Limit on AP latency

[Chris Hunter]

Hi - Im looking at running Aironet APs at remote sites. I would like to know if there are any latency limits or other factors that I need to look into when running APs from a centralized controller.

[Philip91]

Hi Chris,

Here are the recommendations about Flexconnect and WAN Links:

Deployment Considerations

The following section covers the various implementation and operational caveats associated with deploying FlexConnect APs.

WAN Link

For the FlexConnect AP to function predictably, keep in mind the following with respect to WAN link characteristics:

• Latency—A given WAN link should not impose latencies greater than 100 ms. The AP sends heartbeat messages to the WLC once every thirty seconds. If a heartbeat response is missed, the AP sends five successive heartbeats (one per second) to determine whether connectivity still exists. If connectivity is lost, the FlexConnect AP switches to standalone mode (see Operation Modes for operation mode definitions). The AP itself is relatively delay tolerant. However, at the client, timers associated with authentication are sensitive to link delay, and thus a constraint of < 100 ms is required. Otherwise, the client can time-out waiting to authenticate, which can cause other unpredictable behaviors, such as looping.
• Bandwidth—WAN links should be at least 128 kbps for deployments when up to eight APs are being deployed at a given location. If more than eight APs are deployed, proportionally more bandwidth should be provisioned for the WAN link.
• Path MTU—An MTU no smaller than 500 bytes is required.

 

http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/emob73dg/emob73/ch7_HREA.html#pgfId-1108009

Hope that helps...

Kind regards

Philip

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[Abhishek Abhishek]

Cisco strongly recommends that appropriate queuing/policing mechanisms be implemented across the WAN to ensure proper handling of traffic based on its DSCP setting. An appropriate priority queue should be reserved for CAPWAP control traffic to ensure that a FlexConnect AP does not inadvertently cycle between connected and standalone modes because of congestion.

Primary Design Requirements

FlexConnect APs are deployed at the Branch site and managed from the Data Center over a WAN link. It is highly recommended that the minimum bandwidth restriction remains 12.8 kbps per AP with the round trip latency no greater than 300 ms for data deployments and 100 ms for data + voice deployments (see Table 7-4 ). The maximum transmission unit (MTU) must be at least 500 bytes.

Table 7-4 Bandwidth Minimums

Deployment Type	WAN Bandwidth (Min)	WAN RTT Latency (Max)	APs per Branch (Max)	Clients per Branch (Max)
Data	64 kbps	300 ms	5	25
Data + Voice	128 kbps	100 ms	5	25
Monitor	64 kbps	2 sec	5	N/A
Data	640 kbps	300 ms	50	1000
Data + Voice	1.44 Mbps	100 ms	50	1000
Monitor	640 kbps	2 sec	50	N/A

The primary design requirements are:

• Branch size that can scale up to 100 APs and 250,000 square feet (5000 square feet per AP)
• Central management and troubleshooting
• No operational downtime
• Client-based traffic segmentation
• Seamless and secured wireless connectivity to corporate resources
• PCI compliant
• Support for guests