View BCM4317_1569318.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

white paper ieee 802.11g 802.11g-wp104-r www.54g.org 16215 alton parkway ? p.o. box 57013 irvine, ca 92619-7013 phone: 949-450-8700 fax: 949-450-8710 07/02/03 the new mainstream wi reless lan standard today?s popular ieee 802.11b (802.11b) for wireless local area networks (wlans) has changed the face of networking, providing tremendous flexibility for mobile workers and hassle-free internet sharing for home users. the next milestone in the evolution of wlans is the introduction of ieee 802.11g (802.11g). this new ieee standard will dramatically improve the performance of wlans, while providing compatibility with the existing installed base of 802.11b networks. the purpose of this white paper is to: provide an explanation of existing wlan standards describe 802.11g specification requirements set expectations for 802.11g performance discuss 54g?, the high performance implementation of the 802.11g standard wlan m arket the wlan market has grown rapidly as wireless technology has evolved to meet fundamental needs of businesses and technology consumers alike: corporate it departments deploy wlans to support roving employees, reduce the cost of cabling and recabling the physical plant, and provide a rapid response to changes in demand. the mobile worker uses public access wlans in cafes, airports, trains, lobbies, and remote corporate sites to connect to the corporate network or internet. small offices and enterprises use wlans to share internet connections, printers and peripherals, and create backup connectivity solutions while remaining highly scalable and flexible, without the costs of cabling. the home customer uses a wlan to share a broadband internet connection among multiple family pcs without drilling holes and installing cable throughout the home. these customers have adopted wlan solutions to achieve flexibility, connectivity, mobility, and low-cost deployments not available through conventional wired solutions. the numbers speak for themselves?over 35 million wlan nodes have already shipped and the number of nodes is expected to grow to 100 million in 2005. table of contents wlan standards................................................................................................................. ...................... page 2 802.11g performance and characteristics ........................................................................................ ........ page 3 network environment considerations ............................................................................................. .......... page 5 which standard should i deploy? ................................................................................................ ............ page 9 what is 54g??.................................................................................................................. ...................... page 11 conclusion..................................................................................................................... .......................... page 12
ieee 802.11g white paper 07/02/03 broadcom corporation page 2 wlan standards document 802.11g-wp104-r www.54g.org wlan s tandards the foundation of mainstream wlan products began with the original 802.11 standard developed in 1997 by the institute of electrical and electronics engineers (ieee). that base standard continues to be enhanced through document additions that are designated by a letter following the 802.11 name, such as 802.11b, 802.11a, or 802.11g. the letter suffix represents t he task group that defines the extension to the standard. these enhancements bring increases in data rate and functionality leading to rapid progression of the wlan market. the following table briefly summarizes the enhancements related to data rate (the wlan physical layer). more information is available at http://grouper.ieee.org/groups/802/11. ieee 802.11b ratified by the ieee in july 1999, 802.11b extends the original ieee 802.11 direct sequence spread spectrum (dsss) standard to operate up to 11 mbps in the 2.4-ghz unlicensed spectrum using complementary code keying (cck) modulation. the four data rates of 1, 2, 5.5, and 11 mbps are specified on up to three non- overlapping channels, and the lowest two rates are also allowed on up to 13 overlapping channels. ieee 802.11a ratified by the ieee at the same time as 802.11b, the ieee 802.11a (802.11a) standard operates in the 5-ghz spectrum. the 802.11a standard was designed for higher bandwidth applications than 802.11b, and includes data rates of 6, 9, 12, 18, 24, 36, 48, 54 mbps using orthogonal frequency division multiplexing (ofdm) modulation on up to 12 discrete channels. ieee 802.11g in july 1999, the 802.11g subcommittee was tasked to extend the 2.4-ghz unlicensed spectrum to data rates faster than 20 mbps. the resulting 802.11g standard was ratified in june 2003. the 802.11g standard provides optional data rates of up to 54 mbps, and requires backward compatibility with 802.11b devices to protect the substantial investments in today?s wlan installations. the 802.11g standard includes mandatory and optional components. it specifies ofdm (the same technology used in 802.11a) and cck as the mandatory modulation schemes with 24 mbps as the maximum mandatory data rate, but it also provides for optional higher data rates of 36, 48, and 54 mbps. table 1: ieee 802.11 specifications 802.11b 802.11a 802.11g standard approved july 1999 july 1999 june 2003 maximum data rate 11 mbps 54 mbps 54 mbps modulation cck ofdm ofdm and cck data rates 1, 2, 5.5, 11 mbps 6, 9, 12, 18, 24, 36, 48, 54 mbps cck: 1, 2, 5.5, 11 ofdm: 6, 9, 12, 18, 24, 36, 48, 54 mbps frequencies 2.4?2.497 ghz 5.15?5.35 ghz 5.425?5.675 ghz 5.725?5.875 ghz 2.4?2.497 ghz
white paper ieee 802.11g 07/02/03 broadcom corporation document 802.11g-wp104-r 802.11g performance and characteristics page 3 www.54g.org 802.11g p erformance and c haracteristics data rate, range, throughput, and compatibility vary among the three wlan standards. these variations are caused by differences in frequency, modulation schemes, and number of data rates. 802.11g d ata r ates the 802.11 standard technologies all support multiple data rates to allow clients to communicate at the best possible speed. data rate selection is a tradeoff between obtaining the highest possible data rate while trying to minimize the number of communication errors. whenever there is an error in the data, the systems must spend time to retransmit the data until it is error free. each 802.11 client performs a procedure to select the best data rate. the 802.11g clients can select from the widest possible range of both ofdm data rates of 54, 48, 36, 24, 18, 12, 9, and 6 mbps, and the cck rates of 11, 5.5, 2, and 1 mbps. m arket a cceptance of wlan s tandards 802.11b the industry standard for wlans has been 802.11b. products based on 802.11b gained mainstream acceptance as the first wireless networking products with acceptable speeds, affordable prices, and universal compatibility as certified by the wi-fi alliance. more than 95% of today?s wlan infrastructure includes 802.11b products. 802.11a the first 802.11a based products became available late 2001. these products provide data rates of up to 54 mbps in the 5-ghz frequency band. even though the technology delivers greater data rates, it has had limited market acceptance. this has been due primarily to its lack of backward compatibility with 802.11b products, shorter connectivity range, and higher deployment costs. 802.11g the next mainstream wireless lan standard is 802.11g. this technology satisfies the bandwidth needs of the market globally and economically, while remaining compatible with the installed base of mainstream products. 802.11g approval and certification the ieee 802.11g standard was approved in june 2003. the ieee standards body, however, does not validate interoperability or compliance with the standard; an industry association (wi-fi alliance) performs these tasks. the wi-fi alliance is already building a testing program to certify 802.11g interoperability based on the 802.11g standard. the wi-fi ? certification for 802.11g products is expected in the summer of 2003. the 802.11g certification program follows the wi-fi alliance?s successful 802.11b and 802.11a certification programs. products conforming to the draft 802.11g standard have been available since late 2002. products shipped prior to june may be upgraded via software download to ensure standards compliance.
ieee 802.11g white paper 07/02/03 broadcom corporation page 4 802.11g performance and char acteristics document 802.11g-wp104-r www.54g.org 802.11g r ange and d ata r ate as distance from the access point increases, 802.11 based products provide reduced data rates to maintain connectivity. the 802.11g standard has the same propagation characteristic as 802.11b, because it transmits in the identical 2.4-ghz frequency band. because 802.11b and 802.11g products share the same propagation characteristics, implementations provide roughly the same maximum range at the same data rate. because 5-ghz radio signals do not propagate as well as 2.4-ghz radio signals, the 802.11a product range is limited compared to the 802.11b or 802.11g product range. the following figure illustrates the expected data rate of each technology at different ranges. figure 2: expected 802.11a, 802.11b, and 802.11g data rates at varying distance from access point
white paper ieee 802.11g 07/02/03 broadcom corporation document 802.11g-wp104-r network envi ronment considerations page 5 www.54g.org typically, 2.4-ghz 802.11g networks have the same coverage as 2.4-ghz 802.11b networks. the 802.11b standard uses cck modulation, whereas 802.11g uses both cck modulation for backward compatibility and ofdm modulation to achieve better throughput at a given distance. the 802.11a standard also uses ofdm modulation, but there is more signal loss as it travels through objects because it uses a higher frequency. figure 3: relative range of 802.11b, 802.11g, and 802.11a devices n etwork e nvironment c onsiderations one of the major benefits of the 802.11g standard is the mandate for 802.11g and 802.11b devices to communicate with each other. at all 802.11b rates, 802.11b devices communicate with 802.11g products as if they were 802.11b products. however, 802.11g products behave differently when using ofdm data rates if there are 802.11b devices in the network environment. understanding this behavior is important in setting performance expectations (given the large installed base of 802.11b clients) and the planning of network capacity until 802.11b clients are replaced with 802.11g clients (the presence of an 802.11a 5-ghz network has no effect on these scenarios). the following scenarios show how the type of network environment is determined both by the network infrastructure and client devices. 802.11b-o nly l egacy e nvironment when the ap and all clients are 802.11b, communication occurs at 802.11b data rates. overhead communication between the products effectively limits the maximum tcp throughput to 5.8 mbps. when the products are communicating at greater distances and lower data rates, the throughput is correspondingly reduced.
ieee 802.11g white paper 07/02/03 broadcom corporation page 6 network environment considerations document 802.11g-wp104-r www.54g.org 802.11g t hroughput throughput is not the same as data rate for networking systems, because of overhead, environment, and network composition. the throughput of 802.11g products can depend on whether there are 802.11b products nearby. performance is best in environments where an 802.11g access point (ap) is only communicating with 802.11g clients in a homogeneous wlan. in these environments, the data rate within 75 feet is 54 mbps and the throughput is 22?24 mbps when using transmission control protocol (tcp). in the interest of maximizing performance in the presence of 802.11b products, the 802.11g aps coordinate the use of the transmission medium with protection mechanisms (see sidebar). because the protection mechanisms require overhead communication, compatibility is provided at the expense of throughput. the cts-to-self protection mechanism lowers the maximum tcp throughput to approximately 15 mbps, as shown in the following table. 802.11g c ompatibility because 802.11g uses the same radio signaling (cck) as 802.11b at the lower four 802.11g data rates, it is fully backward compatible with 802.11b. this enables networks to continue supporting 802.11b enabled devices when migrating to the higher performance standard. protection mechanism: air traffic control the 802.11g standard provides protection mechanisms for managing communication in a mixed 802.11b/g environment. the 802.11b radios do not hear when the airspace is busy with 802.11g ofdm signals. protection mechanisms prevent 802.11b clients from transmitting after improperly assessing that the airspace is empty while 802.11g ofdm signals are being transmitted. the 802.11g products still communicate at the same 802.11g ofdm data rates when protection is in use, but a short 802.11b rate message signals to 802.11b products to not transmit for a specified duration because an 802.11g ofdm message is immediately following. the 802.11b protection messages cause signaling overhead and result in reduced throughput to the user. the ap directs clients to use protection through a signaling mechanism specified within the 802.11g standard. enterprise-class 802.11g aps may allow users to tune the protection mechanism algorithm to optimize network system performance (some 802.11g aps may allow the administrator to override the use of the protection mechanism for a performance improvement in light traffic networks). the 802.11g standard allows 802.11g clients to use one of several protection mechanisms in a mixed 802.11b/g environment. the wi-fi alliance will test for one of two signalling methods: rts/cts and cts-to-self. request to send (rts) is analogous to a pilot?s take off request to an air traffic control tower?the pilot waits to use the airspace until verifying with the control tower that the airspace is clear. the clear to send (cts) message is like the clearance from the tower. the cts-to-self protection mechanism method sends a cts message using an 802.11b rate to clear the air, and then immediately follows with data using an 802.11g date rate. the cts-to-self protection mechanism provides a maximum tcp throughput of 14.7 mbps. with any of the protection mechanisms, 802.11g throughput is still greater than 802.11b throughput at the same distance. table 2: expected maximum throughput for ieee 802.11 environments distance (feet) 802.11b (mbps) 802.11a (mbps) 802.11g- only (mbps) 802.11g mixed environment with cts-to-self (mbps) 802.11g mixed environment with rts/cts (mbps) 10 5.8 24.7 24.7 14.7 11.8 50 5.8 19.8 24.7 14.7 11.8 100 5.8 12.4 19.8 12.7 10.6 150 5.8 4.9 12.4 9.1 8.0 200 3.7 0 4.9 4.2 4.1 250 1.6 0 1.6 1.6 1.6 300 0.9 0 0.9 0.9 0.9
white paper ieee 802.11g 07/02/03 broadcom corporation document 802.11g-wp104-r network envi ronment considerations page 7 www.54g.org 802.11g-o nly when the ap and all clients are 802.11g, communication occurs at the highest possible tcp throughput. the 802.11g ap detects that all of the clients are 802.11g and instructs the network not to use any protection method. without a protection mechanism engaged, throughput of 24 mbps or greater is possible. 802.11g ap, m ixed c lients when the ap is 802.11g and there is a mixture of 802.11g clients and 802.11b clients, the ap senses both technologies on the network. the 802.11g ap instructs 802.11g clients to use a protection mechanism. effectively, 802.11g clients function at reduced 802.11g tcp throughput (up to 15 mbps), which is faster than the 802.11b client that communicates at a maximum throughput of up to 5.8 mbps. 802.11b ap, 802.11g c lient when the ap is 802.11b and the client is 802.11g, the 802.11g client is able to successfully associate and communicate with the 802.11b ap. communication between the ap and the 802.11g client uses cck modulation and achieves typical 802.11b speeds. an 802.11g client can always function as an 802.11b client. figure 4: 802.11g-only environment figure 5: 802.11g ap, mixed client environment figure 6: 802.11b ap, 802.11g client environment 802.11g access point 802.11g client g access point ?full g throughput g clients ?full g throughput 802.11g client g access point ?operates in mixed g mode b client ?behaves as a b client g client ?faster than b , slower than g only 802.11g access point 802.11g client 802.11b client 802.11b access point 802.11g client b access point ?full b throughput g client ?behaves as a b client
ieee 802.11g white paper 07/02/03 broadcom corporation page 8 network environment considerations document 802.11g-wp104-r www.54g.org m ultiple 802.11g ap s , m ixed c lients when there are multiple 802.11g aps and a single 802.11b client on the same channel, all overlapping 802.11g aps signal the use of the protection mechanism. effectively, 802.11g clients function at a reduced 802.11g tcp throughput (up to 15 mbps), which is faster than the 802.11b client, which communicates at a typical 802.11b tcp throughput (up to 5.8 mbps). the aps can also be configured to use different channels for their 802.11g clients so that the 802.11g-only networks do not need to use a protection mechanism. this allows 802.11g clients to have full tcp throughput as if they were in an 802.11g-only network. figure 7: multiple 802.11g aps, mixed clients 802.11g access point client g 1 g access points ? both downshift to communicate seamlessly with each client clients g1, g2, g3 ? operates in mixed g mode ? faster than b , slower than g only mode bclient ? full throughput, but a ffects entire network client g 2 client g 3 client b 802.11g access point
white paper ieee 802.11g 07/02/03 broadcom corporation document 802.11g-wp104-r which standard should i deploy? page 9 www.54g.org w hich s tandard s hould i d eploy ? with any network technology, there are tradeoffs between performance and cost. with wireless technologies, other factors such as range and capacity should also be considered. table 3 summarizes typical user requirements and the characteristics of wlan technology. in most cases, 802.11g provides the correct mix of characteristics for the different categories of user requirements. upgrading to 802.11g is the easiest and least expensive choice, because it can be done gradually, without sacrificing the current wlan infrastructure. the 802.11g aps automatically support existing 802.11b clients while providing increased speed to 802.11g clients. planning network migration as network managers plan upgrades from existing wireless 802.11b networks, the two basic technologies to consider are 802.11g and 802.11a/g. an upgrade to 802.11g is a simple proposition. users equipped with 802.11g-enabled notebooks will gain immediate access to the 802.11b network. these users will experience a throughput boost as aps are upgraded to 802.11g. as budget allows, dual-band 802.11a/g products can be deployed to meet the demand for more network capacity while remaining backward compatible. the dual-band aps may need to be more closely spaced to ensure coverage for 802.11a clients. transmit power control can be enabled in the 802.11g network to optimize performance of closely spaced access points. because 802.11g is forecast to rapidly replace 802.11b, a dual-band a/b ap solution becomes immediately obsolete. table 3: wlan user requirements and technology characteristics in the u.s. typical wlan user requirements type of wlan peak speed capacity range 802.11b compatible budget enterprise high variable variable yes high public access low medium high yes medium small business medium medium high yes low home medium low high yes low wlan technology characteristics wlan technology peak speed capacity range 802.11b compatible cost 802.11b medium low high yes low 802.11a high high low no medium 802.11g high medium high yes low 802.11a/g high high high yes high
ieee 802.11g white paper 07/02/03 broadcom corporation page 10 which standard should i deploy? document 802.11g-wp104-r www.54g.org e nterprise enterprise wlans are typically an overlay to a wired infrastructure serving the needs of mobile workers for e-mail, web browsing, and intranet access when they are away from their desks. coverage is typically more important than connection rate. enterprises can benefit from the higher bandwidth and backward compatibility of 802.11g networks today, and can outfit densely populated environments or plan for wired network replacement with dual-band 802.11a/g networks. it is expected that enterprise customers will future-proof their networks by providing 802.11g connections on the client side, and upgrade infrastructure as budget permits. p ublic a ccess ?h otspots (w i -f i zone?) compatibility and range matter most to hotspot operators and public access wlan customers. public wlan hotspots must be certain that their aps can communicate using mainstream standards that offer connectivity to the widest possible range of subscribers. today, nearly all hotspot traffic is 802.11b. public access operators remain in the 2.4-ghz band because it offers twice the range and four times the coverage area of the 5-ghz alternative, and public access customers continue to use the 2.4-ghz spectrum to maximize connectivity. as hotspots upgrade, they will add 802.11g to their networks to add range and preserve interoperability. s mall b usiness a small business wlan needs to cover small to medium-sized areas and support a variety of applications, such as e-mail, web browsing, and large file transfer. because of good performance characteristics, costs, and range, 802.11g again makes the most sense. the 802.11g standard offers compelling value by minimizing the number of aps, lowering deployment costs, while future proofing the installation with a mainstream standard. many small businesses may simply require a single 802.11g ap and no wired infrastructure at all. h ome many homeowners today have multiple computers and want to share a common internet connection. for these uses, low-cost 802.11g or 802.11b solutions suffice. as the number of home network devices expand and bandwidth-hungry applications grow (such as gaming, home-wide audio and video streaming, and home security), an 802.11g wlan provides up to five times the performance of an 802.11b wlan. the 802.11g solutions provide the bandwidth for added devices and new applications, with a range that covers most homes with one or two aps.
white paper ieee 802.11g 07/02/03 broadcom corporation document 802.11g-wp104-r what is 54g?? page 11 www.54g.org w hat is 54g?? 54g? is the maximum performance implementation of the ieee 802.11g standard and is fully compliant. 54g? technology provides data rates of up to 54-mbps with the highest throughput allowed by the specification and provides the industry?s best range and latest security. the 54g? logo can be found only on products that achieve this high level of performance (see figure 8). 54g??m aximum p erformance 802.11g the 54g? implementation is designed to exceed the requirements of the ieee 802.11g standard, as shown in table 4. the 54 mbps data rate and short slot turnaround time are optional in the standard but are included in 54g?. these features more than double the expected throughput of a product that just meets the standard. the receiver sensitivity of 54g? products far exceeds th e specification for maximum range, and transmit power control is included in 54g? to enable optimized multiple ap deployments. all 54g? products are wpa certified and embed hardware-accelerated aes security, which future-proofs users in advance of the ieee 802.11i (802.11i) standard due to be adopted next year. l ook for the 54g? l ogo the 54g? logo indicates that a product is a maximum-performance implementation of the 802.11g standard, is fully backward compatible with 802.11b products, and is compatible at maximum performance with any other product bearing the 54g? logo. it provides consumers with an easy way to find high-performance wlans based on the 802.11g standard, and protects them from investing in 802.11g solutions where the highest data rate is less than 54 mbps. major wireless networking and pc vendors are shipping 54g? products, ensuring a broad selection of compatible, high-performance products. figure 8: 54g? logo table 4: 54g? pushes the performance limits of 802.11g 54g? specification 802.11g standard highest mandatory data rate 54 mbps 24 mbps shortest mandatory slot time 9 s 20 s maximum receiver sensitivity ?92 dbm ?80 dbm transmit power control included not specified next generation aes security included not specified
document 802.11g-wp104-r broadcom corporation 16215 alton parkway p.o. box 57013 irvine, ca 92619-7013 phone: 949-450-8700 fax: 949-450-8710 ? 2003. all rights reserved printed in the u.s.a. broadcom ? , the pulse logo, and 54g? are trademarks of broadcom corporation and/or its subsidiaries in the united states and certain othe r countries. wi-fi ? and wi-fi zone? are trademarks of the wi-fi alliance. all other trademarks are the property of their respective owners. broadcom corporation reserves the right to make changes without further notice to any products or data herein to improve reliab ility, function, or design. information furnished by broadcom corporation is believed to be accurate and reliable. however, broadcom corporation does not assume any liability arising out of the application or use of this information, nor the application or use of any prod uct or circuit described herein, neither does it convey any license under its patent rights nor the rights of others. ieee 802.11g white paper 07/02/03 c onclusion the ieee 802.11g standard will drive the next growth wave in wireless networking. products built to the ieee 802.11g standard are compelling because they: provide a five-fold increase in wlan speed over current networks remain fully backward compatible with the popular ieee 802.11b based products offer better range and coverage than current networks this new wlan technology provides flexibility, connecti vity, mobility, and affordability that is not available through conventional wired solutions. 54g? is 802.11g implemented at the highest levels of the standard, and available today. 54g? is fully backward compatible with 802.11b. 54g? products used together provide the highest levels of speed, reach, and security for maximum performance.

▲Up To Search▲

Price & Availability of BCM4317

	To Download BCM4317 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .