Here is the report below, showing some of the WAN speeds. It is a good reference to have it. The following chart relates various circuit types with their respective speeds.
(1) channel (1/24) of a DS1
Also known as a T1
(28) DS1s (or T1s) Also a T3
(1) DS3 @ 44.736mbits/sec with SONET (Synchronous Optical NET) overhead = 51.840mbits/sec
(1) STS1 on Optical Carrier facilities
(9) OC-1s (NOT COMMONLY USED)
(12) OC-1s or (4) OC-3s
(18) OC-1s (NOT COMMONLY USED)
(24) OC-1s (NOT COMMONLY USED)
(36) OC-1s (NOT COMMONLY USED)
(48) OC-1s or (4) OC-12s or (16) OC-3s
(192) OC-1s or (4) OC-48s or (64) OC-3s
This multiplexing scheme is set by the equipment manufacturers and has pretty much been adopted as standard in the Telecommunication industry. Therefore, rarely will you see implementations of the less common bandwidth aggregations like OC-9, OC-18, and etc. The OC-3 is technically an exception to this as it was needed to allow the upper-level hierarchy to work.
All speed values are expressed in Kb (Kilo bits per second), Mb (Mega bits per second), or Gb (Giga bits per second).