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USER’S MANUAL OF WLAN BROADBAND ROUTER
Version: 2.1
58
4.7
What are potential factors that may causes interference?
Factors of interference:
¾
Obstacles: walls, ceilings, furniture… etc.
¾
Building Materials: metal door, aluminum studs.
¾
Electrical devices: microwaves, monitors and electrical motors.
Solutions to overcome the interferences:
9
Minimizing the number of walls and ceilings.
9
Position the WLAN antenna for best reception.
9
Keep WLAN devices away from other electrical devices, eg: microwaves,
monitors, electric motors, … etc.
9
Add additional WLAN Access Points if necessary.
4.8
What are the Open System and Shared Key authentications?
IEEE 802.11 supports two subtypes of network authentication services: open system and
shared key. Under open system authentication, any wireless station can request
authentication. The station that needs to authenticate with another wireless station sends
an authentication management frame that contains the identity of the sending station.
The receiving station then returns a frame that indicates whether it recognizes the
sending station. Under shared key authentication, each wireless station is assumed to
have received a secret shared key over a secure channel that is independent from the
802.11 wireless network communications channel.
4.9
What is WEP?
An optional IEEE 802.11 function that offers frame transmission privacy similar to a
wired network. The Wired Equivalent Privacy generates secret shared encryption keys
that both source and destination stations can use to alert frame bits to avoid disclosure to
eavesdroppers.
WEP relies on a secret key that is shared between a mobile station (e.g. a laptop with a
wireless Ethernet card) and an access point (i.e. a base station). The secret key is used to
encrypt packets before they are transmitted, and an integrity check is used to ensure that
packets are not modified in transit.
4.10
What is Fragment Threshold?
The proposed protocol uses the frame fragmentation mechanism defined in IEEE 802.11
to achieve parallel transmissions. A large data frame is fragmented into several
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USER’S MANUAL OF WLAN BROADBAND ROUTER
Version: 2.1
59
fragments each of size equal to fragment threshold. By tuning the fragment threshold
value, we can get varying fragment sizes. The determination of an efficient fragment
threshold is an important issue in this scheme. If the fragment threshold is small, the
overlap part of the master and parallel transmissions is large. This means the spatial
reuse ratio of parallel transmissions is high. In contrast, with a large fragment threshold,
the overlap is small and the spatial reuse ratio is low. However high fragment threshold
leads to low fragment overhead. Hence there is a trade-off between spatial re-use and
fragment overhead.
Fragment threshold is the maximum packet size used for fragmentation. Packets larger
than the size programmed in this field will be fragmented.
If you find that your corrupted packets or asymmetric packet reception (all send packets,
for example). You may want to try lowering your fragmentation threshold. This will
cause packets to be broken into smaller fragments. These small fragments, if corrupted,
can be resent faster than a larger fragment. Fragmentation increases overhead, so you'll
want to keep this value as close to the maximum value as possible.
4.11
What is RTS (Request To Send) Threshold?
The RTS threshold is the packet size at which packet transmission is governed by the
RTS/CTS transaction. The IEEE 802.11-1997 standard allows for short packets to be
transmitted without RTS/CTS transactions. Each station can have a different RTS
threshold. RTS/CTS is used when the data packet size exceeds the defined RTS
threshold. With the CSMA/CA transmission mechanism, the transmitting station sends
out an RTS packet to the receiving station, and waits for the receiving station to send
back a CTS (Clear to Send) packet before sending the actual packet data.
This setting is useful for networks with many clients. With many clients, and a high
network load, there will be many more collisions. By lowering the RTS threshold, there
may be fewer collisions, and performance should improve. Basically, with a faster RTS
threshold, the system can recover from problems faster. RTS packets consume valuable
bandwidth, however, so setting this value too low will limit performance.
4.12
What is Beacon Interval?
In addition to data frames that carry information from higher layers, 802.11 includes
management and control frames that support data transfer. The beacon frame, which is a
type of management frame, provides the "heartbeat" of a wireless LAN, enabling
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USER’S MANUAL OF WLAN BROADBAND ROUTER
Version: 2.1
60
stations to establish and maintain communications in an orderly fashion.
Beacon Interval represents the amount of time between beacon transmissions. Before a
station enters power save mode, the station needs the beacon interval to know when to
wake up to receive the beacon (and learn whether there are buffered frames at the access
point).
4.13
What is Preamble Type?
There are two preamble types defined in IEEE 802.11 specification. A long preamble
basically gives the decoder more time to process the preamble. All 802.11 devices
support a long preamble. The short preamble is designed to improve efficiency (for
example, for VoIP systems). The difference between the two is in the Synchronization
field. The long preamble is 128 bits, and the short is 56 bits.
4.14
What is SSID Broadcast?
Broadcast of SSID is done in access points by the beacon. This announces your access
point (including various bits of information about it) to the wireless world around it. By
disabling that feature, the SSID configured in the client must match the SSID of the
access point.
Some wireless devices don't work properly if SSID isn't broadcast (for example the
D-link DWL-120 USB 802.11b adapter). Generally if your client hardware supports
operation with SSID disabled, it's not a bad idea to run that way to enhance network
security. However it's no replacement for WEP, MAC filtering or other protections.
4.15
What is Wi-Fi Protected Access (WPA)?
Wi-Fi’s original security mechanism, Wired Equivalent Privacy (WEP), has been
viewed as insufficient for securing confidential business communications. A longer-term
solution, the IEEE 802.11i standard, is under development. However, since the IEEE
802.11i standard is not expected to be published until the end of 2003, several members
of the WI-Fi Alliance teamed up with members of the IEEE 802.11i task group to
develop a significant near-term enhancement to Wi-Fi security. Together, this team
developed Wi-Fi Protected Access.
To upgrade a WLAN network to support WPA, Access Points will require a WPA
software upgrade. Clients will require a software upgrade for the network interface card,
and possibly a software update for the operating system. For enterprise networks, an
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USER’S MANUAL OF WLAN BROADBAND ROUTER
Version: 2.1
61
authentication server, typically one that supports RADIUS and the selected EAP
authentication protocol, will be added to the network.
4.16
What is WPA2?
It is the second generation of WPA. WPA2 is based on the final IEEE 802.11i
amendment to the 802.11 standard.
4.17
What is 802.1x Authentication?
802.1x is a framework for authenticated MAC-level access control, defines Extensible
Authentication Protocol (EAP) over LANs (WAPOL). The standard encapsulates and
leverages much of EAP, which was defined for dial-up authentication with
Point-to-Point Protocol in RFC 2284.
Beyond encapsulating EAP packets, the 802.1x standard also defines EAPOL messages
that convey the shared key information critical for wireless security.
4.18
What is Temporal Key Integrity Protocol (TKIP)?
The Temporal Key Integrity Protocol, pronounced tee-kip, is part of the IEEE 802.11i
encryption standard for wireless LANs. TKIP is the next generation of WEP, the Wired
Equivalency Protocol, which is used to secure 802.11 wireless LANs. TKIP provides
per-packet key mixing, a message integrity check and a re-keying mechanism, thus
fixing the flaws of WEP.
4.19
What is Advanced Encryption Standard (AES)?
Security issues are a major concern for wireless LANs, AES is the U.S. government’s
next-generation cryptography algorithm, which will replace DES and 3DES.
4.20
What is Inter-Access Point Protocol (IAPP)?
The IEEE 802.11f Inter-Access Point Protocol (IAPP) supports Access Point Vendor
interoperability, enabling roaming of 802.11 Stations within IP subnet.
IAPP defines messages and data to be exchanged between Access Points and between
the IAPP and high layer management entities to support roaming. The IAPP protocol
uses TCP for inter-Access Point communication and UDP for RADIUS request/response
exchanges. It also uses Layer 2 frames to update the forwarding tables of Layer 2
devices.
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USER’S MANUAL OF WLAN BROADBAND ROUTER
Version: 2.1
62
4.21
What is Wireless Distribution System (WDS)?
The Wireless Distribution System feature allows WLAN AP to talk directly to other APs
via wireless channel, like the wireless bridge or repeater service.
4.22
What is Universal Plug and Play (uPNP)?
UPnP is an open networking architecture that consists of services, devices, and control
points.
The ultimate goal is to allow data communication among all UPnP devices
regardless of media, operating system, programming language, and wired/wireless
connection.
4.23
What is Maximum Transmission Unit (MTU) Size?
Maximum Transmission Unit (MTU) indicates the network stack of any packet is larger
than this value will be fragmented before the transmission. During the PPP negotiation,
the peer of the PPP connection will indicate its MRU and will be accepted. The actual
MTU of the PPP connection will be set to the smaller one of MTU and the peer’s MRU.
The default is value 1400.
4.24
What is Clone MAC Address?
Clone MAC address is designed for your special application that request the clients to
register to a server machine with one identified MAC address.
Since that all the clients will communicate outside world through the WLAN Broadband
Router, so have the cloned MAC address set on the WLAN Broadband Router will solve
the issue.
4.25
What is DDNS?
DDNS is the abbreviation of Dynamic Domain Name Server. It is designed for user own
the DNS server with dynamic WAN IP address.
4.26
What is NTP Client?
NTP client is designed for fetching the current timestamp from internet via Network
Time protocol. User can specify time zone, NTP server IP address.
4.27
What is VPN?
VPN is the abbreviation of Virtual Private Network. It is designed for creating point-to
point private link via shared or public network.

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