The whole issue lies in the separation of functionality between the radio part (the WLAN card) and the main processor. In some cases, the WLAN card will actually do most of the stuff (802.11 reception and transmission, encryption/decryption, but also handling of management frames, etc.), while the CPU will be idling most of the time, being there only for management (I mean web interface, SNMP, etc. management) and bridging/routing to the Ethernet. In other cases, the WLAN card will do very little (the time-critical stuff, mainly), and the CPU will do most of the job. And of course you have many combinations in between.
Now, to build an AP using easily available parts, you need a card that will either do everything (but know how to do the AP side of things), or a card that won't do much, but will give you enough hooks so that you can do the stuff yourself in software. If you have a card that does everything by itself but only knows the client side of things, you're stuck (as is the case with most WLAN cards available, which can only be used as clients).
Hostap is a special mode in the firmware of Intersil Prism family chips that allows you to do just that: it does the critical stuff in the card as usual, but it allows you to receive and send management frames, and all sorts of other things that allow you to control most of the behaviour of the card to act as an AP. There is also another mode on that chipset, using additional firmware to download onto the card (tertiary firmware), where the card will do most of the AP-related stuff by itself. That is what most low-end AP vendors use.
One of the advantages of doing the stuff on the main CPU rather than in the card is that you can control things a lot more: you have a "real" machine (depending on the type of host you use), and you can use all usual tools. This allows new encryption types to be used, for instance. The drawback is that is uses more CPU, of course.
Hope that helps,
Jacques.
At 15:41 07/02/2003, visakhae wrote:
Hello Jacques, thanks a lot for ur answer on dynamic key mapping. Please can you explain me concept of host based ap(hostap)and firmware based APs. How do they differ in concept? And how the place where encrption is done is affected by with these two types of APs?Thanks in advance. regards, Visakha. *************************************************************************** This message is proprietary to Future Software Limited (FSL) and is intended solely for the use of the individual to whom it is addressed. It may contain privileged or confidential information and should not be circulated or used for any purpose other than for what it is intended. If you have received this message in error, please notify the originator immediately. If you are not the intended recipient, you are notified that you are strictly prohibited from using, copying, altering, or disclosing the contents of this message. FSL accepts no responsibility for loss or damage arising from the use of the information transmitted by this email including damage from virus. *************************************************************************** -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
-- Jacques Caron, IP Sector Technologies Join the discussion on public WLAN open global roaming: http://lists.ipsector.com/listinfo/openroaming -- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
