37 Client ID
Time of successful delivery Message content
The interface between DMS and dispatcher client shall use publish-subscribe model, similar to based on OGC Event Service specification [OGC 08-133], with the ES
functionality implemented at the DMS, and the dispatcher acts as a subscribing client to the DMS.
9.3 Implementation
Within the OWS-9 architecture, WS-ReliableMessaging agents need to be implemented at Client DMS Component on the client side, and at the DMS. Since there is always two-
way communications, both sides need to implement RMS and RMD components.
WS-ReliableMessaging is a mature standard with several open-source implementations available. For the testbed implementation we choose to use Apache Sandesha2
[SANDESHA2] that supports up to Committee Draft 4 of the specification being developed under OASIS WS-RX technical committee, but in principle any available WS-
ReliableMessaging implementation could also serve the function
9.4 Lessons Learned
We discover that WS-ReliableMessaging only covers some aspects of the DMS communications reliability requirements. Moreover it mandates the use of SOAP
between the client and DMS. On one hand SOAP has the advantage of providing a placeholder for arbitrary metadata such as for provenance or security purposes. On the
other hand, it introduces some complexity with respect to integration of the DMS functionalities with the aircraft client.
The OWS-9 DMS is designed to be “transparent” to the client-server protocol. The use of SOAP and the intention to make the DMS as transparent as possible to the different
clients and web services eventually create an issue on the client implementation. If the OWSs already use SOAP, DMS insertion requires that the client’s original SOAP
envelope to be enclosed in another SOAP envelope to communicate with the DMS. This is rather tricky to do and requires modification of the middleware that the client typically
uses to intercept the original SOAP envelope. To solve this issue, more feedback is required from all stakeholders including client to devise which protocol solution to be
used; potentially to use different transport than HTTP or SOAP
9.5 Future Work
We identified that a cleaner client-DMS interface needs to be defined, and a simpler protocol possibly without SOAP has to be identified, to have a better and more
transparent integration with aircraft client implementation. The issue of client network
38 mobility is another aspect which solution is not covered by OWS-9 DMS and should be a
priority for future work.
10 Message Prioritization Module
According to the OWS-9 RFQ Annex B, the DMS shall: Transmit high-importance and short-to-expire messages ahead of low-importance
and long-to-expire messages. Message priority shall be determined by message expiration time, or message
type. The DMS shall parse message content to determine message type.
Client shall be allowed to assign priority to specific message types.
10.1 Scope of Work
