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Resource-Based CAC 621

for DSBM status. The maximum configurable priority value is 128, however, so another interface configured with a higher priority could win the election and become the DSBM.

Table 8-23 lists the commands used to enable and define the DSBM in Example 8-20, which also shows the example SBM configuration.

Table 8-23 SBM Commands

Command

Mode and Function

 

 

ip rsvp bandwidth

Enables RSVP on an interface

 

 

ip rsvp dsbm candidate [priority]

Configures the interface to participate as a contender in

 

the DSBM dynamic election process, whose winner is

 

based on the highest priority

 

 

ip rsvp dsbm non-resv-send-limit rate

Configures the average rate, in kbps, for the DSBM

kbps

candidate

 

 

ip rsvp dsbm non-resv-send-limit burst

Configures the maximum burst size, in KB, for the

kilobytes

DSBM candidate

 

 

ip rsvp dsbm non-resv-send-limit peak

Configures the peak rate, in kbps, for the DSBM

kbps

candidate

 

 

Example 8-20 Enabling DSBM on an Ethernet Interface

interface Ethernet2

ip address 145.2.2.150 255.255.255.0 no ip directed-broadcast

ip pim sparse-dense-mode no ip mroute-cache media-type 10BaseT

ip rsvp bandwidth 7500 7500 ip rsvp dsbm candidate 100

ip rsvp dsbm non-resv-send-limit rate 500 ip rsvp dsbm non-resv-send-limit burst 1000 ip rsvp dsbm non-resv-send-limit peak 500

Monitoring and Troubleshooting RSVP

This section covers a few details about the commands used to troubleshoot RSVP installations. Table 8-24 lists other RSVP commands that can be useful in monitoring and troubleshooting RSVP.

622 Chapter 8: Call Admission Control and QoS Signaling

Table 8-24 RSVP Monitoring and Troubleshooting Commands

Command

Mode and Function

 

 

show ip rsvp neighbor [interface-type

Displays current RSVP neighbors

interface-number]

 

 

 

show ip rsvp request [interface-type

Displays RSVP-related request information being

interface-number]

requested upstream

 

 

show ip rsvp reservation [interface-type

Displays RSVP-related receiver information currently

interface-number]

in the database

 

 

show ip rsvp sbm [detail] [interface-name]

Displays information about a SBM configured for a

 

specific RSVP-enabled interface or for all RSVP-

 

enabled interfaces on the router

 

 

show ip rsvp sender [interface-type

Displays Resource Reservation Protocol (RSVP)

interface-number]

PATH-related sender information currently in the

 

database

 

 

Verifying synchronization is the first step in troubleshooting RSVP. Without synchronization, RSVP has no means to prevent an H.323 gateway from moving into the alerting state and consuming resources that may not be available. To verify synchronization, use the show call rsvp-sync conf command.

Example 8-21 shows the output from the show call rsvp-sync conf command.

Example 8-21 The show call rsvp-sync Command

Router# show call rsvp-sync conf

VoIP QoS: RSVP/Voice Signaling Synchronization config:

Overture Synchronization is ON

Reservation Timer is set to 10 seconds

This output tells you that synchronization is enabled and the reservation timer will wait a maximum of 10 seconds for a reservation response.

To display statistics for calls that have attempted RSVP reservation, use the show call rsvpsync stats command.

Example 8-22 shows a sample output from the show call rsvp-sync stats command.

Example 8-22 The show call rsvp-sync stats Command Output

Router# show call rsvp-sync stats

 

VoIP QoS:Statistics Information:

 

 

 

 

Number of calls for which QoS

was initiated :

18478

Number

of

calls

for which

QoS

was torn down :

18478

Number

of

calls

for which

Reservation Success

was notified : 0

 

 

 

 

 

 

 

Resource-Based CAC 623

Example 8-22 The show call rsvp-sync stats Command Output (Continued)

Total Number of PATH Errors encountered : 0

Total Number of RESV Errors encountered : 0

Total Number of Reservation Timeouts encountered : 0

The show call rsvp-sync stats command offers a quick glance at reservation successes and failures on the router. A high number of errors or timeouts may indicate a network or configuration issue.

You can use the show ip rsvp installed command to display information about local interfaces configured for RSVP and the current reservations on the interfaces. In Example 8-23, the show ip rsvp installed command shows that Ethernet interface 2/1 has four reservations but serial interface 3/0 has none.

Example 8-23 The show ip rsvp installed Command

Router# show ip rsvp installed

RSVP:Ethernet2/1

BPS To From Protoc DPort Sport Weight Conversation 44K 145.20.0.202 145.10.0.201 UDP 1000 1000 0 264 44K 145.20.0.202 145.10.0.201 UDP 1001 1001 13 266 98K 145.20.0.202 145.10.0.201 UDP 1002 1002 6 265 1K 145.20.0.202 145.10.0.201 UDP 10 10 0 264 RSVP:Serial3/0 has no installed reservations Router#

The current amount of reserved bandwidth for this interface is 187 kbps, as shown in the following:

44 kbps + 44 kbps + 98 kbps + 1 kbps = 187 kbps

With this information, you have the ability to compare the actual bandwidth reserved versus the maximum bandwidth configured on Ethernet 2/1 using the ip rsvp bandwidth command. Reserved bandwidth approaching the maximum can result in RSVP rejections.

You can obtain more detail about current reservations with the show ip rsvp installed detail command. Example 8-24 shows an output of this command.

Example 8-24 Sample show ip rsvp installed detail Command Output

Router# show ip rsvp installed detail

RSVP:Ethernet2/1 has the following installed reservations

RSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201, Protocol is UDP, Destination port is 1000, Source port is 1000

Reserved bandwidth:44K bits/sec, Maximum burst:1K bytes, Peak rate:44K bits/sec Resource provider for this flow:

WFQ on hw idb Se3/0: PRIORITY queue 264. Weight:0, BW 44 kbps

continues

624 Chapter 8: Call Admission Control and QoS Signaling

Example 8-24 Sample show ip rsvp installed detail Command Output (Continued)

Conversation supports 1 reservations

Data given reserved service:316 packets (15800 bytes) Data given best-effort service:0 packets (0 bytes) Reserved traffic classified for 104 seconds

Long-term average bitrate (bits/sec):1212 reserved, 0M best-effort RSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201, Protocol is UDP, Destination port is 1001, Source port is 1001

Reserved bandwidth:44K bits/sec, Maximum burst:3K bytes, Peak rate:44K bits/sec Resource provider for this flow:

WFQ on hw idb Se3/0: RESERVED queue 266. Weight:13, BW 44 kbps

Conversation supports 1 reservations

Data given reserved service:9 packets (450 bytes)

Data given best-effort service:0 packets (0 bytes)

Reserved traffic classified for 107 seconds

Long-term average bitrate (bits/sec):33 reserved, 0M best-effort

RSVP Reservation. Destination is 145.20.0.202, Source is 145.10.0.201,

Protocol is UDP, Destination port is 1002, Source port is 1002

Router#

In this example, the reservation on Ethernet 2/1 has met the criteria of the voice-like profile and has been admitted into the priority queue. (A weight of 0 identifies the flows that have matched the voice-like profile.) The reservation on Serial 3/0 has not met the criteria of the voice-like profile and so has been admitted to a reserved WFQ.

RSVP CAC Summary

Remember the following factors regarding the use of RSVP as a CAC mechanism:

In current Cisco IOS Software, H.323 synchronization is initiated by default.

RSVP packets (path and resv) travel as best-effort traffic.

WFQ must be enabled on an interface/PVC as a basis for LLQ.

RSVP is a true end-to-end CAC mechanism only if configured on every interface that a call traverses.

For the unique capability to serve as both an end-to-end CAC mechanisms, and to guarantee the QoS for the entire duration of the call, RSVP does incur some “costs” on the network, as follows:

Signaling (messaging and processing).

Per flow state (memory).

Postdial delays.

Resource-Based CAC 625

RSVP does not provide for call redirection after call setup if a link in the network should fail. Another mechanism, such as dial-peer preferences, must be configured to serve this function.

RSVP is not yet supported on the Cisco IP Phones.

Table 8-25 evaluates the RSVP mechanism against the CAC evaluation criteria described earlier in this chapter.

Table 8-25 RSVP CAC Evaluation Criteria

Evaluation Criteria

Value

 

 

VoX supported

VoIP/H.323 only

 

 

Toll bypass or IP telephony

Currently Toll bypass only

 

 

Platforms and releases

Cisco IOS gateways in Release 12.1(5)T and 12.2

 

 

PBX trunk types supported

All

 

 

End to end, local, or IP cloud

End to end between originating gateway and terminating

 

gatekeeper (provided all intermediate nodes are RSVP

 

configured)

 

Could be used at WAN edge with DiffServ backbone

 

 

Per call, interface, or endpoint

Per call

 

 

Topology awareness

Yes

 

 

Guarantees QoS for duration of call

Yes

 

 

Postdial delay

Yes

 

 

Messaging network overhead

Path/resv and periodic keepalives