Transport Layer

The TCP/IP transport layer protocols ensure that packets arrive in sequence and without error, by swapping acknowledgments of data reception, and retransmitting lost packets. This type of communication is known as "end-to-end." Transport layer protocols at this level are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

TCP Protocol

TCP enables applications to communicate with each other as though connected by a physical circuit. TCP sends data in a form that appears to be transmitted in a character-by-character fashion, rather than as discrete packets. This transmission consists of a starting point, which opens the connection, the entire transmission in byte order, and an ending point, which closes the connection.

TCP attaches a header onto the transmitted data. This header contains a large number of parameters that help processes on the sending machine connect to peer processes on the receiving machine.

TCP confirms that a packet has reached its destination by establishing an end-to-end connection between sending and receiving hosts. TCP is therefore considered a "reliable, connection-oriented" protocol.

UDP Protocol

UDP, the other transport layer protocol, provides datagram delivery service. UDP does not verify connections between receiving and sending hosts. Because UDP eliminates the processes of establishing and verifying connections, applications that send small amounts of data use UDP rather than TCP.

Application Layer

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
RIP and RDISC routing protocols

Standard TCP/IP Services

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.

UNIX "r" Commands

The UNIX "r" commands enable users to issue commands on their local machines that run on the remote host. These commands include the following:

rcp
rlogin
rsh

Instructions for using these commands are in rcp(1), rlogin(1), and rsh(1) man pages.

Name Services

The Solaris operating environment provides the following naming services:

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+).

Directory Service

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).

File Services

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.

Network Administration

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 Manager™ software is an example.

Routing Protocols

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".

How the TCP/IP Protocols Handle Data Communications

When a user issues a command that uses a TCP/IP application layer protocol, a series of events is initiated. The user's command or message passes through the TCP/IP protocol stack on the local machine. Then the command or message passes across the network media to the protocols on the recipient. The protocols at each layer on the sending host add information to the original data.

Protocols on each layer of the sending host also interact with their peers on the receiving host. Figure 2-1 shows this interaction.


2. TCP/IP (Overview) Introducing the Internet Protocol Suite TCP/IP Protocol Architecture Model Internet Layer


	Transport Layer The TCP/IP transport layer protocols ensure that packets arrive in sequence and without error, by swapping acknowledgments of data reception, and retransmitting lost packets. This type of communication is known as "end-to-end." Transport layer protocols at this level are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP Protocol TCP enables applications to communicate with each other as though connected by a physical circuit. TCP sends data in a form that appears to be transmitted in a character-by-character fashion, rather than as discrete packets. This transmission consists of a starting point, which opens the connection, the entire transmission in byte order, and an ending point, which closes the connection. TCP attaches a header onto the transmitted data. This header contains a large number of parameters that help processes on the sending machine connect to peer processes on the receiving machine. TCP confirms that a packet has reached its destination by establishing an end-to-end connection between sending and receiving hosts. TCP is therefore considered a "reliable, connection-oriented" protocol. UDP Protocol UDP, the other transport layer protocol, provides datagram delivery service. UDP does not verify connections between receiving and sending hosts. Because UDP eliminates the processes of establishing and verifying connections, applications that send small amounts of data use UDP rather than TCP. Application Layer 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 RIP and RDISC routing protocols Standard TCP/IP Services 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. UNIX "r" Commands The UNIX "r" commands enable users to issue commands on their local machines that run on the remote host. These commands include the following: `rcp` `rlogin` `rsh` Instructions for using these commands are in `rcp`(1), `rlogin`(1), and `rsh`(1) man pages. Name Services The Solaris operating environment provides the following naming services: 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+). Directory Service 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). File Services 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. Network Administration 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 Manager™ software is an example. Routing Protocols 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". How the TCP/IP Protocols Handle Data Communications When a user issues a command that uses a TCP/IP application layer protocol, a series of events is initiated. The user's command or message passes through the TCP/IP protocol stack on the local machine. Then the command or message passes across the network media to the protocols on the recipient. The protocols at each layer on the sending host add information to the original data. Protocols on each layer of the sending host also interact with their peers on the receiving host. Figure 2-1 shows this interaction.