Peer-to-Peer Protocol (P2PP)
Encyclopedia
Peer-to-Peer Protocol is an Application-layer protocol that can be used to form and maintain an overlay among participant nodes. It provides mechanisms for nodes to join, leave, publish, or search for a resource-object in the overlay. It maintains information about nodes in a routing table
. Because of potentially large content, a node's routing table only contains a subset of these nodes. If a node can't accomplish the request, it searches for one who can, by performing a nextHop operation to a destination from the routing table (recursive-routing).
(TLV) objects. It can be either a request or a response. The response header contains a response code (see codes). They cannot be combined in one message if an unreliable transport is used, due to limitations of UDP MTU.
negotiated at join, Additional Fields: their inclusion is left to the overlay implementer.
Uptime (32 bits)
Resource-Info: Number of Neighbors (16 bits), CPU Utilization (8 bits), CPU Utilization of this peer on a scale of 1 to 100, bandwidth Utilization (8 bits), on a scale of 1 to 100, Peer Bandwidth (32 bits), kilo bits per second
.
1xx (Provisional), response data which provides an update on the progress of the request. These responses are only sent when request is sent over an unreliable transport in a recursive manner.
2xx (Success), response data which indicates that the request has been processed successfully in some sense.
3xx (Redirect), response data which indicates that the request should be redirected.
4xx (Request Failure), response data which indicates that the request has failed.
If the request was received over TCP, it SHOULD be forwarded over TCP.
A peer issuing the request MAY request to receive a copy of the routing and neighbour tables of recipient.
480 Alternative Service response, demands resending request over TCP directly to the peer which generated this response.
The request SHOULD be sent over TCP if its size exceeds UDP MTU.
The response is matched to the appropriate request transaction by the transaction-ID.
Iterative routing : (can be sent to multiple peers at the same time), the peer sends a request to another peer which replies with the network address of the peer to which the request should be forwarded; the requesting peer has control over peers the request is forwarded. UDP can send messages limited by MTU. TCP needs a connection establishing with each requested node (what takes time due to three-way handshake). It is preferred to use UDP for lookups (by sending only resource-ID), and TCP to send whole resource-object once, when node responsible for it has been found. TCP used to maintain routing tables causes increasing of necessary connections up to 320. If request sent over UDP and response extends MTU, 413 Message Too Large, returned.
Routing table
In computer networking a routing table, or Routing Information Base , is a data table stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics associated with those routes. The routing table contains information about the...
. Because of potentially large content, a node's routing table only contains a subset of these nodes. If a node can't accomplish the request, it searches for one who can, by performing a nextHop operation to a destination from the routing table (recursive-routing).
Basic functions of the protocol are
- Resource publishing and look-up.
- P2P networkPeer-to-peerPeer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...
maintenance. - Heterogeneous connectivity.
- P2PP is a request–response protocol
Messages
A message is a P2PP protocol message that performs a certain function. It begins with a header followed by a sequence of type-length-valueType-length-value
Within data communication protocols, optional information may be encoded as a type-length-value or TLV element inside of the protocol. TLV is also known as tag-length value....
(TLV) objects. It can be either a request or a response. The response header contains a response code (see codes). They cannot be combined in one message if an unreliable transport is used, due to limitations of UDP MTU.
Type-length-value objects
Peer-Info: a variable length TLV object, can include Uptime, Neighbour/resource-utilization, and NAT and firewall TLV objects, Peer-ID (variable): fixed-length output of the hash functionHash function
A hash function is any algorithm or subroutine that maps large data sets to smaller data sets, called keys. For example, a single integer can serve as an index to an array...
negotiated at join, Additional Fields: their inclusion is left to the overlay implementer.
Additional Information Fields
Unhashed ID of this peer. This is only included in a DHT-based overlay.Uptime (32 bits)
Resource-Info: Number of Neighbors (16 bits), CPU Utilization (8 bits), CPU Utilization of this peer on a scale of 1 to 100, bandwidth Utilization (8 bits), on a scale of 1 to 100, Peer Bandwidth (32 bits), kilo bits per second
Bitrate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
.
Response codes
( same as used in SIP )1xx (Provisional), response data which provides an update on the progress of the request. These responses are only sent when request is sent over an unreliable transport in a recursive manner.
2xx (Success), response data which indicates that the request has been processed successfully in some sense.
3xx (Redirect), response data which indicates that the request should be redirected.
4xx (Request Failure), response data which indicates that the request has failed.
Request / Response Rules
Requests cannot be combined.If the request was received over TCP, it SHOULD be forwarded over TCP.
A peer issuing the request MAY request to receive a copy of the routing and neighbour tables of recipient.
480 Alternative Service response, demands resending request over TCP directly to the peer which generated this response.
The request SHOULD be sent over TCP if its size exceeds UDP MTU.
The response is matched to the appropriate request transaction by the transaction-ID.
Routing
Recursive routing : the request traverses the peers until it reaches the peer responsible for the resource-object if it exists; the peer issuing has no control over peers the request traverses.Iterative routing : (can be sent to multiple peers at the same time), the peer sends a request to another peer which replies with the network address of the peer to which the request should be forwarded; the requesting peer has control over peers the request is forwarded. UDP can send messages limited by MTU. TCP needs a connection establishing with each requested node (what takes time due to three-way handshake). It is preferred to use UDP for lookups (by sending only resource-ID), and TCP to send whole resource-object once, when node responsible for it has been found. TCP used to maintain routing tables causes increasing of necessary connections up to 320. If request sent over UDP and response extends MTU, 413 Message Too Large, returned.