On the bright side, support for other standards that enable VoIP and wireless technologies is consistently good. In the case of QoS, which is essential for a successful VoIP implementation, not only are standards like DiffServ and 802.1p there, the implementations are mature. For example, all the vendors support features that make it possible to maintain Layer 2 QoS settings (802.1p) through a router, which can sometimes be problematic because routers strip off Layer 2 frames and thus lose initial Layer 2 priority settings (which means there won't be any prioritization if the frame encounters Layer 2 switching after going through a router). Most VoIP-phone vendors will turn on Layer 2 and Layer 3 QoS, and all the vendors can rebuild Layer 2 QoS settings as frames emerge from the router based on Layer 3 QoS settings.
All the vendors can police QoS settings and reset them based on factors such as VLAN and IP address. And they can do all this magic in ASICs--read: at or close to true wire speed.
We were surprised to learn from our reader poll that only 8 percent of you are using DiffServ or its equivalent, ToS (Type of Service), for marking priorities at Layer 3. However, 15 percent of you plan to do this by year's end. A much larger number of you prioritize packets based on TCP or UDP ports (33 percent) or by IP address (again, 33 percent), and more of you plan to do so in 2003. You'll be glad to know that all four vendors claimed to have this capability, as well as many variations, all done in ASICs. All four vendors' chassis support lots of redundancy. For example, all offer redundant power supplies and CPU cards. A bad power supply would cause no downtime, and a bad CPU would require just a minute or so to switch to the backup card. Although this is a lot quicker than installing a replacement card, the downtime would probably be enough to be noticed by end users.
Alcatel and Enterasys indicated they could upgrade some nonspecified features without any downtime, and all the vendors allowed storage of multiple software images, which can be handy when upgrading to a new image causes problems. In most cases, however, downtime still is measured in a minute or more when upgrading software or switching images because a reboot is always required.
We were encouraged that all the vendors offered GUI applications that could manage QoS from end to end. Although it's possible to set up QoS on the command line, the reality is that QoS takes a lot of expertise and time to set up and maintain on multiple switches and routers. The GUIs can handle ACLs (access-control lists) and store and update configuration and software revisions.
