The document discusses Ethernet Automatic Protection Switching (EAPS) and G.8032 Ethernet Ring Protection Switching (ERPS). It provides an overview of the evolution of EAPS from version 1 to version 2, and compares EAPS to ERPS. Key aspects of ERPS such as its objectives, terms and definitions, supported features in different versions, operations during idle and failure states, and timers are described. ERPS provides sub-50ms protection switching for traffic in a ring topology to prevent loops.

1. Extreme Networks Confidential and Proprietary. © 2011 Extreme Networks, Inc. All rights reserved.Extreme Networks Confidential and Proprietary. © 2011 Extreme Networks, Inc. All rights reserved.
Piotr Szołkowski (Pre-Sales Engineer Extreme Networks)
Extreme Networks Confidential and Proprietary. Internal Use Only
EAPS year 2000 = ERPS G.8032 year 2012?
Reinvention of Ethernet Ring Topology

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EAPS Refresh
Ethernet Automatic Protection Switching

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EAPSv1
• Introduced in year 2000 as cost effective alternative to SDH networks
• Described in RFC 3619 – October 2003
• Supported Features
• Single Ring Protection
• Revertive behavior
Ring Ring Ring

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EAPSv2
• Extension of EAPSv1 to multi-ring topologies
• Supported Features
• Multi Ring Protection
• Revertive behavior
Ring
Ring
Ring
Ring
Ring
Ring

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ERPS Overview
G.8032 Ethernet Ring Protection Switching

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G.8032 Objectives
EthernetRing Protection Switching (ERPS)/G.8032 provides sub-50ms protection and
recovery switching for Ethernet traffic in a ring topology and at the same time ensure that
there are no loops formed at the Ethernet layer.
- Protection switching on Ethernet layer
- Use of Ethernet OAM frames called R-APS messages for protection behavior
- Preventing any loops by a blocking mechanism
- VLAN based protection switching
- Sub-50ms protection switching
- Support of adminstrative commands
Ring Ring Ring

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G.8032 Terms and Definitions
• Ring Protection Link (RPL) – Link designated by mechanism that is
blocked during Idle state to prevent loop on Bridged ring
• RPL Owner – Node connected to RPL that blocks traffic on RPL during
Idle state and unblocks during Protected state
• Link Monitoring – Links of ring are monitored using standard ETH CC
OAM messages (CFM)
• Signal Fail (SF) – Signal Fail is declared when ETH trail signal fail
condition is detected
• No Request (NR) – No Request is declared when there are no outstanding
conditions (e.g., SF, etc.) on the node
• Ring APS (R-APS) Messages – Protocol messages defined in Y.1731 and
G.8032
• Automatic Protection Switching (APS) Channel - Ring-wide VLAN used
exclusively for transmission of OAM messages including R-APS
messages
Source: ITU-T Q9 – SG 15
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G.8032 (06/2008)
• Revision Approved in June 2008
• Supported Features
• Single Ring Protection
• Revertive behavior
• State based flush logic
Ring

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G.8032 (04/2009)
• Amendment approved in April 2009
• Supported Features
• Multi-Ring protection with R-APS Virtual Channel
• Revertive behavior
• State based flush logic
• Flush propogation
Major
Sub
Major
Sub Sub

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Extreme Networks Confidential and Proprietary. Internal Use Only
G.8032 (03/2010)
• Revision Approved in March 2010
• Supported Features
• Multi-Ring protection with/without R-APS Virtual Channel
• Revertive/non-revertive behavior
• Flush logic with Node-ID and BPR (Blocked Port Reference) mechanism
• Administrative commands (Manual/Forced switch, Clear)
• Ability to block RPL at both ends of link
• Multiple (logical) ERP Instances over a given physical ring
Ring
Major
Sub
Major
Sub Sub
Major
Sub
Sub

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Extreme Networks Confidential and Proprietary. Internal Use Only
G.8032 Interconnected Rings
• Interconnection Node
 Connects between Ethernet rings
• Major Ring
 Constitutes a closed ring
 Is controlled by its own ERP
instance with its own RPL
• Sub-Ring
 Is connected to a Major Ring or
upper Sub-Ring via the Interconnection
Nodes and does not constitute a
closed ring
 Is controlled by its own ERP instance
with its own RPL
G.8032 Supports for a network of interconnected rings based following
terminology.
Major
Sub
Major
Sub Sub
Major
Sub
Sub
Major
Major
Sub

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G.8032 R-APS Virtual Channel
The 2010 version supports two implementation options for R-APS control
channel of the Sub-Ring.
In the first option, R-APS messages are encapsulated and transmitted over R-APS Virtual
Channel configured on the Major Ring.
In the second option, R-APS messages are terminated at the Inteconnecting Nodes but
not blocked at the RPL of the Sub-Ring.
Major
Sub Sub
Major
R-APS Channel
of Major Ring
R-APS Channel
of Sub-Ring
with R-APS
Virtual Channel
Sub
Major
R-APS Channel
of Sub-Ring
without R-APS
Virtual Channel
Physical Ring
R-APS Virtual Channel
R-APS
Channel
 with R-APS Virtual Channel
 without R-APS Virtual Channel
Major
Sub

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G.8032 Timers
• G.8032 specifies the use of different timers to avoid race conditions
and unnecessary switching operations
• WTR (Wait to Restore) Timer – Used by the RPL Owner to verify that the ring has
stabilized before blocking the RPL after SF Recovery
• Hold-off Timers – Used by underlying ETH layer to filter out intermittent link faults
• Faults will only be reported to the ring protection mechanism if this timer expires
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ERPS Operations - Ring Idle State
1. Physical Topology has all nodes connected in a ring architecture
3. Logical Topology has all nodes connected without a loop
5. Signal Failure as defined in Y.1731 is trigger to ring protection
• Loss of Continuity
• Server Layer failure (e.g. Physical Link Down)
(ETH-CC) CCM (Continuity Check Message)
Extreme Networks Confidential and Proprietary. Internal Use Only 1717
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
2. ERP guarantees no loop by blocking the RPL link
RPL (Ring Protection Link)
Ethernet Ring Port
4. Each link is monitored by its 2 adjacent nodes using ETH-CC (OAM messages)

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ERPS Operations – Link Failure
Extreme Networks Confidential and Proprietary. Internal Use Only 1818
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
1. Link/Node Failure is detected by the nodes adjacent to the failure.
Failure

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ERPS Operations – Link Failure
1. Link/Node Failure is detected by the nodes adjacent to the failure.
Extreme Networks Confidential and Proprietary. Internal Use Only 1919
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
2. Nodes adjacent to the failure block the failed link and reports this failure to the ring using R-APS (SF) message
with node ID and BPR
(SF) Signal Fail

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ERPS Operations – Link Failure
1. Link/Node Failure is detected by the nodes adjacent to the failure.
2. Nodes adjacent to the failure block the failed link and reports this failure to the ring using R-APS (SF) message
with node ID and BPR
3. R-APS (SF) message triggers;
- RPL Owner unblocks the RPL
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RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
- All nodes flush FDBs
(SF) Signal Fail

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ERPS Operations – Link Failure
1. Link/Node Failure is detected by the nodes adjacent to the failure.
2. Nodes adjacent to the failure block the failed link and reports this failure to the ring using R-APS (SF) message
with node ID and BPR
3. R-APS (SF) message triggers;
- RPL Owner unblocks the RPL
- All nodes flush FDBs
Extreme Networks Confidential and Proprietary. Internal Use Only 2121
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(SF) Signal Fail
4. All Ethernet ring nodes receiving a second R-APS (SF) messages perform the FDB flush again due to the node
ID and BPR based mechanism.

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ERPS Operations – Link Failure
1. Link/Node Failure is detected by the nodes adjacent to the failure.
2. Nodes adjacent to the failure block the failed link and reports this failure to the ring using R-APS (SF) message
with node ID and BPR
3. R-APS (SF) message triggers;
- RPL Owner unblocks the RPL
- All nodes flush FDBs
Extreme Networks Confidential and Proprietary. Internal Use Only 22
5. Stable SF condition.
22
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(SF) Signal Fail
4. All Ethernet ring nodes receiving a second R-APS (SF) messages perform the FDB flush again due to the node
ID and BPR based mechanism.

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ERPS Operations – Failure Recovery
1. When failed Link recovers the traffic is kept blocked on the nodes adjacent to the recovered link
Extreme Networks Confidential and Proprietary. Internal Use Only 2323
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port

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ERPS Operations – Failure Recovery
1. When failed Link recovers the traffic is kept blocked on the nodes adjacent to the recovered link
2. The Nodes adjacent to the recovered link transmit R-APS (NR) messages indicating that they do not have local
request present
Extreme Networks Confidential and Proprietary. Internal Use Only 2424
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(NR) No Request

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ERPS Operations – Failure Recovery
1. When failed Link recovers the traffic is kept blocked on the nodes adjacent to the recovered link
2. The Nodes adjacent to the recovered link transmit R-APS (NR) messages indicating that they do not have local
request present
3. When the RPL Owner receives R-APS (NR) messages it STARTS WTR timer
Extreme Networks Confidential and Proprietary. Internal Use Only 2525
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(NR) No Request

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ERPS Operations – Failure Recovery
1. When failed Link recovers the traffic is kept blocked on the nodes adjacent to the recovered link
2. The Nodes adjacent to the recovered link transmit R-APS (NR) messages indicating that they do not have local
request present
3. When the RPL Owner receives R-APS (NR) messages it STARTS WTR timer
4. Once WTR timer expires RPL Owner node blocks RPL and transmits R-APS (NR, RB) messages
Extreme Networks Confidential and Proprietary. Internal Use Only 2626
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(NR) No Request
(RB) Root Blocked

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ERPS Operations – Failure Recovery
1. When failed Link recovers the traffic is kept blocked on the nodes adjacent to the recovered link
2. The Nodes adjacent to the recovered link transmit R-APS (NR) messages indicating that they do not have local
request present
3. When the RPL Owner receives R-APS (NR) messages it STARTS WTR timer
4. Once WTR timer expires RPL Owner node blocks RPL and transmits R-APS (NR, RB) messages
5. Nodes that receive the message Flush FDBs and unblock their previously blocked ports
Extreme Networks Confidential and Proprietary. Internal Use Only 2727
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(NR) No Request
(RB) Root Blocked

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ERPS Operations – Failure Recovery
1. When failed Link recovers the traffic is kept blocked on the nodes adjacent to the recovered link
2. The Nodes adjacent to the recovered link transmit R-APS (NR) messages indicating that they do not have local
request present
3. When the RPL Owner receives R-APS (NR) messages it STARTS WTR timer
4. Once WTR timer expires RPL Owner node blocks RPL and transmits R-APS (NR, RB) messages
6. Ring is now back in Idle State
5. Nodes that receive the message Flush FDBs and unblock their previously blocked ports
Extreme Networks Confidential and Proprietary. Internal Use Only 2828
RPL Owner
Node
RPL Neighbor
Node
Ethernet Ring NodeEthernet Ring Node
Ethernet Ring Node
Ethernet Ring Node
RPL (Ring Protection Link)
Ethernet Ring Port
(NR) No Request
(RB) Root Blocked

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G.8032 Signaling Channel Information
•ERP uses R-APS messages to manage and coordinate the protection switching
•R-APS defined in Y.1731 - OAM common fields are defined in Y.1731.
• Version – ‘00000’ – for this version of Recommendation
• OpCode – defined to be 40 in Y.1731
• Flags – ‘00000000’ – should be ignored by ERP
Extreme Networks Confidential and Proprietary. Internal Use Only 30
1 2 3 4
8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 18 7 6 5 4 3 2 1
MEL Version (0) OpCode (R-APS) Flags (0) TLV Offset (32)
R-APS Specific Information
( Optional TLV starts here: otherwise End TLV)
End TLV (0)
1
5
...
37
last
Defined by Y.1731 Defined by G.8032 Non-specified content

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R-APS Specific Information
• Specific information (32octets) defined by G.8032
• Request/Status(4bits) – ‘1011’ = SF | ’0000’ = NR | etc.
• Status – RB (1bit) – Set when RPL is blocked (used by RPL Owner in NR)
• Status – DNF (1bit) – Set when FDB Flush is not necessary
• NodeID (6octets) – MAC address of message source node (Informational)
Extreme Networks Confidential and Proprietary. Internal Use Only 31
1101 FS
1110 Event
1011 SF
0111 MS
0000 NR
RB 0 RPL Unblocked
1 RPL Blocked
DNF 0 Flush FDB
1 Do not Flush
BPR 0 Ring Link 0 Blocked
1 Ring Link 1 Blocked
1 2 3 4
8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 18 7 6 5 4 3 2 1
Request/
State
Reserved 1 Node ID (6 octets)
R
B
D
N
F
Status
Reserved
(Node ID)
Status
Reserved 2 (24 octets)
B
P
R

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ERPS vs. EAPS
Extreme Networks Confidential and Proprietary. Internal Use Only
Feature EAPS ERPS Comments
Node hierarchy Master node concept RPL node concept RPL node in ERPS does not
terminate control packets
like EAPS.
Keepalive packets Initiated and terminated at
master.
NR and NR-RB packets can
be considered as keepalive.
Terminated at blocked port.
RPL node does not
terminate packets.
Ring ports Called Primary and Secondary.
Secondary ring port is blocked in
normal, steady state operation.
i.e. Complete state.
Considered peer ports at all
node except at RPL node
where one of the ring ports is
the RPL port and blocked.
Break in ring Link-down PDU sent from failed
nodes causing Master to open
secondary port.
SF packets sent by node
detecting fault whereby RPL
opens blocked RPL port.
Multiple ring support V2 support introduced Controller
and Partner nodes that oversee
the blocking of port on shared link
to prevent super-loops.
V2 support by introducing sub-
rings that are not complete
rings but complete their path
through interconnected nodes
and the use of Virtual channel
that can span multiple rings.
ERPS topology design is a
complexity left to the
network administrator while
EAPS handles the
complexity within the
protocol.
Control packets Master terminates all control
packets for EAPSv1. Controller
and Partner terminate control
packets for EAPSv2.
R-APS packets. Terminated by
blocked port. Cannot transmit
them on blocked ports.
Packets supported are:
NR, NR-RB, SF, FS, MS.

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EAPS vs. ERPS Contd.
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Feature EAPS ERPS Comments
CFM Not directly tied to EAPS, but can
be used in conjunction with EAPS
to signal faults in the network for
which EAPS can react to.
Basis for the protocol to
function. The R-APS packets
are built on the Y.1731 packet
format. UP MEPs are required
for Virtual channel to work.
Revertive and non-
revertive mode of
operation
Only revertive supported. Non-
revertive planned in the future.
Both are supported in v1 and
v2 of the protocol.
Administrative
operations
None Force and Manual switch
opertions supported in both v1
and v2.
Timers Used to send periodic control
packets, signal failure in the ring,
and detect super loop conditions.
Used to determine change in
state. E.g. Delay timers like
WTR, WTB, Guard timer and
Hold-off timers what determine
when to act on an event
Multiple ring breaks EAPSv2 is designed such that it
attempts to recover from multiple
ring segment failures.
In ERPS v2, all cases of
keeping connectivity up in
case of multiple breaks are not
handled.
Vendors have chosen to
have proprietary
implemtations in G.8032
where standards have failed
to describe recovery
situation due to multiple
failure in v2. These
implementations have
shortcomings.

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EAPS vs. ERPS Contd.
Extreme Networks Confidential and Proprietary. Internal Use Only
Feature EAPS ERPS Comments
VPLS Provides redundancy for L2 edge
rings connected to VPLS core.
(Patent Pending)
Not supported. G.8032 standards do not preclude
such support.
PBB Supports PBB SVLAN/CVLAN to
BVLAN redundancy.
Not supported. G.8032 standards do not preclude
such support.
Spatial Reuse Multiple EAPS domains can be
defined on a physical ring, which
each domain blocking a different
set of protected vlans. Allows
user to optimize link utilization.
G.8032 provides spatial
reuse of defining mutlple
G.8032 domain on a
single physical ring with
each domain protecting
different set of protected
vlans.
Priority Domains Supports defining priorities
between rings that are configured
for Spatial Reuse
Not supported. G.8032 standards do not preclude
such support.
Multicast
Optimizations
Supports patented multicast
convergence optimizations,
including temporary flooding.
¨U.S. Patent
entitled: CONVERGENCE OF
MULTICAST TRAFFIC
Patent No.: 7,856,019
Issue Date: December 21, 2010
Not supported. G.8032 standards do not preclude
such support.

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