Traffic generation

Traffic generation

Traffic is a flow of data in a communication channel. For example, web traffic is the data that is sent or received by a user's web-browser. During the development of telecommunication systems it is very important to precisely simulate various kinds of traffic generated, for example, by a wireless device.There are two kinds of data networks: circuit-switched and packet-switched. The traffic in the former model is generated constantly (for example, in IS-95 networks a data packet is sent every 20 ms, not depending on whether there is any data to send or not). In the packet-switched networks the traffic has bursty nature, i.e. sometimes there the data is transmitted only if there is something to transmit.

There are at least two approaches for traffic generation in packet-switched networks: the 3GPP2 model and the 802.16 model. The 3GPP2 model is much more complex to implement but it is supposed to give more precise results. The 802.16 model is much simpler in realization.

3GPP2 model

The 3GPP2 model is described in [http://www.3gpp2.org/Public_html/specs/C.R1002-0_v1.0_041221.pdf CDMA2000 Evaluation Methodology Version 1.0 (Revision 0)] . This document describes the following types of traffic generators:
* Downlink:
** HTTP/TCP
** FTP/TCP
** WAP
** near real-time Video
** Voice
* Uplink:
** HTTP/TCP
** FTP/TCP
** WAP
** Voice
** Mobile Network Gaming

The main idea is to partly implement HTTP, FTP and TCP protocols. For example, an HTTP traffic generator simulates the download of a web-page, consisting of a number of small objects (like images). A TCP stream (that's why TCP generator is a must in this model) is used to download these objects according to HTTP1.0 or HTTP1.1 specifications. These models take into account the details of these protocols' work. The Voice, WAP and Mobile Network Gaming are modelled in a less complicated way.

802.16 model

The 802.16 model is much simpler. It was proposed in several [http://www.wirelessman.org/tg3/contrib/ 802.16 TG3 contributions] . The idea is to define three basic models:
* Interrupted Poisson Process (IPP)
* Interrupted Discreet Process (IDP)
* Interrupted Renewal Process (IRP)and mix them together in order to simulate different kinds of web-traffic. Every interrupted process may be either in ON or OFF state. The packets are generated only in ON state. The lengths of ON and OFF periods, sizes of the packets and intervals between them are defined separately in each model, so these models differ in the way their parameters are defined. These models may be mixed together, for example: 4IPP means a mix of four IPP flows with different parameters.HTTP and FTP is simulated as 4IPP; VoIP is simulated as IDP, 2IDP, 4IDP; Video is simulated as 2IRP.


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