Some basic Questions about MAC layer & datarate

[sirene]

I am not quite sure if it is the right place to ask this particular question ; if not , I apologize and would be more than happy to be informed about the right place to ask this question.

There is an Access Point (AP) , which is the central manager of a network : it keeps track of how many nodes are connected to it, when to download, when to upload, what amount of data each node has etc.
It has 3 TDM cycle for (i) downloading, (ii)uploading & (iii)association for new nodes when it has enough resource to accomodate new ones.
It will send the downlink data one by one , dividing the time cycle between them, according to dataload,priority of each station. It will send token to the stations for uplink transmission, and the stations will send data according to the token.

My questions are:

* When the AP sends downlink data to nodes, is it more convenient to broadcast the data,so that the specific node can pick it , or it is convenient unicast ?

* Similarly, is it efficient to broadcast the token message or unicast?

* Usually the data load will be higher in the Uplink cycle, i.e. when the nodes send data to the AP, or in the downlink cycle,where the AP sends data to the nodes?

* Is it possible for the nodes to directly receive data from one another, without using AP as the forwarder?

One more thing, the objective of this network is to ensure lowest overhead, lowest delay/jitter possible, i.e. successful multimedia transmission along with data transmission.

Thanks.

 

[aaea3]

hi sirene
u should learn about 7 layer and know at which layer access point belong to and when data moves from node to it or from it to node data have header which contain address which data go to and not bradcast to each nodes
regards

 

[sirene]

hi sirene
u should learn about 7 layer and know at which layer access point belong to and when data moves from node to it or from it to node data have header which contain address which data go to and not bradcast to each nodes
regards

Hi aaea3,
Thank you very much for your kind reply. I knew a little bit about the 7 layer, which made me think of AP as a layer2 device, please correct me if I am wrong.

Actually I wanted to know, which will cause lowest overhead : broadcast or unicast . Apparently unicast causes low overhead, but I am not pretty sure :s
And my another question is also related to the amount of overhead : I wanted to know, infrastructure mode causes low overhead, or ad-hoc mode .
Please let me know the appropriate place to ask this question,if I have placed it wrongly.
Thanks again.

 

[sheraz.pervaiz]

Wireless Access Point works at Layer 2. At layer 2, the unicast and broadcast have same overhead in terms of bytes. Because only difference is that unicast will have specific destination address, whereas the destination MAC address of broadcast is always all Fs(i.e FF-FF-FF-FF-FF-FF).

But broadcast are resource intensive activity, this can slow down your access point. Thus one of our goals in networking is to minimize the number of broadcasts.

 

[sheraz.pervaiz]

Two or more wireless devices can operate without the help of WAP, this is called Ad hoc network, more scientific name for this kind of network is iBSN i.e independent Basic Service Network.

 

[sirene]

Thank you very much, sheraz.pervaiz
the unicast and broadcast point is clear to me, thanks.
Actually I was talking about the infrastructure mode, because I want an AP to be the manager of the system. I read a little about ad-hoc networks, which made me think that there cannot possibly exist an AP to monitor and initiate and allocate time slots to the stations.
I came across Direct Link Setup (DLS) in 802.11e, which is also initiated by the AP.
So, I was wondering, if it is possible for AP to take the decision but the stations to communicate independently based upon the decision.
May be I could not make my point clear ; what I am talking is a topology, like in a meeting, the coordinator decides the time for each speaker to speak, and then just sits idle ; the speakers know when they can speak, so they start speaking to anyone they like to, but without bothering the coordinator anymore ; and since only one is allowed to talk in any specific time, so no quarrel among them