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Adaptive Relay

  • Id: RS-017.
  • Status: Placeholder.
  • Type: Implementation.

Abstract

This specification extends Relaynet Core (RS-000) to keep latencies low when the underlying network (e.g., the Internet) is available.

Table of contents

  1. Introduction
  2. Local PDC Between Gateways
  3. Store-and-Forward vs Cut-Through Mode Selection
  4. Open Questions

Introduction

Relaynet was originally conceived to connect two nodes that might never be connected through a traditional network infrastructure, so a store-and-forward pattern was naturally adopted. With this approach, the data travels through one or more intermediaries, where each will keep a copy of the data until it safely reaches the next node in the route.

This approach helps ensure that data will reach its destination, but it adds latency and complexity when the two nodes can actually communicate directly – For example, when the Internet is available.

In those cases where the target endpoint of a parcel can be reached, the gateway could deliver the parcel immediately and directly, without a courier or a public gateway. It may even start transmitting the parcel as soon as the first few bytes are received, since the target endpoint is one of the first few fields in a RAMF message. This approach is known as cut-through mode in networking.

When a gateway operates in cut-through mode, it will not use a Cargo Relay Binding to connect to a courier. Instead, it will use a binding for local Parcel Delivery Connections (PDCs) to get incoming parcels from its public gateway.

The following diagram shows how parcels would be delivered in a centralized service (one with clients and servers) using cut-through mode:

Note that bindings will remain unchanged, but the roles of client and server would change: The private gateway will become an Internet-based PDC client to public endpoints and a local PDC client to the public gateway. Similarly, this will be transparent to applications and endpoints, and only gateways need to be changed to support this specification.

The role of the public gateway in this scenario would be analogous to that of STUN servers: To allow computers in private networks to get data from the Internet as if they were Internet hosts.

This technique can be seen as a form of adaptive switching in computer networking – Hence the name of this specification.

Local PDC Between Gateways

The local PDC between the private gateway and the public gateway will be almost identical to one between an endpoint and its gateway, except that the private gateway MUST NOT deliver parcels to the public gateway.

Given the nature of the connection, when the private gateway requests a certificate from the public gateway, it would be requesting a Gateway Certificate for itself.

The private gateway SHOULD send any Parcel Delivery Deauthorizations (PDDs) before signalling that it is ready to collect parcels, so that the public gateway can discard any parcels that should not be sent.

Store-and-Forward vs Cut-Through Mode Selection

The private gateway MUST attempt to deliver each parcel to its target endpoint immediately, unless the gateway can be certain that the endpoint will not be reachable.

For example, if the gateway has the ability to know whether the computer is connected to the Internet, it could preemptively run in store-and-forward mode with parcels that should reach the Internet.

Open Questions

  • How can the private gateway send key rotation and certificate revocation messages? Maybe bindings for local PDCs should be changed so that the parcel delivery and parcel delivery acknowledgement messages becomes more generic, like message delivery and message delivery acknowledgement, respectively.
  • Should private gateways be allowed to deliver parcels via its public gateway as well? That would effectively negate the need for VPNs when using Relaynet.