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operation & maintenance Guide
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Unique Access Solutions
OAM: Application-driven Evolution
Presented by:
Yaakov (J) Stein
Chief Scientist
OAM-YJS Slide 2
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 ?
Why do we pay for services ?
OAM-YJS Slide 3
The simple answer is that one doesn’t pay for the serviceone pays for Quality of Service guarantees
In our voice model
But what does QoS meanand why are we willing to pay for it ?
To explain, we need to review some history
Paying for QoS
QoS
price
BE
toll qualitywith mobility
OAM-YJS Slide 4
Everyone knows that the father of the telephone wasAlexander 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 wasTheodore Vail
Father of the telephone
OAM-YJS Slide 5
Theodore Vail -
Theodore Who?Son of Alfred Vail (Morse’s coworker)Ex-General Superintendent of US Railway Mail Service First general manager of Bell TelephoneFather of the PSTN
Why is he so important?Organized PSTNEstablished principle of reinvestment in R&DEstablished Bell Telephones IPR divisionExecuted merger with Western Union to form AT&TSolved 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 6
What’s the difference ?
In the Bell-Watson modelthe customer pays once, but is responsible for
• installation• wires• wiring
• operations• power• fault repair• performance (distortion and noise)
• infrastructure maintenancewhile the Bell company is responsible only for
providing functioning telephones
In the Vail model the customer pays a monthly feebut the provider assumes responsibility for everythingincluding fault repair and performance maintenance
the telephone company owns the telephone sets and even the wires in the walls !
+
OAM-YJS Slide 7
In order to justify recurring paymentsthe 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
Service Level Agreements
OAM-YJS Slide 8
System trafficrouting protocols, DNS, DHCP, time delivery, system update, OAM, tunneling and VPN setup
Business processes database access, backup and data-center, B2B, ERP
Communications - interactivevoice, video conferencing, telepresence, instant messaging,remote desktop, application sharing
Communications – non-interactiveemail, broadcast programming, music
video : progressive download, live streaming, interactive
Information gatheringhttp(s), Web 2.0, file transfer
Recreationalgaming, p2p file transfer
Malicious DoS, malware injection, illicit information retrieval
Some Applications
OAM-YJS Slide 9
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 percentageand these parameters are not necessarily independent
For example,
TCP throughput drops with PLR
What do applications need ?
1000 B packets50 ms RTT
OAM-YJS Slide 10
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 throughputbut 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 throughputbut not necessarily low PLR (audio and video codecs have PLC)
Interactive applications require • low RT delayIt may be more scalable for a SP to measure 1-way delays
Some rules of thumb
OAM-YJS Slide 11
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 usingOperations, 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 operationsfor example• OAM may trigger protection switching, but doesn’t switch• OAM may detect provisioned links, but doesn’t provision them
Monitoring an SLA
OAM-YJS Slide 12
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 13
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/inhibitionThe OAM overhead started to explode in size !
When SONET/SDH was designed bounded overhead was reserved for OAM functions
Early OAM
OAM-YJS Slide 14
OAM is more complex for Packet Switched Networks
in addition to the previous defects : • loss of signal• bit errorswe 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 for Packet Switched Networks
OAM-YJS Slide 15
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, …)
What about Ethernet ?
OAM-YJS Slide 16
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 FMwhat does continuity mean if when a link goes downthe network automatically reroutes around the failure ?
The Ethernet CL problem is solved by overlaying CO functionality :• flows or• EVCs
What’s the problem with CL ?
OAM-YJS Slide 17
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 onlyslow protocol, limited functionalitysome management functions
• Service OAM – Y.1731, 802.1ag (CFM)any network configurationmultilevel OAM functionality
In some cases one may need to run bothwhile in others only service OAM makes sense
Link layer OAM is only for a single link, which is necessarily COService OAM is most frequently used for infrastructure networks,
which are also CO
Ethernet OAM
OAM-YJS Slide 18
MEPs and MIPs
OAM-YJS Slide 19
The other L2 used today is MPLS
OAM mechanisms that work well for Ethernetcan not be used as-is for MPLS
This is because :• 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-TPwhich is basically MPLS + strong OAM (FM + PM)and functionalities dependent on OAM, such as protection switching
What about MPLS ?
OAM-YJS Slide 20
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
What about IP ?
OAM-YJS Slide 21
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 Protocola protocol for FM :• BFD Bidirectional Forwarding Detectionand two sophisticated protocols for PM : • OWAMP One Way Active Measurement Protocol• TWAMP Two Way Active Measurement Protocol
OWAMP and TWAMP are the only OAM protocolswith full security features !
OAM-YJS Slide 22
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/MPLSbut already has more sophisticated PM ones
Summary