Internet DRAFT - draft-helvoort-mpls-tp-ring-protection-switching
draft-helvoort-mpls-tp-ring-protection-switching
MPLS Working Group H. van Helvoort, Ed.
Internet-Draft Huawei Technologies
Intended status: Standards Track J. Ryoo, Ed.
Expires: October 20, 2014 ETRI
April 18, 2014
MPLS-TP Ring Protection Switching (MRPS)
draft-helvoort-mpls-tp-ring-protection-switching-06.txt
Abstract
This document describes a mechanism to address the requirements for
protection of the Multi-Protocol Label Switching Transport Profile
(MPLS-TP) Label Switched Paths (LSP) in a ring topology. The
mechanism defined herein is designed to support point-to-point as
well as point-to-multipoint LSPs.
The MPLS-TP section layer OAM is used to monitor the connectivity
between each two adjacent nodes using the mechanisms defined in the
[RFC6371].
The Automatic Protection Switching (APS) protocol is used for
coordination of protection switching actions between the ring nodes.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on October 20, 2014.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Contributing authors . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in this Document . . . . . . . . . . . . . . 4
2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. Ring protection schemes . . . . . . . . . . . . . . . . . . . 4
3.1. Wrapping . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Wrapping protection scheme applicability . . . . . . 5
3.1.2. P-t-p LSP example . . . . . . . . . . . . . . . . . . 5
3.1.3. P-t-mp LSP example . . . . . . . . . . . . . . . . . 7
3.2. Steering . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.1. Steering protection scheme applicability . . . . . . 11
3.2.2. P-t-p LSP example . . . . . . . . . . . . . . . . . . 11
3.2.3. P-t-mp LSP example . . . . . . . . . . . . . . . . . 13
4. MRPS characteristics . . . . . . . . . . . . . . . . . . . . 16
4.1. Switching types . . . . . . . . . . . . . . . . . . . . . 16
4.2. Operation types . . . . . . . . . . . . . . . . . . . . . 17
4.3. Traffic types . . . . . . . . . . . . . . . . . . . . . . 17
4.3.1. Bandwidth sharing . . . . . . . . . . . . . . . . . . 17
4.3.2. Bandwidth and QoS considerations . . . . . . . . . . 17
4.3.3. Point-to-point and point-to-multipoint traffic . . . 18
5. APS protocol . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. Transmission and acceptance of APS requests . . . . . . . 20
5.2. APS PDU structure . . . . . . . . . . . . . . . . . . . . 20
5.3. Ring node APS states . . . . . . . . . . . . . . . . . . 21
5.3.1. Idle state . . . . . . . . . . . . . . . . . . . . . 21
5.3.2. Switching state . . . . . . . . . . . . . . . . . . . 22
5.3.3. Pass-through state . . . . . . . . . . . . . . . . . 22
5.3.4. APS state transitions . . . . . . . . . . . . . . . . 23
6. Protection switching triggers . . . . . . . . . . . . . . . . 25
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6.1. Manual control . . . . . . . . . . . . . . . . . . . . . 25
6.1.1. Commands not signaled on the APS protocol . . . . . . 25
6.1.2. Commands using the APS protocol . . . . . . . . . . . 26
6.2. Automatically initiated commands . . . . . . . . . . . . 26
6.3. APS state machine . . . . . . . . . . . . . . . . . . . . 27
6.3.1. Initial states . . . . . . . . . . . . . . . . . . . 27
6.3.2. State transitions when local request is applied . . . 28
6.3.3. State transitions when remote request is applied . . 32
6.3.4. State Transitions when request addresses to another
node is received . . . . . . . . . . . . . . . . 35
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
8. Security Considerations . . . . . . . . . . . . . . . . . . . 38
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . 38
10.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix A. Ring protection requirements compliance . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction
Ring topologies are well known in SDH and SONET networks and is
proven to be very effective and simple in terms of protection
switching. Similar to SDH networks, MPLS networks can be built over
ring topologies. Such networks allow for a simple, fast recovery
time, and efficient protection mechanisms similar to the protection
mechanisms in SDH, as well as high bandwidth utilization achievable
by using the packet switching statistical multiplexing.
MPLS shared protection ring can be viewed as equivalent to SDH MS
shared protection ring architecture [G.841].
The protection ring consists of two counter-rotating rings,
transmitting in opposite directions relative to each other. Both
rings carry working and protection traffic.
The bandwidth on each ring is divided so that a part of ring capacity
is dedicated for the working traffic and another part is dedicated to
the protection traffic. The protection bandwidth on one ring is used
to transport the working traffic from the other ring in case of
failure. Part of ring bandwidth can also be dedicated to carry
unprotected non-preemptable traffic (NUT).
1.1. Contributing authors
Italo Busi (Alcatel-Lucent), Haiyan Zhang (Huawei Technologies), Han
Li (China Mobile Communications Corporation), Ruiquan Jing (China
Telecom).
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2. Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.1. Abbreviations
APS Automatic Protection Switching
CCW Counterclockwise
EXER Exercise
FS Forced Switch
LP Lockout of Protection
LW Lockout of Working
NMS Network Management System
MPLS Multi-Protocol Label Switching
MPLS-TP MPLS Transport Profile
MRPS MPLS-TP Ring Protection Switching
MS Manual Switch
NR No request
NUT Non-preemptable Unprotected Traffic
OAM Operation, Administration and Maintenance
PDU Payload Data Unit
PS Protection Switching
QoS Quality of Service
RR Reverse Request
SF Signal Fail
WTR Wait to Restore
3. Ring protection schemes
3.1. Wrapping
The Wrapping technique implies that the node detecting a failure
sends out an APS request to the (opposite to the failure) node
adjacent to the failure. The APS request is transmitted over the APS
communication protocol, as defined in [RFC6371]. When a node detects
a failure or receives an APS request through APS protocol addressed
to this node, the traffic of all working LSPs/tunnels transmitted
towards the failed span is switched to the protection LSPs/tunnels in
the opposite direction (away from the failure). This traffic travels
around the ring to the other node (adjacent to the failure) where it
is switched back onto the working LSPs/tunnels. The nodes that
performed the protection switching revert back to the normal traffic
flow when the failure or APS request is cleared.
For each normal or working MPLS-TP LSP/tunnel, the protection LSP/
tunnel MUST be established in the opposite direction though all nodes
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in the ring. Labels assigned for the protection LSPs/tunnels MUST be
associated with the labels assigned for working LSPs/tunnels to allow
proper traffic switching between the working and protection LSPs/
tunnels.
3.1.1. Wrapping protection scheme applicability
Wrapping protection scheme provides for fast and simple recovery of
p-t-p and p-t-mp LSPs in case of single or multiple failures in the
ring. The protection mechanism in terms of nodes behavior, data
path, signaled APS protocol messages is the same in all cases. In
some scenarios with large networks additional latency may be
introduced during protection switching in the ring because protection
traffic travels along the all the ring.
3.1.2. P-t-p LSP example
+---+ [P1] +---+
| F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ [W1]\[P6]
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ [W2]/[P5]
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C |
+---+ [P4] +---+
Figure 1: Labels allocation example for p-t-p LSP protection with
wrapping protection switching
Working labels:
A[W1]->B[W2]->C[W3]->D
Protection labels:
A[P1]->F[P2]->E[P3]->D[P4]->C[P5]->B[P6]->A
Working and protection labels association:
[W1]<->[P6]
[W2]<->[P5]
[W3]<->[P4]
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3.1.2.1. Link failure example
+---+ [P1] +---+
| F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ [W1]\[P6]
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ X
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C |
+---+ [P4] +---+
Figure 2: Wrapping protection switching operation for p-t-p LSP in
case of link failure
When the failure occurs between the nodes B and C, these nodes send
APS request to each other around the ring. Node B switches the
traffic of LSP 1 from working label [W1] to the protection label [P6]
in the opposite direction (CCW). This traffic travels around the
ring to the node C where it is switched from protection label [P4] to
the working label [W3] and sent to the node D where it is dropped
from the ring.
Traffic flow and labels use when the link failure occurs:
A[W1]->B[P6]->A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D
3.1.2.2. Node failure example
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+---+ [P1] +---+
| F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ X
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ X
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C |
+---+ [P4] +---+
Figure 3: Wrapping protection switching operation for p-t-p LSP in
case of node failure
When node B fails or becomes isolated because of two failed links,
nodes A and C send APS request to each other around the ring. Node A
switches the traffic of LSP 1 to the protection label [P1] in the
direction opposite to normal flow. This traffic travels around the
ring to the node C where it is switched from the protection label
[P4] to the working label [W3] and sent to the node D where it is
dropped from the ring.
Traffic flow and labels use when the node B failure occurs:
A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D
3.1.3. P-t-mp LSP example
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+---+ [P1] +---+
LSP 1 <-- | F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/[W5] [W1]\[P6]
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\[W4] [W2]/[P5]
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C | --> LSP1
+---+ [P4] +---+
Figure 4: Labels allocation example for p-t-mp LSP protection with
wrapping protection switching
Working labels:
A[W1]->B[W2]->C[W3]->D[W4]->E[W5]->F
| | |
v v v
LSP 1 LSP 1 LSP 1
Protection labels:
A[P1]->F[P2]->E[P3]->D[P4]->C[P5]->B[P6]->A
Working and protection labels association:
[W1]<->[P6]
[W2]<->[P5]
[W3]<->[P4]
[W4]<->[P3]
[W5]<->[P2]
3.1.3.1. Link failure example
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+---+ [P1] +---+
LSP 1 <-- | F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/[W5] [W1]\[P6]
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\[W4] X
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C | --> LSP 1
+---+ [P4] +---+
Figure 5: Wrapping protection switching operation for p-t-mp LSP in
case of link failure
When the failure occurs between the nodes B and C, these nodes send
APS request to each other around the ring. Node B switches the
traffic of LSP 1 from working label [W1] to the protection label [P6]
in the opposite direction (CCW). This traffic travels around the
ring to the node C where it is switched from protection label [P4] to
the working label [W3] and sent to the nodes D and F where it is
dropped from the ring.
Traffic flow and labels use when the link failure occurs:
A[W1]->B[P6]->A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D[W4]->E[W5]->F
| | |
v v v
LSP 1 LSP 1 LSP 1
3.1.3.2. Node failure example
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+---+ [P1] +---+
LSP 1 <-- | F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ X
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ X
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C | --> LSP1
+---+ [P4] +---+
Figure 6: Wrapping protection switching operation for p-t-mp LSP in
case of node failure
When node B fails or becomes isolated because of two failed links,
nodes A and C send APS request to each other around the ring. Node A
switches the traffic of LSP 1 to the protection label [P1] in the
direction opposite to normal flow. This traffic travels around the
ring to the node C where it is switched from the protection label
[P4] to the working label [W3] and sent to the nodes D and F where it
is dropped from the ring.
Traffic flow and labels use when the node B failure occurs:
A[P1]->F[P2]->E[P3]->D[P4]->C[W3]->D[W4]->E[W5]->F
| | |
v v v
LSP 1 LSP 1 LSP 1
3.2. Steering
The Steering technique implies that the node detecting a failure
sends an APS request to the node adjacent to the failure (away from
the failure). The APS request is processed by all intermediate nodes
in the ring. All nodes in the ring MUST analyze which LSPs are
affected by the failure or APS request. This analysis is based on
the ring node maps configured at each node in the ring and LSP maps
provided at each source node (that adds traffic onto the ring) and
sink node (that drops the traffic from the ring). For each affected
LSP the source node and the sink node switches the traffic from
working LSPs/tunnels to the protection LSPs/tunnels and restore
normal traffic flow when the failure or APS request is cleared.
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3.2.1. Steering protection scheme applicability
Steering protection scheme provides for recovery of p-t-p and p-t-mp
LSPs in case of single or multiple failures in the ring. The
protection mechanism different for p-t-p and p-t-mp LSPs in terms of
nodes behavior and data path. Signaled APS protocol messages are the
same. Steering mechanism introduces less latency comparing to
wrapping during protection switching in the ring but it requires more
complex configuration. It also may affect the protection time
because of more complex operation of switching nodes.
3.2.2. P-t-p LSP example
+---+ [P1] +---+
| F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ [W1]\
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ [W2]/
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C |
+---+ +---+
Figure 7: Labels allocation example for p-t-p LSP protection with
steering protection switching
Working labels:
A[W1]->B[W2]->C[W3]->D
Protection labels:
A[P1]->F[P2]->E[P3]->D
3.2.2.1. Link failure example
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+---+ [P1] +---+
| F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ \
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ X
\ /
+---+ +---+
LSP 1 <-- | D |-------------| C |
+---+ +---+
Figure 8: Steering protection switching operation for p-t-p LSP in
case of link failure
When the failure occurs between the nodes B and C, these nodes send
APS request to each other around the ring. Nodes A and D analyze
these requests and determine that LSP 1 is affected by the failure.
Node A switches the traffic of LSP 1 to the protection label [P1] in
the direction opposite to normal flow. This traffic travels around
the ring to the node D where it is dropped from the ring.
Traffic flow and labels use when the link failure occurs:
A[P1]->F[P2]->E[P3]->D
3.2.2.2. Node failure example
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+---+ [P1] +---+
| F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ X
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ X
\ /
+---+ +---+
LSP 1 <-- | D |-------------| C |
+---+ +---+
Figure 9: Steering protection switching operation for p-t-p LSP in
case of node failure
When node B fails or becomes isolated because of two failed links,
nodes A and C send APS request to each other around the ring. Nodes
A and D analyze these requests and determine that LSP 1 is affected
by the failure. Node A switches the traffic of LSP 1 to the
protection label [P1] in the direction opposite to normal flow. This
traffic travels around the ring to the node D where it is dropped
from the ring.
Traffic flow in case of node B failure is presented below.
A[P1]->F[P2]->E[P3]->D
3.2.3. P-t-mp LSP example
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+---+ [P1] +---+
LSP 1 <-- | F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/[W5] [W1]\
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\[W4] [W2]/
\ /
+---+ [W3] +---+
LSP 1 <-- | D |-------------| C | -> LSP 1
+---+ [P4] +---+
Figure 10: Labels allocation example for p-t-mp LSP protection with
steering protection switching
Working labels:
A[W1]->B[W2]->C[W3]->D[W4]->E[W5]->F
| | |
v v v
LSP 1 LSP 1 LSP 1
Protection labels:
A[P1]->F[P2]->E[P3]->D[P4]->C
| | |
v v v
LSP 1 LSP 1 LSP 1
3.2.3.1. Link failure example
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+---+ [P1] +---+
LSP 1 <-- | F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ [W1]\
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
[P3]\ [W2]/
\ /
+---+ +---+
LSP 1 <-- | D |------X------| C | -> LSP 1
+---+ +---+
Figure 11: Steering protection switching operation for p-t-mp LSP in
case of link failure
When the failure occurs between the nodes C and D, these nodes send
APS request to each other around the ring. Nodes A, C, D and F
analyze these requests and determine that LSP 1 is affected by the
failure. Node A duplicates the traffic of LSP 1 to the working label
[W1] and the protection label [P1]. Node C detects that normal flow
of LSP 1 is not affected and continues receiving working label [W2]
without performing protection switching. Nodes D and F detect that
normal flow of LSP 1 is affected and switch to protection labels [P3]
and [P1] respectively.
Traffic flow and working labels use when the link failure occurs:
A[W1]->B[W2]->C->X
|
v
LSP 1
Traffic flow and protection labels use when the link failure occurs:
A[P1]->F[P2]->E[P3]->D->X
| |
v v
LSP 1 LSP 1
3.2.3.2. Node failure example
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+---+ [P1] +---+
LSP 1 <-- | F |-------------| A | <- LSP 1
+---+ +---+
/ \
[P2]/ [W1]\
/ \
+---+ +---+
| E | | B |
+---+ +---+
\ /
X [W2]/
\ /
+---+ +---+
| D |------X------| C | -> LSP 1
+---+ +---+
Figure 12: Steering protection switching operation for p-t-mp LSP in
case of node failure
When node D fails or becomes isolated because of two failed links,
nodes E and C send APS request to each other around the ring. Nodes
A, C and F analyze these requests and determine that LSP 1 is
affected by the failure. Node A duplicates the traffic of LSP 1 to
the working label [W1] and the protection label [P1]. Node C detects
that normal flow of LSP 1 is not affected and continues receiving
working label [W2] without performing protection switching. Node F
detects that normal flow of LSP 1 is affected and switch to
protection label [P1].
Traffic flow and working labels use when the node failure occurs:
A[W1]->B[W2]->C->X
|
v
LSP 1
Traffic flow and protection labels use when the node failure occurs:
A[P1]->F[P2]->E[P3]->X
|
v
LSP 1
4. MRPS characteristics
4.1. Switching types
MRPS mechanism MUST support bi-directional protection switching type.
In bi-directional switching, the traffic passing in both directions
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the monitored MPLS-TP section layer, including the affected direction
and the unaffected direction, is switched to protection LSPs/tunnels.
4.2. Operation types
MRPS mechanism MUST support revertive protection operation type,
which implies that the traffic will returns to (or remains on) the
working LSPs/tunnels after the failure or APS request is cleared.
MRPS mechanism MAY support non-revertive protection operation type,
which implies that the traffic will remain on the protection LSPs/
tunnels after the failure or APS request is cleared.
4.3. Traffic types
4.3.1. Bandwidth sharing
The bandwidth on each ring MUST be shared so that part of ring
bandwidth capacity is guaranteed for the normal traffic and part is
used for the protection traffic in case of failure on the ring. The
protection part of the ring bandwidth rotating in one direction is
used to carry the normal traffic from the ring rotating in other
direction in case of failure.
Part of ring bandwidth MAY also be dedicated to carry Non-preemptable
Unprotected Traffic (NUT).
4.3.2. Bandwidth and QoS considerations
The MRPS mechanism provides for the connectivity restoration of the
normal traffic affected by a ring failure. The protection mechanism
itself does not distinguish between different types of QoS associated
with the given LSPs. It is also not aware of the bandwidth allocated
or guaranteed for the protected or unprotected LSPs.
In the MPLS-TP ring, in order to guarantee the bandwidth and QoS of
the LSPs, normal or unprotected, traffic management and engineering
measures SHOULD be taken. For example, the bandwidth and QoS
parameters allocated for each protection LSP/tunnel can be equal to
the bandwidth and QoS parameters of the associated working LSP/
tunnel.
Bandwidth and QoS parameters calculation and allocation for the
normal and protection LSPs/tunnels are out of scope of this document.
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4.3.3. Point-to-point and point-to-multipoint traffic
Both point-to-point and drop-and-continue point-to-multipoint MPLS-TP
LSPs/tunnels MUST be protected by MRPS. The APS protocol
functionality as well as the node's reaction on different APS
requests in case of ring failure SHOULD be identical for p-t-p and
p-t-mp traffic.
5. APS protocol
The MRPS protection operation MUST be controlled with the help of the
APS protocol. The APS processes in the each of the individual nodes
that form the ring SHOULD communicate using MPLS-TP Section OAM APS
PDUs.
The APS protocol MUST carry the ring status information and APS
requests, both automatic and externally initiated commands, between
the ring nodes.
Each node on the ring MUST be uniquely identified by assigning it a
node ID. The maximum number of nodes on the ring supported by the
APS protocol is 127. The node ID SHOULD be independent of the order
in which the nodes appear on the ring. The node ID is used to
identity the source and destination nodes of each APS request.
Each node SHOULD have a ring map containing information about the
sequence of the nodes around the ring. The method of configuring the
nodes with the ring maps is TBD.
When no protection switches are active on the ring, each node MUST
dispatch periodically APS requests to the two adjacent nodes,
indicating No Request (NR). When a node determines that a protection
switching is required, it MUST send the appropriate APS request in
both directions.
+---+ A->B(NR) +---+ B->C(NR) +---+ C->D(NR)
-------| A |-------------| B |-------------| C |-------
(NR)F<-A +---+ (NR)A<-B +---+ (NR)B<-C +---+
Figure 13: APS communication between the ring nodes in case of no
failures in the ring
A destination node is a node that is adjacent to a node that
identified a failed span. When a node that is not the destination
node receives an APS request and it has no higher priority local
request, it MUST transfer the APS request as received. In this way,
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the switching nodes can maintain direct APS protocol communication in
the ring.
+---+ C->B(SF) +---+ B->C(SF) +---+ C->B(SF)
-------| A |-------------| B |----- X -----| C |-------
(SF)C<-B +---+ (SF)C<-B +---+ (SF)B<-C +---+
Figure 14: APS communication between the ring nodes in case of
failure between nodes B and C
Note that in the case of a bidirectional failure such as a cable cut,
two nodes detect the failure and send each other an APS request in
opposite directions.
o In rings utilizing the wrapping protection, when the destination
node receives the APS request it MUST perform the switch from/to
the working LSPs/tunnels to/from the protection LSPs/tunnels if it
has no higher priority active APS request.
o In rings utilizing the steering protection, when a ring switch is
required, any node MUST perform the switches if its added/dropped
traffic is affected by the failure. Determination of the affected
traffic SHOULD be performed by examining the APS requests
(indicating the nodes adjacent to the failure or failures) and the
stored ring maps (indicating the relative position of the failure
and the added traffic destined towards that failure).
When the failure has cleared and the Wait-to-Restore (WTR) timer has
expired, the nodes sourcing APS requests MUST drop their respective
switches (tail end) and MUST source an APS request carrying NR code.
The node receiving from both directions such APS request (head end)
MUST drop its protection switches.
A protection switch MUST be initiated by one of the criteria
specified in Section 6. A failure of the APS protocol or controller
MUST NOT trigger a protection switch.
Ring switches MUST be preempted by higher priority APS requests. For
example, consider a protection switch that is active due to a manual
switch request on the given span, and another protection switch is
required due to a failure on another span. Then a APS request MUST
be generated, the former protection switch MUST be dropped, and the
latter protection switch established.
MRPS mechanism SHOULD support multiple protection switches in the
ring, resulting the ring being segmented into two or more separate
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segments. This may happen when several APS requests of the same
priority exist in the ring due to multiple failures or external
switch commands.
Proper operation of the MRPS mechanism relies on all nodes having
knowledge of the state of the ring (nodes and spans) so that nodes do
not preempt existing APS request unless they have a higher-priority
APS request. In order to accommodate ring state knowledge, during
protection switch the APS requests MUST be sent in both directions.
5.1. Transmission and acceptance of APS requests
A new APS request MUST be transmitted immediately when a change in
the transmitted status occurs.
The first three APS protocol messages carrying new APS request SHOULD
be transmitted as fast as possible. For fast protection switching
within 50 ms, the interval of the first three APS protocol messages
SHOULD be 3.3 ms. Then APS requests SHOULD be transmitted with the
interval of 5 seconds.
5.2. APS PDU structure
Figure 15 depicts the format of an APS packet that is sent on the
G-ACh. The Channel Type field is set to indicate that the message is
an APS message. The ACH MUST NOT include the ACH TLV Header
[RFC5586] meaning that no ACH TLVs can be included in the message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|0 0 0 0|0 0 0 0 0 0 0 0| APS Channel Type (0xXX) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| APS message (TBD) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: G-ACh APS Packet
APS message structure is TBD.
The following fields MUST be provided:
o Destination Node ID: The destination node ID MUST always be set to
value of a node ID of the adjacent node. Valid destination node
ID values are 1-127.
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o Source node ID: The source node ID MUST always be set to the value
of the node ID generating the APS request. Valid source node ID
values are 1-127.
o APS request code: A code consisting of four bits as specified
below.
+-------------+-----------------------------+----------+
| Bits 4-1 | Condition, State | Priority |
| (MSB - LSB) | or external Request | |
+-------------------------------------------+----------+
| 1 1 1 1 | Lockout of Protection (LP) | highest |
| 1 1 0 1 | Forced Switch (FS) | |
| 1 0 1 1 | Signal Fail (SF) | |
| 0 1 1 0 | Manual Switch (MS) | |
| 0 1 0 1 | Wait-To-Restore (WTR) | |
| 0 0 1 1 | Exerciser (EXER) | |
| 0 0 0 1 | Reverse Request (RR) | |
| 0 0 0 0 | No Request (NR) | lowest |
+-------------+-----------------------------+----------+
5.3. Ring node APS states
Idle state: A node is in the idle state when it has no APS request
and is sourcing and receiving NR code to/from both directions.
Switching state: A node not in the idle or pass-through states is in
the switching state.
Pass-through state: A node is in the pass-through state when its
highest priority APS request is a request not destined to or sourced
by it. The pass-through is bidirectional.
5.3.1. Idle state
A node in the idle state MUST source the NR request in both
directions.
A node in the idle state MUST terminate APS requests flow in both
directions.
A node in the idle state MUST block the traffic flow on protection
LSPs/tunnels in both directions.
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5.3.2. Switching state
A node in the switching state MUST source APS request to adjacent
node with its highest APS request code in both directions when it
detects a failure or receives an external command.
A node in the switching state MUST terminate APS requests flow in
both directions.
As soon as it receives an APS request from the short path, the node
to which it is addressed MUST acknowledge the APS request by replying
with the RR code on the short path, and with the received APS request
code on the long path.
This rule refers to the unidirectional failure detection: the RR
SHOULD be issued only when the node does not detect the failure
condition (i.e., the node is a head end), that is, it is not
applicable when a failure is detected bidirectionally, because, in
this latter case, both nodes send an APS request for the failure on
both paths (short and long).
The following switches MUST be allowed to coexist:
o LP with LP
o FS with FS
o SF with SF
o FS with SF
When multiple MS APS requests over different spans exist at the same
time, no switch SHOULD be executed and existing switches MUST be
dropped. The nodes MUST signal, anyway, the MS APS request code.
Multiple EXER request MUST be allowed to coexist in the ring.
A node in a ring switching state that receives the external command
LW for the affected span MUST drop its switch and MUST signal NR for
the locked span if there is no other APS request on another span.
Node still SHOULD signal relevant APS request for another span.
5.3.3. Pass-through state
When a node is in a pass-through state, it MUST transmit on one side,
the same APS request as it receives from the other side.
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When a node is in a pass-through state, it MUST allow the traffic
flow on protection LSPs/tunnels in both directions.
5.3.4. APS state transitions
All state transitions are triggered by an incoming APS request
change, a WTR expiration, an externally initiated command, or locally
detected MPLS-TP section failure conditions.
APS requests due to a locally detected failure, an externally
initiated command, or received APS request shall pre-empt existing
APS requests in the prioritized order given in Section 5.2, unless
the requests are allowed to coexist.
5.3.4.1. Transitions between the idle and pass-through states
The transition from the idle state to pass-through state MUST be
triggered by a valid APS request change, in any direction, from the
NR code to any other code, as long as the new request is not destined
for the node itself. Both directions move then into a pass-through
state, so that, traffic entering the node through the protection LSPs
/tunnels are by-passed across the node.
A node MUST revert from pass-through state to the idle state when it
detects NR codes incoming from both directions. Both directions
revert simultaneously from the pass-through state to the idle state.
5.3.4.2. Transitions between the idle and switching states
Transition of a node from the idle state to the switching state MUST
be triggered by one of the following conditions:
o a valid APS request change from the NR code to any code received
on either the long or the short path and destined to this node
o an externally initiated command for this node
o the detection of an MPLS-TP section layer failure at this node.
Actions taken at a node in idle state upon transition to switching
state are:
o for all protection switch requests, except EXER and LP, the node
MUST execute the switch
o for EXER, and LP, the node MUST signal appropriate request but not
execute the switch.
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A node MUST revert from the switching state to the idle state when it
detects NR codes received from both directions.
o At the tail end: When a WTR time expires or an externally
initiated command is cleared at a node, the node MUST drop its
switch, transit to Idle state and signal the NR code in both
directions.
o At the head end: Upon reception of the NR code, from both
directions, the head-end node MUST drop its switch, transition to
Idle state and signal the NR code in both directions.
5.3.4.3. Transitions between switching states
When a node that is currently executing any protection switch
receives a higher priority APS request (due to a locally detected
failure, an externally initiated command, or a ring protection switch
request destined to it) for the same span, it MUST upgrade the
priority of the switch it is executing to the priority of the
received APS request.
When a failure condition clears at a node, the node MUST enter WTR
condition and remain in it for the appropriate time-out interval,
unless:
o a different APS request of higher priority than WTR is received
o another failure is detected
o an externally initiated command becomes active.
The node MUST send out a WTR code on both the long and short paths.
When a node that is executing a switch in response to incoming SF APS
request (not due to a locally detected failure) receives a WTR code
(unidirectional failure case), it MUST send out RR code on the short
path and the WTR on the long path.
5.3.4.4. Transitions between switching and pass-through states
When a node that is currently executing a switch receives an APS
request for a non-adjacent span of higher priority than the switch it
is executing, it MUST drop its switch immediately and enter the pass-
through state.
The transition of a node from pass-through to switching state MUST be
triggered by:
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o an equal, higher priority, or allowed coexisting externally
initiated command
o the detection of an equal, higher priority, or allowed coexisting
failure
o the receipt of an equal, higher priority, or allowed coexisting
APS request destined to this node.
6. Protection switching triggers
Protection switching action MUST be conducted when:
o they are initiated by operator control (e.g., manual switch,
forced switch, and lockout of protection) without a higher
priority APS request being in effect on addressed span or entire
ring
o an MPLS-TP Section SF is declared on the associated span and
without a higher priority APS request (e.g., lockout of
protection, forced switch) being in effect on addressed span or
entire ring and the hold-off timer has expired
o the wait to restore timer expires.
6.1. Manual control
Externally initiated commands are entered by the operator through the
Network Management System (NMS) or the Craft interface.
6.1.1. Commands not signaled on the APS protocol
The node MUST support the following commands that are not transferred
by the APS protocol:
o Clear: This command clears the externally initiated command and
WTR timer at the node to which the command was addressed. The
node-to-node signaling following removal of the externally
initiated commands MUST be performed using the NR code.
o Lockout of Working: This command prevents the normal traffic
transported over the addressed span from being switched to the
protection LSPs/tunnels by disabling the node's capability of
requesting the protection switching for this span in case of
failure. If any normal traffic is already switched on the
protection LSPs/tunnels, the switch MUST be dropped. If no other
APS requests are active on the ring, the NR code MUST be
transmitted. This command has no impact on any other span. If
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the node receives the APS request from the adjacent node from any
side it MUST perform the requested switch. If the node receives
the request addressed to the other node it MUST go to the pass-
through state.
6.1.2. Commands using the APS protocol
The node MUST support the following commands that are transferred by
the APS protocol:
o Lockout of Protection (LP): This command prevents any protection
activity and prevents using protection switches anywhere in the
ring. All existing switches in the ring MUST be dropped.
o Forced Switch to protection (FS): This command performs the ring
switch of normal traffic from the working LSPs/tunnels to the
protection LSPs/tunnels for the span between the node at which the
command is initiated and the adjacent node to which the command is
directed. This switch MUST occur regardless of the state of the
spans adjacent to this node unless it is satisfying a higher
priority APS request.
o Manual Switch to protection (MS): This command performs the ring
switch of the normal traffic from the working LSPs/tunnels to the
protection LSPs/tunnels for the span between the node at which the
command is initiated and the adjacent node to which the command is
directed. This occurs if the node is not satisfying an equal or
higher priority APS request.
The node MAY support the following commands that are transferred by
the APS protocol:
o Exercise - (EXER): This command exercises ring protection
switching on the addressed span without completing the actual
switch. When the command issued the RR responses are checked, but
no normal traffic is affected.
6.2. Automatically initiated commands
Automatically initiated commands can be initiated based on MPLS-TP
section layer and equipment performance criteria and received APS
requests.
The node MUST support the following APS requests that are initiated
automatically:
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o Signal Fail (SF): This command is issued when the MPLS-TP section
detects signal failure condition. When the tail-end detects the
failure it MUST generate the APS request towards the head-end.
o Wait-To-Restore (WTR): This command is issued when MPLS-TP section
detects that the SF condition has cleared. It is used to maintain
the state during the WTR period unless it is pre-empted by a
higher priority APS request. The Wait to Restore time SHOULD be
configured by the operator in 1 minute steps between 0 and 72
hours. The default value SHOULD be 5 minutes.
o Reverse Request (RR): This command MUST be transmitted to the
tail-end node over the short path as an acknowledgment for
receiving the APS request.
6.3. APS state machine
6.3.1. Initial states
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+-----------------------------------+----------------+
| State | Signaled APS |
+-----------------------------------+----------------+
| A | Idle | NR |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| B | Pass-trough | N/A |
| | Working: no switch | |
| | Protection: pass through | |
+-----+-----------------------------+----------------+
| C | Switching - LP | LP |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| D | Idle - LW | NR |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
| E | Switching - FS | FS |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| F | Switching - SF | SF |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| G | Switching - MS | MS |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| H | Switching - WTR | WTR |
| | Working: switched | |
| | Protection: switched | |
+-----+-----------------------------+----------------+
| I | Switching - EXER | EXER |
| | Working: no switch | |
| | Protection: no switch | |
+-----+-----------------------------+----------------+
6.3.2. State transitions when local request is applied
In the state description below 'O' means that new local request will
be rejected because of exiting request.
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=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP C (Switching - LP)
LW D (Idle - LW)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear N/A
WTR expires N/A
EXER I (Switching - EXER)
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-trough) LP C (Switching - LP)
LW B (Pass-trough)
FS O - if current state is due to
LP sent by another node
E (Switching - FS) - otherwise
SF O - if current state is due to
LP sent by another node
F (Switching - SF) - otherwise
Recover from SF N/A
MS O - if current state is due to
LP, SF or FS sent by
another node
G (Switching - MS) - otherwise
Clear N/A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP N/A
LW O
FS O
SF O
Recover from SF N/A
MS O
Clear A (Idle) - if there is no
failure in the ring
F (Switching - SF) - if there
is a failure at this node
B (Pass-trough) - if there is
a failure at another node
WTR expires N/A
EXER O
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=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP)
LW N/A - if on the same span
D (Idle - LW) - if on another
span
FS O - if on the same span
E (Switching - FS) - if on
another span
SF O - if on the addressed span
F (Switching - SF) - if on
another span
Recover from SF N/A
MS O - if on the same span
G (Switching - MS) - if on
another span
Clear A (Idle) - if there is no
failure on addressed span
F (Switching - SF) - if there
is a failure on this span
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP)
LW O - if on another span
D (Idle - LW) - if on the same
span
FS N/A - if on the same span
E (Switching - FS) - if on
another span
SF O - if on the addressed span
E (Switching - FS) - if on
another span
Recover from SF N/A
MS O
Clear A (Idle) - if there is no
failure in the ring
F (Switching - SF) - if there
is a failure at this node
B (Pass-trough) - if there is
a failure at another node
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
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------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP)
LW O - if on another span
D (Idle - LW) - if on the same
span
FS E (Switching - FS)
SF N/A - if on the same span
F (Switching - SF) - if on
another span
Recover from SF H (Switching - WTR)
MS O
Clear N/A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP)
LW O - if on another span
D (Idle - LW) - if on the same
span
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS N/A - if on the same span
G (Switching - MS) - if on
another span release the
switches but signal MS
Clear A
WTR expires N/A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP)
LW D (Idle - W)
FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear A
WTR expires A
EXER O
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP)
LW D (idle - W)
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FS E (Switching - FS)
SF F (Switching - SF)
Recover from SF N/A
MS G (Switching - MS)
Clear A
WTR expires N/A
EXER N/A - if on the same span
I (Switching - EXER)
=====================================================================
6.3.3. State transitions when remote request is applied
The priority of remote request does not depend on the side from which
the request is received.
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR A (Idle)
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-trough) LP C (Switching - LP)
FS N/A - cannot happen when there
is LP request in the ring
E (Switching - FS) - otherwise
SF N/A - cannot happen when there
is LP request in the ring
F (Switching - SF) - otherwise
MS N/A - cannot happen when there
is LP, FS or SF request
in the ring
G (Switching - MS) - otherwise
WTR N/A - cannot happen when there
is LP, FS, SF or MS
request in the ring
EXER N/A - cannot happen when there
is LP, FS, SF, MS or WTR
request in the ring
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I (Switching - EXER) -
otherwise
RR N/A
NR A (Idle) - if received from
both sides
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP C (Switching - LP)
FS N/A - cannot happen when there
is LP request in the ring
SF N/A - cannot happen when there
is LP request in the ring
MS N/A - cannot happen when there
is LP request in the ring
WTR N/A
EXER N/A - cannot happen when there
is LP request in the ring
RR C (Switching - LP)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR D (Idle - LW)
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP C (Switching - LP)
FS E (Switching - FS)
SF E (Switching - FS)
MS N/A - cannot happen when there
is FS request in the ring
WTR N/A
EXER N/A - cannot happen when there
is FS request in the ring
RR E (Switching - FS)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP C (Switching - LP)
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FS F (Switching - SF)
SF F (Switching - SF)
MS N/A - cannot happen when there
is SF request in the ring
WTR N/A
EXER N/A - cannot happen when there
is SF request in the ring
RR F (Switching - SF)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS) - release
the switches but signal MS
WTR N/A
EXER N/A - cannot happen when there
is MS request in the ring
RR G (Switching - MS)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR H (Switching - WTR)
EXER N/A - cannot happen when there
is WTR request in the ring
RR H (Switching - WTR)
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
I (Switching - EXER) LP C (Switching - LP)
FS E (Switching - FS)
SF F (Switching - SF)
MS G (Switching - MS)
WTR N/A
EXER I (Switching - EXER)
RR I (Switching - EXER)
NR N/A
=====================================================================
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6.3.4. State Transitions when request addresses to another node is
received
The priority of remote request does not depend on the side from which
the request is received.
=====================================================================
Initial state New request New state
------------- ----------- ---------
A (Idle) LP B (Pass-trough)
FS B (Pass-trough)
SF B (Pass-trough)
MS B (Pass-trough)
WTR B (Pass-trough)
EXER B (Pass-trough)
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
B (Pass-trough) LP B (Pass-trough)
FS N/A - cannot happen when there
is LP request in the ring
B (Pass-trough) - otherwise
SF N/A - cannot happen when there
is LP request in the ring
B (Pass-trough) - otherwise
MS N/A - cannot happen when there
is LP, FS or SF request
in the ring
B (Pass-trough) - otherwise
WTR N/A - cannot happen when there
is LP, FS, SF or MS
request in the ring
B (Pass-trough) - otherwise
EXER N/A - cannot happen when there
is LP, FS, SF, MS or WTR
request in the ring
B (Pass-trough) - otherwise
RR N/A
NR B (Pass-trough)
=====================================================================
Initial state New request New state
------------- ----------- ---------
C (Switching - LP) LP C (Switching - LP)
FS N/A - cannot happen when there
is LP request in the ring
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SF N/A - cannot happen when there
is LP request in the ring
MS N/A - cannot happen when there
is LP request in the ring
WTR N/A - cannot happen when there
is LP in the ring
EXER N/A - cannot happen when there
is LP request in the ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
D (Idle - LW) LP B (Pass-trough)
FS B (Pass-trough)
SF B (Pass-trough)
MS B (Pass-trough)
WTR B (Pass-trough)
EXER B (Pass-trough)
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
E (Switching - FS) LP B (Pass-trough)
FS E (Switching - FS)
SF E (Switching - FS)
MS N/A - cannot happen when there
is FS request in the ring
WTR N/A - cannot happen when there
is FS request in the ring
EXER N/A - cannot happen when there
is FS request in the ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
F (Switching - SF) LP B (Pass-trough)
FS F (Switching - SF)
SF F (Switching - SF)
MS N/A - cannot happen when there
is SF request in the ring
WTR N/A - cannot happen when there
is SF request in the ring
EXER N/A - cannot happen when there
is SF request in the ring
RR N/A
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NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
G (Switching - MS) LP B (Pass-trough)
FS B (Pass-trough)
SF B (Pass-trough)
MS G (Switching - MS) - release
the switches but signal MS
WTR N/A - cannot happen when there
is MS request in the ring
EXER N/A - cannot happen when there
is MS request in the ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
------------- ----------- ---------
H (Switching - WTR) LP B (Pass-trough)
FS B (Pass-trough)
SF B (Pass-trough)
MS B (Pass-trough)
WTR N/A
EXER N/A - cannot happen when there
is WTR request in the ring
RR N/A
NR N/A
=====================================================================
Initial state New request New state
I (Switching - EXER) LP B (Pass-trough)
FS B (Pass-trough)
SF B (Pass-trough)
MS B (Pass-trough)
WTR N/A
EXER I (Switching - EXER)
RR N/A
NR N/A
=====================================================================
7. IANA Considerations
Channel Types for the Generic Associated Channel are allocated from
the IANA PW Associated Channel Type registry defined in [RFC4446] and
updated by [RFC5586].
IANA is requested to allocate further Channel Type as follows:
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o 0xXX Automatic Protection Switching (APS)
Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Security Considerations
This document does not by itself raise any particular security
considerations.
9. Acknowledgements
Special thanks to Igor Umansky for his contribution.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
10.2. Informative References
[RFC5654] Niven-Jenkins, B., Nadeau, T., and C. Pignataro,
"Requirements for the Transport Profile of MPLS", RFC
5654, September 2009.
[G.841] ITU-T, , "Types and characteristics of SDH network
protection architectures", Recommendation G.841, Feb 2010.
[RFC6371] Busi, I. and D. Allan, "Operations, Administration, and
Maintenance Framework for MPLS-Based Transport Networks",
RFC 6371, September 2011.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", RFC 4446, BCP 116, April 2006.
Appendix A. Ring protection requirements compliance
Ring protection requirements are specified in the [RFC5654]
Section 2.5.6. This section summarizes the coverage of these
requirements by MRPS mechanism.
Generic topology-specific requirement:
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91 Interoperability between the ring and mesh networks in term of
protection switching is achieved by:
* using a non-preemptable unprotected traffic type (NUT) in the
ring for the LSPs traversing the ring that are protected with
end-to-end linear protection.
* implementing segmented linear protection on the ring edge
nodes
Optimization criteria:
a. There is only one APS OAM session per ring.
b. Only two network elements, which are adjacent to addressed span
or node are involved in protection switching event.
c. MRPS requires one protection label on each span to protect one
working LSP.
d. Management operations are applied per node/per span, rather than
per path. Dedicated procedures for ring upgrade are supported by
using operator commands, provided by the ring protection
algorithm. Static provisioning of limited amount of parameters
is considered.
e. MRPS mechanism does not affect control plane.
General criteria:
92 MRPS mechanism operates provides for recovery of protected
traffic within a ring domain without affecting other parts of the
network.
93 Current version of this draft describes protection mechanism
operating in the single ring domain. Multiple rings interworking
is for further study.
94 Unidirectional and bidirectional paths are protected by MRPS, due
to the fact that the protection mechanism is bidirectional.
95 Unidirectional P2MP paths are protected with the same mechanism
as unidirectional by wrapping scheme. Steering scheme provides
different mechanisms for P2P and P2MP paths.
96 Irrelevant for this draft.
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97 MRSP mechanism operates at the MPLS-TP section layer and does not
depend on number of LSPs passing addressed section/span.
98.A Configuration of protection LSP is proportional to the number
of working LSPs. Operation of protection switching is
independent of number of working/protection path.
98.B Configuration of protection LSP is proportional to the number
of nodes in the ring. Operation of protection switching is
independent of number of nodes.
98.C Configuration and operation of MRPS is done per ring and is
independent of number or rings interconnects.
99 MRPS mechanism operates in a ring protection domain without
affecting attached networks. An MPRS ring may be connected to a
general MPLS-TP network with no constraint.
100 Recovery technique of MRPS relies on standard MPLS label swapping
operation. Protection algorithm relies on well established MS-
SPRing/BLSR mechanism.
101 MRPS mechanism is agnostic to the server layer technology and the
associated infrastructure.
102 Protection switching in MRPS is bidirectional.
103 Protection switching in MRPS is revertive in case or wrapping
scheme and configurable in case of steering scheme.
104 MRPS supports operator commands and automatic evens as protection
triggers. Each one is identified via dedicated code in APS
protocol.
105 MRPS supports operator commands to lockout/disable the protection
switching per span and per entire ring.
106.A MRPS supports ring protection operation in case of multiple
requests in the ring.
106.B MRPS supports traffic protection in case multiple failures in
the ring.
107 Supported through wait-to-restore timer.
108 Best effort traffic that can be carried in unprotected LSPs (via
NUT feature) and in all of the protection bandwidth.
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109 Supported through sharing the protection bandwidth of each span
between all other spans in the ring.
Authors' Addresses
Huub van Helvoort (editor)
Huawei Technologies
Email: huub.van.helvoort@huawei.com
Jeong-dong Ryoo (editor)
ETRI
Email: ryoo@etri.re.kr
Italo Busi
Alcatel-Lucent
Email: italo.busi@alcatel-lucent.com
Haiyan Zhang
Huawei Technologies
Email: zhanghaiyan@huawei.com
Han Li
China Mobile Communications Corporation
Email: lihan@chinamobile.com
Ruiquan Jing
China Telecom
Email: jingrq@ctbri.com.cn
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