Q5: In a BSS with no AP (ad hoc network), we have five stations: A, B, C, D, and
ID: 643725 • Letter: Q
Question
Q5:
In a BSS with no AP (ad hoc network), we have five stations: A, B, C, D, and E. Station A needs to send a message to station B. Answer the following questions for the situation where the network is using the DCF protocol:
A. What are the values of the To DS and From DS bits in the frames exchanged?
B. Which station sends the RTS frame and what is (are) the value(s) of the address field(s) in this frame?
C. Which station sends the CTS frame and what is (are) the value(s) of the address field(s) in this frame?
D. Which station sends the data frame and what is (are) the value(s) of the address field(s) in this frame?
E. Which station sends the ACK frame and what is (are) the value(s) of the address field(s) in this frame?
Explanation / Answer
Ad hoc network:
In computer networking,an ad hoc network refers to a network connection established for a single session and does not require a router or a wireless base station.
DCF protocol:
DCF is defined as Distributed Coordination Function.The basic DCF protocol is a carrier sense multiple access with collision avoidance.
a.)The values of To DS and From DS bits in the frames:
Data frames:
The content of the address fields of the data frames is dependent upon the values of the To DS and From DS bits.
b.)RTS frame:
In RTS the data is send by CSMA/CA.The RTS frame needs to be sent by the station that wants to send the data frame,station A in this case.There are two addresses in the frame(address 1 and adderess 2).The value of address 1 is the recipient of the data frame that follows(address 1=B's address);the value of address 2 is the address of the station that will send data frame (address 2=A's station);Note that since the channel is a broadcast channel,every nonhidden station will recieve the RTS frame,but address 1 emphasizes that station B needs to respond to the RTS frame.
RA-Reciever address indicating the MAC address of the station that shall recieve frame.
TA-Transmitter address indicating the MAC address of the station which has transmitted frame.
FCS-frame check sequence.
c.)CTS
In CTS the data is send by a CSMA/CA.
FCS-Frame check sequence
RTS/CTS frame:
The RTS/CTS frames provide an optimal collision reduction scheme for APs within hidden station(STAs).If any WLAN node has any frame to be sent it will send out RTS frame.This serves two functions sending station to reserve the RF link and also indicates all the other stations not to transmit.
d.)Data frame station and the values of address fields:
< MAC Header >
CSMA/CA is used to send the dataframe.The content of the address fields of data frames depends on values of "ToDS" and "FromDS" bits.Where the content of the field is shown as NA than it is not applicable.
e.)ACK frame and the values of the address fields:
FCS-Frame check sequence
The recieving station sends an acknowledgement frame to the sending station after recieving the data without any error.If the acknowledgement frame is not recieved within the pre-determined time period by the transmitter than the transmitter re-sends the data frames.
To/From DS values Meaning To DS=0,From DS=0 A Data frame direct from one STA to another STA within the same IBSS,as well as management and control type frames. To DS=0,from DS=1 Data frame exiting the DS. To DS=1, From DS=0 Data frame destined for the DS. To DS=1, From DS=1. Wireless distribution system(WDS) frame being distributed from one AP to another AP.Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.