Embodiments of the present disclosure provide techniques and configurations for a rack assembly. In one embodiment, a tray to be disposed in a rack assembly may comprise a plurality of sleds with individual sleds including one or more compute nodes; and a networking element coupled with a sled of the plurality of sleds and configured to communicatively connect the sled to one or more other components of the rack assembly via an optical communication system. The optical communication system may include an external optical cable configured to communicatively connect the networking element with the rack assembly. Other embodiments may be described and/or claimed.