Cabletron Systems SPECTRUM, Руководство пользователя

Страница: 99 / 150

Accessing the AToM MIB Window 5-3
ATM Configuration
The remainder of the window contains a list box which displays the following
information about each of the currently configured PVCs; use the scroll bar to the
right of the list to view additional connections, if necessary:
Interface
The device interface on which the PVC was configured. Index numbers are
assigned in an XXXXYY format, where X = slot index times 10,000, and Y = port
index; note that the redundant interfaces on each 7A06-01 NIM share a single IF
index, and changes in the active interface will be transparent to this window.
VPI
Displays the Virtual Path Identifier assigned to the connection; current versions of
7A06-01 firmware allow values from 0–3. Virtual Path Identifiers are used to
group virtual connections, allowing for channel trunking between ATM switches.
Each VPI can be configured to carry many different channels (designated by
VCIs) between two points.
VCI
Displays the Virtual Channel Identifier assigned to the connection; allowable
values are 0–1023 for each VPI. Each assigned VCI must be unique within its
defined VPI: for example, you can assign a VCI of 14 as many as four times: once
with a VPI of 0, once with a VPI of 1, and so on. Remember, it is the combined VPI
and VCI designations assigned to a channel that creates the grouping of virtual
connections.
AAL Type
This field indicates which AAL protocol type is currently in use on the Virtual
Channel Circuit (VCC). An instance of this object only exists when the local VCL
end-point is also the VCC end-point, and the ATM Adaptation Layer (AAL) is in
use. The ATM Adaptation Layer maps user, control, and management data into or
out of the information field of ATM cells of a virtual connection. The possible
Protocol Type Values are:
• 1 (AAL1) — this protocol is used in Constant Bit Rate (CBR) services, which
require information to be transferred at a constant rate after the virtual
connection has been established.
• 34 (AAL3/4) — the protocol used for connectionless or connection-oriented
transfer of data which may be sensitive to loss but not to delay.
• 5 (AAL5) — the protocol used for connection-oriented data transfer that
requires better error detection than available with AAL 3/4. (Note, however,
that the AAL5 protocol itself does not support multiplexing.)
• other — which may indicate a user-defined AAL type.
• unknown — which indicates that the AAL type cannot be determined.