7.3 Related Works on Mobile Content Distribution in VANETs
7.3.1 Cooperative Downloading of General Contents in VANETs
In (Nandan et al. 2005), Nandan et al. first studied cooperative downloading in VANETs. They proposed SPAWN, a pull-based, peer-to-peer content downloading protocol for VANETs that extends BitTorrent. Later, they proposed “AdTorrent” (Nandan et al. 2006), which is a semi-push-based peer-to-peer protocol for vehicles to download advertisements they are interested in. In both SPAWN and AdTorrent, the peer and content selection mechanisms have a high overhead and are not scalable, especially when most of the vehicles are interested in downloading popular contents. Also, they suffer from the “coupon collector problem,” which enlarges downloading delay. Moreover, they use Transport Control Protocol (TCP) for content delivery, which performs poorly over multihop lossy wireless links in highly mobile VANETs.
220.127.116.11 Network Coding for Content Downloading
To avoid such problems, many researchers resort to network coding (Ahlswede et al. 2000; Ho et al. 2006). Lee et al. proposed CodeTorrent (Lee et al. 2006), a pull-based content distribution scheme using network coding, where vehicles need to explicitly initiate requests to download a piece of content. CodeTorrent restricts the peer selection and content delivery to the one-hop neighborhood of a vehicle, thus eliminating the need of multi-hop routing. Also, the use of network coding mitigates the peer and content selection ...