Traffic metering is another form of traffic shaping. A number of protocols such as AppleTalk exhibit a tendency to transmit packets unevenly, which is sometimes known as creating trains of packets. Traffic metering spaces out the trains prior to transmission by temporarily storing packets in buffers to make sure the network isn't overloaded. Metering also can be used at the edge of a network to mitigate the effect of bursts.
Putting it all together
No matter which QoS capabilities a switch or router implements, the device works by itself to get data to its destination. For example, a packet could proceed through the first few devices and links with no problem, and then encounter a link that prevents proper QoS from being provided. Because the devices that the packet has already traversed function independently, they can't take steps to avoid the defective link.
But forthcoming policy-based management systems will ultimately tie all the QoS capabilities discussed above into one cohesive system to ensure end-to-end QoS.
Policy servers in conjunction with existing network monitoring and management software will monitor the network to determine optimum QoS settings and dynamically configure routers and switches.
The policy servers will also consult network directories such as Novell Directory Services to determine the appropriate service levels specific users and applications require. Policy servers and directories will typically use Lightweight Directory Access Protocol to communicate.
Policy servers still aren't available, but the products are expected to start shipping soon. Bay is scheduled to release a policy server next quarter based on its NetID TCP/IP address management software platform. Called Optivity Policy Services, the new product will work with Bay's Contivity Extranet Switches, Accelar Routing Switches and all Bay routers running BayRS routing software.
3Com also is expected by year-end to ship a stand-alone policy-based management system. Called PolicyPowered Networking, the product will work with 3Com's CoreBuilder 3500 and 9000 LAN backbone switches, SuperStack II LAN edge switches and PathBuilder WAN access and backbone switches.
Cisco is scheduled to debut CiscoAssure Policy Networking in the first quarter of 1999. The policy-based management system will support Cisco routers and Catalyst 5000 and 8000 LAN switches.
Cabletron pioneered the idea of policy-based management in 1994 when it announced SecureFast Virtual Networking. SecureFast wasn't successful in gaining market acceptance, but the technology will be incorporated in Cabletron's upcoming policy server. The company has not yet released a ship date for the new server.