1. Bandwidth

2. Learning Objectives: explain the importance of bandwidth when transmitting data; explain how different types of communication media govern the bandwidth available ; cables, wireless, optical

3. Bandwidth maximum transmission rate of a communications channel –measured in bits per second (bps) –Kbps, Mbps, Gbps a measure of the capacity of a communications channel

4. Why is Bandwidth important? the greater the bandwidth: –the more information the channel can carry, –the faster the information can travel to its destination –more users connected to the network without loss of speed multimedia data require high bandwidth connections –due to the large size of the data files  1 track mp3 = 4MB = 32Mbits  HD video requires 4x bandwidth of standard –low bandwidth = ‘jerky’ & unsynchronised video –need high bandwidth for streaming or video conferencing e.g. iPlayer, YouTube, Skype

5. Bandwidth CommunicationsBandwidth Dial-up (modem/telephone line) 56Kbps Broadband (ADSL)up to 20Mbps Wireless (WiFi)54Mbps LAN (wired)100Mbps (1Gbps) Leased Line (DSL)up to 1Gbps

6. ADSL Broadband Advantages: uses existing copper telephone line for connection to the Internet –no extra installation of cable is required (good for domestic installation) ADSL provides an ‘always on' Internet access –telephone can be used at the same time. Disadvantages: needs to be connected to a telephone exchange within a workable distance –no use for remote locations downstream bandwidth is different to the upstream bandwidth. –downstream bandwidth is greater than upstream majority of ADSL connections used to download from the Internet, –takes longer to upload an image than to download –takes longer send an email with attachments than to receive

7. ADSL Broadband Factors which affect the bandwidth on ADSL: distance from the telephone exchange electrical interference on the telephone line local AM radio stations causing interference other devices connected to the telephone line –e.g. fax machines

8. Learning Objectives: explain how different types of communication media govern the bandwidth available ; cables, wireless, optical

9. Bandwidth CommunicationsBandwidth Copper cable (LAN)100Mbps (1Gbps) Fibre Optic (LAN/WAN)20Mbps Wireless (WiFi, WLAN)54Mbps Mobile (GPRS)~100Kbps Mobile (3G)7Mbps

10. Copper Cable used to cable LANs data is sent via electrical pulses –using copper wire 100Mbps bandwidth most common –1Gbps & 10Gbps possible relatively cheap to install –compared to optical cables limited to ~100m maximum length –beyond this the data signal becomes too weak prone to electrical interference –results in corrupted or lost data packets –reducing the overall data transmission rate

11. Optical Cable used to cable LANs over long distances –>100m  100+km uses infra-red lasers to convert data into light pulses –electrical 0s & 1s converted into light on/light off pulses uses optical cable (fibre optic cable) to carry the data cable consists of multiple thin glass strands

12. Optical Cable

13. used to cable LANs –over long distances (>100m  100+km) uses infra-red lasers to convert data into light pulses –electrical 0s & 1s converted into light on/light off pulses uses optical cable (fibre optic cable) to carry the data cable consists of multiple thin glass strands not susceptible to electrical interference –very little data loss –higher transmission rates than copper cables

14. Optical Cable used to cable LANs –over long distances (>100m  100+km) uses infra-red lasers to convert data into light pulses –electrical 0s & 1s converted into light on/light off pulses uses optical cable (fibre optic cable) to carry the data cable consists of multiple thin glass strands not susceptible to electrical interference –very little data loss –higher transmission rates than copper cables >10Tbps bandwidth possible –domestic cable ~20Mbps (Virgin Media cable ADSL)

15. Wireless used to connect LANs –over short distances (<100m) bandwidth less than copper cable or fibre optics –54Mbps 802.11n most common (2010) –~100Mbps now possible with 802.11n distance limited to ~50m indoors (100m outdoors) –signal attenuated by walls, steel …. prone to electrical interference –microwave ovens, mobile ‘phones, X-ray machines … –results in corrupted data packets & reduced data rate