Network-on-Chip (NoC) is a new on-chip communication paradigm for future IP-core based System-on-Chip (SoC), designed to remove a number of limitations of today’s on-chip interconnect solutions. A NoC interconnects cores by means of a packet switched micro-network, which improves scalability and reusability, resulting in a shorter time to market. A typical NoC will be running many applications concurrently, which results in shared network capacity between different kinds of traffic flows. Due to the diverse characteristic of applications, some traffic flows will require real-time communication guarantees while others are tolerant to even some loss of data. In order to provide different levels of Quality-of-Service (QoS) for traffic flows, the communication traffic is separated into different service classes. Traffic in NoC is typically classified into two service classes: the guaranteed throughput (GT) and the best-effort (BE) service class. The GT class offers strict QoS guarantees by setting up a virtual path with reserved bandwidth between the source (GT-producer) and destination (GT-consumer), called a GT-path. The BE class offers no strict QoS guarantees, but tries to efficiently use any network capacity which may become available from the GT traffic. The GT traffic may not fully utilize its bandwidth reservation if its communication volume varies, leading to time intervals where there is no GT traffic using the bandwidth reservation. These intervals are referred to as slack-time. If the slack can not be used this leads to unnecessarily reduced performance of BE traffic, since a part of the available network capacity becomes blocked. This thesis deals with methods to efficiently use the slack-time for BE traffic. The contributions include three new dynamic schemes for slack distribution in NoC. First, a scheme to inform the routers of a GT-path about available slack is evaluated. The GT-producer plans its traffic using a special playout buffer, and issues control packets containing the actual amount of slack-time available. The results show that this scheme leads to decreased latency, jitter and packet drops for BE traffic. Secondly, an extension to this scheme is evaluated, where slack is distributed among multiple GT-paths (slack distribution in space). This opens up the possibility to balance the QoS of BE traffic flows which overlap with the GT-paths. Thirdly, a scheme to distribute slack among the links of a GT-path (slack distribution in time) is proposed. In this approach, arriving GT-packets, at a certain router along the GT-path, can wait for a maximum defined amount of time. During this time, any waiting BE traffic in the buffers can be forwarded over the GT-path. The results confirm that this is especially important during high BE-traffic load, where this technique decreases the jitter of BE traffic considerably.

Recently, network on chip (NoC) architectures are being

proposed for implementing multi-core systems for realtime

multi-media applications. The communication

traffic of those systems will be a mix of guaranteed

throughput (GT) and best effort (BE) traffic. GT traffic

not only lead to under-utilization of communication links

and routers, but also leads to degradation of QoS

parameters for BE traffic. We propose a dynamic routing

scheme for reducing jitter in the latency of BE traffic

affected by the GT traffic. Our results from modeling and

simulation indicate that a significant improvement in

jitter can be achieved.

It is possible to concurrently run multiple

applications on IP-core based SoC built using Network

on Chip (NoC) paradigm. Some applications require

predictable and guaranteed on-chip communication

performance. In this paper we propose a new approach

for using underutilized reservation of guaranteed

throughput (GT) traffic to improve the performance of

best effort (BE) traffic. We have modeled our scheme for

a mesh topology NoC on a simulation platform. The

results show that the proposed scheme leads to

significant improvement in BE performance.

Efficient routing schemes are essential if Network on

Chip (NoC) architectures are to be used for implementing

multi-core systems for real-time multi-media applications.

These systems will be characterized by internal communication

traffic which is a mix of traffic requiring guaranteed

throughput (GT) and other traffic requiring some other QoS

properties like latency and less packet drops. Communication

resources are generally reserved for providing GT

performance. In this paper we propose a dynamic scheme for

improving packet drop probability of other traffic by

intelligently utilizing the under-utilized reserved

communication resources of GT traffic. We demonstrate the

effectiveness of our scheme by simulation.