Due to the ongoing pandemic, it’s been a while since I last traveled abroad and had some time to have a look how roaming has evolved. But things are slowly getting better and I recently had the opportunity to go on a quick trip to Austria. And I’ve been very positively surprised that my favorite … Continue reading VoLTE Roaming in the Wild
If you want to humble yourself as a VoLTE engineer at a point in time when you think you have more or less understood how VoLTE works, make a trace of a VoLTE conference call with a few participants and try to analyze that. You get back down to earth pretty quickly as complexity of … Continue reading VoLTE Conference Calls – The Telco Engineer’s Darling!
Recently I wanted to have a closer look at how authentication works for the XCAP protocol that is used in VoLTE by mobile devices to control things such as call forwarding settings. At first I thought that the topic is so far off the beaten path that I need to have a look in the … Continue reading VoLTE – GBA Authentication For XCAP
When GSM was designed, the network and the voice service running over it were inseparable. That’s because the GSM network was designed in the 1980s as a mobile voice network. Fast forward 20 years and the picture had changed significantly with LTE having been designed as a wireless network that only transports IP packets. Agreed, … Continue reading VoLTE and VoWifi – Wireless Telephony Has Truly Become Network Independent
Even if you have a VoLTE capable phone and use it in a VoLTE capable home network, chances are that when push comes to shove and you have to make an emergency call, it’s not done over VoLTE. Instead, CS-Fallback is used to establish the emergency call in GSM or UMTS. But at some point, … Continue reading VoLTE – Some Thoughts On Emergency Calls
If your uplink bandwidth at home is limited and you use Skype or other Internet based voice services you’ve probably experienced more than once that when someone else in your household starts uploading cat videos, your Skype call goes south. That’s because the voice packets are treated like all other packets and start queuing up … Continue reading VoLTE and Quality of Service – The Ultimate Test
It’s a bit sad but unfortunately still true, in some places there is still better GSM coverage than LTE. Network operators using VoLTE thus need to be able to hand-over an ongoing VoLTE call to a GSM circuit switched channel when the user leaves the LTE coverage area. The method to do this is referred … Continue reading VoLTE – Some Thoughts on SR-VCC
Continuing my mini-series on how VoLTE works in practice I’ve recently taken a closer look at how DTMF tones are transported over IMS. You might argue that DTMF tones are old technology but they are still used a lot today. Examples are entering the PIN to your voicemail system from the phone or sending a … Continue reading VoLTE – Some Thoughts on DTMF
In the previous blog post on VoLTE I discussed how speech codecs are negotiated during connection establishment. VoLTE uses the AMR and WB-AMR codecs that are adaptive and can encode the voice stream in several data rates and qualities. In the case of WB-AMR, voice streams can be sent with data rates between 6.6 and … Continue reading VoLTE – Some Thoughts On Bandwidth Negotiation
In the good old fixed line SIP world, the originator of a speech call told the other side which speech codecs it supported. The other side then picked a suitable codec and informed the originator about the choice. That was it and things were ready to go. In VoLTE, you might have guessed, it’s not … Continue reading VoLTE – Some Thoughts On Codec Negotiation