User's Manual

SPEEDLAN 9200 User Guide Part # 34357-MNL Rev.03
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1 Select Enabled or Disabled.
2 Click Apply.
Explanation of this feature
Despite having two physical interfaces, a SPEEDLAN 9200 router can experience
congestion. That is because the interfaces' bit rates are not matched. Specifically,
packets can ingress (enter) the Ethernet interface faster than they can egress (exit) the
wireless interface. If this occurs briefly, it is called short-term congestion, which can
cause increased packet delay and/or jitter. If congestion lasts too long, it can cause
packet discard ("loss"). Long-term congestion in a SPEEDLAN 9200 will typically only
occur when it receives excessive unthrottled UDP traffic at its Ethernet interface. TCP
traffic will self-throttle, typically experiencing only short-term congestion, if any.
A SPEEDLAN 9200 mitigates short-term congestion by providing priority egress
queuing at its wireless interfaces. With priority queuing, packets may be transmitted in a
different order than they were received. This allows favoring network management,
VoIP, and SCADA over SMTP, ftp, and NNTP (for example).
How does Priority Queuing work? The packets are prioritized into a hierarchy of
queues, based on class of traffic. The highest priority queue packets are serviced first.
When the highest queue is emptied, the next lower queue is serviced. The SPEEDLAN
9200 has four levels of priority queues. Queue 1 (the highest queue serviced) contains
"management" traffic (i.e., RIP, Mesh, K2, SNMP). Queue 2, the next lower queue
serviced, contains "real-time" traffic (i.e., VOIP, Video, SCADA). Queue 3, the next
lower queue serviced, contains "non-real time interactive" traffic (i.e., HTTP, SSH and
Telnet). Queue 4 (the lowest level queue serviced) contains all traffic that doesn't fit into
one of the first three queues.
Services
Network "Services" describe specific sessions between clients and servers, servers and
servers, or clients and clients on your network. Examples of servers that provide
services are web servers, FTP servers and email servers. Service definitions allow you to
forward public services inward to the internal (privately addressed) servers on your
network.