PNNI Private Network to Network Interface Principles Topology - PDF document

PNNI – Private Network to Network Interface Principles Topology concepts Routing Protocols Topology aggregation Call setup and routing algorithm PNNI-1 S-38.121 / S-04 / RKa, NB ATM background • ATM = Asynchronous Transfer Mode • Connection oriented – VCI (Virtual channel identifier) – VPI (Virtual path identifier) • Information is sent in fixed-size packets, in cells – 5 bytes header + 48 bytes data ÿ cell length 53 bytes • Two types of interfaces – UNI (User-network interface) • Connects end user with switch – NNI (Network-network interface) • Between two switches • Both UNI and NNI can be divided into a private and a public version PNNI-2 S-38.121 / S-04 / RKa, NB

In the ATM Forum model PNNI interconnects private networks Public UNI B-ICI B-ICI = B-ISDN Inter Public Public Carrier Interface ATM network network user ATM Private network Private network user or switch or switch PNNI = Private Network-to- PNNI Private UNI Network Interface PNNI 1.0 specification is af-pnni-0055.000, dated March 1996, over 365 pages PNNI-3 S-38.121 / S-04 / RKa, NB Private-Network-to-Network Interface (PNNI) is intended for interconnection of private network ATM switches • PNNI includes both a routing and a signaling protocol. • Requirements include scalability, efficiency, QoS support, fault tolerance in case of link and node failures and interoperability with other protocols. • PNNI routing, like OSPF routing, is based on network topology information which may be aggregated. • PNNI supports hierarchy. • PNNI signaling is inherited from the ATM-Forum UNI signaling. Additions are source routing and crankback. PNNI-4 S-38.121 / S-04 / RKa, NB

The reference model of a PNNI node Management Topology protocol Topology protocol Route Topology Information calculation database exchange UNI NNI signaling signaling UNI NNI Call control signaling signaling Cell flow Cell flow Switching matrix PNNI-5 S-38.121 / S-04 / RKa, NB PNNI routing functions include • Finding neighbors, links and link states using the Hello protocol. Establishment of Peer Groups . • Synchronization of the Topology databases by exchanging PNNI Topology State Elements ( PTSE s) horizontally inside a peer group. • Election of Peer Group Leaders ( PGL ) based on PTSEs. • Aggregation of topology information (task of PGL). • Building up the routing hierarchy (PGL passes to the parent group an aggregated description of his peer group) PNNI-6 S-38.121 / S-04 / RKa, NB

PNNI topology concepts and topology protocols PNNI-7 S-38.121 / S-04 / RKa, NB Peer group is the key concept in PNNI routing • A peer group is a set of logical nodes, such that they have the same topology information. A.4.1 – This includes both the information about the group A.4.2 itself as well as the description of the rest of the A.4.3 network. A.4.4 • Nodes have a common address prefix (e.g. A.4) for the sake of efficient coding. A.4.6 A.4.5 – The prefix is a configuration parameter set by the operator. PG(A.4) • A reasonable size of a peer group is max. tens of nodes (e.g. 20 .... 50). PNNI-8 S-38.121 / S-04 / RKa, NB

Example topology (1) A.2.3 A.2.2 B.1.1 A.2.1 B.2.1 A.1.3 A.3.1 B.1.2 B.2.2 B.1.3 A.1.2 C.2 B.2.5 B.2.3 A.3.4 A.1.1 A.3.2 C.1 A.4.1 B.2.4 A.3.3 A.4.2 A.4.3 A.4.4 A.4.6 Physical nodes and physical links A.4.5 PNNI-9 S-38.121 / S-04 / RKa, NB Example topology (2) PG(A.2) A.2.3 A.2.2 PG(B.1) PG(A.1) PG(B.2) B.1.1 A.2.1 PG(A.3) B.2.1 A.1.3 PG(C) A.3.1 B.1.2 B.2.2 B.1.3 A.1.2 C.2 B.2.5 B.2.3 A.3.4 A.1.1 A.3.2 C.1 A.4.1 B.2.4 A.3.3 A.4.2 A.4.3 A.4.4 A.4.6 Logical nodes and logical links A.4.5 PG(A.4) PNNI-10 S-38.121 / S-04 / RKa, NB

Example topology (3) PG(A) PG(B) PG(A.2) A.2.3 A.2.2 PG(B.1) PG(A.1) PG(B.2) B.1.1 A.2.1 PG(A.3) B.2.1 A.1.3 PG(C) A.3.1 B.1.2 B.2.2 B.1.3 A.1.2 C.2 B.2.5 B.2.3 A.3.4 A.1.1 A.3.2 C.1 A.4.1 B.2.4 A.3.3 A.4.2 A.4.3 A.4.4 A.4.6 A.4.5 PG(A.4) PNNI-11 S-38.121 / S-04 / RKa, NB Example hierarchical topology Top PG(A) PG(B) PG(A.2) A.2.3 A.2.2 PG(B.1) PG(A.1) PG(B.2) B.1.1 A.2.1 PG(A.3) B.2.1 A.1.3 PG(C) A.3.1 B.1.2 B.2.2 B.1.3 A.1.2 C.2 B.2.5 B.2.3 A.3.4 A.1.1 A.3.2 C.1 A.4.1 B.2.4 A.3.3 A.4.2 A.4.3 A.4.4 A.4.6 A.4.5 PG(A.4) PNNI-12 S-38.121 / S-04 / RKa, NB

Peer groups form a hierarchy • Address resolution decreases higher in the hierarchy, i.e. the prefix becomes shorter. The length of the prefix tells the level in the hierarchy. The numbering of levels starts from the top. • The peer group leader ( PGL ) aggregates the description of PG(A) the group and passes it up in PG(A.2) the hierarchy to the next PG(A.1) 2 PG(A.3) higher level peer group. 1 A.1.3 1 A.1.2 • PGL also receives external 4 2 A.1.1 3 topology info and distributes it in its group. PG(A.4) PNNI-13 S-38.121 / S-04 / RKa, NB The topology consists of logical nodes and logical links On upper levels: • A logical node represents the child peer group. PG(A) – In practice the functions of PG(A.2) the logical node are taken care of by the PGL of the child group. PG(A.1) 2 PG(A.3) 1 • Logical link = direct link connecting A.1.3 1 A.1.2 child peer groups 4 2 A.1.1 3 In the lowest level peer group • Logical node = physical node. PG(A.4) • Logical link = physical link PNNI-14 S-38.121 / S-04 / RKa, NB

Election of peer group leader is largely automatic and does not interfere setting up connections Tasks of the PGL are • to aggregate the group topology description • pass it upwards in the group hierarchy A.4.1 • receive topology information sent by the parent group A.4.2 A.4.3 and distribute it in its group A.4.4 Election of PGL • Election of the PGL is based on collected topology A.4.6 A.4.5 information. • To be elected a node needs to have a high enough PG(A.4) priority and it must know the identity of the parent group • The priority of the elected PGL is increased for stability • Not all nodes need to be eligible. • PGL can be re-elected automatically without operator interference. PNNI-15 S-38.121 / S-04 / RKa, NB PNNI Topology State Elements describe the topology PNNI Topology State Elements (PTSEs) are built of data sent by the Hello protocol and distributed into the peer groups. PTSE identity and order Header PTSE aging Sender identity Sender Sender routing capability, eligibility and PGL priority information Link (horizontal/vertical) and node parameters: Topology information divided into attributes and metrics Internal and External (also non-PNNI) addresses, Reachability to which the node will route traffic information PNNI-16 S-38.121 / S-04 / RKa, NB

The peer group topology is aggregated by abstracting its real structure into a logical node Complex Node Representation (CNR) of logical node A.4: Port 3 Exception Spoke with default attributes bypass Spoke with exception attributes A.4.1 Port 1 Port 2 A.4.2 A.4.3 A.4.4 Nucleus A.4.6 A.4.5 Spoke with default attributes PG(A.4) PNNI-17 S-38.121 / S-04 / RKa, NB Hello protocol works on a well defined VCC between neighbors • The Hello protocol works continuously and reveals link failures. • Hello protocol data is used to form the initial version of the topology database. The Hello packet contain Logical Logical node A node B ATM End System Address Hello Node ID Hello Port ID of the link Peer group ID PNNI-19 S-38.121 / S-04 / RKa, NB

When neighbors have been identified by Hello protocol, topology databases are synchronized Logical Logical node B node A PTSE-header advertisement New info PTSE-requests yes PTSEs PTSE-ack (headers) Update the DB PTSE-header advertisement PNNI-20 S-38.121 / S-04 / RKa, NB PNNI flooding protocol is similar to OSPF-flooding Logical Logical node B All other neighbors node A PTSEs except the sender PTSE-ack (headers) Refresh timer New info Remove old info from DB yes Update the DB PTSEs Timer PTSEs Event PTSE-ack (headers) (significant change) • Send frequency of PTSEs is a compromise between probability of misrouting and the need to minimize the amount of PTSE-information. • What a significant change is, is configurable. PNNI-21 S-38.121 / S-04 / RKa, NB

ATM Addresses • 19 octet address + 1 octet selector • Peer group ID at most 13 octets – 8 * 13 = 104 levels • 10 levels should be enough in international networks peer group ID node sel peer group ID node sel max. 104 levels PNNI-22 S-38.121 / S-04 / RKa, NB Parent peer groups are similar to lowest level peer groups Logical group node (logical node) has • ATM End System Address (a different SEL than PGL) PG(A) • Virtual Channel Connections (VCCs) are set PG(A.2) up between logical group nodes for communication between them PG(A.1) 2 PG(A.3) 1 • PGL is elected in the parent group as well A.1.3 1 A.1.2 4 2 • PGL is not needed on the topmost level A.1.1 3 PG(A.4) PNNI-23 S-38.121 / S-04 / RKa, NB