Table 1 The primitive operations used in the SPS algorithm

AddClientnodes(n _i )

Node n _i adds client nodes until n _i is full-loaded or no more client nodes can be found. Specifically, n _i first searches its neighbors to find and add nodes. After that, if n _i is still under-loaded, n _i searches its neighbors’ neighbors to find and add client nodes.

ChangeRole(n _i )

Node n _i changes its role.

ExistBiggerSPCandidate(n _i )

n _i sends messages to its neighbors to check whether its neighbors’ super-peer candidates have higher capacity than CanSP(n _i ). If that is the case, true is returned. Otherwise, false is returned.

NotifyNewSPcandidates (n _i )

n _i notifies its neighbors to update their sets of super-peer candidates to be CanSP(n _i ).

RetriveUpdateSPc(n _i )

Node n _i checks whether there is a message about new super-peer candidates UpdSP. If such a message exists, UpdSP is returned. Otherwise, null is returned.

RetriveNewSPCandidates(n _i )

Node n _i computes its new set of super-peer candidates CanSP(n _i ) according to its retrieved set of super-peer candidates through communication with its neighbors.

RemoveFailedSPIfExist(n _i ).

Node n _i checks whether there is a message about super-peer failure. If such a message exists, the failed super-peer contained in the message is removed from the super-peer candidates of n _i .

Search&JoinUnderLoadedSP(n _i )

Node n _i sends query messages to super-peers contained in its super-peer candidates to check these nodes’ workloads. If a super-peer that is under-loaded is found, n _i joins this super-peer.

SPFailureHander(n _i )

When the super-peer of n _i (i.e., SP(n _i )) fails, n _i removes SP(n _i ) from its set of super-peer candidates and empties its super-peer. n _i also notifies its neighbors of the failure of SP(n _i ).

TransferClients(n _i )

When a super-peer n _i has to change its role to be a client peer, n _i transfers its client peers (if any) to super-peers that are randomly selected from its set of CanSP(n _i ).

UpdateSPCandidates(n _i ,UpdSP)

Node n _i updates its set of super-peer candidates to be UpdSP, which is an ordinary set to store updated super-peer candidates.