Vo LT E
Ke
y
Te c
hn
ol
og
y
Sh
Digitization of Speech Signals Signal
Signal
6 7 8 9 10 1 2 3 4 5
4
4 3 2 1
Time
2
2
Time
-1 -2 -3 -4
Sampling: Obtaining discrete PAM signal samples from continuous signals at a specified time interval
4
4
2
-2 …
0010 0100 0100 0010 1010 …
-2 -4
Quantizing: Rounding off infinite values of PAM signal samples to a finite set of values
Coding: Converting quantized signal samples to binary digit streams of fixed length
00100100001001000010010 100100 0 … Deco 0 0 … ding
ing
Cod
Digital transmission provides high reliability, low interference, and enhanced security.
Voice quality deteriorates.
Voice quality deteriorates.
Common Speech Codecs G.711 G.722 G.723.1 …
Provides good QoS. Implements stable transmission. Requires high bandwidth.
3GPP
GSM HR GSM FR GSM EFR
Requires low bandwidth. Cannot adjust codec rates based on bandwidth.
3GPP
HR AMR FR AMR UMTS AMR UMTS AMR2
Adjusts codec rates based on bandwidth.
ITU-T
G.722.2
3GPP
UMTS AMR-WB FR AMR-WB …
ITU-T
Provides good QoS. Requires high bandwidth.
Codec Negotiation After codec negotiation, the preferred codec is used between two NEs, improving voice quality.
Codec negotiation
Reduced transmission delay
Improved QoS and codec conversion-free
Reduced CPU usage, and codec conversion-free
Analog signals
Reduced link resource usage
Compress speech signals.
Coding/Decoding
Compress speech signals.
G.711
Coding/Decoding
Coding/Decoding
Analog signals
Coding/Decoding
Key NEs in Codec Negotiation Performs GSM codec negotiation and conversion with the IM-MGW during LTE-CS calls.
Provides services for CS subscribers.
MGCF
MSC server
IMS Core
Performs non-GSM codec negotiation and conversion during LTE-CS calls and eSRVCC handovers.
SRVCC IWF Performs codec negotiation and conversion with the SBC functioning as the ATCF/ATGW during eSRVCC handovers.
SBC
IM-MGW
MGW
EPC
LTE
2G/3G
Codec Negotiation Flow Codec negotiation flow during an LTE-to-CS call Codecs supported by UE_A (contained in an INVITE message)
SBC INVITE
1
2
Codecs supported by the local MSC server (configured using ADD TCCAP)
3
1
3
4
Ⅰ
183 The IMS core does not perform codec negotiation.
IMS core INVITE
2
183
1
2
3
INVITE
Codecs contained in the incoming INVITE message
MGCF/ IM-MGW
1
2
Codecs supported by the local MSC server (configured using ADD MGW)
5
3
4
3
2
Ⅱ
IAM
APM
2
Codecs supported by the local MSC server (configured using ADD MGW)
3
IAM Ⅲ
MSC server/ MGW
Codecs contained in the incoming 2 IAM message
4
2
NEs participating in codec negotiation
3
2
Codecs supported by the RNC (configured using ADD RNC)
2
1
Ⅳ
Codec lists based on which the common codecs are ordered
3
3
5
3
2
3
4
Codecs supported by UE_B (contained in a Call Confirmed message)
The preferred codec 2 is selected for bearer establishment.
4
3
2
TC Support A transcoder (TC) is used when the sending and receiving ends of a call cannot use the same codec. The system supports three types of TC: ordinary TC, Gigabit Ethernet transcoder (GETC), and frame process transcoder (FPTC). A GETC consists of two ordinary TCs. 1
2
TC
TDM
11
FR
G.7
TC
TDM
11 G.7
G.711
I P
I P
Converts codecs between G.711 over TDM and a compressed speech codec over IP (FR, HR, or EFR)
Converts codecs from G.711 over TDM to G.711 over IP
3
4
GETC
HR
T C
FR
Converts between different compressed speech codecs.
5
C
G.711
I P
T
T C
11 G.7
I P
Converts between G.711 codecs with different parameter settings (ptime, for example).
C
T C
FR I P
Converts between codecs of the same type but with different or incompatible rate sets.
6
GETC 11 G.7
FR I P
I P
T
G.711
C
G.711
I P
T
GETC
FPTC
BICC
SIP
Converts UP headers and frame formats.
Next issue
Key Features – eSRVCC Solution Brief introduction The LTE network at the initial phase covers only hotspots and is limited in continuous coverage. When a subscriber moves from an LTE network to a 2G/3G network during an active call, the call is interrupted. The eSRVCC solution has been introduced to address this issue. Prepared by: Guan Hougang (content), Tang Suwen (figures)
Core Network Documentation Dept. Copyright © Huawei Technologies Co., Ltd. 2015. All rights reserved.
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