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# Chord Node Join

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### Chord Node Join

1. 1. HOW NODE JOINS OR LEAVE IN PEERTO PEER NETWORKPresented by:Chaitanya Pratap SinghMCA(4th Semester)South Asian University, new Delhi.
2. 2. NODE JOIN (PEER JOIN) Joining peer sends a "join" request to the boot peer, and gets a GUID back. Joining peer sends a "copy routing table" to the boot peer. Joining peer finds the correct peers it should have in its own routing table.
3. 3. THE JOIN REQUEST The first peer to join the network apart from the boot peer, will connect to the boot peer and send a "join" message. The boot peer responds with a new GUID to the joining peer.
4. 4. THE COPY ROUTING TABLE REQUEST After getting a GUID, the joining peer requests to get a copy of the boot peers routing table.
5. 5. FINDING THE CORRECT PEERS FOR THEROUTING TABLE the joining peer uses this routing table to find the peers it should really have in its routing table.
6. 6. LEAVING NODE When a peer no longer wants to be part of a P2P network, it will send a "leave" request to all peers in its routing table
7. 7. CONT… if A has B in its routing table, B does not necessarily have A in its routing table. Thus, if A leaves a Chord network, it would have to find the peers in the network that has A in its routing table. In other words, find those peers which have distance(X, A) closest to 20, 21, 22 etc. Once those peers are found, the leaving peer (A) will send a leave message to each of them.
8. 8. CHORD STATE AND LOOKUP (1) Basic Chord: each m=6 node knows only 2 2m-1 N1 other nodes on the ring 0  Successor N56 N8  Predecessor (for ring K54 lookup(K54) management) N51 Lookup is achieved by N14 forwarding requests N48 around the ring through successor pointers  Requires O(N) hops N42 N21 N38 8 N32
9. 9. CHORD STATE AND LOOKUP (2) Finger table N8+1N14 Each node knows m m=6 N8+2N14 N8+4N14 other nodes on the ring 2m-1 N8+8N21  Successors: finger i of n N1 N8+16 N32 0 points to node at n+2i (or N8+32 N42 successor) N56 lookup(K54) N8  Predecessor (for ring K54 +1 management) N51 +2  O(log N) state per node +4 Lookup is achieved by N48 +16 +8 N14 following closest +32 preceding fingers, then successor N42  O(log N) hops N21 N38 9 N32
10. 10. JOINING THE RING Three step process:  Initialize all fingers of new node  Update fingers of existing nodes  Transfer keys from successor to new node
11. 11. JOINING THE RING — STEP 1 Initialize the new node finger table  Locate any node n in the ring  Ask n to lookup the peers at j+20, j+21, j+22…  Use results to populate finger table of j
12. 12. JOINING THE RING — STEP 2 N8+1N14 N8+2N14 Updating fingers of m=6 N8+4N14 existing nodes 2m-1 N8+8N21 N1 N8+16 N28 N32 0  New node j calls 6 N8+32 N42 N56 N8 update function on existing nodes that N51 12 must point to j  Nodes in the ranges N48 N14 +16 -16 [j-2i , pred(j)-2i+1]  O(log N) nodes need to be updated N42 N21 N38 N28 12 N32
13. 13. JOINING THE RING — STEP 3  Transfer key responsibility  Connect to successor  Copy keys from successor to new node  Update successor pointer and remove keys  Only keys in the range are transferred N21 N21 N21 N21N32 N32 N28 N32 N28 N32 N28 K24 K24 K24 K24 K30 K24 K30 K30 K30
14. 14. NODE JOIN ALGORITHM
15. 15. CONT…