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Dual Channel ISDN on Linux? 14

Posted by Cliff from the do-you-breathe-with-one-nostril? dept.
Dionysus asks: "I have a 3ComImpact IQ connected to my serial port. Right now I'm only using 1 channel. How can I make it use both channels? I looked at isdn4linux, and it seems that one channel is all I can get. I don't have this problem in Win98 nor in OS/2. Please help."
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Dual Channel ISDN on Linux? More

Dual Channel ISDN on Linux?

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  • Posted by FreeVil:

    Now, there seems to be a little confusion as to what is what in the ISDN support for Linux and FreeBSD.

    isdn4Linux/isdn4bsd are drivers for passive ISDN devices. These are adapter cards that just pass bits to the telco switch over your ISDN line. The driver must support the switch's protocol. The code at this point only supports euro-ISDN compliant switches. Most US telcos have Nortel or AT&T 5ESS. The FCC forbids you to crash your telco's switch by using incompatible (unapproved/nonconforming) protocol. If AT&T or Nortel release protocol specs without nondisclosure, then we can have open source passive ISDN drivers. Until then, we are SOL.

    ISDN "modems" are drop-in replacements for analog modems. They have firmware to handle call setup and other D-channel protocol, and they emulate asynchronous modem operation over one (or more if it has MP PPP support) B channels. If you have an external unit, you will not be able to use the full dual-channel BRI bandwidth without a special serial port adapter that supports 230Kbps. Some internal ISDN modems support 230Kbps DTE speeds. You will need the same kind of software setup as you would need for a modem.

    ISDN bridges and routers are external boxes that usually have one or more ethernet interfaces and an ISDN interface. They will usually do DHCP/bootp, NAT, protocol (IPX/SPX) tunnelling and some rudimentary firewalling. They will usually support multiple ethernet hosts connecting to a gateway machine across the ISDN. Setting these up requires an ethernet and maybe a crossover cable. The device itself requires a serial console device like a null-modem cable and a terminal emulator program to configure it. After that, these can usually be administered remotely via telnet or web browser.

  • I run MacOS and mkLinux - I set up the modem with the modem setup program (tollsaver, 2 channel) under MacOS. It seems to set the defaults in the firmware, thus no need for a special init string.

    In my case, I never had to specify an init string...

    -Josh

  • isdn4linux is focused on the add in isdn cards and the european ones at that. So the information there is not exactly accurate.

    I currently have a ZyXEL omni.net plus using both channels under linux. But when I first got it I had a little trouble figuring it out.

    Here is what I had to do. First you have to use the modem's built in capability to communicate by MPP, or multi-point PPP. Set the second channel call on the isdn TA real low so it will try to make the second channel bond with very little traffic.

    In pppd land use PAP or CHAP to authenticate with your ISP. Then you should be off to the races.

    Doing all this will require you to spend some quality time with your isdn TA's manual since you will have to figure out the initialization string to get it to work. And there is no standard for isdn TA's so my string may mean nothing to your isdn TA.

    But just so you can get an idea of what I mean I will include it and break it down for you.

    AT&E1S83.7=1&K44BP1&J3

    The AT you should already be familiar with. &E1 tells the modem to operate at 56k (because my telco doesn't provide a d channel). S83.7=1 sets the isdn's "Speech Bearer service" this is handy for getting a lower rate on calls if your telco operatest this way. &K44 sets compression on, I personally don't get much out of this, YMMV. BP1 is very important, make sure you find the equivalent for your TA, it enables bandwidth allocation protocol which is what your TA is going to use with your ISP's equivalent to get two channels to bond. &J3 enables multilink PPP.

    So to summarize, make sure you are using multilink PPP and that your TA is able to use the Bandwidth Allocation Protocol. Do not use v.120 to connect, use PPP. v.120 is a very loose standard and many ISP dial-in boxes will not support channel bonding in this protocol. Then finally use PAP/CHAP to authenticate in pppd scripts. Read the PPP Howto on how to do that.

    This is no gauranteed fix for you but I wanted to let you know it is very possible to bond both channels of ISDN using linux to achieve 115kbps or more.
  • I had the exact same problem a few weeks ago. I'm
    using the older version of the TA that you have - the 3com Impact.

    It turned out that I wasn't using PAP authentication. I've heard that PAP is part of the MLPPP spec, and unless you authenticate using PAP, the modem won't know that you want MLPPP, hence, only one channel. All I had to do was make sure I
    had pppd doing PAP, and bingo...

    However, I had a helluva time getting pppd to authenticate using PAP. Enable debugging so you can see all the LCP negotiation.

    Dream
  • at least, if it's an external device. If it hooks up to a serial port, or presents a serial port interface to the machine (like internal POTS modems), then the software ain't got a lot to do with dual or single channel operation.

    If it's not the init string, it may well be your ISP's end. I know that the PortMaster 3 (and probably most work-alikes) will dump the second channel until you get authorized, and won't pick it back up unless the ISP's RADIUS record says you're allowed multiple simultaneous ports.

    I spent a good 24 hours staring at pppd, isdn4linux, and the associated kernel stuff a few months ago trying to figure out why I couldn't get both channels of my ISDN line connected, at the urging of my ISP's "technical staff". Once I read up a little on the equipment they were using, I figured the problem out. It only took another couple of days to convince them that it really was their problem.

    Just 'cuz they do it for a living doesn't mean they don't make mistakes, no matter how hard they protest otherwise.
  • I also have an external Impact IQ, and this init string works for dual:
    ATS60=56S61=1S70=0S71=1S80=1

    S71 is the key here, so if I want single channel, I use this:
    ATS60=56S61=1S70=0S71=0S80=1

    Note that this is for a 56/112Kbps ISP, if you've got 64/128Kbps some of your settings may be different.
  • I have a USR Courier I-Modem, and after playing with it for a while, I eventually found that the init string was incorrect. Dont know if they use the same at commands, but for what it's worth, here's the init string I came up with: AT&d2&f1*P=0*D0=1 Also, oftentimes you have to specify when you are dialing to dial both numbers, such as: ATDT5557600 & 5557600 if 5557600 is the number of your ISP.
  • I have an Ascend pipeline 15, and s71 is the key in mine too. you may have to change the S60=56 to S60=64 or S68=64, to get 64/128K connections. You will have to read the init string section of your manual.
  • I have the same modem and Dual channel works great. I used the newest version of pppsetup. You will have to use either PAP *or* CHAP, depending upon what your isp allows. I've used both with different ISPs in the past year and both work ok. You DO need the right init string though. here is the init string i currently use for chap, right from my /etc/ppp/ppp.chatscript: "" "AT E0 V1 &D=2 &C=1 S0=0" OK "ATS84=0" OK change the ATS84 to equal 1 for PAP. Thats all.
  • I have the same modem and Dual channel works great. I used the newest version of pppsetup. You will have to use either PAP *or* CHAP, depending upon what your isp allows. I've used both with different ISPs in the past year and both work ok. You DO need the right init string though. here is the init string i currently use for chap, right from my /etc/ppp/ppp.chatscript:

    "" "AT E0 V1 &D=2 &C=1 S0=0" OK "ATS84=0" OK

    change the ATS84 to equal 1 for PAP.
    Thats all.
  • I just Purchased a netcommander and looked over all of the isdn4linux pages and didn't see anything that mentioned it. It has an at&t chipset. Sorry to post here, but if anyone has any ideas i would appreciate any info.

    Pointer
  • There is some information on the Traverse Technologies web site - http://www.traverse.com.au/ - of course it is for their ISDN cards, but the start/stop script does show how to get multilink (synchronous) PPP working.

    And it works for me for 128k ISDN.

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