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Chapter 8 Wireless Configuration
ZyXEL NWA-3160 Series User’s Guide
106
ATC assigns priority based on packet size, since time-sensitive applications such as Internet 
telephony (Voice over IP or VoIP) tend to have smaller packet sizes than non-time sensitive 
applications such as FTP (File Transfer Protocol). The following table shows some common 
applications, their time sensitivity, and their typical data packet sizes. Note that the figures 
given are merely examples - sizes may differ according to application and circumstances.
When ATC is activated, the device sends traffic with smaller packets before traffic with larger 
packets if the network is congested. 
ATC assigns priority to packets as shown in the following table.
You should activate ATC on the ZyXEL Device if your wireless network includes networking 
devices that do not support WMM QoS, or if you want to prioritize traffic but do not want to 
configure WMM QoS settings. 
8.3.3  ATC+WMM
The ZyXEL Device can use a mapping mechanism to use both ATC and WMM QoS. The 
ATC+WMM function prioritizes all packets transmitted onto the wireless network using 
WMM QoS, and prioritizes all packets transmitted onto the wired network using ATC. See 
 for details of how to configure ATC+WMM.
Use the ATC+WMM function if you want to do the following: 
• enable WMM QoS on your wireless network and automatically assign a WMM priority to 
packets that do not already have one (see 
). 
• automatically prioritize all packets going from your wireless network to the wired network 
(see 
8.3.3.1  ATC+WMM from LAN to WLAN
ATC+WMM from LAN (the wired Local Area Network) to WLAN (the Wireless Local Area 
Network) allows WMM prioritization of packets that do not already have WMM QoS 
priorities assigned. The ZyXEL Device automatically classifies data packets using ATC and 
then assigns WMM priorities based on that ATC classification.
Table 28   Typical Packet Sizes
APPLICATION
TIME 
SENSITIVITY
TYPICAL PACKET SIZE 
(BYTES)
Voice over IP (SIP)
High
< 250
Online Gaming
High
60 ~ 90
Web browsing (http)
Medium
300 ~ 600
FTP
Low
1500
Table 29   Automatic Traffic Classifier Priorities
PACKET SIZE (BYTES)
ATC PRIORITY
1 ~ 250 
ATC_High
250 ~ 1100 
ATC_Medium
1100 + 
ATC_Low