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.
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.
Ethernet is a data link layer protocol - layer 2
IP is a layer 3 (network layer) protocol used for routing
Network Layer
Network
ports protocol
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.
The network layer (Internet Layer in TCP/IP model) is the second layer of the TCP/IP model. IP (Internet Protocol), ARP (Address Resolution Protocol), RARP (Reverse Address Resolution Protocol), ICMP (Internet Control Message Protocol) and IGMP (Internet Group Management Protocol) are the protocols at this layer. http://www.omnisecu.com/tcpip/internet-layer.htm
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).