VOLTE’S QUALITY OF SERVICE: CHOOSING A BEARER
In a previous post, voice over LTE’s deployment by mobile operators to compete with voice over IP has been discussed. That post covered some precautionary steps to follow for an “unrisky” deployment process. A couple of ideas are to add and might be useful to consider while performing an optimized deployment.
The 3GPP (3rd Generation Partnership Project) has defined the quality of service level identifier (QCI*); this indicator is provided to the radio access node in a new “channel” (bearer) establishment’s process, allowing the radio access node to identify the minimum level of quality it has to ensure for every data packet transiting through this “channel”. To each « bearer » corresponds a QCI for the network in use, depending on transiting packets’ control options: reported size, admittance threshold, and link layers protocol configuration. The 3GPP has defined 9 options with varying Quality of Service and guaranteed throughput rates** depending on their use. For instance, a QCI of 3 offers suitable parameters for online games’ data transport while a QCI of 7 would be required to transport voice, video streams’ loading and interactive games through the same channel to optimize the QCI’s cost effectiveness***. It is during the bearer’s election and its QoS that the operator would decide which services will go through that channel: consequently, all services going through the defined channel will have the same minimum quality of service. Usually, operators do not deploy the 9 recommended classes of QoS (each class’s deployment being very expensive), but rather define a default class and add one or two more classes for special needs, the default channel is mainly used for signaling (service request) and establishing dedicated bearer for various services; thus VoLTE would always use a specific bearer. The first question to ask is what are exactly the services related to VoLTE that should go through this same channel: for example, will online games (which have very strict requirements in terms of quality of service), or videos, go through the same channel as VoLTE or go through a different one? If the operator is not using all the channels suggested by the 3GPP, will it group services under the same class and, if so, which one (?), grouping being of course a serious cause for VoLTE quality decline. A profitability assessment is hence to be conducted, depending on the qualitative analysis of estimated needs. Demand for voice’s quality in LTE networks is steadily growing and the number of simultaneous voice calls that can be managed is to be checked. One element of the solution is SPS (Semi Persistent Scheduling****). In short, to send a data packet over the network, a request is generated for the network which then points to where the packet could be sent, and the process is repeated for every packet; for voice data, a voice call generating a given number of data packets during a minimal time range, once the maximum volume of parallel communications that can be processed is exceeded, other communications are rejected or placed on hold. A precise admittance control study (how many parallel calls can be processed?) is then very important. Another element to consider is the VoLTE low dedicated energy consumption for devices, unlink other forms of voice over IP. Finally, Studies show important discrepancies in operators’ networks quality due to deployed features or not.
*QCI: QoS Class Identifier
**Guaranteed Bit Rate (GBR) or non-Guaranteed Bit Rate (non-GBR) ***http://en.wikipedia.org/wiki/QoS_Class_Identifier
