The Teleport Tether is a block added by Additional Pipes. This block will keep chunks loaded while the player is absent, either in SMP where you don't have to be logged in, or in SSP where you don't have to be near the chunks you want to keep loaded. These are very useful for machinery, cooling systems, Refineries or EE systems as you don't have to worry that they'll stop.
There is a limit on the number of chunks each non-op player can load in SMP.
This block was formerly known as the ChunkLoading Block (renamed to Teleport Tether in April 15, 2012 update of AdditionalPipes).
The EMC value per block is 728. (8 Iron = 256 * 8 or 2048 EMC + 1 Lapis Lazuli = 864 EMC, added togther the total is 2912 EMC then divided by four (the recipe makes four Teleport Tether's per time) = 728 EMC per Teleport Tether.
The Teleport Tether is very simple to use, simply place down and the area around it will be kept in the server memory.
A World Anchor has the same function, but will keep a bigger area loaded (3x3 chunks). In terms of EMC, the Teleport Tether is 18216 EMC cheaper for the same area (1 World Anchor or 9 Teleport Tethers).
A Dimensional Anchor works on a similar principle, but has an adjustable loading area of 1x1, 3x3, 5x5, 7x7 and 9x9 chunks. A Dimensional Anchor costs 10496 EMC.