Performance Evaluation of ROHC Reliable and Optimistic Mode for Voice over LTE

Voice over LTE (VoLTE) is crucial for mobile network operators in order to avoid falling back to 3G or 2G for voice services. Since VoLTE uses IP as transport protocol, RObust Header Compression (ROHC) is a mandatory feature to reduce header overhead and transport efficiency. ROHC defines two different bidirectional modes -- (R)eliable and (O)ptimistic -- with significant differences in implementation and operation. The relevant specifications do not give any recommendation on which mode should be preferably used for VoLTE. This work contributes a comprehensive performance evaluation of ROHC R-mode and O-mode. The main result is that while R-mode has a better technical performance in some aspects, the impact on the voice quality is statistically not significant. The performance evaluation was conducted by means of a testbed with an implementation of both RoHC modes, providing full reference QoE results for voice audio quality.