Each service user is identified by a sap address

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Unformatted text preview: point at which a service is provided by a protocol entity to a user is called a Service Access Point (SAP) (see reference [1]). Each service user is identified by a SAP address. Service data units submitted to a SAP are processed in the order of submission. processing order is maintained for service data units submitted to different SAPs. CCSDS 132.0-B-1 Page 2-3 No September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL NOTE – Implementations may be required to perform flow control at a SAP between the service user and the service provider. However, CCSDS does not make any recommendations for a scheme for flow control between the user and the provider. The followings are features common to all the services defined by this Recommendation: a) unidirectional (one way) services: one end of a connection can send, but not receive, data through the space link, while the other end can receive, but not send; b) unconfirmed services: the sending user does not receive confirmation from the receiving end that data has been received; c) incomplete services: the services do not guarantee completeness, but some services may signal gaps in the sequence of service data units delivered to the receiving user; d) sequence-preserving services: the sequence of service data units supplied by the sending user is preserved through the transfer over the space link, although there may be gaps and duplications in the sequence of service data units delivered to the receiving user. NOTE – This Recommendation assumes that these services are provided at the end points of a space link. However, this Recommendation makes no assumptions concerning how these end points are composed or configured either on-board a spacecraft or in a ground system. In a ground system, the services defined by this Recommendation may be extended or enhanced with Space Link Extension Services (reference [B5]). 2.2.2 SERVICE TYPES Overview The TM Space Data Link Protocol provides three service types (asynchronous, synchronous, and p...
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This document was uploaded on 03/06/2014.

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