The tariff error allowance for DS1 service is 1080 ES per day or 10 UAS
per day. The modern networks are good enough now so that we try to make
them error free but that is a goal not a standard.
The modern networks are self-healing with automated diagnostics and
protection switching. The protection switching is required to execute
in less than 50ms. During these switching operations a small burst of
CVP could be experienced.
Richweb would suggest opening a ticket with Telco when the ES (errored seconds)
is greater than 40 or 50 ES a day. Most copper-based T1s will have anywhere from 3 to
10 ES a day, especially when the day in question involves a temperature fluctuation (hot to cold or cold to hot - copper cables expand and contract). A t1 that is delivered on fiber all the way
into the DEMARC will often never have any errors at all, except during grooming (usually in the middle of t he nite). Copper t1s that are delivered into a building via an exterior NID (pedastal) that is exposed to the weather can often exhibit unreliable performance in rainy weather as well. If you have a copper t1 that seems to very in quality with the weather then open a ticket and have the telco tech check the NID for stray wires, or connections that are too loose or too tight (heat related expansion can stretch a cable to become loose, or get to close to another cable causing cross talk or signal scrambling / shorting).
Applications running across a t1 WAN can run fine with occasional ES; users will usually never notice less than 30 or 40 ES a day unless they come in 10 to 15 sec bursts. Its when you have a t1 that is experiencing 60+ ES a day when your applications may to start to have some issues. At 300 to 500 ES, you probably will get user complaints, and notice apps stalling on
UAS (Unavailable Seconds) are much more severe - essentially its a second where the entire framing is lost and the line is totally down. A 5 second burst of UAS can result in a minute or more for the line to resync and apps to recover. A t1 taking any UAS at all should be called in for repair.