-
Ethernet OAM Overview
Operations, Administration & Maintenance Standards
-
Ethernet Operations, Admin & Maintenance
OAM standards developed to make Ethernet carrier grade
Protocols developed to enable operationally efficient carrier
Ethernet services over multi-vendor, multi-operator networks
Key Functions
Proactive network and service monitoring
Rapid fault detection & isolation
Performance / Service Level Agreement (SLA) parameters
measurement: on-demand or continuously
Service usage measurement for billing & capacity management
When Deployed End-to-End
Ethernet becomes carrier grade, capable of carrying real-time,
critical services with high availability and QoS
-
Ethernet OAM Standards Overview
Core Access
10/100/GbE
Base TX / FX /
LX / SX
MEF & ITU-T Y.1731 Service
802.1ag, Y.1731, MEF Connectivity
IEEE 802.3ah Link
Access OAM Layer
Customer
Network
Customer
Network
Transport
Network
Demarcation
Point
Standards
OAM Layer Function / Focus
Service end-to-end service (customer) view, reflected in SLAs
Connectivity Network & service connectivity & performance monitoring, topology-aware, multi-domain
Link focused on single-hop links, 1st mile transport
-
802.3ah Link Layer OAM
Designed for 1st mile / single-hop links
Typically Provider Edge (PE) to Customer Edge (CE)
Does not propagate beyond the link
Key functions:
Discovery: demarcation point device discovery & loopback capability
Remote failure indication: dying gasp, link fault & critical events
Fault isolation: customer or provider network, unidirectional failures
Port-level loopback: remote or locally activated, layer 1 only, disruptive
Performance & Status Monitoring with threshold alarms
ProvidersNetwork
1st Mile
% frame errors
# coding symbol errors
Unrecoverable error(e.g. power: dying gasp)
LOS (directional)
Critical events
stats
alarms
OAMPDUs:
- Loopback
- Continuity
-
Connectivity & Service OAM
End-to-End Ethernet Service OAM
IEEE 802.1ag, ITU-T Y.1731 and MEF
OAM standards are based on a common
multi-domain network model
Model reflects services delivered by
multiple providers at different levels
Goal is to ensure OAM is contained
within pre-defined maintenance levels
Customer
Site 1
Operator 2Operator 3
Provider
CustomerCustomer
Site 2
Operator 1
Access Links, 802.3ah(fail-over link in grey)
Service Demarc
802.1ag
Maintenance Intermediate Point (MIP)
Maintenance Endpoint (MEP)
CPE CPE
Provider Domain
Operator A Bridges
Customer OAM Level
Provider OAM Level
Operator OAM Level
Link OAM
Layer 2
Data Path
Operator B Bridges
Multi-Domain Network Model
-
OAM Management Entities & Components
Maintenance Intermediate Point (MIP)
Maintenance Endpoint (MEP)
Acronym Description
MEP Maintenance Endpoint
MIP Maintenance Intermediate Point
ME Management Entity (relationship between 2 MEPs)
MA / MEG Maintenance Assc (802.1ag) / Entity Group (Y.1731)
Logical Group of MEs at same level
on same S-VLAN
Pt-to-Pt or Multipoint EVC
Operator A
Operator B
Service Provider (S)
B
SS
B
B
B
B
B
B
BS
B
AA
A A
A
A
Operator A MEG
Operator A ME
S
A A
S
S
A
-
802.1ag / Y.1731 Connectivity Fault Management (CFM)
Fault Detection using Continuity Check Messages
EVC
Failure
Alarm
CCM
NOCCCM Timeout
Alarms
Fault Verification Using Loopback Messages (Ping)
EVC
Failure
LBR
LBM
Fault Isolation Using Linktrace Messages
EVC
Broken Link
LTR
LTM
Fault Notification, Alarm Indication Signal (Y.1731 only)
EVC
Broken Link
AIS
Per Service
Alarms
Can also be used to loopback a test traffic stream
(e.g. throughput measurement)
802.1ag
Unicast only
Y.1731
Unicast & multicast
-
Y.1731 Performance Monitoring (PM)
DMM time-stamped packet sent to far-end
Far-end device responds with DMR
carrying original timestamp
Originating device compares timestamp to
current time to calculate delay
No clock-sync required between endpoints
Frame Loss Ratio Using CCM (dual-ended)
EVC
Broken Link
Tx / Rx Counters
CCM
Frame Delay (FD) / Delay Variation (FDV)
Measurements, 1-Way
1DM time-stamped
packets
Synchronized Clocks
DMR
DMM
EVC
DMM
DMR
Frame Delay (FD) / Delay Variation (FDV)
Measurements, Round-Trip
-
Connectivity & Services OAM Summary
Accedian Networks has also developed in-service throughput testing
based on Y.1731 LBM / LBR frames (patent pending)
OAM Function 802.1ag Y.1731 Method
CFM
Fault Detection CCM
Fault Verification /
Loopback LBM / LBR (Ping)
Fault Isolation LTM / LTR
Discovery LTM / LTR & Multicast LBM*
Fault Notification AIS / RDI
PM
Frame Loss CCM, LTM / LTR
Frame Delay DM (1 way), DMM / DMR
Delay Variation DM (1 way), DMM / DMR
* Y.1731 only
-
Incorporating 802.1ag/Y.1731 into Service Endpoints
802.3ah (link OAM) not interoperable with 802.1ag / Y.1731 (Connectivity OAM) -
some vendor-specific methods & emerging MEF 17 standard
802.3ah lacks: performance monitoring, fault propagation beyond 1st mile (link
faults not sent end-to-end), link trace & loopback response for fault verification &
isolation, L2/3 & per-flow traffic loopback.
NIDs enable 802.1ag / Y.1731 OAM functionality end-to-end
Demarcation
Point
CPE CPE
802.3ah
or no OAM
802.3ah
or no OAM
Demarcation
Point
CPE CPE
802.1ag / Y.1731 OAM
802.1ag / Y.1731 OAM
ProvidersNetwork
ProvidersNetwork
SukhoiHighlightNetwork Interface Device
-
Ethernet OAM is a good start but not sufficient
ProvidersNetwork
Over 100 remote base
stations homing into the
MSC
MSC / BSC
Challenging OAM PERFORMANCE of
High speed/high capacity pipes with 100s of
service flows handed-off at MSCs.
Ethernet OAM/PMs is often only supported
on a per-port or low-count VLAN basis and
only in a round-trip fashion.
Aggregation Network Elements having a
hard time computing high-accuracy/high
granularity one-way OAM/PMs for several
100s of flows on a single high speed port.
NE-based Ethernet OAM/PM currently
unusable for throughput verification, a key
SLA component
Forklift upgrades often required
Service Assurance vendors supporting
advanced, standards-based Ethernet
OAM/PM often brought-in to the rescue
Single 1G or 10G pipe
with hundreds of service
flows.Aggregator
-
OAM Function
ImplementationSoftware based implementation
(network processor)Dedicated silicon packet processing, hardware-based, real-time
Delay / Delay Variance
Measurement
~1 ms resolution, variable accuracy
not sufficient to monitor real-time
services and SLAs
1 s delay / jitter measurement resolution with < 20 s accuracy
One-Way Delay
Measurements
Typically only provides round-trip
measurements. SLAs commonly
specify one-way delay requirements.
Provides both one-way and round-trip measurements in multi-flow,
multi-site, multi-service and multicast configurations.
Multi-Flow MonitoringNEs can monitor A Few Flows -varies by network element & traffic load
Up to 100 Concurrent Flows / SLAs with no performance hit
Loopback Testing
Limited OAM loopback packet
processing capacity; delay added to
loopback traffic. No throughput testing.
Hardware-based architecture enables advanced, in-service throughput
testing of CIR, EIR up to full wire-speed
Frame Loss
Measurement
Standards provide synthetic frame loss based only on OAM frames
In-line, hardware-based packet processing provides Real Frame Loss
(RFL) - orders of magnitude more precise than Synthetic
measurements. RFL is required to validate high-performance SLAs.
OAM Uniformity over
Multi-Vendor / Carrier /
Technology Networks
Interoperability, OAM version and
feature support uneven.
Enables an overlay of the latest , full OAM functionality and advanced
complementary testing end-to-end without network element upgrades
Service creation,
traffic conditioning &
OAM alignment
Many access platforms do not support
advanced rate limiting, filtering and
shaping to optimize QoS.
OAM should be established at the service endpoints to provide valid
results. NIDs provide service mapping, OAM and conditioning at the
service demarc for complete end-to-end coverage.
802.1ag / Y.1731
Reach
OAM in access platforms limits visibility
of the problematic last mile, leaving this segment unmanaged.
OAM enabled in NIDs at the demarc point provide connectivity and
service OAM visibility directly to the customer site
Deploying 802.1ag/Y.1731 using NIDs vs. NEs
-
Ethernet OAM, Conclusions
Establishing end-to-end OAM is a key part of delivering
high-performance, carrier-grade Ethernet services.
OAM CFM provides operational efficiency, rapid per-
service fault identification, verification and isolation for
high availability services over multi-operator networks.
OAM Performance Monitoring provides means to
monitor and report key SLA and service usage metrics.
Standards are evolving: multi-vendor interoperability
issues and varying levels of feature support is common.
Establishing OAM using NIDs provides uniform, end-to-
end service management over any network topology.
Hardware-based NIDs also enable highly scalable
service creation and assurance functionality directly at
the service endpoints.