Specifications

Configure a Packet OC-3 Interface
IC-98
Cisco IOS Interface Configuration Guide
Select a Packet OC-3 Interface
The Packet OC-3 interface is referred to as pos in the configuration commands. An interface is
created for each POS found in the system at reset time.
If you need to change any of the default configuration attributes or otherwise reconfigure the Packet
OC-3 interface, use one the following commands in global configuration mode:
Set the MTU Size
To set the maximum transmission unit (MTU) size for the interface, use the following command in
interface configuration mode:
The value of the bytes argument is in the range 64 to 4470 bytes; the default is 4470 bytes.
(4470 bytes exactly matches FDDI and HSSI interfaces for autonomous switching.) The no form of
the command restores the default.
Caution Changing an MTU size on a Cisco 7500 series router will result in recarving of buffers and resetting
of all interfaces. The following message is displayed:
%RSP-3-Restart:cbus complex88
Configure Framing
To configure framing on the Packet OC-3 interface, use one of the following commands in interface
configuration mode:
Configure an Interface for Internal Loopback
With the loopback internal command, packets from the router are looped back in the framer.
Outgoing data gets looped back to the receiver without actually being transmitted. With the
loopback line command, the receive (RX) fiber is logically connected to the transmit fiber (TX) so
that packets from the remote router are looped back to it. Incoming data gets looped around and
retransmitted without actually being received.
Command Purpose
interface pos slot/port (Cisco 7200)
or
interface pos port-adapter (Cisco 7500)
Select the Packet OC-3 interface and enter interface
configuration mode.
Command Purpose
mtu bytes Set the MTU size.
Command Purpose
pos framing-sdh Select
SDH STM-1 framing.
no pos framing-sdh Revert to the default
SONET STS-3c framing.