That Pings
That Pings
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What does ping delay say about the network performance?
Ping is a utility used to test connectivity and to measure round trip delay between network devices. Ping works by sending an ICMP echo-request packet to the destination and expects an ICMP echo-reply in return. The time taken for this process to occur is recorded and displayed on the output screen. The following are some examples of how the timer is affected under different network conditions.
Test #1. Ping across a vast distance
C:it-pathways.com>ping satellite-hop
Pinging satellite-hop with 32 bytes of data:
Reply from satellite-hop: bytes=32 time<765ms TTL=128
Reply from satellite-hop: bytes=32 time<760ms TTL=128
Reply from satellite-hop: bytes=32 time<765ms TTL=128
Reply from satellite-hop: bytes=32 time<765ms TTL=128
Ping statistics for satellite-hop:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 760ms, Maximum = 765ms, Average = 764ms
Discussion: Studies suggest that the human ear can begin to notice delays 125ms or greater. Needless to say, if we tried to use any real-time applications across the link on Test #1 we would not have a positive experience because the delays have been recorded at 764 milli-seconds on average. One point of note, this is a rare example where high delay is not caused by a busy network. This is simply a case where the packet has to travel really, really far and it takes a lot of time to do so.
Test #2. Ping another PC in the same office
C:it-pathways.com>ping Pathways-PC1643
Pinging Pathways-PC1643 with 32 bytes of data:
Reply from Pathways-PC1643: bytes=32 time<2ms TTL=128
Reply from Pathways-PC1643: bytes=32 time<1ms TTL=128
Reply from Pathways-PC1643: bytes=32 time<1ms TTL=128
Reply from Pathways-PC1643: bytes=32 time<1ms TTL=128
Ping statistics for Pathways-PC1643:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 1ms, Maximum = 2ms, Average = 1ms
Discussion: This is about as good as it will get. The initial 2ms delay may have been due to an arp resolution. This type of lightning response is only really seen on a Local Area Network (LAN). A WAN will normally take 10ms to 50ms depending on the distance.
Test #3. Ping another PC across a WAN
C:it-pathways.com>ping Pathways-WAN-PC32
Pinging Pathways-WAN-PC32 with 32 bytes of data:
Reply from Pathways-WAN-PC32: bytes=32 time<40ms TTL=128
Reply from Pathways-WAN-PC32: bytes=32 time<40ms TTL=128
Reply from Pathways-WAN-PC32: bytes=32 time<285ms TTL=128
Reply from Pathways-WAN-PC32: bytes=32 time<40ms TTL=128
Ping statistics for Pathways-WAN-PC32:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 40ms, Maximum = 285ms, Average = 101ms
Discussion: This computer is some distance away and the results are consistent with our latency expectations of a WAN. The third response shows a large increase in latency. This may be a sign of congestion.
Test #4. Terrible Ping response from another PC across the WAN
C:it-pathways.com>ping Pathways-WAN-PC47
Pinging Pathways-WAN-PC47 with 32 bytes of data:
Reply from Pathways-WAN-PC47: bytes=32 time<3005ms TTL=128
Request timed out.
Reply from Pathways-WAN-PC47: bytes=32 time<2950ms TTL=128
Reply from Pathways-WAN-PC47: bytes=32 time<3852ms TTL=128
Ping statistics for Pathways-WAN-PC47:
Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
Approximate round trip times in milli-seconds:
Minimum = 2950ms, Maximum = 3852ms, Average = 3269ms
Discussion: Windows Ping times out at 4000ms (4 seconds) by default so the timed out request may just be that the reply did not arrive in time (as opposed to the packet being lost). This type of high latency plays havoc with the TCP retransmission delay timers, the last thing you would want on this network is a lost packet. TCP Performance would be highly impacted.
Test #5. No ping response
C:it-pathways.com>ping Pathways-PC947
Pinging Pathways-PC947 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for Pathways-PC947:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
Discussion: This response can actually be produced under 4 circumstances:
1. The destination PC is protected by a firewall that does not allow ICMP
2. The destination PC is not working (or disconnected)
3. There is a faulty router between the source and destination PC
4. The destination address is incorrect
About the Author
Want to learn how accurately to monitor network performance?
Andres Villalva B.IT, AssDip(Eng), CCNP, MasterCNE is a co-founder of IT-Pathways.com and writes articles based on over fifteen years of experience in the Information Technology industry. Find IT Cover Letters, IT Resumes, Interview Tips, Training, Online Learning and more at it-pathways.com.