Service Interface for Real Time Information
CEN/TS 15531  (prCEN/TS-OO278181 )

 Overview

What Services Does SIRI provide

SIRI is made up of a number of functional services. Click on the images to see.

 Functional Services    Ancillary Services

What is SIRI for?

SIRI allows pairs of server computers to exchange structured real-time information about schedules, vehicles, and connections, together with general informational messages related to the operation of the services. The information  can be used  for many different purposes, for example:

  • To provide real time-departure from stop information for display on stops, internet and mobile delivery systems.
  • To provide real-time progress information about individual vehicles.
  • To manage the movement of buses roaming between areas covered by different servers.
  • To manage the synchronisation of guaranteed connections between fetcher and feeder services.
  • To exchange planned and real-time timetable updates.
  • To distribute status messages about the operation of the services.
  • To provide performance information to operational history and other management systems

How is Siri used?

Each system wishing to exchange information implements the SIRI protocols as XML services.

SIRI comprises a general communications architecture, and a number of specific services which operate within that architecture. The communications architecture supports two different patterns of interchange.

  • A synchronous request/response protocol: each exchange of data consists of a request message from a client consumer, and a response message from a producer server.
  • An asynchronous subscribe/publish protocol: the  client subscribes to information by sending a message to the server containing both request information, and sensitivity criteria with which to filter messages. The producer server establishes a subscription for the consumer and will send messages back to the consumer whenever the criteria are satisfied, until the subscription ends.  This pattern is 'stateful', that is to say, both parties in the interaction must manage the use of subscriptions that persist over time through successive interactions.

In both cases messages consist of XML documents, whose tags and content  are exactly specified by the SIRI XML Schemas.

SIRI allows implementers to make different tradeoffs as to message size, use of bandwidth, frequency of update, verbosity of data, sensitivity to change, etc.  This is reflected in particular in support for two different patterns of message exchange to return data from a producer server to a consumer client.

  • A direct delivery protocol: the data returned in response to a request or subscription consists of a single delivery message, sent directly from the producer server to a client consumer.
  • A fetched delivery protocol: the data returned in response to a request or subscription is delivered through an exchange of messages, comprising a notification from the producer server to a client consumer, followed by a request / response interaction from the consumer to the client to fetch the actual payload data. This is also a stateful pattern of communication.

SIRI also has protocols to monitor the system status.

What Can be Exchanged?

SIRI comprises eight different concrete services, each consisting of request and delivery message pairs, and all using a common architecture, terminology, reference data.

  • Production Timetable Service: Supports the dynamic exchange of planned schedules, including updates. These may be used by AVMS systems to predict and monitor vehicle progress.
  • Estimated Timetable Service: Supports the exchange of  target schedules in real time, including updates. These may be used by AVMS systems to predict and monitor vehicle progress.
  • Stop Timetable Service: Provides information about schedules for arrivals and departures at a Stop point.
  • Stop Monitoring Service: Provides information about arrivals and departures at a Monitoring, i.e. Stop point.
  • Vehicle Monitoring Service: Provides information about the movement of a vehicle, and its progress against the target schedule.
  • Connection Timetable Service: Provides information about schedules for for interchanges at a connection point.
  • Connection Monitoring Service: Provides information for interchanges at a connection point  to support guaranteed connection services
  • General Message Service: Supports the exchange of  general messages. 

On what standards is SIRI based?

SIRI is built on other Standards, in line with normal CEN practice .

The primary standard is  Transmodel

Siri has been evolved from a number of National standards, notably VDV 454, VDV453, Trident and RTIGXML  

Who uses SIRI?

SIRI is supported by many real-time and passenger information supplierts and is ised in Europe and else where. See  iImplementations.

Futhermore SIRI breakls down into two components: a general framwork and a set of servcies. The general framwork has been used by other standards such as UTMC XML

What Features does Siri lack?

Version 1.0 of SIRI contains only a basic set of services. 

It has a modular structure and additional services can be added in future.

A Facility monitoring  and a Situation Exchaneg version wer added ion 1.3

Further services already being considered include Control action,

Compliance levels

SIRI includes a wide range of optional features. Each option capability is named. Individual companies may choose to mandate a particular set of features as their choice  

How is the Schema Managed?

SIRI is managed by a CEN Working Group -  TC278 WG3 SG7. The group decides what changes shoudl be added.  A ssytematic versioingf system is needed. The original version (1.0) is kept stable and unchanged from teh STandard as issued. A Working  version is kept with subsequent fixes or minor changes to facilitate implementation. Currently the latest fixed version is 1.3. A new open version 1.4a is available.  A revision of SIRI will be undertaken in 2011/2012.