Wireless IP Phones - duplex question
tomset
Member Posts: 79 ■■□□□□□□□□
What up wireless gurus!
I was thinking about this the other day. Wireless LANs operate in half-duplex mode. So how can people have conversations using wireless IP phones? Is the conversation choppy since you can't talk and listen at the same time?
It doesn't seem like wireless IP phones would be designed that way so what am I missing?
I was thinking about this the other day. Wireless LANs operate in half-duplex mode. So how can people have conversations using wireless IP phones? Is the conversation choppy since you can't talk and listen at the same time?
It doesn't seem like wireless IP phones would be designed that way so what am I missing?
Next up:
CCIP
CCIP
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tech-airman
Member Posts: 953
What up wireless gurus!
I was thinking about this the other day. Wireless LANs operate in half-duplex mode. So how can people have conversations using wireless IP phones? Is the conversation choppy since you can't talk and listen at the same time?
It doesn't seem like wireless IP phones would be designed that way so what am I missing?
tomset,
Are you talking (pun intended) about 802.11a, 802.11b, 802.11g, 802.11n, or don't know? -
tiersten
Member Posts: 4,505
The voice data is compressed and split up into packets. The bandwidth of the wireless connection is greater than the bandwidth of a single call. If your link is at capacity then yes, you'd get a choppy sounding call.I was thinking about this the other day. Wireless LANs operate in half-duplex mode. So how can people have conversations using wireless IP phones? Is the conversation choppy since you can't talk and listen at the same time?
It doesn't seem like wireless IP phones would be designed that way so what am I missing? -
tomset
Member Posts: 79 ■■□□□□□□□□
tech-airman wrote: »tomset,
Are you talking (pun intended) about 802.11a, 802.11b, 802.11g, 802.11n, or don't know?
I'm talking about 802.11g.
Tiersten -
Let me see if I can clarify what I'm asking. If you and I are having a phone conversation, there may be times when I talk and you talk at the same time. When that happens, I talk and can hear you talk at the same time. That requires a full-duplex connection (which the POTS network is). If you're now using a half-duplex connection, we wouldn't be able to talk (and hear each other at the same time). Doing so would cause a collision on the half-duplex connection. Am I wrong?Next up:
CCIP -
tiersten
Member Posts: 4,505
Why are you assuming that a VoIP call will monopolise the entire connection? It is a packet switched network and not circuit switched.Let me see if I can clarify what I'm asking. If you and I are having a phone conversation, there may be times when I talk and you talk at the same time. When that happens, I talk and can hear you talk at the same time. That requires a full-duplex connection (which the POTS network is). If you're now using a half-duplex connection, we wouldn't be able to talk (and hear each other at the same time). Doing so would cause a collision on the half-duplex connection. Am I wrong?
VoIP splits up the data into packets. The packets are sent to the other side. If the link isn't at capacity then there are points in time where the network is free. Packets from the other side can come in at this point. From the point of view of the users, they're having a full duplex voice call. -
tomset
Member Posts: 79 ■■□□□□□□□□
Why are you assuming that a VoIP call will monopolise the entire connection? It is a packet switched network and not circuit switched.
VoIP splits up the data into packets. The packets are sent to the other side. If the link isn't at capacity then there are points in time where the network is free. Packets from the other side can come in at this point. From the point of view of the users, they're having a full duplex voice call.
You are familiar with how a half-duplex connection works, right? Bandwidth can't overcome the restrictions of a half-duplex connection no matter how much bandwidth you might have. The duplex settings of the link will still determine how the link will operate. The wireless AP and the wireless IP phone use the same frequency to transmit and receive. If they try to talk to each other at the same time, collisions will occur and both devices will have to wait the random back-off period before re-transmitting.
It just seems like you wouldn't be able to have as smooth a conversation on a wireless IP phone as you would with a traditional POTS or landline VoIP call.Next up:
CCIP -
tiersten
Member Posts: 4,505
Yes. I know what a half duplex connection is.You are familiar with how a half-duplex connection works, right?
If my VoIP call is using g729 then it is split up into 10ms packets and consumes 8kbps assuming no extensions etc... Every second, the phone needs to send 1KB and receive 1KB. Is the fact that WiFi is half duplex going to adversely affect this requirement?Bandwidth can't overcome the restrictions of a half-duplex connection no matter how much bandwidth you might have. The duplex settings of the link will still determine how the link will operate. The wireless AP and the wireless IP phone use the same frequency to transmit and receive. If they try to talk to each other at the same time, collisions will occur and both devices will have to wait the random back-off period before re-transmitting.
Yes. You're just switching sides really quickly but from the point of view of the callers, they've got a full duplex connection.It just seems like you wouldn't be able to have as smooth a conversation on a wireless IP phone as you would with a traditional POTS or landline VoIP call.
There is a inherent delay in using packet switching due to the need to actually packetize the data. The restrictions caused by having a half duplex network link aren't going to be significant enough for users to actually notice because the packet sizes are so small. Your POTS call is going to be going over a packet switched network at some point anyway. -
dynamik
Banned Posts: 12,312 ■■■■■■■■■□
Tomset, I don't think you're taking into account how many milliseconds that all occurs in. -
networker050184
Mod Posts: 11,962 Mod
Tomset, I don't think you're taking into account how many milliseconds that all occurs in.
+1
The delay is so small that a person wouldn't notice it.An expert is a man who has made all the mistakes which can be made. -
schpenxel
Registered Users Posts: 23 ■□□□□□□□□□
networker050184 wrote: »+1
The delay is so small that a person wouldn't notice it.
Exactly. Packets are moving at nearly the speed of light.. even if they can only go one way at once it's still so fast you can't hear the milisecond of delay
