C++ Network and Networking Programming, Informatyka
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Introduction to
Networking
I
1 Networking and Network Programming
2 TCP/IP Overview
3 WinSock Overview
4 Visual C++
Chapter 1
n
1
3
Networking
and Network
Programming
Networking and Network Programming
4
Part I
n
Introduction to Networking
The purpose of this book is to show you how to make network-aware applications that
run on the Microsoft Windows and Windows NT operating systems using the Win-
dows Sockets (WinSock) Application Programming Interface (API). To that end, sev-
eral practical examples are examined that utilize the basic functionality of WinSock.
Network operating systems, such as Windows for Workgroups and Windows NT,
provide basic file and printer sharing services. This most basic level of functionality is
provided “out of the box.” Network-aware applications are programs that use the capa-
bilities of a collection of connected computers. Network-aware programs range from
custom applications that transfer data among computers on a network to mainstream
applications that enable electronic mail and remote database access. The WinSock API
is a library of functions that a programmer can use to build these network-aware
applications. WinSock has its roots in Berkeley sockets as introduced in the Berkeley
Software Distribution of UNIX. WinSock uses the TCP/IP (Transmission Control Pro-
tocol/Internet Protocol) suite, which provides the formal rules of behavior that govern
network communications between all computers running this particular computer net-
working protocol.
Before I begin the examination of network programming, look at the basics of com-
puter networking in general. A network can be loosely defined as a collection of two or
more computers that have some sort of communication path between them. A network
can be loosely classified as either a local area network (LAN) or wide-area network
(WAN). The use of the terms
LAN
and
WAN
is somewhat misleading because which
term you use is relative to the particular network installation you’re describing. Gener-
ally speaking, a LAN covers a much more geographically restricted area than does a WAN.
Whereas a LAN may connect computers within an office building, a WAN may con-
nect computers spread across the country. With the advances in networking hardware
and software, many widely dispersed LANs can now be connected to form a much larger
homogeneous WAN. Devices known as
bridges
and
routers
allow for this connection of
disparate LANs. Computer networks aren’t new, but they weren’t accepted in the per-
sonal computer realm until perhaps the late 1980s, when computer firms began offer-
ing cost-effective and reliable networking for the desktop PC. At that time, the primary
goal of the PC network was to provide a central repository for files and to allow printers
to be shared among many users. It hasn’t been until relatively recently that businesses
have realized the true potential of a PC network.
Chapter 1
n
Networking and Network Programming
5
Goals of Networking
The goals of PC networking have been expanding over the last few years—from simple
file and printer sharing to access of fax machines, modems, and enterprise-wide elec-
tronic mail systems. All the while, the essential goals of networking have always been to
share resources and to provide a medium for communications.
Resource Sharing
For the sake of this discussion, a network resource is either a device or a capability on
the network that’s available for use by network users. The computer that the network
resources are attached to is called the
server.
The other computers that access those re-
sources over the network are called clients. The typical PC network user today takes
shared file and printer access for granted. But there are now other resources that also
can be made available to the user. Among them are fax machines, modems, compute
servers, and database servers.
Files
The traditional use of PC networks has been and probably always will be to act as a
repository for files. By storing files in a common location accessible to coworkers, for
example, much productivity can be gained. Several products exist from Microsoft and
other vendors that provide this capability. Windows for Workgroups is one such prod-
uct. It’s classified as a peer-to-peer network, which means that there’s no dedicated,
central-file server. Instead, any computer on the network can share files with any other;
any computer on the network can act as either a client, server, or both. Windows NT
and Windows NT Advanced Server expand on this idea by providing a much more robust
file-sharing capability and better file system security.
Figure 1.1 shows two computers labeled Computer A and Computer B. Each has ac-
cess to files on the File and Print Server and stored on the computer server. To illustrate
the difference between the central-file server model and the peer-to-peer model, exam-
ine the following scenario, where Computer A has a file on its hard disk that it would
like to make available to Computer B. In the central-file server model, Computer A must
connect to the File and Print Server, place the file on the server’s hard disk, and then
inform Computer B that the file is available. Computer B then connects to the File and
Print Server and accesses the file deposited there by Computer A. Using a peer-to-peer
network, Computer A could simply give Computer B permission to access the file on
Computer A’s hard disk.
6
Part I
n
Introduction to Networking
FIGURE 1.1.
File and printer
resource sharing.
Computer A
Computer B
File and Print Server
Laser Printer
At a minimum, a computer network with a file server, whether it be centralized or peer-
to-peer, prevents the use of the infamous “sneaker net” whereby files are transferred
between computer users by first putting the desired files onto a floppy disk and then
walking that floppy over to the designated recipient.
Printers
Another popular use of PC networks is to make printers available to all network users.
This obviously provides a great cost savings by reducing the number of expensive print-
ers and the cost of the maintenance and management of those devices. Windows for
Workgroups and Windows NT provide printer-sharing capabilities. As Figure 1.1 shows,
the two computers labeled Computer A and Computer B, as well as the File and Print
Server computer, have access to the laser printer attached to the File and Print Server.
When the user seated at Computer A prints a document, it’s sent to the File and Print
Server where it’s printed. If a user at Computer B tries to print a document while Com-
puter A’s document is still printing, Computer B’s document is stored in a temporary
location on the File and Print Server. This process is called printer spooling. As soon as
the first submitted print job belonging to Computer A’s user is complete, the next job,
belonging to Computer B’s user, is begun.
A Windows NT-based network fully supports the remote management of networked
printers. An administrator of a Windows NT network can monitor the status (to see if
the paper is out, for example) of a remotely located printer and also manipulate the queue
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Introduction to
Networking
I
1 Networking and Network Programming
2 TCP/IP Overview
3 WinSock Overview
4 Visual C++
Chapter 1
n
1
3
Networking
and Network
Programming
Networking and Network Programming
4
Part I
n
Introduction to Networking
The purpose of this book is to show you how to make network-aware applications that
run on the Microsoft Windows and Windows NT operating systems using the Win-
dows Sockets (WinSock) Application Programming Interface (API). To that end, sev-
eral practical examples are examined that utilize the basic functionality of WinSock.
Network operating systems, such as Windows for Workgroups and Windows NT,
provide basic file and printer sharing services. This most basic level of functionality is
provided “out of the box.” Network-aware applications are programs that use the capa-
bilities of a collection of connected computers. Network-aware programs range from
custom applications that transfer data among computers on a network to mainstream
applications that enable electronic mail and remote database access. The WinSock API
is a library of functions that a programmer can use to build these network-aware
applications. WinSock has its roots in Berkeley sockets as introduced in the Berkeley
Software Distribution of UNIX. WinSock uses the TCP/IP (Transmission Control Pro-
tocol/Internet Protocol) suite, which provides the formal rules of behavior that govern
network communications between all computers running this particular computer net-
working protocol.
Before I begin the examination of network programming, look at the basics of com-
puter networking in general. A network can be loosely defined as a collection of two or
more computers that have some sort of communication path between them. A network
can be loosely classified as either a local area network (LAN) or wide-area network
(WAN). The use of the terms
LAN
and
WAN
is somewhat misleading because which
term you use is relative to the particular network installation you’re describing. Gener-
ally speaking, a LAN covers a much more geographically restricted area than does a WAN.
Whereas a LAN may connect computers within an office building, a WAN may con-
nect computers spread across the country. With the advances in networking hardware
and software, many widely dispersed LANs can now be connected to form a much larger
homogeneous WAN. Devices known as
bridges
and
routers
allow for this connection of
disparate LANs. Computer networks aren’t new, but they weren’t accepted in the per-
sonal computer realm until perhaps the late 1980s, when computer firms began offer-
ing cost-effective and reliable networking for the desktop PC. At that time, the primary
goal of the PC network was to provide a central repository for files and to allow printers
to be shared among many users. It hasn’t been until relatively recently that businesses
have realized the true potential of a PC network.
Chapter 1
n
Networking and Network Programming
5
Goals of Networking
The goals of PC networking have been expanding over the last few years—from simple
file and printer sharing to access of fax machines, modems, and enterprise-wide elec-
tronic mail systems. All the while, the essential goals of networking have always been to
share resources and to provide a medium for communications.
Resource Sharing
For the sake of this discussion, a network resource is either a device or a capability on
the network that’s available for use by network users. The computer that the network
resources are attached to is called the
server.
The other computers that access those re-
sources over the network are called clients. The typical PC network user today takes
shared file and printer access for granted. But there are now other resources that also
can be made available to the user. Among them are fax machines, modems, compute
servers, and database servers.
Files
The traditional use of PC networks has been and probably always will be to act as a
repository for files. By storing files in a common location accessible to coworkers, for
example, much productivity can be gained. Several products exist from Microsoft and
other vendors that provide this capability. Windows for Workgroups is one such prod-
uct. It’s classified as a peer-to-peer network, which means that there’s no dedicated,
central-file server. Instead, any computer on the network can share files with any other;
any computer on the network can act as either a client, server, or both. Windows NT
and Windows NT Advanced Server expand on this idea by providing a much more robust
file-sharing capability and better file system security.
Figure 1.1 shows two computers labeled Computer A and Computer B. Each has ac-
cess to files on the File and Print Server and stored on the computer server. To illustrate
the difference between the central-file server model and the peer-to-peer model, exam-
ine the following scenario, where Computer A has a file on its hard disk that it would
like to make available to Computer B. In the central-file server model, Computer A must
connect to the File and Print Server, place the file on the server’s hard disk, and then
inform Computer B that the file is available. Computer B then connects to the File and
Print Server and accesses the file deposited there by Computer A. Using a peer-to-peer
network, Computer A could simply give Computer B permission to access the file on
Computer A’s hard disk.
6
Part I
n
Introduction to Networking
FIGURE 1.1.
File and printer
resource sharing.
Computer A
Computer B
File and Print Server
Laser Printer
At a minimum, a computer network with a file server, whether it be centralized or peer-
to-peer, prevents the use of the infamous “sneaker net” whereby files are transferred
between computer users by first putting the desired files onto a floppy disk and then
walking that floppy over to the designated recipient.
Printers
Another popular use of PC networks is to make printers available to all network users.
This obviously provides a great cost savings by reducing the number of expensive print-
ers and the cost of the maintenance and management of those devices. Windows for
Workgroups and Windows NT provide printer-sharing capabilities. As Figure 1.1 shows,
the two computers labeled Computer A and Computer B, as well as the File and Print
Server computer, have access to the laser printer attached to the File and Print Server.
When the user seated at Computer A prints a document, it’s sent to the File and Print
Server where it’s printed. If a user at Computer B tries to print a document while Com-
puter A’s document is still printing, Computer B’s document is stored in a temporary
location on the File and Print Server. This process is called printer spooling. As soon as
the first submitted print job belonging to Computer A’s user is complete, the next job,
belonging to Computer B’s user, is begun.
A Windows NT-based network fully supports the remote management of networked
printers. An administrator of a Windows NT network can monitor the status (to see if
the paper is out, for example) of a remotely located printer and also manipulate the queue
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