13. asyncppp: Configuration Async PPP

13.1 asyncppp_whichppp: pppd, ipppd, async PPP, sync PPP - what are they? Which should I use?

async PPP is a character-based protocol which is usually used over analog serial lines (async = asynchronous). You have to use the program pppd for it, and use it with the ttyI* devices.

In contrast, Sync PPP is a bit-oriented protocol (sync = synchronous), for which the original pppd cannot be used. Michael Hipp has written an adapted version called ipppd which will use ipppd* net devices.

With i4l you can have both. It all depends on what your ISDN counterpart supports. If it immediately begins to send frames, then you've probably reached an sync PPP machine. If you can log in via same terminal screen, and then can start pppd, this can be an indication of async PPP.

Usually using sync PPP works fine, and it is slightly more efficient. To take advantage of newer features of the pppd, use async PPP.

13.2 asyncppp_config: How do I configure async PPP?

Just set up a normal pppd, but tell it to use one of the ttyI* devices, e.g. /dev/ttyI0. You can set up several pppd's with different configuration on different ttyI* devices.

It is very important to set up the authentication information properly. Improper authentication is probably the most frequently reported problem on the mailing list. Please, work through section pap completely yourself, before asking others for help.

On problems also check out the section about the syncppp problems, since many configuration problems are common for pppd (async PPP) and ipppd (sync PPP).

13.3 asyncppp_logindelay: How can I reduce login delay?

You can write out a login session with ("Debug-Log"), and see which options the other computer is refusing. Next time, configure ipppd without these unused options. A further side effect is that such unused options increase the redundance (e.g. when the other computer has bugs and refuses the options incorrectly). To create a log file, see "How to I create a log for ipppd".

13.4 asyncppp_fast: How can I increase my transfer rates with PPP?

You can add more channels with MPPP (see question 2channel_mppp). For everyone for whom that's to expensive and who use async PPP, there's a little trick. With the option "asyncmap 0" you can avoid escaping all control characters (ASCII32). If the other side goes along with this, you can increase the transfer rate by about 12%.

13.5 asyncppp_log: How can I get a log for pppd?

See this question for Sync PPP, it works the same way for pppd.

13.6 asyncppp_suddendeath: Establishing the connection works fine, but pppd crashes just after that (i.e. the first bytes gets through, but then everything stops)

This is probably due to an incorrect block size on your side. Initialize your ttyI* device with AT&B512 or even smaller block sizes.