OAM:
Application-driven Evolution
Presented by:
Yaakov (J) Stein
Chief Scientist
Unique Access Solutions
Why do we pay for services ?
Generally good (and frequently much better than toll quality)
voice service is available free of charge (Skype, Fring, Nimbuzz,
…)
So why does anyone pay for voice services ?
Similarly, one can get free
• (WiFi) Internet access
• email boxes
• file storage and sharing
• web hosting
• software services
So why pay ?
OAM-YJS Slide 2
Paying for QoS
The simple answer is that one doesn’t pay for the service
one pays for Quality of Service guarantees
In our voice model
price
toll quality
with mobility
BE
QoS
But what does QoS mean
and why are we willing to pay for it ?
To explain, we need to review some history
OAM-YJS Slide 3
Father of the telephone
Everyone knows that the father of the telephone was
Alexander Graham Bell
(along with his assistant Mr. Watson)
But Bell did not invent the telephone network
Bell and Watson sold pairs of phones to customers
The father of the telephone network was
Theodore Vail
OAM-YJS Slide 4
Theodore Vail Theodore Who?
Son of Alfred Vail (Morse’s coworker)
Ex-General Superintendent of US Railway Mail Service
First general manager of Bell Telephone
Father of the PSTN
Why is he so important?
Organized PSTN
Established principle of reinvestment in R&D
Established Bell Telephones IPR division
Executed merger with Western Union to form AT&T
Solved the main technological problems
• use of copper wire
• use of twisted pairs
Organized telephony as a service (like the postal service!)
Vailism is the philosophy that public services should be run as closed
centralized monopolies for the public good
OAM-YJS Slide 5
What’s the difference ?
In the Bell-Watson model
the customer pays once, but is responsible for
• installation
• wires
• wiring
• operations
+
• power
• fault repair
• performance (distortion and noise)
• infrastructure maintenance
while the Bell company is responsible only for
providing functioning telephones
In the Vail model the customer pays a monthly fee
but the provider assumes responsibility for everything
including fault repair and performance maintenance
the telephone company owns the telephone sets and even the wires in the walls !
OAM-YJS Slide 6
Service Level Agreements
In order to justify recurring payments
the provider agrees to a minimum level of service in an SLA
SLAs should capture Quality of user Experience (QoE)
but this is often hard to quantify
So SLAs usually actually detail measurable network parameters
that influence QoE, such as :
•
•
•
•
•
availability (e.g., the famous five nines)
time to repair (e.g., the famous 50 ms)
information rate (throughput)
information latency (delay)
allowable defect densities (noise/distortion)
Availability (basic connectivity) always influences QoE
It is hard to predict the effect of the other parameters on QoE
even when there is only one application (e.g., voice)
When multiple applications are in use - it may be impossible
OAM-YJS Slide 7
Some Applications
System traffic
routing protocols, DNS, DHCP, time delivery, system update, OAM,
tunneling and VPN setup
Business processes
database access, backup and data-center, B2B, ERP
Communications - interactive
voice, video conferencing, telepresence, instant messaging,
remote desktop, application sharing
Communications – non-interactive
email, broadcast programming, music
video : progressive download, live streaming, interactive
Information gathering
http(s), Web 2.0, file transfer
Recreational
gaming, p2p file transfer
Malicious
DoS, malware injection, illicit information retrieval
OAM-YJS Slide 8
What do applications need ?
Some applications only require availability
Some also require minimum available throughput
Some require delay less then some end-end (or RT) delay
Some require packet loss ratio (PLR) less than some percentage
and these parameters are not necessarily independent
For example,
TCP throughput drops with PLR
1000 B packets
50 ms RTT
OAM-YJS Slide 9
Some rules of thumb
Mission Critical (and life critical) applications require
• high availability
If there are any MC applications
then system traffic requires high availability too
MC applications do not necessarily require strict throughput
but always indirectly require
• a certain minimal average throughput
• bounded delay
If the MC application uses TCP then it requires
• low PLR
Real-time applications require
• sufficient throughput
but not necessarily low PLR (audio and video codecs have PLC)
Interactive applications require
• low RT delay
It may be more scalable for a SP to measure 1-way delays
OAM-YJS Slide 10
Monitoring an SLA
The Service Provider’s justification for payment
is the maintenance of an SLA
To ensure SLA compliance, the SP must :
• monitor the SLA parameters
• take action if parameter is dropping below compliance levels
But how does the SP verify/ensure that the SLA is being met ?
Monitoring is carried out using
Operations, Administration, Maintenance (OAM)
The customer too may use OAM to see that the SP is compliant !
Technical note:
OAM is a user-plane function
but may influence control and management plane operations
for example
• OAM may trigger protection switching, but doesn’t switch
• OAM may detect provisioned links, but doesn’t provision them
OAM-YJS Slide 11
Operations, Administration, Maintenance
Traditionally, one distinguishes between 2 OAM functionalities :
1. Fault Monitoring
• OAM runs continuously/periodically at required rate
• detection and reporting of anomalies, defects, and failures
• used to trigger mechanisms in the
• control plane (e.g. protection switching) and
• management plane (alarms)
• required for maintenance of basic connectivity (availability)
2. Performance Monitoring
• OAM run :
• before enabling a service
• on-demand or
• per schedule
• measurement of performance criteria (delay, PDV, etc.)
• required for maintenance of all other QoE attributes
OAM-YJS Slide 12
Early OAM
Analog channels and 64 kbps digital channels
did not have mechanisms to check signal validity and quality
Thus
• major faults could go undetected for long periods of time
• hard to characterize and localize faults when reported
• minor defects might be unnoticed indefinitely
As PDH networks evolved, more and more OAM was added on :
• monitoring for valid signal
• loopbacks
• defect reporting
• alarm indication/inhibition
The OAM overhead started to explode in size !
When SONET/SDH was designed
bounded overhead was reserved for OAM functions
OAM-YJS Slide 13
OAM for Packet Switched Networks
OAM is more complex for Packet Switched Networks
in addition to the previous defects :
• loss of signal
• bit errors
we have new defect types
• packets may be lost
• packets may be delayed
• packets may delivered to the wrong destination
The first PSN-like network to acquire OAM was ATM (I.610)
Although technically ATM is cell-based, not packet-based
OAM-YJS Slide 14
What about Ethernet ?
Carrier Ethernet has replaced ATM as the default layer-2
Ethernet is by far the most widespread network interface
Ethernet has some advantages as compared to ATM
• it has network-wide unique addresses
• it has a source address in every packet
but some aspects make Ethernet OAM more difficult
• ConnectionLess (CL)
• multipoint to multipoint
• overlapping layering – need OAM for operator, SPs, customer
• some specific problematic ETH behaviors (flooding, multicast, …)
OAM-YJS Slide 15
What’s the problem with CL ?
OAM makes a lot of sense in Connection Oriented environments
• connections last a relatively long amount of time
• there is some SLA at the connection level
For CL networks, the network path is neither known nor pinned
So it doesn’t really make sense to talk about FM
what does continuity mean if when a link goes down
the network automatically reroutes around the failure ?
The Ethernet CL problem is solved by overlaying CO functionality :
• flows or
• EVCs
OAM-YJS Slide 16
Ethernet OAM
For many years there was no OAM for Ethernet
(LANs don’t need OAM)
now there are two incompatible ones!
• Link layer OAM – 802.3 clause 57 (EFM OAM, 802.3ah)
single link only
slow protocol, limited functionality
some management functions
• Service OAM – Y.1731, 802.1ag (CFM)
any network configuration
multilevel OAM functionality
In some cases one may need to run both
while in others only service OAM makes sense
Link layer OAM is only for a single link, which is necessarily CO
Service OAM is most frequently used for infrastructure networks,
which are also CO
OAM-YJS Slide 17
MEPs and MIPs
OAM-YJS Slide 18
What about MPLS ?
The other L2 used today is MPLS
OAM mechanisms that work well for Ethernet
can not be used as-is for MPLS
This is because :
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MPLS does not use absolute addresses
MPLS packets do not carry source addresses
when using LDP MPLS is not pure CO
LSPs are unidirectional entities
The IETF has defined LSP ping that provides basic OAM
• continuity
• trace route
The ITU defined Y.1711, but it has not seen widespread use
The MPLS community is now working on MPLS-TP
which is basically MPLS + strong OAM (FM + PM)
and functionalities dependent on OAM, such as protection switching
OAM-YJS Slide 19
What about IP ?
It makes sense to monitor IP (IPv4/IPv6) performance as well
• IP is the most popular end-to-end protocol
• IP connectivity can be purchased
(although perhaps not widely with SLAs)
But from the OAM point of view, IP is the hardest of all
• the IP protocol suite does not define anything beneath L3
• IP is always pure ConnectionLess
In certain cases it may make more sense
to jump directly to application flows
OAM-YJS Slide 20
IP OAM
For IP, one usually talks about OAM between end-points
The IETF defines an all-purpose OAM+control protocol :
• ICMP
Internet Control Message Protocol
a protocol for FM :
• BFD
Bidirectional Forwarding Detection
and two sophisticated protocols for PM :
• OWAMP
One Way Active Measurement Protocol
• TWAMP
Two Way Active Measurement Protocol
OWAMP and TWAMP are the only OAM protocols
with full security features !
OAM-YJS Slide 21
Summary
It is advantageous to run networks as provided services
Service Provider income depends on SLA compliance
SLA compliance requires OAM – FM and PM
OAM protocols now exist for all relevant technologies :
• TDM – SDH
• Ethernet
• MPLS
• IP
Ethernet is leading in OAM functionality,
but MPLS-TP is rapidly catching up
IP can not have FM tools as robust as Ethernet/MPLS
but already has more sophisticated PM ones
OAM-YJS Slide 22