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

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 devices, computing resources, information resources, and communicationdevices that are linked together withcables or wirelesslywith radio waves orlight.

Combined wireless and cabled network


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.


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.


Networking Basics


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


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.



• 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



• 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



• 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



• 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.



• 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.


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


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


Bus Topology


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


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.


Network Topologies

Star Topology


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.


Star-Bus Hybrid Topology

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).


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.


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.



Networking Hardware

Devices on a network with unique physical (MAC) addresses


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.


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.


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).


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.


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.


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.


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.

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.



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

Packets, Frames, and Cells• Some networks require extra capacity for high-speed

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.



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.


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.


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.


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.


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.


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


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.


Transport Protocols

• Wireless Network (contid)

• Four main IEEE wireless specifications today:

Summary of 802.11 wireless communications technologies


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.


Transport Protocols

• UNIX and Linux OSs are compatible with the 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.


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.


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.

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 long-distance network that became the foundation of the Internet.


Communications Protocols• The protocols developed for ARPANET,

Transmission Control Protocol (TCP), and Internet Protocol (IP), or the combination called (TCP/IP), are now used worldwide over the Internet and on most other networks.


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



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



• 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 which converts to the decimal value 129.5.10.1

• 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.



• 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.


IP address classes




– 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


• 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



Using TCP/IP subnet masks



• Computers and network devices that use IP addressing 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 network resources.– IP addressing makes it possible to send a packet along the

best or fastest route for the type of information it contains.



• 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.


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.



• 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).



• 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.



• 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



• Static IP Address:– On some networks there are some 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.



• 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.



• In Mac OS X Leopard and Snow Leopard, wired and wireless network connections are configured 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

• 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.


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


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


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

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