There is growing interest in capturing and analyzing Internet traffic characteristics in pursuit of insights into its evolution. We present a study of one of the few sources of publically available long-term Internet traffic workload data, namely the NLANR PMA archive of packet header traces. Trace samples were collected at a number of academic, research, and commercial sites during years 1998-2003. We consider four metrics of traffic: bytes, packets, flows, and number of source-destination pairs. We also analyze the composition of traffic by protocol.