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802.11n: High Throughput, Not Just Fast Wireless
eggboard writes "Unstrung reveals that the 802.11 working group is spawning 802.11n, a high-throughput task group to work on increasing the actual data:symbol ratio in wireless networks while also boosting speed to 108 Mbps to 320 Mbps. Most people who use 802.11a, b, or g know that actual net throughput, or the real data that's carried, is a fraction of the cited rate: maybe 7 Mbps in the 11 Mbps 802.11b flavor and 25 Mbps in the 54 Mbps a and g flavors. The goal of 802.11n is to increase speed, sure, but also to increase the percentage of symbols that don't bear overhead. The bad news: they predict 2005 or 2006 for completion."
Maybe not for you but not having a job makes anything cost prohibitive. Well I have a job but not MUCH of I job I should say. I have enough to pay for living and with what little extra I have I'd like to be able to get a wireless card, specifically one that I won't have to buy again in a year or 2 when the specs change.
Visit www.seriouslythough.com
The speeds quoted are burst speeds. Assuming
binomial distribution of arriving packets (and that is the regular assumption), the throughput
for any packet based transmission is ~60% of the
burst speed. So 7MBPS out 11 is right what you
should expect.
Throughput on 802.11b networks is actually only around 3-4 Mbps in optimal conditions, less than 50% of the theoretical maximum.
I just wanted to point out that if we accepted 11Mbps and 54Mbps as the speeds of 802.11b and 802.11a/g then we would have to call regular fast ethernet 200Mbps. 802.11b is 5.5Mbps full-duplex and a and g both are 27Mbps full duplex. It is true that the radio signals are capable of carrying 11 and 54 respectively, but half of this bandwidth is dedicated for each direction, so that the MAXIMUM one-way speed you can achieve with 802.11a/g is 27Mbps. This means that if they're hitting real-life numbers of 24Mbps (I doubt it) of data throughput, then they're doing really well - about 88% of theoretical. That's as good as you can really expect from wired networks, in terms of throughput to bandwidth ratios.
I did not design this game/I did not name the stakes/I just happen to like apples/And I am not afraid of snakes-AniD
Maybe they should concentrate on approving the 11g standard first.
Just to comment on the "users of 11g" stuff: The implementations you are currently seeing in the shops are based upon more or less early *drafts* of the standard. The fit will really start hitting the shan when people start combining devices from different manufacturers: Incompatibilities range from different modulation schemes (TI) over incompatible MAC protocol elements (dataset identifiers in AP capabilities) to legacy support (some old legacy devices refuse to associate with APs supporting the new modulation modes due to excessive supported-rates-list lengths).
The origin of the slow effective transfer speed by the way is the MAC layer timing. Each information frame is transfered independently and ACK'ed by the receiving station on MAC layer -- the time delays in these frame exchanges take up enough time to reduce the effective transfer rate to about half for the 54Mbps mode. Besides QoS 11e will introduce burst frame acknowledge which should improve the situation considerably and therefore the new modulation schemes may actually make sense.
If you can find an access-point that will do 802.1x properly with rolling keys, you are in great shape, even with RC4 WEP. The WEP attacks that have been published exploit a vulnerability with poorly-chosen IV values, and if enough encrypted packets are captured, the keys can be inferred. But, if you rekey on a frequent basis, and use a "modern" implementation of WEP which avoids the weak IV values, then you will be fine. Unfortunately, I don't know which SOHO access-point devices currently support an optimum 802.1x implementation. On the client side, Windows XP SP1 does it right, and I believe that Meetinghouse has client implementations for Linux and Mac OSX.
- Technically we call it "100baseT Full Duplex"
- The 100 refers to 100 bits/second as a maximum channel capacity, not the maximum transfer rate between two hosts. it takes multiple hosts using the channel at the same time to saturate the channel.
- Half of the bandwidth of 802.11b is NOT set for " each direction". The full amount can be used for either direction.. it's half duplex. Further, the 11mbps refers to the radio channel, not any " direction".
- Full channel usage happens with multiple hosts, not with only two. with two hosts.. just like ethernet, but the delays and wait times are larger, adn there is more protocol overhead, due to the lack of collision detection.
IEEE 802.3 CSMA/CD
IEEE Std 802.3z-1998, Gigabit Ethernet.
IEEE Std 802.3aa-1998, Maintenance Revision #5 (100BASE-T).
IEEE Std 802.3ab-1999, 1000BASE-T.
IEEE Std 802.3ac-1998, VLAN TAG.
IEEE Std 802.3ad-2000, Link Aggregation.
IEEE Std 802.3ae-2002, 10Gb/s Ethernet.
IEEE Std 802.3ag-2002, Maintenance Revisions #6.
P802.3af, DTE Power via MDI.
P802.3ah, Ethernet in the First Mile.
P802.3aj, Maintenance #7 Task Force.
P802.3ak, 10GBASE-CX4 Task Force.
No big deal.