s SNA or on AppleTalk. Most traffic-shaping devices use queuing algorithms. The queuing technique pri- oritises traffic according to its class. Different classes of traffic are then shunted to different queues. Each queue is serviced with a frequency depending on the priority accorded to the traffic in the queue. Active intervention in TCP connections between end stations allows more granu- lar control over bandwidth and latency of TCP flows than does the use of queuing algorithms. In fact, most bandwidth management devices rely on queuing mech- anisms for traffic management. Such active intervention involves actions such as altering TCP window size, altering maximum segment size and altering retransmis- sion times. The first step in the running of a traffic-shaping device is traffic discovery. The unit would be attached to an Internet access router and run, and a web browser can usually be used to view a network traffic profile. Such a profile will show current and peak rates for the applications running. It will also show the number of times each application has been instantiated. It should also give information on its success in achieving the user-specified rules. 13 Traffic Management A unit might, for example, be designed to control traffic headed to and from WAN pipes running at E1 (2.048 Mbps) or slower, so theoretically any higher rate would suffice. Even when handling flows consisting entirely of short (64-byte) packets, PacketShaper does not drop traffic until the load exceeds 55 Mbps. Latency is low and constant, with measurements around 500 us. After enabling traffic shaping and configuring PacketShaper to constrain band- width to T1 (1.544 Mbps), it is possible to send UDP traffic through PacketShaper rates of up to 2.3 Mbps. This is approximately 50% faster than should have been allowed by the shaping contract. A baseline test for traffic shaping devices determines the maximum number of concurrent TCP connections that can be handled. Tarantula from ArrowPoint Communications (acquired by Cisco System