ADC Kentrox And 3Com Aggregate ATM WAN Traffic

ADC's AAC-3 and 3Com's AccessBuilder 9600 are a clean match against one another, offering nearly identical physical ports and software with support for mostly the same set of standards, including a prestandard implementation of the ATM Forum's IMA specification. Physically, they both offer dual power supplies and hot-swappable cards. They are both managed via VT-100 terminal emulation over telnet, a direct cable connection or inband. And they both allow for SNMP management. On the other hand, they both lack support for a few key standards. Neither unit supports ATM ILMI (Interim Local Management Interface, an approach to automatic switch and circuit configuration), ATM SVCs (Switched Virtual Circuits) or PNNI (Private Network-to-Ne twork Interface) routing. Neither unit provides a full gamut of voice optimization services, with voice compression absent from both. But this is a reflection of the state of the market--for example, most carriers don't yet offer SVC service. Large, But Flexible These are not the smallest units available for ATM access, but they are the most flexible. Smaller, more fixed-configuration units like 3Com's AccessBuilder 9100/9300 and ADC Kentrox's AAC-1/AAC-2 are available at a substantially lower cost. But we wanted to examine units that service a broader range of traffic, so we opted for midsize units. The units take the same approach to installation and configuration. We found 3Com's configuration screens to be slightly more cumbersome, in part because of 3Com's use of virtual interfaces defined on top of physical ports. In addition, its interface uses deeply nested menus and doesn't offer the keystroke shortcuts that ADC's interface does. But both units are simple to configure, and the real work is in the up-front planning. ATM is a complex technology, requiring careful network design and tuning. However, configuring these boxes is fairly trivial if you've done your homework. You quickly get the hang of assigning traffic streams a VPI/VCI (Virtual Path Identifier/Virtual Channel Identifier) pair, then setting up ATM traffic parameters. Traffic streams are generally represented in cells per second, so you might have to do a few calculations on your own to get the traffic parameters just right. These units sit at the edge of the network, typically with few paths through the cloud, making them that much simpler to configure. Both vendors have done a good job of laying out text menus, which clearly present all configuration options, so you don't need to memorize a command language syntax. Although both interfaces are intuitive, we lean toward ADC's approach, which puts more information on the screen and allows for hot keys for quick shortcuts. In our performance testing, the 3Com AccessBuilder outperformed the ADC Kentrox AAC-3 under load, principally because of the way the AccessBuilder prioritizes traffic. But the ADC unit offers more flexibility, aggressive pricing and a better management interface. In a conservative network, the ADC AAC-3 has the edge in ATM WAN access. ADC Kentrox AAC-3 Multi-Service Access Concentrator The design of ADC Kentrox's AAC-3 is more flexible and modular than that of 3Com's AccessBuilder 9600, with a better set of system management tools and aggressive pricing. The AAC-3 delivers excellent circuit emulation (CBR) services, with good VBR (variable bit rate) performance when network conditions are conservatively managed. However, we experienced a high degree of data loss and latency when we attempted to oversubscribe available bandwidth. Two chassis models are offered: the eight-slot AAC-3 and the four-slot AAC-2. In contrast to the AccessBuilder 9600's meager four-line cards , the AAC-3 will support seven. One slot is reserved for the system controller, whereas two slots must be used for management and switching/multiplexing in the 3Com device. The AAC-3 provides any-port-to-any-port switching by default; this is available only when 3Com's STX switching module is installed to the 9600. In the AAC-3, physical layer modules slide into one side of the midplane, lined up with a protocol module on the opposite side. For example, for ATM UNI on a DS-3, you match an ATM cell protocol module with a DS-3 physical layer module. 3Com's AccessBuilder, in contrast, requires line- and protocol-specific combination cards, making the AAC-3 more flexible as networks evolve. Some modules, however, must be replaced as you move above T1/E1 speeds. Protocol modules offer a great deal of flexibility, falling into three broad categories: cell, packet and circuit emulation. A combination quad packet/CBR card gives you both in one slot. The set of line interfaces also exceeds that of the 3Com unit. For example, ADC offers a single card with three V.35/EIA-530 ports and one DSX-1 interface; thus a single line card could deliver frame relay, a PBX interconnect, ATM DXI and video over V.35 service.

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