the net- work fabric. When traffic arrives at a switch in a store-and-forward net- work, it is stored, examined for errors and destination information, and forwarded to the next hop along the path-hence the name, store and for- ward. Packet switching is one form of store-and-forward technology. Store-and-Forward Switching Thus, from some far-away and beleaguered island, where all day long the men have fought a desperate battle from their city walls, the smoke goes up to heaven; but no sooner has the sun gone down than the light from the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Protocols line of beacons blazes up and shoots into the sky to warn the neighboring islanders and bring them to the rescue in their ships. The Iliad by Homer, circa 700 BC The first store-and-forward networks were invented and used by the early Greeks and Romans. Indeed, Mycenae learned of the fall of Troy because of a line of signal towers between the two cities that used fire in each tower to transmit information from tower to tower. An opening on the side of each tower could be alternately opened and blocked, and using a rudimentary signaling code, short messages could be sent between them in a short period of time. A message could be conveyed across a large country, such as France, in a matter of hours, as Napoleon discov- ered and used to his great advantage. The earliest modern store-and-forward networks were the telegraph networks. When a customer handed over a message in the form of a flimsy yellow paper that was to be transmitted, the operator would transmit the message in code over the open wire telegraph lines to the next office, where the message printed out on a streaming paper tape. On the tape would appear a sequence of alternating pencil marks and gaps, or spaces, combinations of which represented characters-a mark repre- sented a one, 