Abstract WAP bridges the gap between the wireless mobile world and the internet. The Wireless Application Protocol (WAP) , is a collection of protocols and transport layers which allow mobile and portable communication devices such as mobile phones and Personal Digital Assistants (PDA’s), to receive information over the airwaves such as personal computers users obtain information over the internet. . WAP is simply a protocol- a standardized way that a mobile phone talks to a server installed in the mobile phone network. 1 -1- Introduction WAP is a hot topic that has been widely hyped in the mobile industry and outside of it.
It has become imperative for all Information Technology companies in Nordic countries and beyond to have a WAP division. Many advertising agencies and “dotcoms” have announced WAP services. From the user’s perspective, using WAP is much like surfing the net on a personal computer; the mobile device is fitted with a small, or not so small, display which can be used just like a desktop browser. Information sources can be selected which are then downloaded and their content is displayed. Hyper Text links and buttons can then be pressed to move around from page to page in a very simple way.
In this respect, there is very little difference between WAP browsing and desktop surfing, but, behind the scenes there are considerable differences because of the medium through which the information must travel, over radio waves rather than along hard-wired or telephone lines. 2 -2- Importance of WAP • It provides a standardized way of linking the Internet to mobile phones, thereby linking two of the hottest industries anywhere. • Its founder members include the major wireless vendors of Nokia, Ericsson and Motorola, plus a newcomer Phone. com. Compared to the wired networks there are many constraints in this wireless world. Less band width * More latency * Less connection stability * Less predictable availability .In order to meet the requirements for mobile operations the solutions must be: Inter operable-terminals from different manufacturers are able to communicate with the services in the mobile networks. Scalable-mobile network operators are able to scale services to customer needs. Efficient-provides quality of services suited to the behavior and characteristics of the mobile world. Reliable-provides a consistent and predictable platform for deploying services. 3 -3-
Secure-enables services to be extended over potentially unprotected mobile networks while still preserving the integrity of user data, protects the devices and services from security problems such as denial of service. WAP also has its detractors and controversies: • It is very difficult to configure WAP phones for new WAP services, with 20 or so different parameters needing to be entered to gain access to a WAP service. • Compared with the installed base of Short Message Service (SMS) compliant phones, the relative number of handsets supporting WAP is tiny. WAP is a protocol that runs on top of an underlying bearer.
None of the existing GSM bearers for WAP- the Short Message Service (SMS), Unstructured Supplementary Services Data (USSD) and Circuit Switched Data (CSD) are optimized for WAP. • There are many WAP Gateway vendors out there competing against each other with largely the same standardized product. This has led to consolidation such as the pending acquisition of APiON by Phone. com. • Other protocols such as SIM Application Toolkit and Mobile Station Application Execution Environment (MexE) are respectively already widely supported or designed to supercede WAP. WAP services are expected to be expensive to use since the tendency is to be online for a long Circuit Switched Data (CSD) call as the end user uses features such as interactivity and selection of more information. Without specific tariff initiatives, there are likely to be some surprised WAP users when they see their mobile phone bill for the first time after starting using WAP. 4 -4- Infrastructure of WAP WML Filter HTML WML WML Web server HTML WAP Proxy WML Filter WAP Proxy TeleVAS Server WML
WML: Wireless Markup Language: A Tag based display language providing navigational support, data input, hyper links, text and image representation and forms. HTML: Hyper Text Markup Language TeleVAS: Telephony Value Added Service 5 -5- The Wireless Application Protocol embraces and extends the previously conceived and developed wireless data protocols. Phone. com created a version of the standard HTML (Hyper Text Markup Language) Internet protocols designed specifically for effective and cost-effective information transfer across mobile networks. Wireless terminals incorporated a HDML (Handheld Device Markup Language) microbrowser, and Phone. om’s Handheld Device Transport Protocol (HDTP) then linked the terminal to the UP. Link Server Suite which connected to the Internet or intranet where the information being requested resides. The Internet site content was tagged with HDML. This technology was incorporated into WAP- and renamed using some of the many WAP-related acronyms such as WMLS, WTP and WSP. Someone with a WAPcompliant phone uses the in-built microbrowser to: 1. Make a request in WML (Wireless Markup Language), a language derived from HTML especially for wireless network characteristics. 2.
This request is passed to a WAP Gateway that then retrieves the information from an Internet server either in standard HTML format or preferably directly prepared for wireless terminals using WML. If the content being retrieved is in HTML format, a filter in the WAP Gateway may try to translate it into WML. A WML scripting language is available to format data such as calendar entries and electronic business cards for direct incorporation into the client device. 3. The requested information is then sent from the WAP Gateway to the WAP client, using whatever mobile network bearer service is available and most appropriate. -6- WAP PROTOCOL STACK WAP has a layered architecture as shown in the diagram below: Wireless Application Environment (WAE) Wireless Session Protocol (WSP) Wireless Transaction Protocol (WTP) Wireless Transport Layer Security (WTLS) Wireless Datagram Protocol (WDP) Bearers eg: Data, SMS, USSD WTP provides the protocol that allows for interactive browsing (request/response) applications. It supports three transaction classes: unreliable with no result message, reliable with no result message, and reliable with one reliable result message.
Essentially, WTP defines the transaction environment in which clients and servers will interact and exchange data. The WDP layer operates above the bearer layer used by your communications provider. Therefore, this additional layer allows applications to operate transparently over varying bearer services. While WDP uses IP as the routing protocol, unlike the Web, it does not use TCP. Instead, it uses UDP (User Datagram Protocol) which does not require messages to be split into multiple packets and sent out only to be reassembled on the client.
It is based on WWW and Mobile Telephony technologies. The primary objective of the WAE is to provide the operators and service providers an interoperable environment on which they can build applications and services which, in turn, can be used in a wide variety of hand-held client terminals. WAE includes the micro-browser that contains functionality for using not only WML and WML Script as previously stated, but also Wireless Telephony Application, namely (WTA and WTAI) telephony services and programming interfaces as well as content formats including welldefined data formats, images, phone book ecords and calendar information. The main idea behind the wireless application environment is to create a general application environment based mainly on existing technologies and philosophies of the World Wide Web . this environment should allow service providers, software manufactures or hardware vendors to integrate their application so they can reach a wide variety of different wireless platforms in an efficient way. However, WAE does not dictate or assume any specific man-machine-interface model, but allows for a variety of devices, each with its own capabilities and probability vendor-specific extras.
WAE has already integrated the following technologies and adapted them for use in wireless environment with low power handled devices. HTML, java script, HDML forms the basis of the wireless markup language and the scripting language WMLscript. The exchange formats for the business cards and phone books vcard and for calendars vcalendar have been included. URLs known from the web can be used. Furthermore, a 9 -9- wide range of mobile telecommunication technologies have been adopted and integrated into the wireless telephony application.
Besides relying on mature and established technology, WAE has a focus on devices with very limited capabilities, narrow band environments and special security and access control features. The fist phase of the WAE specification developed a whole application suite, especially for wireless clients as presented in the following sections. One global goal of the WAE is to minimize over-the-air and resource consumption on the hand held device. A client issues an encoded request for an operation on a remote server.
Encoding is necessary to minimize the data sent over the air and to save resources on the handheld devices. Decoders in a gateway now translate this encoded request in to a standard request as understood by the origin servers. This could be a request to get a web page or a request to setup a call. The gateway transfers this request to the appropriate origin server as if it came from a standard client. The origin servers will respond to the request. The gateway now encodes this response and its content and transfers the encoded response with the content to the client.
The WAE logical model does not only include this standard request/response scheme, but also push devices. Then an origin server pushes content to the gateway. The gateway encodes the pushed content and transmits the encoded pushed content to the client. With in a client several user agents can reside. User agents include such items as browsers, phone books, messages editors etc. WAE does neither specify the number of user agents nor their functionality, but assumes basic WML user agents that support WML, WML script or both. Domain specific user agents with varying architectures can be implemented.
WTA user handles access to and interaction with mobile telephone features (such as call control). 10 – 10 – Origin servers Response with content Gateway Encoded responses with content Client WTA User agent Web browser Push content Encoders & Decoders Other content server request Encoded push content WML User agent Encoded request Other WAP User agent WAE Logical Model WIRELESS SESSION PROTOCOL A sandwich layer that links the WAE to two session services- one connection oriented operating above the Wireless Transaction Protocol and a connectionless service operating above the Wireless Datagram Protocol.
The Wireless Session Protocol provides the Wireless Application Environment a consistent interface with two services: connection-oriented service to operate above the Transaction Layer Protocol (WTP) and a connectionless service that operates above either secure or non-secure datagram service (WDP). 11 – 11 – Currently the protocols of the WSP family provide HTTP/1. 1 functionality and semantics in a compact encoding, long lived session state with session suspend and resume capabilities, a common facility for reliable and unreliable data push as well as a protocol feature negotiation.
These protocols are optimized to be used in lowbandwidth bearer networks with relative long latency in order to connect a WAP client to a HTTP server. WSP provides shared state between a client and a server to optimize content transfer . HTTP a protocol WSP tries to replace with in the wireless domain, is stateless, which already causes a lot of problems in fixed networks. State is needed in web browsing eg: to resume browsing in exactly the same context in which browsing has been suspended. This is an important feature for clients and servers.
Client users can continue to work where they left the browser or when the network was interrupted, or users can get their customized environment every time they start browser. Content providers can customize their pages to clients needs and do not have to retransmit the same pages over and over again. WSP offers following features needed for content exchange between operating clients and servers. Session management: WSP introduces sessions that can be established from a client to a server and maybe long lived. Sessions can also be released in an orderly manner. Important for mobile applications are suspending and resuming a session.
Capability of negotiation: Clients and servers can agree on a common level of protocol functionality during session establishment. Content encoding: WSP defines an efficient binary encoding for the content it transfers. WSP offers content typing and composite objects. 12 – 12 – While WSP is a general purpose session protocol WAP has specified Wireless Session Protocol /Browsing (WSP/B) which comprises the protocols and services most suitable for browsing type applications. In addition to the general features WSP/B offers the following features HTTP/1. 1 functionality: WSP/B supports the functions of HTTP/1. . Offers such as extensible request/reply methods, composite objects and content type negotiation. WSP/B is a binary form of HTTP/1. 1. Thus HTTP/1. 1 content headers are used to define content type, character set encoding languages etc. , but binary encoding are defined for well known headers to reduce the protocol overheads. Exchange of session headers: Client and server can exchange request/reply headers that remain constant over the life time of the session. These headers may include content types, character sets, languages, device capabilities and other static parameters.
WSP/B will not interpret header information but passes all headers directly to service users. Push and pull data transfer: Pulling data from the server is supported by the WSP/B by using the request/response mechanism from HTTP/1. 1. WSP/B supports three push mechanisms for the data transfer. a confirmed data push with in the an existing session context, a non confirmed data push with in an existing session context and a non confirmed data push with out an existing session context. Asynchronous data requests: Optionally WSP/B supports a client that can send multiple requests to a server simultaneously.
This improves the efficiency for the requests and replies can be now coalesced to in to fewer messages. Latency is also improved, for each result can be send to the client as soon as it is available. 13 – 13 – WIRELESS TRANSACTION PROTOCOL: Runs on top of a datagram service such as User Datagram Protocol (UDP); part of the standard suite of TCP/IP protocols, to provide a simplified protocol suitable for low bandwidth mobile stations. WTP offers three classes of transaction service: unreliable one way request, reliable one way request and reliable two way request respond.
Interestingly, WTP supports Protocol Data Unit concatenation and delayed acknowledgement to help reduce the number of messages sent. This protocol therefore tries to optimize the user experience by providing the information that is needed when it is needed- it can be confusing to received confirmation of delivery messages when you are expecting the information itself. By stringing several messages together, the end user may well be able to get a better feel more quickly for what information is being communicated. The Wireless Transaction Protocol operates efficiently over either secure or non-secure wireless datagram networks.
It provides three different kinds of transaction services, namely unreliable one-way, reliable one-way and reliable two-way transactions. This layer also includes optional user-to-user reliability by triggering the confirmation of each received message. To reduce the number of messages sent, the feature of delaying acknowledgements can be used. WTP is designed to run on very thin clients, such as mobile phones. WTP offers several advantages to higher layers including an improved reliability over datagram services, such as web browsing.
There are three classes of transaction services. Class0 provides unreliable message transfer without any result message. Class1 and Class2 provide reliable message transfer, class1 without and class2 with exactly one reliable result message. Class0, Class1, Class2 can have an optional user acknowledgement. WTP achieves reliability using duplicate removal, retransmission, acknowledgement and unique transaction identifiers. No WTP class 14 – 14 – requires any connection setup or teardown phase. This avoids unnecessary overheads on the communication link.
WTP allows for asynchronous transactions, abort of transactions, concatenation of messages and can report the success or failure of reliable messages. A special feature of WTP is the ability to provide user acknowledgement or alternatively an automatic acknowledgement by WTP entity. If user acknowledgement is required, a WTP user has to confirm every message received by the entity. The three service primitives offered by the WTP are TR-Invoke to initiate a new transaction, TR-Result to send back the result of the previously initiated transaction and TR-Abort to abort an existing transaction.
The PDU s exchanged between two WTP entities for normal transaction are the invoke PDU, ack PDU and result PDU. WTP Class 0 Cass 0 offers an unreliable transaction service with out any result messages. The transaction is stateless and hence cannot be aborted. The service is requested with the TR-Invoke. req primitive. Parameters are the source address (SA), source port (SP), destination port (DP), destination address (DA). The A flag determines whether the responder entity should generate an acknowledgement or a user acknowledgement is to be used. WTP layer will transmit the user data (UD) transparently to the destination.
The class type, C indicates the class to be class 0. The transaction handle H provides a simple index to uniquely identify the transaction and is an alias for the tuple (SA, SP, DA, DP). The WDP entity at the initiator sends an invoke PDU which the responder receives. The WDP entity at the responder generates a TR-Invoke. ind primitive with the same parameters as on initiator side except for H’ which now is for the responder side. In this the responder does not acknowledge the message and the initiator does not perform any retransmission and is recommended to use only when a datagram service is required. 5 – 15 – Initiator TR-SAP TR-Invoke. req (SA,SP,DA,DP,A,UD,C=0,H) Invoke PDU responder TR-SAP TR-Invoke. ind (SA,SP,DA,DP,A,UD,C=0,H’) WTP Class0: WTP Class 1: Class 1 offers a reliable transaction service but without a result message. The initiator sends an invoke PDU after a TR-invoke. req from a higher layer. Here C=1, class being 1. The responder signals the incoming invoke via the TRinvoke. ind primitive to the higher layer and acknowledges automatically with out user intervention. For the initiator the transaction ends with the reception of cknowledgement, the responder keeps the transaction state for some time to be able to retransmit the acknowledgement if it receives the same invoke PDU again indicating a loss of acknowledgement. 16 – 16 – Initiator TR-SAP TR-Invoke. req (SA,SP,DA,DP,A,UD,C=1,H) Invoke PDU Ack PDU TR-Invoke. cnf (H) responder TR-SAP TR-Invoke. ind (SA,SP,DA,DP,A,UD,C=1,H’) TR-Invoke. res (H’) WTP Class1: WTP Class 2; Class 2 transaction service provides the classical reliable request/response transaction with one reliable message. The initiator requests a service, the WTP entity sends the invoke PDU to the responder.
The responder indicates the request with the TR-Invoke. ind primitive to a user. The responder waits for the processing of the request, the user on the responder’s side can finally give the result UD* to the WTP entity on responder side using TR-Result. req. Now the result PDU can be sent back to the to the initiator which implicitly acknowledges the invoke PDU. Thus the initiator can indicate the successful transmission of the invoke message and the result with the two service primitives TR-Invoke. cnf and TR-Result. ind. A user may respond to 17 – 17 – this result with the TR-Result. es then an acknowledgement PDU is generated which finally triggers the TR-Result. cnf primitive on the responder’s side. Initiator TR-SAP TR-Invoke. req (SA,SP,DA,DP,A,UD,C=2,H) Invoke PDU responder TR-SAP TR-Invoke. ind (SA,SP,DA,DP,A,UD,C=2,H’) TR-Invoke. cnf (H) TR-Result. ind (UD*, H) Result PDU TR-Result. req (UD*,H’) Ack PDU TR-Result. cnf (H’) TR-Result. res (H) WTP Class2: 18 – 18 – WIRELESS TRANSPORT LAYER SECURITY WTLS incorporates security features that are based upon the established Transport Layer Security (TLS) protocol standard. Includes data integrity checks, privacy on the WAP Gateway to client leg and authentication.
The Wireless Transport Layer Security protocol is based on Transport Layer Security (TLS) or formerly known as Secure Sockets Layer (SSL). It is designed to be used with other WAP protocols and to support narrow-band networks. It uses data encryption with a method that is negotiated at the start of the session to provide privacy, data integrity, and authentication and denial-of-service protection. The latter is needed in cases when data is replayed or not properly verified. When that happens, WTLS detects the misuse and rejects the data in order to make many typical denial-ofservice attacks harder to accomplish.
It is up to the applications to enable or disable WTLS features. Whether that happens, it depends to their security requirements and the characteristics of the underlying network, namely, does it use security services at the lower layer. WTLS can provide different levels of security (for privacy, data integrity and authentication) and has been optimized for low band width, high delay bearer net works. WTLS take in to account the low processing power and very limited memory capacity of the mobile devices for cryptographic algorithms. WTLS supports datagram and connection oriented transport layer protocols.
Before data can be exchanged via WTLS, a secure session has to be established. Figure shown below illustrates the sequence of service primitives needed for “full hand shake“. The originator and the peer of the secure session can both interrupt session establishment any time; eg: if the parameters proposed are not acceptable. 19 – 19 – Originator SEC-SAP SEC-Create. req (SA,SP,DA,DP,KES,CS,CM) Peer SEC-SAP SEC-Create. ind (SA,SP,DA, DP,KES,CS,CM) SEC-Create. cnf (SNM,KR,SID,KES’,CS’,CM’) SEC-Create. res (SNM,KR,SID,KES’,CS’,CM’) SEC-Exchange. ind SEC-Exchange. req SEC-Exchange. es (CC) SEC-Exchange. cnf (CC) SEC-Commit. req SEC-Commit. ind SEC-Commit. cnf WTLS establishing a secure session 20 – 20 – The first step is to initiate the session with the SEC-Create primitive. Parameters are source address (SA), source port(SP), of the originator, destination address(DA),destination port(DP) of the peer. The originator proposes a key exchange suite(KES) a cipher suite(CS) and a compression method(CM). The peer answers with parameters for the sequence number mode(SNM) the key refresh cycle(KR), (how often keys are refreshed with in this secure session) the session dentifier (SID) (which is unique with each peer )and the selected key exchange suite (KES’),cipher suite(CS’),compression method(CM’). The peer also issues a SECExchange primitive. This indicates that the peer wishes to perform public key authentication with the client, ie the peer requests a certificate from the originator. The first step of the secure session creation, the negotiation of the security parameters and suites, is indicated on the originators side, followed by a request for a certificate. The originator answers with its certificate and issues SEC-Commit. req primitive .
This primitive indicates that the hand shake is completed for the originator’s side and that the originator now wants to switch in to the newly negotiated connection side. The certificate is delivered to the peer side and the SEC-Commit is indicated. The WTLS layer of the peer sends back a confirmation to the originator. This concludes the full handshake of the for secure session setup. After setting up a secure connection between the two peers, user data can be exchanged. This is done using the simple SEC-Unitdata primitive as shown in figure below. 21 – 21 – Sender SEC-SAP SEC-Unitdata. eq (SA,SP,DA,DP,UD) Receiver SEC-SAP SEC-Unitdata. ind (SA,SP,DA,DP,UD) WTLS Datagram Transfer SEC-Unitdata has the same function as the T-DUnitdata on the WDP layer; it transfers a datagram between a sender and a receiver. The higher layers may use SEC-Unitdata instead of T-DUnitdata . Thus the parameters, SA, SP, DA, DP, UD are same. Although WTLS allows for different encryption mechanisms with different key lengths, it is quite clear that due to computing power of the handheld devices and export regulations in some countries, the encryption provided cannot be very strong.
However applications or users are free to put stronger encryption on top of the whole protocol stack if required (and allowed ) – the appropriate algorithms are available world wide. Future work in the WTLS layer comprises consistent support for application level security ( eg: digital signatures ) and different implementation classes with different capabilities to select from. 22 – 22 – WIRELESS DATAGRAM PROTOCOL Allows WAP to be bearer independent by adapting the transport layer of the underlying bearer.
WDP presents a consistent data format to the higher layers of the WAP protocol stack thereby conferring the advantage of bearer independence to application developers. The Wireless Datagram Protocol in WAP architecture covers the Transmission Layer Protocols in an Internet model. As a general transport service, WDP offers to the upper layers an invisible interface independent of the underlying network technology used. In consequence of the interface common to transport protocols, the upper layer protocols of the WAP architecture can operate independent of the underlying wireless network.
By letting only the transport layer deal with physical networkdependent issues, global interoperability can be acquired using mediating gateways. The bearer services, over which WAP is designed to operate, include short message, circuit-switched data and packet data services. Since the bearers offer different types of quality of service with respect to throughput, error rate and delays, the WDP is designed to either compensate for or tolerate these changes. Also, WDP lists all the bearers that are supported and the techniques applied when transmitting data over a certain bearer.
These lists will change with new bearers being added as the wireless market grows. At the T-SAP WDP offers a consistent datagram transport service independent of the underlying bearer. The closer the bearer service to IP, smaller the adaptation can be. If the bearer already offers IP services, UDP (User Datagram Protocol) is used as WDP. WDP offers source and destination port numbers used for multiplexing and demultiplexing of data respectively. The service primitive to send a datagram is T-Dunitdata. req with the destination address (DA), destination port user data(UD) as mandatory DP), source address(SA), source port(SP) and parameters. 23 – 23 – T-DUnitdata. req (DA,DP,SA,SP,UD) T-SAP T-SAP T-DUnitdata. ind (SA,SP,UD) T-DUnitdata. req (DA,DP,SA,SP,UD) T-DError. ind (EC) WDP Service Primitives Destination and source address are unique addresses for the receiver and sender of the user data. The TDUnitdata. ind service primitive indicates the reception of data. Here destination and port addresses are optional parameters. If a higher layer requests a service the WDP cannot fulfill, this error is indicated with T-DError. ind service primitive.
An error code (EC) is returned indicating the reason for the error to the higher layer. However, this primitive must not be used by the WDP to indicate problems with the bearer service, only for local problems, such as a user data size that is too large. If any error happen when WDP datagrams are sent from one WDP entity to another (eg: destination is unreachable, no application is listening to the specified destination or port etc. ) the wireless control message protocol (WCMP) provides error handling mechanisms for WDP. WCMP can be used by the WDP nodes and gateways to 24 – 24 – report errors.
Typical WCMP messages are destination unreachable (route, port, address unreachable), parameter problem, (errors in the packet header), message too big, reassembly failure or echo request/reply An additional WDP management entity supports WDP and provides information about the changes in the environment which may impact on the correct operation of WDP. Important information is the current configuration of the device, currently available bearer services, processing and memory resources etc. Design implementations of these management is considered vendor specific and thus outside the scope of WAP.
If the bearer already offers IP transmission, WDP (ie. , UDP in these case ) relies on the segmentation and reassembly capabilities of the IP layer as specified. Otherwise, WDP has to include these capabilities, which is, eg. necessary for the GSM SMS. The WAP specification provides many more adaptations to almost all bearer services currently available or planned for the future. (WAP Forum 1998q), (WAP Forum 1998b) Optimal WAP Bearer SHORT MESSAGE SERVICE CIRCUIT SWITCHED DATA UNSTRUCTURED SUPPLEMENTARY SERVICES DATA GENERAL PACKET RADIO SERVICE 25 – 25 – SHORT MESSAGE SERVICE
Given its limited length of 160 characters per short message, SMS may not be an adequate bearer for WAP because of the weight protocol of the protocol. The overhead of the WAP protocol that would be required to be transmitted in an SMS message would mean that even for the simplest of transactions several SMS messages may in fact have to be sent. This means that using SMS as a bearer can be a time consuming and expensive exercise. Only one network operator- SBC of the US- is known to be developing WAP services based on SMS. CIRCUIT SWITCHED DATA Most of the trial WAP based services use CSD as the underlying bearer.
Since CSD has relatively few users currently, WAP could kick start usage of and traffic generated by this bearer. However, CSD lacks immediacy- a dial up connection taking about 10 seconds is required to connect the WAP client to the WAP Gateway, and this is the best case scenario when there is an complete end to end digital call- in the case of the need for analog modem handshaking (because the WAP phone does not support V. 110 the digital protocol, or the WAP Gateway does not have a digital direct connection such as ISDN into the mobile network), the connect time is increased to about 30 seconds. 6 – 26 – UNSTRUCTURED SUPPLEMENTARY SERVICES DATA Unstructured Supplementary Services Data (USSD) is a means of transmitting information or instructions over a GSM network. USSD has some similarities with SMS since both use the GSM network’s signaling path. Unlike SMS, USSD is not a store and forward service and is session-oriented such that when a user accesses a USSD service, a session is established and the radio connection stays open until the user, application, or time out releases it.
This has more in common with Circuit Switched Data than SMS. USSD text messages can be up to 182 characters in length. USSD has some advantages and disadvantages as a tool for deploying services on mobile networks: • Turnaround response times for interactive applications are shorter for USSD than SMS because of the session-based feature of USSD, and because it is NOT a store and forward service. According to Nokia, USSD can be up to seven times faster than SMS to carry out the same two-way transaction. Users do not need to access any particular phone menu to access services with USSD- they can enter the Unstructured Supplementary Services Data (USSD) command direct from the initial mobile phone screen. • Because USSD commands are routed back to the home mobile network’s Home Location Register (HLR), services based on USSD work just as well and in exactly the same way when users are roaming. • • • • Unstructured Supplementary Services Data (USSD) works on all existing GSM mobile phones. Both SIM Application Toolkit and the Wireless Application Protocol support USSD.
USSD Stage 2 has been incorporated into the GSM standard. Whereas USSD was previously a one way bearer useful for administrative purposes such as service access, Stage 2 is more advanced and interactive. By sending in a USSD2 27 – 27 – command, the user can receive an information services menu. As such, USSD Stage 2 provides WAP-like features on EXISTING phones. • USSD strings are typically complicated for the user to remember, involving the use of the “*” and “#” characters to denote the start and finish of the USSD string.
However, USSD) strings for regularly used services can be stored in the phonebook, reducing the need to remember and reenter them. As such, USSD could be am ideal bearer for WAP on GSM networks. GENERAL PACKET RADIO SERVICE The General Packet Radio Service (GPRS) is a new packet-based bearer that is being introduced on many GSM and TDMA mobile networks from the year 2000 onwards. It is an exciting new bearer because it is immediate (there is no dial up connection), relatively fast (up to 177. kbps in the very best theoretical extreme) and supports virtual connectivity, allowing relevant information to be sent from the network as and when it is generated. There are two efficient means of delivering proactively sending (“pushing”) content to a mobile phone: by the Short Message Service which is of course one of WAP bearers or by the user maintaining more or less a permanent GPRS (mobile originated) session with the content server. However, mobile terminated IP traffic might allow unsolicited information to reach the terminal.
Internet sources originating such unsolicited content may not be chargeable. A possible worse case scenario would be that mobile users would have to pay for receiving unsolicited junk content. This is a potential reason for a mobile vendor NOT to support GPRS Mobile Terminate in their GPRS terminals. However, by originating the session themselves from their handset, users confirm their agreement to pay for the delivery of content from that service. Users could make their requests via a WAP session, which would not therefore need to be blocked. As such, a WAP 28 – 28 – ession initiated from the WAP microbrowser could well be the only way that GPRS users can receive information onto their mobile terminals. Since all but the early WAP enabled phones will also support the General Packet Radio Service, WAP and GPRS could well be synergistic and be used widely together. For the kinds of interactive, menu based information exchanges that WAP anticipates, Circuit Switched Data is not immediate enough because of the need to set up a call. Early prototypes of WAP services based on Circuit Switched Data were therefore close to unusable.
SMS on the other hand is immediate but is ALWAYS store and forward, such that even when a subscriber has just requested information from their microbrowser, the SMS Center resources are used in the information transfer. As such, GPRS and WAP are ideal bearers for each other. Additionally, WAP incorporates two different connection modesWSP connection mode or WSP connectionless protocol. This is very similar to the two GPRS Point to Point services- connection oriented and connection less. WAP certainly will be important for the development of GPRSbased applications.
Because the bearer level is separated from the application layer in the WAP protocol stack, WAP provides the ideal and defined and standardized means to port the same application to different bearers. As such, many application developers will use WAP to facilitate the migration of their applications across bearers once GPRS based WAP protocols are supported. 29 – 29 – Beneficants from WAP END USER: Mobile phones have become dominant tools in communications and at the same time the internet has become a de facto platform for information.
By adopting a common protocol the end user will be provided with more value added services which are easy to access and easy to use directly from mobile phone Telephony oriented services will be made easier to understand and to use. OPERATORS: The operators can differentiate by launching special services, for example for banking stock trading, directory services etc. A further differentiation is that the protocol makes it possible to tailor-make specific menus with in the mobile phones, facilitating the use of the services. This customization can be made over the air.
INDUSTRY: The telecommunication industry will be able to avoid overlapping costs and investments if there is a common, open platform and tool for wireless messaging. This is one of the first and important step in the evolution of wireless data/messaging services which will increase the usage of data in wireless networks. 30 – 30 – Future directions: Even if WAP technology is developed recently and the first wireless terminal device is entering the market WAP is just one step in a direction of new and better technologies. The WAP services that are offered today seem to be complex to survive.
The future of wireless telephony, 4G or 3G will be making use of the packet switching network such as GPRS. This will bring the wireless communication in to another dimension and will give opportunities for transmission of both pictures and videos. Conclusion: The WAP technology has a structured architecture designed and is based on the standards of the original WWW model. Since the technology has been developed by the WAP Forum, it has become a technology with an architecture that is scalable, interoperable, efficient, reliable and secure. In the future we ill see the technology a part of the day today life and the users of the wireless terminals will be able to read news, buy consort tickets and get access to intra and extranet. However the WAP technology in the near future will meet the user requirements that it will have difficulties to deliver. The need for sending pictures and video is increasing day by day and hence WAP technology may be overtaken by some other technologies which have the aforementioned capabilities such as GPRS or UMTS. 31 – 31 – The WAP WSP specification defines the WSP push operation and a WSP push PDU (Protocol Data Unit).
A push operation is not specified for the HTTP protocol, used by the WAP Gateway server to communicate with content hosts. To support pushes, the server has to provide an application interface to allow server based applications to generate a push to a mobile client. The support of pushes on the client side depends on the capabilities of the handsets to handle pushed content. The Nokia OTA configuration proposal to the WAP Forum describes the use of a connectionless push over the SMS bearer, to transfer the configuration data to the handset.
WIRELESS TELEPHONY APPLICATION DELAYED The so-called Wireless Telephony Application (WTA) was only defined by the WAP Forum in June 1999. The WTA gives WAP some of the features that SIM Application Toolkit incorporates such as access to phone report and call handling. LACK OF COOKIES FOR SESSION MANAGEMENT 32 – 32 – There are no “cookies” for session management, i. e. to hold the session together. Cookies are used on the fixed Internet to identify the web browser and thereby assist in providing customized and streamlined services. Instead, some WAP applications use indexes in the URL as an alternative.
The cookie information is transmitted via HTTP headers. Because WAP WSP is based on HTTP headers, it should be possible to transmit cookie information to the clients. The problem may be the clients itself, which may currently not support the handling of cookie HTTP header information or to save this information to a persistent storage in the mobile phone. PREMATURE ENCRYPTION ENDPOINT The Wireless Transport Layer Security defines encryption between the Mobile Station and the WAP Gateway. The “endpoint” of the encrypted WTLS data is the WAP Gateway proxy server.
To have a secure connection to a content host (e. g. banking server) the Gateway proxy server has to establish secure (https) connections to this hosts. In this case the proxy server has access to the decrypted data received via WTLS from the mobile station or from the content host via https. SMALL DOWNLOADABLE UNIT SIZE WAP incorporates no compression techniques for the textual content, although the WML markup commands are compressed. Additionally, the “deck”- the smallest unit of downloadable information in Wireless MarkUp Language- is limited to a maximum of 1400 bytes.
This means that applications need to be specifically designed to be very code efficient by using templates and variables and keeping information on the server and using the cache on the phone. WML byte code converting defines a (maybe inefficient) compression technique by string tables. With this technique duplicate strings in the WMLC bytecode are avoided. This reduces the size of the data to transfer to the mobile client. The WSP SDU size of 1400 bytes is a default value. An increased size may be negotiated by a mobile client within the WSP capabilities.
The WAP transport layer (WTP) is able to handle greater SDU sizes than 1400 too, by using SAR (Segmentation and Re-assembly). However, programmers need to be aware of them when they commence WAP application design. WAP Clients and Gateways WAP is a client server philosophy, requiring a microbrowser in the mobile phone and a WAP Gateway connected to the mobile network. By early 2000, WAP clients such as the Nokia 7110 were becoming available in quantity and other phone vendors such as Alcatel and Motorola have announced that they are introducing support for the Wireless Application Protocol across their entire product range.
However, since WAP requires a larger screen size and more memory to handle the WAP stack, it costs more to produce a WAP handset and will therefore mean more expensive mobile phone prices. WAP phones will therefore be distinguishable from their non WAP counterparts to the informed observer- and will have the “WWW:MMM” branding anyway- which the WAP Forum founders have agreed on to depict 33 – 33 – WAP terminals. Support by mobile phones for WAP will be the simple largest determinant of when WAP is a success. SIM Application Toolkit is another wireless protocol that enables a similar functionality set to WAP.
SIM Application Toolkit has been around for longer than WAP and is at a later stage of development and deployment than WAP but is a GSM only technology that has not been widely adopted by leading mobile phone vendors such as Nokia and Ericsson. SIM Application Toolkit is supported by perhaps a quarter of the installed base of GSM phones. It may be that application developers need to support BOTH WAP and SIM Application Toolkit AND standard SMS in their Gateways so that the applications and services can be offered to ALL mobile phone users, rather than just a subset.
Widespread reach is of course essential in maximizing use of the services and helping build a wireless Internet portal that is popular with all mobile phone users. Despite today’s lack of an installed base of WAP capable mobile phones, there are several vendors of WAP Gateways that network operators, content providers and application developers can work with to develop WAP-based services. WAP Gateways are installed into the mobile phone network to provide a gateway between the Internet and different mobile nonvoice services such as the Short Message Service, Circuit Switched Data and General Packet Radio Service.
The WAP Gateway is essentially a piece of middleware, taking information from a web server, processing it, and sending it out over the mobile network to a WAP client. Of the WAP Forum members, there are about a dozen suppliers of WAP Gateways. WAP Gateway suppliers include CMG, Nokia, Ericsson, Phone. com (formerly Unwired Planet), Materna and Motorola. SMS Server platform suppliers such as Sendit and Tecnomen have NOT developed their own WAP Gateway. Phone. com announced its acquisition of APiON in September 1999. FORMATION Motorola, Nokia, Ericsson and the US software company Phone. om (formerly Unwired Planet) were the initial partners that teamed up over two years ago in mid 1997 to develop and deploy the Wireless Application Protocol (WAP). WAP is an attempt to define the standard for how content from the Internet is filtered for mobile communications. Content is now readily available on the Internet and WAP was designed as the (rather than one) way of making it easily available on mobile terminals. The WAP Forum was formed after a US network operator Omnipoint issued a tender for the supply of mobile information services in early 1997.
It received several responses from different suppliers using proprietary techniques for delivering the information such as Smart Messaging from Nokia and HDML from Phone. com (then called Unwired Planet). Omnipoint informed the tender responders that it would not accept a proprietary approach and recommended that that various vendors get together to explore defining a common standard. After all, there was not a great deal of difference between the different approaches, which could be combined and extended to form a powerful standard.
These events were the initial stimulus behind the development of the Wireless Application Protocol, with Ericsson and Motorola joining Nokia and Unwired Planet as the founder members of the WAP Forum. PHILOSOPHY 34 – 34 – The Wireless Application Protocol takes a client server approach. It incorporates a relatively simple microbrowser into the mobile phone, requiring only limited resources on the mobile phone. This makes WAP suitable for thin clients and early smart phones. WAP puts the intelligence in the WAP Gateways whilst adding just a microbrowser to the mobile phones themselves.
Microbrowser-based services and applications reside temporarily on servers, not permanently in phones. The Wireless Application Protocol is aimed at turning a mass-market mobile phone into a “network-based smartphone”. As a representative from Phone. com (formerly Unwired Planet) on the board of the WAP Forum commented “The philosophy behind Wireless Application Protocol’s approach is to utilize as few resources as possible on the handheld device and compensate for the constraints of the device by enriching the functionality of the network”.
The Wireless Application Protocol is envisaged as a comprehensive and scaleable protocol designed for use with: • • • any mobile phone from those with a one line display to a smart phone any existing or planned wireless service such as the Short Message Service, Circuit Switched Data, Unstructured Supplementary Services Data (USSD) and General Packet Radio Service (GPRS). Indeed, the importance of WAP can be found in the fact that it provides an evolutionary path for application developers and network operators to offer their services on different network types, bearers and terminal capabilities.
The design of the WAP standard separates the application elements from the bearer being used. This helps in the migration of some applications from SMS or Circuit Switched Data to GPRS for example. any mobile network standard such as Code Division Multiple Access (CDMA), Global System for Mobiles (GSM), or Universal Mobile Telephone System (3GSM). WAP has been designed to work with all cellular standards and is supported by major worldwide wireless leaders such as AT Wireless and NTT DoCoMo. multiple input terminals such as keypads, keyboards, touch-screens and styluses. • • 35 – 35 –