Tech Stories from the Trenches

At this point, you are ready to test the dial-up connection. Select the entry you just configured for multilink and start dialing. When prompted, enter the correct username, password, and destination domain. The first time I used my connection, I was surprised to hear both modems dial almost simultaneously.

When the RAS server answers the call, a notification box appears, informing you that the second line is being bundled with the first. When both lines are connected, the aggregate connection speed appears--it's really cool to see 55.2Kbps in place of 28.8Kbps. As I cruise the Internet, the transmit and receive lights blink almost synchronously on both modems. The connection really looks like one line, because the multilink protocol fragments and reconstructs the packets traveling on this connection as a unit.

You can view this multilink connection in the Dial-Up Networking Monitor. Select each line to see its connection speed. In the Summary view, the monitor displays the connection with the name you defined for the dial-up entry. When you expand the icon, the monitor displays each line individually.

Multilink Throughput
Next, I wanted to test throughput on the 55.2Kbps connection. At the Microsoft FTP site, I used the native FTP command and a third-party GUI to download a text file of just less than 500KB. With the native FTP command, my throughput rate from Microsoft was 10.21Kbps. With the third-party GUI utility, throughput was 10.18Kbps. Then, I downloaded a 1.2MB binary file from Microsoft with the native FTP command--the download took 204 seconds with a transfer rate of 6.24Kbps, which is closely matched by the third-party FTP utility. Last, I downloaded a 700KB binary file that took 119 seconds and reported an overall throughput of 5.92Kbps.

Download speed is difficult to evaluate fairly because so many factors are unrelated to either modem speed or the speed of the system you are downloading from. The biggest variable is the time of day. During my test, the highest transfer rate was 10.21Kbps and the slowest was 4.38Kbps. During off-hours on a single PPP connection, I got a maximum download speed from my Internet Service Provider (ISP) of about 3.5Kbps; in my mind, a rate nearly double that speed easily justifies an MPPP connection. Even when the Net slows down, the bundled connection is nearly double the speed you get with a single line. MPPP certainly makes browsing the Internet a lot more comfortable.

An MPPP connection can increase your download speed by more than 100 percent on small files and up to 100 percent on files that are more than 1MB. The bad news is that very few ISPs support MPPP. Network vendors offer several MP routers, but ISPs are not installing them for public access.

Another piece of bad news is that you cannot use MP with the callback feature of a RAS client. The RAS server stores only one phone number for each user, so only one modem can return the call.

However, I think MP is a good solution for branch offices that need a faster connection to corporate, as long as you have two phone lines available and an NT server at the corporate data center. MP does not require special hardware, is cheaper than ISDN, and competes well with ISDN speeds, especially if the modems at both ends are of the 56Kbps variety.