VOIP questons

[jes]

I have been reading about the application of VOIP at Howstuffworks.com and other places. I still have some questions about the difference between circuit switching and packet switching. I am hoping that someone here has the answers that I am looking for.

As I understand it, the physical connection stays open for the duration of the call with circuit switching and with packet switching the sending unit sends voice files (something like *.wav files) to the recieving unit freeing the line considerably. Does this mean that the communication can only move in one direction at once? What happens when one person is talking and the other buts in to say something?

[Variable]

VOIP does not use circuit switching itself, since it is packet based and works over TCP/IP it is packet switched. If your connection to the internet is over a phone line then you would have a circuit switched connection and a packet switched connection. The basic idea is that a circuit switched connection is point-to-point and dedicated. A packet switched network can send packets over different routes; it is not a dedicated connection generally. That is what routers are for. Assume you send 100 packets to your friend in Idaho from your home, 50 of those packets may flow through a router in Chicago and 50 may get routed through a router in New York. The path the data travels is not set or dedicated. Routers make decisions on the best route based on how busy their neighbors are. It would be dedicated if you made a phone call to your friend over a regular telephone line. Communication goes both ways on either network. When you are on a phone line what happens if both of you talk at once? Send and receive come down different pairs of wires. The same thing happens in a TCP/IP connection.

[jes]

Alright, thank you. I think that you have cleared that up for me. My first question when I read your reply was “If the line is not dedicated then why is the signal not slow?” but then I remembered something that I had read in Howstuffworks.com about how much dead air you could cut out of most phone conversations. It seems that VOIP can take advantage of that through packet switching because it isn't so linear as the circuit switching.

What would you be looking for from your Internet connection if you wanted to use VOIP? I have heard that you don't want to much latency in the signal. How much is too much? I am sure that the download and upload bandwidths would be a factor. Is there anything else?

[Variable]

Biggest impacts on VOIP are probably encryption and active packet filtering. Anything that slows down processing can affect voice quality. If you are downloading large files, and eating up your total throughput, that will affect it as well, of course. Any modern broadband is capable of VOIP generally speaking. You’re still confusing the mediums as if they are separate from each other. That is not necessarily the case. You could be using both methods at the same time. All your internet traffic is packet switched. It could be running over a circuit switched link as well.

[jes]

The Internet traffic would be packet switched but there could also be some circuit switching involved? Such as through a layer 3 switch?

I was told about a year ago any that satellite Internet would not be able to handle VOIP very well because the signal would contain to much latency because of the distance between the satellite and the dish. You don't agree with that?

[Variable]

No, a layer three switch can look at the Network layer; it can make decisions based on IP addresses. Don’t confuse devices with methodologies just yet or you will get further confused. You need to understand the concepts first.

A circuit switch is a like your light switch, when it is on there is a dedicated path of electrons passing down the wire to the end point and back. Imagine you have a lamp and turn it on, this is a circuit. The same applies to plain old telephones. When you call your friend, there is a connection made from your telephone to his, it is the same as the light switch and lamp; a dedicated connection. No one else can pick of their phone and butt into your conversation, the call exists between you two and that is that… With packet switching there is no need for a dedicated connection between two end points, but that does not mean there cannot be one. Packet switching and circuit switching are not opposites. If you have a dial up modem and connect to an ISP and then use your browser to surf the web you are using both methods at the same time, in some sense. A better way to understand it is that, the two methods describe how connections are made between devices. Circuit switched is a physical connection and dedicated, while Packet switching uses self-addressed IP packets that routers "route" to their destination over a shared network. Without routers no connection is made between end points in Packet switching. Packet switching is “logical” and Circuit switching is “physical” using the vernacular of the network models.

As for satelites, of course I would agree. Anyone who watches the news has seen a correspondent talk to the host of a show and there is a gap in the conversation as one person talks and the other person hears it. This is latency introduced by satelite communication. But that has nothing to do with circuit switching and packet switching in the conventional networking. I would imagine that all modern satelites use digital packets but how they are encapsulated within microwaves or whatever transmission method they use is a different topic.

[jes]

We seem to be having two conversations here so...

Conversation #1 Circuit switching and packet switching can be used in the same communication session but no at the same time, is that right? I think that I understand

Conversation #2 Is the latency that is introduced by satelite communication caused by the relays within the satelite itself?
ex: If you sent a communication over 10000 miles that was through a direct connection would there be as much latency as there would be if you send a communication relayed trough a satelite when the total distance was 10000 miles?