Efficient transport of voice over IP over cellular links

Abstract

A bstmct-Internet and cellular technologies are merging t o decrease transport costs and enable IP-based applications t o hundreds of millions of cellular users. Real time voice services will continue t o be dominant in future cellular systems and t o reduce system costs it is desirable t o base all services, including voice, on IP. However, the radio spectrum must be efficiently used t o provide mass-market services a t reasonable prices, but Internet protocol headers are large in size. Moreover, data discarding policies are poorly suited to the error-proneness of cellular links. Protocol overhead for IP-based voice services can be reduced by compressing headers, e.g. with the Compressed Real Time Protocol (CRTP). CRTP, however, does not perform well over cellular links since it is not robust in the face of errors. ROCCO, a header compression scheme suitable for cellular systems, delivers more packets t o the user than CRTP at realistic error rates with a better average compression ratio. Voice services in cellular systems should also be able t o use damaged speech data. This can be done using the UDP Lite protocol which provides a more flexible checksumming policy that enables delivery of data possibly usable t o the application. This paper shows that CRTP/UDP fails t o deliver sufficient service quality a t the error rates of a cost-efficient cellular system and t h a t ROCCO combined with UDP Lite can provide an IP-based voice service over such cellular systems.

Survey of Header Compression Techniques over Multiprotocol Label Switching (MPLS)

“…With this signalling, the de-compressor asks for a context update from the compressor and during this time interval, all the packets will be discarded. Thus, CRTP does not perform well on error prone links such as wireless links [102] [103].…”

Robust header compression (ROHC) in next-generation network processors

“…Coupled with transport and link layer protocols capable of partitioning checksum coverage into sensitive and insensitive regions [9], ROCCO was designed to perform well with audio and video codecs which tolerate bit errors in data frames. Studies showed that ROCCO compressed headers to half of the size of those provided by CRTP and remained robust over links with BER rates an order of magnitude higher [10]. In July 2000, Ericsson and Japan Telecom successfully completed a field trial of VoIP over WCDMA using ROCCO [11].…”