6/12/97 By David A. Ranch Key: +-----------------------------+ | Pros are denoted with a "+" | | Cons with a "-" | +-----------------------------+ --- ISDN Routers: + One of the best things about the newer ISDN routers is that you can upgrade their flash-based software for free. So as the new software versions come out, you get more reliability, and more features. + ISDN routers also do all of the PPP processing themselves so your computer is free to do more useful processing + routers are platform independant so regardless of operating system type, all of your machines can use your ISDN connection. - Routers are more expensive than T/As. The cheapest I've seen is about $400 for a very "cheap" unit. - Routers are not nessisarily easy to setup. If you don't know a lot about ISDN, PPP, PAP/CHAP, etc... you might be in for an unpleasant suprise. --- --- ISDN T/As: + Most T/As cost about $300 or less + T/As don't need a ethernet card for connectivity + T/As are simple to install (as easy as a analog modem) - Your PC's serial port becoming a bottleneck for performanceand placing more (see the serial port section below) - Higher traffic latency compared to a router due to the SYNC-to-ASYNC conversion. This can be a major issue for network based game players. (see the serial port section below) : A (1) B-channel connected router should get about a 20ms ping time to its default gateway : A (1) B-channel connected serial T/A usually gets a ping time of about 70ms on a 115,200 b/s serial port and about 45ms on a 460,800 b/s serial port - PPP processing load is placed on your machine's CPU vs. a router's dedicated processor. --- --- Advanced serial ports for T/As: - Most PCs today come with 16550A [Asyncronous] serial ports which are commonly restricted to serial rates of 115,200 b/s. With an ISDN line running at 128,000 b/s, not to mention 4:1 Stac compression, the serial port obviously becomes a major bottlebeck (115,200 vs 512,000). - Note: Many people are downplaying the 115,200 bottleneck because they say that most users use Windows95/NT's build-in Stac compression. Though this helps since the traffic is compressed before it even hits the serial port, you still: - cannot access the full speed of the ISDN line - Utilize the CPU for compression thus slowing down your machine for other tasks - Increase traffic latency over hardware-based internal T/A compression. + But users can ow users can buy cheap serial port cards to overcome these issues: Chip Buffer Space MAX DTE Rate ----- -------------- ------------ 16550 - 16byte buffers - 115200 b/s 16650 - 32byte buffers - 460800 b/s 16750 - 64byte buffers - 921600 b/s + Here are a few good vendors: + ByteRunner (www.byterunner.com) : 16650 : ~$29 + Lavalink (www.lavalink.com) : 16650 : ISA and PCI versions : $? + Turbocom (www.turbocom.com) : 16750 : ~$80 Ps. If you are using an older serial card that has the serial UART (big 40-pin chip) socketed on it, you should be able to just buy a newer UART chip like a 16650 UART, plug it into your existing card, and be ready to go! [Do this at your OWN risk] ******************** * Syncronous Cards * ******************** + In addition to higher speed and buffered serial cards, some ISDN T/As can use Syncronous connections and avoid the higher latency conversion issues compared to using standard Asyncronous serial ports (as described above). - www.sangoma.com: They sell a Sync card that is supported by Windows 95/NT and Linux which can operate at 2.048Mb/s. Unfortunately, it costs ~$600! (6/11/97) - If you have heard of other Sync cards for PCs, please drop me a note about it! --- --- Types of ISDN accounts from ISPs: Type 1: One IP address - Get a dynamic ISDN dial-up IP address (cheapest ISP account) and support ONLY one machine behind the router or T/A now without any significant changes to your home or ISP setup except for the ISDN equipment. Type 2: Multiple NAT or MASQ'ed IP addresses: - If you get an Ascend ISDN Pipeline router and you are dialing into a Ascend Max400x with the nessisary configurations (Max DHCP) implimented, you can allow for MANY machines behind your ISDN router to use the Internet simultaneously. Note: Having to dial into an Ascend Max *ONLY* for NAT (Network Address Translation) support is a unique limitation of Ascend while many other ISDN router vendors (like Zytel) can support NAT functionality without having to use DHCP. + Some ISDN routers, like some Zytel units) also offer a feature very similar to Linux's IP Masqurading where your (1) ISP provides TCP/IP address is translated into to MANY private addresses for a small home LAN without the cost of getting multiple IPs from your ISP. - But, Zytel's MASQ can't hold a candle to Linux's MASQ. :) Type 3: Full subnet from your ISP - Here, you will pay extra to your ISP to get your own subnet of IPs. This is the most flexible design but it also can cost a lot of money depending on the ISP and the number of IP addresses you want. ---end