Latency is the time period between a signal being sent and a signal being received

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63
votes
8answers
36k views

How much network latency is “typical” for east - west coast USA?

At the moment we're trying to decide whether to move our datacenter from the west coast to the east coast. However, I am seeing some disturbing latency numbers from my west coast location to the east ...
38
votes
7answers
10k views

Troubleshooting latency spikes on ESXi NFS datastores

I'm experiencing fsync latencies of around five seconds on NFS datastores in ESXi, triggered by certain VMs. I suspect this might be caused by VMs using NCQ/TCQ, as this does not happen with virtual ...
25
votes
13answers
46k views

Why is the response on localhost so slow?

I am working on a tiny little PHP project for a friend of mine, and I have a WAMP environment setup for local development. I remember the days when the response from my local Apache 2.2 was immediate. ...
11
votes
3answers
1k views

Determining a realistic measure of requests per second for a web server

I'm setting up a nginx stack and optimizing the configuration before going live. Running ab to stress test the machine, I was disappointed to see things topping out at 150 requests per second with a ...
10
votes
4answers
4k views

Why do mobile networks have high latencies? How can they be reduced?

I'm increasingly seeing mobile networking technologies being used to get internet access in areas where it is otherwise not available. While mobile networking is usually not yet viable as the primary ...
9
votes
6answers
12k views

How does geography affect network latency?

I have the option of hosting our database/web server at a managed hosting company on the East Coast (US) or one on the West Coast (US). Our company is based out of New York City, and both hosting ...
8
votes
2answers
4k views

Internet latency map

I would like to see a latency map, showing the lowest latencies achieved between various destinations around the world. What is for example the lowest latencies achieved between Denmark and India. ...
7
votes
4answers
3k views

High latency, yet ping shows low latency

We're seeing latencies of ~100-300ms for services accessing a remote resource within the same subnet, yet when we use ping (ping size was of a similar size as of packets sent normally), we see ...
7
votes
3answers
1k views

Does routing distance affect performance significantly?

When I say routing distance, I mean on a global scale. For instance, if my target audience is in China, do I look for a host within China?
7
votes
5answers
9k views

Tuning NFS for minimum latency

How can I achieve low latency for NFS exports in order to e.g. have developers work nicely in Eclipse/Visual Studio with their workspaces mounted over NFS?
7
votes
3answers
391 views

TCP Window Scaling for Satellite Connections

A satellite connection generally has a RTT around 500ms. Connections generally suffer sub-optimal transfer speeds, in spite of large amounts of bandwidth because TCP acknowledgements take too long to ...
7
votes
1answer
2k views

High latency/drops between Cisco switches in two locations. How to troubleshoot?

I'm receiving user complaints about poor network application performance between two parts of a large warehouse facility. The software is a curses-based terminal application running on a Linux server. ...
6
votes
2answers
3k views

Data obtained from ping: is it round trip or one way?

I have 2 servers, each in two separate locations. I need to host an application on one, and the database server on the other. From the app server, if I ping the database server, on average I get ...
6
votes
6answers
3k views

OpenVPN over TCP, terrible latency but only on Win7 x64

I know TCP encapsulated over TCP is a terrible idea in general, but I can deal with the occasional decreased performance and MTU issues, and the snowball effect TCP within TCP provides where error ...
6
votes
1answer
2k views

Limit incoming and outgoing bandwidth and latency in linux

I realise many similar questions have already been asked, but so far I've yet to find a solution to my problem. I have a virtual linux server (running Debian Squeeze) that I use for testing of ...
5
votes
1answer
1k views

Esxi with iSCSI SAN slows down with many multiple VMs running

I have a server with ESXi 5 and iSCSI attached network storage(4x1Tb Raid-Z on freenas). Those two machines are connected to each other with Gigabit ethernet, and a procurve switch in between. After ...
5
votes
1answer
262 views

Hardware/topology recommendations for low latency UDP network

I'm setting up a LAN comprised of 60 end nodes that are receiving a high volume of UPD datagrams from one master server. The server sends 60 unique datagrams every 100ms, each datagram is 64 bytes. ...
5
votes
2answers
95 views

Trans-atlantic VOIP

We're a Canadian business on the east coast and will soon be opening up a new call centre in Australia. This new call centre will be handling our graveyard shift and will be overlapping with the ...
5
votes
3answers
3k views

Akamai vs smaller CDN for small/medium-size ecommerce traffic? (caching, latency, NetStorage)

The small/medium sized online retail company I work for uses Akamai as our CDN for static images, but I'm wondering whether it might be hurting rather than helping and, if it's suboptimal, what we ...
4
votes
7answers
5k views

Latency in TCP/IP-over-Ethernet networks

What resources (books, Web pages etc) would you recommend that: explain the causes of latency in TCP/IP-over-Ethernet networks; mention tools for looking out for things that cause latency (e.g. ...
4
votes
4answers
3k views

finding the best network latency between two countries

I know there are many tools to test for bandwidth and latency, but they all rely on having at least one host from which you can run those tests. I wonder whether there's an online source or some ...
4
votes
8answers
3k views

Latency in Internet connections from Europe to USA

I'm looking for a (cheap) Web hoster. Basically all the hosting providers that I can find, and match my requirements are located in the USA. But my target audience is in (Western-)Europe, I know for ...
4
votes
2answers
297 views

Why do tracert latencies not add up to ping latency?

One might expect the sum of the tracert latencies to equal 267ms:
4
votes
1answer
5k views

How to troubleshoot latency between 2 linux hosts

The latency between 2 linux hosts is about .23ms. They are connected by one switch. Ping & Wireshark confirm the latency number. But, i dont have any visibility into what is causing this latency. ...
4
votes
2answers
205 views

Networking Hardware Suggestions For Low-Latency Networking

We've come to the stage of our project where we want to take the software to the next level, generally response times of 20µs or less. Software wise its as good as it gets (though there's room for a ...
4
votes
8answers
6k views

How can I control the network latency?

My company is developing a network software and its network stability is very important. So my supervisor want me to set up the testing environment for our QA team. I can take care of almost ...
4
votes
2answers
151 views

OS parameters tuning for latency improvement

We are trying to improve the average latency of Java proxy application. The Java application receives a message from a client and proxies it to a necessary server. The protocol is binary, ...
4
votes
1answer
328 views

Combining Heroku with custom external services (e. g. Varnish or Postgres on EC2)

I'm planning to set up a Django site on Heroku. It will run on Heroku's Cedar stack, which allows Python apps, but doesn't include or support HTTP upstream caching with Varnish like the other stacks ...
4
votes
3answers
182 views

run local MySQL instance for fast mysql_real_escape_string calls

Currently all MySQL data/API calls are handled by a remote DB cluster (i.e. network latency is a factor in total script execution time). To reduce execution time in this context, would it be sensible ...
4
votes
2answers
458 views

How to find the lowest latency midpoint between two geographic locations?

I'm looking for a geographic location (not service) to host internet services that will give me the lowest latency on connections from two other locations. How would I best determine the most ideal ...
4
votes
1answer
708 views

Hyper-V guests: intermittent latency

I am seeing latency on a Hyper-V host and its guests lately. When I run ping -f from a Linux prompt, I see the dots "pulsate" like a heartbeat indicating 2 successive latency spikes within 1 second ...
4
votes
1answer
2k views

low latency TCP settings on windows 2008 R2

I am running a third party software on a W2008 server. This client connects to a server via TCP. The average ping times between the two are 1ms. However, when I check the tcp connection in resource ...
3
votes
3answers
225 views

Monitoring Internet latency

I've been using smokeping to monitor internet latency (for early problem detection) at 8.8.8.8 for several months. On Friday the average latency went from 12ms to 55ms and has been at the 55ms plateau ...
3
votes
2answers
593 views

Cisco ASA Latency

What is the typical latency added when using a Cisco firewall such as ASA 5505? Are we talking less than 50 microseconds?
3
votes
2answers
8k views

What is best tool to measure network latency?

How do you measure network latency in Windows ? I know ping as one of the tool. Can Windows Performance monitor do it ? Any ideas which counters should I add to measure it. This is for SharePoint ...
3
votes
1answer
228 views

iproute: disable “tc” command

I'm after running this command to simulate a network latency of 500ms with 100ms std deviation: tc qdisc add dev eth2 root netem delay 500ms 100ms Trouble is, I forget how to cancel this command! My ...
3
votes
2answers
863 views

LatencyTop on Centos 6.2

What do I need to do to get LatencyTop working on Centos 6.2? Does it involve compiling a debug kernel with some extra flags? Both the man page and the website are very short of information. ...
3
votes
1answer
982 views

tcpdump udp data capture latency

I am using tcpdump to capture UDP packets and analyze network latency between a UDP broadcaster and my server. To calculate latency I compare the source host timestamps reported in UDP application ...
3
votes
3answers
295 views

Network Latency and Timing as shown by Chrome

I'm trying to understand why a static image being served by IIS is taking ~ 182 ms to load. Using chrome I captured the following timing information. When I request the same image by opening ...
3
votes
1answer
6k views

what is acceptable datastore latency on VMware ESXi host?

Looking at our performance figures on our existing VMware ESXi 4.1 host at the Datastore/Real-time performance data Write Latency Avg 14 ms Max 41 ms Read Latency Avg 4.5 ms Max 12 ms People ...
3
votes
2answers
142 views

Appropriate network monitoring tool(s) for logging hiccups

I have a customer who has problems with our software crashing from time to time. Unfortunately, if you unplug the network cable in the middle of a transaction our software will crash every time and ...
3
votes
2answers
437 views

Another benefit of Lighttpd in front of Apache

I have read in a site that another benefit of having Lighttpd in front of Apache is lower number of child processes. Lighttpd will handle keep-alive and client requests while child processes of Apache ...
3
votes
2answers
2k views

sssd and ldap authentication cache

On our box running OpenSUSE 12.2 we have installed OpenLDAP and sssd daemon. We are using these two services for user authentication. Recently we created a script which creates new web-users for our ...
3
votes
1answer
255 views

different ACK behaviors (slowing down throughput?)

I'm running netio (http://freshmeat.net/projects/netio/) on one machine (opensolaris) and contacting two different Linux machines (both on 2.6.18-128.el5 ), machine A and machine B. Machine A has a ...
3
votes
1answer
372 views

Can Linux RAID 1 account for high latency?

Scenario: we're running a large (3TB total in cluster) Solr installation in EC2. I'm only concerned about disk performance on the read side of things. We suspect that we are limited by disk I/O and ...
3
votes
1answer
427 views

Apache Benchmark is slow from public network, magnitudes faster locally. What are some things I do to speed this up?

I am testing my Linode Ubuntu 14 64bit server out, it's the most basic server available from them. I am using Apache Benchmark to test the server, as well as a multithreaded script I wrote in Python, ...
3
votes
1answer
848 views

Diagnose cause of long running requests in IIS 7.0

We are running an ASP.NET web application on IIS 7.0, Windows Server 2008 R2, with SQL Server 2008 R2 for DB. On weekends, when the traffic is high, the request queue length in the IIS servers ...
3
votes
3answers
644 views

Small TCP Window on WAN between 2 Locations

Site A: Denver datacenter. 60MBPS. Site B: Chicago. 100MBPS. ICMP pings: Packets: Sent = 176, Received = 176, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 74ms, ...
2
votes
2answers
158 views

Set up server far away from target audience? [closed]

I live in Canada, and I want to move out of online web hosting and host stuff on my own server. The problem is, my website caters to a huge amount of US traffic, about 90 percent of traffic is US. ...
2
votes
9answers
2k views

Measure data transfer throughput?

How can I benchmark the network transfer speed of my servers? We already have an existing file server, but it is fairly old. We recently got a donation of a (relatively) newer P4 box, and I wanted to ...