Sometimes it is a hard sell, but the factor most overlooked when designing high speed networks is that of designing for low latency. Bandwidth and over/under subscription are only part of the network design. Low latency networks (regional RTTs of 1-5 milliseconds; campus RTTs in the sub millisecond range for GiGE, and microsecond range for 10 GiGE) by their nature solve a lot of QoS problems, often relegating QoS as a method to be used in emergency cases only, such as DoS attacks. Here is something I have been thinking is not too far over the horizon: commodity 48 port x 10/100 GiGE switches; 10 GiG NICs on the desktop; commodity-priced 10,40, or 100 GiGE WAN links; while user bandwidth requirements rise at a much slower rate. Some switch vendors even today have 48 port 10 GiGE switches in the $25K range. My rule of thumb is that 1 GiGE link is an order of magnitude lower latency than a 100 Mbps link, and a 10 GiGE link is an order of magnitude lower latency than a GiGE link. -----Original Message----- From: Sean Donelan [mailto:sean@donelan.com] Sent: Tuesday, November 09, 2010 9:26 PM To: nanog@nanog.org Subject: Current trends in capacity planning and oversubscription While the answer is always it depends, I was wondering what the current rules of thumb university network engineers are using for capacity planning and oversubscription for resnets and admin networks? For K-12, SETDA (http://www.setda.org/web/guest/2020/broadband) is recommending: - An external Internet connection to the Internet Service Provider of at least 100 Mbps per 1,000 students/staff - Internal wide area network connections from the district to each school and between schools of at least 1 Gbps per 1,000 students/staff How does that compare with university and enterprise network rules of thumb?