QoS matching for VoIP

April 18th, 2008

Voice over IP is, as you know for sure, very time-sensitive traffic. That is why VoIP signaling and payload traffic should receive enough bandwidth and as less jitter and delay as possible.

QoS is an important tool to assign VoIP traffic more preference over “normal” traffic. Important for QoS tools to function correctly is placing different kinds of traffic in different queues. To place traffic in different queues, traffic should be classified. All VoIP traffic should be classified and placed in the same queue or given the same priority. I usually use the following ACL’s to match VoIP signaling and payload traffic.

VOIP SIGNALING


ip access-list extended VOIP-SIGNALING
  permit tcp any any eq 1720
  permit tcp any any range 11000 11999
  permit udp any any eq 2427
  permit tcp any any eq 2428
  permit tcp any any range 2000 2002
  permit udp any any eq 1719
  permit udp any any eq 5060

VOIP PAYLOAD


ip access-list extended VOIP-PAYLOAD
  permit udp any any range 16384 32767

The following table gives some basic explanations for the different permit statements:

Protocol	Matching criteria
H.323 / H.225	TCP/1720
H.323 / H.245	TCP/11xxx
Media Gateway Control Protocol (MGCP)	UDP/2427 and TCP/2428
Skinny Client Control Protocol (SCCP)	TCP/2000-2002
Simple Gateway Control Protocol (SGCP)	TCP/2000-2002
H.323 / H.225 RAS	TCP/1719
Session Initiation Protocol	UDP/5060
Real-Time Transport Protocol (RTP)	UDP/16384-32767, even ports only
Real-Time Control Protocol (RTCP)	UDP/16384-32767, odd ports only

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