1

Module 4

PHYSICAL MEDIA

2

Physical Media Types Covered

• Coaxial Cable• Twisted Pair• Fiber Optic Cable • WAN Cables

7

6

5

4

3

2

1

3

Coaxial Cables• 10Base2 (ThinLAN) - 10 Mbps baseband, 2 for 200 (actually 185 meters)

• 10Base5 (ThickLAN) - Maximum data transfer speed of 10 Mbps, uses baseband transmission; 500 meters maximum cable length

Baseband transmission is a type of digital data transmission in which each medium (wire) carries only one signal, or channel, at a time. In contrast, Broadband transmission enables a single wire to carry multiple signals simultaneously.

4

Coax - 10Base2 (ThinLAN)

• Cable Type - RG-58A/U

• Impedance - 50

• Terminated with 50 terminators

• Connection method - BNC (as opposed to the F connector used for cable TV)

• Grounding - As determined by local electrical code

5

Coax - 10Base2 Rules

• Minimum distance between two nodes: 0.5m (1.64 ft)

• Maximum number of nodes / segment: 30

• Maximum segment length: 185m (606.7 ft)

6

Coax - 10Base5 (Thick LAN)

• Impedance - 50

• Terminated with 50 terminators

• Connections - ‘N’ type connections to terminate. ‘Vampire’ tap for node connections.

• Grounding - Grounded at one point only.

7

Coax - 10Base5 Rules

• Minimum Distance between two nodes: 2.5m

• Maximum number of nodes / segment: 100

• Maximum segment length: 500m

8

WARNING

Breaking any of these rules will cause excessive error conditions!

9

Twisted Pair Cable

• Cable Type: Low grade telephone cable through to cat.5. (data cables normally cat.3 to cat.5)

• Shielding: Shielded (STP) Unshielded (UTP)

• Connectors: RJ45, Telco, IBM Type 1 connector (genderless), 9 pin.

• Use: 10BaseT, 100BaseTX, 100VG ANYLAN, Token Ring

10

Twisted Pair Rules

• Cable must be twisted

• Maximum distance depends on quality of cable, shielding and speed of transmission

• Maximum cable length for Cat3, Cat4 and Cat5 is 100m

11

Fiber Optic

• Cable type determined by - diameter of core, diameter of cladding (e.g.. 62.5 /125)

• Light source - Single mode- Laser, Multimode - LED

• Connectors - SC, ST, MIC

• Use - FOIRL, 10BaseFL, FDDI, 100BaseF, Fiber Channel, SONET/SDH (for WAN) Gigabit Ethernet (future)

12

FOIRL: Fiber Optic Inter-Repeater Link is a vendor independent standard means for connecting only 2 repeater units based on the IEEE 802.3 fiber optic specification. It is being replaced by 10BaseFL. 10BaseFL segments can be up to 2000 meters.

FDDI: Fiber Distributed Data Interface handles data rates of up to 100Mbps; typical application: used as backbone for campus and wide-area networks. FDDI networks are token-passing networks, using dual-ring topology over fiber-optic transmission media.

Fiber Channel is a technology for serially transmitting data between computer devices at a data rate of up to 1 Gbps.

SONET/SDH: Synchronous Optical Network is an optical fiber-based network standard; handles 51.8Mbps to 2.48Gbps. SDH is its international equivalent.

13

Fiber Optic Rules

• Maximum distance determined by type of cable and light source used.

• Need to ensure cable connection is from TX on one device to RX on the other

14

Fiber Optic Safety Considerations

• Never look at the output of a fiber optic transmitter

• Do not handle unterminated fiber

• Do not attach connectors to fiber as special skills and tools are required.

15

WAN Cables

• Cable Type: Various

• Shielding: Shielded & Unshielded cable

• Connectors: RS232 (‘D’ type 25, 15, 9 pin), X.21, V.35

• Common pairs use: TX/RX, CTS/RTS, Control/Indicate

• Uses: RS232, X.21, V.35

16

WAN Cable Rules

Cable Distance + Cable quality = Maximum Speed

17

Cable Connectivity

TO PSTN/NETWORK

MODEMPC

TO PSTN/NETWORK

MODEMROUTER

HUBPC

PC

PC

HUB

TWISTED PAIRLAN CABLE

WAN CABLE

WAN CABLE

Host connection to network device in a LAN environment

End system to network access point (WAN environment)

18

Simple RS232 25 pin straight through DTE/DCE

TX RX

RX TX

PIN 2

PIN 3 PIN 3

PIN 2

TO PSTN/NETWORK

DCEDTE

PC

19

Logical pinout groupings

DATA

CONTROL

Pinouts used to transferthe data (such as TX/RX)

Pinouts used to control theflow of data such as RTS/CTS(used in DTE/DCE handshaking)

20

Use of straight through and cross over cabling

TX RXRX TX

PIN 2

PIN 3 PIN 3

PIN 2

DCEDTE

DTE DTE

PIN 4

PIN 5 PIN 5

PIN 4 CTSRTS

MODEM

PC

RTSCTS

TX TXRX RX

PIN 2

PIN 3 PIN 3

PIN 2

PIN 4

PIN 5 PIN 5

PIN 4 RTSCTS

RTSCTS

NOTE: More pinouts may be required

21

Twisted pair cable connectivity in a LAN environment

MDI-XMDI

PC

HUB

LANcard

MDI=Media Dependent Interface

X in MDI-X=Crossed

MDI (for LAN) is equivalent to DTE (for WAN) & MDI-X (for LAN) is equivalent to DCE (for WAN).

22

MDI to MDI-X connectionMDI-XMDI

PC

HUB

12

36

12

36

Twisted pair cabling

23

Use of straight through and cross over cabling

MDI

PC

STRAIGHTTHROUGH

CABLE

MDI-X

HUB

MDI-XMDI

PC HUB

MDI

ROUTER

MDI-X

SWITCH

CROSSOVER

CABLE

CROSSOVER

CABLE

STRAIGHTTHROUGH

CABLE

Hubs and Switches are MDI-X devicesHosts and Routers are MDI devices

24

Summary• Media Types

- Coaxial Cable- Twisted Pair- Fiber- WAN Cables

• Safety Considerations for Fiber

• Connectivity Conventions- WAN Cables = DTE/DCE- Twisted Pair LAN = MDI/MDI-X