ZyXEL Communications ISG50 User Manual

 Chapter 25 Bandwidth Management

ISG50 User’s Guide

Server A has a configured rate that equals the total amount of available bandwidth and a higher 
priority. You should regard extreme over allotment of traffic with different priorities (as shown here) 
as a configuration error. Even though the ISG50 still attempts to let all traffic get through and not 
be lost, regardless of its priority, server B gets almost no bandwidth with this configuration.    

• See 

 for an example of how to set up web surfing policies with bandwidth 

restrictions.

• See 

 for a description of DSCP marking.

Bandwidth management is very useful when applications are competing for limited bandwidth. For 
example, say you have a WAN zone interface connected to an ADSL device with a 8 Mbps 
downstream and 1 Mbps upstream ADSL connection. 

Here is an overview of what the rules need to accomplish. See the following sections for more 
details.

• SIP traffic from VIP users must get through with the least possible delay regardless of if it is an 

outgoing call or an incoming call. The VIP users must be able to make and receive SIP calls no 
matter which interface they are connected to. 

• HTTP traffic needs to be given priority over FTP traffic.
• FTP traffic from the WAN to the DMZ must be limited so it does not interfere with SIP and HTTP 

traffic.

Priority and Over Allotment of Bandwidth Effect

A

1000 kbps

Yes

1

999 kbps

B

1000 kbps

Yes

2

1 kbps