VoLTE is a crucial service for mobile operators, not only because of the promised improvements in call quality that will create additional user demand, but because this technology enables them to eventually terminate their legacy, circuit-switched voice 2G/3G network infrastructure in favor of consolidating voice traffic on the LTE network platform.
Gradually, VoLTE will allow many operators to refarm spectrum away from 2G/3G to LTE, which will significantly lower voice infrastructure costs. Once VoLTE is widely deployed, research firm iGR expects the number of VoLTE subscribers to grow significantly – at a CAGR of 187 percent between 2012 and 2017.
The technical complexity that operators ultimately mastered in 3G networks now needs to be resolved again as operators prepare for VoLTE. Hurdles to overcome include interconnectivity with other LTE and non-LTE networks, roaming and call handoff, and operators will also be looking to create new services with VoLTE, which will require deeper integration with the IMS core to more fully leverage SIP and other functions. In summary, successful deployment of VoLTE necessitates substantial changes to a number of new and existing network elements. It’s a perilous time for mobile providers, as VoLTE subscribers will have no tolerance for lesser quality voice.
The Latency Factor
VoLTE commands a significant shift in how mobile operators think about success in mobile broadband networks. So far, operators have defined quality primarily in terms of speed and throughput, or bandwidth. For example, NTT Docomo has been ramping up its LTE network for several years, gradually increasing its LTE speeds and user numbers, as this chart illustrates:
Milestones in Docomo’s LTE Data Transmission Speeds
|Launch||Max. Downlink||Max. Uplink||# Subscribers|
|Dec 2010||75 Mbps||25 Mbps||0.12 million|
|Nov 2012||100 Mbps||37 Mbps||5 million|
|March 2013||112.5 Mbps||37.5 Mbps||10 million|
|Oct 2013||150 Mbps||50 Mbps||15 million|
With VoLTE, the focus on speed has been reversed completely.
What Docomo and other operators are quickly realizing is that with VoLTE, network performance is not just about speed – it’s also a question of delivering on consumers’ expectations for improved performance benefits by reducing latency.
Latency is defined as the time it takes for a source to send a packet of data to a receiver and is typically measured in milliseconds. The lower the latency (the fewer the milliseconds) the better the network performance and the more “real time” the voice will sound to the subscriber.
This means that the introduction of IPsec security to LTE must be achieved in such a way that it doesn’t contribute to latency. This is not the case with all security solutions, and definitely not the case once the smaller packet sizes typical of voice traffic begin to dominate the pattern of network traffic
Dodging the Real-time Packet Bullet
The trend towards smaller packet sizes will continue unabated as streaming video and VoLTE come to the fore. (There was a 100%+ growth rate over the last year for both services.) More than 80% of all data bursts in mobile broadband networks are less than 100 KB/s and require an immediate ‘response’ for the applications to perform as expected and without any perceivable quality difference by the subscriber. Therefore, the majority of real-time mobile applications is much more sensitive to latency than throughput.
When including VoLTE, where the payload packet size would be around 64 bytes, the quantity of small packets to be processed by the network nodes will increase significantly, even if the total throughput remains unchanged. If the network elements, including security, aren’t capable of handling this pattern of traffic, the result will be a slow, painful experience that means the bulk of application packets will not be processed quickly enough or may even be dropped, causing the applications to slow, stall or crash or degrade the quality of the voice call
The imperative of avoiding latency may require changes to the physical elements of the transport network (including buffering and queuing mechanisms, signaling processing, packet transmission and the X2 interface) that were designed with less stringent needs in mind. However, careful selection of the right security solution at the outset – as in the case of NTT Docomo – means that there is no need to change the security gateway. If the security gateway has the performance and scalability characteristics that Stoke has engineered into their solution from the start, the operator is covered in terms of performance, protection and latency.
Stoke Security eXchange is engineered to provide encryption functions with latency levels below 30 microseconds, even with VoLTE traffic. This is a very small percentage of the total latency budget of up to 100 milliseconds (100,000 microseconds) In other words, you don’t have to choose between secured and fast.