1. 1 Version 3.0 Module 3 Networking Media

2. 2 Version 3.0 Cable Specifications Cables have different specifications and expectations pertaining to performance: –What speeds for data transmission can be achieved using a particular type of cable? –What kind of transmission is being considered? –How far can a signal travel through a particular type of cable before attenuation of that signal becomes a concern? 3.1.6

3. 3 Version 3.0 Cable Specifications Some examples of Ethernet specifications which relate to cable type include: –10BASE-T –10BASE5 –10BASE2 10BASE-T refers to the speed of transmission at 10 Mbps. The type of transmission is baseband, or digitally interpreted. The T stands for twisted pair. 3.1.6

4. 4 Version 3.0 Coaxial Cable Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements, located in the center of the cable, is a copper conductor. Surrounding the copper conductor is a layer of flexible insulation. Over this insulating material is a woven copper braid or metallic foil that acts as the second wire in the circuit and as a shield for the inner conductor. 3.1.7

5. 5 Version 3.0 Coaxial Cable 3.1.7

6. 6 Version 3.0 Coaxial Cable For LANs, coaxial cable offers several advantages. –It can be run longer distances than shielded twisted pair, STP, and unshielded twisted pair, UTP, cable without the need for repeaters. –Coaxial cable is less expensive than fiber-optic cable, and the technology is well known. 3.1.7

7. 7 Version 3.0 Shielded Twisted-Pair Shielded twisted-pair cable (STP) combines the techniques of shielding, cancellation, and twisting of wires. Each pair of wires is wrapped in metallic foil. The four pairs of wires are wrapped in an overall metallic braid or foil. STP affords greater protection from all types of external interference, but is more expensive and difficult to install than UTP. The metallic shielding materials in STP need to be grounded at both ends. 3.1.8

8. 8 Version 3.0 Unshielded Twisted-Pair Unshielded twisted-pair cable (UTP) is a four-pair wire medium used in a variety of networks. Each of the 8 individual copper wires in the UTP cable is covered by insulating material. In addition, each pair of wires is twisted around each other. This type of cable relies solely on the cancellation effect produced by the twisted wire pairs, to limit signal degradation caused by EMI and RFI. CAT 5 is the one most frequently recommended and implemented in installations today. 3.1.9

9. 9 Version 3.0 Unshielded Twisted-Pair Unshielded twisted-pair cable has many advantages. It is easy to install and is less expensive than other types of networking media. However, the real advantage is the size. Since it has such a small external diameter, UTP does not fill up wiring ducts as rapidly as other types of cable. 3.1.9

10. 10 Version 3.0 Optical Media The laws of reflection and refraction illustrate how to design a fiber that guides the light waves through the fiber with a minimum energy loss. The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction: –The core of the optical fiber has to have a larger index of refraction (n) than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding. –The angle of incidence of the light ray is greater than the critical angle for the core and its cladding. When both of these conditions are met, the entire incident light in the fiber is reflected back inside the fiber. This is called total internal reflection, which is the foundation upon which optical fiber is constructed. 3.2.5

11. 11 Version 3.0 Optical Media The part of an optical fiber through which light rays travel is called the core of the fiber. If the diameter of the core of the fiber is large enough so that there are many paths that light can take through the fiber, the fiber is called “multimode” fiber. Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber. 3.2.6

12. 12 Version 3.0 Optical Media Every fiber-optic cable used for networking consists of two glass fibers encased in separate sheaths. One fiber carries transmitted data from device A to device B. The second fiber carries data from device B to device A. This provides a full-duplex communication link. 3.2.6

13. 13 Version 3.0 Multimode Fiber-Optic Cable A standard multimode fiber-optic cable uses an optical fiber with either a 62.5 or a 50-micron core and a 125- micron diameter cladding. This is commonly designated as 62.5/125 or 50/125 micron optical fiber. A micron is one millionth of a meter (1µ). 3.2.6

14. 14 Version 3.0 Single-Mode Fiber-Optic Cable Single-mode fiber consists of the same parts as multimode. The outer jacket of single-mode fiber is usually yellow. The major difference between multimode and single-mode fiber is that single-mode allows only one mode of light to propagate through the smaller, fiber-optic core. The single-mode core is eight to ten microns in diameter. Nine-micron cores are the most common. 3.2.6

15. 15 Version 3.0 Single-Mode Fiber-Optic Cable Because of its design, single-mode fiber is capable of higher rates of data transmission (bandwidth) and greater cable run distances than multimode fiber. Single-mode fiber can carry LAN data up to 3000 meters. Multimode is only capable of carrying up to 2000 meters. Lasers and single-mode fibers are more expensive than LEDs and multimode fiber. Because of these characteristics, single-mode fiber is often used for inter-building connectivity. 3.2.7

16. 16 Version 3.0 Wireless Networks The IEEE 802.11 standard was developed for wireless networks. Key technology contained within the 802.11 standard is Direct Sequence Spread Spectrum (DSSS). DSSS applies to wireless devices operating within a 1 to 2 Mbps range. A DSSS system may operate at up to 11 Mbps but will not be considered compliant above 2 Mbps. 3.3.1

17. 17 Version 3.0 Wireless Networks The IEEE 802.11b standard increased transmission capabilities to 11 Mbps. 802.11b may also be called Wi-Fi™ or high-speed wireless and refers to DSSS systems that operate at 1, 2, 5.5 and 11 Mbps. 802.11b devices achieve the higher data throughput rate by using a different coding technique from 802.11, allowing for a greater amount of data to be transferred in the same time frame. 3.3.1

18. 18 Version 3.0 Wireless Networks A wireless network may consist of as few as two devices. The nodes could simply be desktop workstations or notebook computers. Equipped with wireless NICs, an ‘ad hoc’ network could be established which compares to a peer-to-peer wired network. A problem with this type of network is compatibility. Many times NICs from different manufacturers are not compatible. To solve the problem of compatibility, an access point (AP) is commonly installed to act as a central hub for the WLAN "infrastructure mode". 3.3.2

19. 19 Version 3.0 Wireless Networks Performance of the network is affected by signal strength and degradation in signal quality due to distance or interference. The transmitting unit will drop the data rate from 11 Mbps to 5.5 Mbps, from 5.5 Mbps to 2 Mbps or 2 Mbps to 1 Mbps. 3.3.3

20. 20 Version 3.0 Wireless Networks When a source node sends a frame, the receiving node returns a positive acknowledgment (ACK). This can cause consumption of 50% of the available bandwidth. This overhead when combined with the collision avoidance protocol overhead reduces the actual data throughput to a maximum of 5.0 to 5.5 Mbps on an 802.11b wireless LAN rated at 11 Mbps. 3.3.3