The application layer defines standard Internet services and network applications that anyone can use. These services work with the transport layer to send and receive data. Many application layer protocols exist. The following list shows examples of application layer protocols:
Standard TCP/IP services such as the ftp, tftp, and telnet commands
UNIX “r” commands, such as rlogin and rsh
Name services, such as NIS+ and domain name system (DNS)
File services, such as the NFS service
Simple Network Management Protocol (SNMP), which enables network management
FTP and Anonymous FTP – The File Transfer Protocol (FTP) transfers files to and from a remote network. The protocol includes the ftp command (local machine) and the in.ftpd daemon (remote machine). FTP enables a user to specify the name of the remote host and file transfer command options on the local host's command line. The in.ftpd daemon on the remote host then handles the requests from the local host. Unlike rcp, ftp works even when the remote computer does not run a UNIX-based operating system. A user must log in to the remote computer to make an ftp connection unless the remote computer has been configured to allow anonymous FTP.
You can now obtain an enormous amount of materials from anonymous FTP servers that are connected to the Internet. Universities and other institutions set up these servers to offer software, research papers, and other information to the public domain. When you log in to this type of server, you use the login name anonymous, hence the term “anonymous FTP servers.”
Using anonymous FTP and setting up anonymous FTP servers is outside the scope of this manual. However, many books, such as The Whole Internet User's Guide & Catalog, discuss anonymous FTP in detail. Instructions for using FTP to reach standard machines are in System Administration Guide: Resource Management and Network Services. The ftp(1) man page describes all ftp command options that are invoked through the command interpreter. The ftpd(1M) man page describes the services that are provided by the daemon in.ftpd.
Telnet – The Telnet protocol enables terminals and terminal-oriented processes to communicate on a network that runs TCP/IP. This protocol is implemented as the program telnet (on local machines) and the daemon in.telnetd (on remote machines). Telnet provides a user interface through which two hosts can communicate on a character-by-character or line-by-line basis. The application includes a set of commands that are fully documented in the telnet(1) man page.
TFTP – The Trivial File Transfer Protocol (tftp) provides functions that are similar to ftp, but the protocol does not establish ftp's interactive connection. As a result, users cannot list the contents of a directory or change directories. A user must know the full name of the file to be copied. The telnet(1) man page describes the tftp command set.
DNS – The domain name system (DNS) is the naming service provided by the Internet for TCP/IP networks. DNS provides host names to the IP address service. DNS also serves as a database for mail administration. For a complete description of this service, see System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP). See also the resolver(3RESOLV) man page.
/etc files – The original host-based UNIX™ naming system was developed for standalone UNIX™ machines and then adapted for network use. Many old UNIX™ operating systems and machines still use this system, but it is not well suited for large complex networks.
NIS – Network Information Service (NIS) was developed independently of DNS and has a slightly different focus. Whereas DNS focuses on making communication simpler by using machine names instead of numerical IP addresses, NIS focuses on making network administration more manageable by providing centralized control over a variety of network information. NIS stores information about machine names and addresses, users, the network itself, and network services. NIS namespace information is stored in NIS maps. For more information on NIS Architecture and NIS Administration, see System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).
NIS+ – NIS+ provides centralized control over network administration services, such as mapping host names to IP and Ethernet addresses, verifying passwords, and so on. See System Administration Guide: Naming and Directory Services (FNS and NIS+).
FNS – Federated Naming Service (FNS), supports the use of different autonomous naming systems in a single Solaris operating environment. FNS allows you to use a single, simple naming system interface for all of the different name services on your network. FNS conforms to the X/Open federated naming (XFN) specification. FNS is not a replacement for NIS+, NIS, DNS, or /etc files. Rather, FNS is implemented on top of these services and allows you to use a set of common names with desktop applications. See System Administration Guide: Naming and Directory Services (FNS and NIS+).
The Solaris operating environment supports LDAP (Lightweight Directory Access Protocol) in conjunction with the iPlanet Directory Server 5.x, as well as other LDAP Directory Servers. The distinction between a Naming Service and a Directory Service is in the differing extent of functionality. A directory service provides the same functionality of a naming service, but provides additional functionalities as well. See System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).
The NFS application layer protocol provides file services for the Solaris operating environment. You can find complete information about the NFS service in System Administration Guide: Resource Management and Network Services.
The Simple Network Management Protocol (SNMP) enables you to view the layout of your network and view the status of key machines. SNMP also enables you to obtain complex network statistics from software that is based on a graphical user interface. Many companies offer network management packages that implement SNMP. SunNet ManagerTM software is an example.
The Routing Information Protocol (RIP) and the Router Discovery Protocol (RDISC) are two routing protocols for TCP/IP networks. They are described in Routing Protocols.