Understanding Quality of Service

Quality of Service (QoS) refers to the ability of a network to offer an enhanced level of service to certain types of traffic. For example, Voice-over-IP (VoIP) traffic requires lower latency and jitter than web and e-mail traffic. Multapplied SD-WAN can be used to implement almost any type of traffic management strategy. 

The following table shows the sensitivity of some common applications to network bandwidth, latency, and jitter. 


applications table

A network with ideal QoS would give each application the level of service it required, even when more than one application is active on the network. For example, VoIP traffic would receive low-latency, low-jitter service while web browsing traffic receives high-bandwidth service. 

One default profile comes pre-installed with Multapplied SD-WAN. This profile offers great performance for most networks. It has four service levels, as follows: 


40% of bandwidth is reserved for real-time traffic. 

The following packets are classified as real-time: 

  1. ICMP packets up to 500 bytes 
  2. Inter-Asterisk eXchange version 2 (IAX2) traffic 
  3. SIP and H.323 control traffic 
  4. Packets with DSCP expedited forwarding requested 

This profile will classify VoIP traffic correctly on networks using IAX2 or phones that send traffic with the DSCP expedited forwarding class. On other networks, it may be necessary to identify VoIP traffic using source or destination network matching. 


20% of bandwidth is reserved for interactive traffic, classified as follows: 

  1. DNS traffic 
  2. Microsoft RDP traffic 
  3. TCP acknowledgements 
  4. SSH traffic. (To avoid classifying SCP traffic as interactive, SSH is limited to 20 packets per second per connection.) 

This is the default class. Packets not matching any filter are classified as routine. 20% of bandwidth is reserved for this traffic. 


20% of bandwidth is reserved for bulk traffic, classified as follows. 

  1. FTP traffic On ports 20, 21 only; data traffic on other ports will not be matched. 
  2. HTTP/S traffic part of flows greater than 2 MB