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GLOSSARY

E1, E2, E3, E4, E5
E-MAIL
E-MAIL VIRUS
EDGE DEVICE
EDGE ROUTER
ETHERNET
EGP - EXTERIOR GATEWAY PROTOCOL
EXTRANET


• E1 signal format carries data at a rate of 2.048 million bits per second and can carry 32 channels of 64 Kbps each. E1 carries at a somewhat higher data rate than T-1 (which carries 1.544 million bits per second) because, unlike T-1, it does not do bit-robbing and all eight bits per channel are used to code the signal.
  E1 and T-1 can be interconnected for international use.
  E2 (E-2) is a line that carries four multiplexed E1 signals with a data rate of 8.448 million bits per second.
  E3 (E-3) carries 16 E1 signals with a data rate of 34.368 million bits per second.
  E4 (E-4) carries four E3 channels with a data rate of 139.264 million bits per second.
  E5 (E-5) carries four E4 channels with a data rate of 565.148 million bits per second.
  

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• E-MAIL (electronic mail) is the exchange of computer-stored messages by telecommunication. (Some publications spell it email; we prefer the currently more established spelling of e-mail.) E-mail messages are usually encoded in ASCII text. However, you can also send non-text files, such as graphic images and sound files, as attachments sent in binary streams. E-mail was one of the first uses of the Internet and is still the most popular use. A large percentage of the total traffic over the Internet is e-mail. E-mail can also be exchanged between online service provider users and in networks other than the Internet, both public and private.
  

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• E-MAIL VIRUS is computer code sent to you as an e-mail note attachment which, if activated, will cause some unexpected and usually harmful effect, such as destroying certain files on your hard disk and causing the attachment to be remailed to everyone in your address book. Although not the only kind of computer virus, e-mail viruses are the best known and undoubtedly cause the greatest loss of time and money overall. The best two defenses against e-mail viruses for the individual user are (1) a policy of never opening (for example, double-clicking on) an e-mail attachment unless you know who sent it and what the attachment contains, and (2) installing and using anti-virus software to scan any attachment before you open it. (However, some e-mail viruses may be so new when your receive them that your anti-virus software may not yet be familiar with it.) Business firewall servers also attempt, but not always successfully, to filter out e-mail that may carry a virus attachment.
  The Melissa virus macro virus and the ILOVEYOU virus are among the best publicized of recent e-mail viruses. Each of these also spawned copycat variations with different words in the subject line.
  Microsoft has been criticized for allowing its widely-used Outlook e-mail program to be so easily exploited by virus creators. Some users indicate that other e-mail programs such as Eudora offer the user more protection.
  

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• EDGE DEVICE is a physical device that can pass packets between a legacy type of network such as an Ethernet network and an ATM network, using Data Link layer and Network layer information. An edge device does not have responsibility for gathering network routing information, but simply uses the routing information it finds in the network layer using the route distribution protocol. An edge router is an edge device
  

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• EDGE ROUTER a term used in asynchronous transfer mode (ATM) networks, an edge router is a device that routes data between one or more local area networks (LANs) and an ATM backbone network, whether a campus network or a wide area network (WAN). An edge router is an example of an edge device and is sometimes referred to as a boundary router. An edge router is sometimes contrasted with a core router, which forwards packets to computer hosts within a network (but not between networks).
  

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• ETHERNET is the most widely-installed local area network (LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel.
  An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.
  Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second).
  

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• EGP, Exterior Gateway Protocol is a protocol for exchanging routing information between two neighbor gateway hosts (each with its own router) in a network of autonomous systems. EGP is commonly used between hosts on the Internet to exchange routing table information. The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen. Each router polls its neighbor at intervals between 120 to 480 seconds and the neighbor responds by sending its complete routing table. EGP-2 is the latest version of EGP.
  

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• EXTRANET is a private network that uses the Internet protocol and the public telecommunication system to securely share part of a business's information or operations with suppliers, vendors, partners, customers, or other businesses. An extranet can be viewed as part of a company's intranet that is extended to users outside the company. It has also been described as a "state of mind" in which the Internet is perceived as a way to do business with other companies as well as to sell products to customers. An extranet requires security and privacy. These require firewall server management, the issuance and use of digital certificates or similar means of user authentication, encryption of messages, and the use of virtual private networks (VPN) that tunnel through the public network.
  

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