Channelized E1/T1 difference and troubleshooting

                   If you are working for a ISP or coordinating with them for circuit related issues you would have heard about E1/T1 and the alarms on them.Most of them are not comfortable working on layer 1 and 2 issues as they find it difficult to sit inside a NOC and understand what is happening in the layer 2 path.


E1 and T1 are digital telecommunication carrier standards which are time multiplexed(many into one) into a single carrier to transmit and receive.Both of them use simultaneously channels each of 64Kbps , which can be bundled together for a higher bandwidth or used as a individual channel.For example i can bundle 8 channels in a E1 to use 512Kbps for a site and use the rest 24 for other site.

Key difference of E1 and T1 is the number of channels, which can be transmitted simultaneously over the given physical medium.

                                                                 E1                                    T1
Data Rate                                              2048kbps                         1.544Mbps
Simultaneous channels                             32                                      24


 If you are working in a NOC and have access to devices on which E1/T1's are terminated, you could do  couple of things before engaging ISP. For instance a show controller E1/T1 output  might help you identify if the issue is at remote site,ISP or local site looking at the alarms, looking at the counters you can determine it's a clocking/framing issue. On my personal experience i was able to solve flapping issue just by providing a soft loop which is a simple command on the router.


Here are few links with flow chart that could  help you understand/troubleshoot E1's and T1's in a structured approach.

T1 Troubleshooting
http://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/10205-t1-flchrt-main.html

E1 Troubleshooting
http://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/14163-e1-flchrt-main.html

E1 PRI troubleshooting
http://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/14164-e1-flchrt-pri.html?referring_site=bodynav

E1 error event troubleshooting
http://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/14161-e1-flchrt-error.html?referring_site=bodynav

E1 Alarms Troubleshooting
http://www.cisco.com/c/en/us/support/docs/wan/t1-e1-t3-e3/14159-e1-flchrt-alarm-1.html?referring_site=bodynav

E1/T1 loop back testing and troubleshooting
http://www.cisco.com/c/en/us/support/docs/voice/device-signaling/116492-trouble-t1e1-00.html