1 Network Connectivity. 2 A network is composed of communications media such as communications cable, used to link computers, printers, disk storage,

1

Network Connectivity

2

• A network is composed of communications media such as communications cable, used to link computers, printers, disk storage, CD-ROM arrays, and network communications equipment

• The basic principle of networking is similar to connecting telephones for communications

• The hardware components of a computer network are computers, printers, communications cable, and internetworking devices such as bridges, switches, routers, and hubs

Basic Networking

3

Telephone and Computer Networks Compared

4

• Computer networks also have software components consisting of client and server network operating systems

• Windows 95, Windows 98, Windows NT 4.0 Workstation, Windows 2000 Professional, and Windows XP Professional are examples of client operating systems

• A client operating system is one that enables a workstation to run applications, process information locally, and communicate with other computers and devices over the network

Basic Networking

5

• A workstation is a computer that has a CPU, and can run applications locally, or obtain applications and files from another computer on the network

• Sometimes the term workstation is confused with the term terminal

• The difference is that a terminal has no CPU or local storage for running programs independently

Basic Networking

6

• A network operating system (NOS) is one that enables the coordination of network activities and the sharing of resources – network communications, shared printing, shared access to files, and shared access to software, for example

• A server is a computer running a NOS, which provides resources, such as shared files and programs that are accessed by clients

Basic Networking

7

Reasons for a Network

• Networks were invented for three interrelated reasons: to share resources, save money, and increase productivity

• Most important, networks allow organizations to save money by sharing resources

• Windows NT Server 4.0, Windows 2000 Server, and Windows .NET Server offer several ways to save money and time by centralizing software and client operating system installation through a server

8

Sharing Resources in an Office

9

The Development of Network Operating Systems

• Novell NetWare was one of the first network operating systems, initially demonstrated in 1982 at the National Computer Conference as a groundbreaking PC networking system

• Windows 3.1, released in 1992, was one of the first Windows-based operating systems with network capabilities, enabling it to connect to NetWare, Microsoft, and other networks

• Workgroups (pre-defined groups of member computers) provide the ability to limit resource sharing on the basis of group membership

10


• Windows 95 represents yet another major step into networking because it expands peer-to-peer networking and has the ability to connect to more kinds of networks

• Windows XP Home Continues that expansion and comes with better networking capabilities for home use

• Representing a different Windows operating system track, Windows NT 3.1 was released just a little later than Windows 3.1, but Windows NT 3.1 was intended for industrial strength networking from the beginning

11


• In 2000 Microsoft brought two new names for Windows NT: Windows 2000 Server and Windows 2000 Professional (Workstation)

• Windows 2000 has evolved into two products, Windows XP and Windows .NET Server, both containing the core elements of the Windows 2000 kernel

• Both Windows 2000 and Windows XP have built-in options to configure home and small office networks

12


• Besides the NetWare and Windows-based operating systems, there are several others designed for networking:– UNIX

– Banyan Vines

– Pathworks

– LAN Manager

• All are server operating systems that may be in use on networks, and that run on small to mid-sized computers

13

The Basics of Network Topologies

• A topology is the design of the network, as if you were looking at it from above in a helicopter, or following the path information takes when it goes from one computer to another

• The star topology is one in which there is a hub in the middle, with cable segments coming out of the hub in all directions, as shown in Figure 8-5

• The hub sends the signal onto each segment, which has a computer at the end

14

Star Topology

15

The Basics of Network Topologies

• A network hub serves as an exchange point for data to be sent from one user or device to another

• More common today in place of hubs are switches

• Switched networks use switches in place of hubs

• The switch learns what devices are located on each of the segments attached to it, and only transmits the information on the segment where the destination device resides

• Traffic is not transmitted on all segments at once, as happens on hubs

16

Packets, Frames, and Cells

• Each computer or network device translates data into individual units, and then places the units onto the network cable

• Each data unit is called a packet or frame

• These terms are sometimes used interchangeably, but they are not the same

• Both consist of data and transmission control information contained in a header that is appended to the front of the data

17


• The difference is that a packet contains routing information that can be read by specialized devices that are able to forward packets to specific networks

• The actual data is placed after the header information, and followed by a footer or trailer that enables detection of a transmission error

18


• Older networks transmit at speeds of 2 Mbps 4 Mbps (megabits per second), 10 Mbps, and 16 Mbps

• Newer networks transmit at 100 Mbps to 10 Gbps and faster, or consist of segments that transmit at 10 Mbps, 100 Mbps, 1 Gbps, or 10 Gbps

• Network backbones, which are segments that join main networks, typically run at 100 Mbps or higher

19


• A cell is a data unit designed for high-speed

communications; it has a control header and

a fixed-length payload

• The payload is that portion of a frame, packet,

or cell that contains the actual data, which

might be a portion of an e-mail message or

word-processing file

20


• One element of the cell header is path information that enables the cell to take the route through the network that is most appropriate to the type of data carried within the cell

21


• A protocol is 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 NOS and the types of devices that are connected

22

Connecting to a Network

• Computers and internetworking devices connect to a network through a network interface card (NIC)

• A NIC is usually a card that goes into a computer’s expansion slot, or that is built into a network device or a computer

• Each NIC has a unique hexadecimal address, called a device or physical address, which identifies it to the network

• It is also called the Media Access Control (MAC) address

23

Devices on a Network With Unique Physical Addresses

24

Connecting to a Network

• Some NICs also transform data into radio frequency communications for wireless networks

• The software logic consists of one or more programs called firmware because it resides in a programmable chip on the card

• Communication between the operating system and its NIC, like communication between the operating system and various input, output, and storage devices, is controlled by driver software written by the manufacturer of the device

25

Ethernet

• In Ethernet communications, only one station on the network should transmit at a given moment

• If two or more stations transmit at the same time, frames collide

• The transmission control method used by Ethernet is called Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

• In CSMA/CD, the NICs of computers and devices check the network communications cable for a carrier signal that contains an encoded frame

26

Ethernet

• 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

27

Ethernet

• Modern networks that use Ethernet are designed in a star topology, in which the internetworking devices simulate a logical bus

• Fast Ethernet (100 mb/s) is becoming commonplace, and most NICs are currently designed to handle either 10 or 100 Mbps communications

28

Ethernet

• All versions of Ethernet are compatible with popular network operating systems such as:– UNIX

– NetWare

– Windows NT, 2000, XP, and .NET Server

– Windows 3.x

– Windows 95/98/Me

– Mac OS

– Banyan Vines

– Pathworks

29

Communications Protocols

• The development of communications protocols (the protocols that carry data between two communicating stations, and are encapsulated in Ethernet or token ring transport protocols) has been interrelated to the network operating systems in which they are used

• One of the first widely accepted was the Internet Packet Exchange (IPX) protocol developed to enable a NetWare file server to communicate with its client workstations

30

Communications Protocols

• Researchers implemented and combined two protocols for use on the Advanced Research Projects Agency network, ARPANET, which was the long-distance network that set the foundation for the Internet

• The ARPANET protocols now used worldwide over the Internet are Transmission Control Protocol (TCP) and Internet Protocol (IP)

31

TCP/IP

• TCP/IP is one of the oldest protocols, initially developed for long-distance networking on ARPANET, and now used on most networks

• One of the strongest influences on TCP/IP use has been the growth of the Internet

• UNIX has always used TCP/IP as its main network communications protocol

• TCP was developed for extremely reliable point-to-point communications between computers on the same network

32

TCP/IP

• TCP/IP is also compatible with the following operating systems:

– Windows 3.1 and 3.11

– Windows 95/98/Me

– Windows NT 3.0, 3.5, 3.51, and 4.0

– Windows 2000/XP/.NET Server

– Mac OS

– Banyan Vines

33

TCP/IP

• Some of the communication functions performed by TCP are:

– 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

34

TCP/IP

• The IP portion of TCP/IP is used to make sure that a frame or packet reaches the intended destination

• IP performs the following complementary functions with TCP:

– Handles packet addressing

– Handles packet routing

– Fragments packets, 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

35

TCP/IP

• IP addressing uses the dotted decimal notation that consists of four 8-bit binary numbers (octets) separated by periods

• There are five IP address classes, Class A through Class E, each used with a different type of network

• The address classes reflect the size of the network, and whether the packet is unicast or multicast

36

TCP/IP

• In the unicast method of transmission, one copy of each packet is sent to each target destination

• In the multicast method, the recipients are placed in a group, such as a group of all eight workstations since they are on the same network

• Classes A through C are intended as unicast addressing methods, but each class represents a different network size

• Class A is used for the largest networks composed of up to 16,777,216 nodes

37

TCP/IP

• Class A networks are identified by a value between 1 and 126 in the first position of the dotted decimal address

• The network ID is the first eight bits, and the host ID is the last 24 bits

• Class B is a unicast addressing format for medium-sized networks composed of up to 65,536 nodes, and it is identified by the first octet of bits ranging from decimal 128 to 191

38

TCP/IP

• The first two octets are the network ID, and the last two are the host ID

• Class C addresses are used for unicast network communications on small networks of 256 nodes or less

• The first octet translates to a decimal value in the range of 192 to 223, and the network ID is contained in the first 24 bits, while the host ID is contained in the last eight bits

39

TCP/IP

• Class D addresses do not reflect the network size, only that the communication is a multicast

• Unlike Classes A through C, the four octets are used to specify a group of nodes to receive the multicast, which consists of those nodes that are multicast subscription members

• Class D addresses are in the range from 224.0.0.0 to 239.255.255.255

• A fifth address type, Class E, is used for experimentation, and addresses range from 240 to 255 in the first octet

40

TCP/IP

• Computers and devices that use IP addressing actually have two addresses: a physical address and an IP address

• The use of two addresses provides better insurance that a packet will reach the right destination, while expending the fewest network resources

• TCP/IP works with a range of associated protocols that make this a powerful combination for networks of all sizes and types

41

AppleTalk

• AppleTalk is a network communications protocol used between Macintosh computers

• It is designed primarily as a peer-to-peer protocol, rather than for combined peer-to-peer and client-to-server communications

• As a peer-to-peer protocol, AppleTalk establishes equal communications between networked Macintosh computers, without the need for a server

• AppleTalk performs three essential services: remote access to files over a network, network print services, and access to computers running MS-DOS or Windows operating systems

42

Peer-to-Peer Networking Using AppleTalk and No Server

43

Implementing Communications Protocols in an Operating System

• Most computer operating systems are designed to support one or more communications protocols

• In general, there are two steps involved in setting up a communications protocol in an operating system

• The first is to install the protocol software that is written for that operating system

• Step two is to bind the protocol with the NIC

44


• Binding the protocol enables the NIC to format data for that protocol, and identify the most efficient methods for transporting it within Ethernet or token ring

• When two or more protocols are used, binding also enables the NIC to set a priority for which protocol to process first

45


• The Mac OS up through version 9.x provides one of the easiest methods for setting up communications protocols

• In the Mac OS, you use a Control Panel to designate a port for network communications associated with the NIC

• In Mac OS X, setting up network communications is also simplified, but with more options than in Mac OS 9.x

46


• Through the Mac OS X Network panel, you can fully configure your Mac to use TCP/IP and TCP/IP network services, including the following:

– Manual configuration of IP address and subnet mask

– Automatic configuration of the IP address using DHCP

– Identification of the nearest router by IP address

– Identification of Domain Name Service (DNS) servers by IP address

– Identification of search domains by IP address

47


• Most UNIX systems have TCP/IP networking support built in, and some of these automatically run a network configuration program when you first boot the computer with an installed NIC

• For some versions of UNIX, including Red Hat Linux, you must configure a loopback device, which is used to provide your computer with an internal IP address, even when it is not connected to the network

48


• Communications protocols are set up in Windows 95/98/Me and Windows NT 4.0 through the Network icon in the Control Panel

49

Integrating Different Operating Systems on the Same Network

• The key to implementing multiple operating systems on one network is to select a transport protocol and communications protocols that are supported in all of the operating systems that must be connected

• Ethernet is particularly well suited to a network that has different operating systems

• In situations where TCP/IP is not supported by all operating systems, then multiple protocols can be configured, such as a combination of AppleTalk, TCP/IP, and IPX/SPX

50

Routers

• Routers are used to join networks, either locally or remotely

• Routers are designed to look at routing information in packets before forwarding those packets to another network

• Routers also make excellent firewalls because networks connected to a router can be divided into subnets as a way to control incoming and outgoing traffic to each subnet

51

Local and Wide Area Networks

• A local area network (LAN) is one in which the service area is relatively small, such as a network in an office area, or one spread through a floor in a building

• A wide area network (WAN) is one that offers networking services over a long distance, such as between cities, states, or countries

• There are several interrelated elements that can be used to determine the intersection of a LAN with a WAN

• One element is that the network topology may change between the two, such as a LAN that uses a ring topology and a WAN that uses a star

• Another factor is a change in cable type

Documents

1 Network Connectivity. 2 A network is composed of communications media such as communications cable, used to link computers, printers, disk storage,