The WTA user agent has the capability for interfacing with mobile network services available to a mobile telephony device, that is, setting up and receiving phone calls.. A user agent se
Trang 1Network architecture supporting
wireless applications
The Wireless Application Environment (WAE) architecture is designed to support Mobile Terminals (MTs) and network applications using different languages and character sets WAE user agents have a current language and accept content in a set of well-known character encoding sets Origin server-side applications can emit content in one or more encoding sets and can accept input from the user agent in one or more encoding sets Wireless Telephony Application (WTA) is an application framework for telephony ser-vices The WTA user agent has the capability for interfacing with mobile network services available to a mobile telephony device, that is, setting up and receiving phone calls The Wireless Application Protocol (WAP) Push framework introduces a means within the WAP effort to transmit information to a device without a previous user action In the client/server model, a client requests a service or information from a server, which transmits information to the client In this pull technology, the client pulls information from the server
6.1 WAE ARCHITECTURE
The WAE architecture includes networking schemes, content formats, programming lan-guages, and shared services Interfaces are not standardized and are specific to a particular implementation WAE can work with a browser and a class of user agents used in the World Wide Web (WWW)
In the Internet WWW, applications present content to a client in a set of standard
data formats that are browsed by client side user agents known as Web browsers A user
agent sends requests for one or more data objects or content to an origin server, which responds with the requested data expressed in one of the standard formats known to the user agent [i.e., Hypertext Markup Language (HTML)] The WWW logical model is shown in Figure 6.1
Mobile Telecommunications Protocols For Data Networks Anna Ha´c
Copyright 2003 John Wiley & Sons, Ltd.
ISBN: 0-470-85056-6
Trang 2User agent
Response (content)
Request (URL)
Origin server
CGI scripts, etc.
Content
Figure 6.1 WWW logical model.
Encoded request
Encoded response
Gateway
Encoders and decoders
Origin server
CGI scripts, etc.
Content
WAE
user
agent
Client
Request
Response (content)
Figure 6.2 WAE logical model.
All resources on the WWW are named using Internet standard Uniform Resource Loca-tors (URLs) All classes of data on the WWW are given as specific types, allowing the user agent to correctly distinguish and present them appropriately The WWW defines
a variety of standard content formats supported by most browser user agents, including the HTML, the JavaScript scripting language, and other formats like bitmap image for-mats The WWW defines a set of standard networking protocols allowing any browser to communicate with any origin server, for example, Hypertext Transfer Protocol (HTTP) The WAE logical model is shown in Figure 6.2 In the WAE model, the content is transported using standard protocols in the WWW domain and an optimized HTTP-like protocol in the wireless domain The content and services in WAE architecture are hosted on standard Web origin servers using proven technologies like Common Gateway Interface (CGI) The content is located by using WWW standard URLs WAE supports
Trang 3WAE ARCHITECTURE 95
Mobile Network Services such as Call Control and Messaging WAE architecture supports low bandwidth and high latency networks and considers CPU processing constraints in MTs WAE assumes the existence of gateway functionality responsible for encoding and decoding data transferred from and to the mobile client The purpose of the encoding content delivered to the client is to minimize the size of data sent to the client Over The Air (OTA), and to minimize the computational energy required by the client to process the data The gateway functionality can be added to origin servers or placed in dedicated gateways
The main elements of the WAE model are WAE user agents, content generators, standard content encoding, and WTA WAE user agents interpret network content ref-erenced by a URL Content generators are the applications or services on origin servers, like CGI scripts, that produce standard content formats in response to requests from user agents in MTs Standard content encoding allows a WAE user agent to navigate Web content WTA is a collection of telephony-specific extensions for call and feature control mechanisms providing advanced Mobile Network Services
WAE is based on the architecture used for WWW proxy servers The situation in which
a user agent, a browser, must connect through a proxy to reach an origin server, the server that contains the desired content, is very similar to the case of a wireless device accessing
a server through a gateway Most connections between the browser and the gateway use WAP Session Protocol (WSP), regardless of the protocol of the destination server URL refers only to the destination server’s protocol and has no bearing on what protocols may be used in intervening connections The gateway performs protocol conversion by translating requests from WSP into other protocols, and translating the responses back into WSP Content conversion performed by the gateway is analogous to HTML/HTTP proxies available on the Web In the HTTP scheme, the browser communicates with the gateway using WSP The gateway provides protocol conversion functions to connect to
an HTTP origin server
WAE logical layers include user agents such as browsers, phone books, message editors, and so on, and services and formats including common elements and formats accessible to user agents such as Wireless Markup Language (WML), WMLScript, image formats, vCard (electronic business card) and vCalendar (electronic calendar and schedul-ing exchange) formats, and so on The WAE client components are shown in Figure 6.3 WAE allows the integration of domain-specific user agents with varying architectures and environments A WTA user agent is specified as an extension to the WAE specifi-cation for the mobile telephony environments The WTA extensions allow for accessing and interacting with mobile telephone features, like call control, and other applications assumed on the telephones, such as phone books and calendar applications The features and capabilities of a user agent are decided by those who implement them
WAE services and formats include the WML, the WMLScript (Wireless Markup Script-ing Language), WAE applications, and WAE-supported content formats
WML is a tag-based document language It is an application of a generalized markup language and is specified as an Extensible Markup Language (XML) document type WML is optimized for specifying presentation and user interaction on limited capability devices such as telephones and wireless MTs WML and its supporting environment are designed using certain small narrow-band device constraints including small displays,
Trang 4User agents
Services / formats
WTA user agent
WML user agent
Other agents
Other applications and services
WMLScript
WAP Protocol stack and services
Device OS/services
WML
Other srvs.
& formats
Figure 6.3 WAE client components.
limited user input facilities, narrow-band network connections, limited memory resources, and limited computational resources
The WML features include
• support for text and images;
• support for user input;
• navigation and history stack;
• international support;
• Man–Machine Interface (MMI) independence;
• narrow-band optimization; and
• state and context management
WMLScript is a lightweight procedural scripting language enhancing the standard browsing and presentation facilities of WML with behavioral capabilities, supporting more advanced user interface, adding intelligence to the client, providing a convenient mechanism to access the device and its peripherals, and reducing the need for round trips
to the origin server WMLScript is an extended subset of JavaScript for narrow-band devices and is integrated with WML for future services and in-device applications WAE user agents can use URL services WAE components extend the URL semantics, for example, in WML, in which URL fragments are extended to allow linking to particular WMLScript functions WAE allows formats for data types including images, multipart messages, and user agent-specific formats
WML user agent logical architecture is shown in Figure 6.4 A user submits a request
to the origin server using a WML user agent, which requests the service by using a URL
Trang 5WAE ARCHITECTURE 97
CGI scripts, etc.
Content
WML
user
agent
WAE
services
Gateway WML encoder
WMLScript
Figure 6.4 WML user agent logical architecture with gateway.
scheme operation The origin server replies by sending a single deck in a textual format
On their way back to the client, textual decks are expected to pass through a gateway where they are converted into formats better suited for OTA transmission and limited-device processing The gateway does all the necessary conversions between the textual and binary formats A WML encoder (or tokenizer) in the gateway converts each WML deck into its binary format Encoded content is then sent to the client to be displayed and interpreted
The user agent may submit one or more additional requests, using a URL scheme, for WMLScript as the user agent encounters references to them in a WML deck On its way back, a WMLScript compiler takes the script as input and compiles it into byte code that
is designed for low bandwidth and thin mobile clients The compiled byte code is then sent to the client for interpretation and execution
Figure 6.5 shows WML user agent logical architecture without a gateway WAE does not specify the location where the actual encoding and compilation is done The origin servers may have built-in WML encoders and WMLScript compilers Some services may
CGI scripts, etc.
Content
WML user agent WAE services
WML encoder
WMLScript compiler WML dec
Figure 6.5 WML user agent logical architecture without a gateway.
Trang 6be statically stored (or cached) in tokenized WML and WMLScript byte code formats, eliminating the need to perform fast conversion of the deck
The WAE architecture is designed to support MTs and network applications using dif-ferent languages and character sets WAE user agents have a current language and accept content in a set of well-known character encoding sets Origin server–side applications can emit content in one or more encoding sets and can accept input from the user agent
in one or more encoding sets
6.2 WTA ARCHITECTURE
WTA is an application framework for telephony services The WTA user agent has the capability for interfacing with mobile network services available to a mobile telephony device, that is, setting up and receiving phone calls Figure 6.6 shows a configuration
of the WTA architecture In this figure, the WTA user agent, the repository (persistent storage), and WTA Interface (WTAI) interact with each other and the other entities in
a WTA-capable mobile client device The WTA user agent is able to retrieve content from the repository and WTAI This ensures that the WTA user agent can interact with mobile network functions like setting up calls and device-specific features like using the phonebook The WTA user agent receives network events that can be bound to content, thus enabling dynamic telephony applications
Network events available to the WTA user agent are the result of actions taken by services running in the WTA user agent itself Telephony events initiated from outside the device are also passed to the WTA user agent and the network text message events
Man −machine interface
WTA user agent
Repository
Device-specific features Network layer
Network events and signaling
Mobile network
WTA server
Other applications
Direct user interactions WTAI libraries
Mobile
client
WAP gateway
Figure 6.6 WTA architecture.
Trang 7WTA ARCHITECTURE 99
WAE user agent
Mobile
client
WAP gateway
Firewall (optional) Internet
Mobile network
Man−machine interface
Device-specific features Network layer
Network events and signaling
WTAI Public Library
Direct user interaction
Other applications
Figure 6.7 WAE user agent and WTA Public Library.
that are explicitly directed toward another user agent The network events caused by the WML user agent do not affect the WTA user agent
WTAI Public Library contains functions that can be called from any WAE application
as shown in Figure 6.7 and provides access to telephone functionality This library allows WML authors to include click-to-phone functionality within their content, to avoid users typing the number by using the default MMI
In Figure 6.7, the WAE user agent and WTAI Public Library interact with each other and the other entities in a WTA-capable mobile client The WAE user agent only retrieves
its content via the WAP gateway and only has access to the WTAI Public Library
func-tions These functions expose simple functionality such as the ability to place a call, but
do not allow fully featured telephony control Only a WTA user agent is able to fully control the telephony features of the device The WAE user agent is not able to receive and react to telephony and network text events
Figures 6.6 and 6.7 show logical separations of the two user agents They can coexist
on the same device and are likely to be implemented with common code elements The WTA server is a Web server delivering content requested by a client A WTA user agent, like an Internet Web browser, uses URLs to reference content on the WTA server
A URL can be used to reference an application on a Web server, for instance, a CGI script, that is executed when it is referenced The applications can be programmed to perform
a wide range of tasks, for example, generate dynamic content and interact with external entities By referencing applications on a WTA server, it is possible to create services that use URLs to interact with the mobile network, such as an Intelligent Network node, and other entities, such as a voice mail system The concept of referencing applications
Trang 83
2 3
1a
1a 1b
1b
Access to a URL (via the repository) Access to a URL (via the WTA server) Service Indication (Push)
Network event (transformed to WTA event in client)
WAP gateway Mobile
network
WTA server
Figure 6.8 Initiation of WTA services.
on a WTA server provides a simple and powerful model on how to seamlessly integrate services in the mobile network with services executing locally in the WAP client WTA services appear to the client in the form of various content formats, such as WTA–WML, WMLScript, and so on The WTA user agent executes content that is persistently stored in the client’s repository or content retrieved from a WTA server The WTA user agent can act on events from the mobile network, for instance, an incoming call Figure 6.8 shows how to initiate a WTA service in the WTA user agent The WTA user agent executes content within the boundary of a well-known context The service defines the extent of a context and its associated content The start of a service is marked by the initiation of a new context, and the termination of a context marks the end of a service The repository is a persistent storage module within the MT that may be used to eliminate the need for network access when loading and executing frequently used WTA services The repository also addresses the issue of how a WTA service developer ensures that time-critical WTA events are handled in a timely manner The repository addresses the issues of how the WTA services developer preprogram the device with content, and how the WTA services developer improves the response time for a WTA service The repository can be accessed by a service using one of the following methods:
• A WTA event associated with a channel is detected, and the user agent invokes a URL
as specified by the associated channel;
• The end user accesses services stored in the repository through an implementation-dependent representation (for instance, a menu containing the labels of the channels)
of the allowed services (channels explicitly specified as user accessible by the channel definition) in the repository;
• The content of URL retrieved from the repository may be given to the user agent by providing the URL in content or delivering it by Service Indication (SI)
The WTA applications, that is, content loaded or otherwise received from the WTA server, may access the repository
Trang 9WTA ARCHITECTURE 101
WTA server
WAP gateway
WTA services WTA port
Mobile
client
WAE port
WAE services
Internet
Figure 6.9 WDP port numbers and access control.
A WTA service invoking WTAI functions enables access to local functions in the mobile client These functions allowing for setting up calls, and accessing the users local phone book, must ensure that only authorized WTA services are permitted to execute The trusted mobile telephony service provider, which provides an acceptable level of security
in the network, can choose to run all WTA services itself not allowing other providers
or it can choose to delegate the administration of its WTA services to a third party The Wireless Datagram Protocol (WDP) uses predefined port numbers to separate a WTA service from a common WAE service as shown in Figure 6.9 A WTA session established
by the WTA user agent must use one of the dedicated, secure WTA ports on the gateway The WTA user agent must not retrieve WTA content outside the WTA session WTA content received outside the WTA session and Service Indication addressing the WTA user agent but delivered outside a WTA session shall be discarded
The repository is used to store WTA content persistently This provides a mechanism that ensures timely handling of content related to WTA services initiated by WTA events and has the following characteristics:
• The repository contains a set of channels and resources
• Resources are data downloaded with WSP (that is, WTA–WML deck) and are stored along with their metadata, that is, content type and the HTTP 1.1 entity tag, and location (URL)
• A channel is a resource that contains a set of links and resources and has identity and freshness
• Channels in the repository have a freshness lifetime (the HTTP 1.1 expiry date header), beyond which time they are considered stale Stale channels are subject to automatic removal by the user agent Resources are subject to automatic removal from the repos-itory if the channel does not reference them
• If the repository contains a channel that is not stale, it is guaranteed that the repository contains all resources named in that channel The loading and unloading of a channel
is an atomic operation in that no user agent will recognize the presence of the channel until all the content in the channel has been successfully stored in the repository
Trang 10WML Deck #1
WML Deck #2
WML Script object
WBMP image
Figure 6.10 Repository.
• A label may be associated with a channel to give a textual description of the service indicated by the channel
Resources in the repository may be referenced by more than one channel A resource
is present in the repository if one or more channels reference it Figure 6.10 shows how channels may share resources stored in the repository
WTA services are created using WTA–WML and WMLScript Telephony functions can
be accessed from WMLScript through the WTAI, which also provides access to telephony functions from WTA–WML by using Uniform Resource Identifier (URIs) URIs form a unifying naming model to identify features independently of the internal structure of the device and the mobile network The WTA services reside on the WTA server The client addresses WTA services by using URLs
Examples of WTA services include
• Extended set of user options for handling incoming calls (incoming call section): The
service is started when an incoming call is detected in the client A menu with user options is presented to the user Examples of options are
Accept call
Redirect to voice mail
Redirect to another subscriber
Send special message to caller
• Voice mail: The user is notified that he or she has voice mails and retrieves a list of
them from the server The list is presented on the client’s display When a certain voice mail has been selected, the server sets up a call to the client and the user listens to the selected voice mail