17th December 2001 Tim Adye 1

Using a Cable Using a Cable Modem at HomeModem at Home

Tim Adye

Particle Physics Department

Rutherford Appleton Laboratory

PPD Christmas Lectures

17th December 2001

17th December 2001 Tim Adye 2

Home Internet Options

• Traditional dialup modem• Maximum baud rate 56 kbits/s (often less)• Can be unreliable• Dialup times ~30s• “Free” services available, but often heavily oversubscribed

• ISDN• 64 kbits/s (can be doubled by using two lines)• Fast dialup: ~1s• Available anywhere

• ADSL• 500/250 kbits/s (download/upload)• Only available in some areas?• Various companies

17th December 2001 Tim Adye 3

Home Internet Options

• Cable modem• 512/256 kbits/s (cheaper 64 kbits/s option available)• “Always on”• Only available in some areas• NTL and Telewest• Cheapest “broadband” option, if available

• I have a 512 kbits/s NTL Cable Modem (Oxford).• Everyone I know with broadband internet access has an

NTL Cable Modem• The rest of this talk is on this option only

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Cable Modem Availability and Price

• NTL claims to be available in Abingdon, Bicester, Oxford, Wallingford, Wantage, Newbury, Reading• Not everywhere in those areas• Check you area at www.ntl.com/broadband

• uses your postcode

• Could also check www.telewest.co.uk

• NTL Cable Modem cost• £35/month (includes cable modem box rental); or• £30/month + £149 (to buy cable modem box)• Includes phone line• Can also be combined with cable TV

• better deal if you have both

• Installation is £25

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My experience of the NTL service

• Arranging for an engineer to call (installation or service) is really slow and frustrating• Notoriously bad call centre

• NTL engineers were excellent• Installed phone, cable TV, cable modem sockets just where

I wanted them (at different ends of the house)• Took a couple of hours

• Service has been pretty reliable• ~4 overnight outages since February• One longer problem

• Took several days to arrange for an engineer to call

• Fix was trivial (removing an attenuator on the coax cable) – now I know what to try

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Installation• Cable modem box

• Size of a large paperback (single edition LotR?)

• Coax cable to socket in the wall

• Socket does not need to be near TV/phone sockets

• Requires ethernet (10Base-T) or USB on your PC• Works with Windows, Linux, or Mac

• I’ve only used Windows

• Brief tests with Manny’s Linux PC were unsuccessful

• USB only with Windows 98/ME/2000+

• Supports DHCP, so software setup is simple• just like a laptop at RAL

• Using more than one PC is complicated• Even switching PCs isn’t trivial

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Documentation

• NTL Documentation is really basic• Usually enough to get you started

• It took me some time to discover more details• Firewall configuration• Transparent web cache• Cable modem diagnostics• Speed tests

• … until I discovered these excellent pages• http://homepage.ntlworld.com/robin.d.h.walker/

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Speed

• Bandwidth limited at• 512 kbits/s download• 128 kbits/s upload

• Could be slower if demand is heavy• I usually see the full rate, but maybe Oxford is a luddite area

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What it feels like• With a 56kbits/s modem (usually connecting at 33 kbits/s)

• Convenient ssh connections to RAL/CERN/SLAC• Unreliable connection could interrupt work at the wrong time

• Most X-Windows applications (eg. xterm, emacs) unusable• PAW possible, but slow

• No problem downloading small files (up to ~1 MB)

• With cable modem• Reliable ssh connections• X-windows mostly OK

• xterm, emacs, PAW nearly as good as at RAL

• “Heavy” applications still sluggish, but many normally run locally, eg. Netscape, Acrobat

• No problem downloading medium-sized files (up to ~20 MB)• Accessing PPD NT disk shares can still be slow

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Advantages of being “Always On”

• No dial up time

• No contention with phone

• Can run servers• Allows access to your home machine from work

• Useful to pick up files you forgot to bring to work

• Can run ftp, web, login – I just use sshd

• IP address changes every few days, so need to use DNS service, eg. DNS2Go

• NTL forbid high bandwidth ftp/web servers

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Security implications of being “Always On”

• Need to be more careful about security• Hackers scan for security holes• More chance they’ll find you if you are always connected,

and have the same address

• Unless you really know what you’re doing, make sure you disable• “File and printer sharing” (Windows)• All unused inetd services (Linux)

• Consider setting up a firewall• After trying several firewalls for Windows (eg. ZoneAlarm), I

use Tiny Personal Firewall (www.tinysoftware.com)

• Virus checking is even more important

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Accessing RAL

• RAL “internal” web pages and services are not directly available• Eg. PPD internal page, RAL Information for Staff, PPD Unix

systems, NT disk shares

• Sometimes there are alternatives• RAL Notices can be accessed with a password• ssh to csf and then to PPD Unix• NT disks can be read via ftp

• You can also set up a “virtual private network” connection to RAL (AKA “PPTP”) …

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Accessing RAL: VPN

• After logging in with your Federal ID/password, you tunnel “inside the firewall”

• See RAL PC Support pages (Network services : PPTP)

• NB. PC Support pages only accessible within RAL!• Slower than a direct connection

• Also useful when at CERN, SLAC, etc.

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Conclusions

• Once installed, cable modem is fast and reliable• If you have £35/month to spare

• Be careful of hackers

• PPTP to RAL can be very useful