What is a large-scale data-communications network? Apparently an ordinary question, but Jeff Doyle takes this up in the preface of his book ‘OSPF and IS-IS: Choosing an IGP for large-scale networks’ (www.awprofessional.com).
He begins by observing that data communication networks and ideas about them have been around since long before the advent of computers. “For example, when Alexander Graham Bell and Theodore Vail founded American Telephone and Telegraphy Company (AT&T) in 1885, they had no intention of providing telegraph service. But they understood that the network they were building could be used for transmitting more than just telephony signals.”
Doyle also gives examples of how wide-area communication has been around for as long as man has had a need to share information over a range greater than voice can cover. “Many ancient civilisations used signal fires to communicate quickly over a long distance. In feudal Japan, villages sent paper lanterns aloft in the evenings, rising on hot air created by the same fire that illuminated them, to notify nearby villages of their safety.”
Another example is of petroglyphs – the carvings of figures and symbols on the sides of rocks created by hunting, warring, or travelling parties of Native Americans over the centuries in the south-western US. “Although some might have been intended as merely decorative, many petroglyphs are thought to be signals and messages left by one party for other parties expected to pass that way. These carvings put an interesting twist on data communications: The signal remains stationary while the transmitting and receiving nodes move around.”
Returning to the question of defining a large-scale network, Doyle finds it too narrow to base a definition on the number of nodes and links. Instead, the scale of a network is defined by its complexity, he argues. “A small-scale network is one that can be easily managed by direct human intervention; hence early telegraph networks could be considered small-scale even though they covered a very large geographic area. In terms of IP networks, a small-scale network is one that can be routed statically and requires no automated management systems.”
The author then lays down various attributes of a large-scale network, including: complex interactions between individual nodes; complex path diversity requiring load balancing, traffic monitoring and strong loop avoidance; link metrics; diverse data transport requirements; and stringent requirements for security and reliability.
OSPF (Open Shortest Path First) and IS-IS (intermediate system to intermediate system) can easily be run in a network of any size, he avers. “But their true value is in their capability to perform consistently as their network domain grows large. No other IGP (Interior Gateway Protocol) for IP networks can reliably route the world’s largest networks.”
Suggested study for techies.
“At the final interview, we had to face a test based on Twitter?”
“When you had to answer through a series of tweets?”
“No, they showed us a few tweets and we had to guess who… without tweeting around for the answer!”