Download FlexNETfunctions

Connecting The World
FlexNET Access and Link
Functions
The Bridge Function Explained
Radio 2
IP 192.168.3.1
Radio 1
IP: 192.168.4.1
Bridge 1
IP: 192.168.5.1
Ethernet 1
IP: 192.168.1.1
Ethernet 2
IP: 192.168.2.1
By default all Interfaces have their own IP, These IP’s should be removed as needed.
In a typical access network both Radio’s are added to
the bridge one Ethernet is also very common
Radio 2
Radio 1
Bridge 1 :Enabled
IP: 192.168.5.1
Ethernet 1
IP: 192.168.1.1
Ethernet 2
IP: 192.168.2.1
The Bridge Interface is a virtual interface
which lets you bind all the interfaces to one
IP address (Bridge) RN900 supports 2
Bridges,
The RN810 and RN820 always have both
radio’s and 1 ethernet in a bridge and this
cannot be modified. 700/800 has one
bridge available
2
Bridge Example
Wireless clients group 1
(With RN900)
Wireless clients group 2
Bridge 1: Radio 1 and Ethernet 1
Bridge 2: Radio 2 and Ethernet 1
group 1 network
Firewall
group 2 network
Firewall
3
Signal strength explained
•
The signal percentage shown in each device is a percentage , to find a more familiar RSL
figure in dB the percentage figure can be divided by 3.
•
Any SNR of over 33dB is depicted as 100%
•
The device drive is updated every 10 seconds and the browser needs to be refreshed, The
level is only reliable when wireless traffic is applied.
(100%)
4
Some Radio features
5
OFDM
Each 20 MHz Channel is composed of 52 independent sub-carriers
The 802.11a standard supports eight data rates from 6 Mbps to 54 Mbps (6 Mbps, 9 Mbps, 12 Mbps,
18 Mbps, 24 Mbps, 36 Mbps, 48 Mbps, and 54 Mbps). Each data rate employs the same 52 subcarriers but they use different modulation and forward error correction (FEC) techniques.
6
802.11a Data rates
•
As the data rate goes up, the modulation gets more complex.
–
More complex modulations = more fragile Signal
–
More fragile signal = lower range
–
G data rates the same but provides CCK for 11 and 5.5Mbps and QPSK for 2 and 1Mbps
Data Rate
(Mbps)
Modulation
Type
Error
Correction
6
BPSK
1/2
9
BPSK
3/4
12
QPSK
1/2
18
QPSK
3/4
24
16-QAM
1/2
36
16-QAM
3/4
48
64-QAM
2/3
54
64-QAM
3/4
7
Medium Reservation (RTS/ CTS)
“Hidden stations” – The problem – The solution
 Problem:
A
B
C
> A sends to B
> C doesn’t detect that, so C might also
start sending to B
> Collision of messages at B: both
messages lost
 Occurs in larger cells (typical
outdoor)
RTS: I want to send to B 500 bytes
CTS: OK A, go ahead, so everybody quiet
Data: the 500 bytes of data from A to B
ACK: B received the data OK, so an ACK
> Loss of performance
> Error recovery required
 Solution: MAC level RTS/CTS
> Adds overhead, but provides robustness
 Configuration option :
> Threshold: RTS only used for packets
larger than this option
8
Message fragmentation
Hit
A hit in a large frame requires re-transmission of a large frame
Fragmenting reduces the frame size and the required time to retransmit
• IEEE 802.11 defines:
– MAC level function to transmit large messages as smaller frames (user
definable)
– Improves performance in RF polluted environments
– Can be switched off to avoid the overhead in RF clean environments
9