1. KT VoLTE status and commercial interconnected
ITU Workshop on “Voice and Video over LTE” Geneva, Switzerland, 1 December 2015
KT VoLTE status and commercial interconnected
VoLTE service in South Korea
June Young Jeon
Principal Research Engineer

2. Contents In
1. KT’s Business and Korean Market 2. Commercial Interconnected VoLTE Service 3. Achievements & Issues 4. Conclusion

3. KT: Corporate Profile Subsidiaries In
Established
December 10, 1981
Revenue
USD 23.4 Billion(2014)
Stock Listing
Korea, New York, London
No. of Employees
23,754(as of Sep. 2014)
Communications, IT Services, Media & Contents, Capital, Security
Subsidiaries
7 Subsidiaries(USA, China, Japan, etc.)
10 Offices
Overseas subsidiaries and offices
Fixed Phone
Broadband
Mobile
Pay-TV
17.3M (58.6%)
8.1M (42.4%)
17.2M (30.3%)
7.0M (25.1%)

4. Global Telecommunications Infrastructure Comparison
▣ The world’s highest level of broadband penetration rate
▣ Outstanding LTE connection and wireless penetration rate
Broadband Penetration rate
Time on LTE
Wireless Penetration rate
% of all households
Measures portion of time connected to LTE
Source: Open Signal, 2014
 Source: OECD Internet Economy Outlook 2013
 Source: OECD (2013)

5. Korean Market and KT’s market shareIn
▣ Wireline and wireless markets saturated, while Pay TV market is growing
▣ KT is leading wireline and Pay TV market, and is second in wireless market
Telecom Market Size Trend
KT‘s Market Share (as of Feb 2015)
Growth rate of Wireless (2%) and Wireline (2%) implies market saturation
Pay TV growing most rapidly: 19%
Wireline: 42% (1st)
Wireless: 30.4% (2nd)
Pay TV: 28.6% (1st)
- Rolled out VoLTE service(Oct, 2012)
- Supporting UICC portability between mobile operators(From Jul, 2014)
- Launched VoLTE international roaming service with NTT DoCoMo(Oct, 2015)
- Completed Nation-wide VoLTE Interoperability (Oct, 2015)
(Unit: mil.)

6. Contents In
1. KT’s Business and Korean Market 2. Commercial Interconnected VoLTE Service 3. Achievements & Issues 4. Conclusion

7. World’s 1st commercial Interconnected VoLTE Service
▣ Commercial Rollout (Jun. 2015)
South Korea’s mobile network operators announced the commercial interconnected VoLTE service
GSMA Awards Certificate of Special Recognition for Launch of World’s
First Commercial Interconnected VoLTE Service in South Korea

8. Legacy Interworking Architecture
SKT Network
KT Network
MGCF
IMS
Legacy
Circuit
UE-B
MGW
EPC/
E-UTRAN
HSS
TAS
MME
PCRF
CSCF
BGCF
MGCF
UE-A
LGUplus Network
E-UTRAN
SGW
PGW
MGW
Legacy
Circuit
MGCF
IMS
UE-C
MGW
EPC/
E-UTRAN
Control Plane(SIP)
User Plane(RTP media)

9. Dedicated Working Group
▣ TTA-WG9102 : VoLTE interworking specification between Korean MNOs
ㆍMembers
TTA(Telecommunications Technology Association), KT, SKT, LG Uplus
ㆍPeriod ~
ㆍPurpose: to complete core protocols and transmission specifications
call flow (ex, video announcement, ring back tone, early-session)
SIP header, Reason header, SDP parameter, SIP numbering plan
codec, response code, session timer
device capability of voice-video switching
IBCF requirements for interworking
* TTA-WG9101: Specification of VoLTE Terminal for UICC Portability between Mobile Operators
* TTA-WG9103: Rich Communication Suite(RCS) Interworking Specification for Mobile Network Operator

10. Evolution of Interworking Architecture
KT Network
Other Networks
HSS
TAS
MME
PCRF
CSCF
BGCF
MGCF
MGCF
IMS
UE-A
Legacy
Circuit
UE-B
E-UTRAN
SGW
PGW
MGW
MGW
EPC/
E-UTRAN
KT Network
Other Networks
HSS
TAS
ENUM
MME
PCRF
CSCF
IBCF
IBCF
IMS
UE-A
UE-B
E-UTRAN
SGW
PGW
TrGW
TrGW
EPC/
E-UTRAN
Control Plane(SIP)
User Plane(RTP media)

11. Practical Implementation
▣ Standard : IR Interworking
Routing of SIP signalling over the IMS NNI requires use of SIP URIs.
Session requests based upon E.164 format Public User Identities require conversion into an NNI routable SIP URI format.
▣ Implementation in Korea : Routing in TEL URI format
The Absence of Tier 1 ENUM causes a branch at terminating network
KT Network
Other Networks
other
ENUM
Query : B
 SIP URI
kt ENUM
NPDB
Query : B
 Routing Number ① ③
MGCF ②
INVITE in TEL URI Format
CSCF
IBCF
IBCF
CSCF

12. Contents In
1. KT’s Business and Korean Market 2. Commercial Interconnected VoLTE Service 3. Achievements & Issues 4. Conclusion

13. Process of Service Interconnection
6th stage
3.8 million
12th stage
20 million
18th stage
55 million
Interworking Test
Trial Service
Commercialization
‘15.05
‘15.07
‘15.08
‘15.10
▣ Milestones
`15.05~`15.07
- User device / network / charging test in commercial network
`15.07~`15.07
- Trial service(50 subscribers for each operator)
`15.08~`15.10
- Migration of 55 million subscribers on a stage-by-stage basis

14. Achievements ▣ Switching Interconnection Traffic – Circuit to Packet
MGCF
IBCF
With the vitalization of VoLTE services, other various supplementary services are expected to be provided creating benefits for both users and operators as listed below;
- User side: high-quality voice/video call, etc.
- Operator side: increase in subscribers, revenue, and efficiency of network resource usage.
▣ Enriching customer experience
- Seamless switch between voice and video, faster connection speeds
Media Type
VoLTE 3G
Voice
Wideband (HD Voice)
Narrowband
Video
VGA (480 X 640)
QCIF (176 X 144)

15. Interworking Issues in Commercialization Stage
▣ End-to-End codec negotiation and media connection issues
- Operator specific UE Spec
RTP
- RTP timeout
Media
- one-way call
SIP Header
- Header matching error
SDP
- Parameter processing error
SDP
(6%)
SIP header
(15%)
통신사별 독자 단말규격으로 E2E 코덱협상 실패 및 미디어연결 이슈 발생
임시방안 : CS망 우회 라우팅
조치방안 : 단말 보완, IBCF/TrGW 정합기능 추가
UNI 규격 협의 이전의 단말과 이후의 단말
to IBCF’s malfunction
RTP
(35%)
Media
(18%)

16. Contents In
1. KT’s Business and Korean Market 2. Commercial Interconnected VoLTE Service 3. Achievements & Issues 4. Conclusion

17. Conclusion ConclusionIn
▣ Summary
- Forming a dedicated working group in 2012
- Rolling out the commercial interconnected VoLTE service in 2015
- Providing HD-Voice and Video interconnection service
Need a long time for interoperability test
Call quality degradation due to E2E codec negotiation directly
Ex) on Jan, 2015, We tested VoLTE roaming services between KT and CMCC through RAVEL, but couldn’t make a video call because of having no transcoding node.
The direct interworking is impossible due to a difference portrait/landscape ,although the both of KT and CMCC’s devices are supported of all codecs.(VGA, H.264 etc.)
▣ Considerations
- Transcoding overhead for existing operator-specific terminal
- Further discussion on UNI specifications in detail
- Global E-NUM for international interworking