Here are some Keys with its explanation :

"SDH" = Synchronous Data Hirarchy
"OC" = Optical Carrier levels (SONET)
"STM" = Synchronous Transport Modules (SDH)
"ATM" = Asynchronus Transfer Mode
"POS" = Packet over SONET / SDH frames
"HDLC" = High-Level Data Link Control
"PPP" = Point-to-Point Protocol
"STS" =
"FDDI" = Fibre Distributed Data Interface

There a lot more 3 character shortcuts. We will add them later. With these here you can (at least) listen to the experts, make not a dump face, but smile.

SM = single mode / long distance
MM = multi mode / short distance
"E" = E-carrier system equivalent of "T" that uses all 8 bits per channel; used in Europe, Australiy, South America, = countries other than U.S. Canada, and Japan....
"T" = T-carrier system in U.S., Canada, and Japan....
"DS"= digital signal (that travels on the T-carrier or E-carrier)...

n Europe, South America and parts of Asia we have E1 and E3 and in the US and Canada and Japan they use T1 and T3 (DS3).

Parts of this table were received by e-mail from an unknown internet user.

Carrier Technology	rated Speed (brutto)	Physical Medium	explanation
ISDN - the basis of all calculations	BRI: 64 (Kilobit per second) to 128K PRI: 23 (T-1) or 30 (E1) assignable 64K channels plus control channel	BRI: (basic rate interface) Twisted-pair PRI: (primary rate interface) T1 or E1	BRI: faster home and small business access - PRI: Medium and large enterprise access
DS1/T-1	1.544 Mbps	Twisted-pair, coaxial cable, or optical fiber	Large US-company to US-ISP and US-ISP to Internet infrastructure
E-1	2.048 Mbps	Twisted-pair, coaxial cable, or optical fiber	32-channel European 2 Mbps Standards
T-1C (DS1C)	3.152 Mbps	Twisted-pair, coaxial cable, or optical fiber	Large company to ISP ISP to Internet infrastructure
DS2/T-2	6.312 Mbps	Twisted-pair, coaxial cable, or optical fiber	Large company to ISP ISP to Internet infrastructure
E-2	8.448 Mbps	Twisted-pair, coaxial cable, or optical fiber	Carries 4 multiplexed E1 signals
Ethernet	10 Mbps	10BASE-T (twisted-pair); 10BASE-2 or -5 (coaxial cable); 10BASE-F (optical fiber)	Most popular business local area network (LAN)
IBM Token Ring/802.5	16 Mbps (also 4 Mbps)	Twisted-pair, coaxial cable, or optical fiber	Second most commonly-used local area network after Ethernet
E-3 CCITT G.751	34.368 Mbps	Twisted-pair or optical fiber	Carries 16 x E1 signals
T-3 M13/Cbit	44.736 Mbps	Twisted-pair or optical fiber	Carries ?? x T1 signals
OC-1	51.84 Mbps	Optical fiber	ISP to Internet infrastructure - This is the Basic rate for SONET
Fast Ethernet	100 Mbps	100BASE-T4 (twisted pair); 100BASE-TX (twisted pair); 100BASE-FX (optical fiber)	Workstations with 10 Mbps Ethernet cards can plug into a Fast Ethernet LAN
FDDI	100 Mbps	Optical fiber	Large, wide-range LAN usually in a large company or a larger ISP
T-3D (DS3D)	135 Mbps	Optical fiber	ISP to Internet infrastructure Smaller links within Internet infrastructure
E4	139.264 Mbps	Optical fiber	Carries 4 x E3 channels Up to 1,920 simultaneous voice conversations
OC-3 / STM-1	155.52 Mbps	Optical fiber	Large company backbone Internet backbone
E5	565.148 Mbps	Optical fiber	Carries 4 E4 channels Up to 7,680 simultaneous voice conversations
OC-12 / STM-4	622.08 Mbps	Optical fiber	Internet backbone
Gigabit Ethernet	1 Gbps	Optical fiber (and "copper" up to 25 meters)	Workstations/networks with 10/100 Mbps Ethernet will plug into Gigabit Ethernet switches
OC-24	1.244 Gbps	Optical fiber	Internet backbone
SciNet	2.325 Gbps (15 OC-3 lines)	Optical fiber	Part of the vBNS backbone
OC-48 / STM-16	2.488 Gbps	Optical fiber	Internet backbone
OC-192 / STM-64	10 Gbps (9953,28 Mbps)	Optical fiber	Backbone
OC-256	13.271 Gbps	Optical fiber	Backbone
OC-768	40 Gbps	Optical fiber	Backbone