The Basics

Wednesday, May 30, 2007

Basic Description of NoC
The communication infrastructures based in NoC has Network Elements(NE) and Network Interfaces(NI).
The packet travel across the Network Elements while the Network Interfaces provide an interface with the IP.
Using switching elements eliminate the skew of the clock signal, which is present in SoCs design with high integration level, as well as cross-talk and other sub-micra technology effects.

A NoC is described by 5 main characteristic:
* Topology: Arrangement of the Network Elements.
* Switching: The way the data is transfered from the input port to the output port.
* Routing: Determine message path.
* Flow Control: Dinanmic allocation of the channels.
* Buffering: The way the packets are store when they cannot be processed.
* Arbitration: Plans the use of channels and buffers.

These five main characteristics, in addition with other less important, generate a big architectural design space.
By using NoC in the communication infrastructure we achieved the division of computation and communication.
NoC stands out in reusability, scalability and parallelism in communications.
NoC systems fulfill power restrictions and clock distribution.

Why a simulation phase?
One limitation in the models based in NoC is the necessity of software tools with the ability to abstract the capacity of a particular communication infrastructure, therefore it allows the correspondence among the requirements of a given application and the capacities of the architecture.
The simulation phase covers the necessity of obtaining the NoC communication infrastructure suited for a particular application. This phase will increase the efficiency by selecting the appropriate parameters, allowing a better latency and throughput. If the needed NoC were simpler than the one used at first, the simulation phase would improve the area and the power consumption.

Utopian Transport Company Example
A similar example of the network analysis is the logistic of an utopian road transport company where you can control the traffic lights and signals, the insertion rate of new traffic, the number of roads, the ratio of low-traffic(trailers) and fast-traffic(ferraris), the policy of the roads(for example one road just for Ferraris or one just for trucks), and a lot of more possibilities.
The number of variables influencing both the latency and the capacity of the system is too big, despite I only showed a few. Due to this huge number of variables you cannot take pen&paper and design the best values of these variables in your particular situation, thus the solution is approaching the optimization problem with a simulation phase that gives you the best values for your particular situation.
An example that shows simple traffic situations was designed and written by Martin Treiber. In that example you can evaluate traffic situations, how all the variables fit together; how the traffic insertion rate, the ratio of traffic type and the behaviour of every vehicle in conflict situations are critical in the performance of the traffic system.
Now click the link and play a little bit.
This simple example can helps to understand the importance of modeling a correct system.
But imagine a more complex example, with 40 roads, 80 crossroads, 50 traffic lights, 30 origin packets nodes(therefor vehicles origin nodes) , 50 destination packets nodes(therefor vehicles destination nodes), different traffic insertion rates and different insertion patterns per origin node. Now you are able to figure out how important could be the model phase in a "real example".

As in the traffic example in NoC there are variables that determine the latency and the capacity of the network.
I have described 5 main characteristic defining a NoC, but in the modeling process there are much more variables. Each of the main characteristic can be splited in sub-characteristics. Therefor the number of modeling variables depends on the complexity of a particular sub-caractaristic. But the NoC architectural variables are NOT the only ones presented in the simulator. As in the traffic example there are other components defining the behaviour of, for example, the traffic generation rate, traffic ratio, traffic insertion pattern, simulation time and traffic weight among others components.

Posted by Rayco Hern├índez Moreno at 10:59 PM  


Post a Comment