Testing Voice over LTE (VoLTE) on your device. January 2016 Sandy Fraser

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Wendy Lindsey
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1 Testing Voice over LTE (VoLTE) on your device January 2016 Sandy Fraser

2 Agenda Page 2 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WiFi Calling, EVS

3 Agenda Page 3 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WiFi Calling, EVS

4 IMS - IP Multimedia Subsystem how it all began 3GPP defined IMS in 1999 IMS as the framework for delivery of multimedia services was standardized in 3GPP rel.5 for delivery of Internet services on GPRS. This was updated and extended to CDMA and WLAN. In 2009 a group of over 40 organizations, operators, vendors etc. came together to form One Voice, whose aim was essentially to decide or drive the method of voice delivery on LTE through IMS. GSMA finally adopted VoLTE in 2010, and so did many of the industry big companies The first use of IMS through the Verizon LTE network in the USA accelerated the use of IMS development for mobile devices. Page 4

5 Support for Voice with LTE 2G/3G Circuit Switched calls have an allocated resource even during times of inactivity - even when nothing is being said Inefficient use of available bandwidth Access times between requesting resource and being able to talk were too slow to enable a reaction based allocation plus reduced flexibility for resource allocation An LTE UE will generally only be provided resources when it is necessary even for voice Allows efficient use of network resources. If we are saying nothing we will require no network resources Places stress on the network to ensure suitable access timing and quality of service (QoS). LTE transportation is fully IP no circuit switched services Page 5

6 Voice with LTE: What is the goal and how to get there To deliver same standard of voice call with VoLTE as is delivered by 2G/3G The long term solution for voice is to use VoIP and an IMS based core network, there are already many networks fully operational For networks which do not support IMS or have incomplete coverage, several fall back technologies are required: CSFB (Circuit Switched Fall Back) - single radio approach SVLTE or Dual Standby approach (Simultaneous Voice and Data LTE) - dual radio approach SRVCC (Single Radio Voice Call Continuity) Voice on LTE with CS backup CSFB, SVLTE and SRVCC all involve some level of I-RAT behavior Page 6

7 Agenda Page 7 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WiFi Calling, EVS

8 P-CSCF: Proxy-Call Session Control Function of IMS Assigned to an IMS-capable UE terminal through various means, and does not change for the duration of the registration. May be in the home domain or in the visited domain. Facilitates the routing path for mobile originated or mobile terminated session requests. It is responsible for allocating resources for the media flows (bandwidth management) It can also compress/decompress SIP messages using SigComp, which improved signaling efficiency and reduces the RTT over slow radio links. It provides subscriber authentication, and is responsible for the security of the messages between the network and the user (ex: may establish IPsec). It may include a Policy Decision Function (PDF), which authorizes media plane resources e.g. QoS over the media plane Page 8

9 SIP and IMS SIP (Session Initiation Protocol) was initially designed to work in an open homogeneous IP network SIP provides the signaling required to support call set-up procedures SIP also provides many other services (caller id, multi-party & emergency calls ) SIP server IP Network PSTN IP Network 3G GSM Telephone Network Page 9

10 Agenda Page 10 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WLAN Calling, EVS

IMS Uses SIP (Session Initiation Protocol) User A REGISTER OK CSCF Proxy User B REGISTER OK Optional AKAv2 authentication and IPsec SIP (Session Initiation Protocol) e.g.

11 IMS Uses SIP (Session Initiation Protocol) User A REGISTER OK CSCF Proxy User B REGISTER OK Optional AKAv2 authentication and IPsec SIP (Session Initiation Protocol) e.g. INVIT E, T RYING, RING, OK, BYE etc. INVITE TRYING RING OK ACK RTP/RTCP INVITE TRYING RING OK ACK SDP (Session Description Protocol) e.g. m (media), a (attribute) etc. m=audio RTP/AVP a=rtpmap:98 AMR/8000 a=fmtp:98 mode-set=7 RTP (Real-time Transport Protocol) e.g. AMR encoded speech RTCP (RT Control Protocol) e.g. Send/receive quality metrics BYE ACK BYE ACK CSCF = Call Session Control Function Page 11

12 IMS Uses SIP (Session Initiation Protocol) User A REGISTER CSCF Proxy User B REGISTER CSCF Proxy OK OK INVITE TRYING INVITE TRYING RING OK ACK RING OK ACK User A Router/IP network IP User B BYE ACK RTP/RTCP BYE ACK SIP messages go via proxy server RTP voice traffic ~ peer to peer (or via other network nodes) CSCF = Call Session Control Function Page 12

13 RTP RTP is used for the delivery of the user data Page 13

14 RTCP Control information RTCP (RFC3550) Packet Loss Rate Jitter Timing Information RTCP XR (RFC3611) Delay Signal Level Noise Level Call metrics Buffering Page 14

15 SIP logging with Wireshark Call tracing Detailed RTP and SIP message decodes Ladder diagrams (call flow) Page 15

between the key generation between LTE and normal network IP Sec Normal IP traffic IP Header Data

16 IP Sec Tunnel Mode (VPN like) Entire original IP datagram encrypted, Client to Server Transport Mode Between two end points AH added to protect against alteration of datagrams while in transit Differences between the key generation between LTE and normal network IP Sec Normal IP traffic IP Header Data Transport Mode IP Header AH Data Tunnel Mode New IP Hdr AH IP Header Data More IPSec info in RFC4301, 4302, 4303 Page 16

17 SigComp (SIP Signalling Compression) SIP/SDP signalling stack State full Compressor /De-compressor RTP/RTCP Media stack Compresses text based SIP and SDP messages Up to 3:1 compression Standardized by the IETF RoHC working group Page 17

UE s can have multiple data streams, Multiple PDN s, Addresses, Port numbers etc.

18 VoIP QoS and Multiple PDN s Strict packet delay-based QoS QoS will vary by allocation, by application and will be heavily dependent on system capacity. UE s can have multiple data streams, Multiple PDN s, Addresses, Port numbers etc. All with different parameters: Default DRB or Dedicated DRB Guaranteed or non Guaranteed Bit Rate Packet delay budget e.g. 50 to 300ms Packet Error rate e.g to 10-6 Example from Keysight UXM, E7515A Page 18

19 Traffic Flow Template (TFT) Create, Modify or Deactivate dedicated or default bearers Dedicated bearers associated with default bearer Sort IP packets based on; IP protocol; e.g. UDP, TCP IP address Port number or range Priority Type of Traffic (traffic class) Page 19

20 GBR, TFT, QoS, DRB s signalled to UE GBR TFT Example from Keysight UXM, E7515A Message Editor Negotiated QoS Page 20

21 Agenda Page 21 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WLAN Calling, EVS

22 Semi-persistent scheduling (SPS) Normal LTE operation each SF is allocated individually. For highly repeatable applications such as voice this is un-necessarily wasteful of the DL signalling channel bandwidth. In voice we normally only need a few 100 s of bits at regularly spaced intervals. SPS is used to tell the UE to use specific resources for a fixed time period and can reduce significantly the DL signalling bandwidth required. SPS can be UL or DL specific Normal allocation - Each time a PDSCH allocation is made, PDCCH resources are required Normal SPS SPS allocation reduced PDCCH signalling Page 22

23 TTI bundling If at the cell edge UE can either increase power or increase coding rate to ensure reception at enb If the UE cannot increase its power - enb gets power headroom status reports from each UE - the UE can be instructed to use TTI bundling. TTI bundling prevents round trip ACK/NACK delays by transmitting all Redundancy versions in successive TTI s. DL signalling is reduced (less ACKs/NACKs) and round trip delay is minimised. TTI RV# NACK NACK NACK ACK Normal transmission with HARQ feedback delay of 4ms for each 8ms HARQ cycle up to 28ms for final ACK. TTI RV# ACK ACK ACK Bundled TTI HARQ process 0 in 4 consecutive TTI s (different RV). Total feedback delay is only 8ms. Page 23

ROHC - Robust Header Compression Typical VoIP Header for IPv4 = 40bytes Typical VoIP Header for IPv6 = 60Bytes With a typical voice rate of 12kbps, uncompressed IPv6

24 ROHC - Robust Header Compression Typical VoIP Header for IPv4 = 40bytes Typical VoIP Header for IPv6 = 60Bytes With a typical voice rate of 12kbps, uncompressed IPv6 headers represent approximately 60% of the data sent / received LTE network efficiency very poor without RoHC Robust Header Compression is therefore required for LTE VoIP Page 24

25 Agenda Page 25 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WLAN Calling, EVS

26 SVLTE Simultaneous Voice and LTE Two simultaneous radios connected separately. No radio interoperability required UE is voice enabled through CDMA2000 1xRTT plus data on LTE In area s of poor LTE coverage, handover from LTE to ehrpd is possible irrespective whether a voice call is active or not LTE CDMA ehrpd Page 26

27 CSFB Circuit Switched Fall Back UE is not VoLTE enabled, voice calls must be Circuit Switched on 2G/3G 1. UE receives incoming Voice page in LTE 2. UE sends extended service request 3. Network sends RRC Release with Redirect to send UE to 2G/3G May include existing LTE packet data connections (depending on UE capability) LTE 2G/3G Page 27

SRVCC Single Radio Voice Call Connectivity UE can no longer maintain LTE coverage, cell conditions in 2G/3G are advantageous IMS - VoLTE voice calling in LTE coverage areas, Circuit

28 SRVCC Single Radio Voice Call Connectivity UE can no longer maintain LTE coverage, cell conditions in 2G/3G are advantageous IMS - VoLTE voice calling in LTE coverage areas, Circuit Switched calls in 2G/3G Quickly handover from LTE to legacy 2G/3G at LTE edge using Packet Switched Handover method May include existing LTE packet data connections LTE 2G/3G Page 28

29 SMS over SGs What if my LTE network does not support IMS, how do I get 2G/3G SMS while in LTE? SMS over SGs Normal circuit switched native SMS is encapsulated message within NAS messaging SGs is actually the interface between the MME and MSC, normally used for mobility management processes between 2G/3G and LTE Requires combined attach with SMS only update IE. Page 29

30 Agenda Page 30 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WLAN Calling, EVS

31 To Test VoLTE Today, You Need: IMS/VoLTE capable device IMS/VoLTE capable Base Station / Network emulator IMS Server Somebody to talk to: Either another UE or IMS Client emulator Audio Analysis Page 31

32 E7515A UXM LTE FDD/TDD, 2G, 3G Comprehensive support for VoLTE testing UXM Test Set VoLTE UE VoLTE Feature Support IPv4, IPv4v6, IPv6 Multiple bearers/ PDNs Dedicated bearers RoHC TTI bundling SPS SRVCC CSFB Keysight IMS-SIP server and client Page 32

Voice/Video connection, call waiting, SMS forwarding, PRACK support AKAv2 authentication, IP Sec, SMS

33 Keysight E6966B-1FP IMS/SIP Server Easy to install and use Windows XP/7 PC-based IMS-SIP server (P-CSCF emulator) IPv4, IPv6, supports registration of multiple soft client and (via UXM) VoLTE UE, RUI/GUI Voice/Video connection, call waiting, SMS forwarding, PRACK support AKAv2 authentication, IP Sec, SMS sending Message Logging, error insertion Proven interop with VoLTE UEs Integrated UXM IMS Detail Log Page 33

1, G729, GSM, ilbc, Speex/wb voice codecs AMR/AMR-WB Octet-align, bandwidth-efficient, Mode-set negotiation and fixing H264, H263,

34 Keysight E6966B-2FP IMS/SIP Client Easy to install and use Windows XP/7 PC-based IMS-SIP client IPv4, IPv6, Voice, Video, SMS, RUI/GUI EVS, AMR, AMR-WB, G711 a/ulaw, G722/.1, G729, GSM, ilbc, Speex/wb voice codecs AMR/AMR-WB Octet-align, bandwidth-efficient, Mode-set negotiation and fixing H264, H263, H video codecs with H264 level and packetization mode selection Play test files, audio loopback, auto-answer, audio level cal features, scope display VAD (SCR/DTX), Echo cancellation, jitter buffering Proven voice interop with VoLTE UEs Page 34

Keysight U8903B Audio Analsyser Comprehensive support for VoLTE testing PESQ and PoLQA supported Low residual distortion Wide measurement bandwidth

35 Keysight U8903B Audio Analsyser Comprehensive support for VoLTE testing PESQ and PoLQA supported Low residual distortion Wide measurement bandwidth Flexible choice of analog and digital interface (AES/SPDIFor DSI) options Characterize signal to noise ratios Apply weighting functions and filters Page 35

36 Audio Test Scenario Audio quality measurements on the Keysight U8903B Page 36

37 Voice / Video Loopback Simple test UXM Test Set VoLTE UE UXM Test Set Video loopback (IMS feature) SIP registration procedure Negative registration processes Test call set up Soft client must enable loopback No quality measurements VoLTE UE VoLTE UE 2 phone Testing UE to UE interaction Test with reference/ commercial phones Page 37

38 Voice Quality Testing with U8903B Audio Analyser PESQ and PoLQA supported Test UE loop-back USB sound card USB Keysight IMS-SIP server & client Soft client loop-back VoLTE UE Audio Line in/out Ethernet Keysight UXM RF Reference source Degraded source Headphone/mic jack Keysight IMS-SIP server & client U8903B Audio Analyser VoLTE UE U8903B Audio Analyser Ethernet Keysight UXM RF Headphone/mic jack Reference source Degraded source Page 38

39 Voice Quality Testing DL voice Quality Testing Keysight IMS-SIP server & client Keysight UXM Ethernet USB sound card USB RF Reference source (DL) Audio Line in/out Headphone/mic jack VoLTE UE U8903B Audio Analyser Degraded Source (DL) Page 39

USB RF Degraded source (UL) Audio Line in/out Reference

40 Voice Quality Testing UL voice Quality Testing Keysight IMS-SIP server & client Keysight UXM Ethernet USB sound card USB RF Degraded source (UL) Audio Line in/out Reference source (UL) Headphone/mic jack VoLTE UE U8903B Audio Analyser Page 40

41 Audio Test Scenario Human Jury Testing and/or PESQ with IP Impairments Delay/Jitter/Loss insertion Keysight IMS-SIP server Ethernet VoLTE UE Keysight UXM VoLTE UE RF U8903B Audio Analyzer RF Audio in/out headphone jack Audio in/out headphone jack Page 41

42 Agenda Page 42 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components IMS call, SIP call-flow Access Network features for VoLTE What happens when out-of-coverage: flavors of fallback IMS and Voice test, Keysight VoLTE solutions What is next WLAN Calling, EVS

43 WLAN Calling (VoWLAN) Secure IP calls on un-trusted connections IMS IPsec Termination HSS AAA PCRF P-CSCF LTE enodeb MME IMS Server S-GW P-GW WiFi RAN Untrusted WLAN IPsec Termination epdg S2b epdg Evolved Packet Data Gateway Page 43

44 WLAN Calling (VoWLAN) Other VoWLAN considerations Handovers Large LTE cells, Small WLAN coverage decisions on when/if to HO or cell (re)select. Network operator and UE operation vary dramatically. Interoperability will be key QoS UE s fighting with other users for priority, how do we test MOS? MOS will likely vary more with signal quality and cell congestion rather than the radio format Security IPSec, or is provider specific login required Why use your call time (minutes) allowance on WLAN calling rather than free skype or facetime? P-CSCF addressing could be through epdg signalling Page 44

45 Enhanced Voice Services (EVS) codec Designed to rate match with existing AMR codecs (AMR-WB interoperability mode) Vastly increase bit rate to 128 kbps allowing music and mixed content Source controlled rate, switchable per frame Voice activity detection (VAD), sound activity detector, comfort noise generator (CNG) Jitter buffer management, error concealment mechanism to nullify lost packets and minor transmission errors, Channel Aware Mode lists the EVS standards Characteristic GSM FR AMR WB-AMR G EVS Bandwidth 200 to 3400Hz 200 to 3400Hz 50 to 7000Hz 50 to 24000Hz Frame Size 20ms 20ms 20ms 20ms Bit Rates (kbps) to to to 128 Technology RPE-LPT ACELP ACELP ACELP and Transform Coding Adopted Designed for PSTN Voice PSTN Voice VoIP (not LTE) LTE / VoIP / Mixed content Page 45

46 CHANNEL Transmit EVS Encoder ACELP based encoder BWE encoder (b/w extension) Encoded audio frame (50 frame/s rate dependent on codec mode) 16 bit PCM 8, 16, 32, 48 khz Core and DTX switching MDCT based encoder A to D conversion DTX, CNG encoder RTP payload formatting AMR WB-IO encoder Page 46

47 CHANNEL Receive EVS Decoder Impaired received audio frame (50 frame/s rate dependent on codec mode) ACELP based decoder BWE decoder (b/w extension) 16 bit PCM 8, 16, 32, 48 khz RTP payload decoding Jitter Buffer Mgt (JBM) Core and DTX switching MDCT based decoder A to D conversion DTX, CNG decoder AMR WB-IO decoder Page 47

48 Channel Aware Encoding EVS is designed for Packet Switched Networks Primary Frame Encoding (Low freq: ACELP based) (High freq: TBE based) Pre- Processing Frame Criticality Configuration Primary + Redundant Frame Bit Packer Redundant Frame Coding Primary frame encoding minimizes data based on VAD etc. Redundant frame coding creates a redundant version for the critical parameters The redundant frames are used to fill gaps for the overall payload data The redundancy then provides some robustness in a system with packet loss Page 48

49 Enhanced Voice Services (EVS) Designed for LTE - Summary Supports HD voice and entertainment quality audio Designed for packet switched networks (VoLTE) Inter-operable with AMR-WB Wide range of bit rates and bandwidths for excellent flexibility Feature rich CODEC Source controllable rate (SCR) Comfort noise generator (CNG) Discontinuous Transmission (DTX) Variable bit rate (VBR) Jitter buffer management (JBM) Channel aware mode (designed for systems with packet loss) EVS primary mode AMR-WB IO compatibility mode Page 49

50 Summary Page 50 Intro: a very brief history of IMS, Legacy (CS) vs. LTE (PS) domain considerations Architecture of IMS, components P-CSCF IMS call, SIP call-flow RTP, RTCP Access Network features for VoLTE SPS and TTI Bundling What happens when out-of-coverage: flavors of fallback CSFB, SRVCC IMS and Voice test, Keysight VoLTE solutions What is next WiFi Calling, EVS

51 Useful References ITU-T P.862. Perceptual evaluation of speech quality (PESQ) ITU-T P.863. Perceptual Objecting Listing Quality Assessment (POLQA) UXM Website. Keysight IMS/SIP GSMA IR.92 IMS Profile for Voice and SMS 3GPP TS IP Multimedia call control protocol based on SIP and SDP, UE conformance specification 3GPP TS Security Aspects of early IP Multimedia Subsystems (IMS) 3GPP TS IP Multimedia Subsystems (IMS) Multimedia telephone: Media handling and interaction 3GPP TS Speech and video telephony terminal acoustic test specification 3GPP TS IP Multimedia Core Network Subsystem Multimedia Telephony Service and supplementary services 3GPP TS IP Multimedia Subsystem (IMS) Stage 2 Page 51

52 Thank You!!! Questions and Answers Page 52 Technologies 2015

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