Análisis: Estudiante 1

As we are to assume, the battery consumption results are correlated with the bandwidth con- sumption, as well as the transmission interval. The relation between the battery consump- tion and the bandwidth consumption is shown in Figure 4.30, and the relation between the battery consumption and the transmission interval is shown in Figure 4.31. With the band- width, we mean the combined bandwidth usage of the uplink and downlink directions, and with the transmission interval, we mean the average time between receiving or sending of a message. The figures sum up the battery consumption measurement results for one client connection presented under the results earlier. For example, the “TURN server signaling” scenario means the battery consumption is measured on a mobile TURN server that re- lays signaling data of one client, whereas the “TURN server keepalives” scenario means that only keepalives of one client (between the client and its peer) are relayed. The “TURN client keepalives” scenario then again measures the battery consumption of a mobile TURN

TURN server keepalives TURN server signaling TURN server voice data TURN client keepalives STUN server keepalives STUN client keepalives

TURN server keepalives TURN server signaling TURN server voice data TURN client keepalives STUN server keepalives STUN client keepalives 0
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client that exchanges keepalives with its peer through a TURN server. We will first take a look at the results of a mobile phone acting as a STUN or TURN client. When the impact of keepalives only was observed, the battery duration was at a relatively acceptable level considering that messages were sent regularly over a radio channel. However, it is worth noticing that the consumed bandwidth was very low, that is, 32 bit/s on the STUN client and 66.9 bit/s on the TURN client.

If we consider that a peer implementing the ICE functionality is behind a NAT and part of a P2PSIP overlay, it also has to exchange signaling messages with its peers. We can assume that in such a case the battery duration is less than 5 hours. Naturally, the battery consumption can be even higher depending on the type of data being exchanged between the client and its peers over the connection created using ICE.

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Figure 4.31: Battery duration and transmission interval

The mobile phones are by default much more suitable to work as STUN servers rather than TURN servers. This is because TURN servers implement all the same functionality as STUN servers, and additionally they take care of relaying messages between the client and its peer. A STUN server simply has to respond to incoming requests and ignore received indications. Yet, the difference of being a STUN or TURN server for one client is very subtle if only keepalives are being transmitted, even if the TURN server is relaying the keepalives of the client and its peer.

Next, let us consider a case where a publicly reachable peer is part of a P2PSIP overlay and is capable of working as a STUN and TURN server. The impact of the peer’s own overlay maintenance signaling drains the battery so fast that the battery consumption that a few

STUN or TURN clients’ keepalives cause on the peer is very little. Of course, the situation changes if the number of clients grows, or if some type of data is being relayed in addition to keepalives.

In a 3G Wideband Code Division Multiple Access (WCDMA) network, there are three dif- ferent Radio Resource Control (RRC) states to match the power consumption level to the required traffic level [23]. For the highest power consumption state the typical power con- sumption is 200-400 mA [25]. According to [23], when there is not much data to transmit the battery consumption roughly halves. In the lowest connected state, where the phone can be paged but cannot transmit data, only 1-2 percent of the highest state’s power is con- sumed. In our measurements, the mobile phone acting as a STUN or TURN client sending keepalives, or as a STUN or TURN server relaying keepalives from a single client con- sumed on average 99-104 mA knowing the phone’s battery capacity to be 930 mAh. For a TURN server relaying overlay maintenance signaling or voice data the average power consumption was 205-233 mA. STUN client with signaling consumed on average 192 mA. Based on this, we can conclude that the mobile phone in our keepalive measurements used mostly the middle RRC state, since it did not send or receive messages that frequently, whereas the signaling data and voice data utilize mostly the highest RRC state. The fact that HSDPA was used for the downlink should not make a big difference, as reported in [18] which measures the difference in power consumption between plain 3G and HSDPA in a similar setup. Compared to the standby time, which is 350 hours, the mobile phone drains the battery 37.4 times faster by sending keepalives (STUN client with one connection). In the case of voice data relaying (TURN server relaying one connection), the mobile phone’s battery lasts half an hour longer than the talk time is specified to last.