Specifications

APPENDIX B
DATA LINK SPECIFIC INFORMATION
This appendix contains information necessary to relate specific data
link types to the maintenance operations.
B. 1 DDCMP
The Digital Data Communication Message Protocol
(DDCMP) Data Link is a
point-to-point channel and allows exclusive maintenance operation in
its maintenance mode. It does not require message padding.
B. 2 LAPB
The LAPB Data Link is the frame level of
X.25. It is a point-to-point
channel and allows exclusive maintenance operation for loopback only.
It does not require message padding.
B.3 Ethernet
The Ethernet Data Link is the Digital Equipment Corporation
implementation
of the inter-company Ethernet Data Link. It allows
concurrent maintenance operation and is a multiaccess channel. As
such it has specific protocol types and multicast addresses that go
with it. It requires message padding.
Refer to the the Ethernet Product Architecture Specification and the
DNA Ethernet Data Link Architectural Specification for specific
functions and requirements. For example, the Product Architecture
Specification requires that the Loop Server and the Console Server
cannot be off while the data link
is on.