Guide to Novell NetWare 3.x Administration, Enhanced Edition

Chapter 5

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Chapter 3 - Designing the Network

Describe the process of transmitting data on a NetWare LAN

Identify and describe the hardware and software that connect computers to a NetWare LAN

Apply your knowledge of LAN systems to develop a recommendation for a network system

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Computers communicate over LANs by sending blocks of data called packets Each packet contains the data to be transmitted and the

control information that the receiving computer uses to identify and process the packet

Hardware and software perform the complex task of transmitting data packets over a network

LAN communications rely on standards that allow different manufacturers to work together, and several organizations help set and control the standards that provide worldwide interoperability

LAN Communications

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The International Standards Organization (ISO) introduced the Open Systems Interconnect (OSI) model to help standardize network implementation The OSI model helps illustrate the basic principles of

network communication This seven layer model acts as a blueprint to help network

designers and developers build reliable network systems that interoperate

Each layer of the OSI model is responsible for a particular function

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The seven layers of the OSI model: The application layer consists of software that users

interact with, enabling them to do their work The presentation layer organizes data to be transmitted

into machine-readable form The session layer initiates and maintains a communication

session with the network system The transport layer manages end-to-end data delivery

using two protocols: TCP and UDP

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The seven layers of the OSI model (cont.): The network layer supplies the information needed to route

packets through the proper network paths to arrive at the destination address

The data link layer is the computer network’s delivery system and is responsible for using the destination address to send the packet through the system

The physical layer consists of the network cable system and connectors, which are responsible for transmitting the packet out as a series of bits

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The first aspect of the physical network system is the media, the transmission system used to send electronic signals Most network media used today are in the form of cables or

wires that run to each network computer Another method used to transmit signals is that of wireless,

involving light and radio waves Three major factors to be considered for medium selection:

bandwidth (transmission capacity), resistance to EMI (susceptibility to outside electrical or magnetic fields), and installation cost

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Physical Layer: Twisted-pair Cable The most common medium for LANs The cable is either unshielded (UTP) and can be affected

by external electrical voltages and magnetic fields, or is shielded (STP) and is protected from these fields by external metal foil

Made of single-strand wire pairs twisted together Twisted-pair cabling comes in six categories Two types of connectors are used on the ends of twisted-

pair cable: RJ-45 (used with UTP) and IBM data connectors (used with STP)

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Physical Layer: Coaxial Cable The name coaxial derives from the two conductors in the

cable sharing the same axis At the center of the cable is a fairly stiff wire encased in

insulating plastic, the plastic is surrounded by the second conductor, which is a wire mesh tube that also serves as a shield, and the outside is a strong insulating plastic tube

Coaxial cable is available in a variety of types and thicknesses for different purposes

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Physical Layer: Fiber-Optic Cable Fiber-optic cable looks similar to coaxial cable, but it

consists of light-conducting glass or plastic fibers at the center of a thick tube of protective cladding surrounded by a tough outer sheath

Pulses of light are transmitted through the cable by lasers or LEDs and received by photo detectors

Fiber-optic is much lighter and smaller than coaxial or twisted-pair, and can support much higher data rates over longer distances

Fiber-optic is used primarily to connect servers

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Physical Layer: Infrared Infrared is wireless medium based on infrared light from

LEDs Infrared signals can be detected by direct line-of-sight

receivers, or by indirect receivers capturing reflected signals off walls or ceilings; they cannot penetrate walls or other opaque objects

Infrared transmissions are cost-efficient and capable of high bandwidths and can be a good way of connecting wireless LANs when all computers are located in a single room or office

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Physical Layer: Narrowband Radio Radio waves are used on a wireless network to transmit

data The line-of-sight focusing that infrared requires is not

needed The workstation must be located within a reasonable

distance from the base station or hub, or the transmission quality can be poor

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The second aspect of the physical network system is the topology, the physical geometry of the network wiring Choosing the method to connect networked computers is

an important aspect of a network system that uses bounded media

Network administrators must be familiar with a network’s topology in order to attach new computers, or isolate network problems to a faulty segment of the cable

Major LAN topologies: Linear bus, ring, and star

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Physical Layer: Star Topology Derives its name from the fact that the cables radiate from

a central point, usually called the hub The hub device connects the network cables and passes

the signals from one cable to the next The type of hub you need depends on the access system

used by the network cards Star topologies are more reliable and easier to troubleshoot

than other topologies, but they are costlier due to the increased amount of cabling

Star networks are wired with a patch panel

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Physical Layer: Linear Bus Topology Connects computers in series by running a cable from one

computer to the next The method of attaching computers to the bus depends on

the network card and cable system Each end of a linear bus network requires a terminator to

prevent echo signals from interfering Primary advantages: small amount of cable needed, and

the ease of wiring computers Primary disadvantages: adding or removing computers,

and troubleshooting

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Physical Layer: Ring Topology Similar to linear bus, except the ends of the cable are

connected instead of terminated Each computer in the ring receives signals and then

retransmits them to the next computer Advantages: because signals are regenerated at each

device, they can travel longer distances, and ring is easier to troubleshoot than linear bus

Disadvantages: extra cable needed to complete the ring’s circle, difficulty adding/removing devices

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Data Link Layer Components: The data link components control the way the network

cable system transmits and receives signals, and as a result, the components selected for the data link layer determine which topologies and cable types can be used

When using an already existing cable system, select data link products that best support it

The data link layer components consist of the NICs and card driver programs

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Data Link Layer: Network Interface Cards The NIC acts as the interface between the network’s data

link and physical layers Driver software is needed to control the NIC and provide an

interface between the data link layer and network layer software

Novell has developed a set of driver specifications called the Open Data Interface (ODI)

Microsoft’s driver specifications are called the Network Driver Interface Specifications (NDIS)

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Data Link Layer: NICs (cont.) Only one signal can be sent on the network cable at any

one time, and a media access method is necessary to control when computers transmit

In the token passing method, access to the network is controlled by a token, which is a special packet passed from one computer to the next to determine which machine can use the network

In the contention access method, a node transmits a message when it detects an unused channel, this is called CSMA/CD

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Data Link Layer: Token Ring Networks IBM originally designed the token ring system Token ring consists of workstations connected by twisted-

pair cables to a central hub, or MSAU Although it may appear to be a star arrangement, the

network signals actually travel in a ring Token ring is fast, reliable, fault tolerant, and generally

easy to troubleshoot Token ring cards are more expensive than other network

cards, and the star requires extra wiring

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Data Link Layer: Ethernet Networks The members of the Ethernet family are 10Base2,

10BaseT, 100BaseT, and 1000BaseT 10Base2 is based on the linear bus topology on coaxial

cable and uses the CSMA/CD system The term 10Base2 stands for 10 Mbps baseband using

digital baseband signals over two 100-meter coaxial cable segments

10Base2 is often referred to as ThinNet and is not as prevalent today because of better 10BaseT or 100BaseT networks

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Data Link Layer: Ethernet Networks 10BaseT is based on the star topology and uses the

CSMA/CD system The term 10BaseT stands for 10 Mbps baseband using

twisted-pair cable Advantages: 10BaseT network cards are less expensive

than others; network performance is excellent under light-to-medium network loads

Disadvantages: Additional cost for wiring and concentrators, network performance is hampered when many workstations are transmitting

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Data Link Layer: Ethernet Networks 100BaseT is an extension of the 10BaseT system The term 100BaseT stands for 100 Mbps baseband

network using twisted-pair cable Advantages: higher network performance for networks

requiring fast data transmission, such as those using video Disadvantages: shorter maximum cable run lengths in

some cable systems; higher costs for higher speed hubs and NICs

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Data Link Layer: Ethernet Networks 1000BaseT networks allow half and full duplex operation at

speeds of 1000 Mbps Use the 802.3 Ethernet frame formats Use the CSMA/CD access method with support for one

repeater per collision domain Address backward-compatibility with 10BaseT and

100BaseT technologies Gigabit Ethernet products have become reliable to where

they are now used in production networks

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Data Link Layer: Bridges & Switches Bridges connect same topology networks During network operation, the bridge watches packets on

both networks and builds a table of workstation node addresses. When it sees packets destined for MAC addresses on the other network, it sends the packet out on that network

A switch can be thought of as a mulitport bridge, with each port behaving like a miniature bridge

Workstations can connect to a switch instead of a hub and have their own dedicated bandwidth

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Network Layer: Routers Routers are used to create internetworks by connecting

different topology networks Routers access datagram information containing the logical

network address and control data The router information in the datagram packet allows

allows a router to find the correct path and, if necessary, break up the datagram for transmission on a different network system

Because of this, routers require more processing time than bridges

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Protocol Stacks The network’s protocol stack is responsible for formatting

requests to access network services and to transmit data Delivering data packets throughout a network system is the

responsibility of its data link and physical layer components; the functions of the network, transport and session layers are built into a network operating system protocol stack

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Protocol Stacks: IPX/SPX IPX/SPX is Novell’s system that implements the session,

transport, and network layers Internetwork Packet eXchange (IPX) manages packet

routing and formatting at the network layer The key advantage of IPX is that it offers automatic

addressing for network nodes Sequential Packet eXchange (SPX) operates at the

transport layer and guarantees delivery of packets by receiving acknowledgements for each sent

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Protocol Stacks: NetBEUI and AppleTalk NetBEUI is Microsoft’s own protocol stack and is

integrated into Windows for Workgroups, Windows 95/98 and Windows NT products

NetBEUI is one of the easiest protocols to use, but cannot be used in large internetwork environments

The AppleTalk protocol suite was originally developed so that Macintosh computers could communicate in peer-to-peer networks, and it currently provides connectivity for a variety of computer systems

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Chapter Summary

Network communication depends on packets of information being passed from one computer to another. Understanding how information packets flow through a network system means knowing the functions of the seven layers of the OSI model. Each layer of the OSI model is responsible for a particular function, and the modular approach makes it easier to understand and work with network components

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Chapter Summary

Cable types used with today’s LANs include shielded and unshielded twisted-pair, coaxial, and fiber-optic. Infrared and narrowband radio transmission are used in wireless networks. The physical geometry of a bounded medium is called its topology. Major physical topologies include ring, linear bus, and star

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Chapter Summary

Regardless of the topology used, only one machine can transmit on a network at any given time, and with some, a method of access control must be used to avoid data collisions. Access control methods can be contention or token based. Ethernet 10Base2, 10BaseT, 100BaseT, and 1000BaseT networks use a contention system, in which computers attempt to transmit whenever they sense an open period on the network. On busy networks, however, when two or more machines sense an open period and try to transmit at the same time, a collision occurs. With the CSMA/CD system, each machine waits a random time period before retrying its transmission

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Chapter Summary

Token ring networks use the token passing system. A token is passed around the network when no data packet is being transmitted. A machine needing to transmit must wait for the token. When received, it transmits its token without any collisions. Collisions cause CSMA/CD systems to slow under heavy network transmission loads, but token passing systems offer more uniform, predictable performance. Repeaters, bridges, switches, routers are devices that enable administrators to expand networks and reduce collisions or broadcast traffic

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Chapter Summary

Protocols are the languages used to implement the OSI layers. Popular protocols encountered as a network administrator are Novell NetWare’s IPX/ SPX; TCP/IP, used by UNIX and the Internet; NetBEUI, used in Windows-based networks; and AppleTalk, for Macintosh computers. NetWare 6 servers use the IP protocol by default. Earlier versions used IPX/SPX by default, but could be configured to handle TCP/IP and AppleTalk. TCP/IP is popular in UNIX environments and international WANs, such as the Internet