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