Each peer MUST know a few other peers in the same overlay and they work together to provide uniform routing and storage service.

1
Each peer MUST know a few other peers in the same
overlay and they work together to provide uniform
routing and storage service. The information
about other peers may look like what the above
figure show indexed by the Peer ID and some
associated features under the Peer ID. In term
of service discovery, the feature named Service
Capability may help. So each peer could get its
service capabilities on its own, for example, it
could provide STUN or TURN or something else. It
could distribute these information by using
overlay maintenance mechanism in DHT algorithm
and keep it accurate by using keepalive between
it and peers in its routing state.
2

1. If there is a request for a key sent by Peer A,
   we assume that the destination of this request is
   Peer D and it will traverse Peer B and Peer C.
2. The idea for service discovery comes from
   messages in P2P will traverse a few peers and
   these peers know more information about other
   peers in its routing states.
3. So if a peer want to find which peers could
   provide which type of service, it could sends a
   message to the overlay and carry information by
   which the immediate peers know what it want and
   collect information it needs.
4. As the figure on the right, we assume X,Y and Z
   could provide a kind of service which A needs. In
   the end, X and Y and Z are learned by A.

find peers with TRUN service for me?
Peer X Y Z
Peer X Y
Request
Response