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Guide to Operating Systems,
4th ed.
Chapter 9: Network Connectivity
Objectives
• Explain networking basics, such as network
topologies, networking hardware, packaging data
to transport, and how devices connect to a network
• Describe network transport and communications
protocols, and determine which protocols are used
in specific computer operating systems
• Explain how to integrate different operating
systems on the same network
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Networking Basics
• Network – a system of computing devices,
computing resources, information resources, and
communication
devices that are
linked together with
cables or wirelessly
with radio waves or
light.
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Networking Basics
• The basic principle of networking is similar to
connecting telephones.
• In a telecommunications system that uses cell
phones, the cell phone connects to a base station
through a cell tower within its local area using radio
waves.
• Each base station is connected to a mobile
telephone switching office (MTSO), which connects
and coordinates cell phone and land-line
communications.
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Networking Basics
• Computer networking that uses wireless
communications is similar in that each computer
connects to a wireless access point within its area.
• The wireless access point is connected to a larger
network or the Internet as a way to coordinate
communications in the same or different wireless
cell or on a cabled network.
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Networking Basics
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Networking Basics
• Networks have hardware and software elements.
• Hardware components:
–
–
–
–
Computers
Printers
Communications cable
Networking devices
• Software components
– Client and server operating systems
– Device drivers
– Networking protocols
• Rules for network communications
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Client and Server Operating Systems
• Client OS – enables a workstation to run
applications, process information locally, and
communicate with other computers and devices
over a network.
– Examples of Client Oss:
• WindowsXP/Vista/7, UNIX/Linux, Mac OS X and Snow Leopard
– Workstation – a computer that has a CPU and can run
applications locally or obtain applications and files from another
computer on a network.
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Client and Server Operating Systems
• Server OS – coordinates network activities,
authenticates clients to access the network, and
enables client workstations to access shared
network resources such as printers, files, or
software.
– Examples of server OSs:
• Windows Server 2003/Server 2003 R2, Server 2008/Server
2008 R2, UNIX/Linux (can be either client or server), and Mac OS
X server Linux
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Client and Server Operating Systems
• Security – another important function of a server
OS.
– Can be used to test the credentials of clients before clients are
allowed to access network resources.
• Basic way to do this: user account and passwords
– Authentication
– Certificate services – digital certificates to verify that a user or
entity (a file) is trustworthy.
• Important on networks that involve money and secure data
transactions.
– Statement of Health (SoH) – certifies that the client is secure
and is current on OS updates
• Available in Windows Server 2008/R2
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Client and Server Operating Systems
• Security – another important function of a server
OS.
– Remote Installation Services (RIS) – used to install client
OSs on a mass scale (Windows Server 2003/R2)
– Windows Deployment Services (WDS) – updated version of
RIS that became available in Windows Server 2008/R2
– When you use RIS or WDS to install a client OS, you create an
OS image containing specific settings, and then the image is
downloaded and installed on the clients.
– Centralizes installation of software and OSs on client
workstations.
• Saves time and money
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Client and Server Operating Systems
• Publishing an application – Windows Server
2003/Server 2003 R2 and Server 2008/Server
2008 R2 enables Windows XP/Vista/7 clients to
install custom configured application software from
a central Windows server via the clients’ local
Control Panels.
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Client and Server Operating Systems
• Assigning applications – A Windows Server
2003/Server 2003 R2 and Server 2008/Server
2008 R2 feature that enables a client to
automatically start a particular version of software
through a desktop shortcut or menu selection, or by
clicking a file type.
– Clicking a document with a .doc or .docx extension.
– If user accidentally deletes the shortcut, it is automatically
reinstalled the next time the user logs onto the network.
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Local and Wide Area Networks
• Networks are often classified by their reach (scope).
• Local area network (LAN) – the service area is
relatively small, such as a network in an office area
contained on one floor or in one building.
• Wide area network (WAN) – offers networking
services over a long distance, such as between
cities, states or countries
– Often connect LANs over a long distance
– Example of a simple WAN – using a cable or DSL modem to
connect to your ISP, which connects you to other networks
worldwide
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Network Topologies
• Topology – the physical design of the network,
(physical topology) or the path data takes when it
goes from one computer to another (logical topology).
– Bus topology – designed as a straight line (central cable) to
which all computers and devices attach with two end points that
must be terminated to keep the signal from reflecting back
along the path
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Bus Topology
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Network Topologies
• Ring topology – the data-carrying signal goes from
station to station around a logical ring like in a circle of
computers connected to one another until it reaches the
target destination.
– There is no beginning or, end point.
– No terminators.
– No longer used much in LANs – found in some WANs
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Network Topologies
• Star topology – computers or devices (nodes) on
the network connect to a central device such as a
switch or wireless access point.
– In a cabled network, the switch sends the signal onto the
segment that has the destination computer for the particular
communication that is transmitted.
– Every segment is terminated inside the switch at one end and
inside the computer at the other end.
– Most popular network topology because it has the most
flexibility in terms of providing for future growth and adding
high-speed networking capability.
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Network Topologies
Star Topology
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Network Topologies
• Star-bus hybrid topology – combines the logical
communications of a bus with the physical layout of a
star.
– Each segment radiating from the star (central connecting
device) is like a separate logical bus segment but with only one
or two computers attached.
– The segment is still terminated at both ends but the advantage
is that there are no exposed terminators as on a regular bus
topology.
– On each segment, one end is terminated inside the switch and
the other is terminated at the device on the network.
– You can connect multiple switches, access points, and other
network devices to expand the network in many directions.
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Star-Bus Hybrid Topology
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Networking Hardware
• The hardware that supports networking includes
network interface cards, communications media
such as cables or wireless media and various
devices that control the flow of information through
and beyond the network (switches, bridges, and
routers).
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Networking Hardware
• Network interface card (NIC) – a card that goes
into a computer’s expansion slot, or that is built into
a network device or a computer, or that plugs into a
USB port.
• The NIC is equipped with a connector that enables
it to attach to the network communications cable, or
an antenna that enables it to communicate via
radio waves.
• Each NIC has a unique hexadecimal address,
assigned by the manufacturer (a device / physical
address) which identifies it to the network.
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Networking Hardware
• The physical address is also called the Media
Access Control (MAC) address.
– Used much like a postal address because it enables
communications to be sent to specific destination computers on
the same network.
• The software logic on a NIC consists of one or
more programs (firmware) residing in a
programmable chip on the NIC card.
• Communication between the OS and the NIC is
controlled by driver software written by the
manufacturer of the NIC.
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Networking Hardware
Devices on a network with unique physical (MAC)
addresses
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Networking Hardware
• Cables and Wireless Media – A communication
medium is anything through which data is transmitted.
• Twisted-pair cable – consists of one or more pairs
of twisted copper wires bundled together within a
plastic outer coating.
– Wires are twisted to reduce electromagnetic interference (EMI)
or noise.
– Comes in two configurations: Unshielded Twisted Pair (UTP)
and Shielded Twisted Pair (STP).
• STP is faster and more reliable than UTP but it is more expensive
and less flexible.
• UTP is the most often used on LANs today.
– Twisted-pair cable comes in several categories with variations
of Cat 5 and Cat 6 as most common.
• Reflects the speed and type of communications that can be
carried on the cable.
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Networking Hardware
• Coaxial cable (coax) – A copper wire surrounded by
several layers: a layer of insulating material, a layer
of woven or braided metal, and a plastic outer
coating.
– More expensive and cumbersome than twisted pair.
–
–
–
–
Not often used in LANs today.
Not used for WANs.
Mostly used for home Internet connections.
Cable television (CATV) uses coax cable.
• Most connections are made using hybrid fiber/coax (HFC) cable
that consists of optical fibers (fiber optic) and copper cables (coax)
in different combinations.
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Networking Hardware
• Fiber-optic cable – consists of dozens or hundreds
of thin strands of glass or plastic that transmit signals
using light.
– Can carry more signals than wire cables.
–
–
–
–
Are significantly faster.
Are less prone to electrical interference.
Much more difficult and expensive to install and modify.
Most local and long-distance phone companies have replaced existing
phone lines with fiber optic cable.
– Businesses use fiber-optic cables on high-traffic network backbones
(main connecting links between networks).
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Networking Hardware
• Wireless transmissions are carried by radio
frequencies (RF) or light (infrared) including radio
waves and microwaves.
• Cell phones also use wireless technology but
broadcast in a different frequency range than
wireless LANs.
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Networking Hardware
• Network Devices – used to connect computers
and network-attached devices like printers to each
other and to connect networks to each other.
– NIC – Each device (node) connected to a network must have a
NIC which connects through a cable or wireless antenna to a
hub, switch, bridge, router, or wireless access point, which in
turn connects to a LAN or WAN.
– Hubs – were once used in bus and star LANs to connect
computers or devices to a local network but have been
superseded by switches.
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Networking Hardware
• Network Devices (contid.)
– Switch – like a hub but more “intelligent”.
• Communications that go through hubs are broadcast to all
segments attached to the hub.
• A switch only transmits the information to the segment where the
destination device resides.
– Wireless access point – a device that connects wireless
devices to a wired network.
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Networking Hardware
• Network Devices (contid.)
– Bridge – Used to link network segments that are close
together.
• Used to extend segments, such as when more stations must be
added, but the primary segment already contains the maximum
length of cable or number of stations permitted by network
standards.
• Used to segment a network into smaller networks as a way to
control traffic and reduce bottlenecks at busy network
intersections.
• Can be used to link segments that use different cable types.
• Network administrators today use switches instead of bridges.
• Switches provide additional logic that enables them to move
network traffic more efficiently than the old-style bridges.
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Networking Hardware
• Network Devices (cont.)
– Router - used to connect networks.
• Connect dissimilar networks.
• Can be programmed to act as a firewall to filer communications.
– Hardware or software that secures data from being accessed outside
a network and can prevent data from leaving the network.
• Keeps tables of network addresses that identify each computer on
the network along with the best “routes” to other network
addresses.
• Can use routing information in network packets to route individual
packets to the proper destination.
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Packets, Frames, and Cells
• Each network device translates data into individual
units and then places the units onto the network
media for transmission.
– Each data unit is called a packet or frame.
– Packet – contains routing information that allows the packet to
be forwarded to specific networks.
– Frame – contains information about the specific sending or
receiving device
– The actual data is placed after the header information and
followed by a footer (trailer) that enables detection of a
transmission error.
Basic packet format
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Packets, Frames, and Cells
• Some networks require extra capacity for highspeed transmissions more than 1Gbps (networks
that have a high proportion of multimedia
applications or on which large files are regularly
transmitted).
• Cell – data unit designed for high-speed
communications.
– Has a control header and a fixed-length payload.
• Payload – that portion of a frame, packet, or cell that contains the
actual data.
– One element of the cell header is path information that enables
the cell to take the route through the network that is most
appropriate for the type of data carried within the cell.
• Exact format of a frame, packet, or cell is determined by the type of
protocol used on a network.
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Networking Protocols
• Protocol – A set of formatting guidelines for
network communications (like a language), so that
the information sent by one computer can be
accurately decoded by another.
• Protocols also coordinate network communications
so that data is transported in an orderly fashion,
preventing chaos when two or more computers
want to transmit at the same time.
• A network may use several different protocols,
depending on the types of communications and the
types of devices that are connected.
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Networking Protocols
• Protocols are used for:
– Coordinating transport of packets and frames among network
devices.
– Encapsulating data and communication control information.
– Providing communications to accomplish a specific function.
• Such as enabling the destination computer to tell the source
computer, to slow its transmission speed because it is too fast
for the destination computer.
– Enabling communications over a long-distance network, such as
the Internet.
– Enabling remote users to dial into networks, access virtual private
networks, or access networks through cable and wireless
technologies.
– Transporting test, network status, and other network management
information.
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Transport Protocols
• Two of the most important types of protocols are
those that coordinate transport and those that
communicate and coordinate how data is
encapsulated and addressed.
– Ethernet
– Wireless
• Standards for Ethernet and wireless networking are
defined as part of the standards established by the
Institute of Electrical and Electronics Engineers
(IEEE) through its 802 standards committee
– The 802 standards are followed by network administrators and
manufacturers to ensure all network devices will be able to
communicate with each other.
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Transport Protocols
• Ethernet – only one station should transmit at a
given moment.
– If two or more devices transmit at the same time, frames
collide.
– The transmission control method used is called carrier sense
multiple access with collision detection (CSMA/CD).
• The NICs of computers and devices check the network
communications cable for a carrier signal that contains an
encoded frame.
• If the device’s NIC detects a carrier signal, and if the NIC decodes
its own device address within the frame, it forwards that packet to
its firmware for further decoding.
• If the frame does not contain its device address, then the NIC
does not process the signal any further.
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Transport Protocols
• Ethernet (cont.)
– When the detected carrier signal is twice (or more) the strength
of a normal carrier signal, this indicates that at least two
network stations transmitted at the same time.
• In this situation, a collision occurred, and a transmitting station
sends a “jam” signal to warn all other stations.
• After the jam signal is sent, every station waits a different amount
of time before attempting to transmit again.
– Networks that use Ethernet are designed in a bus topology or a
star-bus topology.
• Ethernet star-bus hybrid networks are the most commonly used
networks.
– Typical speeds supported today are 100 Mbps (Fast Ethernet)
and 1 Gbps (Gigabit Ethernet).
– 10 and 100 Gbps Ethernet are mostly used on Ethernet
backbones.
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Transport Protocols
• Ethernet (cont.)
– All versions of Ethernet are compatible with popular OSs such
as:
•
•
•
•
•
UNIX/Linux
Windows XP/Vista/7
Windows Server 2003/Server 2003 R2
Windows Server 2008/Server 2008 R2
Mac OS X Leopard and Snow Leopard
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Transport Protocols
• Wireless Network – Can be described by its MAC
(Medium Access Control) protocol.
• The most prevalent protocol used in a wireless
LAN is carrier sense multiple access with
collision avoidance (CSMA/CA) – a variation of
CSMA/CD used in Ethernet.
– A wireless station that wants to transmit, listens for other
transmissions.
– If there are transmissions, it will wait a specified amount of time
and then listen again.
– If there are no transmissions, the station will begin transmitting.
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Transport Protocols
• Wireless Network (contid)
• Four main IEEE wireless specifications today:
Summary of 802.11 wireless communications technologies
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Transport Protocols
• A transport protocol is interfaced with an OS
through three elements:
– Network driver specification built into the OS;
– A NIC;
– A NIC driver.
• Network OS are built to offer special elements
(hooks) in the OS kernel (program code), that
enable the OS to interface with a network.
– Microsoft and 3COM designed the Network Device Interface
Specification (NDIS) and Windows-based NDIS drivers for this
purpose.
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Transport Protocols
• UNIX and Linux OSs are compatible with NDIS
driver through using open source software, such as
NDISwrapper.
• Mac OS X is also compatible with NDISwrapper
when using a nonproprietary NIC (Intel) in a Mac.
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Transport Protocols
• When you set up an OS to work on an Ethernet or
wireless network, the first step is to purchase an
Ethernet or wireless NIC for the computer running
the OS.
– If the NIC is for a wired network, the NIC cable interface must
also match the type of cable used on the network.
• Choose a wireless NIC if no cable is needed.
• After the NIC is installed in an open expansion slot
in the computer, the next step is to boot the OS
and install the NIC driver software, which links the
NIC into the network computing hooks in the
kernel.
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Transport Protocols
• After the NIC setup is complete, and the computer
is connected to the network, the OS, NIC, and
driver handle the work of converting data created at
the computer to an Ethernet or wireless format for
transport over the network.
– The same three elements also enable the computer to receive
packets or frames and convert them into data that the computer
can interprete.
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Communications Protocols
• The development of communications protocols (the
protocols that carry data between two
communicating stations, and are encapsulated in
Ethernet or wireless transport protocols) is related
to the network OSs in which they are used.
– Today, all OSs discussed in this book use the TCP/IP family of
protocols (protocols developed for the Internet).
• In the early 1980’s, researchers implemented and
combined two protocols for use on the U.S.
Department of Defense Advanced Research
Projects Agency Network (ARPANET), the longdistance network that became the foundation of the
Internet.
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Communications Protocols
• Transmission Control Protocol (TCP)
– Developed for extremely reliable point-to-point communications
between computers on the same network.
– This protocol establishes communication sessions among
applications on two communicating computers, making sure
there is a mutually agreeable “window” of transmission
characteristics.
– TCP performs some of the following communication functions:
•
•
•
•
Establishes the communication session between two computers
Ensures that data transmissions are accurate
Encapsulates, transmits, and receives the payload data
Closes the communication session between two computers
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Communications Protocols
• Internet Protocol (IP)
– Used to make sure that a packet reaches the intended
destination.
– IP performs the following complementary functions with TCP:
• Handles packet addressing
• Handles packet routing
• Fragments packet, as needed, for transport across different types
of networks
• Provides simple packet error detection in conjunction with the
more thorough error detection provided by TCP
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Communications Protocols
• TCP/IP comes in two version IPv4 and IPv6
– IPv4 is the most commonly used version, but has a limitation in
that the world is nearly out of new IP addresses.
• IPv4 uses a dotted decimal notation that consists of four 8-bit
binary numbers separated by periods to produce an IP address
used to identify a computer or network device and the network it is
on.
– The format is:
10000001.00000101.00001010.00000001
decimal value 129.5.10.1
which converts to the
• Part of the address designates a unique identifier for a network
called the network identifier (NET_ID).
– A school or corporation
• Part of the address is the host identifier (HOST_ID).
– Distinguishes a computer or network device from any other computer
or device on a network.
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Communications Protocols
• There are five IP address classes of IPv4 IP
addresses.
• The address classes reflect the size of the network,
and whether the packet is unicast or multicast.
– Unicast – one copy of each packet is sent to each target
destination.
• If there are eight workstations designated to receive a packet, the
packet is transmitted eight times.
– Multicast – The recipients are placed in a group. Only one
packet is sent to the group, via a router or switch, which then
sends the packet to each group member.
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Communications Protocols
IP address classes
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Communications Protocols
– Class A – assigned to large networks – can have up to
16,777,216 nodes
• Class A network address example – 122.0.0.0
– Class B – assigned to medium networks – can have up to
65,536 nodes
• Class B network address example – 132.155.0.0
– Class C – assigned to small networks – can have up to 256
nodes
• Class C network address example – 220.127.110.0
– Class D – used for multicasts (sent to multiple nodes)
– Class E – used for experimentation
– Broadcast address: 255.255.255.255 – sent to all nodes on a
network
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Communications Protocols
• Classless interdomain routing (CIDR) – newer
way of addressing that ignores address class
designation.
– Puts a slash (/) after the dotted decimal notation.
• Example: 165.100.0.0/14
– CIDR provides more IP address options for medium-sized
networks.
• Subnet mask – used to identify networks or
subnetworks (subnet) within a larger network setup
– On large networks, subnets allow an administrator to create
smaller networks to limit network traffic and congestion on
network segments
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Communications Protocols
Using TCP/IP subnet masks
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Communications Protocols
• Computers and network devices that use TCP/IP
protocol have two addresses:
– MAC address – address burned into the NIC
– IP address – assigned by network administrator
• The use of two addresses provides better
insurance that a packet will reach the right
destination, while expending the fewest resources.
– IP addressing makes it possible to send a packet along the
best or fastest route for the type of information it contains.
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Communications Protocols
• IPv6 – A newer TCP/IP version that uses 128-bit
addresses to solve the shortage of IPv4 addresses.
– Provides more specialized networking implementations, such
as voice, video, and multimedia applications.
– All new OSs support various levels of IPv6.
• TCP/IP works with a range of associated protocols
that make this a powerful combination for networks
of all sizes and types.
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Communications Protocols
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Communications Protocols
• Three steps involved in setting up a
communications protocol in an OS:
– Installing the protocol in the OS.
– Binding the protocol to the NIC.
– Configuring protocol communications parameters.
• Installing and Binding a Protocol
– Combined into one procedure.
– Usually automatic when you install the OS.
• TCP/IP is automatically installed unless you specify that it should
not be installed.
– Binding – Enables the NIC to format data for that protocol and
identify the most efficient methods for transporting it.
• When two or more protocols are used, binding also enables the
NIC to prioritize which protocol to process first.
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Communications Protocols
• Configuring a Protocol – To configure the
protocol communication parameters:
– Configuring an IPv4 address;
– Configuring an IPv6 address;
• Which may also require the NET_ID length or IP prefix length.
– Specifying the subnet mask (also called the netmask);
– Designating a default gateway (the device that links the
network to other networks, such as the Internet).
– Specifying a preferred DNS server (provides lookup of IP
addresses and computer/device names);
– Specifying an alternate DNS server (used when preferred DNS
server is busy or cannot be reached).
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Communications Protocols
• If a network uses automatically assigned IP
addressing through a Dynamic Host
Configuration Protocol (DHCP) server, then all
you need to do to configure TCP/IP is to specify
automatic addressing.
– Two advantages:
• Not necessary to know any of the TCP/IP configuration
parameters, because they are automatically assigned by DHCP.
• DHCP Ensures that no two computers are assigned the same IP
address.
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Communications Protocols
• Automatic Private IP Addressing (APIPA)
– Available in Windows XP/Vista/7, Server 2003/R2, Server
2008/R2.
– If automatic addressing is selected but there is no DHCP server
on the network, the OS assigns the IPv4 address from a
reserved range of 169.254.0.1 – 169.254.255.254
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Communications Protocols
• Static IP Address:
• On some networks there are some computers
computers and devices that must have an IP
address that is manually assigned and never
changes (servers, switches, routers, etc…)
– Important for devices that will be well known and used by other
devices for services
– Servers are normally given a static IP address.
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Communications Protocols
• Most UNIX/Linux OSs have TCP/IP networking
support built in.
– Some automatically run a network configuration program when
you first boot the computer with an installed NIC.
– NIC device drivers are loaded in the kernel.
– When the configuration program runs, you must supply
information about the network connection, such as the IP
address.
– If TCP/IP networking is not automatically configured when you
first boot, it can be configured later by using the ifconfig
command.
• A utility typically found in the /etc or /sbin directories, which
enables you to assign an IP address, turn on the network
interface, and assign a subnet task.
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Communications Protocols
• In Mac OS X Leopard and Snow Leopard, wired and
wireless network connections are configured using
the Network option from the System Preferences
windows.
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Communications Protocols
Configuring a wireless network connection
in Mac OS X Snow Leopard
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Integrating Different Operating
Systems on the Same Network
• The key to implementing multiple OSs on one
network is to select a transport protocol and
communications protocols that are supported in all
of the OSs that must be connected.
• Ethernet and TCP/IP are supported by most
operating systems.
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Chapter Summary
• A network is a system of resources and productivity tools
that communicate with each other enabling us to share
information over short and long distances
• Networks are roughly categorized as LANs or WANs,
depending on their areas of service (LANs typically cover a
building or floor of a building and WANs are long-distance
networks that join LANs and individual users)
• Networks are designed in standardized topologies (bus, star,
ring, star-bus hybrid) and use standardized communications
means, such as frames, packets, and protocols
• Protocols are important to network because they act as a
common language for communication between devices and
provide reliability, delivery of data and monitor networks for
problems
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Chapter Summary
• Modern computer operating systems use TCP/IP, which is
the communications protocol preference for networks and
the Internet
• IPv4 is in greatest use today, but networks will eventually
convert to IPv6 because it offers a greater range of
addresses, better security, and other network improvements
• Networking devices such as hubs, bridges, switches, and
routers enable network connectivity (hubs and bridges are
becoming obsolete) Each device is used to achieve different
connectivity goals based on its capabilities
• Cabled Ethernet and wireless networks are used separately
and also combine to enable flexible networking
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Chapter Summary
• Windows operating systems, UNIX, Linux, and Mac OS X all
offer tools for configuring TCP/IP communications, including
IP address, subnet mask, gateway, and DNS parameters
• Current Windows operating systems, UNIX, Linux, and Mac
OS X Leopard and Snow Leopard can be integrated on the
same network, in part because they all support TCP/IP as
their default communications protocol and are compatible
with Ethernet
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