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2.7.3
 
Real-Time Control Protocol 
Real-Time Control Protocol (RTCP) [16]is a protocol used in conjunction with RTP. 
RTCP packets are sent periodically from each participant in an RTP session to all other 
participants in the session using Internet Protocol Multicast (IP-M). These packets do 
not encapsulate media chunks as in RTP, but contains sender/receiver reports that can 
be useful for the application. 

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3.1 TMMS Service based on GPRS: : Overview 
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3
TMMS Service based on GPRS 
In this chapter we will first give a brief introduction to GPRS, which is the technology 
our end-to-end mobile service in this chapter is based on. This introduction is based on 
how GPRS is specified in[25]. We continue this chapter with presenting how we have 
chosen to design our GPRS based service, before we finish the chapter with an 
evaluation of the service we have designed, based on the criteria and scenarios given in 
2.5. 
3.1
 
Overview 
In the 1990’s it was decided that it was necessary to develop a Third Generation (3G) 
cellular technology that was able to use both voice and data communications. Since these 
things take long time to deploy, companies developed interim protocols and standards 
that open for data transmission over the existing Second Generation (2G) infrastructure. 
This was called Second and a half Generation (2,5G) and GPRS is a part of the 2,5G 
infrastructure [20].
3.1.1
 
Architecture 
GPRS provides an end-to-end packet transfer service, in contrast to e.g. the data transfer 
service provided by GSM which is circuit switched. The intention of using packet 
switching is to use the network resources more efficient. This makes it cheaper to use 
then a circuit switched base service as well. 
It depends on a Radio Access Network (RAN) from the Public Land Mobile Network 
(PLMN), which can be GSM/Enhanced Data rates for Global Evolution (EDGE) Radio 
Access Network (RAN) (GERAN)[xx] or Universal Terrestrial Radio Access Network 
(UTRAN)[xx]. These radio interfaces are named the Um and the Uu reference points, 
respectively, in the 3GPP specifications. 
It is operator specific how to charge for GPRS usage, but most likely a charging scheme 
based on usage rather than duration will be enforced. This means that customers can stay 
connected and will only be charged for the packets transferred during the session. 
Another charging scheme is to charge for service access per month, like NTT DoCoMo's 
i-mode concept [26].
The main concept of GPRS is that for the new GPRS radio channel, the GSM system 
can allocate between one and eight time slots within a Time Division Multiple Access 
(TDMA) frame. These time slots are allocated on demand. 

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3.1 TMMS Service based on GPRS: : Overview 
Page 29 of 93 
GPRS defines two different bearer service types: 
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