Oversubscription - Distribution switching - WLAN

[jean-francois.suret]

Hi All,

Cisco guidance often mentions the use of 20:1 over-subscription for Campus LAN / Access switches (https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Campus/HA_campus_DG/hacampusdg.html#wp1108631)

However , the document is dated from 2008, and does not describe potential WLAN scenarios.

Is such guidance still applicable when endpoints are Wireless Access point ?

Are there any "official" supporting document describing this ? ( and potentially depending on the density of users per WAP ?)

Best Regards

[Reza Sharifi]

Hi,

Not sure if I have seen an official document on this as every environment is different, and as you said, it depends on the number of APs you have and the density per AP. One thing for sure is that the speed of the wireless is continuously growing and these days you find APs with multiple one Gig copper and soon if not already out APs with 10gig interfaces.  The other big factor is your Internet speed, if your Internet speed is at 100Mb, it really doesn't matter if the interface to the APs is one 1Gig or multiple as the 100Mb Internet access is your chock point. Anyway, if you are connecting access to distro or core switches in a redundant environment, use Portchannels and start with 2 10Gigs uplinks and added more links as needed.

HTH 

[Joseph W. Doherty]

I don't know of any "official" documentation, but if you treat the number of wireless hosts as you might wired hosts off the same port (i.e. off a downstream switch), you'll probably be in the right ballpark.

As to recommendations like 20:1, you must take that with a large grain of salt. As host NICs have gone from 10Mbps to 100Mbps to gig (also keep in mind, generally wireless hosts have much less bandwidth), traffic to/from those hosts have not also increased by 100x (altough it has increased).

[Deepak Kumar]

Hi,

I have also seen the same but seems outdated. We (me and my team) considering AP's maximum speed or Switch interface Maximum speed, any of lower will choose as highest speed used by the per AP. 

I never referred to the Client's count on per AP because Wireless is working on the half duplex and per AP is having its maximum capacity as well.

While designing a Small or mid-size network, I always try to reach about 20:1 to 35:1 oversubscription on access switches (as per requirement & resources) and 10:1 to 20:1 on the Core switch and finally 6:1 to 10:1 on the Server farm.

Sometimes, we are considering the Internet speed as well but keep in mind that you have 20 to 30% traffic for the Internet only (if you have facilities as Servers (ERP, DNS, Application etc) in your rack). I know it is getting change and we are moving to cloud and hybrid cloud. Same time Internet, LAN and intranet speed is also getting an increase. 

Keep in mind that this is a basic Idea and it will change as per the client's requirement and resource availability.

Regards,

Deepak Kumar