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Historically one of the faster private line services available from many telcos, the T-3 is now consider on the lower end of transport rates, with SONET, DWDM and native Ethernet services available at significantly higher rates. Still, it has been, and continues to be, used to support a variety of high performance applications, including CAD/CAM, imaging, and access to the Internet.

The T-3 operates at 44.736 Mbps and has the capacity to carry 28 T-1 circuits, which is the equivalent of 672 DS-0 circuits. Originally specified for delivery over coaxial cable, the T-3 is more commonly provisioned today over optical fiber. Since there is still no standard for T-3 over optical fiber (unless it is multiplexed into a SONET payload), such fiber solutions are proprietary.

T-3 Applications

Imaging applications are becoming a part of our everyday lives. Image scanning and storage require large data storage areas along with high performance transport links to handle the high traffic volumes. Traditionally, leased lines have been the solution. Increasingly, those leased connections are T-3. Often, as shown in the diagram on the visual, a routing device terminates the T-3 connection and distributes the T-3 traffic flows among some population of users (e.g., workstations and LANs).


Another popular application of point-to-point T-3 facilities is high-speed access to the Internet for large enterprises. This application of T-3 technology is also shown to the right. Generally, any high performance data application can benefit from the deployment of T-3 connections between locations. The applications reviewed on the visual are just a few that fall into that category.

Several high performance data networking services are commonly accessed via T-3 connections. These are listed on the visual. Carriers are currently offering high-speed frame relay service based on T-3 connectivity to the network. The high bandwidth of the T-3 supports large numbers of users (i.e., PVCs) on a single access connection. In addition, each user can have a CIR in the multi-megabit range on a T-3 access circuit.

ATM networks, with their SVC-based switching capability, are often accessed via T-3 connections. In this case, the switching operations inherent in ATM add a degree of flexibility to the use of the T-3 connection not typically found in point-to-point T-3 environments unless external CPE switching capability is deployed somewhere in the network.


The increasing popularity of switched LAN technology has provided another impetus for the deployment of T-3 connectivity in the WAN. Switched LANs are capable of high performance because of their high-speed backplane switch fabrics. At the workgroup level, backplane bandwidth of 4 Gbps is not uncommon. Users of a switched LAN thus obtain wire-speed connectivity within the LAN.

Interconnection of switched LANs across a campus is typically not too difficult. Because right-of-way issues are not usually a problem in a campus environment, optical connectivity is often deployed to interconnect workgroup switches with campus-level switches, thus extending wire-speed performance across the campus.

Interconnecting high performance, switched campus networks across the wide area, however, remains problematic. Right-of-way issues typically preclude the installation of a private backbone between intercampus locations. The use of T-3 circuits to interconnect campus switches across the WAN offers a fairly cost-effective way to ensure high performance across the entire network.


<mp3>http://podcast.hill-vt.com/podsnacks/2007q3/t-3.mp3%7Cdownload</mp3> | T-3