Abstract: A grid router for routing data over a grid sessionwise, involves multiple devices forwarding data according to sessions over an unreliable network between the devices. The devices include a first group of mailbox units to handle the sessions and a second group of egress units to forward session data to devices external to the network. The mailbox units and egress units are connected in a CLOS network such that each mailbox unit is accessible by each egress unit. The router further includes a distributed entity, which assigning specific sessions to specific mailbox units and to specific egress units and further defomes quality of service (QoS) levels for each session in the presence of congestion in either the network or the devices.