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Basic Service Set (BSS) to another. Two adjoining Basic Service Sets form an
Extended Service Set (ESS) if they are defined by a common ESSID.
If a common ESSID is defined, a wireless client to roam from one area to another.
Although reassociation is specified in 802.11, the mechanism that allows AP-to-
AP coordination to handle roaming is not specified.
• Authentication
Authentication is the process of proving a client identity, and in IEEE 802.11this
process takes place prior to a wireless client associating with an AP. By default,
IEEE 802.11 devices operate in an Open System, where essentially any wireless
client can associate with an AP without the checking of credentials. True
authentication is possible with the use of the 802.11 option known as Wired
Equivalent Privacy or WEP, where a Shared Key is configured into the AP and its
wireless clients. Only those devices with a valid Shared Key will be allowed to be
associated to the AP.
• Privacy
By default, data is transferred "in the clear"; any 802.11-compliant device can
potentially eavesdrop like-PHY 802.11 traffic that is within range. The WEP
option encrypts data before it is sent wirelessly, using a 40-bit encryption
algorithm known as RC4. The same Shared Key used in authentication is used to
encrypt or decrypt the data; thus only wireless clients with the exact Shared Key
can correctly decipher the data.
.
3.2 VOICE OVER IP
In the truest form of the concept, voice over IP is a network level application. When a
user places a VoIP call over an internet Service provider, his call is switched through the
PSTN (public switched telephone network) to a Voice over IP gateway which interfaces
the PSTN to the ISP’s network which may in turn interface with the internet. The VoIP
gateway then routes the call to the VoIP gateway nearest the destination which then
interfaces onto the PSTN on the other side. When the VoIP gateway at the destination
side receives the Voice packets they are collected and after some Segmentation and
reassembly are sent on through the PSTN.
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