Could someone explain to me simply what is the difference between SONET and T-Carrier?

I know that the ISP generally uses SONET on their infrastructure (Ciscopress 2017, section, http://www.ciscopress.com/articles/article.asp?p=2832405&seqNum=5), but we could often see that the leased lines offered by the ISP mentioning E1 or T1 are referred to as T-Carrier. So I'm a little bit confused.

Also, as the E1 and T1 line provides a dedicated bandwidth, does the ISP guarantee, like the E1 and T1 lines, a minimum bandwidth with IP/MPLS or VPLS?

1 Answer 1


Very briefly, SONET/SDH is a high bandwidth optical WAN technology. T-carrier is an electrical (digital) WAN technology.

SONET/SDH is (was) typically used for backbone and inter-provider circuits. T-carrier is (was) used for lower bandwidth leased lines for subscribers.

SONET bandwidth typically starts at around 150Mb and goes up to 10Gb. T-carrier typically starts at 1.5 Mb and tops out at around 45Mb.

Both technologies were developed for voice telephony, but were adapted for data transmission.

Bandwidth guarantees depend on the carrier. They may or may not make guarantees depending on the level of service you buy.

Both technologies are on their way out, being rapidly replaced by long range Ethernet

  • Thanks for the response. I read also the DWDM is now widely used, so does it mean that Ethernet over DWDM is now a common technic ?
    – bdes31
    Commented Jan 24, 2018 at 17:26
  • Yes, that is correct.
    – Ron Trunk
    Commented Jan 24, 2018 at 18:03
  • @bdes31 we almost only use DWDM with redundant 200Gb connections throughout our MPLS ring.
    – user36472
    Commented Jan 24, 2018 at 18:41

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