The Packet Shapers have a complex system of hierarchical policy specification. You can assign a guaranteed minimum rate of traffic to particular flows or classes of flows. You can also prevent new connections from being established when there is no longer sufficient capacity for them.

You can adjust the ways unused capacity will be allocated to lower-priority flows, and even lock out certain kinds of traffic. You can also assign priorities rather than specific rates to traffic flows. Some of the complexity can be reduced with Packet Shaper's automatic discovery, mechanism, which attempts to classify flows and conversations on its own. Packeteer also ships pre- designed software Policy Modules to help administrators get started quickly.

The suggested retail prices for the Packet Shaper 1000, 2000, and 4000 are $ 3,450, $ 7,250, and $ 14,500, respectively. The Packeteer products have been in production for close to two years, and many of the company's claims have been confirmed in practice. So far, no one has brought forward any evidence of TCP/IP stacks that misbehaved with Packet Shaper products. Packeteer does have patents pending on some elements of its rate-control process, but the company contends that the mechanisms it uses within packets are standards-compliant.

Queuing-Based Products If Packeteer represents the purest support for TCP rate control, Xedia (Littleton, Ma) represents the purest support for queuing. Xedia produces a line of five dedicated hardware devices called Access Points, which are aimed at different maximum throughput levels. The Access Point T1 products support four or eight T1 lines running frame relay or PPP, and they include an integrated DSU/CSU with bandwidth test. There's really no place to put a separate Internet access router; these access point products appear to be ready to handle the whole job, not just traffic throttling.

The Access Point 45 supports T3 throughput, and the Access Point ATM supports ATM at T3 rates. The Access Point 10 and the Access Point100 include Ethernet interfaces at 10Mbits/sec and 100Mbits/sec, respectively (these products don't have WAN interfaces as the others do). Xedia has had substantial success in getting some prominent ISPs to adopt its products. The Xedia devices implement the CBQ algorithm, which are a public domain and thus an open technique. (It was developed at Lawrence Berkeley Labs.) As with the Packeteer products, users can define a hierarchy of traffic classes and assign rate commitments or priorities to them.

One potential shortcoming of queuing is the difficulty of setting admission policies, which prevent new flows on full links. Flows that have minimum requirements should not be allowed when there is insufficient capacity to assign an additional flow.

The prices for the Access Point products range from $ 4,995 to $ 16,995. The Access Point 100 has the highest rated throughput of any of the bandwidth managers on the market.