To make mobile IP telephony over cellular radio systems an economically viable alternative to circuit-switched voice, it is an absolute requirement that the 40-octet IP/UDP/RTP headers on IP telephony packets be reduced in size to conserve bandwidth and radio spectrum.We evaluate the performance of the default header compression scheme for IPAJDPIRTP, CRTP (RFC-2508), over links built on cellular radio access technology. We find that CRTP does not perform adequately over such links, and suggest that a more robust header compression scheme must be developed to make IP telephony over cellular economically viable. 'Evaluation o f CRTP Performance over Cellular Radio Links MIKAEL PEGERMARK, LULE UNIIVERSITY OF TECHNOLOGY HANS H A N N U , LARS-ERIK J O N S S O N , AND KRISTER SVANBRO, ERICSSON ERISOFT AB1P telcphony gaining v having several hundred million users, it seems inevitable fhat so&e future wireless telephony systems will be based on IP technology. What we know today as cellular phones may, in addition to telephony and video, have IP stacks, Web browsers, e-mail clients, networked games, and so on. If based on IP, telephony service will be much more flexible than today. This document concentrates on the problem of providing a good IP solution for speech, but it is understood that applications for video, games, and so forth will also have to be supported.It is vital for cellular phone systems to use radio resources efficiently in order to support a sufficient number of users per cell. Only then can deployment costs be kept low enough. It will also be important to provide sufficiently high-quality voice and video. In particular, voice service should be as good as users expect from the cellular phone systems of today. A lower quality may only be accepted if costs are significantly reduced.The radio channels used in cellular systems have very high bit error rates (BER) due to shadow fading, multipath fading, and continuous mobility. The radio signals of one user will interfere with those of other users, so with the desired number of users per cell BERs will be high. Even after error correcting channel coding, the remaining BER can be as high as 10-3 (one in 1000) or even 10-2 (one in 100) for some users some of the time.The only cost efficient way to achieve sufficient voice quality over such channels appears to be to use clever speech coders and decoders that can tolerate some damage to the encoded sound data. It is not feasible to use a link layer that delivers all data reliably through an automatic repeat request (ARQ) scheme with link-local retransmission. Intolerably high delays would be the result. If the long maximum delays caused by an ARQ scheme were acceptable, it would be better to spread the signal over time in order to reduce the BER rather than using an ARQ protocol. Nor is it feasible to have the link layer discard all damaged frames. The large fraction of discarded frames would result in insufficient speech quality.Unless explicitly stated otherwise, the numbers and figures presented in t...
This document describes lower layer guidelines for robust header compression (ROHC) and the requirements ROHC puts on lower layers. The purpose of this document is to support the incorporation of robust header compression algorithms, as specified in the ROHC working group, into different systems such as those specified by Third Generation Partnership Project (3GPP), 3GPP Project 2 (3GPP2), European Technical Standards Institute (ETSI), etc. This document covers only lower layer guidelines for compression of RTP/UDP/IP and UDP/IP headers as specified in [RFC3095]. Both general guidelines and guidelines specific for cellular systems are discussed in this document.
-The world of telecommunications is currently going through a shift of paradigm from circuit switched, connection oriented information transfer towards packet switched, connection-less transfer. For application independence and to decrease costs for transport and switching it is attractive to go IP all the way over the air interface to the end user equipment, i.e., to not terminate the IP protocols before the air interface. A major reason to avoid using voice over IP over the air interface has, up to now, been the relatively large overhead imposed by the IP/UDP/RTP headers of voice packets. This paper presents a novel header compression scheme, ROCCO, that can compress the large headers to a minimum of one octet and is robust against the errors imposed by cellular links. Its performance is excellent both in terms of robustness and compression efficiency. Moreover, system capacity simulations are presented, which show that ROCCO gives significantly higher system capacity than the other current header compression candidate, CRTP. Finally it is argued that with ROCCO voice over IP over wireless becomes feasible from a spectrum-efficiency point of view.
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.
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