Service desk in ITIL is a broader term than a Helpdesk. Actually, Helpdesk is supposed to be just a part of service desk. Redmine can support different ways of service desk organization, such as the following:
For example, if you run a large international customer service, you may have teams in different time zones, and operating in different languages because operators are supposed to receive requests and respond to customers in their own language. Unbelievably, Redmine is capable of supporting such a use-case scenario out of the box.
Possible scenarios of Redmine usage include the following: