ISO 20217:2015 download free

06-22-2021 comment

ISO 20217:2015 download free.Space data and information transfer systems — Spacecraft onboard interface services — File and packet store services.
ISO 20217 defines the Spacecraft Onboard Interface Services (SOIS) File and Packet Store
Services (FPSS). The definition encompasses specification of the service interface exposed to
onboard software (user applications and libraries) as well as the conceptual mapping of the
FPSS primitives to the protocols implementing such services.
The SOIS File and Packet Store Services are for use by onboard soitware to:
— Access, and manage files residing in a file sore. The files residing in the file store could contain any type of data, including for example telemetry, commands and command sequences. software updates, imagery. and other science observations.
— Access and manage packets residing in a packet store, It should be noted that the packet store may or may not be aware of, and its actions may or may not be informed by. the contents of a packet.
To achieve this, the FPSS comprise the following services:
— File Access Service (FAS):
— File Management Service (FMS):
— Packet Store Access Service (PSAS);
— Packet Store Management Service (PSMS).
It should be noted that the SOIS File and Packet Store Services do NOT define the file and packet stores themselves, hut only their minimum provided service. The initialization and configuration of the file and packet sores is out of scope for this document.
— section 2. containing the general concepts and assumptions;
— section 3, containing the File and Packet Store Services, in terms of the services provided, services expected from underlying layers, and the service interface:
— section 4. containing the Management Information Base MIB for this service.
In addition, one normative and four infonnative annexes are provided:
— annex A, comprising a Service Contirmance Statement Proforma;
— annex f. containing a discussion security considerations with respect to the specifications of this document:
— annex C. containing a list of acronyms;
— annex D. containing a list of informative references:
— annex E. describing aspects of the POSIX API file functions which might be useful to implementers of the File Access and Management Services.
In accordance with modem data communications practice. spacecraft data fields are often grouped into eight-bit ‘words’ widely known as bytes. Throughout this Recommended Practice, such an eight-bit word is called an ‘octet’. The numbering for octets within a data structure starts with zero.
By CCSDS convention, any ‘spare’ hits shall be permanently set to 0.
1.5.2 I)EI’INITIONS Definitions from the Open Systems Interconnection (OSh Reference Model
The document is defined using the style established by the Open Systems Interconnection OSl) Basic Reference Model (reference lDl I). This model pmv ides a common framework for the development of standards in the field of systems interconnection.
The following terms used in this Recommended Practice are adapted from definitions given
in (reference IDII):
Layer: A subdivision of the architecture, constituted by subsystems of the same rank.
(N i-protocol: A set of rules and ftwinats (semantic and syntactic) which determines the communication behavior of (N f-entities in the performance of N )-functions.
service: A capability of a bycr. and the layers beneath it (service providers), provided to the service users at the boundary between the service providers and the service users.
A file store is considered to be a file system and the associated storage medium.
At the highest level a file system is a way to organize. store. retrieve, and manage information on a permanent storage medium. File stores manage permanent storage and form an integral part most onboard spacecraft data handling systems.
Different types of file systems land file stores) may be considered:
a) Flat file systems. Designed to not have subdirectories. Everything is stored in the root level of die storage media.
b) Hierarchical file systems. Designed to organize information in directories in a tree• like structure.
Either of these may be used to support the FPSS services and no restriction is imposed on the type of file store. This approach ailows complete independence from the technology used to implement the lie store. The way in which this mapping is performed is implementation- specific.
The FPSS allow for multiple client processes on multiple machines for both accessing and updating files. Hence updates to the file from one clicnt should not interfere with access and updates from other clients. It is assumed that cirncurreny cxmirol or locking is handled by the file store itself. In support of this, file locking functionality is provided. An application uJie ‘lock owner’) may lock a tile to various degrees of access exclusive read-only. read- only by all, exclusive access) (mm other user entities. Any user entity may unlock the file.
NOTE — It is implementation-specific if unlocking of files is restricicd to. for example, a ‘super-user’ application,
The current directory within a file store for each application is maintained by the file system. A number of operations are perfonned relative to an application’s current directory. e.g.. creating a file. By default, upon initialization, the application’s current directory is at the root level of the storage media for flat tile systems and at the root level of the tree (or hierarchical file systems. For hierarchical tile systems, each application’s current directory can he changed by request.
A file is where a user stores information. Files are logically organized into one-dimensional arrays of octets. The format of a tile is defined by its content since a tile is solely a container
The packet store services proside interfaces for dumping and selectively dumping packets directly from the packet store system io the spacecraft iele,neiry system.
NOTE — The implementation of the interface from the packet store system to the spacecraft telemetry chain is not specified herc. It may or may not makc usc of other SOIS services.
Each service providcs a consistent, standard interface to onboard softwarc; the intcrfaccs arc described by sets of primitives and related parameters.
From the usWs perspective, use of the FPSS will result in onhoard software that is more portable. easier to develoç. and more tolerant of changes in the spacecraft hardware configuration.
From the spacecraft platform implemenler’s perspective, use of the FPSS will make it easier to control access and management of shared hardware resources (i.e.. mass memories).
The FPSS are operated using service requests and service indications passed between the service user and the service provider.

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