A family of standards by the ITU, describing communication interfaces (I figure they would be physical layer protocols).
G.703 standards are normally the concern of network architects and network managers; they rarely (if ever) arrive at the end user's desk.
Here they are:
- G.703: a 1984 standard defining physical (connector shape, cabling ...) and electrical (voltage, frequency, impedence ...) characteristics for digital transmission.
- G.703 2.048 Mbit/s : transmission facilities running at 2.048 Mbit/s (this is E1 speed) that use the electrical interface specified in G.703
- G.703 641K: transmission facilities that use the G.703 electrical interface and run at 64Kbits/s
There are also G.703 specs for the US 1.544Mbit/s circuits (T1) and for even larger bandwidths.
Many times a G.703 2.048 Mbit/s interface is simply called G.703.
Where could you find a G.703 interface ? Well, suppose you have a LAN with some protocols (I am talking about level 2 protocols, for example: Ethernet and EtherTalk. Don't think about TCP/IP or IPX, OK ?), and that you want to send that stuff over a microwave link.
The microwave radio does not want to know about your Ethernet frames and stuff: it will just provide a G.703 interface, that a nondescript grey box with a couple of LEDs will convert to and from Ethernet, EtherTalk and anything else it understands.