external data networks

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People from two external networks, the Internet and the enterprise, can use the LIC.

In a test network two IBM PCs, xcl01 and xcl02, pretend to be these external networks. They handle all the traffic going into and out of the LIC.

what it is

I chose one PC to pretend to be the Internet to the LIC while it is being built. I really do need access to the Internet: the OS (Operating System) and applications all come from Internet sites. I started with a regular home network: an ISP (Internet Service Provider) modem, a wireless router (although I used the switch, not the wireless access point) and a PC.

LIC topology: external data networks
wireless router


This PC is xcl01 on the rack diagram. The LIC thinks this PC is actually three different paths to the Internet (one for biz01 traffic, one for biz02 and one for adm01). In an ideal world, where money grows on trees, there really will be two ISPs providing access from the Internet to the LIC.

Another PC, xcl02, pretends to be the enterprise network to the LIC. This does the same job as xcl01. The only differences are it has no Internet connection and it is on the other virtual side of the LIC.

the price of bandwidth

The LIC is a bargain for the amount of CPU horsepower you get. The LIC cannot function in the real world without a good connection to the outside world. A good connection means a lot more than a domestic connection to my ISP with an ADSL modem. At home I have an LIC connected to my home network. My home network is connected to the Internet via a cable modem. What I have in spades in terms of CPU, I lack in terms of bandwidth.

A domestic broadband connection is asynchronous. The download speed (from Internet to customer) is much faster than the upload speed. The download bandwidth is bigger. This is the opposite of what the LIC needs. A request from the Internet is small and a reply from an LIC service is big. Also, a dozen customers share each connection: the more people surfing, the less bandwidth each one gets. This is called the contention ratio.

An ISP rents different types of connections to enterprises. These are synchronous links where the download and upload speeds are the same. The connection is dedicated to a customer so the speed is reliable. This all pushes the price up.

A good ISP connection to my shed costs a lot of money. There is no easy solution to my Internet connection bandwidth problem. Synchronous lines are way out of my budget of 99p a year.

  • BT broadband will rent me a 2MB asynchronous line (10:1 contention and no guarantees) for £4,000 a year. This is basically a domestic connection with better technical support.
  • NTL:Telewest will rent me a 2Mb synchronous line (1:1, guaranteed) for £6,300 a year.
  • BTnet will rent me a 10Mb synchronous line (1:1, guaranteed) for £15,000 a year.

Bugger. If I had the business, I could pay for the connection. If I had the connection, could I drum up the business?