It’s All About “Services”

“A business absolutely devoted to service will have only oneworry about profits. They will be embarrassingly large”.

– Henry Ford (1863-1947)“The best way to find yourself is to lose yourself in theservice of others”.

– Mahatma Gandhi (1869-1948)

“Only a life lived in the service to others is worth living.”

– Albert Einstein (1879-1955)“Well, it may be the devil or it may be the Lord / Butyou’re gonna have to serve somebody.”

– Bob Dylan (1941–)

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TELE302 Lecture 2

Network Services

Jeremiah Deng

University of Otago

10 July 2012

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Lecture Outline

1 Review

2 Systems View of Networks

3 Defining “Services”

4 Service Characteristics

5 Service-based Design

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Last Lecture

Systems ApproachNetwork design is art + science.It is about optimization, but also trade-offs.A few things to look at (actually later) -

PerformanceRedundancyHierarchy...

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What is a Network?

A network is a system – the set of components that support orprovide connectivity, communications and network services to users.In network design, we

Identify components of a systemUnderstand how they interface with each other

Network design can then become system planning.

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Generic System Components

UsersNetwork support personnelDeveloperProduct end users

ApplicationsMaybe specific designed for particular users

HostsOSsDevice driversAPI

Networks

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System Components and Interfaces

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Network Services

Sets of network capabilities that can be configured and managedwithin the network.Descriptions given by IETF, ATM Forum“What the network can provide to users”.

Not to be confused with application servicesDefined as levels of -

Performance: capacity, delay, reliabilityFunctions: security, accounting, billing, scheduling, management etc.

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Service-based Networking

Networking used to be about providing connectivity andinteroperability.Services are now very important to the success of networkapplications, and network users.Service-based networking is the concept of developing network designsthat take into account of network services and service support.

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Reliability, Maintainability & Availability (RMA)

Cause of network failures: carrier outages, faulty software,denial-of-service, power failures, human errorsReliability: statistical indicator of the frequency of network failure orservice outage.Maintainability: Statistical measure of the time to restore the systemto fully operational status once failure experienced.Availability: the relationship between the frequency of mission-criticalfailures and the time to restore service:

A =MTBF

MTBF + MTTRMTBF: Mean time between failuresMTTR: Mean time to repair

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Typical Reliabilities

MTBF goal: 5000 hours or 208.33 daysMTTR goal: 1 hourAvailability = MTBF/(MTBF + MTTR) = 5000/5001=99.98%How about 99.999%?

A one hour MTTR covering 11.4 yearsOr 10-min MTTR for a 1.9-year MTBFRealizable on device-levelHard to maintain on systems level

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Network Supportability

80% of life cycle costs of a system are operations and support costs.Three elements of network supportability: operations, maintenance,and human knowledge.Supportability issues should be considered seriously:

Degree of redundancy of critical-path componentsQuality of network components selectedLocation and accessibility of component requiring frequent maintenanceUse of built-in test equipment and monitoring techniques

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Service Characteristics

Useful in network analysis and design:Configuring services in network elements (routers, switches, OSs etc.)Providing input into network design – developing service requirements

Described and provisioned end-to-endConfigurable, measurable and verifiableHierarchical, enabling different services in backbone and accessnetworks

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End-to-end Requirements

Services requirements are end-to-end but also multiple-layered.

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Characterizing Services

Service requests: from users, applicationsService offerings: from the networkService performance requirements: describe specified servicesService metrics: performance requirements coupled to valuesReservations and scheduling: handle future QoS requirements anddeadline applications

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Service Requests

Distinguished by degree of predictability needed in service.Best-effort requests: no control over the network in satisfying theservice

No guarantee, unpredictable;Variable across range of performance values.

Specified requests: based on knowledge or control over the state ofthe system for the operation of the service

Service predictable, or bounded, even guaranteedService metrics applied

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Service Offerings

Service offerings are network counterparts to the service requests fromusers, applications and hosts.Also separated into two groups

Best-effort: non-predictable, e.g. Internet.Specified: predictable, bounded, or guaranteed.

Typical specified service offeringsFrame Relay CIR, SMDS CoS, ATM CoS, etc.

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Service Metrics

Performance requirements and characteristics must be configurable,measurable and verifiable.Service metrics are meant to be measurable quantities.Thresholds: performance characteristics value as the boundarybetween two regions of conformance.Limits: a boundary between conforming and nonconforming regions.Crossing a limit is more serious than crossing a threshold.

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Threshold & Limit

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Mapping service levels to standard service offerings

Service metrics provide the basis for matching service request toservice offering.

E.g., in WAN design, enabling technology choice and specifications

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Service Performance Requirements

Reliability: deterministic & accurate deliveryDelay boundariesAccuracy

Capacity: measurement on transfer ability“Bandwidth”: theoretical capacityThroughput: realizable capacity

Delay measures time differences in information transmission acrossthe system

Latency: on application/task level, macroscopic.Can use ping, tcpdump for measurement.

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Performance Envelopes

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Service Design Integrity

Services that focus on particular function of one component shall beconsidered as an integral part of network design.E.g., security and management can not be dealt as “after thoughts”.

Later add-ons may compromise the performance or security of existingsolutions.

To maintain integrity it requires us to have holistic assessment ofservice requirements (even foresight).An example: Supercomputing on Internet2 backbone network(10Gbps) brought down to 200Mbps by stateful firewalls.

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Recap

What are best effort services, specified services, and guaranteedservices?What are performance characteristics?How can service requirement be mapped to service offering?Why is network supportability important?Reading – McCabe Chapter 1Next Lecture: Quality of Service

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