Policing aggregates of voice traffic with the token bucket algorithm

Estimating correct traffic descriptors is an important issue when deploying IP telephony with quality of service guarantees. Usually, a token bucket is used to police a traffic flow. Such a policer checks (and ensures) that the traffic flow fits inside a traffic envelope. For variable bit rate (VBR) sources normally two traffic envelopes are specified: one dealing with the peak rate and one dealing with the sustainable rate with an associated burst size. These parameters have to be specified when making a reservation with either the resource reservation protocol (RSVP) in case of IntServ or may be specified in a service level specification (SLS) when using DiffServ. This paper shows how to choose the traffic descriptors for aggregate voice traffic for both constant bit rate sources and sources that use voice activity detection. Also the influence of variable packet size on the packet discard ratio (PDR) is shown. A traditional policer discards large packets more frequent than smaller ones. To alleviate this, a modification to the token bucket algorithm is proposed.