MPLS-TP Model
Page 60 7450 ESS MPLS Guide
• MPLS-TP Identifiers (RFC 6370)
• Proactive CC, CV, and RDI using BFD for LSPs (RFC 6428)
• On-Demand CV for LSPs and PWs using LSP Ping and LSP Trace (RFC 6426)
• 1-for-1 Linear protection for LSPs (RFC 6378)
• Static PW Status Signaling (RFC 6478)
The system can play the role of an LER and an LSR for static MPLS-TP LSPs, and a PE/T-PE and
an S-PE for static MPLS-TP PWs. It can also act as a S-PE for MPLS-TP segments between an
MPLS network that strictly follows the transport profile, and an MPLS network that supports both
MPLS-TP and dynamic IP/MPLS.
MPLS-TP Model
Figure 7 shows a high level functional model for MPLS-TP in SROS. LSP A and LSP B are the
working and protect LSPs of an LSP tunnel. These are modelled as working and protect paths of
an MPLS-TP LSP in SROS. MPLS-TP OAM runs in-band on each path. 1:1 linear protection
coordinates the working and protect paths, using a protection switching coordination protocol
(PSC) that runs in-band on each path over a Generic Associated Channel (G-ACh) on each path.
Each path can use either an IP numbered, IP unnumbered, or MPLS-TP unnumbered (i.e. non-IP)
interface.
Figure 7: MPLS-TP Model
Note that in SR OS, all MPLS-TP LSPs are bidirectional co-routed, as detailed in RFC5654. That
is, the forward and backward directions follow the same route (in terms of links and nodes) across
the network. Both directions are setup, monitored and protected as a single entity. Therefore, both
al_0221
MPLS-TP
Tunnel
PW
OAM
PW PW
Services see SDP as per IP/MPLS case
Each direction of TP LSP presented as
undirectional SDP to service
Abstracts underlying LSPs towards SDP;
PSC (linear protection) picks working LSP
MPLS manages independent bidirectional
MPLS-TP LSP paths
Numbered and unnumbered interface
PSC
Path A
Port/
VLAN
Port/
VLAN
Path B
ProtectWorking
Interface Interface
SDP
MPLS-TP LSP
PW
TP Link/
Interface
ETH
Port
PSC
ETH
Port
TP Link/
Interface
PW
LSP
OAM
Server Layer
OAM
LSP A
(bidir)
LSP A
(bidir)
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