  This work performs a preliminary, comparative analysis of the end-to-end
quality guaranteed by Voice over LTE (VoLTE), examining several millions of
VoLTE calls that employ two popular speech audio codecs, namely, Adaptive
Multi-Rate (AMR) and Adaptive Multi-Rate WideBand (AMR-WB). To assess call
quality, VQmon, an enhanced version of the standardized E-Model, is utilized.
The study reveals to what extent AMR-WB based calls are more robust against
network impairments than their narrowband counterparts; it further shows that
the dependence of call quality on the packet loss rate is approximately
exponential when the AMR codec is used, whereas it is nearly linear for the
AMR-WB codec.
