Traffic Engineering

As mentioned at the beginning of this chapter, PNNI is a constrained-based routing protocol. It advertises and keeps in its database information about the status of the links and nodes using metrics and attributes. PNNI supports different link metrics (such as AW, CTD, and CDV) and different attributes (such as AvCR, MaxCR, CLR, and so on) for different classes of service. The support for different link metrics and attributes is one of the enablers of the advanced traffic engineering and QoS routing capabilities.

Different classes of service support different traffic parameters. The traffic parameter administrative weight (AW) is required for all classes of service. Others, such as maximum cell rate (MaxCR), are required for some classes of service but are optional for others. Table 11-2 summarizes the required and optional traffic parameters.

Table 11-2. PNNI Classes of Service and Traffic Parameters

	CBR	VBR-RT	VBR-NRT	ABR	UBR
AW	Required	Required	Required	Required	Required
MaxCR	Optional	Optional	Optional	Required	Required
AvCR	Required	Required	Required	Required	N/A
MaxCTD	Required	Required	Required	N/A	N/A
CDV	Required	Required	N/A	N/A	N/A
CLR0	Required	Required	Required	N/A	N/A
CLR0+1	Required	Required	Required	N/A	N/A
CRM	N/A	Optional	Optional	N/A	N/A
VF	N/A	Optional	Optional	N/A	N/A

Class-Based Routing and Constrained-Based Routing

Evidence of the class-based nature of the PNNI routing protocol can be seen with different commands. The command dsppnni-path displays precalculated routes to specific nodes or to all nodes, for different classes of service, based on AW, cell transfer delay, or cell delay variation.

First, as Example 11-31 shows, you can display the precomputed path from the MGX-8850 toward the two adjacent nodes for the CBR service category.

Example 11-31. Displaying the PNNI Precomputed Paths

 m8850-7a.7.PXM.a > dsppnni-path aw cbr 2 node #/PortId   node id                                            node name --------------- -------------------------------------------------- ---------- D  2/         0 64:160:47.000000000000010001008600.00d058ac2828.01 SES-3a S  1/  16848898 64:160:47.000000000000010002008850.00309409f6ba.01 m8850-7a m8850-7a.7.PXM.a > dsppnni-path aw cbr 3 node #/PortId   node id                                            node name --------------- -------------------------------------------------- ---------- D  3/         0 64:160:47.000000000000010002008950.0004c113ba46.01 m8950-7b S  1/  17569793 64:160:47.000000000000010002008850.00309409f6ba.01 m8850-7a m8850-7a.7.PXM.a > 

You can see that CBR connections terminating in either of these two nodes take a unique path.

The precalculated path from the MGX-8850 PNNI node toward the LS-1010 PNNI node based on administrative weight for the CBR class is as follows (see Example 11-32).

Example 11-32. Displaying Load Sharing Paths

 m8850-7a.7.PXM.a > dsppnni-path aw cbr 4 node #/PortId   node id                                            node name --------------- -------------------------------------------------- ---------- D  4/         0 64:160:47.000000000000010001001010.00503efba601.00 LS-1010    2/    721408 64:160:47.000000000000010001008600.00d058ac2828.01 SES-3a S  1/  16848898 64:160:47.000000000000010002008850.00309409f6ba.01 m8850-7a node #/PortId   node id                                            node name --------------- -------------------------------------------------- ---------- D  4/         0 64:160:47.000000000000010001001010.00503efba601.00 LS-1010    3/  16848897 64:160:47.000000000000010002008950.0004c113ba46.01 m8950-7b S  1/  17569793 64:160:47.000000000000010002008850.00309409f6ba.01 m8850-7a m8850-7a.7.PXM.a > 

You can see in Example 11-32 that the source node is the MGX-8850 and the destination node is the LS-1010. There are two via-nodes in two equal-cost paths. One path traverses the SES-3a PNNI node, and the other path goes across the MGX-8950 PNNI node.

With the command cnfpnni-intf you can configure the class of service-based AW on a PNNI interface (see Example 11-33). You can increase the AW of the CBR service category in PnPort 1:1.2:2, connecting the MGX-8850 with the BPX-SES, and then check the path again.

Example 11-33. Configuring the AW for CBR Traffic on a Link

 m8850-7a.7.PXM.a > cnfpnni-intf 1:1.2:2 -awcbr 10000 m8850-7a.7.PXM.a > dsppnni-path aw cbr 4 node #/PortId   node id                                            node name --------------- -------------------------------------------------- ---------- D  4/         0 64:160:47.000000000000010001001010.00503efba601.00 LS-1010    3/  16848897 64:160:47.000000000000010002008950.0004c113ba46.01 m8950-7b S  1/  17569793 64:160:47.000000000000010002008850.00309409f6ba.01 m8850-7a m8850-7a.7.PXM.a > 

You can see in Example 11-33 that CBR connections now take a unique path through the via-node MGX-8950. The two paths toward the LS-1010 are now of unequal cost.

Finally, as Example 11-34 shows, you can decrease the AW of the CBR service category on the same interface and check the precomputed paths.

Example 11-34. Changing the AW for CBR Traffic

 m8850-7a.7.PXM.a > cnfpnni-intf 1:1.2:2 -awcbr 10 m8850-7a.7.PXM.a > dsppnni-path aw cbr 4 node #/PortId   node id                                            node name --------------- -------------------------------------------------- ---------- D  4/         0 64:160:47.000000000000010001001010.00503efba601.00 LS-1010    2/    721408 64:160:47.000000000000010001008600.00d058ac2828.01 SES-3a S  1/  16848898 64:160:47.000000000000010002008850.00309409f6ba.01 m8850-7a m8850-7a.7.PXM.a > 

The unique and different path that connections now take is through the SES-3a node.

All the routing information, including nodes, link states, and reachability information, is kept in the PNNI internal database. You can see the contents of the PNNI internal database using the command dsppnni-idb, as Example 11-35 shows. To narrow the command's output, you can see information for a specific node and a specific link. You gather the port ID in decimal notation corresponding to a specific PnPort using the command dsppnportidmaps.

Example 11-35. Viewing the PNNI Internal Database Using dsppnni-idb

 29 node index: 1    Local port id.......  16848898     Remote port id.......    262912    Local link index....         1     Remote link index....         1    Local node number...         1     Remote node number...         2    PGL node index......         0     LGN node index.......         0    Transit restricted..       off     Complex node.........       off    Branching restricted        on     PGL..................     false    Ancestor............     false     Border node..........     false    VP capable..........      true     Link type............horizontal    Non-transit for PGL election..       off    node id...............64:160:47.000000000000010002008850.00309409f6ba.01    node name.............m8850-7a                         forward direction                  CBR    RTVBR   NRTVBR      ABR      UBR               ------   ------   ------   ------   ------      AW         5040     5040     5040     5040     5040      MaxCR     96000    96000    96000    96000    96000      AvCR      93293    93293    93293    93293    93293      CTD          56       56       56      n/a      n/a      CDV          10       10      n/a      n/a      n/a      CLR0         10        8        6      n/a      n/a      CLR0+1        8        8        8      n/a      n/a      CRM         n/a      n/a      n/a      n/a      n/a      VF          n/a      n/a      n/a      n/a      n/a m8850-7a.7.PXM.a > 

The output of the command dsppnni-idb specified on a PNNI link shows the routing protocol's class-based nature, as well as its metric and QoS-based characteristics.

You can specify different node characteristics and link colors. To name a couple, a PNNI node has a transit-restricted flag advertised in the nodal info PTSE, and a PNNI link has a VP-capable flag.

Connection Tracing

The PNNI nodes provide connection-tracing capabilities for existing active connections. The connection trace information includes all nodes, cross-connecting ports, VPI/VCIin other words, the complete path. Path trace is a sibling tool that allows the user to see the path of a connection in the process of being established. The path-tracing tool also shows crankback information.

The connection-tracing tool is used with the combination of the commands conntrace and dspconntracebuffers, as you can see in Example 11-36.

Example 11-36. Using the Commands conntrace and dspconntracebuffers

 m8850-7a.7.PXM.a > conntrace 2:1.1:1 -vpi 100 -vci 100 m8850-7a.7.PXM.a > dspconntracebuffers -------------------------------- dspconntracebuffers: next record -------------------------------- Last update time: Mar 7 2002 19:46:31 Result: SUCCESS     Reason: N/A Incoming Port: 16914433   Physical PortId: 2:1.1:1 VPI   : 100   VCI: 100   CallRef: 8093 Node Name: m8850-7a NodeId: 80:160:47.000000000000010002008850.00309409f6ba.01 Outgoing Port: 16848898   Physical PortId: 1:1.2:2 VPI   : 0   VCI: 36   CallRef: 1 Node Name:  NodeId: 80:160:47.000000000000010001008600.00d058ac2828.01 Outgoing Port: 786944   VPI   : 100   VCI: 100   CallRef: 10   Physical PortId: 12.2 m8850-7a.7.PXM.a > 

You can display symmetric information by going to the other end of the connection and performing a connection trace. See Example 11-37.

Example 11-37. Connection Tracing

 SES-3a.1.PXM.a > conntrace 12.2 -vpi 100 -vci 100 SES-3a.1.PXM.a > dspconntracebuffer 12.2 100 100 Last update time: Mar 7 2002 7:17:20 Result: SUCCESS     Reason: N/A Incoming Port: 786944   Physical PortId: 12.2 VPI   : 100   VCI: 100   CallRef: 10 Node Name: SES-3a NodeId: 80:160:47.000000000000010001008600.00d058ac2828.01 Outgoing Port: 262912   Physical PortId: 4.3 VPI   : 0   VCI: 36   CallRef: 1 Node Name:  NodeId: 80:160:47.000000000000010002008850.00309409f6ba.01 Outgoing Port: 16914433   VPI   : 100   VCI: 100   CallRef: 8093   Physical PortId: 2:1.1:1 SES-3a.1.PXM.a > 

NOTE

In this section, we identified an SPVC connection for tracing by providing a port, VPI and VCI. For SVC connection tracing, however, we need to identify the SVC call using the call reference.

Route Optimization

PNNI provides per-link and per-VPI/VCI range schedulable route optimization features. The command cnfrteopt (see Example 11-38) configures the route optimization task. You can see this configuration with the command dsprteoptcnf.

Example 11-38. Route Optimization Using cnfrteopt

 m8850-7a.7.PXM.a > cnfrteopt 2:1.1:1 enable -tod 01:00..03:00 m8850-7a.7.PXM.a > dsprteoptcnf Configuration of Route Optimization: Percentage Reduction Threshold: 30 Port           Enable   VPI/VCI Range    Interval   Time Range 7.35           no 7.36           no 7.37           no 7.38           no 10.1           no 2:1.1:1        yes      all              60         01:00..03:00 m8850-7a.7.PXM.a > 

Alternatively, you can manually trigger the route optimization on a per-port, per-VPI/VCI range, or per-connection basis using the command optrte.

Preferred Routes

One of the most advanced traffic engineering features is the ability to specify a preferred route for an SPVC or SPVP connection. In essence, the user manually specifies the DTL to be used in the setup message. This allows the user to specify the nodes and links a connection should take.

As soon as a preferred route is specified, routing attempts for the connection try to route the connection via the preferred route before attempting any other routes. Generic CAC (GCAC) is checked for the preferred route to verify that the bandwidth requirements can be satisfied at that point in time. Depending on the directed route flag, further routing attempts might take place. When a route is marked as a directed route, the connection tries to route only on the specified preferred route. For nondirected routes, further routing attempts take place if the preferred route fails. This functionality is equivalent to AutoRoute preferred and directed routes.

The routes are stated as the full node/port combination that makes up the complete and fully specified path and are stored in the database. Because you specify the DTL, the preferred route can be specified within only a single peer group.

From a command-line interface perspective, the pref abbreviation creates the preferred route family of commands. The commands addpref, modpref, delpref, dsppref, and dspprefs manipulate the preferred routes. These commands are self-explanatory. The command cnfconpref associates and dissociates the created preferred routes with SPVC and SPVP connections such that many SPVCs can be associated with a single preferred route.