SpaceWire Hot Modules Asaf Baron, Isask'har Walter, Israel Cidon, Ran Ginosar, Isaac Keslassy EE Department, Technion, Haifa, Israel Ofer Lapid Israel Ministry of Defense International SpaceWire Conference September 2007

Hot Module An end unit may receive heavy traffic from several sources The heavy load congests the network Blocks other (light) traffic Enhancing the network will not help Problem is with the end unit, not the network Such unit is a HOT MODULE

S1S2S3S4S5 D1D2D3D4D5 DHS Storage Example network

Reaction Wheel Two main problems S1S2S3 S4 S5 DHS Storage System Performance Source Fairness Router 5 Router 4 Router 3 Router 2 Router 1

Solution #1 Use Packet Level Priority (PLP) Assign low priority to packets that are traveling to the Hot Module Improves System Performance But does not solve Fairness S1S2S3 S4 S5 DHS Storage Reaction Wheel Router 5 Router 4 Router 3 Router 2 Router 1

Solution #2 Problem: traffic sent to Storage (Hot Module), congesting the network Introduce Credits: Before sending to Hot Module, ask for credit No need to modify routers

Credits Improve Performance & Fairness S1S2S3 S4 S5 DHS Storage Reaction Wheel Improves System Performance Solves Fairness Router 5 Router 4 Router 3 Router 2 Router 1

Simulations Use our new SpW simulator and benchmark No more than 2 Sensors have credits at a time

Traffic to Hot Module PLP CREDITSPLP + CREDITS Sensor 5 Sensor 1

Traffic to DHS (non-Hot-Module) PLP CREDITSPLP + CREDITS

Conclusions: Hot Modules incur two effects Source Fairness Solved using Credits Performance Improved using PLP and Credits Using PLP + Credits yields the best results