1) Un-restrained Joint - This type of joint can with stand only hoop pressure. Concrete thrust blocks are required at directional changes to resist longitudinal forces.
eg: Rubber Ring Joint

2) Restrained Joint - It can accommodate both hoop pressure and longitudinal forces. So the necessity of concrete thrust blocks are eliminated.
eg: Tapered Glue Joint, Lock Joint, Flanged Joint & Lamination Joint

there are some differences as you can see. Need to investigate with the potential vendor what they do offer