![]() |
|||
![]()
|
![]() |
![]() Click Here! |
![]() |
100M-bps Ethernet If a dedicated 10M-bps connection to the desktop is not enough, consider 100M-bps. 100M-bps Ethernet has taken the market by storm during the mid-1990s mainly because it is relatively inexpensive. There are two 100M-bps Ethernet campsthe 100BaseT and the 100VG-AnyLAN. After quite a battle between the two camps, it appears that 100Base T has won the majority of the market. It operates in a similar manner as 10BaseT, so customers feel comfortable with the technology. There are also NIC cards and hubs available from a variety of vendors that support both 10M bps and 100M bps. By using these NIC cards, a user can maintain their 10M-bps LANs, and upgrade portions as needed to 100M bps. Typically, the servers would be put on 100M bps connections while the users remained at 10M bps. This would reduce contention for the server, thereby improving performance and response time. Exhibit 3-5-8 shows a 10/100M-bps Ethernet switch.
ATM to the Desktop In the mid-1990s, while Asynchronous Transfer Mode (ATM) was still quite a bit of hype, IBM introduced a way to get ATM to the desktop in a relatively inexpensive fashion. They developed a 25M-bps NIC and hub that allowed users to upgrade the speed to the desktop, while gaining the benefits of ATM. ATM was designed to support the integration of voice, video, and data traffic. Standard LAN technologies such as 10/100M-bps Ethernet, are data-only technologies, with no provision to support the services required by voice and video. Of course, given enough bandwidth, you can put any kind of traffic down a pipe, and it will reach the other end with reasonable quality. The issue arises when there is congestion on the networkthere is no way to guarantee service to voice or video with conventional LAN technologies. 25M bps allowed the entry into ATM technology as well as enabled new desktop applications to be deployed while guaranteeing some level of service to these new applications. Most of the ATM to the desktop is either 25M bps or 155M bps. Needless to say, the market for ATM technology today is not at the desktop. As mentioned earlier, the desktop remains with the Ethernet technologies. The major demand for ATM is in the LAN backbone/campus backbone areas. BACKBONE TECHNOLOGIES LAN Backbone Because there are many LAN segments connecting various users within an organization, these segments must be connected together to facilitate the sharing of departmental information. The hubs that create these segments are usually connected together through some kind of backbone. Routers used to be the backbone device of choice for many organizations. LANs from different departments would feed into a central router, and the router would route traffic from one segment to another. Exhibit 3-5-9 shows a router-based collapsed backbone.
With the advent of LAN switching and VLANs, the routers were moved out of the LAN backbone to focus on WAN connectivity. The LAN switches provide a high speed uplink that allows for these switches to be cascaded together. Also, since switching is performed at Layer 2 (and not Layer 3 as in routers), the processing delay for each frame is much less than with a router. The backbone connecting these switches may be ATM-based, or 100M-bps Ethernet. Work is currently being done on a standard for Gigabit Ethernet. 3Com, Bay Networks, Cisco, and Cabletron have all announced Gigabit Ethernet products ranging from NIC cards for high-end servers, to uplink modules for existing Ethernet switches, to gigabit Ethernet switches to tie all the gigabit uplink ports together. Most of these products will not ship until late 1997 or early 1998. Needless to say, Gigabit Ethernet will not be a desktop technology any time soon, but may be a competitive backbone technology. Campus/Metropolitan Area Backbone Looking toward the campus backbone, organizations with their own fiber have traditionally used Fiber Distributed Data Interface (FDDI) to connect these buildings together. Prior to the Ethernet craze, it was the fastest, most reliable technology available. The technology did not gain a huge following mainly because of the price of fiber and the price of the equipment. Most organizations treated the campus as a WAN, and used WAN connections like T1 or T3 to interconnect the buildings.
|
![]() |
|
Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details. |