InformationWeek
Defining The Business Value Of Technology
October 19, 1998
Strengthen Your Backbone
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Most carrier networks (phone companies or other telecommunications providers) use ATM to carry data information. Many are beginning to run voice traffic over ATM as well. This means ATM networks can be connected over a WAN link with relatively little overhead or translation, and maintain all the quality-of-service features that have been implemented on local networks.
In contrast, while Gigabit Ethernet networks can be linked over an ATM network, there is a considerable amount of work for a router, dividing Ethernet's large (1,518 bytes to 8 Kbytes) packets into ATM's 53-byte packets and maintaining proprietary quality-of-service standards over the WAN link. This means that ATM switches with 10/100-Mbps Ethernet ports will be more expensive than Gigabit switches, for a given level of performance.
Gigabit Ethernet integratessmoothly into existing Ethernet networks, which make up most of the networks in the United States. No conversion is necessary; most Gigabit Ethernet switches also include 10/100-Mbps Ethernet ports, and all types of Ethernet use the same packet size, structure, and protocol.
Administrative Choices
The short-term differences between the two technologies may be a factor for administrators when they choose their backbone technology--primarily the differences in cost andadministration, such as the shorter learning curve that results because administrators experienced with lower-speed Ethernet will find themselves easily familiar with Gigabit Ethernet.
ATM is quite a bit more expensive than Gigabit Ethernet, both for network interface cards (NICs) and for the network infrastructure equipment--switches and routers. Price alone is not usually the issue--in the long run, costs of maintenance, support, and network downtime will be far greater than the original purchase price. However, very few administrators will use a more-expensive technology unless they get some benefit from it.
For now, administrators who need to implement quality of service over a WAN will probably stick with ATM, regardless of cost. This may not be true for much longer, though, as Gigabit Ethernet is closing fast in terms of quality-of-service features, as well as manageability and interoperability. Of course, administrators with an existing investment in ATM may choose to continue with it, although there's no reason not to have both on a network, other than the requirement to have routers between the differing segments.
The remaining issues are much more important for administrators than cost of acquisition. Retraining a large network staff on ATM could be more expensive, in training fees and lost worker-hours, than the hardware. Likewise, if ATM devices take three or four times as long to install and configure, the cost can be significant, even if there is no network downtime associated with it.
The contrast between ATM and Gigabit Ethernet in configuration and administration is significant. ATM products, especially high-end enterprise or carrier-class products, often have a text-based, non-intuitive interface--for example, it requires manually inputting 32-digit hex numbers for each ATM adapter attached to a switch. There is a standard called "well-known addresses" that is supposed to reduce the need to manually enter the number for each adapter, but many cards and switches do not support it, or interoperate with the implementation from another vendor.
In contrast, Ethernet cards and switches, including Gigabit Ethernet ones, can simply be plugged in and will start working. In fact, ports that automatically sense Gigabit as well as 10- or 100-Mbps Ethernet are available, although very few people will use the RJ-45 jacks common to the slower speeds for Gigabit Ethernet--the maximum cable length is about 25 feet, compared with hundreds or even thousands of yards with fiber.
Gigabit Ethernet vendors have typically extended the management interface used for lower-end Ethernet switches and hubs, which results in a straightforward, easy-to-use interface that lets even relatively inexperienced administrators set up virtual LANs, failover links, and other fairly complex features.
These interface issues, as well as most network technicians' lack of familiarity with ATM's underlying format and operation, mean that there will be a need for training, and a period of acclimatization. In contrast, most network technicians are familiar with Ethernet, and there is very little difference between Gigabit Ethernet and the slower speeds. The biggest difference for most administrators will be that Gigabit Ethernet requires fiber optic cables, which is also true of 622-Mbps ATM.
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