| A CHUM (Cooperating ad Hoc networking to sUpport Messaging) network is an ad hoc network in which mobile devices cooperate to reduce connection costs when accessing wireless global networks. This dissertation presents how members of a CHUM network cooperate in order to download and to share data stored in the Internet, such as on-air streaming TV content, interactive mobile game programs, MP3 files, movie clips, etc. This dissertation assumes that mobile devices, called the peers, have two wireless interfaces, one for connecting to outside global networks and the other for forming an ad hoc network. When downloading multimedia content, one of the peers, called the proxy, downloads content via the WWAN connection and distributes the data using its WLAN channel. Each peer in a CHUM takes turns serving as the proxy. The multimedia CHUM network needs to maintain membership information and schedules the next proxy. In an one-tier CHUM network, there is no cooperation between the wireless network and the wired network. The proxy performs the maintenance task of the CHUM network. In contrast, a two-tier CHUM network allows the cooperation between mobile peers and their associated servers in wired networks. The associated server of the proxy, called the master server, maintains peer membership information. With the support from the servers in wired networks, peers receive the benefits of saving telecommunication cost, ad hoc wireless bandwidth and computation power, which results in reducing the consumption of battery power. When downloading a file from the Internet, each participating peer may download a unique portion of the file via its WWAN connection, and exchange the portion with other peers in order to reconstruct the complete file. The servers in the wired network specify for each peer to download a specific portion of the file. The distribution of the portion should be carefully controlled, because all peers become senders and receivers at the same time. Uncontrolled distribution may cause a broadcast storm problem. Two distribution methods are introduced: per-packet based and per-peer based. In the per-packet based method, one packet from a peer is rebroadcasted over the ad hoc network at a time. In contrast, the per-peer based method allows each peer to take turns to transmit some of its packets only to its one-hop neighbor peers until all peers receive the complete content. In some special cases, a newly arrived peer may want to fetch some content already stored in an ad hoc CHUM network rather than from the Internet, which obviates repeated downloading of the content via the cost-based WWAN connection. In this case, the CHUM network becomes a content storage for the participating member peers. The CHUM network may also provide an anonymous connection between the source peer and the receiving peer in order to encourage privacy and to discourage traffic analysis. Two intermediate peers help establish the anonymous connection. |
