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: plin@csie.ntu.edu.tw Email: plin@csie.ntu.edu.tw 1 National Taiwan University Department of Computer Science and Information Engineering Outlines � Introduction � Short Message Service Architecture � Mobile-Terminated � Mobile-Originated � SMS Protocol Hierarchy � The DTE-DCE Interface � Summary 2
National Taiwan University Department of Computer Science and Information Engineering 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 � 3 National Taiwan University Department of Computer Science and Information Engineering 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) 4
National Taiwan University Department of Computer Science and Information Engineering 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. 5 National Taiwan University Department of Computer Science and Information Engineering 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 - -> MS > MS . terminating MSC � Short messages can be stored either in the SIM or in the memory of ME for display on the standard screen of the MS. 6
National Taiwan University Department of Computer Science and Information Engineering 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) and then to the SM MSC (IWMSC) SM- -SC SC . � � Step 2. Step 2. The recipient of the short message can be an MS , a fax machine MS 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 originating 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. 7 National Taiwan University Department of Computer Science and Information Engineering 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. 8
National Taiwan University Department of Computer Science and Information Engineering 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) 9 National Taiwan University Department of Computer Science and Information Engineering 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 is replaced by the GMSC IWMSC GMSC . � The SMS protocol hierarchy consists of 4 layers: SM SM- -AL AL , SM SM- -TL TL , SM- -RL RL , CM CM- -sub sub . SM � 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) and radio resource (RR) management radio resource (RR) management sublayer. (MM) � At the RR management layer the short message service is supported by control channels (e.g., SDCCH or SACCH). 10
National Taiwan University Department of Computer Science and Information Engineering Short Message Transfer Layer � These SM-TL-supported service primitives generate a reference number called Short Short Message Identifier (SMI) for every short Message Identifier (SMI) 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). 11 National Taiwan University Department of Computer Science and Information Engineering 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. 12
National Taiwan University Department of Computer Science and Information Engineering 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- originated 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 � 13 National Taiwan University Department of Computer Science and Information Engineering 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. 14
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