Upper Layer Protocol ID Proposal
Steve Van Trees <vantrees@fuji.sed.stel.com> Mon, 16 May 1994 20:11 UTC
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From: Steve Van Trees <vantrees@fuji.sed.stel.com>
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Subject: Upper Layer Protocol ID Proposal
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Upper Layer Protocol Identifier Proposal 1. Background Various industries have expressed immediate needs for communications that require minimum overhead in the upper layer standards. Coordinated work is ongoing in ITU-T, ISO/IEC JTC 1/SC 21, OSE Implementors Workshop (OIW), and ANSI to address these needs. In particular, the contents of document TD - 5161 and TD - 5183, generated at the ITU-T SG7 meeting 7-18th February, 1994, should be referenced. The approach proposed below combines various efforts going on in ISO, ANSI and ITU-T. This combines Fast Byte proposals in ITU-T with ongoing work for the use of A2CSE. 2. Technical Approach This paper proposes an expansion of the initial ITU-T concepts on fast byte to allow a single byte to act as an Upper Layer Protocol Identifier (ULPI). The general fast byte approach is described in Appendix K of the ITU-T report, but some details are not fully worked out. In the context of this paper, the fast byte would identify current standard OSI implementations using the first octet of the session connection establishment PDU (Session PDU Identifier = H '0D'). As discussed in ITU-T this allows the possibility of using a Fast Byte value (e.g. H '0F'), to indicate a specific alternate stack option. Looked at in the wider context, the Fast Byte should be expanded to recognize this value as a one octet flat address space indicating various stack options. Taking an architectural approach modeled after the ISO 9577 (Network Layer Protocol Identifier) standard, the Fast Byte octet then identifies multiple stack options above transport, and acts as default header for layers as needed. ACSE is being modified to support the eXtended Application Layer Structure (XALS). This work is being progressed both in ANSI and ISO. The modification is in the form of an added functional unit to ACSE to allow the ability to support Application Service Objects (ASOs), recursive use of software, and other benefits of the XALS structure. ACSE with extensions is referred to as ASO Association Control Service Element (A2CSE). At various recent meetings of ANSI and OIW the majority wish was to define a mechanism allowing minimal to no Session and Presentation PCI overhead in an A2CSE stack option. The immediate need within the aeronautical environment is a method to support A2CSE encoded using the unaligned variant of Packed Encoding Rule (PER), immediately following the "fast byte" value indicating this option. While the idea of having that value corresponding to the first octet of the association establishment, was explored, for still greater efficiency, this does not appear to be possible, because A2CSE encoding options could conflict with the H'0D' value for session. 3. Proposal This paper recommends the creation of a Fast-Byte standards document and corresponding registration authority. It recommends that ANSI reserve the initial values of: > one-bit session /\ one-bit session 0 / \ 1 / \ / \ byte-aligned /\ bit /\ 0 / \1 0/ \ 1 / \ / \ / \ 00'D' 8326 + 8822 00 Transparent 10'0' connectionless session 01 BER 00'1' Fast Byte 10 bit-aligned PER 11 byte-aligned PER '01' Fast Byte for Session; '0D' Fast Byte which indicates and is the first octet of traditional Session, Presentation, and ACSE; '20' Fast Byte which indicates and is the first octet of connectionless Session, Presentation, and ACSE; '8' for Fast Byte value which implies byte-aligned transparent data above the Fast Byte value. '9' Fast Byte acting as both byte-aligned Session and Presentation header, and as the first octet of ACSE encoded using BER. 'A' Fast Byte acting as byte-aligned Session and Presentation header followed by ACSE encoded using the PER unaligned variant; 'B' Fast Byte acting as both byte-aligned Session and Presentation header, followed by ACSE encoded the PER octet-aligned variant; 'C' for Fast Byte value which implies bit-aligned transparent data above the Fast Byte value. 'D' Fast Byte acting as both bit-aligned Session and Presentation header, and as the first octet of ACSE encoded using BER. 'E' Fast Byte acting as bit-aligned Session and Presentation header followed by ACSE encoded using the PER unaligned variant; 'F' Fast Byte acting as both bit-aligned Session and Presentation header, followed by ACSE encoded the PER octet-aligned variant;
- Upper Layer Protocol ID Proposal Steve Van Trees
- Re: Upper Layer Protocol ID Proposal D_P_Sanford