Developer:LPEC

Introduction

Linn's UPnP products can be controlled over a home network in an ever increaing number of ways. The primary means of control is, of course, UPnP itself, which subdivides product control into smaller units called services. A DS product, for instance, will provide some standard UPnP AV services:

• AVTransport
• RenderingControl
  
• ConnectionManager
  

and additional Linn-specific services, such as:

• Ds
  
• Volkano
  
• Product
  
• Ui
  

It is possible in Bute and later software releases to control a Linn UPnP product using an alternative mechanism known as the Linn Protocol for Eventing and Control.

This is a basic Telnet-like protocol, which relies on the developer knowing in advance, or having discovered by some means, the TCP/IP of the device to be controlled. Knowing this, LPEC can be accessed by creating a raw socket session to port 23 of the device.

The rest of this document describes the format of the messages that LPEC expects and delivers.

Control

Each service contains actions, which are like methods that can be called on the device with input and output arguments.

An action can be perfomed by sending a message of the following form:

ACTION [id]/[type] [version] [action] "[inarg1]" "[inarg2]" ... "[inargn]"

e.g.

ACTION MediaRenderer/RenderingControl 1 SetVolume "0" "Master" "50"

All messages sent using LPEC get a response. The response to an ACTION message will be a RESPONSE message that reports the values of all the output arguments:

RESPONSE "[outarg1]" "[outarg2]" ... "[inargn]"

The SetVolume example given above has no output arguments, so the message received will simply be a <CR><LF> terminated RESPONSE message.

The following subsequent interaction better illustrates the RESPONSE message:

ACTION MediaRenderer/RenderingControl 1 GetVolume "0" "Master"

RESPONSE "50"

It should be mentioned that all input and output arguments are escaped according to XML escaping rules and enclosed in double-quotes.

Discovery

Although LPEC does not include a mechanism for discovering devices across a home network, it does contain a mechanism for knowing about the sub-devices within a single product.

When an LPEC connection is made the device sends ALIVE messages to describe thesub-devices that are currently available:

<code>ALIVE <id> <udn></code>

e.g.

<code>ALIVE Ds 4c494e4e-0050-c221-71e5-df000003013f</code>
<code>ALIVE Preamp 4c494e4e-0050-c221-71e5-df0000030133</code>
<code>ALIVE MediaRenderer 4c494e4e-0050-c221-71e5-df0000030171</code>