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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IMS/WebRTC Tracing and Test Tools

IMS authors were maybe very wise but probably they were not operation engineers. If you have ever tried to trace all the messages which belong to a certain user/flow, you probably know, what I mean 🙂 Basic VoLTE validation procedures are described at Validating VoLTE document.

In this post I’m getting on a shaky ground. I don’t know all the tools, some tools I know only briefly and I don’t want to promote any particular one (unless it is free :)). I also know that many operators and vendors create their own tools indoors (sometimes quite advanced). However I hope that it makes a sense to briefly list a few tools one can encounter in practice. Would you have any favorite application, please let us know.



The most used protocol analyzer is Wireshark. In my experience 70 – 90 % of all the issues are somehow related to traces and Wireshark is the ultimate tool. Wireshark is free and open and all the authors and contributors deserve our thanks. If you use Wireshark often it pays-off to know a bit more about it, how to adjust the layout, filters, how to follow streams, read statistics etc. – it can save a lot of time and energy.

Wireshark-pic1For developers it is good to know that we can write a dissector for our proprietary protocols. Actually not useful just for developers – if we are not happy with protocol details, we can enhance already existing dissectors too.

The last year we had got a new major version 2, where the Wireshark was ported in Qt.

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News: Are the Codec Wars over?

If you are interested in the WebRTC technology, you probably know what pain it was to define Mandatory To Implement (MTI) codecs. But compromise is not always the best solution. So the key players decided to form an Alliance for Open Media – an open-source project that plans to develop next-generation media formats, codecs and technologies. The Alliance’s founding members are Amazon, Cisco, Google, Intel Corporation, Microsoft, Mozilla and Netflix. The Alliance wants to come with an open-source common standard for media sharing. It is nice to see Google, Microsoft and Mozilla to work together on web standards 🙂 Along with the HTML5 this can push forward the development of real-time communication apps a lot. On the other hand there are still many other players, many different interests, so let’s wait for the first real outcomes.

I admit this news slipped my attention. I noticed only that Edge does support the getUserMedia and then I got a bit lost in what is the WebRTC 1.0, what 1.1 and what is the Next Version (NV) 🙂 There are also other news, e.g. Google introduced a new open-source tool for developers which tests network conditions, and if camera and microphone work properly. If you missed these information as I did, you can find a nice summary with many other updates in the following video


IMS from 10.000 feet

Over and over I need to go through the basics. One would think that everything was already said but sometimes a refresher is a good thing. Especially when we rely a bit on what we guess than on what we really know. I’m not any exception 🙂

There are many changes we can witness these days in operators’ networks.

The core network has become much more complex. We still have the 2G/3G mix in place, we added new LTE network, WiFi network, some operators are even introducing WebRTC GW. I’ll leave aside the IoT/M2M traffic – however very soon it will be the most important guy in town (now 2nd – 3rd biggest source of revenue for mobile operators).

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