Arnt Gulbrandsen
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Sync cards

In a not-so recent thread on the defunct linux-isp list I wrote slightly harshly about Emerging Technologies' driver for its ET/5025 synchronous serial card, which I was using at the time to talk HDLC to a Cisco router at my ISP via a 64k line.

I had been using the ET card for almost a year and was getting rather restless, suspecting the card or driver to be the reason for my much too frequent crashes. David Mandelstam of Sangoma, one of ET's competitors, wrote to me and offered me a substantial discount in return for the card, and for my writing to linux-isp about my experiences with both cards. (I suspect he saw my name, which chanced to be on display in the /etc/hosts files of about a million Slackware boxes, and assumed that I was more of a network guru than I am.)

This was in January or so. I took David up on his offer, and have been using a Sangoma S508 in 24×7 operation for six weeks now. This is how I compare the two (and you can quote me):

ET stability: I had frequent crashes. The frequency seemed to be greater with 2.0 kernels than with 1.2 kernels, I didn't keep count, but perhaps every few weeks the box would crash. My record was three crashes in a day. Sometimes it said skpush 0x1234567, sometimes nothing, and the driver ET ships is a binary kernel module.

Sangoma: Not a crash in the past six weeks. Not a hiccup.

ET installation and configurationa: I wrote my own boot scripts; ET gave me a module and told me to insmod it. Okay by me, I ipfwadm'ed quite a bit so no factory defaults would really suit me. It was a bit tricky, the ET driver and documentation tend to be on the sparse side. One crucial boot message was outright misleading: The driver told me it had found the card on port 0x240 IRQ 7 when it really meant I found it on port 0x240 and I trust you when you say IRQ 7. (And it took me some time to find out — the IRQ jumper was located so it wasn't visible when the card was in the machine.)

It took a long long day for me to get it up and running at first, and five hours when I later reinstalled from scratch (it would probably have been one or two hours if I had gotten that IRQ right or the driver hadn't, uh, misled me).

Sangoma: Extremely verbose redhat-like scripts; I was able to hack them into doing what I wanted and have them work on the first try, but I won't call them or the documentation sparse — it took an hour or more with less * until I understood those boot scripts :) The driver came with source for the 386 bits so I needed correct kernel header files to compile. No great problem; I often don't keep /usr/include/linux correct on all my boxes, but two tries and some disk space is in a day's work.

My total downtime for switching from HDLC/ET to PPP/Sangoma was less than three minutes. I'd spent almost a day poring over the documentation and configuration in advance, and when I was ready I called my ISP and asked them to move me over to PPP. When I saw that I lost IP connectivity I powered down, swapped over, powered up, it worked and I danced a little dance (no kidding).

ET hardware: ISA card, design looked kind of old, but workmanlike. I don't know that much about hardware. Came with a US v.35 cable; I didn't know at the time that US and European cables are different.

Shovelling eight thousand bytes per second doesn't take much performance, so I don't care much about the hardware's performance. I guess those of you with a few multi-mbps links care more.

Sangoma: ISA card, this too looked more like cards used to look a few years ago than a really modern card. Definitely workmanlike. Someone said Sangoma uses a Z80 to do the low-level trickery (ET uses a nifty special-purpose RISC, probably much faster) but the chip which may be the Z80 had a great huge sticker saying Sangoma on it. This old Z80 hacker was disappointed :) US cable here too.

Upgrades: I can't say that one is better than the other yet. I was slightly disappointed by some of ETs upgrades, but I haven't upgraded my Sangoma driver yet, so I won't make any point. ET does have a mailing lists and new versions of the drivers are announced there now and then, Sangoma hasn't and I miss it.

I hope this will be of use to someone wanting to route WAN links using linux. Feel free to send me any questions or refer people who want to do WAN links using linux to me.

If you traceroute me, is some sort of Cisco at one of my ISP's POPs and is a linux box with a Sangoma card and no monitor, two rooms from where I sit.

One important final point. Anyone who wants to use linux to do mission-critical routing should probably keep a spare for every piece of hardware on-site. Remember to make space for that in the budget.