1. 1 COMS 161 Introduction to Computing Title: Local Area Networks Date: September 27, 2004 Lecture Number: 14

2. 2 Announcements This material is from chapter 17 in the book

3. 3 Review Connecting to the Digital Domain

4. 4 Outline LANs

5. 5 Differentiating LANs Transmission media –What are the actual hardware connections between nodes (computers) made from? Topologies –In what way are the various nodes arranged and interconnected?

6. 6 Transmission Media Bounded media –Coaxial cable (like a TV cable) –“Twisted-pair” cable (copper wires) –Optical fiber cable Unbounded media (wireless networking) –RF (radio frequency) –IR (infrared) –Cellular modem

7. 7 Transmission Media Bounded media –Coaxial cable (like a TV cable) Original LAN installations were coax Now almost never used (cost) –“Twisted-pair” cable (copper wires) Generally limited to about 100 meters max (330 ft) Telephone wire (“CAT-3”, or “category 3”) CAT-5 wiring (up to 10 Mbps – 10 million bits per second) CAT-5e wiring (up to 100 Mbps) CAT-6 wiring (emerging “gigabit” standard – up to 1 Gbps)

8. 8 Transmission Media Bounded media (cont’d) –Optical fiber cable Signal is composed of pulses of laser light, not electricity Extremely thin glass strand transmits the light pulse Lower error rates and high data bandwidth (>2 Gbps) Becoming very cost-effective for high speed data needs

9. 9 Transmission Media Unbounded media (wireless networking) –RF (radio frequency) Becoming very common Speeds of 11 Mbps now common (“802.11b”) Faster speeds becoming available (54 Mbps, 108 Mbps) Public access points (“hotspots”) becoming common –Various areas on campus –Downtown areas, such as Manhattan –Airports, hotels, coffee shops, etc. (free or pay)

10. 10 Transmission Media Unbounded media (cont’d) –IR (infrared) An early wireless technique, now mostly unused as RF wireless has advanced Required line-of-sight – works well only within enclosed spaces Still used for some simple ad hoc networking tasks, such as –Laptop-to-PDA –PDA-to-printer –Digital camera uploads –Etc.

11. 11 Transmission Media Unbounded media (cont’d) –Cellular modem Wireless connectivity anywhere that there is appropriate digital cellular service –Various cellular companies are competing –Coverage is still spotty, but improving Up to 120 Kbps – better than dialup

12. 12 Transmission Media NETWORKS ARE BUILT ON PHYSICAL MEDIA TypeUses Maximum Operating Principal Distance (without amplification) Cost Twisted pairSmall LANs300 feetLow Coaxial cableLarge LANs600–2,500 feetMedium Fiber opticNetwork backbones; WANs1–25 milesHigh Wireless/infraredLANs3–1,000 feet (line of sight)Medium Wireless/radioConnecting things that moveVaries considerablyHigh