The Network layer (Layer 3) of the OSI/ISO model is responsible for providing the functional and procedural means of transferring variable-length data sequences from a source host on one network to a destination host on a different network. Its primary function is path determination, or routing. It uses logical addressing (e.g., IP addresses) to identify hosts and employs routing protocols to calculate the best path for packets to traverse the internetwork. This layer encapsulates segments from the Transport layer into packets and passes them down to the Data Link layer.

A. Session layer: Manages, establishes, and terminates connections (sessions) between applications. It does not handle data routing.
B. Physical layer: Responsible for the transmission and reception of unstructured raw bit streams over a physical medium; it has no concept of routing.
D. Transport layer: Provides reliable end-to-end data transfer and error correction but relies on the Network layer to route the data segments.

1. Tanenbaum, A. S., & Wetherall, D. J. (2011). Computer Networks (5th ed.). Pearson Education. In Chapter 5, "The Network Layer," Section 5.1, the text states, "The network layer is concerned with getting packets from the source all the way to the destination... a key design issue is determining how packets are routed from source to destination." (p. 379).

2. ISO/IEC 7498-1:1994, Information technology — Open Systems Interconnection — Basic Reference Model: The Basic Model. Section 7.5.1, "Purpose of the Network Layer," states that this layer provides the means to transfer data between end systems, and Section 7.5.4.2, "Routing," explicitly lists routing as a function of the Network Layer.

3. Kurose, J. F., & Ross, K. W. (2017). Computer Networking: A Top-Down Approach (7th ed.). Pearson. Chapter 4, "The Network Layer: Data Plane," introduces the layer's two key functions: "forwarding" and "routing." The routing function is described as determining the route or path taken by packets as they flow from a sender to a receiver (p. 306).

4. Dordal, P. L. (2019). An Introduction to Computer Networks (2.0 ed.). Loyola University Chicago, Department of Computer Science. Chapter 1, "An Overview of Networks," Section 1.6, "The Network Layer," states, "The network layer is responsible for routing packets from a source to a destination." (p. 23).