Does a MAC-layer broadcast on Wi-Fi get sent to each client directly, or through the router?
I'm trying to find a way to get my Android device to send frequent Wi-Fi packets into the air so I can detect them from multiple base stations for interior positioning. The canonical way to do this is to use Android's Wifi.scan(). Unfortunately that's limited to once every 30 seconds, which isn't frequent enough for my use case.
If I send a UDP broadcast message to 255.255.255.255, that should translate to an MAC-layer destination of ff:ff:ff:ff:ff:ff. My question is whether that packet is sent "directly" to each client on the affiliated network, in which case the clients will have RSSI information that can be used for positioning.
Or, does that broadcast message go only to the router who then distributes it on the next DTIM interval, and in which case the clients wouldn't have any useful information about the broadcaster in terms of their relative position/RSSI.
wireless-networking broadcast
edited Jan 28 at 19:14
Spiff
77.7k10118163
asked Jan 28 at 0:57
RyanRyan
111
add a comment |
I'm trying to find a way to get my Android device to send frequent Wi-Fi packets into the air so I can detect them from multiple base stations for interior positioning. The canonical way to do this is to use Android's Wifi.scan(). Unfortunately that's limited to once every 30 seconds, which isn't frequent enough for my use case.
If I send a UDP broadcast message to 255.255.255.255, that should translate to an MAC-layer destination of ff:ff:ff:ff:ff:ff. My question is whether that packet is sent "directly" to each client on the affiliated network, in which case the clients will have RSSI information that can be used for positioning.
Or, does that broadcast message go only to the router who then distributes it on the next DTIM interval, and in which case the clients wouldn't have any useful information about the broadcaster in terms of their relative position/RSSI.
wireless-networking broadcast
edited Jan 28 at 19:14
Spiff
77.7k10118163
asked Jan 28 at 0:57
RyanRyan
111
add a comment |
I'm trying to find a way to get my Android device to send frequent Wi-Fi packets into the air so I can detect them from multiple base stations for interior positioning. The canonical way to do this is to use Android's Wifi.scan(). Unfortunately that's limited to once every 30 seconds, which isn't frequent enough for my use case.
If I send a UDP broadcast message to 255.255.255.255, that should translate to an MAC-layer destination of ff:ff:ff:ff:ff:ff. My question is whether that packet is sent "directly" to each client on the affiliated network, in which case the clients will have RSSI information that can be used for positioning.
Or, does that broadcast message go only to the router who then distributes it on the next DTIM interval, and in which case the clients wouldn't have any useful information about the broadcaster in terms of their relative position/RSSI.
wireless-networking broadcast
edited Jan 28 at 19:14
Spiff
77.7k10118163
asked Jan 28 at 0:57
RyanRyan
111
I'm trying to find a way to get my Android device to send frequent Wi-Fi packets into the air so I can detect them from multiple base stations for interior positioning. The canonical way to do this is to use Android's Wifi.scan(). Unfortunately that's limited to once every 30 seconds, which isn't frequent enough for my use case.
If I send a UDP broadcast message to 255.255.255.255, that should translate to an MAC-layer destination of ff:ff:ff:ff:ff:ff. My question is whether that packet is sent "directly" to each client on the affiliated network, in which case the clients will have RSSI information that can be used for positioning.
Or, does that broadcast message go only to the router who then distributes it on the next DTIM interval, and in which case the clients wouldn't have any useful information about the broadcaster in terms of their relative position/RSSI.
wireless-networking broadcast
wireless-networking broadcast
edited Jan 28 at 19:14
Spiff
77.7k10118163
asked Jan 28 at 0:57
RyanRyan
111
edited Jan 28 at 19:14
Spiff
77.7k10118163
asked Jan 28 at 0:57
RyanRyan
111
edited Jan 28 at 19:14
Spiff
77.7k10118163
edited Jan 28 at 19:14
Spiff
77.7k10118163
edited Jan 28 at 19:14
Spiff
77.7k10118163
77.7k10118163
asked Jan 28 at 0:57
RyanRyan
111
asked Jan 28 at 0:57
RyanRyan
111
asked Jan 28 at 0:57
RyanRyan
111
111
add a comment |
add a comment |
1 Answer
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All* wireless-to-wireless packets on Wi-Fi are relayed by the AP, always. Even unicasts. Yes, as you suspected, multicasts and broadcasts are buffered by the AP until right after the next DTIM beacon goes out, and then the AP transmits each buffered multicast or broadcast exactly once.
When the AP transmits a buffered multicast or broadcast, it does so at a low-ish data rate that should be able to be reliably received by all clients, because these packets are not Ack'd. Often this low-ish data rate is the lowest rate the AP can use, which makes multicasts and broadcasts very expensive because they always go out at low rates that eat up a lot of airtime. So you really don't want to be sending frequent multicasts or broadcasts on wireless.
So no matter what, when a client of an AP receives a packet, the signal strength it sees is always a reflection of the AP's Tx power and distance, never the original sender's power and distance.
(*All: There's a technology called TDLS (Tunneled Direct Link Setup) that could allow clients to send packets directly to each other without being relayed through the AP, but support for TDLS appears to be very rare, if it exists at all.)
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
add a comment |
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All* wireless-to-wireless packets on Wi-Fi are relayed by the AP, always. Even unicasts. Yes, as you suspected, multicasts and broadcasts are buffered by the AP until right after the next DTIM beacon goes out, and then the AP transmits each buffered multicast or broadcast exactly once.
When the AP transmits a buffered multicast or broadcast, it does so at a low-ish data rate that should be able to be reliably received by all clients, because these packets are not Ack'd. Often this low-ish data rate is the lowest rate the AP can use, which makes multicasts and broadcasts very expensive because they always go out at low rates that eat up a lot of airtime. So you really don't want to be sending frequent multicasts or broadcasts on wireless.
So no matter what, when a client of an AP receives a packet, the signal strength it sees is always a reflection of the AP's Tx power and distance, never the original sender's power and distance.
(*All: There's a technology called TDLS (Tunneled Direct Link Setup) that could allow clients to send packets directly to each other without being relayed through the AP, but support for TDLS appears to be very rare, if it exists at all.)
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
add a comment |
All* wireless-to-wireless packets on Wi-Fi are relayed by the AP, always. Even unicasts. Yes, as you suspected, multicasts and broadcasts are buffered by the AP until right after the next DTIM beacon goes out, and then the AP transmits each buffered multicast or broadcast exactly once.
When the AP transmits a buffered multicast or broadcast, it does so at a low-ish data rate that should be able to be reliably received by all clients, because these packets are not Ack'd. Often this low-ish data rate is the lowest rate the AP can use, which makes multicasts and broadcasts very expensive because they always go out at low rates that eat up a lot of airtime. So you really don't want to be sending frequent multicasts or broadcasts on wireless.
So no matter what, when a client of an AP receives a packet, the signal strength it sees is always a reflection of the AP's Tx power and distance, never the original sender's power and distance.
(*All: There's a technology called TDLS (Tunneled Direct Link Setup) that could allow clients to send packets directly to each other without being relayed through the AP, but support for TDLS appears to be very rare, if it exists at all.)
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
add a comment |
All* wireless-to-wireless packets on Wi-Fi are relayed by the AP, always. Even unicasts. Yes, as you suspected, multicasts and broadcasts are buffered by the AP until right after the next DTIM beacon goes out, and then the AP transmits each buffered multicast or broadcast exactly once.
When the AP transmits a buffered multicast or broadcast, it does so at a low-ish data rate that should be able to be reliably received by all clients, because these packets are not Ack'd. Often this low-ish data rate is the lowest rate the AP can use, which makes multicasts and broadcasts very expensive because they always go out at low rates that eat up a lot of airtime. So you really don't want to be sending frequent multicasts or broadcasts on wireless.
So no matter what, when a client of an AP receives a packet, the signal strength it sees is always a reflection of the AP's Tx power and distance, never the original sender's power and distance.
(*All: There's a technology called TDLS (Tunneled Direct Link Setup) that could allow clients to send packets directly to each other without being relayed through the AP, but support for TDLS appears to be very rare, if it exists at all.)
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
All* wireless-to-wireless packets on Wi-Fi are relayed by the AP, always. Even unicasts. Yes, as you suspected, multicasts and broadcasts are buffered by the AP until right after the next DTIM beacon goes out, and then the AP transmits each buffered multicast or broadcast exactly once.
When the AP transmits a buffered multicast or broadcast, it does so at a low-ish data rate that should be able to be reliably received by all clients, because these packets are not Ack'd. Often this low-ish data rate is the lowest rate the AP can use, which makes multicasts and broadcasts very expensive because they always go out at low rates that eat up a lot of airtime. So you really don't want to be sending frequent multicasts or broadcasts on wireless.
So no matter what, when a client of an AP receives a packet, the signal strength it sees is always a reflection of the AP's Tx power and distance, never the original sender's power and distance.
(*All: There's a technology called TDLS (Tunneled Direct Link Setup) that could allow clients to send packets directly to each other without being relayed through the AP, but support for TDLS appears to be very rare, if it exists at all.)
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
answered Jan 28 at 19:10
SpiffSpiff
77.7k10118163
77.7k10118163
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