Chez INWAP Cable Modem

@HOME from TCI.NET

In the Bay Area, TCI (now known as AT&T Broadband Services) is offering the @HOME service in Fremont and other cities in the San Francisco Bay Area.

Hardware

The LCP cable modem was manufactured by Lan City (which was acquired by Bay Networks, which was acquired by Nortel) and is connected to the Pentium's ethernet card by a twisted pair crossover cable. (A diagram of the network architecture can be found on the @HOME tech info page.) Note: only one computer can be connected to the cable modem; the @Home network assigns a single IP address to the account. (But we uses a proxy/gateway to get around that.)

http://www.cnet.com/Content/Features/Techno/Cablemodems/ has a good article on cable modems. See also www.cablemodemhelp.com and www.timhiggins.com.

Software

Since Windows 95 comes with a TCP stack, the only software that was installed is the @HOME browser (a customized version of Netscape-3.0 with a spinning red ball instead of the Netscape "N" logo). The latest @Home browser is based on the Netscape Communicator version 4.0.

The host name for our PC is "c677793-a.frmt1.sfba.home.com", which is pretty ugly. So we got Infolane to provide a CNAME for us in the Fremont, California, US domain. That way inwap.fremont.ca.us is a registered alias for our IP address.

We later added a second ethernet card and the Sambar proxy server. This allows the other computers in the house to access web sites at cable modem speeds. All the other computers (and the Pentium's second NIC) are using IP addresses that are reserved for private use, such as the range from 192.168.1.1 to 192.168.1.254 as defined in RFC-1918.

Topology

Physical

@Home's RDC (Regional Data Center) is connected to the Internet using links faster than T3 (45 megabits per second). From there, incoming data is shipped to the neighborhood nodes via ATM over fiberoptics. Each node serves a few city blocks. The digital signals are converted analog RF (radio frequency) signals and put onto ordinary coax. All @Home users on the same copper cable have to share bandwidth with each other.

Logical

Up to 4000 homes can be connected to frmt1.sfba.home.com - it's like having a giant virtual twisted-pair hub. There was a disadvantage to this: all 4000 homes in the neighborhood are able to see each other's IPX packets. (Prior to 7-Nov-97, Win95's "Around the House"/"Entire Network" reported about 125 customers who had re-enabled file sharing. Netware/IPX traffic was disabled after being reported in the San Jose Mercury News on 30-Oct-97.)

The "frmt1" zone of sfba.home.com has its own DNS servers, a news server, a mail server, a web server and a caching proxy server. Cached pages come back at full speed, even when the rest of the Internet is bogged down.

Our home

The primary ethernet card on John's PC is connected to the cable modem only. The secondary ethernet card goes to the twisted-pair hub which is our house LAN. The next generation of cable modems is expected use USB instead of ethernet.

How fast is it?

The cable modem chip set is capable if decoding 27 megabits per second as it and all the other cable modems in the area talk to the neighborhood fiber node.

The cable modem is connected to the PC with 10BASE-T twisted-pair ethernet, which limits the burst rate to 10 Mb/s. Actual sustained throughput we measured on a good day was:

Tue, 20 May 1997 at 7:19pm
frame4.tar.gz 37616 Kbytes (36 megabytes, compressed)
38512284 bytes recd in 126.17 seconds (305.24 Kbytes/sec) from cable modem
38512284 bytes sent in  53.66 seconds (717.71 Kbytes/sec) over the LAN
  [305 Kbytes/sec = 2.44 Mbits/sec = twice the speed of a T1 link.]
  [717 Kbytes/sec = 5.76 Mbits/sec = limit of this Pentium's stack and NIC.]
  [The 'sent' test was from the Pentium to a Sun workstation over ethernet.]

Another test in the middle of the night averaged 450 Kbytes/sec (3 x T1).

Cost

Right now, TCI is offering @Home in a few cities in the San Francisco Bay Area. The design requires a very modern cable system, one using fiber optics and ATM between the head end and the neighborhood nodes; only the coax going into the houses is copper cable.

Installed connections in sfba.home.com as of 3-Mar-98:
3766 frmt1	Fremont
 559 plstn1	Pleasanton
 452 lvrmr1	Livermore
 336 cstvl1	Castro Valley
 251 snvl1	Sunnyvale (no new customers are being signed up)
 214 ptbrg1	Pitsburg
 197 ptlum1	Petaluma
 119 pinol1	Pinol
   5 rdc1	Regional Data Center

We were able to take advantage of TCI's special promotional offer. Installation is usually $150, with half off if you have your own ethernet card. But because we ordered before 24-Dec-96, we got a 50% discount, so installation was only $37.50, including them running a separate wire into the den.

The monthly costs are $39.95 for @Home and $11.34 for TCI's basic service.