Anyone serving in the CF does so under certain "Terms of Service." A good way to look at this is an agreement. Upon enrolement, your first Terms of Service are called a "Variable Initial Engagement" (VIE). As the term implies, this period varies in length depending on your particular enrolement plan. For ROTP candidates, it is generally 13 years, broken down as follows:
4 years education
4 years obligatory service
5 years general service
All of these amounts can vary depending on circumstance, but I believe another underlying principle is that the CF is looking for nine years of commissioned service (i.e. after graduation from university). Using myself as an example, if I were joing today under the same circumstances as I did back when the earth was cooling, my VIE would be 11 years (two years, education, three years obligatory service and six years general service - note how general service goes up as obligatory service goes down).
Having said all this, a VIE of 13 years does not mean you have to stay in the CF for 13 years. You can get out as soon as your obligatory service is completed. If you do that though, you may lose out on some of the benefits. Sometimes (depending on the circumstances), you can get out before completing your obligatory service, but there are some significant hurdles to jump and you may have to re-pay the Crown for your subsidized education.
Please note that I am only talking about ROTP here.
After completing a VIE, the next step is an "Intermediate Engagement (IE), which is 25 years of total service (i.e. including, NOT in addition to the years spent on VIE). The final step is an Indefinite Period of Service (IPS), which will take you to retirement age. We also have "Continuing Engagements" (CE), which are used for special circumstances and are beyond the scope of this discussion. ROTP and DEO candidates are not offered CEs on enrolement.
An important thing to note is that regardless of Terms of Service, as long as you have no obligatory service, you can get out at any time (although the process can take up to six months, again depending on a number of factors).
