Joslin, 27, split last season between the Carolina Hurricanes and Charlotte Checkers of the American Hockey League.
He appeared in 44 games with the Hurricanes, collecting four points and 35 penalty minutes. He added three assists in four games with Charlotte.
The Richmond Hill, Ont., native has recorded 16 NHL points (four goals, 12 assists) in 114 career games. He was originally selected by the San Jose Sharks 149th overall in the fifth round of the 2005 NHL Entry Draft.
Mullen, 26, collected 20 points (three goals, 17 assists) in 67 games with the AHL's Manchester Monarchs last season. The Pittsburgh native also appeared in seven playoff games, recording one point and four penalty minutes.