Satellite Reservations Frame length must exceed round- trip delay Reservation slots during frame j are used to reserve data slots in frame j+1 Variable length: serve all requests from frame j in frame j+1 Difficult to maintain synchronization Difficult to provide Qos (e.g, support voice traffic) Fixed length: Maintain a virtual queue of requests Reservation mechanism Scheduler on board satellite Scheduler on ground Distributed queue algorithm All nodes keep track of reservation requests and use the same algorithm to make reservation Control channel access TDMA: Simple but difficult to add more users Aloha: Can support large number of users but collision resolution can be difficult and add enormous delay Slide 16Satellite Reservations • Frame length must exceed round-trip delay – Reservation slots during frame j are used to reserve data slots in frame j+1 – Variable length: serve all requests from frame j in frame j+1 Difficult to maintain synchronization Difficult to provide QoS (e.g., support voice traffic) – Fixed length: Maintain a virtual queue of requests • Reservation mechanism – Scheduler on board satellite – Scheduler on ground – Distributed queue algorithm All nodes keep track of reservation requests and use the same algorithm to make reservation • Control channel access – TDMA: Simple but difficult to add more users – Aloha: Can support large number of users but collision resolution can be difficult and add enormous delay Eytan Modiano Slide 16