2600 AP throughput with Client Link 2.0

[lee.messenger]

Hi,

Can someone please clarify the maximum throughput of a 2600 AP when using CLient Link 2.0.  I see that the datasheet states that it is 450mbps, however,  from my understanding of transmit beamforming (client link 2.0), when traffic is "beamformed" to a client it cannot use spatial multiplexing on

the same antenna as well.  If this is the case, with the 2600 only having 3 transmit antennas,  does this mean that the max throughput to a client when using clientlink is 300mb ?

If not, can someone explain how the AP transmit at 450mbps and beamforms at the same time

Thanks

[Saravanan Lakshmanan]

Beamforming applicable only on legacy devices A/G not for N using HT.

•Beamforming is supported only for legacy orthogonal frequency-division multiplexing (OFDM) data rates (6, 9, 12, 18, 24, 36, 48, and 54 Mbps).

http://www.cisco.com/en/US/docs/wireless/controller/6.0/configuration/guide/c60rrm.html#wp1283389

[lee.messenger]

HI Saravan.

I believe that CLient link version 2 will support 802.11n clients as per the data sheet

http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps12534/data_sheet_c78-709514.html

Cisco ClientLink 2.0 technology to improve  downlink performance and range for all mobile devices, including one-,  two-, and three- spatial stream devices on 802.11n, while improving  battery life on mobile devices such as smartphones and tablets.

Please advise

Thanks

[Scott Fella]

Clientlink in general helps in a mixed environment but has no impact on clients that can connect to 300mps or 450mbps. Many devices that has 2x2 can achieve up to 300mbps on the 5ghz and 3x3 wireless adapters can achieve up to 450mbps. This is achieved by bonding channels and spatial streams. Just remember that clientlink helps devices achieve better data rates at the cell boundaries not if your 5' from the ap.

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[lee.messenger]

Hi Scott,

I understand your answer,  my question would be when does the AP chose to "beamform" and when not, is there some specific criteria it uses.  My understanding is that it does this all the time, and therefore, if it does, from my understanding, this would use up one of the antennas and therefore for the 2600 AP, this would reduce the maximum achievable transmit data rate to 300Mbps. (3 tx antennas 1 for beamform, 2 for spatial multiplexing).

Thanks

[Saravanan Lakshmanan]

when does the AP chose to "beamform" and when not, is there some specific criteria it uses?

I think Scott explained it above, beamforming is not used for the client close to AP or when client hearing AP at good signal and or achiving max available datarate. And beamforming is only for the client having hard time hearing AP or using lower datarate.

Spatial Multiplexing and ClientLink are mutually exclusive technologies:

Although the Access Point’s radio can’t perform Spatial Multiplexing and Beam Forming at the same instance in time, both technologies are leveraged to deliver benefits. When transmitting to an good client, Spatial Multiplexing is used to transmit a unique data stream (also called a spatial stream) on each transmit antenna. When transmitting to edge/affected client, ClientLink uses all antennas again but this time in a different manner by transmitting the same data stream out of 3 antennas but with one/two granularly adjusted in phase to create a gain in a particular direction towards the client.

[Scott Fella]

There is no need to beamform if a device is close to the AP. the 2600 is. 3x4x3 which means three transmit, four receive and three spatial streams. Thus how you can achieve up to 450mbps. A 3602 is 4x4x3 and also can achieve up to 450mbps. Of course not many client devices can support 450mbps. Don't look at clientlink, just research beamforming if you want I understand it better.

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[lee.messenger]

I was researching beamforming and came across the following information(below), which prompted me to ask the question here

If the below is correct, then is it also correct to say that the 2600 with client link 2.0 enabled has a max transmit capability of 300mbps and max receive capability of 450mbps ?

Thanks

From

http://www.digitalairwireless.com/wireless-blog/recent/transmit-beamforming-txbf-explained.html

So when is transmit beamforing actually used in an access point?   Well some vendors do not support this feature in their access point.  I  dont have a list of thsoe that do, but i know of two that do; Cisco and  Ruckus Wireless. (Cisco with their ClientLink and Ruckus as of the 7982  AP).

So when does an access point stop using spatial divison multiplexing  and choose to use tramsmit beamforming.  Your asking yourself why cant  they do both?  Well lets explain:

To perform spatial division multiplexing ( SDM )  you need to send  different spatial streams to the client.  For transmit beamforming you  are sending the SAME spatial stream to the client so if you are a 2X2:2  AP/Client then you cant do both.

An 3X3:3 AP/Client could in theory be sending two SDM streams and 1  beamforming stream; thus improving one of the SDM streams but your data  rate would be 300mbps and not 450mbps.

For a Cisco 3600 4x4:3 AP then again in theory you can deliver 3 SDM  streams and one beamforming stream; thus improving one of the SDM  streams but most importantly you will be loosing one of the SDM streams  so your max data rate will be 450mbps.

If your a 3x3:3 which most access point are, then when you use  transmti beamforming instead of SDM then you data rate is 300mbps not  450mbps as most people think.  Remember the 3rd antennas is taken up  sending one of the other antennas spatial streams and is not sendign one  of its own...

[Scott Fella]

So your saying that its not possible to achieve 450mbps. Look at the 1142, they are 2x3x2 and you can achieve 300mbps.

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[lee.messenger]

I'm not "saying" anything,  I'm asking becuase I don't know the answer and I'm trying to get a better understanding of how Cisco implement this technology.  I thought that this would be the place to go to get the answer.

The 1142 doesn't support client link 2.0 and therefore is irrelevant in this discussion as it will only be beamforming to non-802.11n clients (I think).

Thanks

[Scott Fella]

Maybe this link can explain Cisco's Clientlink v1.0 and v2.0 better.

http://www.cisco.com/en/US/products/ps11983/products_tech_note09186a0080bd3d10.shtml#beam

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[George Stefanick]

Beam-forming is vendor specific. Ruckus by far has the most advanced bean forming solution on the market today IMHO.

How each vendor does it is a secret sauce of sorts. There is no standard specific to this technology. I know Andy Von Naggy did independent testing and didn't see an improvement. I think he tested v1.





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[Saravanan Lakshmanan]

The statements by Ruckus regarding ClientLink are incorrect on three fronts:

1) Client-Link technology is based on custom chipset level enhancements, that are not available in standard chipsets,

2) Client-Link does indeed optimize the form and direction of the Wi-Fi signal by adjusting beam-forming parameters, and

3) Client-Link performs real-time adaptation of the beam on a per-packet and per-client basis.

In addition, ClientLink has numerous advantages over the switched antenna array approach used by Ruckus:

- Enhances performance in both directions: ClientLink enhances performance in both uplink and downlink directions, whereas a switched antenna array only helps in the downlink direction when used with multiple simultaneous clients.

- Faster Dynamic Response: ClientLink adjusts antenna weights on a per-packet basis, and can easily track moving clients, whereas a switched antenna array uses a slow feedback loop and can't keep up with moving clients.

- Better performance in indoor multipath environments: ClientLink digitally can vary its antenna pattern across signal frequency, whereas a switched antenna array must use the same pattern at all frequencies, yielding degraded performance in indoor environments.

- Lower parts cost: ClientLink uses existing antennas with no need for an expensive array.

- Less signal loss: Antenna array solutions require switches that result in signal loss

[Saravanan Lakshmanan]

Thanks on pointing this doc.

[Saravanan Lakshmanan]

you're right!!!

The AP 2600 is similar to the AP 3600, but is a 3X4:3SS so with the AP 2600, Client Link does not

beamform to 3−ss clients. However; it does beamform at legacy and 1 and 2 Spatial Stream rates.

Also, the AP 3600 can beamform to 3SS clients as well. The AP 2600 is similar. However, the extra or redundant radio is for upstream because it is a receive only. Therefore, it is unable to beamform to 3−ss clients but can beamform at the other non−3ss rates.