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.
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:
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.
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