Components of the WAP Architecture

WAP architecture provides a scaleable and extensible application development environment for mobile communication devices. This is achieved through a layered design of the protocol stack (Figure 7-7). Each layer provides a set of functions and/or services to other services and applications through a set of well-defined interfaces. Each of the layers of the architecture is accessible by the layers above, as well as by other services and applications.

Figure 7-7: WAP stack architecture

The WAP architecture separates service interfaces from the protocols that provide those services to allow for evolution of the specifications and selection of the most appropriate protocol for a given context. Many of the services in the stack may be provided by more than one protocol. For example, either HTTP^[6] or WSP may provide the Hypermedia Transfer service.

Bearer Networks

Protocols have either been designed or selected to operate over a variety of different bearer services, including short message, circuit-switched data, and packet data. The bearers offer differing levels of quality of service with respect to throughput, error rate, and delays. The protocols are designed to compensate for or tolerate these varying levels of service.

Since the Transport Services layer provides the interface between the bearer service and the rest of the WAP stack, the transport specifications (e.g., “Wireless Datagram Protocol Specification”^[11]) may list the bearers that are supported and the techniques used to allow the protocols to run over each bearer. The list of supported bearers will change over time with new bearers being added as the wireless market evolves.

Transport Services

The Transport Services layer offers a set of consistent services to the upper layer protocols and maps those services to the 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 data carry sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network. UDP (User Datagram Protocol) and WDP (Wireless Datagram Protocol) are two protocols used to provide the datagram transport service in the WAP architecture.

• Connections  The connection service provides data transport service in which communication proceeds in three well-defined phases: connection establishment, two-way reliable data transfer and connection release. TCP (Transmission Control Protocol)^[7] is a protocol used to provide the connection transport service of IP^[28] bearers for the WAP architecture. In order to cope with the wireless network characteristics, the TCP protocol can be profiled for its use.^[29]

Transfer Services

The Transfer Services provide for the structured transfer of information between network elements. They include, but are not limited to:

• Hypermedia Transfer  The hypermedia transfer services provide for the transfer of self-describing hypermedia resources. The combination of WSP (Wireless Session Protocol)^[15] and WTP (Wireless Transaction Protocol)^[19] provide the hypermedia transfer service over secure and non-secure datagram transports. The HTTP (Hypertext Transfer Protocol)^[6] provides the hypermedia transfer service over secure and non-secure connection-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 multimedia messages such as email or instant messages. MMS Encapsulation^[30] is a protocol used to transfer 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 network requests or data transfers. For example, the Push session establishes that the WAP Device is ready and able to receive pushes from the Push Proxy. The Session Services include, but are not limited to:

• Capability Negotiation  The WAP architecture includes specifications for describing, transmitting, and managing capabilities and preference information about the client, user, and network elements. See “User Agent Profile Specification” for more information.^[26] This allows for customization of information and content returned by the origin server or pushed by the application.

• Push-OTA  The Push-OTA (Over The Air) session service provides for network-initiated transactions to be delivered to wireless devices that are intermittently able to receive data (e.g., modal devices and devices with dynamically assigned addresses). The Push-OTA service operates over the connection-oriented transport service and datagram transport.^[31]

• Sync  The Sync service provides for the synchronization of replicated data.

• Cookies  The Cookies service allows applications to establish state on the client or proxy that survives multiple hypermedia transfer transactions. See “HTTP State Management” for more information.^[32]

Application Framework

The Application Framework provides a general-purpose application environment based on a combination of World Wide Web (WWW), Internet and Mobile Telephony technologies. The primary objective of the Application Framework is to establish an interoperable environment that will allow operators and service providers to build applications and services 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 (including WML and XHTML), scripting, style-sheet languages, and telephony services and programming interfaces, all optimized for use in hand-held mobile terminals. See “Wireless Application Environment Specification” for more information.^[10]

• Push  The Push service provides a general mechanism for the network to initiate the transmission of data to applications resident on WAP devices. See “WAP Push-Architectural Overview” for more information.^[33]

• Multimedia Messaging  The Multimedia Message Service (MMS) provides for the transfer and processing of multimedia 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 color images, 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. In general, the following security facilities offered are:

• Privacy  Facilities to ensure that communication is private and cannot be understood by any intermediate parties that 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 security services include:

• Cryptographic Libraries  This application framework level library provides services for signing of data for integrity and non-repudiation purposes. See “WMLScript Crypto Library” for more information.^[34]

• Authentication  The Security Services provide various mechanisms for client and server authentication. At the Session Services layer, HTTP Client Authentication^[35] may be used to authenticate clients to proxies and application servers. At the Transport Services layer, WTLS and TLS handshakes may be used to authenticate clients and servers.

• Identity  WIM provides the functions that store and process information needed for user identification and authentication.^[12]

• PKI  The set of security services that enable the use and management of public-key cryptography and certificates.^[14][36]

• Secure Transport  The Transport Services layer protocols are defined for secure transport over datagrams and connections. WTLS is defined for secure transport over datagrams and TLS is defined for secure transport over connections (i.e. TCP). See “Wireless Transport Layer Security Protocol” and “WAPTLS Profiling and Tunneling” for more information.^[18][37]

• Secure Bearer  Some bearer networks provide bearer level security. For example, IP networks (especially in the context of IPv6) provide bearer-level security with IPSec^[38].

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/services are available on the device.

• Provisioning  The Provisioning service allows a device to be provisioned with the parameters necessary to access network services. See “WAP Provisioning Architecture Overview” for more information.^[27]

• 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 hypermedia server. The WAP Transport-Level End-to-End Security specification^[39] defines one navigation discovery protocol.

• Service Lookup  The Service Lookup service provides for the discovery of a service’s parameters through a directory lookup by name. One example of this is the Domain Name System (DNS).^[40]

Other Services and Applications

The WAP layered architecture enables other services and applications to use the features of the WAP stack through a set of well-defined interfaces. External applications may access the various services directly. The WAP layered architecture builds upon an extensible set of protocols. This allows the WAP stack to be used for applications and services not currently specified by WAP, but deemed to be valuable for the wireless market. Such applications and services may benefit from adding protocols or particular protocol capabilities. For example, applications, such as electronic mail, calendar, phone book, notepad, and electronic commerce, or services, such as white and yellow pages, may be developed to use the WAP protocols.

^[6]R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, and T. Berners-Lee, “Hypertext Transfer Protocol — HTTP/1.1.” www.rfc-editor.org/rfc/rfc2616.txt. June 1999.

^[11]——, “Wireless Datagram Protocol Specification.”

^[7]J. Postel, “Transmission Control Protocol,” www.rfc-editor.org/rfc/std/ std7.txt. September 1981.

^[28]WAP Forum, “User Agent Profile Specification.”

^[29]——, “WAP Provisioning Architecture Overview.”

^[15]——, “Wireless Session Protocol.”

^[19]——, “Wireless Transaction Protocol Specification.”

^[6]R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, and T. Berners-Lee, “Hypertext Transfer Protocol — HTTP/1.1.” www.rfc-editor.org/rfc/rfc2616.txt. June 1999.

^[30]The utilization of TCP connections over IP may require additional components of the TCP/IP protocol suite. One example for such a component is ICMP.

^[26]ECMA, “Standard ECMA-262: ECMAScript Language Specification.” June 1997.

^[31]WAP Forum, “Wireless Profiled TCP Specification.”

^[32]——, “WAP Multimedia Messaging Service Message Encapsulation.”

^[10]——, “Wireless Application Environment Specification.” Version 2, WAP-236-WAESpec.

^[33]——, “WAP Push OTA Protocol.”

^[34]——, “HTTP State Management.” WAP-223-HTTPSM.

^[35]——, “WAP Push Architectural Overview.”

^[12]——, “WAP Identity Module Specification.”

^[14]——, “WAP Public Key Infrastructure Definition.”

^[36]——, “WMLScript Crypto Library.”

^[18]——, “Wireless Transport Layer Security Protocol.”

^[37]J. Franks, P. Hallam-Baker, J. Hostetler, S. Lawrence, P. Leach, A. Luotonen, and L. Stewart, “HTTP Authentication: Basic and Digest Access Authentication.” www.rfc-editor.org/rfc/rfc2617.txt. June 1999.

^[38]WAP Forum, “WAP Certificate and CRL Profiles.”

^[27]David Flanagan, JavaScript: The Definitive Guide. New York: O’Reilly & Associates, Inc., 1997.

^[39]——, “WAPTLS Profile and Tunnelling.” WAP-219-TLS-20010411.

^[40]S. Kent and R. Atkinson, “Security Architecture for the Internet Protocol.” www.rfc-editor.org/rfc/rfc2401.txt. November 1998.