1. 3GPP Interworking and Multicast retransmission
Group Name: ARC
Source: KETI and Hyundai Motors – JaeSeung Song, Lewis Nkenyereye, Youngjin Ra, and Minbyeong Lee
Meeting Date:

2. Motivation and Background

3. Issues and Use Case
oneM2M IN-CSE, Group Hosting CSE, should aware of MBMS status of a multicast message to be delivered so that it can provide an exact information which members were failed to get the multicast message.
If such information is available at the Group Hosting CSE, Contents provider (AE) can perform retransmission of the message only to the members failed to receive the message
Use Case for a periodic and/or planned file delivery to a large number of vehicles.
Smart vehicles are moving various places.
These smart vehicles are receiving many multicast services such as traffic condition, accident information, detour information.
Based on growing amount of data, the system configuration is adjusted, requiring the delivery of small configuration updates to all vehicle devices.
As vehicles move fast, there will be high chance not to get the delivered multicast message
If some of these multicast delivery fails, the message should be retransmitted to users

4. Current Status
What about some members didn’t receive the multicast msg properly?
 Retransmission should be performed

5. How to support? Required enhancements for multicast retransmission
oneM2M should support the reliable delivery of multicast message
The <group> resource should know the detail information about the MBMS delivery status (i.e. delivery failure)
The <localMulticastGroup> resource should also know the detail information about the MBMS delivery status
oneM2M system should be able to retransmit multicast message to failure MBMS nodes
Two available mechanisms
Unicast to MBMS failure member nodes
If the number of failure member nodes are low, this mechanism is good to be selected
Multicast the same message to the MBMS failure member nodes
If the number of failure member nodes are high, this mechanism is good to be selected
Different multicast group (TMGI) for retransmission is needed

6. Retransmission using Unicast
Member Hosting CSE
3GPP
Group Hosting CSE AE
15. Response
Retransmission using Unicast
If there are failures of multicast delivery, <group> hosting CSE retransmit the message to failed nodes via unicast
CSE sends unicast message delivery to the members in the memberNotDelivered attribute
If unicast delivery is successful, CSE deletes the member from the memberNotDelivered.
After the given number of retransmission, CSE considers the failure nodes are not available anymore and removes the member from the <group> resource
16. Update retransmission related attributes
17. Response
18. retransmit
19. Check failure members
20. Retransmit using Unicast
21. Response
22. Remove members that receive delivery successfully
23. Response
24. If there exist member CSEs that didn’t get the message successfully, AE can repeat again until the given maxRetransmission number

7. Retransmission using Multicast
Member Hosting CSE
3GPP
Group Hosting CSE AE
Retransmission using <Retransmission>
16. Record failure member hosting CSEs
17. Response to AE
18. AE requests retransmission for the message (maxTime, maxNumber, etc),
19. Group Hosting CSE creates <retransmission> resources with other relevant attributes, incl. allocate a new TMGI for retransmission
20. CSE sends unicast message delivery to the members in the memberNotDelivered attribute
21. Response from member hosting CSE
22. Update <Retransmission> resource based on the If unicast delivery is successful, CSE deletes the member from the memberNotDelivered. Increase currentNrRetransmission.
23. Response to AE
24. After the given number of retransmission, CSE considers the failure nodes are not available anymore and removes the member from the <group> resource
15. Response
16. Local processing
17. Response
18. retransmit
19. Prepare retransmission
20. Retransmit using Unicast
21. Response
22. Update <retransmission> for example, remove members that receive delivery successfully
23. Response
24. If there exist member CSEs that didn’t get the message successfully, AE can repeat again until the given maxRetransmission number

8. Retransmission using Multicast
Retransmission using <Retransmission> resource
<Retransmission> resource can be introduced to support multicast retransmission
If there are failures of multicast delivery, <retransmission> resource is created as a child resource of <group>
CSE performs multicast to the members listed in <retransmission> group for the given number of times
For each retransmission, if nodes receive the message properly, these members should be removed from the <retransmission> resource
After performing multicast to the given number of times, the created <retransmission> resource is removed
In this case, 3GPP MBMS TMGI and relevant information to perform 3GPP MBMS should be created and configured for the members specified in <retransmission> resource