T1 Leased Line – 1.544 Mbit/s of fun!

T1 leased lines offer speeds of 1.544 Mbit/s upstream and downstream. T1′s are used in America, Japan and South Korea.

Why 1.544Mbit/s? Well AT&T Long Lines was conducting tests in Chicago. They chose the bit-rate based on the speed that could be achieved over 2km long copper cables (once a safety margin was added). Why 2km? It's because the loading coils and cable vault manholes were 2km apart.

In Europe, E1's are used instead of T1's. E1's offer 2.048Mbit/s downstream and upstream.

Please note that the speeds I’ve mentioned for t1 leased lines and e1 leased lines are transmission speeds. They’re not the speed at which you would transfer data, as transferring data usually requires using additional headers and error-correcting codes. This reduces the amount of bandwidth available for transferring actual data.

Both T1 lines and E1 lines are old solutions. The T1 has been around since 1961. So it's 50 years old! The E1 was ITU certified in 1988. So it is over 20 years old.

In the intervening period, we’ve seen the meteoric rise of Ethernet in corporate LANs and WANs, and in carrier networks. Carriers are increasingly offering 10Mbps, 100Mbps, 1Gbps and 10Gbps links, leaving T1 leased lines behind.

Mid 2010 saw the final specification of 100Gbps Ethernet approved. The rapidly increasing demand for Internet access is forcing ISPs to upgrade their networks. As they do this, they end up with networks that are capable of dealing with 10Mbps, 10Mbps, 1Gbps and 10Gbps circuits.  E1 and T1 leased lines are likely to survive for a little while longer, particularly in areas that are far from the major carriers existing networks. But these circuits time is running out.