Gig-E vs SONET (Cont'd)

Ethernet was confined to the LAN for two reasons: its lack of capacity to handle WAN traffic loads and the low quality of longer-distance data transmission over twisted pair and early cable types, which required the quality checking that Ethernet had eliminated.

Gig-E solved the speed problem, and its lack of quality assurance makes it a better match for packet networking than SONET, because the packet architecture builds its quality control into Level 3. The packet network protocol includes quality checking of each packet at each data switch it passes. If something is wrong with a packet, the protocol can request a retransmission from the previous switch. If a transmission line is cut or a switch fails, the network can automatically reconfigure a new transmission path around the problem and reestablish the session.

These capabilities in large part duplicate the signal quality features built into SONET. What they do not do, since packet networking was designed for data rather than voice, is guarantee voice quality or a 50-millisecond recovery from a line failure or voice-quality transmission, which is unnecessary for data. Computers can tolerate transmission interruptions better than humans.

Tell-tale Difference
On the voice side, as optical cable replaced twisted pair in the voice arena, SONET became the dominant technology for high-quality transmission. Ironically, however, optical transmission also eliminated many of the quality issues of long haul, with the result that today data carriers are switching their metropolitan data networks to Gig-E to get maximum benefit from the higher speeds of optical cable.

This, however, is putting SONET, and the long haul voice carriers, at a potential disadvantage. Voice over Internet Protocol (VoIP) is a reality, not just in WANs but in metropolitan area networks and across the Internet as well. Certainly, VoIP lacks the quality of SONET-managed voice over the switched network, as anyone who as tried Internet telephone knows. However, steady improvements in transmission quality and speed, plus new features such as data packet prioritization, have created a good enough voice signal quality for many uses.

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