Current trends in capacity planning and oversubscription

Holmes,David A dholmes at
Wed Nov 10 13:14:46 CST 2010

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 at] 
Sent: Tuesday, November 09, 2010 9:26 PM
To: nanog at
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 ( is 

- 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
and between schools of at least 1 Gbps per 1,000 students/staff

How does that compare with university and enterprise network rules of 

More information about the NANOG mailing list