how to avoid voip jitter

hi, guys.

Recently I was trying to implement an IP PBX for my company, but I stuck by the jitter issue.

I have a cisco 1760 router with a 10baset WIC-1ENET card, and a cisco

2560G switch, data on vlan1 (native) , voice on vlan2. Already applied Qos on the router.

Everything went good at first, but when I was trying to download a big file from the internet, things happened.

Here's how I did, I made a call from a ip phone to a landline phone, then put the line onhold, landline phone user can hear the on hold music, then I started to download a big file from internet, the landline user will hear music became jitter.

Cant find a way to avoid it, any advice?

Thanks in advance.

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Be sure to implement CBWFQ/LLQ on the output queue of your serial links. We utilize the exact same platform in part of our network, and I can tell you that we can absolutely bury a T1 without any side effects to the VoIP stream. We might see jitter increase by a millisecond or two, but the overall jitter numbers are just that - less than a handful (<

5ms). We routinely see jitter numbers of < 1 ms. Forty (40) ms is your jitter budget.

This is one thing Cisco can do well, as they have superb packet scheduling capabilities in IOS. Do a search on CCO for "CBWFQ/LLQ". Keep it simple, and don't create more than 3 or four total traffic classes. Utilize the VoIP examples they list.

Failing that, post your QoS config. Rest assured, though, what you're trying to do is not unreasonable, and done daily in production networks.

Good luck!

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On Sep 25, 4:54=A0pm, fugettaboutit wrote:

Hi, fugettaboutit, thanks for the input, here is my startup-config:

Building configuration... Current configuration : 3394 bytes ! version 12.4 service timestamps debug datetime msec service timestamps log datetime msec service password-encryption ! hostname DC1760 ! boot-start-marker boot-end-marker ! no logging buffered enable secret 5 $1$c2hG$1vueVcFX1/Rqdwg3uXxZu1 ! no aaa new-model ! resource policy ! clock timezone Pacific -8 clock summer-time Pacific date Apr 6 2003 2:00 Oct 26 2003 2:00 mmi polling-interval 60 no mmi auto-configure no mmi pvc mmi snmp-timeout 180 ! ! no ip dhcp use vrf connected ip dhcp excluded-address ip dhcp excluded-address ip dhcp excluded-address ! ip dhcp pool 1_0 network dns-server default-router ! ip dhcp pool 2_0 network dns-server default-router ! ! ip cef ip ftp username anonymous ip name-server ip name-server ! ! ! ! ! ! class-map match-any SDM-Transactional-1 match protocol citrix match protocol finger match protocol notes match protocol novadigm match protocol pcanywhere match protocol secure-telnet match protocol sqlnet match protocol sqlserver match protocol ssh match protocol telnet match protocol xwindows class-map match-any SDM-Signaling-1 match protocol h323 match protocol rtcp match protocol sip class-map match-any SDM-Routing-1 match protocol bgp match protocol egp match protocol eigrp match protocol ospf match protocol rip match protocol rsvp class-map match-any SDM-Voice-1 match protocol rtp audio class-map match-any SDM-Management-1 match protocol dhcp match protocol dns match protocol imap match protocol kerberos match protocol ldap match protocol secure-imap match protocol secure-ldap match protocol snmp match protocol socks match protocol syslog ! ! policy-map SDM-QoS-Policy-1 class SDM-Voice-1 set dscp ef priority percent 55 class SDM-Signaling-1 set dscp cs3 bandwidth percent 5 class SDM-Routing-1 set dscp cs6 bandwidth percent 5 class SDM-Management-1 set dscp cs2 bandwidth percent 5 class SDM-Transactional-1 set dscp af21 bandwidth percent 5 class class-default fair-queue random-detect ! ! ! ! ! interface FastEthernet0/0 no ip address speed auto ! interface FastEthernet0/0.1 encapsulation dot1Q 1 native ip address ip nat inside ip virtual-reassembly no snmp trap link-status ! interface FastEthernet0/0.2 encapsulation dot1Q 2 ip address ip nat inside ip virtual-reassembly no snmp trap link-status ! interface FastEthernet0/0.3 description $ETH-LAN$ encapsulation dot1Q 3 ip address ip nat inside ip virtual-reassembly no snmp trap link-status ! interface Ethernet1/0 description $ETH-WAN$ ip address 74.xx.xx.78 ip nbar protocol-discovery ip nat outside ip virtual-reassembly full-duplex service-policy output SDM-QoS-Policy-1 ! ip route 74.xx.xx.73 ip http server no ip http secure-server ! ip nat inside source list 1 interface Ethernet1/0 overload ip nat inside source static 74.xx.xx.76 ! ip dns server ! access-list 1 remark SDM_ACL Category=3D2 access-list 1 permit access-list 1 permit access-list 1 permit ! ! control-plane ! ! line con 0 line aux 0 line vty 0 4 login ! end

I have to say this network is my test environment, so we dont have serial port on 1760, I just connect my wic-1enet card to my netpioa T1 router's ethernet port, dont know whether this will cause the issue.

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