9781111306366 ppt ch9

Guide to Operating Systems,
4th
ed.
Chapter 9: Network Connectivity

Guide to Operating Systems, 4th ed. 2
Objectives
2
• 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

Networking Basics
• Network – a system of computing and
communication devices that are linked together with
cables or wirelessly
Combined wireless and cabled network

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

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
– Workstation – computer that has a CPU and can run
applications locally or obtain applications and files from another
computer on a network
• 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

• Security – 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: logins and passwords
– Certificate services – digital certificates to verify that a user or
entity is trustworthy
– Statement of Health (SoH) – certifies that the client is secure
and is current on OS updates (available in Windows Server
2008/R2)
– 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

• Publishing an application – Windows Server
2003/R2 and Server 2008/R2 enables Windows
XP/Vista/7 clients to install custom configured
application software
• Assigning applications – Windows Server feature
that enables a client to automatically start a
particular version of software through a desktop
shortcut
– If user accidentally deletes the shortcut, it is automatically
reinstalled the next time the user logs in

Local and Wide Area Networks
• Networks are often classified by their reach (scope)
• Local area network (LAN) – 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

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

Network Topologies
• Ring topology – the data-carrying signal does from
station to station around a logical ring like a circle of
computers connected to one another
– No longer used much in LANs – found in some WANs
• Star topology – computers or devices (nodes)
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
– Most popular network topology because it has the most
flexibility

Network Topologies
Star Topology

Network Topologies
• Star-bus hybrid topology – combine 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

Networking Hardware
• Network interface card (NIC) – an interface card
or an interface that is built into a device that allows
the device to connect to a network
– Media Access Control (MAC) address - a unique
hexadecimal address, assigned by the manufacturer
• Every NIC has one
• Another name for this address is physical address
• Used much like a postal address because it enables
communications to be sent and received based on the address
• Address is stored in firmware – chip on the NIC that contains
drivers and other software necessary for the NIC to communicate
with OS

Networking Hardware
Devices on a network with unique physical (MAC)
addresses

Networking Hardware
• Cables and Wireless Media – 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
– 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

Networking Hardware
• Coaxial cable (coax) – copper wire surrounded by
several layers for insulation
– Not often used in LANs today
– Mostly used for home Internet connections
– Cable television (CATV) uses coax cable
• Most connections are made using hybrid fiber/coax (HFC) cable
• Fiber-optic cable – consists of thin strands of glass
that transmit signals using light
– Can transmit faster than copper and is not prone to EMI
– Used by businesses on high-traffic network backbones (main
connecting links between networks)
• Wireless transmissions are carried by radio
frequencies or light (infrared) through the air

Networking Hardware
• Network Devices – used to connect computers and
network-attached devices like printers to each
other and to connect networks together
– Hubs – once were popular network devices (being replaced by
switches)
• Communications that go through hubs are broadcast to all
segments attached to the hub
– Switch – “intelligent” hub
• Only transmits information to the segment where the destination
device is located
– Wireless access point – connects wireless devices to a wired
network

Networking Hardware
• Network Devices (cont.)
– Bridge (being replaced by switches) - used to extend segments
or link segments that use different cable types
– Router used to connect networks
• Can be programmed to act as a firewall (hardware or software
that secures data from being accessed outside a network and can
prevent data from leaving the network)
• Router keep tables of network addresses along with the best
“routes” to other network addresses

Packets, Frames, and Cells
• Each network device translates data into individual
units and then places the units onto 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
Basic packet format

Packets, Frames, and Cells
• Cell – data unit designed for high-speed
communications
– Has a control header and a fixed-length payload
– Payload – 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
• Exact format of a frame, packet, or cell is
determined by the type of protocol used on a
network

Networking Protocols
• Protocol – set of formatting guidelines for network
communications (like a language), so that data
sent by one computer can be read by another
• Protocols are used for:
– Communicating transport of packets and frames among network
devices
– Encapsulating data and communication control information
– Providing communications to accomplish a specific function
• Such as, flow control
– Enabling communications over a long-distance network
– Enabling remote users to dial into networks
– Transporting test, network status, and other network management
information

Transport Protocols
• Standards for network communication were
established by the Institute of Electrical and
Electronics Engineers (IEEE) through its 802
standards committee
– 802 standards are followed by network administrators and
manufacturers to ensure all network devices will be able to
communicate with each other
• Ethernet – only one station on a network segment
can transmit at a time
– If two or more devices transmit at the same time, frames collide
– Uses carrier sense multiple access with collision detection
(CSMA/CD)

Transport Protocols
• Ethernet (cont.)
– In CSMA/CD – NIC listens to see if another device is
transmitting, if it does not hear a transmission then it will
transmit
• If two devices on the same segment try to transmit at the same
time, a collision occurs and both transmission are dead
• A “jam” signal is sent to warn all other stations
• Each device waits a different amount of time before attempting to
transmit again
– 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

Transport Protocols
• Wireless – uses carrier sense multiple access with
collision avoidance (CSMA/CA)
– A variation of CSMA/CD
– Four main IEEE wireless specifications today:
Summary of 802.11 wireless communications technologies

Transport Protocols
• A transport protocol is interfaced with an OS
through:
– Network driver specification built into the OS
– A NIC
– A NIC driver
• Microsoft and 3COM designed the Network Device
Interface Specification (NDIS) drivers
– UNIX and Linux are compatible with NDIS driver through open
source software, such as NDISwrapper
– Mac OS X is compatible with NDISwrapper when using a
nonproprietary NIC (Intel)

Transport Protocols
• When purchasing a NIC:
– The NIC cable interface must match the type of cable used on
the network
• Choose a wireless NIC if no cable is needed
• Make sure the current driver is installed to support
the NIC
• After NIC setup is complete, the OS, NIC, and
driver handle the work of converting data to an
Ethernet or wireless format for transport over a
network (same three elements enable receiving
and interpreting data as well)

Communications Protocols
• Communications protocols – carry data between
two communicating devices
– Today, all OSs discussed in this book use TCP/IP family of
protocols (protocols developed for the Internet)
– Developed in early 1980’s for use on the US Dept. of Defense
Advanced Research Projects Agency Network (ARPANET)
• Transmission Control Protocol (TCP)
– 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

• Internet Protocol (IP)
– 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
• TCP/IP comes in two version IPv4 and IPv6
– IPv4 is most commonly used today but has a limitation of
address allocation (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 (known as IP address)

• 5 classes of IPv4 IP addresses
– 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

IP address classes

• Classless interdomain routing (CIDR) – newer way
of addressing that ignores address class
designation
– CIDR provides more IP address options for medium-sized
networks
– Example : 165.100.0.0/14
• 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

Using TCP/IP subnet masks

• 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
• IPv6 – new TCP/IP version 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 IPv6

• 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
– Binding – enables the NIC to format data for that protocol and
identify the most efficient methods for transporting it

• Configuring a Protocol – parameters to configure
include some or all of the following:
– Configuring an IPv4 address
– Configuring an IPv6 address
– 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
server is busy or cannot be reached)

• Dynamic Host Configuration Protocol (DHCP) –
used to automatically assign IP address
information to computers
– Two advantages:
• Not necessary to assign addresses manually
• Ensures that no two computers are assigned the same IP address
• Automatic Private IP Addressing (APIPA)
– Available in Windows XP/Vista/7, Server 2003/R2, Server
2008/R2
– If automatic addressing is selecting 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

• Some computers and devices must have an IP
address that is manually assigned and never
changes (servers, switches, routers, etc…)
– Called a static IP address
– Important for devices that will be well known and used by other
devices for services
• Most UNIX/Linux OSs have TCP/IP networking
support built in
– Some automatically run a network configuration program when
you first boot the computer
• If not, it can be configured later by using the ifconfig command

• In Mac OS X Leopard and Snow Leopard,
configurations are made using the Network option
from the System Preferences windows

Configuring a wireless network
connection in Mac OS X Snow Leopard

Integrating Different Operating
Systems on the Same Network
• Key to implementing multiple OSs on one network:
– Select a transport and communications protocol that are
supported in all of the OSs
• Ethernet and TCP/IP are supported by most
operating systems

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
problemsGuide to Operating Systems, 4th ed. 42

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

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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