Multimedia in VoLTE

It’s very interesting (and well, a bit suspicious) that the main focus of most VoLTE textbooks and trainings is signalling. But from the user-point-of-view, it is the voice data, what matters. As an end-subscriber I don’t care about signalling. My only interest is the call quality. But times they are a changin and engineers are asking about how to improve the overall voice-call quality and user experience. Today we’ll go through the basics as jitter, mouth-to-ear delay, packet loss rate or MOS, needed for QoS analysis.

For real-time multimedia we used to have dedicated telephone/radio networks. That has changed and voice/video streams are transported over IP network now.

We should understand that these IP networks were originally designed for data transport. To transport data we prefer the best-effort service model, which allows an easy network scaling and simple routers’ logic. On the other hand we don’t care much if packets arrive in-order or what are the delays between particular packets. We simply wait until we receive a whole file. If any packet is lost, TCP will re-transmit it.

Packets in Data Networks

It’s a different story with the real-time communication services though. RTC applications are less sensitive to packet loss, but they are very sensitive to packet delay. Usage of IP data network as a carrier brings a lot of challenges which have to be addressed by media protocols and network elements.

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News: Trends in Telco

I like statistics. Sometimes it can be misleading or data can be hard to interpret. But it can help us when we struggle to see the forest for the trees.

The last two years the IP-based mobile technologies were booming. If you are working with 4G networks you know it well. This year however the number of new deployments decreased significantly (Sep 2017, source GSMA).

IP Deployments Sep-17

Well, there can be many reasons for that. Rather than guessing, let’s have a fun and take a look on how popular are some telco topics on Google in the last 3 years.

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News: testRTC Demo

I’m always wondering that there are still (even quite big) companies which rely on manual testing. I’d think that this is mainly caused by short-term orientation of majority of managers. Right, to find a bug we don’t need to have automated tests. But to verify that the system is really working this is the best way to go. At the end a good tool can save a lot of effort and a good regression suite a lot of problems 🙂

The similar idea maybe had the founders of testRTC. In the latest videos we can see demos of their tools.

News: more than HD

T-Mobile USA is on the cutting edge. It was the the first operator who came with HD Voice back in 2013. This month they announced a new upgrade of their network – to Enhanced Voice Services (EVS). From the customer perspective it means a better audio quality – even better than HD. EVS does this with a broader audio frequency range, which translates to richer, more realistic-sounding voice audio. The EVS is supported for both VoLTE and VoWifi. Additionally for the LTE technology it also brings a higher reliability in areas of weaker signal.

T-Mobile has a pending patent for their solution where their customers with EVS compatible phones will benefit even if the B-party  doesn’t have an EVS-capable device. Currently the technology is available for LG G5,  Samsung Galaxy S7 and S7 edge. T-Mobile plans to support four more smartphones by the end of 2016. I wonder what will be the response of Alliance for Open Media for webRTC.

News: WhatsApp pushes the WebRTC

In February WhatsApp and Gmail joined the 1 billion active user club. Whatsapp also announced that it would waive its yearly $0.99 fee. There are also more and more rumours that WhatsApp will add video calling soon to the application.

At the same time, according to a newly released report from Exact Ventures, the market for WebRTC gateways (product and service revenues) is expected to grow to nearly $900 million in 2020. WebRTC GW are becoming the bridges which can interconnect OTTs, Enterprise solutions and Telcos.

WebRTC Interoperability

WebRTC Interoperability

WebRTC GW allows to combine the power of VoLTE with a dedicated information system. Typical example can be a customer care system (e.g. insurance company) connected directly over WebRTC to the end users’ VoLTE handsets. Why the operator should use a handset herself when she can directly see the pictures/videos from your car crash, and the system will store the data along with the call itself in your customer history? Sure there are thousands of other applications starting with health care services and ending with m2m. But the idea remains the same – we want to integrate all communication channels and we want to work with the data later. And this is magnified in the business and industry. According to Exact Ventures even the traditionally consumer-focused web properties like Facebook and WhatsApp are looking to expand their presence in business communications.

News: WebRTC – the way to go

WebRTC was a buzz word a few years ago. The cool demonstrations lead to doubts of many operators and communication companies about their own solution. But this also meant a lot of expectations which couldn’t be fulfilled immediately. WebRTC is a technology not a solution. To introduce it in mobile networks when we go in detail is not without challenges. Anyway the WebRTC is (for someone) slowly gaining its momentum and there are quite a few trials already.

Would you be interested in the GSMA view how to implement the WebRTC in the mobile networks’ context check this whitepaper out –  GSMA WebRTC to complement IP Communication Services.

GSMA - Typical vendor gateway implementation example

GSMA – Typical vendor gateway implementation example

VoLTE Policy Control Summary

In IT and particularly in Telco we are obsessed with abbreviations. My wife always loughs and tries to mimic me when she listens to my calls. Today we should be very careful as many of them start on ‘P’ – PCC, PCRF, PCEF, P-CSCF, PGW, PDN, PDG, PDB, PHB. But no worries, there will be abbreviations starting on other letters as well 🙂

In the IMS we have separated signalling and media data. However a full independence of control and user plane is not desirable. We want to control when the media starts and stops, we want to be sure about media routing, we want to ensure Quality of Service (QoS). And, of course, we want to accordingly charge the users.

In order to achieve these requirements we use two techniques in the VoLTE architecture:

  • Policy and Charging Control (PCC)
  • Differentiated Services (DiffServ)

Policy and Charging Control

PCC functionality comprises of Policy Control (e.g. QoS, media gating, ..) and Flow Based Charging. The ETSI TS 29.212, 29.213, 29.214 and 29.203 define Policy and Charging Control Architecture. There are many PCC functions defined. For us the main 3 PCC elements are:

  • Application Function (AF)
  • Policy Charging and Rules Function (PCRF)
  • Policy Control Enforcement Function (PCEF)
Policy and Charging Control (PCC) Architecture

Policy and Charging Control (PCC) Architecture

Application Function

In VoLTE is the AF incorporated within the Proxy-CSCF. The P-CSCF provides the information related to the control plane signaling. The information is taken from SIP/SDP session setup and it is forwarded to the PCRF via the Rx reference point. Each new SIP message that includes an SDP payload or session events (e.g. session termination, modification) can trigger a new request sent towards the PCRF. This ensures that the PCRF gets the proper information in order to perform reliable PCC.

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