33 332 3321 services to transfer packets general the

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Unformatted text preview: rotocols provide services for transferring various types of SDUs on space links, but the most important services are those for transferring variable-length data units commonly known as Packets, that is, Protocol Data Units of protocols of the Network Layer, such as the Space Packet Protocol (reference [13]), SCPS-NP (reference [14]), and IP (reference [15]). Each packet format transferred by the Space Data Link Protocols must have a Packet Version Number (PVN) authorized by CCSDS. A list of the PVNs presently authorized by CCSDS is contained in reference [16]. A user of this service is a protocol entity that sends or receives Packets with a single PVN. CCSDS 130.2-G-1 Page 3-7 December 2007 CCSDS REPORT CONCERNING THE SPACE DATA LINK PROTOCOLS 3.3.2.2 Services to Transfer Packets Provided by TC-SDLP The TC-SDLP has two services for transferring packets: the MAP (Multiplexer Access Point) Packet Service (or the MAPP Service) and the Virtual Channel Packet Service (or the VCP Service). These services transfer a sequence of Packets over a space link on a MAP Channel (in the case of the MAPP Service) or a Virtual Channel (in the case of VCP Service). Both Sequence-Controlled (Type-A) and Expedited (Type-B) service types (see 3.2.2.2) are provided for these services. The sending user specifies for each Packet whether Type-A or Type-B should be applied. Different users (i.e., Packets with different PVNs) can share a single MAP Channel (in the case of the MAPP Service) or a single Virtual Channel (in the case of the VCP Service), and if there are multiple users on a MAP or VC Channel, the service provider multiplexes Packets with different PVNs to form a single stream of Packets to be transferred on that channel. 3.3.2.3 Service to Transfer Packets Provided by TM-SDLP and AOS-SDLP The TM-SDLP and AOS-SDLP each have a service called the Packet Service for transferring Packets. A sequence of Packets supplied by a sending user is transferred on a single Virtual Channel. These services do not guarantee complete delivery of the Packets supplied by the sending user to the receiving user, nor do they signal gaps in the sequence of Packets delivered to the receiving user. Different users (i.e., Packets with different PVNs) can share a single Virtual Channel, and if there are multiple users on a Virtual Channel, the service provider multiplexes Packets with different PVNs to form a single stream of Packets to be transferred on that Virtual Channel. 3.3.3 ENCAPSULATION SERVICE Packets with authorized PVNs can be directly transferred by the Space Data Link Protocols using the services explained in 3.3.2. Packets that do not have an authorized PVN can be transferred with a service called the Encapsulation Service, defined in reference [17]. With this service, Packets are transferred encapsulated in either Space Packets defined in reference [13] or Encapsulation Packets defined in reference [17]. This service can be used with any Space Data Link Protocol and it uses a service provided...
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This document was uploaded on 03/06/2014.

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