Bell Laboratories began development of Asynchronous Transport Mode (ATM) as a
new backbone technology, enabling the Bell System Companies in the U.S. to move all
of their bearer traffic to a packet-based network rather than a circuit-switched one.
ATM eventually moved out of the labs and began the long road of implementation
in the world??™s networks. While largely successful, many may argue that it is still costprohibitive
when compared to the cost of IP. Still, IP cannot offer the same reliable
service of an ATM transport network, a fact that has slowed the implementation of IP
in many traditional telephone networks.
The primary issue is the lack of support in TCP/IP for real-time traffic such as voice
and video. TCP/IP was developed simply for the transport of data and is far more tolerant
of delays and packet loss. Voice and video, on the other hand, are not so tolerant,
which is why ATM was adopted so quickly.
The ATM protocol answered the primary need for all operators: Quality of Service
(QoS). By laying ATM on top of a SONET fiber backbone, operators can realize a very
robust packet-based backbone capable of moving all of their aggregate traffic.
However, ATM is not the best protocol for voice and video for many reasons. Developers
realized that if they developed a protocol specifically for voice and data, it would consist
of smaller packets delivered much quicker to the end points.
Pages:
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88