**8. Acknowledgments**

This work was supported by the Innovation Center, Ericsson Telecomunicações S.A., Brazil, and CNPq

#### **9. References**

20 Will-be-set-by-IN-TECH

**Original Cable Model x Fitted Cable Model 8 bits Fitted**

**10 bits Fitted 12 bits Fitted 14 bits Fitted 16 bits Fitted 18 bits Fitted 20 bits Fitted 8 bits Original 10 bits Original 12 bits Original 14 bits Original 16 bits Original 18 bits Original 20 bits Original**

**8 bits/tone 10 bits/tone 12 bits/tone 14 bits/tone 16 bits/tone 18 bits/tone 20 bits/tone**

**<sup>50</sup> <sup>100</sup> <sup>150</sup> <sup>200</sup> <sup>250</sup> <sup>300</sup> <sup>350</sup> <sup>400</sup> <sup>450</sup> <sup>500</sup> <sup>0</sup>**

**Cable length (m)**

Fig. 24. Difference between the obtained results using ETSI PE04 cable model and the fitted

Finishing the frequency domain simulations described here, it is shown the impact of uncanceled far-end crosstalk in the achievable data rates of the fourth generation DSL systems even if they use different maximum number of bits/tone. The scenario overview is like the one illustrated in Figure 20. It was used the ESTI PE04 cable model. It was done because no crosstalk models were fitted. Figure 25 illustrates the obtained results, where it becomes clear that the data rate degrades significantly if no attempt is done to control crosstalk effects. The results reinforces that crosstalk mitigation techniques are highly recommended for the fourth

**<sup>50</sup> <sup>100</sup> <sup>150</sup> <sup>200</sup> <sup>250</sup> <sup>300</sup> <sup>350</sup> <sup>400</sup> <sup>450</sup> <sup>500</sup> <sup>100</sup>**

During the last years, broadband technologies over copper increased their end-user bit rates

The fourth generation DSL systems, wish to improve the provided services achieving data rates near 1 Gb/s. As the direct channel attenuation is higher if the copper loop is long, the use of short cables will be inevitable to ensure improved rates. The copper cable reduction process will allow the use of unexplored transmission frequencies, much higher than the current 30

Fig. 25. Performance of 4th generation DSL systems using different values of maximum

**Cable length (m)**

generation DSL systems, allowing them to achieve the best possible performance.

**200 400 600 800 1.000 1.200 1.400 1.600**

number bites/tone impaired by uncanceled FEXT.

**Obtained data rate (Mb/s)**

**Obtained data rate (Mb/s)**

0.4mm cable model.

**7. Conclusion**

due to a step-by-step evolution.


**1. Introduction**

impact (Das & Kangasharju (2006)).

on several key elements:

through a rendering interface.

<sup>4</sup> http://www.tribler.org/trac/

<sup>3</sup> http://www.rasterbar.com/products/libtorrent/

selflessness;

peer);

**0**

**14**

**Protocol Measurements in**

Based on BitTorrent's success story (it has managed to become the number one protocol of the internet in a matter of years), the scientific community has delved heavily in analysing, understanding and improving its performance. Research focus has ranged from measurements (Pouwelse et al. (2004)) to protocol improvements (Tian et al. (2007)), from social networking (Pouwelse et al. (2008)) to moderation techniques (Pouwelse et al. (2005)), from content distribution enhancements (Vlavianos et al. (2006)) to network infrastructure

The BitTorrent protocol currently (October, 20111) accounts for one of the largest percentages of the Internet traffic. Designed to provoke peers to give more in order to get more, the BitTorrent protocol is a prime choice for large data distribution. BitTorrent's design relies

• the use of a particular form of *tit-for-tat* that prevents free riding2 and stimulates peers'

• *optimistic unchoke* lets a peer periodically allow a connection from another peer in order to exchange content; (*choking* is the operation by which a peer closes its connection to another

In this chapter we present a novel approach involving client-side information collection regarding client and protocol implementation. We have instrumented a libtorrent-rasterbar client3 and a Tribler4 client to provide verbose information regarding BitTorrent protocol implementation. These results are collected and subsequently processed and analysed

The aim is to measure and analyze protocol messages while in real-world environments. To achieve this aim, a virtualized infrastructure had been used for realistic environments; apart

• *rarest piece first* aims to distribute all pieces among peers and increase availability.

<sup>1</sup> http://www.sandvine.com/news/global\_broadband\_trends.asp <sup>2</sup> though this can be circumvented as shown in BitThief (Locher et al. (2006))

**BitTorrent Environments**

*University POLITEHNICA of Bucharest*

Razvan Deaconescu ˘

*Romania*

