The WAP architecture provides a scaleable and extensible application development environment for mobilecommunication devices. This is achieved through a layered design of the protocol stack (Figure 7). Each layer providesa set of functions and/or services to other services and applications through a set of well-defined interfaces. Each of thelayers of the architecture is accessible by the layers above, as well as by other services and applications.The WAP architecture separates service interfaces from the protocols that provide those services to allow for evolutionof the specifications and selection of the most appropriate protocol for a given context. Many of the services in thestack may be provided by more than one protocol. For example, either HTTP [RFC2616] or WSP [WSP] may providethe Hypermedia Transfer service.
Bearer Networks
Protocols have either been designed or selected to operate over a variety of different bearer services, including shortmessage, circuit-switched data, and packet data. The bearers offer differing levels of quality of service with respect tothroughput, error rate, and delays. The protocols are designed to compensate for or tolerate these varying levels ofservice.
Since the Transport Services layer provides the interface between the bearer service and the rest of the WAP stack, thetransport specifications (e.g., [WDP]) may list the bearers that are supported and the techniques used to allow theprotocols to run over each bearer. The list of supported bearers will change over time with new bearers being added asthe wireless market evolves.
Transport Services
The Transport Services layer offers a set of consistent services to the upper layer protocols and maps those services tothe available bearer services. The Transport Services transport unstructured data across the underlying bearer networks.These transport services create a common abstraction that is consistent across all the bearers.
The Transport Services include, but are not limited to:
· Datagrams – The datagram service provides data transport in which self-contained, independent entities of datacarry sufficient information to be routed from the source to the destination computer without reliance on earlierexchanges between this source and destination computer and the transporting network. UDP (User DatagramProtocol) [STD0006] and WDP (Wireless Datagram Protocol) [WDP] are two protocols used to provide thedatagram transport service in the WAP architecture.
· Connections – The connection service provides data transport service in which communication proceeds in threewell-defined phases: connection establishment, two-way reliable data transfer and connection release. TCP(Transmission Control Protocol) [STD0007] is a protocol used to provide the connection transport service of IP1bearers for the WAP architecture. In order to cope with the wireless network characteristics, the TCP protocol canbe profiled for its use, see [WP-TCP].
Transfer Services
The Transfer Services provide for the structured transfer of information between network elements.
The Transfer Services include, but are not limited to:
· Hypermedia Transfer – The hypermedia transfer services provides for the transfer of self-describing hypermediaresources . The combination of WSP (Wireless Session Protocol) [WSP] and WTP (Wireless Transaction Protocol)[WTP] provide the hypermedia transfer service over secure and non-secure datagram transports. The HTTP(Hypertext Transfer Protocol) [RFC2616] provides the hypermedia transfer service over secure and non-secureconnection-oriented transports.
· Streaming – The streaming services provide a means for transferring isochronous data such as audio and video.
· Message Transfer – The message transfer services provide the means to transfer asynchronous multimediamessages such as email or instant messages. MMS Encapsulation [MMSEncapsulation] is a protocol used totransfer messages between WAP devices and MMS servers.
Session Services
The session services provide for the establishment of shared state between network elements that span multiple networkrequests or data transfers. For example, the Push session establishes that the WAP Device is ready and able to receivepushes from the Push Proxy.
The Session Services include, but are not limited to:
· Capability Negotiation – The WAP architecture includes specifications for describing, transmitting, and managingcapabilities and preference information about the client, user, and network elements. See [UAProf] for moreinformation. This allows for customisation of information and content returned by the origin server or pushed bythe application.
· Push-OTA – The Push-OTA (Over The Air) session service provides for network-initiated transactions to bedelivered to wireless devices that are intermittently able to receive data (e.g., modal devices and devices withdynamically assigned addresses). The Push-OTA service operates over the connection-oriented transport serviceand datagram transport [PushOTA].
· Sync – The Sync service provides for the synchronisation of replicated data.
· Cookies – The Cookies service allows applications to establish state on the client or proxy that survives multiplehypermedia transfer transactions. See [HTTPState] for more information.
Application Framework
The Application Framework provides a general-purpose application environment based on a combination of WorldWide Web (WWW), Internet and Mobile Telephony technologies. The primary objective of the Application Frameworkis to establish an interoperable environment that will allow operators and service providers to build applications andservices that can reach a wide variety of different wireless platforms in an efficient and useful manner.
The Application Frame work includes, but is not limited to:
· WAE/WTA User-Agent – WAE is a micro-browser environment containing or allowing for markup (includingWML and XHTML), scripting, style-sheet languages, and telephony services and programming interfaces, alloptimised for use in hand-held mobile terminals. See [WAE] for more information.
· Push – The Push service provides a general mechanism for the network to initiate the transmission of data toapplications resident on WAP devices. See [PushArchOverview] for more information.
· Multimedia Messaging – The Multimedia Message Service (MMS) provides for the transfer and processing ofmultimedia messages such as email and instant messages to WAP devices.
· Content Formats – The application framework includes support for a set of well-defined data formats, such as colorimages, audio, video, animation, phone book records, and calendar information.
Security Services
Security forms a fundamental part of the WAP Architecture, and its services can be found in many of its layers. Ingeneral the following security facilities offered are:
· Privacy – facilities to ensure that communication is private and cannot be understood by any intermediate partiesthat may have intercepted it.
· Authentication – facilities to establish the authenticity of parties to the communication.· Integrity – facilities to ensure that communication is unchanged and uncorrupted.
· Non-Repudiation – facilities to ensure parties to a communication cannot deny the communication took place.
The Security Services span all the various layers of the WAP Architecture. Some specific examples of the securityservices include:
· Cryptographic Libraries – This application framework level library provides services for signing of data forintegrity and non-repudiation purposes. See [WMLScriptCrypto] for more information.
· Authentication – The Security Services provide various mechanisms for client and server authentication. At theSession Services layer HTTP Client Authentication [RFC2617] may be used to authenticate clients to proxies andapplication servers. At the Transport Services layer, WTLS and TLS handshakes may be used to authenticateclients and servers.
· Identity – WIM provides the functions that store and process information needed for user identification andauthentication [WIM]· PKI – The set of security services that enable the use and management of public-key cryptography and certificates[WPKI], [WAPCert].
· Secure Transport – The Transport Services layer protocols are defined for secure transport over datagrams andconnections. WTLS is defined for secure transport over datagrams and TLS is defined for secure transport overconnections (i.e. TCP). See [WTLS] and [WAPTLS] for more information.
· Secure Bearer – Some bearer networks provide bearer level security. For example, IP networks (especially in thecontext of IPv6) provide bearer-level security with IPSec [RFC2401].
Service Discovery
Service discovery forms a fundamental part of the WAP Architecture and its services can be found at many layers.
Some specific examples of Service Discovery services include:
· EFI – The External Functionality Interface (EFI) allows applications to discover what external functions/servicesare available on the device.
· Provisioning – The Provisioning service allows a device to be provisioned with the parameters necessary to accessnetwork services. See [ProvArch] for more information.
· Navigation Discovery – The Navigation Discovery service allows a device to discover new network services (e.g.secure pull proxies) during the course of navigation such as when downloading resources from a hypermediaserver. The WAP Transport-Level End-to-End Security specification [TransportE2ESec] defines one navigationdiscovery protocol.
· Service Lookup – The Service Lookup service provides for the discovery of a service’s parameters through adirectory lookup by name. One example of this is the Domain Name System (DNS) [STD0013].
Other Services and Applications
The WAP layered architecture enables other services and applications to utilise the features of the WAP stack through aset of well-defined interfaces. External applications may access the various services directly. The WAP layeredarchitecture builds upon an extensible set of protocols. This allows the WAP stack to be used for applications andservices not currently specified by WAP, but deemed to be valuable for the wireless market. Such applications andservices may benefit from adding protocols or particular protocol capabilities. For example, applications, such aselectronic mail, calendar, phone book, notepad, and electronic commerce, or services, such as white and yellow pages,may be developed to use the WAP protocols.
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