how backward compatibility works in wireless

[ilyas001]

hi guys i don't understand how a 802.11n can use both 2.4ghz and 5 ghz bands at the same time , if you have a network composed of diffrent type of NIC's  what is happening exactelly so the router can be able to connect all of them at the same time ? i also think that a antenna can use only one channel at the time so if for exemple we have 2 antenna connecting two nic's of 802.11n in the 5 ghz frequency it will mean that the wireless network is totally 5 ghz only , then how will the NIC's of 802.11b and g be able to still be connected despite this ? also i read somewhere that the wireless will use a 20 mhz band but i still have the same question , imagine that both antennas are busy in the 40 mhz range ? thanks for your time . also guys a outside question , why do we need to configure the default gateway in a switch i mean if we don't have like two routers on the network what's the goal of this ?

[brwainer]

a device like a router has two radios so that it can communicate on both frequencies at once, but they are actually able to share the antennas because they are operating at different frequencies - this is the same as multiple radio stations through the air, or multiple TV channels on a coax wire. So when you talk about client devices that are on different bands (2.4 or 5) they can communicate simultaneously.

 

Devices that are on the same channel, e.g. everything operating on channel 6 of the 2.4GHz band, has to time share - only one device can communicate at a time. This is scheduled by the router/AP in a normal network, or by all the devices in an ad hoc network (this is why ad hoc networks are always much slower). If there are multiple APs in range of each other on the same channel, they don't make any arrangements to take turns, but they will try not to "talk over" each other.

 

When you start talking about backwards compatible devices, like a g device connecting to an n network, the same still applies, except that when it is the slower device's turn to communicate, the time slot allotted to it will be longer, because it takes longer for it to communicate its data. Likewise, when the AP talks to one such device, it must communicate at a slower rate so the device is able to pick up the data.

 

As for the rest of your questions, I got a little bit lost in what you are asking, so please read what I have answered so far and re-ask your questions as needed.

[ilyas001]

thanks it was very informative ,so from what i understand to use both frequences each antenna needs two radios one for 2.4 and another for 5ghz  5 ghz is faster then 2.4 ghz by nature so when the router i used to communicate with a 2.4 ghz NIC , the connection is slowed down because now one of the antenna's is working at 2.4 ghz speeds . so this is how they can both connect at the same time and this is why it makes the network slower right ? well for the last question it had nothing to do with wireless it was a question about cisco switches config , now i have another question when we say you are connect to the wifi what does this mean because most of the time you need to wait for your turn to use the bandwidth right ? so technically you aren't connected 

[brwainer]

1 hour ago, ilyas001 said:

thanks it was very informative ,so from what i understand to use both frequences each antenna needs two radios one for 2.4 and another for 5ghz  5 ghz is faster then 2.4 ghz by nature so when the router i used to communicate with a 2.4 ghz NIC , the connection is slowed down because now one of the antenna's is working at 2.4 ghz speeds . so this is how they can both connect at the same time and this is why it makes the network slower right ? well for the last question it had nothing to do with wireless it was a question about cisco switches config , now i have another question when we say you are connect to the wifi what does this mean because most of the time you need to wait for your turn to use the bandwidth right ? so technically you aren't connected 

The radios in a given device can share antennas - so if you have a dual band router with 2 antennas, both the 2.4GHz and the 5GHz radios can use both antennas at once. There is no blocking or slowing down of one radio when the other radio is also communicating.

 

You configure the default gateway in a switch so that if you ask the switch to do anything outside the local network, like pinging a public DNS server, it can complete the request. A practical purpose for this would be if you need to manage the switch from another subnet.

 

connecting to a wifi network means that you ask the AP in charge of the network to add you to the list of connected devices. If there is any security configuration for the network, like a password, it will be handled at this time. Once that AP lets you authenticate and join the network, you are connected. Depending on what version of wifi it is, the AP will either poll each device to see if it has anything to send, or the devices will ask for a timeslot to transmit data during a quiet moment

[ilyas001]

3 minutes ago, brwainer said:

The radios in a given device can share antennas - so if you have a dual band router with 2 antennas, both the 2.4GHz and the 5GHz radios can use both antennas at once. There is no blocking or slowing down of one radio when the other radio is also communicating.

 

You configure the default gateway in a switch so that if you ask the switch to do anything outside the local network, like pinging a public DNS server, it can complete the request. A practical purpose for this would be if you need to manage the switch from another subnet.

 

connecting to a wifi network means that you ask the AP in charge of the network to add you to the list of connected devices. If there is any security configuration for the network, like a password, it will be handled at this time. Once that AP lets you authenticate and join the network, you are connected. Depending on what version of wifi it is, the AP will either poll each device to see if it has anything to send, or the devices will ask for a timeslot to transmit data during a quiet moment

thanks mate it was of a great help so there is one radio for each frequency that can use multiple antennas at the same time , and this will not influence the data transmission rate ok . last question what's the difference between spreading a radio frequency and sending over it ? i mean if a antenna can only send to one use at a time how is it possible for it to keep up with multiple frequencies at the same time ?

[brwainer]

23 minutes ago, ilyas001 said:

thanks mate it was of a great help so there is one radio for each frequency that can use multiple antennas at the same time , and this will not influence the data transmission rate ok . last question what's the difference between spreading a radio frequency and sending over it ? i mean if a antenna can only send to one use at a time how is it possible for it to keep up with multiple frequencies at the same time ?

Antennas are passive devices. They are jsut bits of metal shaped a certain way that causes them to resonant with RF frequencies.

[ilyas001]

11 minutes ago, brwainer said:

Antennas are passive devices. They are jsut bits of metal shaped a certain way that causes them to resonant with RF frequencies.

i don't understand , so from what you said i can say that radios make the frequencies in the air so the antennas are only here to transfer using the signal , they don't create it right  ?

[brwainer]

36 minutes ago, ilyas001 said:

i don't understand , so from what you said i can say that radios make the frequencies in the air so the antennas are only here to transfer using the signal , they don't create it right  ?

The radios make and recieve electrical signals. Antennas convert electrical energy in RF radiation and vice versa.