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Installing circuits on the AAC-3 is a straightforward process. You can manage the box using telnet, a directly connected console cable or inband management. Even better, ADC offers SMARTools, a browser-based console that manages the unit via SNMP. SMARTools also is a better interface for administration, providing more performance data at a glance. It's tough to go back to the telnet interface after you've worked with this one. But the steep $2,995 price tag for SMARTools might help you settle with telnet. In contrast, 3Com's ATM Access Manager application--conceptually similar, though not ready for this review--runs only $795.
For Ethernet-based management, ADC requires you to install a PC Card adapter into the chassis; 3Com builds
Ethernet right onto the CPU card of the AccessBuilder. Like the 9600, the AAC-3 can save configurations to a file from within SMARTools or via Trivial FTP. The resulting file is readable, but a checksum prevents the file from being edited externally.
Regardless of which way you manage it, the AAC-3 presents more information and has easier navigation than the 3Com unit. For instance, from the port-configuration screen a single key will take you to the connection configuration screen, physical layer statistics and protocol statistics screen--all associated with the port you are examining. The 3Com interface requires many more keystrokes to navigate its deep menu hierarchy and doesn't provide a per-port filter.
While configuring the boxes was easy, we discovered that the cards have to be firmly seated to be fully operational, more so than with the typical networking device. We experienced problems with clock synchronization, Ethernet bridging and ATM cell delivery, all because of cards jiggling loose duri
ng shipment. While the cards presented themselves on the bus and could be configured, they wouldn't operate correctly. After several hours of frustration, we pulled all the cards out and slammed them into the midplane. Sure enough, our problems were solved.
Reseating the line cards didn't solve the AAC-3's performance problems. The pair of ADC products performed better than 3Com's units in the undersubscribed T1 performance tests, but under heavier loads the AAC-3 didn't manage traffic as well as the AccessBuilder. The more stress applied to the network, the more random performance became. After losing two T1s in our four T1 bundle, high-priority ATM traffic took a substantial hit, while the units strangely continued to buffer and deliver lower-priority Ethernet bridging traffic. However, the highest-priority traffic--CBR services over DSX-1 interfaces--remained consistent.
Our performance analysis indicates the way ADC expects the AAC-3 to be configured. When the total of SCR (sustained cell rate) valu
es is greater than available bandwidth, all traffic is discarded equally, instead of being based on its relative priority. In these conditions, we would have to reduce the SCR values to get the correct behavior. However, it's unrealistic to expect users to reconfigure devices based on network conditions like trunk loss.
3Com Corp. AccessBuilder 9600 With STX
Our tests revealed that the 3Com AccessBuilder 9600 with STX excels in traffic shaping and prioritization, offering stable performance to high-priority streams when we overloaded circuits and introduced trunk problems. Results were not as good in ideal conditions, where the ADC unit provided better throughput and latency.
The AccessBuilder 9600 is a six-slot chassis with redundant power supplies and two reserved slots. It can be configured with the STX module, which provides switching between local ports, so you don't need to distinguish between trunk and port modules. The older CTX card provides ATM multiplexing
onto a card designated to be the trunk. The 9600 is considerably more expensive than the AAC-3. However, 3Com also offers the AccessBuilder 9300 and 9100 units, lower-capacity devices that allow switching among up to seven ATM ports.
The AccessBuilder 9600's limited slot count and card options kept us from completing all of the tests we had designed. It's not possible to run DS-3 ATM, V.35 frame relay, structured T1 CBR, full T1 CBR and Ethernet bridging simultaneously in one chassis--so we scrapped our frame relay testing in favor of examining circuit emulation, native ATM and Ethernet bridging.
The 9600 does allow for direct connection to a structured T1 service, which the AAC-3 does not. Structured T1 allows individual DS-0s to be extracted and cross-connected. The 9600's CBR DSX ports can handle both structured data and voice (in other words, Nx64-Kbps channels with or without A & B signaling), in addition to unstructured DS-1 frame tunneling.
3Com supplied its STX module for this test, a n
ew card that allows for local switching, priority queuing and traffic shaping/policing. While we experienced a few problems getting all services to run, we were able to quickly cure them through a simple code update. Changing software couldn't be much easier--the AccessBuilder acts as an FTP server, letting administrators simply do an FTP put into the box. As with the AAC-3, configurations may also be saved via pointing an FTP client at the unit. Also like the AAC-3, configurations may not be edited offline.
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