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Community Member

Bandwidth aggregation of wireless bridges

We have installed several Aironet 340 wireless bridges on different campuses. These bridges clearly offer a great value in replacing low speed serial links. Has anyone used FEC or MultiLink to aggregate multiple bridge links successfully? I tried FEC and while the configuration worked, with the addition of each bridge pair, available bandwidth decreased. Moving our 24M test file with one bridge took an average of 47 seconds. With two bridge links, slightly longer. With 3 bridge links, the total time to move the file was a few minutes.

At a Cisco Aironet seminar, I was given a handout that graphically illustrated this concept as a way to aggregate bridge link bandwidth (6 bridges = "up to 33 Mbps"), so it must work, right?

8 REPLIES
Community Member

Re: Bandwidth aggregation of wireless bridges

The three links would need to have unique SSID's and unique non-overlapping channels (i.e. Link 1 has a SSID of "first" with channel setting on the root bridge of "1". Link 2 has a SSID of "second" channel "6". Link 3 has a SSID of "third" and channel "11"). Then the links must be managed to prevent any looping. But that is still 11Mbps per link. The highest speed is 11Mbps. The aggregate would be 33Mps.

Bronze

Re: Bandwidth aggregation of wireless bridges

True load balancing does not occur so a single device talking to another device normally only goes across one link, multiple devices need to be used and spread the traffic around. You're configuration options with regard to FEC kind of depend on the switch.

Bronze

Re: Bandwidth aggregation of wireless bridges

If you're using a single file transfer from one MAC address to another MAC address all the time, I don't think FEC will give you any improvement. For the most part, the switches make the decision regarding which link to send packets down based on the source and destination addresses. So a single source to a single destination will always only take one of the links in an FEC bundle. You gain nothing with this kind of test.

Community Member

Re: Bandwidth aggregation of wireless bridges

The test was conducted with multiple PC's hanging off of a remote access switch connected to up to three wireless bridge links (each configured for different freq's) hanging off of an access switch to the network. I expected the traffic on subsequent transfers to fall over to one of the other two bridges available. What I gained was the understanding that there is no net increase in bandwidth achieved through grouping RF bridges counter to Cisco's marketing representation.

Thanks for you response.

Bronze

Re: Bandwidth aggregation of wireless bridges

It appears that the 2900XL switches can round robin traffic based on loading. In this case there may be some performance improvements. This might also result in packets being out of order at the receiving host, causing it to re-order packets and / or tell the other host to re-transmit. Both would result in longer transfer times. I haven't tested this. The only way to confirm this is not happening is to get a sniffer trace and see what's happening on the wire.

Community Member

Re: Bandwidth aggregation of wireless bridges

Would it be possible to load balance with an external router? ie. bridge 1 using frequency 1 on ethernet 1 of router, bridge 2 using frequency 6 on ethernet 2 of router, bridge 3 using frequency 11 on ethernet 3 of router. Would this solution give you a "true" 33 Mbps link on a building to building application?

Community Member

Re: Bandwidth aggregation of wireless bridges

I copied this from todays wirelessonline forum:

Question 74

If you need more than 11mps bandwidth can you "mux" multi systems together to get the higher bandwidth

Answer 74

If you need more than 11Mbps of bandwidth, you can reduce the access point cell size, and put up to 3 access points in a single cell area, and get bandwidth of 33Mbps. Clients, however, will be limited to 11Mbps each.

Community Member

Re: Bandwidth aggregation of wireless bridges

This information is only for WLAN solutions, not bridging. The brdiged solution does not have any one client, just a wireless 'pipe' between locations.

ryan.benner was on the right track with the router solution. The router idea would either be to slow (1720 with 3 Ethernet interfaces, not enough horsepower) or too expensive (3640 with three 10/100 Ethernet interfaces). Layer three (L3) switching would accomplish this though.

Cisco's Packet magazine covered a manufacturing solution that did this type of solution. The article can be found @ http://www.cisco.com/warp/public/784/packet/apr01/small.html#title.

They used a L3 switch at each end (2948G-L3 I think). Each wireless bridge is connected to the switch and setup as separate routed interfaces. Then you use OSPF or EIGRP for round-robin (or any other load balance) over the interfaces.

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