CCSDS 734.2-R-1, CCSDS Bundle Protocol Specification (Red ...

DRAFT CCSDS RECOMMENDED STANDARD FOR CCSDS BUNDLE PROTOCOL SPECIFICATIONNOTE – Some or all of those values might be communicated to the bundle protocol agentby the application on whose behalf the bundle is being originated. In this case,the manner in which the application communicates those values is likewise animplementation matter.B3.3 BUNDLE FORWARDINGB3.3.1 Inclusion of an ECOS extension block in a received bundle that is to be forwardedbut contains no ECOS block is optional; the decision on whether or not to insert a new ECOSblock into a forwarded bundle is an implementation matter. In the event that a new ECOSblock is inserted into a forwarded bundle, the values of the block data fields of that ECOSblock are likewise an implementation matter, provided that they conform to thisspecification.B3.3.2 The forwarding of a bundle that contains a valid ECOS block, whether locallyoriginated or locally inserted upon reception from another bundle protocol agent, shall beconstrained as follows:– If the 0x01 bit of the ECOS block’s flags byte is set to 1 (‘critical’):• Exactly one copy of the bundle shall be forwarded to every neighboring node thathas some plausible prospect of being able to forward the bundle toward its finaldestination without returning it to the local node, a determination that is a matterleft to the bundle protocol agent’s route computation mechanism.NOTE – A conformant bundle protocol agent can at any time arbitrarily decidethat there is only one neighboring node that has some plausible prospectof being able to forward a given bundle toward its final destinationwithout returning it to the local node, in effect disabling this feature ofECOS. Such an implementation decision should not be taken lightly,however, as it might put network assets at risk; this expedient should beavoided unless necessary to preserve the continued operation of thebundle protocol agent.• The bundle shall be queued for transmission as if its class of service were 2(‘expedited’) and its ordinal value were 254, regardless of the actual values ofthese fields.• The bundle shall not be reforwarded in response to custody refusal, the expirationof a custody transfer timer, the presence of a routing loop in the network, or anyother condition. The manner in which this constraint is enforced is animplementation matter.NOTES1 Such reforwarding could result in unbounded bundle transmission explosions.CCSDS 734.2-R-1 Page B-4 February 2012