TalkByText is based on RFC 5194: Framework for Real-Time Text over IP Using the Session Initiation Protocol (SIP).
The TalkByText architecture is based on the Session Initiation Protocol (SIP) as specified in RFC 3261 and the Real-Time Transport protocol (RTP) according to RFC 3550. It transports text according to RFC 4103 (UTF-8).
As such, TalkByText is a fully compliant SIP application, including support for SIP features such as Registrars and SIP Proxies. This means that the TalkByText client can easily interoperate and integrate very well in a wider VoIP enabled environment.
The SIP stacks, as well as the RTP and SDP components, are all in-house development and thus do not rely on third-party components or other IPR. Nevertheless, the various components have undergone rigorous interoperability testing to make sure they are fully compliant with the standard and that they interwork properly with other products and services based on these standards.
Of crucial importance is the ability for this innovative platform to continue to support interconnection to and from existing legacy text telephony devices. Legacy textphones use a range of fairly obsolete PSTN technologies, like ITU V.21 and Baudot. Text telephony is awkward technology even within the PSTN, let alone when transformation to other platforms is required. Most textphone protocols include only very limited signalling, so recognising a textphone call is a tricky problem at the best of times. TalkByText follows the architecturally most elegant and robust solution for interworking between the PSTN and IP, by providing a gateway at the borders of the network. This ensures that no proprietary or obsolete PSTN concepts invade the IP environment. At the IP side, therefore, the entire call set-up, control and media transport is fully native and fully open standards compliant.
In the UK, the gateway uses ITU V.21 at the PSTN side. In addition, a special feature of the PSTN in the UK, called BT TextDirect, provides additional support for text telephony by allowing the use of prefixes to signal the type of call (text or voice) and by offering call progress and status information in text. The TalkByText platform fully supports TextDirect prefix dialling and will process and display status and call progress messages too.
Deaf and hard of hearing people do not just want to talk to other deaf and hard of hearing individuals, they also want to speak to hearing people. TalkByText allows real-time text users to make calls via Text Relay, the UK's text-to-speech relay service. This means that a user of real-time text can hold a seamless conversation with hearing people on a voice phone.
Windows implementation of TalkByText is built on the native 32-bit Windows platform (NT kernel based), i.e. Windows 2000 and Windows XP. It has already successfully been tested on Windows Vista and a Vista-compliant version will be released early 2008 as well. The application supports all standard Windows features and follows best practice for Windows approved software. For example, it fully supports Windows user accounts and will store user settings within user profiles and documents in the user's documents folder. For ease of deployment and administration, TalkByText can be configured and managed centrally across the network via central configuration files. TalkByText for Windows has an open, extensible architecture in the form of a plug-in framework.
This allows the application to support multiple external services, including SMS service providers, various types of central address book schemes and external alerting devices such as pagers and visual alerting systems. In addition to the standard SIP provisions for name resolution (including the ability to use SRV records), TalkByText for Windows fully supports the additional Windows name resolution mechanisms such as WINS, while retaining full compliance with the SIP standard.
TalkByText ships with Orthrus, a Windows service application that acts as a back-to-back user agent. One of the Orthrus "faces" is directed outwards, on your LAN's public IP, while the other side faces inwards to your LAN. Orthrus proxies the SIP signalling as well as the RTP media between these two faces in a completely secure way. Orthrus could run on either the Firewall machine itself or on a separate server, with port mappings from the Firewall to the Orthrus machine. Using port forwarding in this way is entirely secure. SIP traffic can be either TCP or UDP based, with 5060 being the default SIP port. RTP media is UDP based and by default uses ports 8000-8100.
The optional Corporate SMS service is a Windows service application that needs to be installed on a server in your LAN. Communication between the TalkByText clients and the corporate SMS server is TCP based. Communication between the corporate SMS server and the SMS aggregator is HTTP based. Incoming SMS messages and status information is received in the form of HTTP requests. The port number for such requests is configurable.
The optional Central Address Book service is a Windows service application that needs to be installed on a server in your LAN. Communication between the TalkByText clients and the address book is TCP based.
The peer-to-peer address book (optional) has no centralised component, but is based on UDP broadcast messages across the network. The port number for these messages is configurable.
BT TextDirect offers additional support for text telephony by allowing the use of prefixes to signal the type of call (text or voice) and by offering call progress and status information in text. The TalkByText platform fully supports TextDirect prefix dialling and will process and display status and call progress messages as well.
As all text transport in the TalkByText platform is based on Unicode, the platform fully supports all European languages and character sets.
