Dennis,
Although nothing is certain, the fact that you get less than 28.8k connections now does not mean you can't achieve x2 speeds. For the benefit of those concerned about current connection limitations, let's visit how the 56k connection works so we can distinguish between v.34 and x2.
When you make a call from your home, it is carried on what is called a local loop, which is effectively the copper wire pair between your house and the local telephone company central office (CO). The line terminates at the CO into a device called a codec - coder-decoder. The codec converts the analog signal received from your home into digital data, where it is pooled with digital data from other lines, and shipped off to the destination CO. The return signal comes into the codec as digital data, where it is converted to analog form for transmission back down the local loop to your home.
Obviously, all this transmission, coding, and decoding happens quite quickly, as evidenced by zero delay time in real-time voice conversations. It makes no difference whether the signal originating from your house is a persons's voice, or analog noise coming from your modem - it all goes to and from your home to the codec in analog form. In contemporary calls, the exact same process is occurring at the other end of the connection. Noise introduced into the signal at either end of the connection is what slows down transmission speed.
Now comes x2. In this environment, the ISP has a digital conection to the CO at it's end of the connection. In other words, the x2 server modem doesn't transmit analog data to a codec, but instead sends a full 56k data stream in digital form. It gets to skip the codec at it's CO, which effectively let's it communicate directly with the codec at your CO at a full 56k. There is far less noice introduced in this connection, and thus less signal loss. Since it has a full digital path all the way from the ISP to your codec, there will be 56k of data available to transmit down the local loop to you.
That is far different than conventional v.34 connections. It's very possible that you are capable of achieving a 33.6k connection to your codec, but the modem at the other end isn't, so you wind up with something less. When you wind up with a 21.6kb connection, that's the best speed that your modem can negotiate with the ISP's modem. With an x2 modem, you have two negotiations. First, you negotiate a standard v.34 connection for data coming from you to the ISP. That's the low traffic direction, se we don't care nearly as much about a lower speed connection. The second connection is to the downstream side of the local codec for data coming to you. We expect that it will have a full 56k of data to send you, which may or may not be achieved on the final leg to you depending only on the condition of your local loop. x2 will step down in something like 300 bit increments depending on line conditions in order the get the maximum throughput.
Hope that helps. I welcome any corrections and/or additions. |
