32 packet extraction function 4321 the packet

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: al Channel that carries Packets. 4.3.2.2 The Packet Extraction Function shall be used to extract Packets from the Data Field of Transfer Frames received from the Virtual Channel Reception Function. The First Header Pointer, received from the Virtual Channel Reception Function together with the Data Field, shall be used in conjunction with the length field of each Packet contained within the Data Field to provide the delimiting information needed to extract Packets. 4.3.2.3 If the last Packet removed from the Data Field is incomplete, then the Packet Extraction Function shall retrieve the remainder from the beginning of the next Data Field received on the same Virtual Channel. NOTE – The First Header Pointer for the next Data Field is used to determine the length of the remainder, and hence the beginning of the next Packet to be extracted. 4.3.2.4 If the calculated location of the beginning of the first Packet is not consistent with the location indicated by the First Header Pointer, then the Packet Extraction Function shall assume that the First Header Pointer is correct, and shall continue the extraction based on that assumption. CCSDS 132.0-B-1 Page 4-22 September 2003 CCSDS RECOMMENDATION FOR TM SPACE DATA LINK PROTOCOL 4.3.2.5 Extracted Packets shall be delivered to the users on the basis of the PVN in their header. Incomplete Packets are not required to be delivered in cross support situations. NOTE – Idle Packets are discarded. Data Fields that contain only Idle Data are also discarded. 4.3.2.6 An abstract model of the Packet Extraction Function is illustrated in figure 4-13. Packet Service User with PVN M Packet Service User with PVN N Packets Packet Extraction Function for a Virtual Channel Packets Discard Idle Packets Demultiplexing and Extraction of Packtes Transfer Frame Data Fields Virtual Channel Reception Function Figure 4-13: Abstract Model of Packet Extraction Function 4.3.3 VIRTUAL CHANNEL RECEPTION FUNCTION 4.3.3.1 The Virtual Channel Reception Function shall be used to decommutate fields of Transfer Frames of a Virtual Channel. NOTE – There is an instance of the Virtual Channel Reception Function for each Virtual C...
View Full Document

This document was uploaded on 03/06/2014.

Ask a homework question - tutors are online