1. DTN Multicast/Anycast Semantic Models Wenrui Zhao Kevin Fall IETF 63 / DTNRG Aug 2, 2005

2. Message Delivery in DTNs Messages are addressed to Endpoint IDs (EIDs) EIDs refer to one node (unicast), one of a group of nodes (anycast), or all of a group of nodes (multicast) Receivers register EID to receive messages

3. Outline Multicast semantic model Explicit addressing Group addressing Issues with custody transfer Anycast semantic model

4. Explicit Addressing Multicast Message is sent to multiple EIDs Each EID can refer to one node or a group of nodes Message is delivered to all nodes that are referred to by EIDs subject to message lifetime and registration lifetime constraints Open: is it worth having different QoS, etc for each?

5. Group Addressing Multicast Message is sent to an EID that refers to a group of nodes (think: multicast) IP multicast model is not applicable in DTNs due to large delay Data are sent to ‘current’ group members ‘Current’ means approximately ‘at the time of message delivery’ … but what if the members aren’t fully connected(?)

6. Example time Node A Node B message generation earliest delivery join leave

7. Group Addressing Multicast Apps register a membership interval to receive messages Messages sent any time during the specified membership interval are delivered to the node subject to message lifetime and registration lifetime constraints may require a sort of ‘librarian’ or ‘archiver’ service [do you remember SRM and MBONE tools?]

8. Issues with Custody Transfer Bundle may follow multiple paths to destinations Multiple custodians are needed for a bundle, each responsible for a subset of destinations (eek!) Custody is on a per-destination basis Late destinations for group addressing multicast Nodes may register to receive messages after senders have ceased sending a message Need a custodial hosting option (?) Request messages be retained in the network until message expiration ~ ‘really persistent’ May be combined with custodial delivery option

9. Anycast Service (very prelim.) Possibly useful for service location e.g. find nearby gateway supporting IPv4-like URIs Forward a message to any Internet gateway Difference from multicast Receivers of a message should be a current member of an anycast group (makes some assumption re: usage model) Node registers membership lifetime to receive messages Specify for how long from now a node will be a member of an anycast group Can be combined with ‘registration lifetime’ Message is delivered to one node and the delivery time is less than the node’s membership lifetime (how to enforce?) subject to message lifetime and registration lifetime constraints