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Raj JainThe Ohio State University
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PNNI:PNNI:Routing in ATM NetworksRouting in ATM Networks
Raj Jain
Professor of CISThe Ohio State University
Columbus, OH [email protected]
http://www.cis.ohio-state.edu/~jain/
Raj JainThe Ohio State University
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❑ Distribution of topology information
❑ Hierarchical groups
❑ Source routing ⇒ Designated Transit Lists
❑ Crankback and Alternate routing
❑ Addressing
Ref: ATM Forum 94-0471R9, "PNNI Draft Specification(Phase 1)"
Overview
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PNNIPNNI
❑ Private Network-to-network Interface
❑ Private Network Node Interface
SwitchSwitch SwitchSwitchEndSystem
EndSystem
EndSystem
EndSystem
PNNI
ATMNetwork
ATMNetwork
EndSystem
EndSystem
EndSystem
EndSystem
PNNI
ATMNetwork
ATMNetwork
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Features of PNNIFeatures of PNNI❑ Point-to-point and point-to-multipoint connections❑ Can treat a cloud as a single logical link❑ Multiple levels of hierarchy ⇒ Scalable for global networking.❑ Reroutes around failed components at connection setup❑ Automatic topological discovery ⇒ No manual input required.❑ Connection follows the same route as the setup message
(associated signaling)❑ Uses: Cost, capacity, link constraints, propagation delay❑ Also uses: Cell delay, Cell delay variation, Current average
load, Current peak load❑ Uses both link and node parameters❑ Supports transit carrier selection❑ Supports anycast
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Level 1
AddressingAddressing❑ Multiple formats.
❑ All 20 Bytes long addresses.
❑ Left-to-right hierarchical
❑ Level boundaries can be put in any bit position
❑ 13-byte prefix ⇒ 104 levels of hierarchy possible
Level 2 Level 3 Level 4
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Link State RoutingLink State Routing❑ Each node sends “Hello” packets periodically
and on state changes.
❑ The packet contains state of all its links
❑ The packet is flooded to all nodes in the network
A.1.3
A.1.1 A.1.2
A.2.1
A.2.2
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Very Large NetworksVery Large Networks
A.1.3
A.1.1 A.1.2
A.2.1
A.2.2
B.1.1 B.1.2
B.1.3
zC.1.1
C.1.2
B.2.1B.2.3
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Hierarchical LayersHierarchical Layers
A.1.3
A.1.1 A.1.2
A.2.1
A.2.2
B.1.1 B.1.2
B.1.3
zC.1.1
C.1.2
B.2.1B.2.3
A.1A.2
B.1
B.2
C
A
B
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Hierarchical ViewHierarchical View
A.2 B.1 B.1 C
A B C
A.1
A.2
A.1.3
A.1.2B CA.1.1’s View:
A.1.1
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TerminologyTerminology❑ Peer group: A group of nodes at the same hierarchy
❑ Border node: one link crosses the boundary
❑ Logical group node: Representation of a group as a singlepoint
❑ Logical node or Node: A physical node or a logical groupnode
❑ Child node: Any node at the next lower hierarchy level
❑ Parent node: Logical group node at the next higherhierarchy level
❑ Logical links: links between logical nodes
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❑ Peer group leader (PGL):Represents a group at the next higher level.Node with the highest "leadership priority" andhighest ATM address is elected as a leader.Continuous process ⇒ Leader may change any time.
❑ PGL acts as a logical group node.Uses same ATM address with a different selector value.
❑ Peer group ID: Address prefixes up to 13 bytes
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Topology State InformationTopology State Information❑ Metric: Added along the path, e.g., delay
❑ Attribute: Considered individually on each element.
❑ Performance, e.g., capacity or
❑ Policy related, e.g., security
❑ State parameter: Either metric or attribute
❑ Link state parameter. Node state parameter.
❑ Topology = Link + Nodes
❑ Topology state parameter: Link or node state parameter
❑ PNNI Topology state element (PTSE):Routing information that is flooded in a peer group
❑ PNNI Topology state packet (PTSP): Contains one PTSE
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Topology State ParametersTopology State Parameters❑ Metrics:
❑ Maximum Cell Transfer Delay (MCTD)❑ Maximum Cell Delay Variation (MCDV)❑ Maximum Cell Loss Ratio (MCLR)❑ Administrative weight
❑ Attributes:❑ Available cell rate (ACR)❑ Cell rate margin (CRM) = Allocated - Actual
First order uncertainty. Optional.❑ Variation factor (VF) = CRM/Stdv(Actual)
Second order uncertainty. Optional.❑ Branching Flag: Can handle point-to-multipoint traffic❑ Restricted Transit Flag: Supports transit traffic or not
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Database Synchronization and FloodingDatabase Synchronization and Flooding❑ Upon initialization, nodes exchange PTSE headers
(My topology database is dated 11-Sep-1995:11:59)
❑ Node with older database requests more recent info
❑ After synchronizing the routing database, they advertise thelink between them
❑ The ad (PTSP) is flooded throughout the peer group
❑ Nodes ack each PTSP to the sending neighbors, update theirdatabase (if new) and forward the PTSP to all otherneighbors
❑ All PTSEs have a life time and are aged out unless renewed.
❑ Only the node that originated a PTSE can reissue it.
❑ PTSEs are issued periodically and also event driven.
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Information Flow in the HierarchyInformation Flow in the Hierarchy
❑ Information = Reachability and topology aggregation
❑ Peer group leaders summarize and circulate info in theparent group
❑ A raw PTSE never flows upward.
❑ PTSEs flow horizontally through the peer group anddownward through children.
❑ Border nodes do not exchange databases (different peergroups)
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Topology AggregationTopology Aggregation❑ Get a simple representation of a group
❑ Alternatives: Symmetric star (n links) or mesh (n2/2 links)
❑ Compromise: Star with exceptions
AB
FE
H
D C
G
FE
HG
FE
HG
1.251.25
1.251.25
3
2
2
21.5
1.5
1.51.5
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Address SummarizationAddress Summarization
❑ Summary = All nodes with prefix xxx, yyy, ...+ foreign addresses
❑ Native addresses = All nodes with prefix xxx, yyy, ...
❑ Example:
❑ A.2.1 = XX1*, Y2*, W111 A.2.2 = Y1*, Z2*
❑ A.2.3 = XX2*
❑ A.2 = XX*, Y*, Z2*, W111. W111 is a foreign address
xx11xx12xx13y211w111
y111y112y113z211z222
xx21 xx22 xx23
A.2.1 A.2.2
A.2.3
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Address ScopeAddress Scope❑ Upward distribution of an address can be inhibited, if
desired.E.g., Don't tell the competition B that W111 is reachablevia A.
❑ Each group has a level (length of the shortest prefix).
❑ Each address has a scope (level up to which it is visible).
96 80 72 104 96
9672
56
64
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Call Admission ControlCall Admission Control❑ Generic Call Admission Control (GCAC)
❑ Run by a switch in choosing a source route
❑ Determines which path can probably support the call
❑ Actual Call Admission Control (ACAC)
❑ Run by each switch
❑ Determines if it can support the call
Runs ACACRuns GCACChooses Path
Runs ACAC
Runs ACAC
Runs ACAC
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Source RoutingSource Routing❑ Used in IEEE 802.5 token ring networks
❑ Source specifies all intermediate systems (bridges) for thepacket
11 22
44
33
SS 55 DD
1 2 4 5PointerDestination
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Designated Transit ListsDesignated Transit Lists❑ DTL: Source route across each level of hierarchy
❑ Entry switch of each peer group specifies complete routethrough that group
❑ Entry switch may or may not be the peer group leader
❑ Multiple levels ⇒ Multiple DTLsImplemented as a stack
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DTL: ExampleDTL: Example
A.1.1A.1.2
A.1A.2
AB
A.1.1A.1.2
A.1A.2
AB
A.2.1A.2.3
AB
A.2.1A.2.3
AB
B.1B.2B.3
B.1B.2B.3
A.1.1 A.1.2 A.2.1
A.2.2
A.2.3 B.1 B.2 B.3
A.1 A.2 B
A
A.1A.2
A.1A.2
AB
AB
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Crankback and Alternate Path RoutingCrankback and Alternate Path Routing
❑ If a call fails along a particular route:
❑ It is cranked back to the originator of the top DTL
❑ The originator finds another route or
❑ Cranks back to the generator of the higher level sourceroute
A.1.1 A.1.2 A.2.1
A.2.2
A.2.3 B.1 B.2 B.3
A.1 A.2 B
A
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SummarySummary
❑ Database synchronization and flooding
❑ Hierarchical grouping: Peer groups, group leaders
❑ Topology aggregation and address summarization
❑ Designated transit lists
❑ Crankback
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AbbreviationsAbbreviations❑ AFI Authority and format identifier
❑ BIS Border intermediate system
❑ BISPDU Border intermediate system protocol data unit
❑ CAC Connection admission control
❑ CNR Complex node representation
❑ CRM Cell rate margin
❑ DSP Domain specific part
❑ DTL Designated transit list
❑ ES End system
❑ ESI End system identifier
❑ GCAC Generic connection admission control
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❑ IDI Initial domain identifier
❑ IDP Initial domain part
❑ IS Intermediate system
❑ LGN Logical group node
❑ LSAP Link service access point
❑ MaxCR Maximum cell rate
❑ NPDU Network protocol data unit
❑ NSAP Network service access point
❑ OSPF Open shortest path first
❑ PG Peer group
❑ PGL Peer group leader
❑ PTSE PNNI Topology state element
❑ PTSP PNNI Topology state packet
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❑ PNNI Private network-network interface
❑ PVCC Permanent virtual channel connection
❑ PVPC Permanent virtual path connection
❑ RD Routing domain
❑ SAAL Signaling ATM adaptation layer
❑ SNPA Subnetwork point of attachment
❑ TIG Topology information group
❑ TLV Type, length, value
❑ VF Variance factor
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ReferencesReferences❑ B. Dorling, D. Freedman, C. Metz, and J. Burger,
"Internetworking over ATM: An Introduction," PrenticeHall, 1996.
❑ D. Dykeman and M. Goguen, “PNNI Draft SpecificationV1.0,” af-pnni-0055.000, March 1996. ftp://ftp.atmforum.com/pub/approved-specs/af-pnni-0055.000.ps
❑ A. Alles, “Routing and Internetworking in ATM Networks,”Networld+InterOP, March 1995
❑ W.C. Lee, “Topology Aggregation for Hierarchical Routingin ATM Networks,” Computer Communication Review,April 1995.
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References (References (contcont))❑ J.M. Halpern, “ATM Call Routing,” Communication
Systems Design, pp. 30-35.
❑ R. Callon, et al, “Issues and Approaches for IntegratedPNNI,” ATM Forum 96-0355, April 1996.