The root cause of application anomalies donít stop at Layer 3 of the Open Systems Interconnection (OSI) model. In fact, some of the most difficult to diagnose service issues are rooted in, or manifest themselves at the Transport Layer (Layer 4) or higher.
Since the Transport layer is responsible for building and maintaining sessions between devices, it serves to connect the lower layers (1-3) to the higher layers (5-7). It can also be the point of referred pain, when the real source of the problem lies elsewhere.
A methodical process to resolving service issues that reside at Layers 4-7 can clear up ambiguities and accelerate problem resolution. Mike Motta, NI University instructor and troubleshooting expert, and Tony Fortunato Senior Network Performance Specialist and Instructor with the Technology Firm, place typical user complaints into three categories:
Inability to Access Network Resources
In this two-part white paper series, learn to quickly locate and resolve problems across the OSI layers using the Troubleshooting Cheat Sheet.