Introduction
Revised March 31, 2003
The wireless networking world is a’ buzz with the new kid in town, 802.11g. As with most new technologies, some of the buzz is hype, other is rumor, and it’s hard to tell the difference! Fortunately, one of the advantages that I have is detailed test data from the first products to hit the shelves, which I can use to help separate fact from fiction. I’ve also been busy corresponding with both the chip and networking product companies involved in the draft-802.11g market-share battle, most of whom have been very helpful in helping me get a better understanding of this new technology.
Part 1 of this NTK will try to address many of the questions that are being asked about 802.11g and draft-802.11g products. It will also try to answer the practical questions: Should I buy now? And if so, what should I buy?
Although I originally intended to put everything into one NTK, I found that there was just too much to put into one article! Part 2 presents more of the test data that I’ve used to draw my conclusions, including test results from both Broadcom and Intersil-based products. Let’s get started!
What is it?
802.11g is a new IEEE standard for wireless LANs that is currently in draft form, and expected to be ratified (finally approved) in July 2003. I’ll explain more about the implications of this later. Its key claims to fame are 54Mbps raw data rate and 802.11b backward compatibility.
802.11g’s higher speed comes from using the Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme – the same as used in 802.11a. Backward compatibility comes from using the 2.4GHz band, supporting the old Complementary Code Keying (CCK) modulation scheme used by 802.11b, and new “protection” mechanisms described in the 11g draft standard.
802.11g’s negatives are the same as 802.11b’s, i.e. only three non-overlapping channels and interference from cordless phones and microwave ovens. So if you’re having interference problems with your 802.11b network, you’ll still have them with 802.11g.
Broadcom’s 54g FAQ describes some of the technical details of the draft specification, which includes:
-
A new physical layer for the 802.11 Medium Access Control (MAC) in the 2.4 GHz frequency band, known as the extended rate PHY (ERP). The ERP adds OFDM as a mandatory new coding scheme for 6, 12 and24 Mbps (mandatory speeds), and 18, 36, 48 and 54 Mbps (optional speeds). The ERP includes the modulation schemes found in 802.11b including CCK for 11 and 5.5 Mbps and Barker code modulation for 2 and 1 Mbps.
- An optional MAC mechanism called RTS/CTS that governs how 802.11g devices and 802.11b devices interoperate. RTS/CTS is also optional in 802.11b.
The Players
As you’d expect, there are great hopes for 802.11g, and no one wants to miss the boat. Eventually, all the usual suspects will be in the game, but right now, the early going is being lead by consumer networking product companies.
The real battle, however, is being waged by the wireless chip manufacturers, with Broadcom firing the first shot. Since they came late to the 802.11b party, Broadcom is determined to not miss the 802.11g opportunity. They’ve been very aggressive in pursuing the market, starting with the pre-emptive strike they launched at last November’s Comdex. They not only announced a new chipset, but also a number of wireless product partners, a “54g” branding program, and first product in stores by Christmas! And all this for a standard that’s still a work in progress!
Needless to say, Broadcom has stirred things up in the Wireless LAN market, and not exactly endeared themselves to either the Wi-Fi Alliance or the IEEE in the process. Although competitors have been choosing their words carefully so far, the gloves will probably soon come off as products come to market based on Intersil‘s PRISM GT chipset, and competitors start throwing elbows.
The scorecard changes almost daily, but the table below shows the current chipset vs. end-product lineup. Note that some of the manufacturers listed below have announced, but are not yet shipping draft-11g product:
|
Chipset manufacturer
|
Used by
|
|
Broadcom
|
– Apple – Belkin – Buffalo Technology – Linksys |
|
Intersil
|
– Actiontec – NETGEAR – Corega International – D-Link – USI |
|
Atheros
|
– HP (embedded in notebook) – NETGEAR (tri-mode) – TRENDnet |
| Texas Instruments | – TNETW1130 chipset announced. Products planned for April 2003 |
| Agere Systems | – Tri-mode (a/b/g) chipset announced. Reference designs due Q3 2003. |
Work In Progress
As I mentioned previously, the 802.11g IEEE specification, which is the ruling document that 802.11g products must adhere to, is not yet officially released. (Have I said that enough yet?) The current schedule has ratification, i.e. official approval, scheduled to occur in July 2003. Any products appearing before the spec is released can say only that they conform to the 802.11g draft specification.
What manufacturers aren’t making clear however, is what version of the draft spec they conform to. Currently shipping products are designed using a mix of Version 4.0 and 5.0 spec drafts that emerged from the IEEE Task Group G meetings in September and November 2002 respectively.
As I write this at the beginning of February, draft 11g chipmakers are scrambling to incorporate the changes made in the latest Version 6.1 draft that resulted from the January 2003 meeting. The chipmakers are pushing to get the updated firmware in the hands of their customers – the networking product manufacturers – who eventually will make it available to buyers of draft-11g equipment. This could happen as early as late February, but will probably be more like March.
As it turns out, there are significant changes in the various drafts that effect both 802.11b interoperability and throughput performance of draft-802.11g products. The 802.11b interoperability issue is somewhat simpler, so I’ll cover that first.
Short Preamble Only
Updated Feb 10, 2003 – Corrected explanation of the short preamble problem.
Part of the frame that is transmitted by an 802.11 station is called the preamble. The original 802.11 specification (which defined only 1 and 2Mbps operation), defined only a long preamble that uses a 128 bit sync field. When the “high rate”, i.e. 11Mbps, 802.11b standard was created, an optional short preamble using a 56 bit “sync” field was added. This was intended to improve the efficiency of the wireless network for more “real-time” applications such as streaming video and Voice-over-IP telephony applications. Figure 1 has the gory details on the two preambles if you’re interested.
Figure 1: Short and long 802.11 preambles
From: 802.11 Wireless Networks: The Definitive Guide , used by permission [1]
All 802.11 devices in the 2.4 GHz band, including 802.11g devices, must be able to transmit and receive long preamble frames. 802.11g devices are required to be able to transmit and receive both long and short preambles, but support for short preamble in 802.11b devices is optional.
The problem occurs when an 802.11g AP allows the use of Short Preamble by the stations it communicates with (also known as its BSS – Basic Service Set). The AP may also choose to allow legacy stations that do not support Short Preamble to associate with the BSS. If both these conditions are allowed, the legacy stations that aren’t short-preamble-capable will not be able to understand much of the communication in the BSS, and most importantly won’t be able to receive the all-important “Protection” frames. This could result in legacy 11b stations transmitting at the same time as 11g stations, which doesn’t help either one to properly get their data sent!
This 802.11b interoperability problem has been noted in recent articles on draft-802.11g, but it looks as though it may be getting somewhat overstated. First, the short-preamble problem affects only a subset of the 802.11b products in the field. Specifically, ORiNOCO and Symbol cards and those using the Intersil PRISM 2.0 and Agere Systems chipsets.
Second, manufacturers may already have incorporated a fix for this problem into their AP code. (I’ve used both ORiNOCO and PRISM 2.0 based cards in my testing and have yet to run across the problem.) And finally, another reason to relax is that I’m told that the IEEE Task Group g committee will probably address this issue in the 802.11g standard after some additional debate.
Sprechen Sie CCK?
Although it would be great to say that draft-802.11g products really do provide the 5X throughput that vendors love to feature so prominently in their advertising and product packaging, it turns out that reality isn’t that simple. The reasons involve things such as the incomplete nature of draft specifications (and the loopholes they provide), competitive pressures that cause products to ship before they should, and just plain errors and misunderstandings in design and implementation.
Whatever the reason, the fact is that the throughput you see from draft-11g products may vary significantly from product to product from now and probably right up through the release of the spec. The heart of the throughput issue lies in the “protection” mechanism defined in the draft-802.11g spec. To understand what’s going on, I’ll need to peel the onion a layer or two, so bear with me.
Although 802.11b and g equipment operate in the same 2.4GHz frequency band, they primarily use different modulation schemes. 802.11b uses a method called Complementary Code Keying (CCK), and 802.11g uses Orthogonal Frequency Division Multiplexing (OFDM). In simple terms, its like two people being able to hear each other, but unable to communicate because they speak two different languages. In their great wisdom, the IEEE Task Group G quickly realized the basic problem, and mandated two fixes to bridge the gap.
First, they said that 802.11g products must support both the OFDM and CCK modulation methods, giving the newer standard the ability to speak the old one’s language. (A third method, PBCC, was also included, but as an optional method.) But just as a bi-lingual person must receive a clue to switch to the language of the person who is trying to speak to them, a similar mechanism was needed so that 802.11g stations would be able to understand that an 802.11b station was trying to communicate, and clue the 11g station to switch to CCK to have the conversation. This second compatibility feature is known as “protection”.
Protection Optional
“Protection” provides the needed clue that controls whether CCK or OFDM is to be spoken. It uses the RTS / CTS mechanism illustrated in Figure 2 that’s part of the 802.11b spec. When protection is in use, each 802.11g OFDM data packet is preceeded with a CCK RTS (Request To Send).
Figure 2: RTS / CTS
From: 802.11 Wireless Networks: The Definitive Guide , used by permission [1]
Since CCK is spoken, all in-range 802.11b stations (or 802.11g stations using protection) can understand that a station is requesting permission to send data. The target in-range 802.11b or 802.11g station can then respond with a CCK CTS (Clear To Send) and the transmission can begin. Since the RTS and CTS frames contain other information about the data that will then be sent, 802.11g stations can tell whether they can switch back to OFDM, or need to continue speaking CCK to complete the requested communication.
TIP: For a more detailed explanation (with diagrams) of how the protection mechanism works, see this article.
As you might guess, however, this compatibility comes at a price. The RTS / CTS mechanism not only adds the overhead of more bits that need to be transmitted, received, and processed, but it also must take place at the slower 802.11b speed. (Even if someone is speaking your language, if they’re talking too quickly, you still won’t understand them.) All this adds up to a hit to throughput, and throughput is what 802.11g is selling!
The protection mechanism has had significant changes from draft to draft of the 802.11g spec, and may change again in the final spec that is scheduled for July 2003 release. I’ll next take a quick look at the effects that these changes have on the throughput that you’ll see in draft-802.11g products.
Fun with Throughput
The draft spec leaves manufacturers a good amount of performance-tweaking leeway in that it does not state that the “protection” mechanism must be used at all times. This is somewhat of a contradiction since one of the advantages of 802.11g is its interoperability with 802.11b. But since the “protection” mechanism eats throughput, the standards makers didn’t want to saddle all-11g WLANs with protection’s overhead.
As a result, draft-11g chipmakers are experimenting with a number of methods that try to minimize the protection throughput hit, yet still be able to communicate with 802.11b stations. The simplest method is to disable the protection mechanism entirely, yielding an “11g-only” mode. This is still a work in progress, with a mix of nomenclature used to describe it.
|
But disabling protection entirely can cause other problems that I’ll describe later. So manufacturers will most likely try to get as much throughput as possible, while still providing 802.11b protection. This seems to be Broadcom’s approach in the different versions of firmware I’ve seen, and I expect that other vendors will follow similar approaches.
However, no matter what tricks are used, it’s important to understand two key points about the effect of 802.11b protection:
KEY POINT #1: All 802.11g equipment, whether draft or released, will have lower throughput when 802.11b devices are associated (connected) to the 802.11g WLAN. The lowered throughput will be seen even when the 802.11b devices are idle.
My testing so far with only Broadcom-based products shows that the actual throughput in both Point 1 and Point 2 cases varies from product to product. This product-to-product variation will probably also remain in released 802.11g products, but it’s too early to tell for sure.
I go into the throughput reduction issue in more detail in Part 2 of this NTK, but I’ll give some quick examples to give you a flavor for what’s going on.
• All the following tests were taken under best-case signal conditions, with AP / router and client about five feet apart. WEP was not enabled for any tests.
• The results and conclusions presented are based on draft-802.11g products only from Buffalo Tech [see review] and Linksys [see review]. Both products use Broadcom‘s draft-802.11g chipset, but are designed using different versions of the draft standard.
Figure 3 shows a comparison of throughput test runs for the Linksys WAP54G access point and WPC54G CardBus card, compared with the Buffalo Technology WBRG54 and WLI-CB-G54 CardBus card. Both sets of products were the first shipping versions, with original firmware.
Figure 3: Throughput comparison – Linksys vs. Buffalo Tech – original
(click on the image for a full-sized view)
The lower trace shows Buffalo Tech’s first attempt at automatically handling both draft-11g and 802.11b clients, which I dubbed “throughput hopping”. I’m not sure of Buffalo Tech’s exact approach, but it appears that they were periodically adjusting something in the protection algorithm that cut throughput about in half. They might have been periodically turning it off completely, but other experiments that I performed make me doubt that theory.
The upper trace appears to show that Linksys has much steadier throughput, but actually is somewhat inaccurate. It turns out that Linksys’ first efforts had what they called a “warm-up” effect, which Figure 4 shows.
Figure 4: Throughput comparison – Linksys before and after “warmup”
(click on the image for a full-sized view)
The lower trace is the throughput that I got when I powered up both access point and client and then immediately ran a 1 minute throughput test. Further testing showed that throughput got steadily better over about a 20 minute period, which shown in the upper trace.
Note that these throughput effects did not prevent Linksys or Buffalo Tech client cards from working with the other’s router. Both cards associated, transmitted and received data without problems from either router. The main variable was the throughput of the data transmission.
The good news, however, is that the first improvements have already been issued by Buffalo Tech and Linksys. I’ll cover that in the next section.
First Tweaks
As I was preparing this article, I received the Linksys WRT54G draft-11g wireless router, which came with a new firmware revision that was supposed to have improved performance. I also downloaded and installed new firmware for the Buffalo Tech WBRG54 wireless router from their support webpage. Client card drivers and firmware remained the same.
Both routers were set up as access points so that the routing portion’s performance didn’t get in the way. As you’ll see, some progress has been made already in the throughput department.
Figure 5: Throughput comparison – Linksys vs Buffalo – New firmware – Mixed mode
(click on the image for a full-sized view)
Figure 5 shows both pairs of products set to their default modes, which allow both draft-11g and 11b clients to connect. It’s also important to note that there were no 802.11b clients in range for these tests.
You can see that the Buffalo Tech is still hopping along, but that the size of the hops has been greatly reduced. The Linksys (upper trace) doesn’t show as much change, but you can see many more quick dips in throughput (I call these “throughput dropouts”) than in Figure 3. (Don’t attach any significance to the fact that the Linksys trace stops after 1 minute. I got bored and stopped it manually!)
Although these are welcome improvements, I found that average throughput will drop about 25% from what you see in Figure 5 when an 802.11b client just associates (connects) to either the Linksys or Buffalo Tech routers (Key Point #1 in action). Of course, once the 11b client starts transferring data, throughput changes yet again, which I’ll show in the next section.
Sharing the channel Revised March 25, 2003
I saw some change in the way that a channel’s bandwidth is shared when both draft-11g and 11b clients want to use it at the same time in the latest firmware from Linksys and Buffalo Tech, but it’s clear that this area still needs more work. From what I saw, Buffalo Tech seems to provide a better g / b bandwidth sharing than Linksys, but the situation is sure to change for both companies.
My sources tell me that the 6.1 11g spec draft has added changes in the protection mechanism that will result in 11g stations getting a higher probability of airtime in a mixed 11b / 11b network. This means that once vendors incorporate the new changes, 11b devices will still be able to operate in 11g WLANs, but they will get an even smaller share of bandwidth than they do now if 11g stations are active. Once again, I’ll dig down into the details for those who are interested.
Part of what governs how multiple 802.11 devices compete for airtime is called the “contention window” (or “backoff window”). Note that this isn’t something added by 802.11g, but has been around since the original 802.11 spec. As shown in Figure 6, the window is part of the waiting period between data frame transmissions and is used to keep transmissions from crashing into each other. The contention window is divided into consecutively numbered slots, with the number of slots always being 1 less than a power of 2 (15, 31, 63, etc.).
When a station wants to transmit, it randomly selects a slot number, then waits for that slot’s number to come up and transmits the frame. If the station does not receive an acknowledgement that the frame was received, it assumes the transmission failed, increments a mechanism known as the retry counter and increases the window to the next power of 2 (minus 1, of course).
Figure 6: 802.11 Interframe spacing
From: 802.11 Wireless Networks: The Definitive Guide , used by permission [1]
Draft 6.1 says the station should change the contention window based on the supported rates of the network. If the supported rates only include 1, 2, 5.5, & 11, as they do in 802.11b, the maximum initial contention window value (i.e. before any retries are necessary) will be 31. Otherwise it will be 15, which is what 11g clients get. Given that clients pick a random number from 1 to their maximum contention window size, since g stations have a smaller range of numbers to pick from, odds are that 11g clients will get on the air before 11b clients. The actual algorithm is more involved, but the basic mechanism stays the same.
Right now, however, a different set of rules of engagement is being used, as you can see from Figure 7.
Figure 7: Linksys two-way test – NETGEAR MA401
(click on the image for a full-sized view)
This test was done with the latest Linksys firmware and shows how throughput is shared between a Linksys WPC54G draft-802.11g , and NETGEAR MA401 (Intersil PRISM II based) 802.b clients. The Linksys card starts first, and is joined by the NETGEAR card at the 20-second mark. You can see that the Linksys card throughput falls below that of the NETGEAR, and stays there until it finishes its run. The NETGEAR card then continues by itself until it, too, finishes the data it was programmed to send.
I ran 802.11b cards based on Intersil, Atheros, TI, and Agere Systems (Lucent / ORiNOCO) chipsets with both the Buffalo Tech and Linksys gear and found that although each combination had its own unique throughput sharing “signature”, all produced further reduction in 802.11g throughput (Key Point #2). Part 2 of this NTK presents more results from my mixed-mode testing, but the main take-away at this point is that mixed draft (and final) 802.11g networks are eventually going to favor 11g clients when both flavors are trying to use the same WLAN. This may not be what you see in early versions of draft-11g products, but it’s the way of the future.
Next, I’ll see what happens when the protection mechanism is disabled and I try to run an 11g-only network.
Ignore b at your own risk
When you disable the protection mechanism of draft-11g products, you don’t lose the ability to “hear” 802.11b clients, just the ability to understand them. Again using the language analogy, if everyone in a room speaks only Swedish and someone comes in speaking Flemish, although everyone will hear the person, no one will understand what he or she is saying. If the person speaks long and or loudly enough, they will interfere with conversation, and maybe even be able to stop it.
Figure 8: Linksys in “G-only” mode – WAB501 trying to associate
(click on the image for a full-sized view)
Figure 8 shows the results of an experiment that I ran using the Linksys WRT54G router and WPC54G CardBus card. I started a Chariot run between the two Linksys products, with the WRT54G set to its “G-only” mode. In another laptop sitting close by, I had a NETGEAR WAB501 Dual-Band CardBus card (Atheros based) sitting idle, scanning for a network to associate with.
The plot clearly shows an effect on the Linksys pair’s throughput from an 11b client that isn’t even really active, but just sending the messages it needs to try to find a network to join with. Simply put, with protection disabled, 802.11b clients become just like any other 2.4GHz noise source and can interfere with your 802.11g WLAN’s transmissions.
I ran experiments with four different clients, and ran the same experiments on the Buffalo Tech gear. Although the Buffalo Tech’s normal throughput “hop” makes the effect a little harder to see, a similar effect was still present.
I hope that 11g vendors drop the idea of calling the protection-disabled mode “Turbo”, or even “G-only”. But I suppose “11b Protection disabled” isn’t really that sexy, is it?
So now that you know some of the technical “gotchas” of draft-11g products, it’s time to come up for air and see what it all means.
Mix and Match?
The good news from the testing that I’ve done so far is that everything I tested at least connected and transferred data. I didn’t run across the 802.11b “short preamble” problem, and I could use Linksys or Buffalo Tech clients just fine with each other’s APs or routers.
Warning! Marketing Buzzwords at Work!
As if things weren’t confusing enough, the marketing machines at draft-802.11g manufacturers are hard at work all trying to carve out a piece of brand recognition. (After all “draft-802.11g doesn’t sound very sexy does it?)
Wireless chipmaker Broadcom started it all (and you could say started the whole draft-802.11g mess) with their “54g” branding program, which even has its own website.
Although Linksys is listed as a “54g supporter” on the 54g.org website, they’ve launched their own branding campaign for “Wireless-G” (and, of course, “Wireless-B”), saying it’s just their way of trying to “make it easy” for consumers. Actiontec apparently agrees with Linksys and has also branded their upcoming draft-11g products with “Wireless-G”, even though they are based on Intersil’s chipset.
Not to be outdone, D-Link is using “Xtreme G” as their draft-11g rallying cry.
Catchy product names or not, it’s all draft-802.11g at this point!
However, once again, you need to pay attention to what manufacturers are not saying, especially with regard to interoperating with other manufacturers’ draft 802.11g products. To get a feel for this, I looked through manufacturers’ product literature or asked manufacturers: “What is your position as to the interoperability of your products with draft-802.11g products from other manufacturers?”. Here’s what I found:
D-Link
The product description for their AirPlus Xtreme G DWL-2000AP Access Point says “…its transfer rate can be up to five times faster when the wireless network is comprised of other D-Link AirPlus Xtreme G products such as the DWL-G520 Wireless PCI Adapter, DWL-G650 Wireless Cardbus Adapter”.
Buffalo Technology
Their WBR-G54 Access Point data sheet prominently displays the “54g compatible” logo, but doesn’t really explain what the logo means.
Linksys
Has a “54g compatible” logo sticker on their WRT54G router but none of its draft-11g product material says anything specifically about interoperability. All products do, however, say either that they’re compatible and/or interoperable with 802.11b products.
Actiontec (emailed response)
While we always try to ensure interoperability with other manufacturers products, it is impossible to guarantee complete interoperability until there is a testing body in place to qualify each product. This applies to both draft and final specifications.NETGEAR (emailed response)
NETGEAR’s goal is to provide universal compatibility and reliable connections, even though the Wi-Fi 802.11g testing procedure will not be available until Summer 2003. We are thoroughly testing our draft 802.11g products with all currently available Broadcom-based 54g products. Although NETGEAR can’t guarantee interoperability with other non Wi-Fi standard products, current tests of our 802.11g devices with Broadcom-based 54g products work well. We have tested 54g products from 2 different companies and are able to connect and achieve the same or better throughput.
All of which brings me to another key point:
It’s just too early to make general statements, especially given that only products based on one manufacturer’s chipset have had any sort of time in end-users’ hands! More “discoveries” are sure to come as gear based on Intersil and other chipmakers’ products come on-line, and the latest 802.11g draft changes are incorporated into drivers and firmware.
Do you want a guarantee with that?
But let’s say you love the smell of firmware burning in the morning and just have to be on the bleeding edge of technology. Will you have any sort of safety net from those friendly folks who are fanning the flames of your techno-lust? As you might expect, manufacturers are being careful what they say, since they realize what “draft” means, even if they don’t want you to think much about it!
I asked Linksys, Buffalo Tech, Belkin, Actiontec and NETGEAR: “Will you guarantee that your draft-802.11g products will operate with 802.11g released spec products?” Here are their exact responses:
Linksys (from an emailed response)
Linksys 54G Products are guaranteed compatible with other 54G products, as listed on www.54g.org. The are also compatible with 802.11b products. The 802.11g standard has not been finalized. While we suspect that no more than a firmware or driver may be necessary to become 802.11g compliant, we cannot guarantee compatibility with a standard that is not official.
Buffalo Technology(posted on their 54g product webpages)
NOTE TO OUR CUSTOMERS:
As you may know, IEEE802.11g is slated to be certified by the Wi-Fi Alliance in mid 2003. We understand this could affect current 802.11g technology. We are dedicated to ensuring that our customers have the most current and reliable products available on the market today. If the certification materially changes the principal operating features of our pre-standard 802.11g products, we will replace or upgrade any of those products at no charge and provide toll-free technical support. We thank you for your loyalty and confidence in our products.NETGEAR (from an emailed response)
Our official statement is: “The NETGEAR models WG602 (AP) and WG511 (PC Card) are designed and developed to the draft standard of the IEEE 802.11g specification.”
With that said, if the ratification materially changes the principle operating features, NETGEAR expects that a simple firmware upgrade will be available to customers, at no charge, via the Support website. At this time, we can’t guarantee this.Actiontec (from an emailed response)
No, we cannot guarantee it as we do not know what the final spec will look like.
However, we do expect that the changes will only require a firmware update, which we will offer free of charge.Belkin (from an emailed response) Revised March 31, 2003
(Belkin has changed their position.)
Our official guarantee is: Our 54g Wireless Networking products are firmware and drive upgradeable, and we will provide the upgrades on our website if any are necessary.
If you read the above statements carefully, you’ll see that only Buffalo Technology is offering a guarantee that its draft-11g products will work with released 802.11g products.
802.11a vs. 802.11g
Two other topics that I’ve seen a range of claims and counter-claims on is the speed and range of 802.11a vs 11g. Let’s look at the throughput issue first.
From what I can determine, all things being equal, the throughput of 802.11a and 802.11g products should be essentially the same. This is because they use the same modulation scheme (OFDM), which is the main thing that determines how fast the bits can go.
But since reviewers of draft-802.11g products, myself included, are finding slower-than-802.11a throughput, the question is what’s not equal? As it turns out, there are a number of things – some temporary, and others permanent. Let’s break them down:
-
Design maturity – In my opinion, this is the number one issue that is affecting current product performance. For the reasons I’ve outlined in previous sections, these products should come with big “Under Construction” stickers on them. There are new draft changes that need to be rolled into designs, and vendors are still tweaking their algorithms, and in some cases learning the additional challenges that OFDM can bring.
-
802.11b compatibility – Also as I’ve shown, the 802.11b “protection” mechanism will cut throughput when it’s enabled. But since the 11g spec doesn’t mandate protection’s use, vendors are including “no protection” modes that remove the additional overhead
- Operating frequency – This is the big difference and the one that will give 11g the edge in anything other than “open field”, i.e. no obstructions between stations, conditions. Ya can’t change physics, and 5GHz signals will always have a higher signal loss going through walls, etc. than 2.4GHz signals.
The bottom line here is that there is a lot of FUD being generated and conclusions being jumped to based on products that are still very early in their development and low on their learning curves. As things get sorted out, the throughput of 11g equipment when used in a pure 11g environment should be essentially equal to that of 802.11a under best-case signal conditions.
As far as assertions that 11g products will have inferior range to either 11a or 11b products, neither my experience nor the underlying principles support them. First, since 11g operates in the 2.4GHz band, its signal will not suffer as much attenuation as 11a’s 5GHz, and will travel better through the obstacles that most WLAN installations include.The 11a guys have long tried to argue that since they start at a higher throughput, their effective throughput at an equivalent range will still be higher than 11b’s, but test results just haven’t supported that assertion.
But how about 11g’s range being better than 11b’s? Although this article written by Intersil guys says that OFDM will have superior range because it can handle the signal reflections that are typical of indoor environments, my experience again tells me otherwise. In the end, superior design will probably provide one product’s edge over another, and not the use of 11g vs. 11b.
The journey has just begun
The 802.11g standard will eventually take its place among the most-used wireless LAN technologies. When all the bugs are shaken out and this difficult birthing period is only a memory, its combination of high speed, good performance in a residential environment, and compatibility with the huge installed base of 802.11b equipment will make it a virtually guaranteed winner.
But in the meantime, I wouldn’t be so quick to part with my money for draft-11g products just yet. Here’s my short list of why:
-
The benefit doesn’t yet outweigh the risk – Most home wireless LAN users don’t need the extra speed that 11g provides. Their Internet connection speed is limited to about 1Mbps or so and they have only one or two wireless clients – hardly enough to cause problems from bandwidth competition. And more to the point, how many home users really want (or have the skills) to be debugging the products they pay good money for?
-
You haven’t seen most of the players – Most of the current brouhaha is based on Broadcom-based products only. Intersil is just entering the market, and the real OFDM expert, Atheros, won’t be shipping product for a few months yet. Maybe Broadcom is the best of breed, but considering the competition, I wouldn’t bet with my money yet.
-
WPA is coming – This step up in security from WEP is supposed to be rolling out any time now (Q1 / Q2 2003). It will throw another variable into the product selection equation, and has the potential to be another drag on throughput if it’s not implemented correctly, or the chipset it’s run on doesn’t have enough poop to handle the extra load from TKIP. All the current generation chipsets should be able to handle WPA without affecting throughput, but…
-
The next step – It’s likely that where we’ll end up is with tri-mode / dual band products that handle the 802.11a, b, and g standards. I hope vendors will hold off until the 11g standard is at least close to release before launching this salvo. But there’s already a rumor that D-Link will start shipping Atheros-based tri-mode product this month (February).
Revised March 10, 2003 It appears that the “next step” is already here. As of early March, NETGEAR, Linksys and D-Link all announced tri-mode (a/b/g) products, with NETGEAR going with Atheros for their entire product line. These introductions have already resulted in significant price reductions on draft-11g only products.
-
11b isn’t obsolete – The biggest argument heard for buying right now is “I don’t want to buy obsolete stuff”. But 11b isn’t obsolete. It’s the #1 wireless technology right now and that isn’t going to change over night. The 11b product selection is huge, prices are cheap (and likely to get cheaper) as vendors dump 11b product to clear inventories for 11g. 11g preserves your investment in 11b products and lets you make the change when you need / want to.
- The big guys ain’t buyin’ – “Enterprise” buyers know an unfinished technology when they see one, but also sometimes go for it when they see a strategic advantage. They’re not seeing one in 11g yet and only buying for evaluation purposes.
I hope the information I’ve presented will help you separate what’s happening now with the early draft-11g products from what the technology will eventually be capable of when the smoke clears. Part 2 of this NTK presents more of my test results, including my first look at Intersil-based products.
For Further Reading Revised March 12, 2003
-
Intersil’s CommsDesign article has understandable technical background info on 802.11g, including range comparisons
-
Atheros’ Measuring Wireless LAN Performance white paper (PDF file) has practical info for anyone trying to compare wireless products
-
Atheros’ 802.11 Wireless LAN Performance white paper (PDF file) with performance comparisons of draft-11g products in both open-office and residential environments. Also includes eye-opening comparison of first and second-generation 802.11a product performance.
-
[1] Although it doesn’t specifically cover 802.11g, I found Matthew Gast’s 802.11 Wireless Networks: The Definitive Guide (April 2002 ISBN: 0-596-00183-5 $44.95 US, $69.95 CA, £31.95 UK) very helpful in understanding some of the basic 802.11 mechanisms that are being used in 11g’s protection mechanism.