# Forum

## Bandwidth on 802.11b and 802.11g

• I like to ask what is the use and effect of the bandwidth on 802.11b and 802.11g when we send traffic from uplink (wireless clients) through access pint to downlink (Ethernet side)
if we set the bandwidth static.

• Hi Freedom900 of Stockholm:

It would help me answer if you restate your question. And what do you mean by "static".

Thanks. /criss

• I think he means choosing a single data rate (ex. 36 Mbps) rather than choosing auto rate selection.

• I ment by that is to set the value using these formulas, so i i like to ask what is the effect of the utilized bit rate( like 11Mbps or 36 Mbps) to the resutls and the delay time ??
the formulas to convert the byte and microsecond to bits in 802.11

Packets size in bits = DIFS+ PLCP+ (MAC header + FCS+ WEP) + IP packet (IP header +IP payload + UDP header) + SIFS +ACK + Backoff ?¡é?€?|?¡é?€?|.. (1.1)

Number of packet per second = Utilized bit rate / Packets Size in bits?¡é?€?| (1.2).

Whereas DCF (Distributed Coordination Function) Inter Frame Space

DIFS= 2* slot time + SIFS =50μs (multiplied by10-6 multiplied by 11Mbps to convert it to bits). PLCP header= 192 bits,

MAC header= 30 bytes,

FCS= 4 bytes,

WEP= 8 bytes in case of security ON and zero in case of security OFF

IP packets consist of IP header= 20 bytes used to give an ID for the transmitted data,

UDP payload= (variable) bytes,

Short Inter Frame Space SIFS=10μs (multiplied by 10-6 multiplied by 11Mbps to convert it to bits), ACK= 304 bits

Back off= 20μs (multiplied by 10-6 multiplied 11Mbps to convert it to bits)

Utilized bit rate in experiment is set to be 2,11Mbps as maximum and transmission speed is 11Mbps

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