Documentation/Maemo 5 Developer Guide/Architecture/RTCOM

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Revision as of 12:10, 27 October 2009

Contents

Real Time Communications domain

The RTCom domain provides both services and applications for real time Internet communications, such as Voice Over IP / Video calls and Instant Messaging, and also cellular/CS communications on Maemo platform. It also provides and distributes presence information within the system. The architecture consists of a few major components; connection managers which abstract implementation details of different protocols to a common API, mission control to handle transient events and enforce system policies, and user interfaces to present information to the user. There is also a streaming server to handle actual media streaming communications. It is not conceptually a separate architectural element of the framework, but more like one UI implementation. Farsight interface is used to manage media pipelines.

System decomposition view

The diagram below shows the entities of the RTCOM subsystem, dependencies between them, provided interfaces and required external interfaces. The client applications are shown as packages without the fill-color. Different UI components (Messaging, Call, Log Viewer, Desktop Elements, Control Panel Applets) provide user interface layer to the system.

On intermediate layer, there’s a Mission Control package, which handle transient events and enforce system policies, providing application logic services, and libtelepathy-glib component providing GObject-style access to the Telepathy DBUS interfaces.

On lowest level, there are Streaming Engine to handle actual media streaming communications, and Connection managers that abstract implementation details of different protocols to a common API. The interface is modular and platform includes Jabber (instant messaging) and SIP (voice and video calls).

The Telepathy framework is used to handle real time communication related signaling and abstracting all protocol dependencies to a single D-BUS interface.

Centralized addressbook is provided by the Contacts subsystem and used by the RTcom subsystem for all contact information storage and lookup purposes and it also stores transient contacts/states.

RTCOM framework

In Fremantle, RTCom framework provides the following functionality:

  • Support for comprehensive logging
  • SSO related components
  • Suport for heartbeat
  • Device presence profiles
  • Support for BT HFP
  • Location support for presence


telepathy-glib

PurposeProvides GObject abstraction of Telepathy DBUS interfaces
Source packagestelepathy-glib, librtcom-telepathy-glib
LicensesLGPL and Nokia Proprietary
Interfaces usedlibglib, libdbus, libdbus-glib
Interfaces providedlibtelepathy-glib, librtcom-telepathy-glib


telepathy-mission-control

PurposeProvides a way for “end user” applications to abstract some of the details of connection managers to provide a simple way to manipulate a bunch of connection managers at once and remove the need to have in each program the account definitions and credentials.
Source packagestelepathy-glib, librtcom-telepathy-glib
LicensesLGPL and Nokia Proprietary
Interfaces usedlibglib, libdbus, libdbus-glib
Interfaces providedlibtelepathy-glib, librtcom-telepathy-glib


osso-mission-control

PurposeMission control filters
Source packagestelepathy-mission-control
LicensesNokia
Interfaces usedlibmissioncontrol, libosso, libconic, libebook, libhildon1 (libhildon-desktop), mce, libxml2, librtcom-eventlogger, librtcom-eventlogger-plugins, libsignon-glib
Interfaces providedNone


osso-accounts

Source packagesosso-accounts, osso-accounts-plugin-nokia-chat
LicensesNokia
Interfaces usedlibgtk2, libhildon1 (libhildon1, libhildonfm2, hildon-control-panel, libhildonmime, libhildonhelp), libosso-abook, libglade2, libconic, libmcclient
Interfaces providedlibaccounts, libaccounts-glade, libosso-rtcom-accounts


rtcom-eventlogger

PurposeProvides general purpose event log database system.
Source packagesrtcom-eventlogger
LicensesNokia
Interfaces usedlibglib, libsqlite3, libdbus
Interfaces providedlibrtcom-eventlogger


rtcom-eventlogger-plugins

PurposeProvides plugins for the event logging system.
Source packagesrtcom-eventlogger-plugins
LicensesNokia
Interfaces usedlibglib, libsqlite3, librtcom-eventlogger
Interfaces providedNone

Connection Managers

Connection managers can be thought of as a kind of protocol plugins of the system. They conform to Telepathy DBUS interface specification and provide DBUS interface abstraction of some protocol. Each connection manager usually provides support for one protocol. The provided interfaces depend on the capabilities of the connection manager and protocol.

Connection managers only signaling protocols. In case of a media streaming session, SDP or similar negotiation signaling is done in Connection Manager using the signaling protocol, but actual payload streaming is handled by Streaming Engine (Eg: telepathy-stream-engine).

Functionalities provided

  • Support for Skype integrated into Telepathy framework

sofia-sip

PurposeSIP-stack implementation
Source packagessofia-sip
LicensesLGPL
Interfaces usedlibglib, libssl
Interfaces providedlibsofia-sip-ua, libsofia-sip-ua-glib


telepathy-sofiasip

PurposeSIP connection manager
Source packagestelepathy-sofiasip
LicensesLGPL
Interfaces usedlibglib, libdbus, libdbus-glib, libsofia-sip-ua, libsofia-sip-ua-glib, libtelepathy-glib, libssl
Interfaces providedNone


loudmouth

PurposeXMPP-stack implementation
Source packagesloudmouth
LicensesLGPL
Interfaces usedlibglib, libssl, libcertman (libcst)
Interfaces providedlibloudmouth


telepathy-gabble

PurposeXMPP connection manager
Source packagestelepathy-gabble
LicensesLGPL
Interfaces usedlibglib, libssl
Interfaces providedlibglib, libdbus, libdbus-glib, libloudmouth, libtelepathy-glib


Streaming Engines

Media engines handle media streaming needs for multimedia communication methods like voice and video conversation. Generic telepathy-stream-engine provides voice and video streaming capabilities over RTP protocol. If there is a need for other kind of media streaming for some connection manager, it might be reasonable to provide separate media engine for that purpose. Independent of possible other uses, libjingle is used to provide NAT traversal using STUN, GTalk relay and ICE technologies for the GTalk service. libnice provides fully standards compliant ICE implementation.

Functionalities provided

  • Support for QoS analysis and actions, partially based on the (refreshed) implementation of RTCP support.
  • Support for fully standards compliant ICE through libnice.
  • Support for H.264
  • Support for BT HFP.
  • Support for Skype in Telepathy framework.


gst-plugins-farsight

PurposeGStreamer plugins specific to Farsight.
Source packagesgst-plugins-farsight
LicensesLGPL
Interfaces usedlibglib, gstreamer (libgstreamer-pligins-base), libjingle, libgonf2
Interfaces providedNone


farsight2

PurposeThe Farsight project is an effort to create a framework to deal with all known audio/video conferencing protocols. On one side it offers a generic API that makes it possible to write plugins for different streaming protocols, on the other side it offers an API for clients to use those plugins. This package provides the core Farsight 2 library.
Source packagesloudmouth
LicensesLGPL
Interfaces usedlibglib, gstreamer (libgstreamer-plugins-base, libgstreamer-plugins-good, libgstreamer-plugins-bad), libnice, libnice-gstreamer, gupnp
Interfaces providedlibgstfaright


telepathy-farsight

PurposeGlue betweeen Telepathy and Farsight2
Source packagestelepathy-farsight
LicensesLGPL
Interfaces usedlibglib, libdbus (libdbus, libdbus-glib), libgstfarsight, libtelepathy-glib
Interfaces providedlibtelepathy-farsight


libnice

PurposeICE NAT-traversal implementation
Source packageslibnice
LicensesMPL / LGPL
Interfaces usedlibglib, gstreamer (libgstreamer, libgstreamer-plugins-base)
Interfaces providedlibnice, libnice-gstreamer


telepathy-stream-engine

PurposeMedia streaming engine for Telepathy, mostly used for standard RTP-over-UDP streaming.
Source packagestelepathy-stream-engine
LicensesLGPL
Interfaces usedlibglib, libdbus (libdbus, libdbus-glib), libgstfarsight, gstreamer (libgstreamer-plugins-base), libtelepathy-farsight, libgtk2

telepathy-glib

Telepathy Library’s role is to provide common GObject-based C-language API for applications. It wraps Telepathy DBUS interfaces to GObjects and also provides some utility functions for accessing and enumerating DBUS interfaces. It’s code is mostly autogenerated from DBUS interface spec.

PurposeC API for Telepathy DBUS interfaces.
ResponsibiltiesProvides GObject based C-language API to the Telepathy DBUS interfaces along with some utility functions.
NotesMost of Telepathy’s functionality is distributed as DBUS objects where the actual functionality doesn’t necessarily reside within any specific component, but as an abstract object in the DBUS network.
LicenseLGPL


Interfaces used by libtelepathy-glib

Interface nameLicenseDependencyDescription
TelepathyLGPLglib, DBUSRTCom Interface


Mission Control

Communication system policies are usually dependent on application and environment, thus some method external to framework has to exist for handling those. Mission Control thus enforces communication system policies. It also handles configuration information storage, network connectivity from policy point of view and is thus responsible for starting and stopping connection managers and engines. While starting up connection managers and engines, it provides the configuration information. In case of network side event like presence subscription or start of communication session, Mission Control handles these transient events based on system policy and possibly starts associated UI components. Misson Control employs plugin methods to provide possibility to add special event handlers called “mission control filters”. These plugins can provide special device or system dependent function handling.


PurposeEnforces policies, handles startup/connectivity and transient events.
ResponsibilitiesEnforces system policies. Handles Connection Managers, Engines and UI startups. Also handles transient and network side events. Also responsible for connectivity management.
Packagescurlpp, osso-mission-control, osso-rtcom-oma, telepathy-mission-control
LicenseLGPL, Nokia Proprietary

User Interfaces

Messaging UI

Namertcom-messaging-ui
PurposeMessaging application.
Source Packagesrtcom-messaging-ui
LicensesNokia
Interfaces Usedlibglib, libosso, libgtk2, libhildon1 (libhildon1, libhildon-mime, libhildonfm2), libgconf2, libtelepathy-glib, librtcom-telepathy-glib, libmcclient, libosso-abook, libebook, mce, maemo-launcher, librtcom-eventlogger, librtcom-eventlogger-ui, librtcom-eventlogger-plugins, browser-neteal


Messaging UI is a user interface component for instant messaging sessions. It handles all kinds of non-media streaming communications like text chat.

Event logger

Namertcom-eventlogger-ui
PurposeEvent logger widgets.
Source Packagesrtcom-eventlogger-ui
LicensesNokia
Interfaces Usedlibglib, libgtk, libdbus, librtcom-eventlogger, librtcom-eventlogger-plugins, libosso, libosso-abook, libhildon1, libmcclient
Interfaces Providedlibrtcom-eventlogger-ui

Logger is a database engine built into a library for logging all kinds of events. It’s particularly powerful for logging messages (optionally with attachments), calls and network events.


Notification UI

Namertcom-notification-ui
PurposeNotification UI, plugin for the Hildon Status Menu.
Source Packagesrtcom-notification-ui
LicensesNokia
Interfaces Usedlibglib, libosso, libgtk2, libhildon1 (libhildon1, libhildondesktop1, libhildonmime), mce, libtelepathy-glib, libosso-abook, libebook, librtcom-telepathy-glib

This is a Hildon Status menu plugin for RTCom related notifications.

Presence UI

Namertcom-presence-ui
PurposeAccounts presence UI.
Source Packagesrtcom-presence-ui
LicenseNokia
Interfaces Usedlibglib, libosso, libgtk2, libhildon1 (libhildon1, libhildondesktop1), libmcclient, maemo-launcher, liblocation, libnavigation, libcanberra, libosso-abook

This is the presence user interface.


Single-Sign-On (SSO)

SSO subsystem is a separate subsystem providing credential storage and a client library for applications. This way, user is not requested to login or enter credentials as he’s navigating between different service types within single service provider. In case of wide ticket-based system like OpenID (reference) , user can even use the same credential between different service providers as long as service provider accepts tickets from external providers.


PurposeProvides Single-Sign-On functionality.
ResponsibilitiesProvides authentication services and tokens for applications.


Namelibsignon-glib
PurposeGObject interface to SSO functionality.
Source Packagessignon
LicensesNokia
Interfaces Usedlibglib, libxml2
Interfaces Providedlibsignon-glib


Namelibsignonui
PurposeUI elements of the SSO functionality.
Source Packagessignon
LicensesNokia
Interfaces Usedlibglib, libgtk2, libhildon1, libaccounts, libosso-rtcom-accounts, libsignon-glib
Interfaces Providedlibsignonui


Namesignond
PurposeSSO daemon, handling credential storate and authentication.
Source Packagessignon
LicensesNokia
Interfaces Usedlibglib, libxml2, libcurl (libcurl3-openssl), libssl (libcrypto)
Interfaces Providedsignond (ipc)


SSO-subsystem consists of server, here called “signond” and application libraries libsignon-glib and libsignonui. Server stores credentials in optionally encrypted database. It is running under different user id than applications. Application library accesses the storage over IPC mechanism.

Protocol Stack

Realtime communication framework connects to services using protocol plugins. Currently, XMPP/Jabber and SIP are the officially supported protocols. There’s also support for media extension of Jabber called Jingle. As described earlier, each of the protocol plugins create abstraction of some protocol to a common DBUS protocol.

GoogleTalk uses Jingle protocol to handle voice streaming.

Standard Jabber communication always goes through persistent TCP connection to the server. SIP protocol uses either UDP or TCP protocol for signaling. UDP is older and established method, while TCP is more recommended nowadays, mainly due to some particular message size and NAT traversal problems associated with UDP use. Together with SIP, standard RTP is always used for the media.