ETSI TS 103 544-3 V1.3.1 (2019-10)

Publicly Available Specification (PAS); Intelligent Transport Systems (ITS); MirrorLink®; Part 3: Audio

RTS/ITS-98-3

General Information

• Status: Published
• Publication Date: 08-Oct-2019
• Technical Committee: ITS - Intelligent Transport Systems
• Current Stage: 12 - Completion
• Due Date: 30-Sep-2019
• Completion Date: 09-Oct-2019

Standards Content (Sample)

ETSI TS 103 544-3 V1.3.1 (2019-10)






TECHNICAL SPECIFICATION
Publicly Available Specification (PAS);
Intelligent Transport Systems (ITS);
®
MirrorLink ;
Part 3: Audio
CAUTION
The present document has been submitted to ETSI as a PAS produced by CCC and
approved by the ETSI Technical Committee Intelligent Transport Systems (ITS).
CCC is owner of the copyright of the document CCC-TS-012 and/or had all relevant rights and had assigned said rights to
ETSI on an "as is basis". Consequently, to the fullest extent permitted by law, ETSI disclaims all warranties whether express,
implied, statutory or otherwise including but not limited to merchantability, non-infringement of any intellectual property rights of
third parties. No warranty is given about the accuracy and the completeness of the content of the present document.

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2 ETSI TS 103 544-3 V1.3.1 (2019-10)



Reference
RTS/ITS-98-3
Keywords
interface, ITS, PAS, smartphone

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©ETSI 2019.
© Car Connectivity Consortium 2011-2019.
All rights reserved.
ETSI logo is a Trade Mark of ETSI registered for the benefit of its Members.
MirrorLink® is a registered trademark of Car Connectivity Consortium LLC.
RFB® and VNC® are registered trademarks of RealVNC Ltd.
UPnP® is a registered trademark of Open Connectivity Foundation, Inc.
Other names or abbreviations used in the present document may be trademarks of their respective owners.
DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its Members.

3GPP™ and LTE™ are trademarks of ETSI registered for the benefit of its Members and
of the 3GPP Organizational Partners.
oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and
of the oneM2M Partners.
®
GSM and the GSM logo are trademarks registered and owned by the GSM Association.
ETSI

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3 ETSI TS 103 544-3 V1.3.1 (2019-10)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 7
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 7
3.3 Abbreviations . 7
4 Introduction . 8
5 Audio Link Options . 9
6 Audio Link Selection. 13
6.1 General . 13
6.2 Identification of Available Audio Links . 13
6.3 LaunchApplication (AppID, ProfileID) . 13
6.4 TerminateApplication (AppID, ProfileID) . 14
6.5 GetApplicationStatus (AppID, ProfileID) . 15
7 RTP Audio Streaming . 16
7.1 General . 16
7.2 RTP Packet Structure and Header Definition . 16
7.3 RTP Audio Payload Definition . 19
7.3.1 General . 19
7.3.2 48 kHz, 16 Bit Audio Payload (Mono) . 19
7.3.3 48 kHz, 16 Bit Audio Payload (Stereo) . 20
7.3.4 16 kHz, 16 Bit Audio Payload (Mono) . 21
7.4 Establishing the RTP Connection . 21
7.4.1 General . 21
7.4.2 RTP Server within MirrorLink Server . 21
7.4.3 RTP Server within MirrorLink Client . 22
7.5 Client and Server Implementation . 22
8 Voice Command Handling . 24
8.1 General . 24
8.2 VC over RTP with an Established VNC Session . 25
8.3 VC over RTP with an Established WFD Session . 29
8.4 VC over RTP without a VNC/WFD Sessio n . 29
8.5 VC over Bluetooth HFP BVRA . 29
9 Interoperability with Bluetooth . 29
9.1 General . 29
9.2 Bluetooth Profiles relevant for MirrorLink . 30
9.3 Interoperability States - MirrorLink Server Perspective . 30
9.4 Interoperability States - MirrorLink Client Perspective . 32
10 Audio Signal Processing Configuration . 33
10.1 Conversational and Telephony-based Audio . 33
10.2 Bluetooth HFP Noise Reduction/Echo Cancellation . 34
10.3 RTP-based Conversational Audio . 34
10.4 RTP-based Voice Command Audio . 34
11 Latency Switching Sources . 34
11.1 General . 34
ETSI

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4 ETSI TS 103 544-3 V1.3.1 (2019-10)
11.2 Protocol Behaviour of Latency Switching Sources . 34
11.3 Timing Behaviour of Latency Switching Sources . 35
11.4 Use Cases for Latency Switched Sources . 36
11.5 Backward Compatibility of Latency Switched Sources . 38
Annex A (informative): Authors and Contributors . 39
History . 40


ETSI

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5 ETSI TS 103 544-3 V1.3.1 (2019-10)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Intelligent Transport Systems
(ITS).
The present document is part 3 of a multi-part deliverable. Full details of the entire series can be found in part 1 [i.1].
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI

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6 ETSI TS 103 544-3 V1.3.1 (2019-10)
1 Scope
®
The present document is part of the MirrorLink specification which specifies an interface for enabling remote user
interaction of a mobile device via another device. The present document is written having a vehicle head-unit to interact
with the mobile device in mind, but it will similarly apply for other devices, which provide a color display, audio
input/output and user input mechanisms.
The present document defines the MirrorLink Audio architecture, based on an RTP forward and back channel, plus an
possible Bluetooth HFP and A2DP setup.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long-term validity.
The following referenced documents are necessary for the application of the present document.
[1] IETF RFC 3550: "RTP: A Transport Protocol for Real-Time Applications", July 2003.
NOTE: Available at http://tools.ietf.org/html/rfc3550.
[2] Bluetooth Specification: "Hands-free Profile", Audio, Telephony, and Automotive Working
Group, Revision 1.7.2, January 21, 2019.
NOTE: Available at https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=457090.
[3] Bluetooth Specification: "Headset Profile", Car Working Group, Revision V12r00, December 18,
2008.
NOTE: Available at https://www.bluetooth.org/DocMan/handlers/DownloadDoc.ashx?doc_id=158743.
[4] Bluetooth Specification: "Advanced Audio Distribution Profile", Audio, Telephony, and
Automotive Working Group, Revision 1.3.2, January 21, 2019.
NOTE: Available at https://www.bluetooth.org/docman/handlers/downloaddoc.ashx?doc_id=457083.
[5] IETF RFC 2190: "RTP Payload Format for H.263 Video Streams", September 1997.
NOTE: Available at http://tools.ietf.org/html/rfc2190.
[6] IETF RFC 3551: "RTP Profile for Audio and Video Conferences with Minimal Control", July
2003.
NOTE: Available at http://tools.ietf.org/html/rfc3551.
[7] ETSI TS 103 544-12 (V1.3.1): "Intelligent Transport Systems (ITS); MirrorLink®; Part 12: UPnP
Server Device".
[8] ETSI TS 103 544-9 (V1.3.1): "Publicly Available Specification (PAS); Intelligent Transport
Systems (ITS); MirrorLink®; Part 9: UPnP Application Server Service".
[9] ETSI TS 103 544-10 (V1.3.1): "Publicly Available Specification (PAS); Intelligent Transport
Systems (ITS); MirrorLink®; Part 10: UPnP Client Profile Service".
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7 ETSI TS 103 544-3 V1.3.1 (2019-10)
[10] ETSI TS 103 544-15 (V1.3.1): "Publicly Available Specification (PAS); Intelligent Transport
Systems (ITS); MirrorLink® ; Part 15: Application Programming Interface (API) Level 1 & 2".
[11] ETSI TS 103 544-2 (V1.3.1): "Publicly Available Specification (PAS); Intelligent Transport
Systems (ITS); MirrorLink® ; Part 2: Virtual Network Computing (VNC) based Display and
Control".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long-term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TS 103 544-1 (V1.3.1): "Publicly Available Specification (PAS); Intelligent Transport
Systems (ITS); MirrorLink®; Part 1: Connectivity".
[i.2] ITU-T Recommendation G.114 (05/2003): "One-way transmission time", May 6, 2003.
NOTE: Available at https://www.itu.int/rec/T-REC-G.114-200305-I/en.
[i.3] ITU-T Recommendation P.1100 (03/2017): "Narrowband hands-free communication in motor
vehicles", March 1, 2017.
NOTE: Available at https://www.itu.int/rec/T-REC-P.1100-201703-S/en.
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the following terms apply:
pointer event: touch screen action in which the user touches the screen with one (virtual) finger only at a single
location
touch event: touch screen action in which the user touches the screen with two or more separate fingers at different
locations
NOTE: Touch events are used to describe more complex touch action, like pinch-open or pinch-close.
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
A2DP Bluetooth Advanced Audio Distribution Profile
API Application Programming Interface
BT Bluetooth
BTA2DP Bluetooth Advanced Audio Distribution Profile
BTHFP Bluetooth Hands Free Profile
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8 ETSI TS 103 544-3 V1.3.1 (2019-10)
BVRA Bluetooth Voice Recognition Activation
CC CSRC Count
CE Consumer Electronics
NOTE: CE devices are referred to as mobile devices within the present document.
CSRC Contributing SouRCe
HFP Bluetooth Hands-free Profile
HS Head-Set
HSP Bluetooth Headset Profile
HU Head-Unit
NOTE: This term is used interchangeably with the MirrorLink Client.
IOP InterOPerability
IP Internet Protocol
IPL Initial Playback Latency
LSS Latency Switching Sources
MAC Mediaum Access Control
ML MirrorLink
MPL Maximum Playback Latency
PT Payload Type
RFB Remote Framebuffer
RTP Real-time Transport Protocol
SCO Synchronous Connection-Oriented
SOAP Simple Object Access Protocol
SSRC Synchronization SouRCe
UDP User Datagram Protocol
UI User Interface
UIBC User Interface Back Channel
UPnP Universal Plug and Play
URI Uniform Resource Identifier
VC Voice Control
VNC Virtual Network Computing
WFD Wi-Fi Display
XML eXtensible Markup Language
4 Introduction
The present document defines how the MirrorLink Client selects the transport media that the MirrorLink Server shall
use to route audio streams. The MirrorLink Server distinguishes between two audio streams, namely phone and
application audio. It advertises available transport options, using UPnP TmServerDevice:1 services. Audio streams are
specified for the following remote access protocols:
• RTP Real-Time Transport Protocol
• BTA2DP Bluetooth Advanced Audio Distribution Profile
• BTHFP Bluetooth Hands Free Profile
It is the MirrorLink Client's responsibility to select from the advertised audio transport mechanisms how the MirrorLink
Server shall stream the different audio sources. The audio link selection is done according the following priorities
(highest priority first):
1) Keep existing Bluetooth HFP or A2DP connection to another external device, which is not a MirrorLink
Client, if overriding the resource assignment is not allowed.
2) Follow audio link selection using the mechanism described in this clause.
3) Manual Bluetooth pairing (same behaviour as in non-MirrorLink use cases).
MirrorLink Server's speaker shall not be used for audio output.
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9 ETSI TS 103 544-3 V1.3.1 (2019-10)
MirrorLink Server's microphone shall not be used, for voice input if the MirrorLink Client indicates support for voice
command within its UPnP Client Profile.
The present document allows for different transport mechanisms based on the selections the MirrorLink Client has
taken.
The MirrorLink audio architecture, as shown in Figure 1, allows using the Real-time Transport Protocol for streaming
audio captured from the mobile device, to the MirrorLink Client. The audio output from the mobile device is streamed
in an application agnostic manner so that it does not require re-design or modification of existing applications running
on the device.
Audio Audio Audio Speaker Audio
Server Client & Micro
Client Server
Consumer
Automotive
Electronics
Head Unit
Device
Audio / Voice

Figure 1: Audio Setup
The present document covers both audio output from and audio input to the MirrorLink Server device. Unless otherwise
stated, the present document applies for the audio server and the audio client in the same way:
• The audio output will be handled from the audio server on the MirrorLink Server and the audio client on the
MirrorLink Client.
• The audio input will be handled from the audio client on the MirrorLink Server and the audio server on the
MirrorLink Client.
In addition to RTP, the MirrorLink specification allows regular Bluetooth audio connectivity for both phone and media
audio streams.
5 Audio Link Options
MirrorLink allows the MirrorLink Client and Server to use the following audio features:
• Media - Streaming of media audio from the MirrorLink Server to the MirrorLink Client; media audio feature
includes navigation audio.
• Phone - Bidirectional streaming of conversational audio, including in-band ringing.
• VC - Streaming of voice command (VC) audio from the MirrorLink Client to the MirrorLink Server.
The above listed audio features are available over the following connectivity options:
• Bluetooth (BT).
• RTP.
The MirrorLink Server shall advertise the audio features and connectivity options it supports within the UPnP
A_ARG_TYPE_AppList application listings. The MirrorLink Server shall advertise individual audio components, with
all combinations of the supported audio content categories.
EXAMPLE: If the MirrorLink supports an RTP Server for Media and Phone Audio, it shall advertise three RTP
Servers, one showing Media, one Phone, and one Media & Phone support.
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10 ETSI TS 103 544-3 V1.3.1 (2019-10)
This will allow the MirrorLink Client to specifically inform the MirrorLink Server, which feature it is going to use. The
possible audio content categories for the different audio components are listed below:
• RTP Client: Phone Audio, Voice Command In, Phone Audio + Voice Command In.
• RTP Server: Media Audio Out, Phone Audio + Media Audio Out.
• BT A2DP: Media Audio Out.
• BT HFP: Phone Audio, Phone Audio + Voice Command In.
The MirrorLink Server shall include the RTP Server with a value of audioInfo@contentCategory equaling Media
Audio Out (0x01) first in the list of advertised RTP Servers for the same RTP payload types
(A_ARG_TYPE_AppList).
If the MirrorLink Server supports Voice Command over RTP, it shall include the RTP Client with a value of
audioInfo@contentCategory equaling Voice Command In (0x10) first in the list of advertised RTP Clients for
the same RTP payload types (A_ARG_TYPE_AppList).
The MirrorLink Client shall select the audio features and their connectivity option, which the MirrorLink Client is
going to use. The MirrorLink Client shall use the UPnP Application Server service's Launch Application action to
inform the MirrorLink Sever about its selection. The MirrorLink Client shall not launch more than one RTP Client,
RTP Server, BT HFP, and BT A2DP component.
Based on the set of audio components, launched from the MirrorLink Client, the MirrorLink Server and Client shall use
specific audio links for Media, Phone and Voice Command use cases. Table 1 lists the possible combinations of audio
features and their underlying connectivity options on the left side. For each combination, the required audio components
are listed, which shall be launched from the MirrorLink Client to enable it. Note, that some Audio Feature Set
combinations are not possible. The below table shall not be used in case a WFD session, introduced in MirrorLink 1.2,
is established.
Table 1: UPnP Negotiation for Audio Selection (Non-WFD Case)
Audio Feature Combinations and Audio Components launched from the MirrorLink Client to
underlying Connectivity enable the Audio Feature Combination
Media Phone VC BT HFP BT A2DP RTP Server RTP Client
- - - - - - -
- - RTP - - - VC
- - BT Not possible
- RTP - - - Phone Phone
- RTP RTP - - Phone Phone + VC
- RTP BT Not possible
- BT - Phone - - -
- BT RTP Phone - - VC
- BT BT Phone + VC - - -
RTP - - - - Media -
RTP - RTP - - Media VC
RTP - BT Not possible
RTP RTP - - - Phone + Media Phone
RTP RTP RTP - - Phone + Media Phone + VC
RTP RTP BT Not possible
RTP BT - Phone - Media -
RTP BT RTP Phone - Media VC
RTP BT BT Phone + VC - Media -
BT - - - Media - -
BT - RTP - Media - VC
BT - BT Not possible
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11 ETSI TS 103 544-3 V1.3.1 (2019-10)
Audio Feature Combinations and Audio Components launched from the MirrorLink Client to
underlying Connectivity enable the Audio Feature Combination
Media Phone VC BT HFP BT A2DP RTP Server RTP Client
BT RTP - - Media Phone Phone
BT RTP RTP - Media Phone Phone + VC
BT RTP BT Not possible
BT BT - Phone Media - -
BT BT RTP Phone Media - VC
BT BT BT Phone + VC Media - -

NOTE: Entries marked as Not possible in these tables are meant to describe combinations, which are out of
scope from the MirrorLink specification. Behaviour, if supported, is implementation dependent. Entries
should not be used.
BT HFP and BT A2DP may be connected outside the MirrorLink session, i.e. without specifically using the UPnP
mechanisms to launch those. In that case the MirrorLink Client and Server shall make the selection based on the
following table. Components marked with Legacy shall not be launched using the UPnP TmApplicationServer
service's LaunchApplication action. The setup of the legacy Bluetooth connection is outside the scope of the MirrorLink
specifications. The below table shall not be used in case a WFD session, introduced in MirrorLink 1.2, is established.
Table 2: UPnP Negotiation for Audio Selection with Legacy Bluetooth (Non-WFD Case)
Audio Feature Set and underlying Audio Components launched from the MirrorLink Client to
Connectivity enable the Audio Feature Set
Media Phone VC BT HFP BT A2DP RTP Server RTP Client
- BT - Legacy - - -
- BT RTP Legacy - - VC
- BT BT Legacy - - -
RTP BT - Legacy - Media -
RTP BT RTP Legacy - Media VC
RTP BT BT Legacy - Media -
BT - - - Legacy - -
BT - RTP - Legacy - VC
BT - BT Not possible
BT RTP - - Legacy Phone Phone
BT RTP RTP - Legacy Phone Phone + VC
BT RTP BT Not possible
BT BT - Legacy Legacy - -
BT BT RTP Legacy Legacy - VC
BT BT BT Legacy Legacy - -

If an audio use feature is not covered from the audio component selection, done by the MirrorLink Client, the
MirrorLink Server shall fallback to its default configuration.
MirrorLink 1.2 introduces Wi-Fi Display (WFD) based audio/video streaming for MirrorLink. The use of WFD
removes the need to setup a separate RTP forward channel to carry media audio. The MirrorLink Server shall stream
media audio via WFD RTP streaming.
ETSI

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