - - PDF document

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GSM Short Message Service GSM Short Message Service GSM Short - - PDF document

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National Taiwan University Department of Computer Science and Information Engineering GSM Short Message Service GSM Short Message Service GSM Short Message Service GSM Short Message Service Phone Lin Phone Lin Ph.D. Ph.D. Email:

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National Taiwan University

Department of Computer Science and Information Engineering

Phone Lin Phone Lin

Ph.D. Ph.D.

Email: plin@csie.ntu.edu.tw Email: plin@csie.ntu.edu.tw

GSM Short Message Service GSM Short Message Service GSM Short Message Service GSM Short Message Service

National Taiwan University

Department of Computer Science and Information Engineering

2

Outlines

Introduction Short Message Service Architecture Mobile-Terminated Mobile-Originated SMS Protocol Hierarchy The DTE-DCE Interface Summary

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Department of Computer Science and Information Engineering

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Introduction (1/2)

The GSM SMS provides a connectionless transfer of messages with low-capacity and low-time performance. In Dec. 1992, the short message, sent from PC to MS, was delivered in Vodafone GSM in UK. Every GSM SMS can contain up to 140 octets, 160 char. To accommodate longer than 160 char.,

  • SMS concatenation

SMS concatenation

  • SMS compression

SMS compression

National Taiwan University

Department of Computer Science and Information Engineering

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Introduction (2/2)

The SMS operates like a paging service, with the added capability that messages can pass in both directions. The SMS are transported on the GSM SDCCH signaling channel. Two types of GSM short message services have been defined:

Cell Broadcast Service, which periodically delivers short messages to all subscribers in a given area. Point-to-Point Service sends short messages to a specific user. This GSM feature can be considered as an enhanced two-way paging service.

GSM SMS Network Architecture. (Reference P.12-2 Fig. 12.1)

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SMS Architecture: Mobile- Terminated (1/2)

  • Step 1.

Step 1. The short message is first delivered from the message sender (e.g., GSM MS or a paging input device) to a Short Message Service Center (SM Short Message Service Center (SM-

  • SC)

SC).

  • Step 2.

Step 2. The SM-SC is connected to the GSM network through a GSM MSC, SMS GMSC SMS GMSC.

  • Step 3.

Step 3. Following the GSM roaming protocol GSM roaming protocol, the SMS GMSC locates the current MSC of the message receiver and forwards the message to the MSC.

National Taiwan University

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SMS Architecture: Mobile- Terminated (2/2)

  • Step 4.

Step 4. The MSC broadcasts the message to BSS, and BTS page the destination MS.

  • Step 5.

Step 5. The MS used for short message services must contain special software to enable the messages to be decoded and stored. The logical message path is SM SM-

  • SC

SC -

  • > GMSC

> GMSC -

  • >

> terminating MSC terminating MSC -

  • > MS

> MS. Short messages can be stored either in the SIM or in the memory of ME for display on the standard screen of the MS.

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SMS Architecture: Mobile- Originated (1/2)

  • Step 1.

Step 1. An MS may send or reply a short message by delivering to a short message service Inter Inter-

  • working

working MSC (IWMSC) MSC (IWMSC) and then to the SM SM-

  • SC

SC.

  • Step 2.

Step 2. The recipient of the short message can be an MS MS, a fax machine fax machine, or a PC PC connected to the Internet. The logical message path is MS -> IWMSC -> SM-SC

  • Experience indicates that mobile

Experience indicates that mobile-

  • originating traffic
  • riginating traffic

is around 20 percent of mobile is around 20 percent of mobile-

  • terminating traffic.

terminating traffic.

  • Note that

Note that

SMS is a store-and-forwarded service. Short message cannot be sent directly from the sender to the receipt without passing through the SM-SC.

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SMS Architecture: Mobile- Originated (2/2)

To simplify the generation of a short message in an MS, several technologies have been proposed.

  • Predictive Text Input Algorithms

Predictive Text Input Algorithms reduce the number of input keystrokes by predicting the next word the user will generate. New features, e,g., QWERTY keyboard QWERTY keyboard, can be built in the MS to provide simpler access to messaging services.

Three types of short messages:

  • User

User-

  • Specific

Specific messages are displayed to the users.

  • ME

ME-

  • Specific

Specific messages are processed by the ME instead of showing to the users.

  • SIM

SIM-

  • Specific

Specific messages are processed at the SIM card.

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The Role of SM-SC

For supporting high-quality SMS service An SM-SC should be scalable, with high availability high availability and reliability reliability. The SM-SCs are typically implemented on high-speed server platforms. Exiting SM-SC products support TCP/IP access, and many of them can accommodate new data protocols, e.g., Wireless Application Protocol (WAP). SMS MS-MSC Protocol Hierarchy (Mobile Origination) (Reference P.12.4 Fig. 12.2)

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SMS Protocol Hierarchy for Mobile- Originated Messaging

The architecture for mobile-originated messaging and mobile- terminated messaging are similar, with the exception that the IWMSC IWMSC is replaced by the GMSC GMSC. The SMS protocol hierarchy consists of 4 layers: SM SM-

  • AL

AL, SM SM-

  • TL

TL, SM SM-

  • RL

RL, CM CM-

  • sub

sub. In this hierarchy, the protocol between the IWMSC and the SM-SC below the transfer layer is not specified in GSM. The protocol between the MSC MSC and IWMSC IWMSC is GSM MAP, utilizing SS7 TCAP. The layers below the CM-sublayer are the mobility management mobility management (MM) (MM) and radio resource (RR) management radio resource (RR) management sublayer. At the RR management layer the short message service is supported by control channels (e.g., SDCCH or SACCH).

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Short Message Transfer Layer

These SM-TL-supported service primitives generate a reference number called Short Short Message Identifier (SMI) Message Identifier (SMI) for every short message associated with the primitives. This SMI at the MS is not carried between the peer entity at the SM-SC (i.e., a short message may have different SMIs at the MS and the SM- SC sides).

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Four Types of Transfer Protocol Data Units (TPDUs) (1/2)

  • SMS

SMS-

  • SUBMIT (MS

SUBMIT (MS -

  • > SM

> SM-

  • SC).

SC).

Conveys a short message (referred to as transfer protocol user short message (referred to as transfer protocol user data or TP data or TP-

  • UD)

UD) from MS to the SM-SC. TP-UD optionally specifies the validity period validity period that the short message can be buffered in the SM-SC if it cannot be delivered to the recipient immediately.

  • SMS

SMS-

  • DELIVER (SM

DELIVER (SM-

  • SC

SC -

  • > MS).

> MS).

Conveys a short message from the SM-SC to the MS. This TPDU includes a service center timestamp service center timestamp. The SM-SC uses this timestamp to inform the recipient MS about the arrival time of the short message at the SM-TL of the SM-SC. A boolean parameter, More More-

  • To

To-

  • Send

Send, is used to indicate if one or more messages are waiting in the SM-SC for delivery to the recipient MS.

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Four Types of Transfer Protocol Data Units (TPDUs) (2/2)

  • SMS

SMS-

  • STATUS

STATUS-

  • REPORT (SM

REPORT (SM-

  • SC

SC -

  • > MS)

> MS).

This report describes the status of the previously sent mobile-

  • riginated short message.

If the previous short message is not delivered successfully, this TPDU may report permanent errors, e.g.,

  • Validity Period Expiration
  • Incompatible Destination
  • Temporary Errors, e.g., Congestion

This TPDU is optionally initiated by SMS-SUBMIT.

  • SMS

SMS-

  • Command (MS

Command (MS -

  • > SM

> SM-

  • SC).

SC).

Can be a Query Query about the previous submitted short message

  • Cancellation

Cancellation of the status report

  • Deletion

Deletion of the submitted message

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Short Message Relay Layer (1/2)

The short message relay layer (SM short message relay layer (SM-

  • RL)

RL) provides services to transfer TPDUs and the corresponding delivery reports for SM-TL. These SM-RL-supported service primitives generate SM-RL SMI for the messages to be delivered. For a message, the SM-RL SMI at mobile side and SM-RL SMI at the SM-SC are the same.

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Short Message Relay Layer (SM- RL) (2/2)

The SMR entity at the MS communicates with the peer SMR at MSC by using the Short Short Message Relay Protocol (SM Message Relay Protocol (SM-

  • RP)

RP). SM-RP provides the networking functions between MS and SM-SC, which interworks with TCAP/MAP TCAP/MAP in the MSC.

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Four Types of Relay Protocol Data Units (RPDUs) (1/2)

  • RP

RP-

  • DATA (MS <

DATA (MS <-

  • > SM

> SM-

  • SC).

SC).

Invoked by the SM-RL-DATA service primitives. RP-DATA contains the originating address, the terminating address, and the user data containing TPDU. A mobile-terminated RP-DATA may indicate if more waiting message in SM-SC.

  • RP

RP-

  • SM

SM-

  • MEMORY

MEMORY-

  • AVAILABLE (MS

AVAILABLE (MS -

  • > Network).

> Network).

Invoked by the SM-RL-MEMORY-AVAILABLE primitive. SM-RL-MEMORY-AVAILABLE passes the necessary control information to indicate that the MS has memory available to receive one or more messages).

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Four Types of Relay Protocol Data Units (RPDUs) (2/2)

RP-ACK.

Invoked by the SM-RL-REPORT primitives to acknowledge the corresponding RP-DATA or RP-SM-MEMORY-AVAILABLE data units.

RP-ERROR.

Invoked by the SM-RL-REPORT primitive to report any error of a corresponding RP-DATA. An error may occur if (1) the message is too short to contain the complete message type, (2) the message reference is known, (3) the message type is unknown, or (4) the message content is semantically incorrect.

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Department of Computer Science and Information Engineering

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Connection Management Sublayer (CM-Sub) (1/2)

The CM-Sub for SMS provides services to support the SM-RL. In this layer, the Short Message Control (SMC) Short Message Control (SMC) entity at the MS communicates with the peer SMC at the MSC by using the Short Short-

  • Message

Message-

  • Control

Control-

  • Protocol (SM

Protocol (SM-

  • CP)

CP). The MS has two SMC entities.

One handles the MS-Originated (MO) short message and The other handles the MS-Terminated (MT) short message service.

Note that the SMC entities cannot simultaneously perform messaging in both directions.

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The Protocol Elements for SM- CP

  • CP

CP-

  • DATA.

DATA.

Invoked by the SM-CP service primitives MNSMS-DATA or MNSMS-ESTablish. These two primitives deliver RP-DU between the MS and the MSC.

  • CP

CP-

  • ACK.

ACK.

Acknowledges the corresponding CP-DATA. CP-ACK does not contain any specific information elements.

  • CP

CP-

  • ERROR.

ERROR.

Invoked by the SM-CP service primitives MNSMS-ABORT or MNSMS-ERROR, which provide the cause of the messaging procedure error.

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Connection Management Sublayer (CM-Sub) (2/2)

Before any CP message is delivered, an MM MM-

  • connection

connection must be established.

The SMC uses the MNSMS MNSMS-

  • ESTablish

ESTablish primitive primitive to establish an MM-connection and then transfer an RPDU on that MM-Connection.

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The DTE-DCE Interface

An MS includes two parts:

Mobile Terminal (MT), which consists of SIM and ME. Terminal Equipment (TE), which may be a PDA or PC.

The MT and TE are connected either by

An RS232 port RS232 port, An Interface Port (e.g., Interface Port (e.g., IrDA IrDA) ), or A PCMCIA interface PCMCIA interface through the Data Terminal Equipment (DTE) Data Terminal Equipment (DTE)-

  • Data Circuit Terminating Equipment (DCE) protocol

Data Circuit Terminating Equipment (DCE) protocol.

The DTE-DCE Interface defines a set of AT AT commands commands.

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Communication between MT and TE (1/2)

The TE can instruct the MT to send a short message by issuing

AT Command + CMGS = <Length><CR> AT Command + CMGS = <Length><CR><pdu <pdu> >

  • <length>

<length>: the length of the actual data unit in octets

  • <pdu

<pdu> >: the SMS-SUBMIT TPDU

If the MT transmits the packet successfully, it will reply to the TE with the following command.

+CMGS:<ref +CMGS:<ref-

  • no><CR><LF><CR><LF>OK<CR><LF>

no><CR><LF><CR><LF>OK<CR><LF>

  • <ref

<ref-

  • no>

no>: the message reference sent from the SM-SC

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Communication between MT and TE (2/2)

When the MT receives a short message, it will notify the TE with the SMS message received command

+CMT:,<length><CR><LF> +CMT:,<length><CR><LF><pdu <pdu><CR><LF> ><CR><LF>

  • <length>:

<length>: the number of octets of the TPDU

  • <pdu

<pdu>: >: the SMS-DELIVER TPDU

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An Example Given in GSM 07.05 (1/2)

This example illustrates a session to restore the message a session to restore the message parameters from the MS to the TE parameters from the MS to the TE, and set up the set up the cell broadcast cell broadcast number (CBN) number (CBN) identifies that TE would like to receive identifies that TE would like to receive.

Line 1. AT + CRES Line 1. AT + CRES Line 2. OK Line 2. OK Line 3. AT + CSMP?; +CSCA? Line 3. AT + CSMP?; +CSCA? Line 4. +CSMP: 17, 167, 0, 0 Line 4. +CSMP: 17, 167, 0, 0 Line 5. +CSCA: Line 5. +CSCA: “ “358501234567 358501234567” ” Line 6. OK Line 6. OK Line 7. AT + CSDH = 1 Line 7. AT + CSDH = 1 Line 8. OK Line 8. OK Line 9. AT + CSCB = 0 Line 9. AT + CSCB = 0 Line 10. OK Line 10. OK

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An Example Given in GSM 07.05 (2/2)

At line 1, the TE restores setting from nonvolatile memory to volatile memory. At line 3, the TE queries short message parameters. At lines 4 and 5, the MT returns the default values for SMS-SUBMIT and the SM-SC address. At lines 7 and 9,

the TE specifies to show all message headers in text mode. (Code 0: do not show message headers; Code 1 show message headers) and To accept all cell broadcasting messages (CBMs) (Code 0: accept CBMs; code 1: reject CBMs)

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Summary

Short Message Service Architecture Mobile-Terminated Mobile-Originated SMS Protocol Hierarchy The DTE-DCE Interface