Terms in this document are defined in-line when used and are also defined below for reference. The definitions in this section use terminology and concepts that are not explained until later in the specification.
Admitting Peer (AP): A peer in the overlay which helps the Joining Node join the Overlay.
Bootstrap Node: A network node used by Joining Nodes to help locate the Admitting Peer.
Client: A host that is able to store data in and retrieve data from the overlay, but does not participate in routing or data storage for the overlay.
Configuration Document: An XML document containing all the Overlay Parameters for one overlay instance.
Connection Table: Contains connection information for the set of nodes to which a node is directly connected, which include nodes that are not yet available for routing.
Destination List: A list of Node-IDs, Resource-IDs, and Opaque IDs through which a message is to be routed, in strict order. A single Node-ID, Resource-ID, or Opaque ID is a trivial form of Destination List. When multiple Node-IDs are specified, a
Destination List is a loose source route. The list is reduced hop by hop, and does not include the source but does include the
destination.
DHT: A distributed hash table. A DHT is an abstract storage service realized by storing the contents of the hash table across a set of peers.
ID: A generic term for any kind of identifiers in an Overlay. This document specifies an ID as being an Application-ID, a Kind-ID, a Node-ID, a transaction ID, a component ID, a response ID, a
Resource-ID, or an Opaque ID.
Joining Node (JN): A node that is attempting to become a peer in a particular Overlay.
Kind: A Kind defines a particular type of data that can be stored in the overlay. Applications define new Kinds to store the data they use. Each Kind is identified with a unique integer called a
Kind-ID.
Kind-ID: A unique 32-bit value identifying a Kind. Kind-IDs are either private or allocated by IANA (see Section 14.6).
Maximum Request Lifetime: The maximum time a request will wait for a response. This value is equal to the value of the overlay
reliability value (defined in Section 11.1) multiplied by the number of transmissions (defined in Section 6.2.1), and so defaults to 15 seconds.
Node: The term "node" refers to a host that may be either a peer or a client. Because RELOAD uses the same protocol for both clients and peers, much of the text applies equally to both. Therefore, we use "node" when the text applies to both clients and peers, and we use the more specific term (i.e., "client" or "peer") when the text applies only to clients or only to peers.
Node-ID: A value of fixed but configurable length that uniquely identifies a node. Node-IDs of all 0s and all 1s are reserved. A value of 0 is not used in the wire protocol, but can be used to indicate an invalid node in implementations and APIs. The Node-ID of all 1s is used on the wire protocol as a wildcard.
Overlay Algorithm: An overlay algorithm defines the rules for
determining which peers in an overlay store a particular piece of data and for determining a topology of interconnections amongst peers in order to find a piece of data.
Overlay Instance: A specific overlay algorithm and the collection of peers that are collaborating to provide read and write access to it. Any number of overlay instances can be running in an IP
Overlay Parameters: A set of values that are shared among all nodes in an overlay. The overlay parameters are distributed in an XML document called the Configuration Document.
Peer: A host that is participating in the overlay. Peers are responsible for holding some portion of the data that has been stored in the overlay, and they are responsible for routing messages on behalf of other hosts as needed by the Overlay Algorithm.
Peer Admission: The act of admitting a node (the Joining Node) into an Overlay. After the admission process is over, the Joining Node is a fully functional peer of the overlay. During the admission process, the Joining Node may need to present credentials to prove that it has sufficient authority to join the overlay.
Resource: An object or group of objects stored in a P2P network.
Resource-ID: A value that identifies some resources and which is used as a key for storing and retrieving the resource. Often this is not human friendly/readable. One way to generate a Resource-ID is by applying a mapping function to some other unique name (e.g., user name or service name) for the resource. The Resource-ID is used by the distributed database algorithm to determine the peer or peers that are responsible for storing the data for the
overlay. In structured P2P networks, Resource-IDs are generally fixed length and are formed by hashing the Resource Name. In unstructured networks, Resource Names may be used directly as Resource-IDs and may be of variable length.
Resource Name: The name by which a resource is identified. In unstructured P2P networks, the Resource Name is sometimes used directly as a Resource-ID. In structured P2P networks, the
Resource Name is typically mapped into a Resource-ID by using the string as the input to hash function. Structured and unstructured P2P networks are described in [RFC5694]. A SIP resource, for example, is often identified by its AOR (address-of-record), which is an example of a Resource Name.
Responsible Peer: The peer that is responsible for a specific resource, as defined by the Topology Plug-in algorithm.
Routing Table: The set of directly connected peers which a node can use to forward overlay messages. In normal operation, these peers will all be in the Connection Table, but not vice versa, because some peers may not yet be available for routing. Peers may send
messages directly to peers that are in their Connection Tables, but may forward messages to peers that are not in their Connection Table only through peers that are in the Routing Table.
Successor Replacement Hold-Down Time: The amount of time to wait before starting replication when a new successor is found; it defaults to 30 seconds.
Transaction ID: A randomly chosen identifier selected by the originator of a request that is used to correlate requests and responses.
Usage: The definition of a set of data structures (data Kinds) that an application wants to store in the overlay. A usage may also define a set of network protocols (Application IDs) that can be tunneled over TLS or DTLS direct connections between nodes. For example, the SIP Usage defines a SIP registration data Kind, which contains information on how to reach a SIP endpoint, and two
Application IDs corresponding to the SIP and SIPS protocols.
User: A physical person identified by the certificates assigned to them.
User Name: A name identifying a user of the overlay, typically used as a Resource Name or as a label on a resource that identifies the user owning the resource.