My client has imoplemented A Telstra IP Telephony (TIPT) solution with Polycom handsets at all sites, and Telephony service in the Telstra cloud. For the most part, it is working fine, with DSCP markings on voice and call signaling streams. We have implemented outbound QoS policies at the WAN edge. There are a couple of sites where voice quality can regularily be poor (lost bits of voice). We do not see any dropped voice packets in the policy. We have identify that this seems to occur at the same time a site is receving large email flows (SMTP inbuond, Notes 1352 traffic in and outbound). Within in the QoS policy, we have shaped this mail traffic to a peak value in an attempt to mitigate it from utilizing all of the bandwidth. I have been runing NBAR on the WAN interface of the worst effected site, and can see that the 5min Max Bit Rate on SMTP(Input) and Notes (Input and Output) have reached 75% of the actual bandwidth, which also exceeds the peak rate configured in the policy by more than double.
How can I improve the voice quality and what am I doing wrong such that mail traffic is not been limited to the peak rate?
description Telstra BDSL TPIPS Access
ip address 172.16.254.41 255.255.255.252
ip nbar protocol-discovery
rate-limit output 512000 512000 512000 conform-action transmit exceed-action drop
ip ospf network point-to-point
service-policy output TPIPS
shape peak 128000
shape peak 128000
class-map match-all IPWAN_mail
match access-group 101
class-map match-all HTTP
match access-group 151
class-map match-all Telnet
match access-group 100
class-map match-any Voice
match dscp ef
match access-group name Voice
class-map match-any Voice-ctrl
match dscp af31
match access-group name Voice-ctrl
access-list 101 permit tcp host 172.16.4.254 eq smtp any
access-list 101 permit tcp host 172.16.4.254 eq 1352 any
access-list 101 permit tcp host 172.16.4.254 any eq 1352
access-list 101 permit tcp host 172.16.4.254 any eq smtp
Your config shapes outbound traffic from your gateway, and doesn't have any impact on inbound traffic. If the Telstra backbone is not performing similar outbound shaping on its connection to the site then you will find that traffic in that direction (WAN to remote site) is not being subjected to QoS and can result in the symptoms that you are seeing. Remember that voice is full duplex and requires QoS in each direction.
In order for QoS to really work, it needs to be performed end to end - and unfortunately in this instance it also needs your carrier to do it as well on each of their nodes.
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