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T1 and E1 lines are the turtle to the internet's hare. With T1 at 1.544 Mbps and E1 at 2.048 Mbps, they can't compete with the speed of even a budget internet service. However, these legacy leased line services are superior to internet links in other ways. Organizations should be aware of these factors because they never know when they might have a special application requirement.
In a nutshell, T1 and E1 are private, or leased, line services. T1 is used in North America, while E1 is the European equivalent. Because these lines are dedicated, point-to-point services for a single user, they have attractive attributes that are different from generic internet links. Let's take a closer look at the benefits of T1 and E1 lines.
The very nature of a private, leased line is inherently more secure than the public internet. The network belongs to the organization -- and no one else -- because the service provider uses dedicated channels that are not shared with other customers. Data doesn't flow through a shared infrastructure where it could be copied or compromised.
While organizations can still use encryption and VPN tunneling schemes, packets are not exposed to the same conditions compared to traveling through a shared internet service provider infrastructure. For low-bandwidth applications where security trumps speed, T1 and E1 could be the solution.
2. No packet loss and consistent latency
Because organizations are not sharing their leased line with anyone else, application performance is much more consistent and predictable. With internet connections, organizations usually have to worry about packet loss and latency. Oversubscription by a service provider or unusually heavy traffic can trigger packet loss and high latency and degrade UX. Because T1 and E1 lines are dedicated, all the data that goes in will arrive intact on the other end.
While the type of performance loss in internet connections can't happen on a T1 or E1 line, organizations must still make sure users don't send more data than the link speed.
Similarly, latency is not a variable with T1 and E1 as it can be with an internet connection. Packets increase latency with each hop across the internet. Furthermore, congestion at a particular hop could add significantly to the delay. Certain types of traffic, including voice, don't do well with variable delay.
T1 and E1 lines will have some latency as data requires a finite amount of time to travel across a link. The difference is latency will not vary over time like with internet connections. Thus, applications will not be subject to the vagaries of variable delay. The predictable nature of T1 and E1 will help make application performance similarly predictable.
3. Connection symmetry
Unlike most internet connections, T1 and E1 lines are symmetrical. T1 is 1.544 Mbps up and 1.544 Mbps down, and E1's 2.048 Mbps is both up and down as well. Typical internet links, such as cable modems and Asymmetric Digital Subscriber Lines, are asymmetrical as they offer much greater downlink speeds than uplink speeds.
For applications where the majority of traffic is traveling downstream, the asymmetry of internet links is acceptable. But many business applications require a significant amount of traffic in both directions. In such cases, the symmetry of the T1 and E1 links can be a big benefit.
For sure, T1 and E1 are old technologies. But they are well understood and extremely reliable, so they might be the right service for specific network applications.