Router and Routing Designs for 3D Optical Network on Chip Invited speaker: Weigang Hou

1. Router and Routing Designs for 3D Optical Network on Chip Invited speaker:Weigang Hou Northeastern University, Shenyang, P. R. China houweigang@cse.neu.edu.cn http://www.neu-acnl.org

2. Outline 1. Background and Motivation 2. 3D ONoC Topology Structure 3. Router Modeling 4. Routing Algorithm 5. Results and Discussions 6. Conclusion and Future work

3. 1. Background and Motivation

4. Background & Motivation • In Network-on-Chip (NoC), we transfer the computer networking technology to the chip design, which completely solves the problems of bus-based SoC from the perspective of system structure. • But with the increasing number of IP cores per chip, the high power consumption and limited electric switching rate become the bottlenecks of improving the NoC performance. • Under the trend of transition from Integrated Circuit (IC) to Integrate System (IS) in the mid 90’s, the System on Chip (SoC) design technology came into being. • But we urgently need a new architecture that can alleviate the communication pressure by decoupling ICs such as Intellectual Property (IP) cores from the bus communication pipeline. However, existing designs of topology, router and routing algorithm in ONoC still have some drawbacks. • Therefore, the Optical NoC (ONoC) emerges because it has the bit-rate transparency. The ONoC also has the unique advantage of the high bandwidth provisioning for each waveguide.

5. Background & Motivation • There exist homogeneous Optical Routers (ORs) without any simplified designs in the current 3D ONoC topology. • This results in the serious waste of chip resources such as crossbar. • So the 3D torus ONoC should be deployed with simplified heterogeneous ORs. • The existing dimension order routing merely computes a macroscopic lightpath along a set of ORs for each optical packet. • The microcosmic packet forwarding path is not taken into account within each OR. • We need to construct a directed graph model for each router structure, so that we can find a list of microcosmic packet forwarding paths in all ORs along a lightpath. But with the increasing number of IP cores per chip, the communication conflict among IP cores will become worse, thus leading to the low throughput of 2D ONoC. As a result, the 3D ONoC has been proposed by virtue of multi-chip integration. Currently, the 3D ONoC topology utilizes 3D mesh structure. In fact, compared with the 3D mesh structure, the 3D torus has its own advantages due to the loopback feature.

6. 2. 3D ONoC Topology Structure

7. 3D ONoC Topology Structure • Intra-layer optical packet transmission->intra-layer OR • Inter-layer optical packet transmission->vertical OR (More simple!) • According to the characteristics of the aforementioned 3D Torus topology, we decide to design heterogeneous OR structures.

8. 3. Router Modeling

9. Modeling of intra-layer OR • An important point here is that each microcosmic packet forwarding path cannot traverse the IP core as the intermediate node!

10. Modeling of intra-layer OR • Obviously, our intra-layer OR structure deploys with the simple 1 plus 2 crossbar as many as possible so long as the non-blocking communication can be ensured. • It effectively reduces the router expenditure. Switch-level Crossbar-level • In crossbar-level directed graph models, we can check whether the microcosmic packet forwarding path currently changes its transmission direction.

11. Modeling of vertical OR • Obviously, only 1 plus 2 crossbar is used in our vertical router structure. • It further reduces the router expenditure. • The ‘middle’ port supports the optical packet transferring between the vertical OR and the intra-layer OR in the 2nd layer of our 3D Torus topology.

12. 4. Routing Algorithm

13. Microcosmic routing algorithm of intra-layer optical router The selection of forwarding way is performed by the electric control network. Switch-level Open Close

14. 5. Results and Discussions

15. Results and discussions - Maximal chip area-upper bound Traditional 3D mesh design: traditional router integrates the intra-layer and vertical communications so that there exists only one kind of router along with 7 bidirectional ports (east, west, north, south, up, down and injection), thus there are 7 MRs at each edge of this router. the length of each router edge is Our design the long router edge the short router edge thus for our 3D torus topology Width: Length:

16. Results and discussions –Simulation settings Signal-to-noise ratio (SNR) Thermal-sensitive Signal-to-noise ratio (SNRT) Total signal-to-noise ratio (SNR_sum) Total thermal-sensitive signal-to-noise ratio (SNRT_sum) Simulation scenario 1: For the XYZ dimension order routing, we consider seven different cases, each of which corresponds to a certain variation of the routing dimension. Only one optical packet generates under each case. Performance metrics: Simulation scenario 2: We increase the total number of optical packets from 10 to 100, and for each optical packet, the routing dimension variation is randomly selected out from seven cases mentioned above. No optical packet will be blocked. Performance metrics:

17. Results and discussions –Simulation results

18. 6. Conclusion and Future work

19. Conclusions and future work In this paper, • We first discussed the problems of the current 3D ONoC. • We designed a novel 3D Torus topology along with the simplified optical router structures. • We proposed microcosmic routing algorithms. • We executed the mathematical analysis and simulations to demonstrate the effectiveness of our designs. In the near future, • Integrating our designs with adaptive IP-core mapping approach.

20. Thank you! Email: houweigang@cse.neu.edu.cn