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Push/Pull Mode Description
Configuring an Interface for Line Loopback
Engaging line loopback automatically switches the interface to loop timing. It switches back to the
Note
user-specified timing source when the loopback is disengaged.
The default loopback setting is for no loopback. With line loopback, the receive (RX) fiber is logically
connected to the transmit (TX) optical fiber cable so that packets from the remote router are looped back
to it. Incoming data gets looped around and retransmitted to the remote end omitting the received part
which is of no significance.
To configure an interface for line loopback, enter the loop line command:
Step 1
Router(config)# interface pos 3/0
Router(config-if)# loop line
Step 2
To disable line loopback, enter the no loop line command.
For more information about interface subcommands and the configuration options available for the
individual platforms, refer to the publications listed in the
Push/Pull Mode Description
The PA-POS-2OC3 and PA-POS-1OC3 port adapters support a different algorithm (from that of most
port adapters) for handling data. On the transmit side, it can either pull packets from the CPU (Pull
mode) or push packets from the CPU to the port adapter (Push mode). The PA-POS-2OC3 and
PA-POS-1OC3 port adapters were developed with a software architecture that deviates from the design
of previously developed port adapters. A majority of the port adapters allow data to be pulled from the
CPU to their interfaces. By default, the TX DMA mode is Pull for NPE-G1 and Push for NPE-G2. You
cannot change the default TX DMA modes for NPE-G1 and NPE-G2 using the dma model pull enable
command. For NPE-G1, the TX DMA mode is always Pull and for NPE-G2, the TX DMA mode is
always Push.
This functioanlity is implemented startingwith the following Cisco IOS Releases: 12.4(24)T01,
12.4(22)T02, 12.4(20)T03, 12.2(33)SRD02, 12.2(33)SRC04, 12.2(33)SB07, and 12.2(31)SB16.
If you run the dma model pull enable command on NPE-G1, the running configuration shows that the
Pull mode is enabled otherwise the information about Pull mode is not displayed in the running
configuration. Running the dma model pull enable command on NPE-G2 results in an error message.
Only customers who have been advised by Cisco to use this CLI should do so. If you have not been
Caution
advised by Cisco to use the dma model pull enable command, do not do so.
PA-POS-2OC3 Statistics Counters
The PA-POS-2OC3 maintains counts of certain errors. Each error counter is 16 bits. Errors include the
following:
PA-POS-2OC3 Two-Port Packet-over-SONET Port Adapter Installation and Configuration
4-30
Chapter 4
Configuring the PA-POS-2OC3
"Related Documentation" section on page
iv.
OL-3028-06
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