CHAPTER 4: CONNECTING THROUGH A CABLED NETWORK

COMMUNICATIONS MEDIA TYPES

OSI Layer 1: communication media and interfacesFive basic communication media types Coaxial cable: based on copper wire Twisted-pair cable: based on copper wire Fiber-optic cable: glass or plastic cable Hybrid fiber/coax: combines copper and fiber Wireless technologies: radio or microwaves

The suitability of media varies with different networks

Example: uses of coaxial cable Older LANs LANs in areas with signal interference strong Connecting wireless antenna to network device

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COMMUNICATIONS MEDIA TYPES

When choosing the best medium for a LAN or WAN consider capabilities and limitations of media

Factors affecting the choice of LAN or WAN medium Data transfer speed Use in specific network topologies Distance requirements Cable and cable component costs Additional network equipment that might be required Flexibility and ease of installation Immunity to interference from outside sources Upgrade options Security

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COMMUNICATIONS MEDIA TYPES

Backbone cabling: cable that runs between network equipment rooms, floors, and buildings and is often used to connect network devices

Plenum cable: Teflon-coated cable that does not emit a toxic vapor when burned

Used in locations such as a false ceiling through which circulating air reaches other parts of a building

Impedance: total amount of opposition to the flow of current and is measured in ohms

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COAXIAL CABLE

Coaxial cable was the first media type defined with Ethernet standards (early 1980s)

Two types of coaxial cable (coax) Thick: used in early networks, typically as backbone Thin: used to connect desktops to LANs

Has much smaller diameter than thick coax

Use of both thick and thin coaxial cables declining

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THICK COAX CABLE

Thick coax cable (thickwire, thicknet, RG-8) Has relatively large .4-inch diameter Copper or copper-clad aluminum conductor at core Conductor surrounded by insulation Aluminum sleeve wrapped around insulation PVC or Teflon jacket covers aluminum sleeve

The cable jacket is marked every 2.5 m to show where a network-connecting device can be attached

If devices are attached more closely than 2.5 meters, the signal can be impaired and errors may occur

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Figure 4-1 Thick coax (RG-8) cable

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THICK COAX CABLE

Media access unit (MAU) transceiver Connecting device driven by small current (.5 amps) Has 15-pin attachment unit interface (AUI) connector

AUI connects via cable to network cable

Thick AUI cable up to 50 meters long

Impedance of thick coax cable is 50 ohms

Maximum cable segment length is 500 meters

10Base5 10 = the cable transmission rate is 10 Mbps Base = that baseband transmission is used 5 = 500 meters for the longest cable run

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Figure 4-2 Connecting to thick coax cable

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Table 4-1 Thick coax cable (10Base5) properties for Ethernet applications

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THIN COAX CABLE

Ethernet specifications for thin coax cable 50 ohms of impedance (RG-58A/U or Radio Grade 58) Meets criteria in 10Base2 designation

Maximum theoretical speed of 10Mbps Wire runs up to 185 meters (formerly 200) Used for baseband (Base) data transmission

Thin coax has a smaller diameter than thick coax (.2")

Implementing thin coax cable: Cable is attached to a bayonet nut connector (BNC) BNC is connected to a T-connector Middle of T-connector is attached to a NIC Terminator may be attached to one end of a T-connector

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Figure 4-3 A BNC T-connector with a terminator at one end

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THIN COAX CABLE

Advantages of thin coax cable Easier and cheaper to install than thick coax More resistant to EMI and RFI (interferences) than twisted pair

Coax is still found on some legacy networks and in places subject to very high EMI/RFI

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Table 4-2 Thin coax cable (10Base2) properties for Ethernet applications

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TWISTED PAIR CABLE

Twisted-pair cable Contains pairs of insulated copper wires Outer insulating jacket covers wires

Communication specific properties Copper wires twisted to reduce EMI and RFI Length: up to 100 meters Transmission speed: up to 10 Gbps

RJ-45 plug-in connector attaches cable to device Less expensive and more flexible than T-connectors

Two kinds of twisted pair cable: shielded and unshielded (preferred)

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Figure 4-4 Twisted-pair cable with an RJ-45 plug-in connector

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SHIELDED TWISTED PAIR CABLE

Shielded Twisted Pair Cable (STP) Surrounded by braided or corrugated shielding Shielding reduces interference due to EMI and RFI

Further reducing impact of EMI and RFI Interval of twists (lay length) in each pair should differ Connectors and wall outlets should be shielded Have proper grounding

Use medium when strong interference sources nearby Example: heavy electrical equipment

Shielded cable and associated equipment is more expensive than unshielded cable

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Figure 4-5 STP and UTP cables

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UNSHIELDED TWISTED-PAIR CABLE

Unshielded Twisted-Pair Cable (UTP) Consists of wire pairs within insulated outer covering Has no shielding between wires and encasement

UTP is the most frequently used network cable

Reducing EMI and RFI Twist interior strands (like STP) Built-in media filter into network equipment, workstation, and file connection

servers

UTP cables used in 10BaseT networks Category 3: transmission rates up to 16 Mbps Category 4: transmission rates up to 20 Mbps

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UNSHIELDED TWISTED-PAIR CABLE

Category 5 UTP has 100 Mbps transmission rate

Category 5e (enhanced) UTP vs. Category 5 UTP 1 Gbps transmission rate Uses better-quality copper Has a higher twist ratio for better EMI/RFI protection

Category 6 UTP Wire pairs are wrapped within insulating foil Has fire resistant plastic sheath 1 Gbps transmission rate

Category 7 UTP Extremely resistant to EMI/RFI but it requires special connectors and is not as

flexible

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Table 4-3 Ethernet twisted-pair cable standards

http://www.singlepointnetworks.co.uk/cat8cable.asp

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UNSHIELDED TWISTED-PAIR CABLE

Reasons for preferring UTP over STP Fewer points of failure Has no shield that can tear (up through Category 5e) Connectors and wall outlets do not need shielding Proper grounding not as critical to purity of signal

Horizontal cabling (defined by EIA/TIA-568 standard) Cabling connecting workstations/servers in work area Implemented with Categories 5e, 6, and 6e UTPs

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Table 4-4 10BaseT (and in general 100BaseX) unshielded twisted-pair Ethernet specifications

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Table 4-5 10BaseT (and in general 100BaseX) shielded twisted-pair Ethernet specifications

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Figure 4-7 Twisted-pair cable connected to an RJ-45 connector

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FIBER-OPTIC CABLE

Fiber-optic cable One or more glass or plastic fiber cores encased in glass tube (cladding) Fiber cores and cladding are surrounded by PVC cover Signal transmissions consist of light (usually infrared)

Three commonly used fiber-optic cable sizes 50/125 micron

Micron (μm): millionth of a meter 50 represents core diameter 125 represents cladding diameter

62.5/125 micron 100/140 micron

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Figure 4-9 Fiber-optic cable

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FIBER-OPTIC CABLE

Uses of fiber-optic cables Cable-plant backbones

Fat pipe: high bandwidth backbone between floors Connect different buildings in campus environment Joining spread-out LANs into a WAN

Advantages of fiber-optic cables Each cable type has multimode transmission capacity Transmission speeds from 100 Mbps - over 100 Gbps No EMI or RFI problems, data travels by light pulse Low attenuation (attenuation: signal loss during travel) Secure from unauthorized taps

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FIBER-OPTIC CABLE

Disadvantages of fiber-optic cables Fragile More expensive than UTP Requires specialized training to install

Basic characteristics of light transmission Light wavelength is measured in nanometers (nm) Infrared light travels in the range of 700 -1600 nm Three ideal wavelengths (windows): 850 nm, 1300 nm, 1550 nm High-speed transmission typically use the 1300 nm window

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FIBER-OPTIC CABLE

Fiber-optic cable comes in two modes Single-mode: used for long-distance communication

8-10/125 micron cable transmits one wave at a time Communications signal is laser light

Multimode: supports multiple waves (broadband) Comes in two varieties: step index and graded index Cable diameter between 50 and 115 microns Source for multimode cable is light-emitting diode (LED)

Three connector types used with fiber-optic cables Subscriber connector (SC) Straight tip (ST) MTRJ

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Table 4-6 EIA/TIA-568-B specifications for single-mode fiber-optic cable in a cable-plant backbone

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Table 4-7 EIA/TIA-568-B specification for multimode fiber-optic cable in a cable-plant backbone

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HYBRID FIBER/COAX CABLES

Hybrid fiber/coax (HFC) cable Single sheath containing fibers and copper cables Different combinations for different implementations

How HFC cables improve cable networks Increase upstream bandwidth and reduce noise

HFC drawbacks: expensive and not fully installed

Services possible using HFC cables Plain old telephone service (POTS) Over 200 digital TV channels Over 400 digital point channels High-speed, two-way digital data link for PCs

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HIGH-SPEED TECHNOLOGIES FOR TWISTED-PAIR AND FIBER-OPTIC CABLE

High-speed threshold: 10 Mbps

Three technologies enhancing cables for high-speed Fast Ethernet Gigabit Ethernet 10 Gigabit Ethernet 40 and 100 Gigabit Ethernet

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FAST ETHERNET

Fast Ethernet: 100 Mbps data transfer over twisted-pair cable

Two Fast Ethernet technologies 100BaseVG or 100VG-AnyLAN 100BaseX

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THE IEEE 802.3U STANDARD

IEEE 802.3u (100BaseX): standard for Fast Ethernet Versions of 100BaseX: 100BaseT, 100BaseTX, 100BaseT4, 100BaseT2,

100BaseFX

Common properties of standards (except 100BaseT2) All use CSMA/CD media access methods All propagate signal in more than one direction

100BaseT2 transmits signal in timed-delay manner

Signal transmitted with twisted-pair or fiber-optic cable

Limitations and restrictions Signal can only go through one Class I repeater or two Class II repeaters

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THE IEEE 802.3U STANDARD

A Class I repeater introduces delays when performing the Fast Ethernet conversion

For this reason, only one Class I repeater can be put in a single, Fast Ethernet LAN segment

Class II repeaters have all ports of the same Fast Ethernet media type so there is no need for a conversion

Very little delay is introduced by the quick movement of data For this reason, two Class II repeaters are allowed per Fast Ethernet

segment

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Table 4-8 100BaseX communication options

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THE IEEE 802.12 STANDARD

IEEE 802.12: (100BaseVG/100VG-AnyLAN) Abandons CSMA/CD for demand priority

Demand priority Ensures signal travels in one direction Used in star networks linked by a central switch Grants requests one by one

Benefits of demand priority Enables packet travel up to 100 Mbps Security: packet visible only to receiving node Prioritizes multimedia and time sensitive transmissions

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Figure 4-13 Using demand priority

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GIGABIT ETHERNET

Gigabit Ethernet (1000BaseX) Provides data transfer of up to 1 Gbps Uses CSMA/CD access methods Upgrade path for 100BaseX Ethernet networks

Uses of Gigabit Ethernet Alternative for backbone LAN congestion Attract token ring users with star-based topologies

Gigabit Ethernet target Installations using Layer 3 routed communications

Separate standards for fiber-optic and twisted-pair cables

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Table 4-9 Gigabit Ethernet specifications

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10 GIGABIT ETHERNET

10 Gigabit Ethernet or 10GBaseX High-speed networking protocol Competes with other high-speed MANs and WANs Provides fast backbone networking in LANs

True Ethernet with some differences Operates at full duplex (transmission in two directions)

Does not need to employ CSMA/CD No packet collisions by design

How to distinguish various standards By interfaces and transmission characteristics

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40 AND 100 GIGABIT ETHERNET

40 Gigabit (40GBaseX/40GBaseE) and 100 Gigabit (100GBaseX/100GBaseE) are relatively new high-speed Ethernet options

Both are intended to serve two purposes: Enable faster computing services, such as through faster backbone

speeds Provide faster communications for network aggregation points, such

as links to servers and network storage

Shared resources such as Internet Protocol television (IPTV) and streaming media require faster backbone speeds

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40 AND 100 GIGABIT ETHERNET

Network aggregation – refers to central resources such as servers and network storage

Gigabit Ethernet is intended to remove network transport bottlenecks surrounding these aggregated resources

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Table 4-11 40 Gigabit Ethernet specifications

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Table 4-12 100 Gigabit Ethernet specifications

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CONNECTING COMPUTERS TO A CABLED NETWORK

Network Interface Card (NIC) Enables node to connect to cabled network Matches transport methods, bus types, and media

Network connection requires four components Appropriate connector for network medium Hardware and protocol control firmware and drivers Transceiver Controller to support MAC sublayer of Data Link layer

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THE NIC CONNECTOR

Connector designed for specific medium type Examples: twisted-pair, fiber-optic cable, wireless

Older combination NICs have multiple connectors May be used with different media

Newer combination NICs have single connector Select one among: 10BaseT, 100BaseX, 1000BaseTX

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THE ROLE OF FIRMWARE AND NIC DRIVERSFirmware and NIC driver support communications Firmware: software stored on a chip, such as ROM NIC Driver: manages how packets or frames sent

Firmware or driver may automatically detect media

Some NIC drivers can be signed

Driver signing: placing digital signature in driver

Functions of digital signature Ensures driver compatible with operating system Certifies that driver tested for defects or viruses Ensures that driver cannot overwrite new driver

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USING A TRANSCEIVER

Cable connector is attached to transceiver

Transceiver: device that transmits and receives signals on a communications cable

Transceiver may be internal or external to NIC

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THE ROLE OF THE MAC CONTROLLER UNIT

MAC controller unit and firmware work together to encapsulate: Source and destination address information Data to be transported CRC error control information

MAC Controller operates at two sublayers of Layer 2 MAC sublayer: formats frames LLC sublayer: initiates and maintains link between nodes and ensures the

communications link is not broken and remains reliable after it is established

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HALF- AND FULL-DUPLEX NIC COMMUNICATIONS

Two transmission modes for NIC and network equipment Half-duplex: cannot send and receive at the same time Full-duplex: can send and receive simultaneously

Made possible by buffering at NIC Buffering: temporarily storing information

Full-duplex is a good choice on networks Usually faster than half-duplex

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BUSES AND NICS

Bus: data pathway inside the computer

Common bus types (standards) Industry Standard Architecture (ISA) Extended Industry Standard Architecture (EISA) Microchannel Architecture (MCA) Peripheral Computer Interface (PCI) SPARC Bus (SBUS) Universal Serial Bus (USB)

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CHOOSING A NIC

Every NIC is critical for effective communication

Questions to consider when purchasing a NIC Is NIC for host computer, server, or workstation? What kind of throughput does the computer require? What network media and transport methods are in use? Who manufactures the NIC? What is the computer or network equipment bus type? What operating system is used by the computer? Are half-duplex or full-duplex communications used? If NIC is for a special application, how does it attach?

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DESIGNING A CABLED NETWORK

Design choices applicable to most networks Use Ethernet as the transport method Use twisted pair to the desktop Employ fiber-optic cable for the backbone Connect servers to the network at 1 Gbps or 10 Gbps Use the best and fastest options within budget

Scenario: small credit union in two story building Use star-bus hybrid topology Run 100BaseT to computers on both floors Fiber-optic cable run for backbone between floors Connect servers using 1000BaseTX or 10GBaseF

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Figure 4-18 Designing a network for a small credit union

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SUMMARY

High-speed technologies for twisted-pair and fiber-optic cabling include Fast Ethernet, Gigabit Ethernet, 10 Gigabit Ethernet, 40 Gigabit Ethernet, and 100 Gigabit Ethernet

NICs have an important role on networks because these devices connect computers and network devices to network cable.

Important NIC components on a cabled network include a connector, firmware and drivers, a transceiver, and a MAC controller.

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