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12 Mbit/s offered, but how good is the phone line?

Just recently, up to 12Mbps downlink speed is available in our area. Standard uplink speed is 512kbps, 1Mbps uplink is optional.

The most economical option seemed a 8M/1M package. As it later turned out, this is about all we can get on our 2-wire line. Especially a high uplink speed is important for Skype and uploading photos to websites. Shortly after activation of the new speed (I upgraded from 3M/512k), I could see that the uplink was only around 800k and not very stable. The used modulation with options was set to "auto" in the ADSL modem, its a Billion BiPAC 5210S. The result of the handshake was ADSL2+, Annex L. Checking the specs, I found that Annex M uses more bandwidth for the uplink and allows up to 3Mbps.

=>Setting the modulation manually to ADSL2+, Annex M, improved my uplink performance, which is now stable 1Mbps!

Is the standard modem / router box a good router?

I don't have confidence to use this small box as router. E.g. memory and CPU power might become a problem for heavy traffic with multiple users and multithreaded downloads. Furthermore, there are limited features available.
Therefore I operate the modem in bridge mode as modem only. A Linksys WRT54G WLAN router takes care of PPPoE, DHCP, routing, etc. The Linksys router runs under Linux and a couple of feature rich alternative firmware versions are available.

A problem in this configuration is that the modem's admin interface is no longer directly available, as the PPPoE endpoints are not part of the LAN. There is a solution for this, which I will describe later.