(version for book website) e e 681 - lecture 1 kick-off lecture: introduction to survivable...
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(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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 3
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/
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 4
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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 5
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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 6
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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 7
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 8
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 9
Concept of a “transport network”
End-users
Service layer
Logical layer
Physical layersystem
geographical
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 10
“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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 11
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)
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 12
“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 ?)
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 13
Concept of logical capacity management
A
BC
D
K
ZA
BC
D
K
ZA
BC
D
K
Z
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 14
Access Metro and Longhaul transport
Partitioned view of a transport network.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 15
“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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 16
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 17
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 18
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)
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 19
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”
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 20
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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 21
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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 22
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
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 23
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%
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 24
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 25
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 26
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.
E E 681 Lecture #1 © Wayne D. Grover 2002, 2003 27
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