Number of WL clients with WRT54GS


Say I have a ..11g (54Mbps) wireless network and use WRT54GS boxes as router and clients (sveasoft). How much overhead should I expect and which practical bandwidth would each user get in a 8 user scenario...?

Thanks for some real-world comments / experiences on this.


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Doug Johnson
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I don't understand. What units of measure do you expect for measuring "overhead"? Percentage CPU utilization? Also, overhead is normally defined in a before and after senario, such as with and without encryptions, WEP versus WPA, or with and without a VPN tunnel. So, could you rephrase your question in term of: 1. What are you trying to accomplish? What problem are you trying to solve? 2. What topology, hardware, software, and versions do you have to work with? It's kinda rough trying to answer questions without these basics.

Incidentally, I'm guessing you want to know the user loading for a WRT54G. This depends on many things, the most important is what the users are doing. My rule of thumb is: 100 light web and email users. 10 business users doing whatever business users do. 1 file sharing or BitTorrent user.

Reply to
Jeff Liebermann

Yeah, that's better. 54Mbits/sec is the connection speed. Since it's a simplex (tx and rx one at a time) system, you'll never get "wirespeed" performance. In addition, all the 802.11b/g management overhead and necessary inter-packet delays add substantial loss in thruput. I once did a chart of the limits.... digging....

This is stolen from an Atheros PDF at:

formatting link
some additions and corrections by me.

Non-overlapping Modulation Max Max Max Channels ------- | Link TCP UDP | | | | |

802.11b 3 CCK 11 5.9 7.1 802.11g (with 802.11b) 3 OFDM/CCK 54 14.4 19.5 802.11g only 3 OFDM 54 24.4 30.5 802.11g turbo 1 OFDM 108 42.9 54.8 802.11a 13 OFDM 54 24.4 30.5 802.11a turbo 6 OFDM 108 42.9 54.8

The paper claims that encryption is enabled for these calculations, but my numbers seem to indicate that these number are for encryption disabled. Dunno for sure. The Max TCP and Max UDP are the theoretical maximum thruput rates. If you want the detailed calcs, I think I can find my notes. I don't have numbers for the various Turbo and Super modes.

WPA encryption eat about 10-15% additional loss in thruput.

If your backhaul (DSL or Cable Modem) speed is less than the maximum thruput speed, the backhaul will be the limiting factor in thruput.

All the above is for ONE user. There's no additional overhead for adding additional users. For an equal speed wireless connection, the thruput will simply divide equally among the 8 users. It gets messy if each user connects at a different speed. The algorithm is in my never humble opinion, rather stupid. The access point distributes the bandwidth by equalizing the number of packets. A 1Mbit/sec slothish connection will get 1 packet, while a 54Mbit/sec will also get 1 packet. However, it takes the 1 Mbit/sec connection 60 times as long to deliver the one packet as the 54Mbit/sec connection. That means the bandwidth of the 54Mbit/sec connection is drastically reduced in the presence of a 1Mbit/sec connection. Not all access points work on this principle, but the cheap ones tend to do it this way because its easier to implement. The "fair share" algorithm is run at ethernet speeds in the router section, and the wireless part just pumps out packets.

One BitTorrent user will not exclude everyone else. The problem is that BitTorrent will monopolize ALL the available bandwidth. Usually, it's the outgoing bandwidth that gets filled first. You could have all the incoming bandwidth you want, but if the TCP ACK's are being constipated or delayed by filling the outgoing bandwidth, incoming performance will truly suck. At one ISP, we fired off a BitTorrent download of a Linux CDROM image and successfully slowed a fractional OC-3 (about 45Mbits/sec) backhaul to the point where alarms were going off. BitTorrent opened enough simultaneous streams to perform the download very quickly, but did so by literally monopolizing the pipe.

The solution is to use some form of bandwidth management or QoS. Limiting the available bandwidth by user or service is in my opinion mandatory. I also reserve some bandwidth for VoIP which is very time sensitive. I have one system using Snort to detect hacking and abuse, but also to detect use patterns that tend to monopolize the bandwidth. Due to lack of time (and interest) I haven't done much with it.

Huh? I don't understand the question. Without QoS or Bandwidth Management, wireless bandwidth is mostly allocated on a per packet basis in rotation. It's a really brain dead way of doing it. There's no intelligence on the IP layer or above because wireless is 100% bridging, which is all at the MAC layer. At the MAC layer, there's no concept of users, sessions, files, ports, services, etc. Just packets. That's why QoS and BW has to be done at the IP level to be effective. I'm not sure I answered your question, but if you rephrase it, I'll try again.

I have no idea. Wireless routers have three sections: - A wireless access point (bridge) radio: - A router that handles the LAN - WAN stuff: - An ethernet switch to allow local connections: The wireless part is mostly a tangle of encryption and timing. Take away these complications and all wireless bridges are fundamentally the same. There are some differences in implementation at the MAC layer, but the timing and protocol rules are set by FCC part 15 and IEEE 802.11b/g, and do not really vary much by manufactory. There is considerable differences in radio quality and chipset features, but that's not part of this discussion.

The ethernet switch is fairly simple except that some wireless routers (WRT54G) allows independent router control over each switched port.

It's the route features that distinguish the cheapo wireless routers from their overpriced versions. In general, the fancy routers offer much more control over IP layer packets than the cheapo routers. However, you can get the same (or similar) features by simply buying an access point (or buying a cheapo wireless router and configuring it as an access point) and adding a decent Cisco ethernet router. I'm fairly sure all of the important wireless router features are also in the ethernet routers.

What you apparently need/want/interested is bandwidth management and that's a router feature. There's nothing in the bridge/radio section that does anything useful for bandwidth management. Note that Cisco has mostly fairly simple access points and relies on their routers to do the real work.

Sorry. I don't understand your description. I also don't understand how this question relates to your first question and cannot tell if you're building a new network or trying to solve a specific problem on an existing network. How does the home user connect to the office network? Is there a VPN involved? If so where does the VPN terminate? What are the bandwidths available to the home users (dialup, ISDN, DSL, etc)? Are you seriously worried about abuse by your own clients or is this a performance issue? Please organize your questions in terms of "What problem are you trying to solve or what are you trying to accomplish" and then supply "What do you have to work with?".

Reply to
Jeff Liebermann

"Jeff Liebermann" skrev i melding news:

Sorry for using the wrong expression. Say I have a teoretical WL link bandwidth of 54 Mbps (maybe more because of the GS version) and expect 8 users to be connected simultaneously using WPA encryption. In my original question I wondered how much of those 54 Mbps will be eaten up by handshaking, encryption, timeslicing etc,etc.

You mention that one bittorrent user will choke all the others, does this mean that the wless protocol does not have any load-balancing between clients other than setting priority by IP or MAC address from the WRT's config utility? Even if there are network transport request from other users during one client's file transfer the others will not be granted bandwidth before the transfer is terminated?

Do different wl routers / access points handle this differently that the WRT54? I'm not thinking of expensive Cisco eqpmnt but boxes in the sub $500 'area'.

The scenario is one office network connected to a WRT54GS in AP/bridge mode.

6 users will each have a WRT54GS (in client mode) connected to their computer at home. They will do casual business tasks and internet access. Filesharing and other high-demand bandwidth ports are closed at the office's firewall. Would the linksys boxes do sufficiently in this case? If marginal, do you have other suggestions?



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