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

1. CHAPTER 6: 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.

2. Internet Routing Protocols (Overview) IP finds route on a per packet basis. Packet specifies end system 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.

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

4. 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.

5. 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

6. 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.

7. 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.

8. PNNI End System Switch Switch End System ATM Network PNNI ATM Network End System End System ARCHITECTURE • Private Network-to-Network Interface • Private Network-Node-Interface

9. NNI Signaling UNI Signaling ATM Switch ATM Switch ATM Switch ATM Switch ARCHITECTURE (Cont.)

10. 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

11. Management Interface Protocol Topology Protocol Route Determination Topology Database Topology Exchange UNI Signaling NNI Signaling UNI Signaling Call Processing NNI Signaling Cell Stream Cell Stream Switching Fabric Architecture Reference Model ofSwitching System

12. Overview of PNNI Routing Design Concepts PNNI uses several formerly known techniques : • Link State Routing • Hierarchical Routing • Source Routing

13. 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.

14. 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. 1. Concept of Link State Routing

15. 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. Concept of Link State Routing (Ctnd’)

16. Topology Database ATM Switch 2 ATM Switch 1 ATM Switch 4 ATM Switch 3 ATM Switch 2 ATM Switch 4 ATM End User ATM End User ATM Switch 1 B ATM Switch 3 A Concept of Link State Routing

17. 2. Routing Hierarchy Concept Logical Level ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch Real ATM Switches Physical Links ATM Switch (Similar to 2-level hierarchy of OSPF) Can support 104 levels of hierarchy. In practice we need 3 or 4 levels. Multilevel Routing Hierarchy

18. 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.

19. Routing Hierarchy Concept (Cont.) ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch Example:

20. Routing Hierarchy Concept (Cont.) Peer Group N L GN A ATM Switch ATM Switch L GN B L GN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 Peer Group B A.1 C.1 ATM Switch ATM Switch C.3 A.2 ATM Switch ATM Switch A.4 C.4 ATM Switch A.3 ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 PNNI Routing Hierarchy Example:

21. 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. .

22. 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.

23. Peer Group N LGN A ATM Switch ATM Switch LGN B LGN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 A.1 Peer Group B C.3 C.1 ATM Switch ATM Switch A.4 A.2 ATM Switch ATM Switch C.4 A.3 ATM Switch ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 PNNI Terminology • 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. 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.

24. Peer Group N LGN A ATM Switch ATM Switch LGN B LGN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 A.1 Peer Group B C.1 ATM Switch ATM Switch C.3 A.2 A.4 ATM Switch ATM Switch C.4 A.3 ATM Switch ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 • 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.

25. Peer Group N LGN A ATM Switch ATM Switch LGN B LGN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 A.1 Peer Group B C.1 ATM Switch ATM Switch C.3 A.2 A.4 ATM Switch ATM Switch C.4 A.3 ATM Switch ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 • 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.

26. Peer Group N LGN A ATM Switch ATM Switch LGN B LGN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 A.1 Peer Group B C.1 ATM Switch ATM Switch C.3 A.2 A.4 ATM Switch ATM Switch C.4 ATM Switch A.3 ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 • 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.

27. Peer Group N LGN A ATM Switch ATM Switch LGN B LGN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 A.1 Peer Group B C.1 ATM Switch ATM Switch C.3 A.2 A.4 ATM Switch ATM Switch C.4 ATM Switch A.3 ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 • 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.

28. Peer Group N LGN A ATM Switch ATM Switch LGN B LGN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 A.1 Peer Group B C.1 ATM Switch ATM Switch C.3 A.2 A.4 ATM Switch ATM Switch C.4 ATM Switch A.3 ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 • 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.

29. Peer Group N LGN A Peer Group A ATM Switch ATM Switch LGN B LGN C ATM Switch ATM Switch A.1 A.2 A.4 Uplinks ATM Switch ATM Switch A.3 e.g., uplinks from PG A to LGN B and LGN C. ATM Switch • 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.

30. 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.

31. 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.

32. PNNI TOPOLOGY STATE ELEMENT (PTSE): • This unit of information is used by nodes to build and synchronize a • topology databasewithin 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.

33. 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.

34. 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.

35. LGN C LGN A LGNs communicate within peer group by flooding Peer Group N ATM Switch ATM Switch LGN B ATM Switch Summarized Peer Group A topology and resource data PTSE LGN & PGL exchange topology information PGL ATM Switch A.1 Flood information at the peer level ATM Switch A.2 ATM Switch A.4 A.3 ATM Switch Peer Group A PNNI Upward/Downward Information Flow PGLs summarize state information within peer group communicate to higher level peer group. Group Leaders also pass summarized topology information to nodes of lower-level peer groups.

36. Addressing ATM end system address (20 bytes) PNNI uses 19 bytes End System Identifier (ESI) SEL AFI DSP IDP 6 bytes 1 byte Address prefix (13 bytes) • 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.

37. Addressing (Ctnd) ATM end system address (20 bytes) PNNI uses 19 bytes End System Identifier (ESI) SEL AFI • 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). DSP IDP 6 bytes 1 byte Address prefix (13 bytes)

38. Addressing (Cont.) • Nodes in a peer group have the same prefix address bits in common. Address Prefix x Bits ESID SEL Address Prefix x+y Bits ESID SEL Address Prefix x+y+z Bits ESID SEL

39. Addressing (Cont.) • 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.)

40. Level Indicator Peer Group Identifier 1 Byte 13 Bytes 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. Peer Group Identifier

41. 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).

42. PNNI Routing Hierarchy Peer Group N L GN A ATM Switch ATM Switch L GN B L GN C ATM Switch Peer Group C Peer Group A ATM Switch ATM Switch C.2 Peer Group B A.1 C.1 ATM Switch ATM Switch C.3 A.2 ATM Switch ATM Switch A.4 C.4 ATM Switch A.3 ATM Switch B.1 ATM Switch ATM Switch ATM Switch B.3 B.2 Example:

43. 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) 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.) 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

44. 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. 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.)

45. PNNI Information Exchange • 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.

46. PNNI Information Exchange (Ctd) 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.

47. 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.

48. 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.

50. 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.