1008 | SONET/SDHw w w . d e l l . c o m | s u p p o r t . d e l l . c o m • Protection switching is not supported.• POS interfaces cannot be mirrored ports.• Configurable alarm thresholds (SF/SD BER, B1/B 2/B3 TC) are not supported.• The CRC type and S1S0 flag cannot be changed.Configuring POS InterfacesPOS interfaces require several configuration considerations, including• Encapsulation• MTU• Clock SettingsEncapsulationThe E-Series’ POS line card requires PPP encapsulation. A SONET interface without encapsulation isalways administratively down.Packet Over SONET interfaces require several configuration considerations.When enabling encapsulation on an interface, PPP negotiation only begins after it has been turned on usingthe no shutdown command. You can enable authentication and other related commands after negotiation iscompleted. When removing encapsulation using the no encap command on a SONET interface, theinterface is administratively shutdown and all configuration information (IP addresses for example) isdeleted from the interface.Equipment vendors use unique defaults for PPP encapsulation. When configuring PPP encapsulationbetween the E-Series and another vendor’s equipment, verify the following settings:• One side of the link is set using the command clock source internal.• Default SONET settings are compatible. The E-Series defaults to ATM scrambling disabled; flag is C20xCF(207), J0 is 0xCF(207).• A common PPP authentication method is configured. FTOS supports Challenge-HandshakeAuthentication Protocol (CHAP) and/or Password Authentication Protocol (PAP) authentication.• The MTU and IP MTU settings on both ends of the link are the same. If you input the ip mtu commandwith a value which differs from the far-end interface, the interface on the E-Series will go down.• Confirm that the MTU settings are the same on both end of the link. If you configure the ip mtucommand with a different value on the far end of the link, the interface on the E-Series goes down.Note: SONET uses synchronous transport signal (STS) framing. When framing is configuredon an interface, it should only be done when the interface is shut down.
