Grids offer the potential to carry out difficult computing tasks and achieve superior aggregate performance. However, grids are highly complex systems. They consist of heterogeneous resources on disparate hosts from various virtual organizations interconnected via a mixture of communication standards. Monitoring grid resources allows grid schedulers to adapt to changes in the status of these remote resources and the network paths between them. This is crucial to ensuring optimum performance. In this paper we introduce a distributed solution, called GridMAP, to collect network and end-host resource measurements, analyze their performance and feed these statistics and predictions back to schedulers. At this stage, we present our implementation of a passive TCP-SYN-based technique to provide GridMAP with round trip time and throughput measurements and we evaluate our approach against ping and iperf.