At which OSI model layer would a technician likely troubleshoot a VoIP phone connectivity issue?

When dealing with VoIP phone connectivity issues, the primary layer to troubleshoot is the network layer. This layer is responsible for packet forwarding, routing, and the delivery of packets through intermediate networks. VoIP systems rely heavily on the network's ability to correctly route packets to their destination and ensure the quality of service (QoS) needed for voice communication.

At the network layer, issues such as IP addressing, routing protocols, and connectivity between devices are managed. If the VoIP phone is unable to register with a SIP server or if calls do not connect properly, the technician would investigate whether the packets containing VoIP data are being routed correctly and if there are any issues with the IP configuration or network paths.

While other layers like the application, transport, or data link can have implications on VoIP as well, if a VoIP phone isn't able to communicate at all, the network layer would be the first to assess for routing or connectivity problems. For example, the application layer is more focused on the software and user interface aspects of the VoIP application itself, while the transport layer manages the end-to-end communication and might deal with issues like lost packets or retransmissions. The data link layer, on the other hand, deals with physical address resolution and