Telecom standards and digital transmission interfaces

I'll talk a little bit about telecom standards and digital transmission interfaces used in network, serial communication, and carrier-grade WAN systems.

1. Serial / Interface Standards (Older WAN / Device Links)

EIA/TIA-232 (RS-232)

Very common serial communication standard. Used for PC <-> modem, console ports. Short distance (~15 meters). Low speed

EIA/TIA-449

Improved version of RS-232. Higher speed + longer distance. Not widely used (replaced by others).

V.24 (ITU-T V24)

Equivalent to RS-232 electrical signaling. Defines control signals (RTS, CTS, DTR...)

V.35

High-speed serial interface. Used for WAN routers <-> CSU/DSU. Supports synchronous communication. Common in legacy leased lines

X.21

Digital signaling interface (European standard). Used for synchronous WAN connections. More reliable than RS-232

EIA-530

Combines features of RS-232 + RS-449. Supports higher speed balanced transmission. Rare today

2. ISDN (Integrated Services Digital Network)

Digital telephone network standard. Carries voice + data. Mostly obsolete (replaced by broadband).

• Types
  • BRI (2 channels)
  • PRI (23/30 channels

3. Digital Carrier Lines (Leased Lines)

T-carrier system (USA/Japan)

T1: 1.544 Mbps, 24 Voice channels, used in enterprise WAN

T3: 44.736 Mbps, 28 x T1 channels

E-carrier system (Europe/Asia)

E1: 2.048 Mbps, 32 channels (30 data + 2 signaling) E3: 34.368 Mbps

4. xDSL (Digital Subscriber Line)

Internet over copper telephone lines. Used for home broadband

Types:

ADSL (asymetric)

SDSL

VDSL (very high speed)

5. SONET (Synchornous Optical Network)

Fiber-optic transmission standard (mainly USA). Very high-speed backbone network

Level	Speed
OC-3	155 Mbps
OC-12	622 Mbps
OC-48	2.5Gbps
OC-192	10Gbps