(version for book website) E E 681 - Lecture 1 Kick-off Lecture: Introduction to Survivable Transport Networks Wayne D. Grover TRLabs & University of Alberta.

(version for book website)

E E 681 - Lecture 1E E 681 - Lecture 1

Kick-off Lecture: Introduction Kick-off Lecture: Introduction to Survivable Transport to Survivable Transport

NetworksNetworksWayne D. Grover

TRLabs & University of Alberta

© Wayne D. Grover 2002, 2003

E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 2

Outline

• Intro to author: Dr. Wayne Grover

• Educational Objective of course

• Walk-through of course outline and logistics

• Importance and impact of outages - reading assignment

• Concept of a “transport network”

• Restorability, redundancy,

• Reliability and availability

• Relationship of restorability to availability

• First look at all architectures for restoration

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The author: Dr. Wayne Grover

• B.Sc. - Carleton U, Ottawa

• M.Sc. - U. Essex, U.K.

• 10 years BNR (Nortel Networks) Research & Development

• In start-up of TRLabs consortium, 1986 (Founding VP - Research)

• Ph.D. - U. Alberta (‘89) - “Self-healing Networks”

• Research and management roles at TRLabs, 1986- present

• 1992 on Faculty U of Alberta (ECE)

• 2001-2002 NSERC E.W.R Steacie Fellow

• 2002 IEEE Fellow

• web site: http://www.ee.ualberta.ca/~grover/

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E E 681: Educational Objective

• Graduates of E E 681 will have a basic preparation and awareness of current and emerging transport networking alternatives, mechanisms, issues, and design theory, enabling them to continue in:

– research: will be equipped to pursue a thesis project and participate in ongoing graduate research in these areas

– R&D: will be able to contribute to transport networking equipment design and product strategies

– operations: will be able to contribute to network planning and network evolution strategy

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E E 681 : Some specific key objectives

• Graduates of EE 681 will understand the following system-level technology, networking concepts, design and operational issues :

– APS systems, ring-based networking, mesh-restorable networks, ATM backup-VP networks, design theory for ring, mesh and ATM networks,

– rudimentary availability analysis of survivable networks, – distributed mesh restoration and self-organizational principles in

mesh networking– appreciation of recent research topics such as p-cycles, hybrid

networks, ring-to-mesh evolution, others

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Concept of a “transport network”

End-users

Service layer

Logical layer

Physical layersystem

geographical

di,j = 76

M U L T I P L E X

Telephony: 500 DS1s

ATM: 5 STS3c

Video: 8 DS3s

Private networks: 100 DS1

Frame-relay services: 36 DS1

SITE i traffic sources to: SITE j

SERVICES

TRANSPORT

Bulk equivalent= 76 STS-1s

(18)

(30)

(15)

(8)

(5)

Internet: 5 STS3c

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Concept of a “transport network”

• Voice-band switching, Internet, private lines, corporate networks, ATM networks, etc. are all ‘virtual’, logical abstractions implemented within the transport network.

• The transport network sits “just above” the physical transmission systems in a layering sense.

• Individual switched connections, leased lines, pipes between IP routers, etc. do not “make their own way directly” over the fiber systems..

• Rather, traffic of all sorts is “groomed” to fill standard rate “containers” created in the transport network.

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Concept of a “transport network” (2)

• “grooming” at or near clusters of sources (the edge or access network) tries to efficiently fill these containers so they won’t need to be opened again (i.e., processed at a call, cell or packet level), until at or near their destinations.

• Transport network thus sees a composite “demand pattern” (in STS-n units typically) that is the resultant totals of point-to-point container requirements arising from all client network / service layer requirements, e.g., trunk groups, IP pipes, leased lines, private networks, etc.

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Concept of a “transport network”

End-users

Service layer

Logical layer

Physical layersystem

geographical

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“Geographical” or facility routes level

• “node”: – buildings, equipment huts, man-holes, (co-location space)

• generic “link” resource: – conduits, rights-of-way, leased lambda(s)

• main survivability principles: – spatial / physical diversity and high connectivity

• “performance” measure:– network average nodal degree, miles of duct, buried, aerial

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Transmission “System” level

• “node”: – transmission termination and multiplex equipment

• generic “link” resource: – fibers, wavelengths, radio, copper, coax, satellite

• main survivability principles: – 1+1 or 1:N protection-switching for high system availability

• “performance” measure:– system availability (e,g. 99.99.. per regen. section),– protection switching time (e.g., ~ 50 ms)

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“Logical” (capacity management) level

• “node”: – digital (Sonet) and / or optical (wavelength) cross-connects

• generic “link” resource: – standardized logical bandwidth units such as DS1, DS3, STS-n,

ATM VP, wavelengths, wavebands

• main survivability principles: – ring, mesh, backup-VP or p-cycle based real-time restoration re-

routing.

• “performance” measures:– restorability (of spans, nodes)– restoration time (e.g., 150 ms - 2 sec)– end-to-end path availability (e.g., 99.996 on 4,000 km HRDP)– best efforts and / or assured restoration classes – path provisioning time (seconds or days ?)

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Concept of logical capacity management

A

BC

D

K

ZA

BC

D

K

ZA

BC

D

K

Z

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Access Metro and Longhaul transport

Partitioned view of a transport network.

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“Service” level

• “node”: – routers / packet switches, circuit-switches, ATM switches, DS1/0

private networking devices

• generic “link” resource: – IP “pipes”, ATM VCs, trunk groups, private line circuits

• main survivability principles: – routing table updates, dynamic routing, dual homing, limits to switch

size, “they’ll dial again”.

• “performance” measure(s):– cell or packet loss probabilities / denial of service – call blocking, voice echo-delay– call set-up / dial-tone delays - packet jitter, delay time variance

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Concept of a “transport network” (3)

• Airline inter-hub analogy:– a business person from Billings, Montana needs to fly to Kyoto,

Japan.– A regional “commuter” jet brings him/her to Denver.– at Denver, people from all over the region, board a well-filled 747

non-stop to Tokyo– from Tokyo, a regional jet takes him/her to Kyoto

• The pattern is: access - transport - access

• An STS-n, or soon, a DWDM wavelength, is the “747”

• multiplexing and grooming in the access (switches, routers, ATM service nodes) are the regional airlines.

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Concept of a “transport network” (4)

• This is why fully router-based “IP over light” (just as prior “ATM on glass”) is improbable when the short-term hype is replaced by longer term performance, complexity, cost, maintenance and operational assessments.

• The single biggest factor in IP QoS in particular is the average number of router hops in a ‘connection’...

• All other transport industries find an optimum combination of access grooming/muxing and backbone transport; pure “IP over light” implies unpacking and reloading the moving van in every city en-route.

• Or, “would you move a house brick by brick?”

• More likely structure is to stat mux and groom in one or two access stages, then launch into near mesh of non-stochastic high OCn or ?-based transport paths.

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Concept of a “transport network” (5)

• Another layering view:

• For various applications, DWDM, SONET, ATM, even IP (with extensions), can all act as a transport network to higher layers.

fiber

DWDM

SONET

ATM (VP)

IPATM (VC)

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Each layer has a native form of “demand units” that are aggregated into capacity units of the next lower layer

End-users

Service layer

Logical layer

Physical layersystem

geographical

Erlangs, packets, private lines, VCs

#s of: DS-0, DS-1, VPs, STS-n(PL), STSn(IP)

#s of: OC-48, OC-192, wavelengths

#s of fibers, wavelength regens, add-drop

#s of cables, ducts, transponders, spectral allocations

“the transportnetwork”

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Example of how various services map into transport “demands”

Type Bandwidth Type Bandwidth

PL-DS1 0.036 IP-OC12 1.528

PL-DS3 1.0 IP-OC48 6.112

PL-OC3 3.0 IP-100T0.283

PL-OC12 12.0 IP-GIGE 2.830

PL-OC48 48.0 WL-2.5MUX 96.000

IP-DS1 0.005 WL_10 192.000

IP-DS3 0.127 SS 1.000

IP-OC3 0.382Typical service types and corresponding STS1 bandwidth requirements for the transport network

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some terminology (1)

• DCS: digital cross-connect system

• ADM: add/drop multiplexer

• Link (or “channel”): single unit of bandwidth at the respective level of transport management, e.g., STS1, STS3, DS3, etc.

• Path: a concatenation of cross-connected links forming a unit-capacity digital connection between its end points

• Span: set of all (working and spare) links between nodes that are adjacent in the physical graph

• Route: set of span designations that are contiguous on the physical graph

• Pathset: set of link-disjoint paths sharing the same end-nodes

• Working link (or “worker”): link that is in-service, as part of a traffic-bearing ‘working path’.

• spare link (or “spare”): equipped but idle link available for restoration

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some terminology (2)

• Reserve network: the capacitated graph formed from the set of all spare links

• Adjacent: nodes directly connected by a 1-hop route in the physical graph.

• Logically adjacent: nodes directly connected by an edge in the transport graph.

• simple graph: a network graph where there is at most one edge between adjacent nodes

• Multi-graph: a network graph where there can be many links in parallel between adjacent nodes

• Capacitated graph: a graph where all edges have a finite capacity

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Example: use of terms route, span, path, link...

• Span AZ has lost 35 working links

• The restoration pathset is comprised of routes ABCZ, ABDEZ, ABDECZ, AFZ,AFGZ,AFGHZ

• The route ABDEZ supports 5 restoration paths

• 20 spare links on span AB are used in the restoration pathset

• The restorability of span AZ is (20+15)/35 = 100%

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Additional initial concepts / terms *

• Restorability: the fraction of working demand flows affected by a failure that are restored or for which a restoration path set solution is feasible.

• Redundancy: the ratio of spare capacity required in a network to meet restorability goals to working capacity required only to route demands without survivability concerns.

* we will return to all these concepts in greater depth. The aim today is just to create an

initial orientation.

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Additional initial concepts / terms

• Reliability: the probability that a system operates without a service-affecting failure for a given amount of time. R(t) can be thought of as the probability distribution function of time-to-first-failure from a known-good starting state.

• Availability: the probability that a continuously operating system undergoing repair after each failure is found in the “up” state at any random time in the future.

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Relationship of restorability to availability

• Does a “fully restorable” network have 100% availability ?

– No. If the network restorability design is for 100% restorability to all n-failure scenarios, “(n+1) failure” scenarios may be outage-causing.

– In practice commercial / public networks used to have n = 0 (in the sense that no cable cuts would be 100% restorable). In which case addition of redundancy to get to n=1 (full restorability against any single cable cut) gives a massive boost in availability.

– But availability does not reach unity because then dual failure scenarios can then cause outage.

– --> leads to usual economic practice of : design for 100% single-failure restorability, and analyze for the dual failure (un)availability.

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Basic approaches to restoration or… “the whole course in 2 slides”

• APS systems– 1+1– 1:1– 1:N

• rings – UPSR: unidirectional path

switched rings– BLSR: bi-directional line-

switched rings

• mesh– span - restorable– path - restorable

• shared 1:1 backup path protection

• p-cycles

• ring-mesh hybrids– based on access / core

principles– based on forcer clipping

principle