ISP (Internet Service Provider) Route Test or Connection Test Tools use Internet Control Message Protocol (ICMP) with low Time To Live (TTL) values to find and get ping responses from each router or hop between two end points in the Internet. The purpose of these Tools is to detect each router or hop between the two end points and to record the round trip time it takes packets to go to each hop and return.
Route Test Tools gather the collected data into a report. These reports can be used for locating sources of packet loss and latency in an Internet connection. The most effective of these tools, gather data over an extended period of time and detect which hops belong to the ISP servicing the Internet connection. This article explains how to interpret the data to find the source of latency or delay within an Internet connection.
Study the Delay Column
In the test report, look for a column titled “Delay”, “Average Delay” or “ms”. “ms” stands for milliseconds. These reports record round trip times to each hop in milliseconds. Study the Average Delay/ms column for hops where the delay increases significantly compared to the other hops and the delay seems to affect all other hops greater in value. Any change in average delay greater than 5ms is usually significant.
An example would be a report where the average delay jumps from 15ms to 35ms from hops 14 to 15. All hops 16 and above are approximately 35ms or greater. This means a significant delay is induced between hops 14 and 15. Because hops 16 and above stay in the 35ms or greater range, it suggests the increase delay from hops 14 to 15 was not caused by the router’s response to a ping packet. If one of the problems with the Internet connection is delay or latency, then this could be a contributing source.
Not Every Hop with Large Delay Increases is Causing Latency
The purpose of the Time To Live (TTL) value in Internet Protocol (IP) packets is to prevent packets from cycling through the Internet in an endless loop. If router A sends a packet to router B and, through an error in programming, B sends the packet back to A, then that packet can get stuck in an endless loop. Packets in an endless loop will consume bandwidth and eventually cause a network to fail.
Each router within the Internet must subtract 1 from the TTL value before passing a packet on to the next router. If the TTL value goes to zero, the router cannot forward the packet and instead sends an error message back to the packet’s originating IP address giving details of the packet’s demise. This is how route tests and trace routes work.
Some routers take longer to send the error message than to simply forward a packet to the next destination. The reason hop 9 may have a greater delay than say hop 12 in a report is this extra time. For a specific hop to be inducing latency on a route, all hops to follow must have increased round trip times similar to the specific hop in question.
Look for the Best ISP Route Test Tool
The best ISP Route Test Tools will help you interpret their data and will highlight the hops that its algorithms indicate are inducing latency on the network. In addition, they should gather data over an extended period and determine which hops belong to the ISP serving the Internet connection.