TELNET operates at Application Layer in TCP/IP Model. It's an Application to establish a connection to TCP Port Number 23, where a Telnet server application (telnetd) is listening.
TELNET works at the APPLICATION Layer.
Layer 7 - Application Layer
Application Layer
TCP, the Transmission Control Protocol, is a layer-4 protocol (in the 7-layer OSI model).
FTP (File Transfer Protocol) is an application layer, or Layer 7, protocol.
Network Layer
The Hyper Text Transfer Protocol (HTTP) works on Layer 7 on the Application layer of the OSI Model.
The layer of the OSI Model that deals with encryption, would be the sixth layer, the presentation layer. It deals with the SSL/TLS protocol which pretty much just turns your regular HTTP (hypertext transfer protocol) into HTTPS (hypertext transfer protocol secure.) It adds an encryption to certain web pages that would deal with you credit card or any other private information dealt with.
Telnet is an application layer protocol (Layer 7). Its functionality is similar to any of the layer 7 protocols, including DHCP, DNS, FTP, etc.
DNS is an application layer protocol. The application layer of the OSI model is the layer closest to the user and provides network services to the applications of the user. Examples of protocols that operate at the application layer are: DNS, FTP, TFTP, SNMP, TELNET, RLOGIN, SMTP, MIME, NFS, FINGER, BOOTP and SMB.
TCP, the Transmission Control Protocol, is a layer-4 protocol (in the 7-layer OSI model).
FTP (File Transfer Protocol) is an application layer, or Layer 7, protocol.
IP is a layer 3 (network layer) protocol used for routing
Ethernet is a data link layer protocol - layer 2
Network Layer
FTP and Telnet are considered OSI layer 7 protocols. If you are blocking the service, then layer 3 or 4 (network or transport) is responsible.
Network
ports protocol
The Network Layer in the TCP/IP model is responsible for routing data packets between different networks. It determines the best path for data to travel from the source to the destination through various interconnected networks. The Internet Protocol (IP) is the main protocol used at this layer to address and forward packets.
There are actually two different GTP protocols. GTP (Go Text Protocol) is basically an application layer protocol, although the definition is a bit fuzzy. GTP (GPRS Tunneling Protocol) is a transport layer protocol that is used in conjunction with another transport layer protocol (TCP or UDP).