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Information About Configuring Link Latency
Information About Configuring Link Latency
You can configure link latency on the switch to measure the link between an access point and the switch. You
can use this feature with all access points that are joined to the switch where the link can be a slow or unreliable
WAN connection.
TCP MSS
If the client's maximum segment size (MSS) in a Transmission Control Protocol (TCP) three-way handshake
is greater than the maximum transmission unit can handle, the client might experience reduced throughput
and the fragmentation of packets. To avoid this problem, you can specify the MSS for all access points that
are joined to the switch or for a specific access point.
When you enable this feature, the access point selects the MSS for TCP packets to and from wireless clients
in its data path. If the MSS of these packets is greater than the value that you configured or greater than the
default value for the CAPWAP tunnel, the access point changes the MSS to the new configured value.
Link Tests
A link test is used to determine the quality of the radio link between two devices. Two types of link-test
packets are transmitted during a link test: request and response. Any radio receiving a link-test request packet
fills in the appropriate text boxes and echoes the packet back to the sender with the response type set.
The radio link quality in the client-to-access point direction can differ from that in the access point-to-client
direction due to the asymmetrical distribution of the transmit power and receive sensitivity on both sides. Two
types of link tests can be performed: a ping test and a CCX link test.
With the ping link test, the controller can test link quality only in the client-to-access point direction. The RF
parameters of the ping reply packets received by the access point are polled by the controller to determine the
client-to-access point link quality.
With the CCX link test, the switch can also test the link quality in the access point-to-client direction. The
switch issues link-test requests to the client, and the client records the RF parameters (received signal strength
indicator [RSSI], signal-to-noise ratio [SNR], and so on) of the received request packet in the response packet.
Both the link-test requestor and responder roles are implemented on the access point and switch. Not only
can the access point or switch initiate a link test to a CCX v4 or v5 client, but a CCX v4 or v5 client can
initiate a link test to the access point or switch.
The switch shows the link-quality metrics for CCX link tests in both directions (out— the access point to the
client; in— the client to the access point):
• Signal strength in the form of RSSI (minimum, maximum, and average)
• Signal quality in the form of SNR (minimum, maximum, and average)
• Total number of packets that are retried
• Maximum retry count for a single packet
• Number of lost packets
• Data rate of a successfully transmitted packet
Lightweight Access Point Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
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Configuring Link Latency
OL-28697-01
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