GATEWAY SPECIFICATIONS
The Gateway is a multi-dimensional portal of unknown origin. It was discovered after an enemy known as the Conclave fled through it into another dimension.
UPON DISCOVERY
When Starfleet first arrived on Retaria VII little was known about how the Gateway functioned. A period of intense investigation revealed a number of results.
1) Passing into the Gateway was a one way trip only
Upon entering, there was no way to return to the same universe that you entered from.
2) We existed in what is known as a multiverse

That is, there are worlds within worlds. For each action we make, there are any number of possible choices that we can make. Which choice we follow is what determines this reality, but in other worlds we may have chosen another path. Confused?
The easiest analogy is this: You come to a four way stop while driving. You have five choices. Go straight, turn left, turn right, stay where you are, or go backwards. If we go straight, we could have also have gone in one of the other directions and a different fate may have befallen us.
3) The size of the Gateway can be expanded and projected through the control console
The control console was in place when Starfleet arrived at Retaria VII. The Gateway normally is large enough to allow the passage of personnel through the portal under normal operation.
It can also be increased in size to allow passage of equipment such as a land rover or shuttle craft from within the complex.
The Gateway can also be projected into nearby space allowing the passage of an Starfleet vessel through it. This of course result in an incredibly large power drain on the system resulting in a complete shutdown of the Gateway for a period of 48 hours.
4) The Gateway console if multi-functional
The console can be used in order to travel to other dimension in addition to the past or the future by selecting a specific era or Stardate.
5) Passage through the Gateway can result in a time paradox
Under some conditions (differences in counterparts if they exist) travelers would find themselves in an almost catatonic state unable to function until similarities were introduced.
6) The only way to travel to another world was to enter the Gateway on Retaria VII
There is only one Gateway in each dimension and travel must be based from there. Upon passing through the Gateway a second time, the traveler could end up anywhere in time and space.
GATEWAY MODIFICATIONS
Since Taking control of the Gateway, Starfleet has made the following modifications:
1) The console has been enhanced in order to track crew when they pass through the portal
Each crew member is equipped with a tracking device that allows the Gateway operator to scan for there presence throughout the multiverse
2) The Gateway can be opened anywhere
Since remodeling the control console, the operator can now control where the Gateway will open by tracking the location of the crew allowing for them to return to their own dimension.
3) The effects of time paradoxes have been eliminated
The tracking device, also emits a slight phase variance that results in the crew members being able to exist in any time and space regardless of any differences between themselves and their counterparts of other dimensions.