IP SLA has the ability to measure "real-time" WAN connection quality. You can then use the results of the measurement for routing decisions (such as choosing an alternate path). This is especially effective for VoIP connections. The following sample configuration can be used to create a IP SLA Jitter/Packet Loss monitor for use with VoIP deployments:

IP SLA Source

Source(config)#ip sla 100  !Some IOS versions use ip sla monitor
Source(config-ip-sla)#udp-jitter 172.16.1.2 65424 codec g729a
Source(config-ip-sla-jitter)#tos 176 !Marks packets with DSCP EF (IP Precedence 5)
Source(config-ip-sla-jitter)#exit
Source(config)#ip sla schedule 100 recurring start-time now
Source(config)#interface s0/1/0
Source(config-if)#ip address 172.16.1.1 255.255.255.0

IP SLA Responder

Responder(config)#ip sla responder !Some IOS versions use ip sla monitor
Responder(config)#interface s0/1
Responder(config-if)#ip address 172.16.1.2 255.255.255.0