46 lines
2.1 KiB
TeX
46 lines
2.1 KiB
TeX
\documentclass[12pt,a4paper]{article}
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\usepackage[utf8]{inputenc} \usepackage[margin=2cm]{geometry}
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\usepackage{amstext} \usepackage{amsmath} \usepackage{array}
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\newcommand{\lra}{\Leftrightarrow}
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\title{Howework 3 -- Computer Networking}
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\author{Claudio Maggioni}
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\begin{document} \maketitle
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\section*{Exercise 1}
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The EUI-48 MAC address space can have $2^{48} = 281474976710656$ possible addresses. The IPv4 address space has $2^32 = 4294967296$
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addresses while IPv6 has = $2^{128} \approx 3,402823669209385 \cdot 10^{38}$ addresses. In practice, some of the addresses in
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these spaces may be reserved for special purposes (e.g.
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\texttt{FF:FF:FF:FF:FF:FF} as the broadcast MAC address or the
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\texttt{127.0.0.0/8} subnet reserved for loopback networks
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in IPv4) so the number of usable addresses is smaller than
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these figures.
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\section*{Exercise 2}
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$$D = 1010100000_2 = 512_{10} + 128_{10} + 32_{10} = 672_{10}$$
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$$G = 10011_2 = 19_{10}$$
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$$r = |G| - 1 = 4$$
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$$R =D \cdot 2^r \mod G = 10752 \mod 19 = 17$$
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\section*{Exercise 3}
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For 10 Mbps:
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$$t = \frac{100 \cdot 512 b}{10^7\frac{b}{s}} = 5.12 ms$$
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For 100 Mbps:
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$$t = \frac{100 \cdot 512 b}{10^8\frac{b}{s}} = 0.512 ms$$
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\section*{Exercise 4}
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A mechanism that an AP can use to maintain constant reliability (e.g. constant BER) while communicating with a station that is getting farther away from it is to use rate adaptation: once transmission errors are detected through ARQ checks, the AP can switch to a lower transmission rate (akin to TCP's congestion control mechanisms) to counteract interference and lowering signal strength.
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The AP may also decide to boost its transmission power if possible, thus increasing signal strength. However, this technique does not provide a linear increase in signal strength since obstacles or powerful interferences may be present.
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In alternative, if the station is in a ESS and another AP is present in the same subnet, the station may decide to hop from the first AP to the new AP if the latter has a better RSSI. If the DS uses switches, those should be informed of the change of BSS so as to keep their switching tables updated.
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\end{document}
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