ITU-T Workshop on
“Interactions of Vocieband Signal processing
Functions and their End-to-End Coordination”
(Germantown, Maryland, USA.
21 April 2010)
Dynamic Coordination of Signal
Processing Functions Using
ITU-T Rec. G.799.2
Dominic Ho
Ericsson Canada Inc.
Mont-Royal, Quebec, Canada
International
Telecommunication
Union
Motivation
 Modern telephony networks uses voice-quality
enhancement (VQE) features, denoted as Signal Processing
Functions (SPFs), for optimum quality of experience
 For maximum effectiveness of VQE features it is necessary:
- To deploy all applicable VQE features
- To avoid multiple (tandem) application of the same feature
- To exercise the feature at the optimal location along the call
path
 The intent of ITU-T Rec. G.799.2 is to develop the
mechanism framework for the dynamic coordination of
VQEs present on bearer paths for the purpose of improving
overall end-to-end voice quality
International
Telecommunication
Union
2
SPE and SPF
Generic Call Connection:
SPE-1
SPE-2
SPE-3
SPE-0
SPE (Signal Processing Equipment)
AEC
G.160
NR
ALC
G.160
G.169
Network
Mobile
ALE
G.169
SPF (Signal Processing
Function):
• AEC
• ALC
• EC
• ALE
• NR
EC
G.168
International
Telecommunication
Union
3
Scope and Applicability of G.799.2
MSC-O
MGW-O
SC-T
Server
MSC-T
Server
MGW-T
SPNE-T
BSC-O
Circuit-Switched
network
IP packet network
Land
User
Mobile
Phone
G.799.2
Q.115.x
Media Path
Signalling Path
G.799.2 covers the coordination of SPFs in networkInternational
Telecommunication
Union
equipment and in terminal devices
4
Challenges in Mobility Communications




Dynamic SPF insertion/removal due to dynamic call
configuration and modification
Permutation of points of SPF deployment
Variety of topologies : inter-MSC, intra-MSC
Examples of Call Connection Cases:
– Mobile-land calls
– Mobile-mobile calls
– Mobile calls with handover
– Mobile calls with call transfer
– Landline calls transferred to mobile
- AEC
Acoustic
Echo
- AEC
- ALC
- ALE
- ALC
- EC
- ALE
- ALC
- EC
International
Hybrid
Telecommunication
Union Echo
5
Dynamic Coordination Mechanism

Dynamic coordination of SPF is achieved through:
– An encapsulation format (capability list) to facilitate
identification of SPF capabilities from different
equipment/devices in a dynamic manner
– Rules for exchange of capability lists among nodes
in a call-path, for SPF coordination in static and
dynamic call configurations
– SPF engagement rules executed by individual
equipment/devices based on common view of
capabilities available along a given bearer path
International
Telecommunication
Union
6
Capability List Format
7 6 5 4 3 2 1 0
V
F
N
Descriptions
Common Part
SPID
Length
Reserved
ID
Reserved
Len
Entry 1
Attribute
Reserved
ID
Reserved
Len
Entry 2
Attribute


SPF
ID
AEC
0001
ALC
0010
EC
0011
ALE
0100
NR
0101
Common part:
V (3 bits):
F (1 bit):
N (4 bits):
SPID (16 bits):
Length (8 bits):
Version number
Forward / Reverse flag
Number of entries
SPNE/device Identifier
Capability-list size in bytes (common + entries)
Entry part:
ID (4 bits):
Len (4 bits):
Attribute:
Reserved:
SPF entry identifier
Entry size in bytes, including the entry ID byte and the entry Len byte and the attribute bytes
Entry attribute information with zero, one or multiple bytes (To be defined)
International
Telecommunication
Reserved field with a value of 0x00
Union
7
Capability List Exchange
Forward
Capability
List
Received
Forward
Capability
List
Update
 Each entry(cell) corresponds to a
specific Signal Processing Function
 Signal Processing Function includes,
but is not limited to:
• Network Echo Cancellation (EC),
• Acoustic Echo Control (AEC),
• Automatic Level Control (ALC),
Signal Processing
Equipment(SPE)
Reverse
Capability
List
Update
• Noise Reduction (NR),
• Automatic Listener Enhancement
Signal Flow
Reverse
Capability
List
Received
(ALE)
 Capability List received is updated
with new information and sent to next
SPE, if necessary
 Each SPE enables or disables its
function based on Capability view, in
accordance with pre-determined
coordination rules
International
Telecommunication
Union
8
Example of Information Exchange
Forward and reverse capability lists for bear traffic
from left to Right
Forward Capability List
A1
A1
A1
A1
A1
A1
A1
B1
B1
B1
B1
B1
B1
B1
C2
C2
C2
C2
C2
Dn-1
Dn-1
Dn-1
SPE1
SPE2
…
SPEn-1
SPEn
An-1
An-1
An-1
An-1
An-1
Bn
Bn
Bn
Bn
Bn
Bn
Bn
Cn
Cn
Cn
Cn
Cn
Cn
Cn
Dn-1
Dn-1
Dn-1
Dn-1
Dn-1
Reverse Capability List
International
Telecommunication
Union
9
VQE Engagement Rules





AEC :
ALC :
EC :
ALE :
NR :
as
as
as
as
as
close
close
close
close
close
as
as
as
as
as
possible
possible
possible
possible
possible
to
to
to
to
to
the
the
the
the
the
source of acoustic echo
signal source
local loop
destination
signal source
Engagement example in mobile-land call (for bearer traffic from
left to right)
Acoustic
echo
Signal Processing
Functions
SPNE-1
SPNE-2
SPNE-3
Preferred Location for Signal Processing Functions
AEC
High Preference
Medium Preference
Low Preference
NR
High Preference
Medium Preference
Low Preference
ALE
Low Preference
Medium Preference
Telecommunication
High Preference
International
Union
10
Coordination Examples
International
Telecommunication
Union
11
VoIP Mobile-Mobile Call With Handover

Call flow:
- Mobile-mobile call between MS1 and MS2 via media gateways MG1 and MG2
- MS2 experiences a handover
- Mobile-mobile call between MS1 and MS2 via media gateways MG1 and MG3
MG2
ALE
Encoded speech from MS1
ALE
Dec
AEC
AEC
Enc
Dec
ALE
IP
Enc
ALE
MS1
AEC
Enc
AEC
Dec
MG1
Encoded speech to MS1
Enc: Low bit rate encoder
Dec: Low bit rate decoder
ALE: Automatic Listener Enhancement
ALC: Automatic Level Control
AEC: Acoustic Echo Control
MS2
MG3
International
Telecommunication
Union
12
SPF Coordination : Before Handover
For Traffic flow from MS1 to MS2



MG-1
- realizes that it is the first and last SPNE supporting AEC on MS-1MS-2 traffic
- realizes that it is the first SPNE supporting ALC but there is a FBALC downstream
on MS-1MS-2 traffic
MG-2
- realizes that there is an ALC upstream but it is the last one with FBALC on MS1MS-2 traffic
Coordination Outcome
- According to the preference rule, MG-2 continues FBALC support on MS-1MS-2
MG2
traffic, and MG-1 disables ALC on MS-1MS-2 traffic
ALE
ALE
Dec
AEC
AEC
Enc
Dec
ALE
IP
Enc
ALE
MS1
MG1
Enc: Low bit rate encoder
Dec: Low bit rate decoder
ALE: Automatic Listener Enhancement
ALC: Automatic Level Control
AEC: Acoustic Echo Control
AEC
Enc
AEC
Dec
MS2
MG3
International
Telecommunication
Union
13
SPF Coordination : After Handover
For Traffic flow from MS1 to MS2



MG1
- realizes that it is the first and last one with ALC, and it is the first but not the last
with AEC on MS1  MS2 traffic,
MG3
- realizes that there is an AEC upstream closer to the source on MS1  MS2 traffic
Coordination Outcome
- MG1 continues AEC support on MS1  MS2 traffic.
- MG1 dynamically re-enables ALC support on MS1  MS2 traffic.
- MG3 disables its AEC.
MG2
ALE
ALE
Dec
AEC
AEC
Enc
Dec
ALE
IP
Enc
ALE
MS1
MG1
Enc: Low bit rate encoder
Dec: Low bit rate decoder
ALE: Automatic Listener Enhancement
ALC: Automatic Level Control
AEC: Acoustic Echo Control
AEC
Enc
AEC
Dec
MS2
MG3
International
Telecommunication
Union
14
Generic Network Configuration
MSC-O
MGW-O
SC-T
Server
MSC-T
Server
MGW-T
SPNE-T
BSC-O
Circuit-Switched
network
IP packet network
Land
User
Mobile
Phone
G.799.2
Q.115.x
Media Path
Signalling Path
International
Telecommunication
Union
15
Coordination
Voice enhancement
processing functions
Acoustic Echo Control
(AEC)
Noise reduction (NR-O)
for media from the
mobile user
Echo Cancellation (EC)
for Sin from the land
user
Noise reduction (NR-T)
for media from the
land user
MS-O
MGW-O
MGW-T
SPNE-T
Tandem
(results)
Yes
Yes
No
No
Yes
Q115
Yes
Yes
No
No
Yes
G799.2
Enabled
Disabled
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Disabled
Yes
Enabled
Disabled
Disabled
Disabled
No
No
No
Yes
Yes
Yes
No
No
Disabled
Enabled
No
No
No
Disabled
Enabled
No
No
Yes
Yes
Yes
Yes
No
Yes
Disabled
Enabled
Yes
No
Disabled
Disabled
Enabled
No
(Dynamic coordination) G.799.2
International
Telecommunication
Union
16
Q.115.x（Call set-up)
Current Status & Future Plans
 G.799.2 has been approved as an ITU-T Recommendation
end of last year(12/09)
 G.799.2 contains the framework and mechanism for
dynamic coordination of SPF
 Development of protocols to implement G.799.2 will be in
separate ITU-T Recommendations
 SG16 is requesting SG11 and other SDOs for the guidance
on the available protocols, especially for wireless links
International
Telecommunication
Union
17