Bit confused on the context of links? Could you elaborate what links mean? Staff or a new rail link?
Links are used to roster crew. I was told many many years ago that the optimum link size was 24 lines but they vary from depot to depot and company to company.
So basically a 24 line link will have 24 lines deep and 7 days column across.
Each line should be occupied by a name and there should be 24 names in the left hand column and they should start with the Sunday column anjd read across to Saturday. At the end of the week "Joe Bloggs" on line 1 drops down to line 2, and all others similarly, with the person on line 24 bouncing up to line 1 etc etc.
Within the link should be all diagrammed turns at the depot as well as rest days, training days etc as well as spare turns to cover for leave, sickness etc. The link should be structured with a mix of duty times and turn lengths and rest days so that crew get a balanced work / life balance. So as an example "Joe Bloggs" has annual leave booked for Friday and Saturday on line 1 of the base roster, so the rosters will produce a weekly roster every week, and a daily roster for each day. The weekly and daily rosters will have Joe shoen as AL or ALR and will need to find someone else to cover Joe's linked turns on those days. The theoretical cover is using a spare turn driver nearest to the duty, but there are depot agreements to govern how the rostering is achieved.
Depending on (traincrew) depot size there maybe just one or two links or there may be a dozen. For example some drivers might be on a "four day week" with double rest days and a long weekend every three weeks, whereas others might be on a "five day week" with a week of rest days every so many weeks. Then there are part time or jobshare drivers who have their own links, so "Joe Bloggs" brother George might jobshare and have thee weeks off then work a week etc.
Hope this explains some of the link concept