The Answer: Application. The Layer 7 Application Layer of the Open Systems Interconnect (OSI) Reference Model is a service for applications and Operating Systems data transmission, for example FTP, TFTP, SNMP, and SMTP.
The following answers are incorrect: Network. The Network layer moves information between hosts that are not physically connected. It deals with routing of information. IP is a protocol that is used in Network Layer. FTP, TFTP, SNMP, and SMTP do not reside at the Layer 3 Network Layer in the OSI Reference Model.
Presentation. The Presentation Layer is concerned with the formatting of data into a standard presentation such as ASCII. FTP, TFTP, SNMP, and SMTP do not reside at the Layer 6 Presentation Layer in the OSI Reference Model.
Transport. The Transport Layer creates an end-to-end transportation between peer hosts. The transmission can be connectionless and unreliable such as UDP, or connection-oriented and ensure error-free delivery such as TCP. FTP, TFTP, SNMP, and SMTP do not reside at the Layer 4 Transportation Layer in the OSI Reference Model.
The following reference(s) were/was used to create this question: Reference: OSI/ISO.
Shon Harris AIO v.3 p. 420-421
ISC2 OIG, 2997 p.412-413