X.25 was an
ITU standard that enabled packet transmission at speeds between 2.4 and 4.8 Kbits/sec
over traditional telecommunication networks; it was subsequently supplanted by other
technologies, the more prominent being Frame Relay, Asynchronous Transfer Mode
(ATM), and even traditional TDM (modified to be more efficient). And, as mentioned
previously, Ethernet had also been used to offer data services as well. These services
were delivered over a host of transport infrastructures or natively. Over the years,
SONET-based TDM networks have the become dominant transport infrastructure,
especially with the relatively increased deployment of fiber in metro and much more
extensively in core networks. Table 1.4 provides a brief comparison among ATM, Frame
Relay, traditional TDM, and Ethernet.
A typical (albeit partial) telecommunications transport infrastructure is shown in
Figure 1.9. Although specific implementations vary across different telecommunication
Figure 1.8 The network beyond the LAN, segmented into Access, MAN, and WAN
Metro
Backbone
Metro
Backbone
Service Provider Network
Service Provider
Point of Presence (POP)/
Central Offices (COs)
Service Provider
Point of Presence (POP)/
Central Offices (COs)
Customer
Premise
Customer
Premise
Last/first mile Last/first mile Metro Area
Network (MAN)
Metro Area
Network (MAN)
Wide Area
Network (WAN) Access Access
Other Service Connections
(e.
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