H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 664)

643
delivers packets to their destinations as best it can, without any guarantee for such issues as delay, jitter,
packet loss ratio, and reliability.
This service policy is only suitable for applications insensitive to bandwidth and delay, such as WWW,
file transfer and email.
New requirements from new applications
The Internet has been growing along with the fast development of networking technologies. More and
more users take the Internet as their data transmission platform to implement various applications.
Besides traditional applications such as WWW, email and FTP, network users are implementing new
services, such as tele-education, telemedicine, video telephone, videoconference and Video-on-Demand
(VoD). The enterprise users expect to connect their regional branches together through VPN technologies
to carry out operational applications (for example, to access the database of the company or to monitor
remote devices through Telnet).
These new applications have one thing in common, and they all have special requirements for
bandwidth, delay, and jitter. For instance, videoconference and VoD need large bandwidth, low delay,
and low jitter. Mission-critical applications, such as transactions and Telnet, may not require large
bandwidth but require low delay and preferential service during congestion.
The new emerging applications require higher service performance of IP networks. Required network
services during packet forwarding include providing dedicated bandwidth, reducing packet loss ratio,
managing and avoiding congestion, regulating network traffic, and setting the precedence of packets.
To meet these requirements, networks must provide improved services.
For more information about QoS, see ACL and QoS Configuration Guide.
Configuration guidelines
When you configure an ACL and QoS, follow these guidelines:
• You cannot add an ACL rule with, or modify a rule to have, the same permit/deny statement as an
existing rule in the ACL.
• You can only modify the existing rules of an ACL that uses the match order of config. When
modifying a rule of such an ACL, you can choose to change just some of the settings, in which case
the other settings remain the same.
• When you configure rate limit and traffic policing for a behavior, make sure the ratio of CBS to CIR
is more than 100:16. Otherwise, the handling for bursty traffic might be affected.
• If an ACL is referenced by a QoS policy for defining traffic classification rules, the operation of the
QoS policy varies by interface (the definition of software/hardware interface varies with device
models). The specific process is as follows:
If the QoS policy is applied to a software interface and the referenced ACL rule is a deny clause,
the ACL rule does not take effect and packets go to the next classification rule.
If the QoS policy is applied to a hardware interface, packets matching the referenced ACL rule
are organized as a class and the behavior defined in the QoS policy applies to the class
regardless of whether the referenced ACL rule is a deny or permit clause.
• If a QoS policy is applied in the outbound direction of a port, the QoS policy cannot influence local
packets. Local packets refer to the important protocol packets that maintain the normal operation of
the device. QoS must not process such packets to avoid packet drop. Commonly used local packets
are: link maintenance packets, ISIS packets, OSPF packets, RIP packets, BGP packets, LDP packets,
RSVP packets, and SSH packets and so on.