Latency vs. Bandwidth

[anthonymd]

Does anyone know a good resourse for information regarding how latency relates to bandwidth size or if in fact it does?

We have a remote office in Macau and users there complain about how slow one particular application responds over the VPN back to the US. Management want to throw bandwidth at the situation but they also have to understand that distance plays a role in latency. The current average is about ~220ms rt.

[williamsdo]

Hi, if your VPN is using IPSec you could be experience queuing latency due to encryption of the data packets. I am not an expert on queuing so you might want to do some research on that. I do know you can use policy-maps and priorty queuing to correct the problem if indeed that is the problem.

HTH

[jeffreytheall]

they are apples and oranges. latency is merely it takes the packets to get from point A to point B. some applications, especially those dependent on TCP/IP or other connection oriented protocols, are prone to problems associated with latency. this is especially true with networks traversing satellite shots. latency is also added with devices in between the end points, especially firewalls and encryption devices. although VPNs are fingered in causing latency issues, they have also been associated with helping. VOIP protocols seem to benefit from IPSEC tunneling. I don't know why, I just know it works on my network with a VPN tunnel across a satellite shot. It could be the encapsulation helps keep the packets in order. hope this helps.

[Joseph W. Doherty]

Sorry, don't have a good reference for you, but latency very much impacts performance but doesn't relate directly to bandwidth beyond BDP (bandwidth delay product) for TCP, or serialization latency dependency on bandwidth.

The most obvious impact of latency is with applications that are very "chatty", those assuming LAN like latencies. LAN latencies typically are under 1 ms, so in your remote office with 220 ms, every round trip might take about 200x longer. So a 2 second LAN reply could take minutes on the WAN.

Often the most effective "fix" for this issue is usage of a WAN WAFS/WAAS product. Cisco info:

http://www.cisco.com/en/US/products/ps6469/index.html

http://www.cisco.com/en/US/products/ps6870/index.html

PS:

A free web tool you might want to look at: http://www.networkperformancedaily.com/2008/02/netqos_network_estimation_tool.html