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DEFINITY Enterprise Communications Server Release 6
Maintenance for R6vs/si
555-230-127
Issue 1
August 1997
Maintenance Commands and Trouble-Clearing Aids
Page 8-284status link
8
Definitions
Link
A synchronous connection between the system and an adjunct or
another switch. The link consists of three protocol levels. The
change communications-interface links command specifies the
link number.
Level 1
Physical connection of a port on a Processor Interface board to
hardware that serves the same purpose on the adjunct or switch (for
example, a PI board or an SCP board on Audix). Several
components can exist between these two endpoints (modems, DS1
facilities, cables, and so forth).
Level 2
Logical protocol that allows data communication between two
endpoints. BX.25 = LAPB (Link Access Protocol on the B-channel)
protocol. Level 2 = Frames sent. Protocol establishment requires
one end to send a SABM (Set Asynchronous Balanced Mode) frame
and the other to respond with a UA (User Acknowledgment) frame.
Both sides send SABMs until they receive a UA. (level 2 is up and
the Link Status field displays “restarting”) This should be a
temporary condition, because level 3 comes up immediately.
Level 3
Logical protocol that allows multiplexing of many channels to one
level 2 link. BX.25 specifies that this is the X.25 data phase protocol.
Packets are sent at level 3, included in level 2 frames. This protocol
establishes after level 2 establishes when one end sends a Restart
packet, and the other sends a Restart Confirm packet.
Processor channel
Connection of an application running inside the SPE to a specified
channel on a specified link. A number on the change
communication-interface processor-channel form identifies
processor channels. The link and level channel numbers and the
application are specified on the link (for example, dcs) that uses the
processor channel.