pnni (private network node interface or private network-to-network interface)

72
NI (Private Network Node Interface ivate Network-to-Network Interface PNNI is a switch-to-switch protocol developed within the ATM Forum to support efficient, dynamic and scalable routing of SVC requests in a multi-vendor private ATM environment.

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PNNI (Private Network Node Interface or Private Network-to-Network Interface). PNNI is a switch-to-switch protocol developed within the ATM Forum to support efficient, dynamic and scalable routing of SVC requests in a multi-vendor private ATM environment. Internet Routing Protocols (Overview). - PowerPoint PPT Presentation

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Page 1: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI (Private Network Node Interface orPrivate Network-to-Network Interface)

PNNI is a switch-to-switch protocol developed within the ATM Forum to support efficient, dynamic and scalable routing of SVC requests in a multi-vendor private ATM environment.

Page 2: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Internet Routing Protocols (Overview)

IP finds route on a per packet basis. Packet specifies endsystem address. Switch picks next hop.

• A Protocol is run by routers in Internet to update routing tables.

• Routing tables are updated automatically on a topology change, e.g., a node failure will be recognized and avoided.

Page 3: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Internet Routing Protocols (Ctd)Two well-known approaches (Two Religions)

1. Distance Vector Routing Protocols (Distributed)

• Based on Bellman-Ford shortest path algorithm (Distributed Version)• Router maintains best-known distance to each destination and next hop in the routing table.• Each router periodically communicates to all neighbor routers its best-known distance to each destination. • (May take a long time in a large network!!!)• Routers update distances based on the new information.

Page 4: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Internet Routing Protocols (Ctd)

2. Link-State (Topology Broadcast) Routing Protocols (Centralized)

• Each router broadcasts topology information (e.g., link states) to all routers.• Each router independently computes exact shortest paths

using a centralized algorithm.• Each router creates then a NETWORK MAP referred as LINK STATE DATABASE.

Page 5: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

ATM Routing Protocols

Invoked only for connection setup!!!

•Protocols to route connection requests through interconnected network of ATM switches.

•P-NNI Phase 1 completed by ATM Forum in March ’96.

- Will allow switches from multiple vendors to interoperate in large ATM networks

Page 6: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI Phase I consists of 2 Protocols:

1. Routing:

• PNNI routing is used to distribute information on

the topology of the ATM network between switches

and groups of switches.

• This information is used by the switch closest to the

SVC requestor to compute a path to the destination

that will satisfy QoS objectives.

• PNNI supports a hierarchical routing structure

scalable for large networks.

Page 7: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI (Private Network Node Interface or Private Network-to-Network Interface)

2. Signaling:

• PNNI signaling uses the topology and resource

information available at each switch to construct

a source-route path called a Designated Transit List (DTL).

• The DTL contains the specific nodes and links the

SVC request will traverse to meet the requested

QoS objectives and complete the connection.

• Crankback and alternate routing are also supported

to route around a failed path.

Page 8: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

ARCHITECTURE

EndSystem

EndSystem SwitchSwitch End

System

EndSystemSwitchSwitch

EndSystem

EndSystem

EndSystem

EndSystem

ATMNetwork

ATMNetwork

ATMNetwork

ATMNetwork

PNNI

PNNI

•Private Network-to-Network Interface•Private Network-Node-Interface

Page 9: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

ARCHITECTURE (Cont.)

ATMSwitch

ATMSwitch

ATMSwitch

ATMSwitch

ATMSwitch

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UNI Signaling NNI Signaling

Page 10: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Features 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

Page 11: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Architecture Reference Model ofSwitching System

Switching Fabric

RouteDetermination

TopologyDatabase

TopologyExchange

UNISignaling

CallProcessing

NNISignaling

ManagementInterfaceProtocol

UNI Signaling

Cell Stream Cell Stream

NNI Signaling

TopologyProtocol

Page 12: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Overview of PNNI Routing Design Concepts

PNNI uses several formerly known techniques :

• Link State Routing

• Hierarchical Routing

• Source Routing

Page 13: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

CHOICES IN THE BEGINNING• PNNI is a routing protocol requires a routing algorithm.

CHOICE 1. Distance Vector Routing Algorithm used in RIP. * Not selected because:

Not scalable; Prone to routing loops; Does not converge rapidly; and uses excessive overhead control traffic.

CHOICE 2: Link-State Routing (such as OSPF). * Selected because

Scalable; Converges rapidly; Generates less overhead traffic; and is extendible. Extendible means that information in addition to the status of the links can be exchanged between nodes and incorporated into the topology database.

Difference to OSPF: Status of an ATM switch is advertised in addition to the status of the links.

Page 14: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

1. Concept of Link State Routing

• Each ATM switch uses HELLO protocol and sends HELLO packets periodically or on state changes.

• The HELLO packet is flooded to all other switches in the network.

• Each ATM switch exchanges updates with its neighbor switches on the status of the links, the status and resources of the switches, and the identity of each other’s neighbor switches.

• The switch information may include data about switch capacity, QoS, and transit time.

Page 15: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Concept of Link State Routing (Ctnd’)

• This information is important because SVC requests are routed over a path that must meet its QoS objectives.

• This information is used to build a topology database (NETWORK MAP) of the entire network.

• Each ATM switch in the group will have an identical copy of the topology database.

• If a change in topology occurs (e.g., link is broken), then only that change is propagated between the switches.

Page 16: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Concept of Link State Routing (Cont.)

ATMEnd User

ATMSwitch 1

ATM Switch 3

ATMSwitch 4

ATMEnd User

ATMSwitch 2

A B

Topology Database

ATMSwitch 1 ATM

Switch 3

ATMSwitch 2

ATMSwitch 4

Page 17: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

2. Routing Hierarchy Concept(Similar to 2-level hierarchy of OSPF)

Can support 104 levels of hierarchy. In practice we need 3 or 4 levels.

ATMSwitchATM

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LogicalLevel

Real ATMSwitches

PhysicalLinks

Multilevel Routing Hierarchy

Page 18: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Routing Hierarchy Concept (Cont.)• Peer Groups: Switches that share a common addressing scheme are grouped into an area.

• Members of a peer group will exchange information with each other about the topology of the peer group.

An ATM switch, called the Peer Group Leader (PGL), then summarizes this information and exchanges it with other PGLs that represent other PEER GROUPs of switches in the next higher layer of the Peer Group.

Page 19: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Routing Hierarchy Concept (Cont.)

ATMSwitchATM

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Example:

Page 20: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Routing Hierarchy Concept (Cont.)

ATMSwitchATM

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Peer Group NL GN A

L GN BL GN C

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A.1

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B.3B.2

C.1 C.3

C.4

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Peer Group A

Peer Group B

Peer Group C

PNNI Routing HierarchyExample:

Page 21: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Explanation of the Example:

• The three peer groups at the bottom of the figure represent a topology of real ATM switches connected by physical links.

• The switches in peer group A, e.g., will exchange topology and resource information with the other switches in the peer group.

• Switch A.1 is elected the PGL and will summarize the information about peer group A. • In the next higher-level peer group, N, the PGL for A, switch A.1 will exchange the summarized information with the other nodes in N.

• The other PGLs representing B and C will do likewise.

• Switch A.1 will then advertise the summarized information it has gained from the other members of N into its own lower level, i.e., child peer group A.

.

Page 22: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• Remark:

• Each switch in a peer group will have complete information about the topology of the peer group it is part of and partial or summarized information about the outside or external peer groups.

• Hierarchy enables a network to scale by reducing the amount of information a node is required to maintain.

• It contains the amount of real topology information that is transmitted on the network to a local area or peer group. • The information on the network is further reduced by the process of topology aggregation so that a collection of real switches can appear as a single node to other peer groups.

Page 23: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI Terminology

Example : Peer groups A, B, and C consist of real ATM switches connected by physical links. Peer group N consists of three logical group nodes (LGN). The LGNs are summarized representations of the peer groups of actual switches they represent below them.

• PEER GROUP: A peer group is a collection of nodes that share a common addressing scheme and maintains an identical topology database and exchange topology and resource information with each other. Members of a peer group discover their neighbors using a HELLO protocol.

ATMSwitchATM

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Peer Group NLGN A

LGN BLGN C

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A.1A.4

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C.1 C.3C.4

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Peer Group A

Peer Group B

Peer Group C

Page 24: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

•PEER GROUP IDENTIFIER: Members of the same peer group are identified by a common peer group identifier. The peer group identifier is defined from a unique 20-byte ATM address that is manually configured in each switch. (See the addressing subsection!)

•LOGICAL NODE. A logical node is any switch or group of switches that runs the PNNI routing protocol, e.g., all members of PG A and the node above it, LGN A are logical nodes.

ATMSwitchATM

Switch

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Switch

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SwitchATM

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Switch

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Peer Group NLGN A

LGN BLGN C

ATMSwitchATM

Switch

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Switch

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SwitchATMSwitchATM

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Switch

A.1A.4

A.3A.2

B.1

B.3B.2

C.1 C.3C.4

C.2

Peer Group A

Peer Group B

Peer Group C

Page 25: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

•LOGICAL GROUP NODE (LGN). An LGN is an abstract representation of a lower-level peer group for the purposes of representing that peer group in the next higher-level peer group. In other words, representation of a group as a single point.

LGN A represents PG A, LGN B represents PG B, and LGN C represents PG C. Even though an LGN is not a real switch but a logical representation of a group of switches, it still behaves as if it was a real ATM switch.

ATMSwitchATM

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LGN BLGN C

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A.1A.4

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C.1 C.3C.4

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Peer Group A

Peer Group B

Peer Group C

Page 26: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• PARENT PEER GROUP: LGN representing peer group below it, e.g., PG N is a parent peer group.

• CHILD PEER GROUP: Any node at the next lower hierarchy level. In other words, a node that is part of an LGN in the next higher level peer group.

e.g., Peer groups A, B, and C are child peer groups.

ATMSwitchATM

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A.1A.4

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Peer Group A

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Peer Group C

Page 27: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• PEER GROUP LEADER (PGL). Within the peer group, a PGL is elected to represent the peer group as a logical group node in the next higher-level peer group. The PGL is responsible for summarizing information about the peer group upward and passes higher-level information downward.• SWITCH with the highest “leadership priority” and highest ATM address is elected as a leader.Note Continuous process Leader may change any time.

e.g., Each of the peer groups has a PGL shaded in gray, i.e., A.1, B.2, C.2 and LGN A.

ATMSwitchATM

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Peer Group NLGN A

LGN BLGN C

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A.1A.4

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B.1

B.3B.2

C.1 C.3C.4

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Peer Group A

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Peer Group C

Page 28: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

ATMSwitchATM

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LGN BLGN C

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A.1A.4

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Peer Group A

Peer Group B

Peer Group C

• HELLO PROTOCOL. This is a standard link-state procedure used by neighbor

nodes to discover the existence and identify of each other.

• BORDER NODES. A border node is a logical node which has a neighbor that belongs to a different peer group. This is established when neighbor switches exchange hello packets. The links connecting two peer groups are called outside links.

e.g., Nodes A.4, B.2, B.3, and C.1 are border nodes.

Page 29: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

UPLINKS. • An uplink is a logical connection from a BORDER NODE to a higher-level LGN.

• The existence of an uplink is derived from an exchange of HELLO PACKETS between BORDER NODES.• The other members of the peer group are then informed about the existence of the uplink. • An uplink is used by the PGL to construct a logical link between LGN in the next higher-level peer group.

e.g., uplinks from PG A to LGN B and LGN C.

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Page 30: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• LOGICAL LINK: • A connection between 2 nodes.• They interconnect the members of PG N. • Horizontal links are logical links that connect nodes in the same peer group

• ROUTING CONTROL CHANNEL: • VPI=0, VCI=18 is reserved as the VC used to exchange routing information between logical nodes. • An RCC that is established between two LGNs serves as the logical link information needed by LGNs to establish the RCC SVC between other nodes in the peer group which is derived from the existence of uplinks.

Page 31: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• TOPOLOGY AGGREGATION: • This is the process of summarizing and compressing information at one peer group to advertise into the next higher-level peer group. • Topology aggregation is performed by the PGLs. • Links can be aggregated such that multiple links in the child peer group may be represented a single link in the parent peer group.

• Nodes are aggregated from multiple child nodes into a single LGN.

Page 32: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• PNNI TOPOLOGY STATE ELEMENT (PTSE):

• This unit of information is used by nodes to build and synchronize a topology database within the same peer group.

• PTSEs are reliably flooded between nodes in a peer group and downward from an LGN into the peer group it represents.

• PTSEs contain topology state information about the links and nodes in

the peer group. • PTSEs are carried in PNNI topology state packets (PTSP).

• PTSPs are sent at regular intervals or will be sent if triggered by an important change in topology.

Page 33: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• REMARK: (Summary)

Upon initialization nodes exchange PTSE headers. e.g., My topology database is dated 11-March-2001:11:59.

Node with older database requests more recent information. After synchronizing the routing databases, they advertise the

link between them. The ad (PTSP) is flooded through the peer group.

All PTSPs have a lifetime and are unless renewed.

Only the node that originated a PTSP can reissue it.

PTSPs are issued periodically and also event-driven.

Page 34: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• UPWARD AND DOWNWARD INFORMATION FLOW:

Fig. shows the information flow during this process for PG A and LGN A.

• The PGL in A, A1, is responsible for producing information about PG A, summarizing it and then representing A as a single LGN in PG N. This is the upward flow.

* Note that no PTSEs flow upward.

* PTSEs flow downward and horizontally from the PGL.

* This provides the nodes in PG A with visibility outside its peer group and enables them to intelligently route an SVC request.

* External visibility for nodes in a peer group is limited to knowledge about uplinks to other LGNs.

Page 35: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI Upward/Downward Information Flow

PGLs summarize state information within peer group communicate to higher level peer group.

ATM Switch

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Summarized Peer Group A topology and resource data PTSE

LGNs communicate within peer group by flooding

LGN & PGL exchange topology information

Flood information at the peer level

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Group Leaders also pass summarized topology information to nodes of lower-level peer groups.

Page 36: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Addressing• The fundamental purpose of PNNI is to compute a route from a source to a

destination based on a called ATM address. • The called ATM address is an information element contained in the SETUP

message that is sent over UNI from the device to a switch (ATM UNI 3.1 specification).

• Presumably a switch running PNNI Phase I will have in its topology database an entry that will match a portion or prefix of the 20-byte ATM address that is contained in the SETUP message.

• The switch will then be able to compute a path through the network to the destination switch.

PNNI uses 19 bytesATM end system address (20 bytes)

DSP6 bytes

1 byteIDP

Address prefix (13 bytes)

End System Identifier (ESI)AFI SEL

Page 37: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Addressing (Ctnd)

• Addressing and identification of components of the PNNI routing hierarchy are based on the use of ATM end system addresses.

• PNNI routing works off of the first 19 bytes of this address or some prefix of this address.

• The 20th byte is the selector field which only has local significance to the end station and is ignored by PNNI routing.

• Most significant 13 bytes in ATM address field used to define PEER GROUPs.• Nodes in PEER GROUP have common high-order bits.• Allows up to 13 8 = 104 levels in hierarchy. (Practice: 3 — 4 levels enough).

PNNI uses 19 bytesATM end system address (20 bytes)

DSP6 bytes

1 byteIDP

Address prefix (13 bytes)

End System Identifier (ESI)AFI SEL

Page 38: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Addressing (Cont.)• Nodes in a peer group have the same prefix address bits in

common.

Address Prefix

ESID SELx Bits

Address Prefix

ESID SELx+y Bits

Address Prefix

ESID SELx+y+z Bits

Page 39: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

•At the highest level illustrated, the LGNs that make up the high-order LGN have their left x high-order bits the same.

•At the next lower level, the three LGNs shown have their left x+y high order bits the same.

•At the lowest level illustrated, the LGNs have their left x+y+z high order bits the same.(At this level, they are all real physical switches.)

Addressing (Cont.)

Page 40: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Peer Group Generation Process

• Two identifiers are used in PNNI to define the hierarchy and a node placement in the hierarchy.

• The first is the “Peer Group Identifier”. This is a 14-byte value.

• The first byte is a level indicator which defines which of the next 104 left-most bits are shared by switches in the peer group. In other words, what level in the hierarchy the peer group is in.

• Peer group identifiers must be prefixes of ATM addresses.

Level Indicator Peer Group Identifier

1 Byte 13 Bytes

Peer Group Identifier

Page 41: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Peer Group Generation Process (Cont.)• A peer group is identified by its peer group identifier.

• Peer group IDs are specified at the configuration time.

• Neighboring nodes exchange peer group IDs in hello packets.

• If they have the same peer group ID, then they belong to the same peer group.

• If the exchanged peer group IDs are different, then the nodes belong to different peer groups.

• The “Node Identifier” is 22 bytes in length and consists of a 1-byte level indicator, 1-Byte Lowest Level Node Indicator; 20-Bytes ATM address.

• The Node Identifier is unique for each PNNI node in the routing domain. Identifying the ACTUAL-PHYSICAL NODE address.

• A PNNI node that advertises topology information in PNNI topology state packets will include the Node Identifier and the Peer Group Identifier to indicate the originator of the information and the scope (on which level of the hierarchy it is directed to).

Page 42: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

PNNI Routing Hierarchy

ATMSwitchATM

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Example:

Page 43: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

The process of building PNNI peer groups is recursive, i.e., the same process is used at each level in hierarchy. The exceptions are (1) the lowest level peer groups because the logical nodes representing actual switches can have no child nodes and (2) the highest-level peer group because there is no parent to represent it.

PROCEDURE

0. Initiate physical connections or (VPs) between switches (at lowest level).

1. Exchange HELLO messages with physical peer switches by flooding.

2. Determine peer group membership (configure lowest level peer groups)

3. Flood topology-state PTSEs in peer group.

3a. Create the “Topology Database”

3b. Determine the “BORDER NODES”

4. Elect peer group leader.

Peer Group Generation Process (Cont.)

Page 44: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

5. Identify UPLINKS from the BORDER NODES (if any).

6. Build horizontal links between LGNs at the next higher level.

7. Exchange HELLO messages with adjacent-logical nodes (LGNs at that level).

8. Determine peer group membership at that level.

9. Flood topology-state PTSEs in peer group.

9a. Create TOPOLOGY DATABASE

9b. Determine the BORDER NODES

10. Elect peer group leader

11. If highest-level peer group reached, then process complete.

12. Return to Step 5.

PROCEDURE(Cont.)

Page 45: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• A PNNI node will advertise its own direct knowledge of the ATM

network.

• The scope of this advertisement is the peer group.

• The information is encoded in TLVs called PNNI Topology State

Elements (PTSE).

• Multiple PTSEs can be carried in a single PNNI Topology State

Packet (PTSP).

• The PTSP is the packet used to send topology information to a

neighbor node in the peer group.

PNNI Information Exchange

Page 46: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Each switch advertises the following:

Nodal Information: This includes the switch’s ATM address, peer group identifier, leadership priority, and other aspects about the switch itself.

Topology State Information: This covers outbound link and switch resources.

Reachability: ATM addresses and ATM address prefixes that the switch has learned about or is configured with.

PNNI Information Exchange (Ctd)

Page 47: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• PNNI is a topology state protocol logical nodes will advertise link state and nodal state parameters.

• A link state parameter describes the characteristics of a specific link and a nodal state parameter describes the characteristics of a node.

• Together these can form topology state parameters that are advertised by PNNI nodes within their own peer group.

Topology state parameters are either metrics or attributes.

• A topology state metric (added along the path, e.g., delay) is a parameter whose values must be combined for all links and nodes in the SVC request path to determine if the path is acceptable.

• A topological state attribute (considered individually on each elements) is a parameter that determines if a path is acceptable for an SVC request.

Page 48: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Topological state attributes can be further subdivided into two categories:

Performance-related and Policy-related.

Performance-related attributes (e.g., capacity) measure the performance of a particular link or node.

Policy-related attributes (e.g., security) provide a measure of conformance level to a specific policy by a node or link in the topology.

Page 49: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Table: PNNI Topology State Parameters

Metrics Performance/ Resource Attributes

Policy Attributes

Cell Delay VariationCell Delay Variation Cell Loss Ratio for CLP=0Cell Loss Ratio for CLP=0 Restricted Transit FlagRestricted Transit Flag

Maximum Cell Maximum Cell Transfer DelayTransfer Delay

Maximum Cell RateMaximum Cell Rate

Administrative Administrative WeightWeight

Available Cell RateAvailable Cell Rate

Cell Rate MarginCell Rate Margin

Variance FactorVariance Factor

Branching FlagBranching Flag

Page 50: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Cell Delay Variation (CDV)Expected CDV along the path relevant for CBR and VBR-rt traffic.

Administrative Weight (AW)Link or nodal state parameter set by administrator to indicate preference for A NETWORK LINK.

Cell Loss Ratio (CLR)Describes the expected CLR at a node or link for CLP=0 traffic.

Maximum Cell Rate (MCR)Describes the maximum link or node capacity.

Available Cell Rate (ACR)Measure of effective available bandwidth in cells

per second, per traffic class.

Page 51: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Cell Rate Margin (CRM) A measure of the difference between effective bandwidth allocation per traffic class and the allocation for sustainable cell rate (SCR). A measure of the safety margin allocated above the aggregate sustained rate.Variance Factor (VF) A relative measure of the square of the CRM normalized by the variance of the aggregate cell rate on the link.Branching Flag Used to indicate if a node can branch point-to-multipoint traffic.Restricted Transit Flag Nodal state parameter that indicates whether a node supports transit traffic or not.

Page 52: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• The process of generating a PNNI routing hierarchy is an Automatic Procedure that defines how nodes will interact with each other. • It begins at the lowest level in the hierarchy and is based on the information that is exchanged between switches. • The same process is performed at each level of the hierarchy.

PNNI Routing Hierarchy

Page 53: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Peer Group B

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

LGN APeer Group N LGN C

LGN B

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

Peer Group A

A.1

A.2

A.3

A.4

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

SwitchB.1

B.2 B.3

ATMSwitchATM

Switch

ATMSwitchATM

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ATMSwitchATM

Switch

ATMSwitchATM

Switch

Peer Group C

C.2

C.1 C.3

C.4

Page 54: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• Switches in peer group A exchange HELLO packets with their neighbor switches over a special reserved VCC (VPI=0, VCI=18) called the Routing Control Channel (RCC).

HELLO packets contain * A node’s ATM end system address, * node ID, and * its port ID for the link. The HELLO protocol makes the neighboring nodes

known to each other.

• Membership in the peer group is determined based on addressing. Those with a matching peer group identifier are common peer group members.

Page 55: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• Topology information in the form of PTSEs is reliably flooded in the peer group over the Routing Control Channel.

• PTSEs are the smallest collection of PNNI routing information that is flooded as a unit among all logical nodes within a peer group.

• A node’s topology database consists of a collection of all PTSEs received, which represent that node’s present view of the PNNI routing domain.

• The topology database provides all the information required to compute a route from the given node to any address reachable through that routing domain.

Page 56: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• A peer group leader (PGL) is elected based on the leadership priority configured in the switch.

• The PGL represents the peer group as a logical group node in the next higher-level peer group.

• PGLs summarize and circulate info in the parent group.

• Switch A.1 is the PGL for peer group A.

• A logical group node (LGN) is an abstract representation of a lower-level peer group for the purposes of representing that peer group in the next higher-layer peer group.

• LGN A represents peer group A in the next higher-level peer group, i.e., peer group N.

Page 57: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• Because PNNI is recursive, LGN A behaves just like it was a switch in a peer group which in this case is peer group N.

• It is also the responsibility for the PGL to advertise PTSEs that it has collected in higher-level peer groups.

• This enables the switches in peer group A to have at least a partial picture of the entire network.

• Identify uplink and build horizontal links between LGNs.

• An uplink is a connection to an adjacent peer group.

• This is discovered when border switches exchange HELLOs and determine that they are not in the same peer group.

• From the perspective of a switch in peer group A; an uplink is a connection to an LGN in a higher-level peer group.

Page 58: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• A horizontal link is a logical connection between LGNs in the next higher-level peer group. It is in actuality an SVC between PGLs.

• So the horizontal link that connects LGN A and LGN B in peer group N is an SVC between switches A.1 and B.2. It functions as a RCC so that nodes in peer group N can exchange topology information.

• The same process of exchanging HELLOs and flooding PTSEs is performed in peer group N, i.e., PTSEs flow horizontally through the peer group and downward through children.

• Border nodes do not exchange databases (different peer groups).

Page 59: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• CAC is the function performed by ATM switches that determines whether a connection request can be accepted or not.

• This is performed by every switch in the SVC request path.

• But CAC is not standardized, so it is up to individual switch to decide if a connection request and its associated QoS can be supported.

• PNNI uses information stored in the originating node’s topology database along with the connection’s traffic characteristics and QoS requirements, to compute a path.

• But again, CAC is a local switch process that the originating node cannot realistically keep track of.

Generic Connection Admission Control (GCAC)

Page 60: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• Therefore, PNNI invokes a Generic Connection Admission Control. (GCAC) procedure during the path selection process which provides the originating node with an estimate of whether each switch’s local CAC process will accept the connection.

Generic Call Admission Control (GCAC) Run by a switch in choosing 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

Generic Connection Admission Control (GCAC)

Page 61: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Generic Connection Admission Control (Ctd)

Runs ACAC

Runs ACACRuns ACACRuns ACACRuns GCACChooses Path

• Ingress Switch performs GCAC to check QoS-based or route information available.

• Individual switches on path perform actual CAC on receipt of SETUP message.

• When local admission fails, request backtracked to previous switch in path (crankback)

Page 62: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

3. Source Routing Concept• A switch that receives an SVC request from a user-device

over a UNI connection will compute and generate the entire path through the network based on its knowledge of the network.

• Since QoS metrics are advertised and contained in the topology-state database, the first switch has a good idea about what path to take.

• The first switch will designate which switches the SVC request should pass through. This is called Designated Transit List (DTL).

• Note that the Intermediate Switches along the path do not need to perform any path computations.

Page 63: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Source Routing Concept (Ctnd)

• They only perform CAC and forward SVC request by following the information in the source-route path.

• If the SVC request is destined for a switch in another peer group, it will specify all external peer groups the SVC should travel through and direct it to a border switch in an adjacent peer group.

• It will be up to the entry or border switch of the adjacent or intermediate peer group to generate a DTL for its peer group.

• Advantage of source routing => Prevents loops!!!

Page 64: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Source Routing Concept (Cont.)Example:

SS DD11

44

33

22 55

Destination Pointer 1 2 4 5

Page 65: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Designated Transit Lists•PNNI uses source routing to forward an SVC request across one or more peer groups in a PNNI routing hierarchy.

•The PNNI term for the source route vector is designated transit list (DTL)

which is a vector of information that defines a complete path from the source node to the destination node across a peer group in the routing hierarchy.

•A DTL is computed by the source node or the first node in a peer groupto receive an SVC request.

•Based on the source node’s knowledge of the network, it computes a path to the destination that will satisfy the QoS objectives of the request.

•Nodes then simply obey the DTL and forward the SVC request throughthe network.

Page 66: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

Designated Transit Lists•A DTL is implemented as an information element (IE) that is added to

thePNNI signaling messages SETUP and ADD PARTY.•One DTL is computed for each peer group and contains the completepath across the peer group. •In other words, it is a list of nodes and links that the SVC request mustvisit on its way to the destination. •A series of DTLs is combined into a stack with the lowest-level peer

groupon top and highest at the bottom. •A pointer is also included to indicate the DTL node currently visited by SVC. •When the pointer reaches end of DTL, the DTL is removed fromstack and next DTL is processed. •If the SVC request enters a new lowest-level peer group, then a new DTLwill be generated by the ingress switch and placed at the top of the DTLstack for processing.

Page 67: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

DTL EXAMPLE

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

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SwitchATM

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Peer Group NL GN A

L GN BL GN C

ATMSwitchATM

Switch

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ATMSwitchATM

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ATMSwitchATM

SwitchATMSwitchATM

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ATMSwitchATM

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A.1

A.4A.3

A.2

B.1

B.3B.2

C.1 C.3C.4

C.2

Peer Group A

Peer Group B

Peer Group C

(A2,A1,A4)(A,B,C)

(B2,B3)(A,B,C)

(C1,C2,C3)(A,B,C)

End User X End User Y

Suppose User A wishes to establish an SVC with user C and for policy reasons the SVC request can only traverse the path shown in the Figure.

Page 68: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

DTL EXAMPLE (Cont.) • The SVC request is signaled across the UNI to node A.2.

• The node A.2 will use DIJKSTRA’s shortest path algorithm to find the path to the destination. VIEW from A.2!!!!

• Node A.2. knows that User C is reachable through LGN C and that LGN C is reachable through LGN B.

• Node A.2 constructs two DTLs, one to provide a path across PG A and another across PG N. The SVC request is forwarded.

• Not shown but included in a pointer that indicates which node in the DTL is currently being visited.

• When the last node in the DTL is reached, node A.4, is removed and the next DTL in the stack is processed.

• When the SVC request reaches node B.2, a new DTL (B.2,B.3) is popped on top of the stack.

• Node B.2 simply adds a DTL that enables the SVC request to traverse PG B.

• When the SVC request reaches the end of the current DTL (B.2,B.3), it is removed and the next one in the stack is processed.

• When the SVC request reaches node C.1, a new DTL (C.1,C.2,C.3) is popped on top and the call is forwarded to the destination.

• .

Page 69: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

CRANKBACK ALTERNATE ROUTING

• Nodes that generate DTLs (A2, B.2, C.1) in the previous example use information in the topology and resource database that may change while the SVC request is being forwarded.

• This may cause the SVC request to be blocked.

• Short of going all the way back to User A and attempting to reestablish the connection, PNNI invokes a technique called crankback with alternate routing .

• When the SVC request cannot be forwarded according to the DTL, it is cleared back to the originator of the DTL with an indication of the problem. This is the crankback mechanism.

Page 70: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

CRANKBACK ALTERNATE ROUTING (Cont.)

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

Switch

ATMSwitchATM

SwitchATM

SwitchATM

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Peer Group NL GN A

L GN BL GN C

ATMSwitchATM

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SwitchATMSwitchATM

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A.1

A.4A.3

A.2

B.1

B.3B.2

C.1 C.3C.4

C.2

Peer Group A

Peer Group B

Peer Group C

(A2,A1,A4)(A,B,C)

(B2,B3)(A,B,C)

(C1,C2,C3)(A,B,C)

End User A End User C

New DTL of (B.2, B.1, B.3)

Page 71: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

•At that point a new DTL (alternate routing) may be constructed that bypasses the nodes or links that blocked the SVC request but which must match the higher-level DTLs which are further down in the DTL stack.

• If no path can be found, then the request is cranked back to the previous DTL originator.

• If the DTL originator is original source node, then the crankback message is translated into a REJECT and USER A must attempt another connection request.

CRANKBACK ALTERNATE ROUTING (Cont.)

Page 72: PNNI (Private Network Node Interface or Private Network-to-Network Interface)

• In our example, suppose the port on node B.3 that connects the link to node B.2 experienced congestion while the SVC request was being forwarded.

• Node B.3 would realize, after running CAC, that the SVC request could not be satisfied over this port.

• A crankback message would then be sent back to node B.2 indicating a problem with the specified port on node B.3.

• Node B.2 would then recompute a new DTL as shown and forward the SVC request around the failed resource.

•This is illustrated in the Figure.

CRANKBACK ALTERNATE ROUTING (Cont.)