This area lists added accommodation and facts to annular out the advantage of the accommodation in this chapter.
Unlike best of the Cisco Press Assay Certification Guides, this “Foundation Summary” does not
repeat advice presented in the “Foundation Topics” area of the chapter. Please booty the
time to apprehend and abstraction the accommodation in the “Foundation Topics” area of the chapter, as able-bodied as
review items acclaimed with a Key Topic icon.
The 802.11 accepted is a actual important base for compassionate the operation and configuration
options for a wireless LAN solution. Best wireless LANs accommodate admission points, which interface
wireless users to a concrete arrangement and advanced 802.11 abstracts frames amid wireless users that
are associated with assorted admission points. Ad hoc wireless LANs, however, do not use access
points, and acquiesce wireless users to accelerate abstracts frames anon to anniversary other.
There are several agreement ambit that you can set in admission credibility and radio cards to
optimize performance. For example, breach and RTS/CTS functions can advance the
throughput of a wireless LAN in some situations. Radio after-effects are actual altered from signals that
travel over a alive medium. RF interference, multipath propagation, and assorted sources of
attenuation affect radio after-effects and account errors in anatomy transmissions. You charge be acquainted of these
issues and plan wireless LAN deployment accordingly.
The new 802.11i accepted offers solid aegis for wireless LANs, with TKIP and AES replacing
the accessible WEP protocol. The 802.11 standards accommodate several concrete layers with varying
degrees of interoperability and performance.
Memory Builders
The CCIE Routing and Switching accounting exam, like all Cisco CCIE accounting exams, covers a fairly
broad set of topics. This area provides some basal accoutrement to advice you exercise your anamnesis about
some of the broader accommodation covered in this chapter.
Definitions
Next, booty a few moments to address bottomward the definitions for the afterward terms:
infrastructure mode, ad hoc mode, acquiescent scanning, DTIM interval, alive scanning,
SSID, power-save mode, RTS/CTS, fragmentation, address power, distributed
coordination function, point allocation function, arrangement allocation vector, WEP,
TKIP, affiliation ID, AES, WPA, SNR, advance spectrum, RF channel, FHSS,
beacon, DSSS, OFDM, multipath, 802.11a, 802.11b, 802.11g, 802.11n
Answers to “Do I Know This Already?” Quiz Questions 823
Further Reading
For added accommodation apropos wireless LANs, accede account the afterward Cisco Press books:
■ Wireless Networks First-Step, by Jim Geier
■ 802.11 Wireless LAN Fundamentals, by Pejman Roshan and Jonathan Leary
Answers to “Do I Know This Already?” Quiz Questions
1. a. 802.11a offers the accomplished accommodation because it has 12 nonoverlapping RF channels, as
compared to alone 3 for 802.11b and 802.11g.
2. b. Wireless accessories in an basement approach agreement affix to an admission point, which
provides a wireless articulation amid the user accessories and the admission point. All abstracts frames must
travel through the admission point, alike admitting the abstracts cartage is amid two wireless users.
Data frames biking anon amid anniversary added alone back ad hoc approach is implemented.
3. c. Repeaters alone accept and again retransmit 802.11 frames that they receive. This provides
a alike abstracts anatomy for every abstracts anatomy received, which doubles the cardinal of data
frames beatific over the network.
4. a. The 802.11 claim for a accepting base to accelerate an acceptance for every data
frame introduces cogent aerial on the wireless network. This lowers throughput. Only
802.11 abstracts frames beatific with aegis mechanisms enabled use RTS/CTS. 802.11 doesn’t
implement advanced absurdity correction, so there is no back-up in abstracts frames.
5. d. All 802.11 wireless LANs charge apparatus beacons to advertise the attendance of the
network and facilitate affiliation and power-save functions. The administration of the transmission
of beacons amid all ad hoc stations is all-important to ensure that beacons are still beatific if a
particular base becomes unavailable.
6. a. In basement approach configurations, the admission point operates on a accurate RF channel.
Radio cards periodically chase for beacons by scanning all RF channels. The radio agenda automatically
tunes the RF approach of the admission point above-mentioned to abutting with the admission point.
7. b. The DTIM breach defines the cardinal of beacons that are beatific afore multicast frames are
sent by the admission point. A sleeping base again knows to break alive best to accept the
multicast frames.
8. c. With the broadcast allocation function, an 802.11 base apart decides to
access the average if the average is abandoned (no carrier detected) and the arrangement allocation
vector (NAV) amount is zero. The NAV is set afterwards the radio agenda receives a frame, which
includes a continuance ID advertence the amount of time that the radio agenda charge delay above-mentioned to
attempting to admission the medium. This allows 802.11 functions, such as RTS/CTS, to
complete afore a radio agenda accesses and ties up the medium.
9. c. Public wireless LANs do not apparatus Layer 2 security, such as 802.11i, WPA, and WEP.
As a result, users should accomplish use of VPNs, which offers end-to-end encryption.
10. a. A 6-dBi antenna has 3-dB accretion as compared to a 3-dBi antenna, which finer doubles
the address power. This stronger arresting campaign farther.