In other words there is a set of scids each of which

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Unformatted text preview: her set of SCIDs (each of which consists of 8 bits) for spacecraft that use the AOS-SDLP (for which the value of TFVN is 2). If a spacecraft uses the TC-SDLP on the forward link and the AOS-SDLP on the return link, it must be assigned two SCIDs, one for the TC-SDLP (TFVN=1) and the other for the AOS-SDLP (TFVN=2). How the SCIDs should be assigned to spacecraft is specified in reference [18]. 4.3.4 MASTER CHANNEL IDENTIFIER The concatenation of a TFVN and a SCID is known as a Master Channel Identifier (MCID), and it is the identifier that uniquely identifies the spacecraft. All Transfer Frames with the same MCID on a Physical Channel constitute a Master Channel (MC). A Master Channel consists of one or more Virtual Channels, each of which is identified with a VCID. The concatenation of an MCID and a VCID is called a Global Virtual Channel Identifier (GVCID). In most cases, a Physical Channel carries only Transfer Frames of a single MCID, and in these cases the Physical Channel is identical with the Master Channel identified with the MCID. But a Physical Channel may carry Transfer Frames with multiple MCIDs (with the same TFVN) and in these cases the Physical Channel consists of multiple Master Channels. That is, Transfer Frames associated with multiple spacecraft may be multiplexed into a single Physical Channel, but the length of all Transfer Frames must be the same if TM-SDLP or AOS-SDLP is used. Transfer Frames of different Space Data Link Protocols must not be multiplexed on a Physical Channel. 4.3.5 PHYSICAL CHANNEL NAME A Physical Channel is identified with a Physical Channel Name, which is set by management and not included in the header of Transfer Frames. CCSDS 130.2-G-1 Page 4-4 December 2007 CCSDS REPORT CONCERNING THE SPACE DATA LINK PROTOCOLS 4.3.6 MULTIPLEXER ACCESS POINT IDENTIFIER The TC-SDLP uses an optional identifier called the Multiplexer Access Point Identifier (MAP ID) that is used to create multiple streams of data within a Virtual Channel. All the Transfer Frames on a Virtual Channel with the same MAP ID constitute a MAP Channel. If the MAP ID is used, a Virtual Channel consists of one or multiple MAP Channels. Both Virtual Channels and MAP Channels can be used for multiplexing streams of SDUs. MAPs also provide the capability of segmenting Packets and other privately formatted SDUs and must be used if Packets or SDUs whose lengths exceed the maximum length that can be carried by Transfer Frames are to be transferred (see 4.5.2). 4.4 RETRANSMISSION 4.4.1 GENERAL The TC-SDLP has the capability to retransmit lost or corrupted data to ensure delivery of SDUs in sequence, without gaps or duplication, over a space link. This capability is provided by a retransmission control mechanism realized by the Communications Operation Procedure-1 (COP-1), which is defined in reference [4], when the Sequence-Controlled (Type-A) Service is used. This Service only guarantees complete delivery of SDUs over the space link, and if the SDUs traverse a larger network of which the space link is an element, it does not guarantee com...
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