Voice over LTE - call without fallback with a very fast call. How we did it
We recently completed the VoLTE tests in Moscow. This is a continuation of the evolution of the LTE network. As you know, LTE is characterized by a higher data transfer rate compared to the existing GSM and 3G networks. Initially, the architecture of LTE-networks deployed in 2G / 3G-environment in Russia is not “sharpened” to the voice. To receive a voice call, the LTE terminal hangs up the packet session and temporarily switches to a 2G / 3G network (the procedure is called Circuit Switched FallBack). It takes time - up to several seconds to complete this transition and return back to the LTE network after the end of the conversation.
Evolution of voice mobile network.
The Huawei OSTA 2.0 chassis on which the tested IMS core is built.
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Among the main advantages - the time from pressing the "call" button in the LTE network to the first call from another subscriber in most cases will be no more than a second. Speech intelligibility will also improve compared to traditional networks through the use of wideband codecs.
The evolution of mobile networks leads to the fact that in fourth-generation networks, such as LTE networks, telephony is implemented on the basis of data transmission, and traditional circuit-switched networks (Circuit Switched) cease to develop. Everything goes into the data.
Roughly speaking, from the point of view of the LTE network, voice is just one of the data transfer functions. But unlike, for example, from the Internet pages, voice transmission imposes strict requirements on the quality of the network. The essence of the requirements - the presence of certain thresholds for the losses and delays of packets. At the same time, the quality should be end-to-end, all the way through the packets - and this is: radio subsystem, PS Core, transport. Voice transfer to the packet network makes a handover in a 2G / 3G network unnecessary - if the subscriber is registered in the LTE network and the operator’s infrastructure supports VoLTE, the call will be processed in the LTE network.
Transferring communications to a single IP transport environment allows you to expand the range of services, for example, add voice to video calls and, at the same time, send mail or participate in chat. By the way, we also tested video calls. Unlike 3G networks, video resolution is no longer limited to a channel of 64K and the picture can be of quite decent quality (limited by the allowed codecs and the capabilities of the terminals themselves).
Naturally, you can talk about these advantages if both subscribers use VoLTE in a conversation between themselves.
The tests were carried out in the test zone of VimpelCom OJSC on Huawei equipment. During the tests, calls were checked between subscribers in the LTE network, calls between subscribers in different LTE and 2G / 3G networks, as well as redirection to subscribers that are in the coverage area of ​​networks of any of their listed generations. We checked how the network and devices behave when they switch from the LTE network to the 3G network coverage area during a call (if the LTE coverage deteriorates / loses, the technology is Single Handover by Single Radio Voice Call Continuity).
Here is the circuit diagram of the LTE-2G / 3G connection:
Establishing a connection between a VoLTE subscriber and a subscriber located in a traditional network.
And this is the LTE-LTE call:
Packets of voice leave from your phone with high priority and come to the phone of the called subscriber. This is how a full packet network should work.
To fully work with VoLTE technology, the terminal requires support for the standard at the chipset level. This approach will allow to save the experience gained by subscribers in traditional networks and to optimize such an important parameter as the lifetime of the battery of the phone.
At the moment, most of the phones sold in Russia do not have such support. For other phones, it is still closed at the software level. For tests, we used Android-based phones, which manufacturer specifically - until we say, so as not to be considered advertising.
Currently, in the LTE networks of Russia, voice services and SMS are possible thanks to the use of CSFB (Circuit Switched FallBack) technology - temporary switching in the 3G / 2G network to establish a voice connection. After the end of the call, the devices are returned to LTE, which entails significant delays in connection organization and inefficient use of network resources. This technology will exist for quite a long time, since it will take quite some time until all operators implement VoLTE support in their LTE networks and make agreements between themselves, until this point, CSFB will be required for telephony in roaming.
We are the first to implement fully functional (with QoS and SR VCC support) VoLTE technology in Russia (as part of test operation). If you are already connected to one of our LTE networks, after some time you will be able to feel for yourself how pleasant it is to get rid of the overhead projector of many old technologies.
Evolution of voice mobile network.
The Huawei OSTA 2.0 chassis on which the tested IMS core is built.
')
Among the main advantages - the time from pressing the "call" button in the LTE network to the first call from another subscriber in most cases will be no more than a second. Speech intelligibility will also improve compared to traditional networks through the use of wideband codecs.
The evolution of mobile networks leads to the fact that in fourth-generation networks, such as LTE networks, telephony is implemented on the basis of data transmission, and traditional circuit-switched networks (Circuit Switched) cease to develop. Everything goes into the data.
Roughly speaking, from the point of view of the LTE network, voice is just one of the data transfer functions. But unlike, for example, from the Internet pages, voice transmission imposes strict requirements on the quality of the network. The essence of the requirements - the presence of certain thresholds for the losses and delays of packets. At the same time, the quality should be end-to-end, all the way through the packets - and this is: radio subsystem, PS Core, transport. Voice transfer to the packet network makes a handover in a 2G / 3G network unnecessary - if the subscriber is registered in the LTE network and the operator’s infrastructure supports VoLTE, the call will be processed in the LTE network.
Transferring communications to a single IP transport environment allows you to expand the range of services, for example, add voice to video calls and, at the same time, send mail or participate in chat. By the way, we also tested video calls. Unlike 3G networks, video resolution is no longer limited to a channel of 64K and the picture can be of quite decent quality (limited by the allowed codecs and the capabilities of the terminals themselves).
Naturally, you can talk about these advantages if both subscribers use VoLTE in a conversation between themselves.
Tests
The tests were carried out in the test zone of VimpelCom OJSC on Huawei equipment. During the tests, calls were checked between subscribers in the LTE network, calls between subscribers in different LTE and 2G / 3G networks, as well as redirection to subscribers that are in the coverage area of ​​networks of any of their listed generations. We checked how the network and devices behave when they switch from the LTE network to the 3G network coverage area during a call (if the LTE coverage deteriorates / loses, the technology is Single Handover by Single Radio Voice Call Continuity).
Here is the circuit diagram of the LTE-2G / 3G connection:
Establishing a connection between a VoLTE subscriber and a subscriber located in a traditional network.
And this is the LTE-LTE call:
Packets of voice leave from your phone with high priority and come to the phone of the called subscriber. This is how a full packet network should work.
Telephones
To fully work with VoLTE technology, the terminal requires support for the standard at the chipset level. This approach will allow to save the experience gained by subscribers in traditional networks and to optimize such an important parameter as the lifetime of the battery of the phone.
At the moment, most of the phones sold in Russia do not have such support. For other phones, it is still closed at the software level. For tests, we used Android-based phones, which manufacturer specifically - until we say, so as not to be considered advertising.
How does it work now (before VoLTE)?
Currently, in the LTE networks of Russia, voice services and SMS are possible thanks to the use of CSFB (Circuit Switched FallBack) technology - temporary switching in the 3G / 2G network to establish a voice connection. After the end of the call, the devices are returned to LTE, which entails significant delays in connection organization and inefficient use of network resources. This technology will exist for quite a long time, since it will take quite some time until all operators implement VoLTE support in their LTE networks and make agreements between themselves, until this point, CSFB will be required for telephony in roaming.
What does it mean?
We are the first to implement fully functional (with QoS and SR VCC support) VoLTE technology in Russia (as part of test operation). If you are already connected to one of our LTE networks, after some time you will be able to feel for yourself how pleasant it is to get rid of the overhead projector of many old technologies.
Source: https://habr.com/ru/post/229093/
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