The CPT 50 rings
architecture is raised over the CPT 50 standalone framework. CPT 50 in a ring
provides a ring-based protection to the data path and the control path.
A ring can be
subtended from a single CPT 600 or CPT 200 in a linear or close-ended form and
are termed as single-homed rings. It can also be subtended from two
interconnected CPT 600 or CPT 200 and are termed as dual-homed rings. From a
CPT 600, 20 open-ended and 10 closed-ended single-homed rings can be subtended
and up to 10 dual-homed rings can be subtended. From a CPT 200, six open-ended
and three closed-ended single-homed rings can be subtended and up to three
dual-homed rings can be subtended.
The CPT-50 support
MPLS-TP based transport over the single-homed and dual-homed rings.
E-Line is realized
using VPWS across the rings. E-LAN is realized using VPLS across the rings and
using local switching within a CPT-50. Carrier Ethernet is not supported across
the ring. Carrier Ethernet services in this case indicate E-Line and E-LAN
services realized through P2P and P2MP Ethernet switching .
CPT 50 in ring mode
can be provisioned through CTC only. This section describes the scenarios in
which a ring can be configured using CPT 50 and the supported software
MPLS-TP Tunnels in a Ring
MPLS-TP tunnels in a
ring can be created manually using CTC or Cisco IOS mode. BFD-based fault
detection for MPLS-TP tunnels is supported at 50ms granularity using software
mechanisms. It is also possible to create unprotected MPLS-TP tunnels. Only
MPLS-TP data path circuit is supported over a ring. Protected MPLS-TP tunnels
cannot be created in an open-ended ring as there is no alternate path available
in such a configuration.
In a dual-homed ring,
it is possible to create protected MPLS-TP Tunnels to WRC or PRC across the
dual-homed ring and the inter-RC link spans.
VPWS in a Closed-Ended Rings
The VPWS port-based
pseudowires can be created through MPLS-TP tunnels that are created within a
ring or across rings. You cannot create a pseudowire in a ring if the chassis
on which the corresponding attachment circuit exists, is down
VPLS in a Closed-Ended Ring
CPT 50 in a
closed-ended ring can participate in the open ring or hub-and-spoke models of
CPT supports local
switching in a ring. Local switching allows switching of Layer 2 data between
two attachment circuits on the same CPT 50 in the ring. In local switching
(also known as hairpin connection), frames from one interface are switched to
another interface on the same CPT 50 in a ring.
VPWS and VPLS in a Dual-Homed Ring
In a dual-homed ring,
CPT 50 can participate in VPWS and VPLS by using either unprotected or
protected pseudowires, terminating either at WRC or PRC.