When a Provider Edge (PE) router receives a Frame Relay protocol packet from a subscriber site, it removes
the Frame Relay header and Frame Check Sequence (FCS) and appends the appropriate Virtual Circuit (VC)
label. The removed Backward Explicit Congestion Notification (BECN), Forward Explicit Congestion
Notification (FECN), Discard Eligible (DE) and Command/Response (C/R) bits are (for DLCI-DLCI mode)
sent separately using a control word.
MPLS Transport Profile
MPLS transport profile (MPLS-TP) tunnels provide the transport network service layer over which IP and
MPLS traffic traverse. Within the MPLS-TP environment, pseudowires (PWs) use MPLS-TP tunnels as the
transport mechanism. MPLS-TP tunnels help transition from SONET/SDH TDM technologies to packet
switching, to support services with high bandwidth utilization and low cost. Transport networks are connection
oriented, statically provisioned, and have long-lived connections. Transport networks usually avoid control
protocols that change identifiers (like labels). MPLS-TP tunnels provide this functionality through statically
provisioned bidirectional label switched paths (LSPs).
For more information on configuring MPLS transport profile, refer to the Cisco ASR 9000 Series Aggregation
Services Router MPLS Configuration Guide.
MPLS-TP supports these combinations of static and dynamic multisegment pseudowires:
• Static-static
• Static-dynamic
• Dynamic-static
• Dynamic-dynamic
MPLS-TP supports one-to-one L2VPN pseudowire redundancy for these combinations of static and dynamic
pseudowires:
• Static pseudowire with a static backup pseudowire
• Static pseudowire with a dynamic backup pseudowire
• Dynamic pseudowire with a static backup pseudowire
• Dynamic pseudowire with a dynamic backup pseudowire
The existing TE preferred path feature is used to pin down a PW to an MPLS-TP transport tunnel. See Preferred
Tunnel Path for more information on configuring preferred tunnel path. For a dynamic pseudowire, PW status
is exchanged through LDP whereas for static PW, status is transported in PW OAM message. See Configuring
PW Status OAM for more information on configuring PW status OAM. By default, alarms are not generated
when the state of a PW changes due to change in the state of MPLS TP tunnel carrying that PW.
Circuit Emulation Over Packet Switched Network
Circuit Emulation over Packet (CEoP) is a method of carrying TDM circuits over packet switched network.
CEoP is similar to a physical connection. The goal of CEoP is to replace leased lines and legacy TDM networks.
CEoP operates in two major modes:
• Unstructured mode is called SAToP (Structure Agnostic TDM over Packet)
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
88
Implementing Point to Point Layer 2 Services
MPLS Transport Profile
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