CSFB to VoLTE - The evolution of circuits to packets

The basis of traditional telephone networks is circuit-switching technology. Further on the telecom industry evolved and packets replaced circuits.  

CSFB (Circuit Switch Fallback) is a technology that supports voice and SMS services in 4G networks using the 2G/3G systems.

VoLTE (Voice over LTE), on the other hand, means that a call is made through a 4G network (Making calls over IP). 

Further on we will discuss the following topics:

The development of the Core Network

You need to know the context that leads to such technology in order to fully understand the concept of LTE Core Network.

In the 2G network (GSM), the architecture was built based on circuit-switching (CS), meaning circuits were settled between the caller and the called device throughout the network. It is circuit-switched because the core network uses SS7-based protocols that in certain configuration requires allocation of dedicated channels for said signaling.

Telecommunications worked this way until the GPRS network appeared. It came with a new technology called packed-switching that was added to the circuit-switching. Along with this upgrade of the core network, data is being carried in packets without the formation of dedicated circuits. Some of the most important benefits of this development are flexibility and efficiency, although the circuits still carried voice and short text messages (SMS).
When the third-generation of mobile telephony was created the concept remains the same, but some of the elements evolved. In 3G, the core network had two main components: circuit and packet.

It was then decided that the LTE core network would not keep the circuit-switched domain technology anymore and that the LTE EPC would be an evolution of the packet-switched architecture used in GPRS and 3G. The EPC has a “flat” IP architecture that allows the network to handle a great amount of data traffic in an efficient and cost-effective manner using Diameter protocols.

Circuit switching vs Packet switching

Circuit SwitchingPacket Switching
Circuits traffic only for voiceData traffic and VoLTE
Dedicated wires for communication between the nodesThe communication is done using a shared wire
Circuits travel using the same coursePackets travel individually
Circuits need and book the entire bandwidthCircuits need only the bandwidth they use and they don't book any
It consumes a lot of bandwidthIt doesn't waste bandwidth

CSFB vs VoLTE​

CSFB (Circuit Switch Fallback) is a technology that supports voice and SMS services in 4G networks using the 2G/3G systems.

VoLTE (Voice over LTE), on the other hand, means that a call is made through a 4G network (Making calls over IP).

Ideally, you would want to make use of VoLTE because IP calls do not require a 2G/3G coverage in that particular area, but the downside to this is that it requires the phone to support VoLTE, in order to make it possible. There are very few phone models in circulation today that support VoLTE out of the box. So depending on the situation, activating it requires the manufacturer’s support, and you may be ignored if you are not a pretty big mobile operator.

CSFB diagram

CSFB allows access to calls and SMS services for phones that work on a 4G network but doesn’t support VoLTE. When a phone is on 4G, and you want to make a call with it, the network will simply move to 3G to make the call possible through circuit-switching. This requires the presence of a 2G/3G coverage in the same area as the 4G network due to the cooperation between these networks.

CSFB ensures that operators provide users with the service they pay for. The only downside to this is that the operator will have to keep older generation networks operating within the same coverage area. Managing a single type of network might be simpler than managing two or more types.

If you are an operator that already has a 2G/3G network standing and you afford to maintain the costs, then CSFB might work for you. 

If you are an LTE-only operator and deploying VoLTE is too expensive and you have to rely the voice traffic on the CSFB roaming agreements, you could try 2Greet.

To finalize the dispute about which technology is preferable you will have to look at things within the context of your business model.

Our solution for CSFB

Yate-based CSFB solutions for operators – highly scalable and suitable for any operator size and structure, private networks included. We offer affordable Core Network equipment and we practice public prices, unlike any other vendor on the market. 

  • Affordable
    $28.050 for each solution. The prices are public on the website for all our products.
  • Free tech support
    You get 6 months of free technical support
  • Scalable
    You can start with a small deployment and extend the network as you grow the number of subscribers
  • Easy to buy
    The purchase process is smooth and you get all the information you need easy
  • YateUCN

    ✔ IMS - Intended for new or existing LTE networks and for upgrading GSM/GPRS networks to LTE. It integrates the IMS layers for VoLTE – P-CSCF, I/S-CSCF, IWF, and BGW.

    ✔ CSFB - Implements the functions and protocols of GSM/GPRS core networks, acting as an MSC/VLR/SGSN/GGSN/GMSC in a single server.

MiniCore - LTE Core Network for tests and research

Full test Core Network for MVNOs or MNOs. It is a great testing equipment for our Yate products. Additional components can be installed on the same hardware on demand.

You can use MiniCore to test VoLTE and CSFB in your network. The main advantage of it is that it has pre-installed all our Core Network software components, such as YateUCN, YateHSS/HLR or YateSMSC.

  • Affordable
    $10.915. The prices are public on the website for all our products.
  • You get access to a small-scale LTE and GSM Core Network for tests
  • Multi-IMSI and multi-MSISDN features
  • Can use both SIGTRAN/SS7 and Diameter for signaling so you can run multiple types of tests
  • Has multiple communication protocols and interfaces for fully documented research
  • Free tech support
    You get 6 months of free technical support