Chord. Retrieved June 8, 2012, from Oxford Music Online: xxx.xxxxxxxxxxxxxxxxx.xxx Oxford Dictionary of Music. (2012c). Course. Retrieved December 18, 2012, from Oxford Music Online: xxx.xxxxxxxxxxxxxxxxx.xxx Oxford Dictionary of Music. (2012c). Scoring. Retrieved January 24, 2012, from Oxford Music Online: xxx.xxxxxxxxxxxxxxxxx.xxx Päffgen, P. (2002). Die Gitarre; Geschichte, Spieltechnik, Repertoire (2. überarbeitete und erweiterte Neuauflage ed.). Mainz: Xxxxxx.
Chord. The nodes in Chord [26] are identified by a hash of 160 bits, typically obtained from the IP address of the node (although it is not a requirement), and sorted in a circle (ring topology). The packets are always sent in one direction (clockwise) via the ring until they arrive at the destination node. Thus, each node in Chord needs to know only its successor. However, to speed up the delivery process, each node stores log2(N) items in its routing table (fingers). The first finger is a pointer to the node with a distance equal to 20 (=1), which is the next node (successor). The second finger is a pointer to a node with distance equal to 21 (=2), the successor of the successor. The third finger points to a node with distance equal to 22 (=4), and successively, the last finger points to a node with distance equal to 2159, which corresponds to a node that is a half-ring away. Each node is better acquainted with its nearest neighbourhood than distant nodes. The key/value pairs are stored at the first node, whose identifier is equal to or greater to the key, measured with the same distance function used in the routing. Chord uses consistent hashing [27] to ensure an even spread of keys among the nodes. To make the system fault tolerant, each node also has a pointer to its predecessor. The routing algorithm runs a stabilization protocol that periodically checks for consistency of immediate successor and predecessor pointers. The look-up procedure finds the finger that is closest to the desired key and sends to that node pointed by that finger a get_value message with the key. This node will in turn route the message to the node from its finger table with the closest identifier to the key. This process ends when a node that receives the message does not know any other node that is closest to the specified key. However, if the node has the key/value entry, it will send it back to the requester node. This procedure requires, at most, log2(N) messages and, as discussed above, the routing table managed by each node consisting of the same amount of entries. Thus, when a node joins or leaves the overlay network, it results in log2(N) message exchanges. There exist a number of other systems employing a similar ring topology. For example, Xxxxx et al. [28] have studied a variety of optimization techniques for DHTs, such as replication strategies, erasure coding, server selection, iterative and recursive routing, proximity routing, and neighborhood selection. DHash++ is a r...
