Transmission Media II (06.523) Types and properties of physical transmission media II

Characteristics and limitations Memorise table from workbook :-(

Electrical signalling Analogue signals on analogue networks Digital signals on digital networks Digital signals on analogue networks Analogue signals on digital networks

Connection standards ITU-TSS (International Telegraph Union - Telecommunications Standardisation Sector) V. series (DTE to PSTN) X. series (DTE to Public Digital Data Network) I. Series (DTE to Integrated Service Digital Network)

Control lines Purpose Typical lines

Example: RS232-C 25 pin 1. Shield 2. Transmitted Data (TXD) 3. Received Data (RXD) 4. Request to Send (RTS) 5. Clear to Send (CTS) 6. DCE Ready (Data cable enable?) 7. Signal ground …

Example: RS232-C 9 pin 1. Carrier Detect (CD) 2. Receive Data (RXD) 3. Transmit Data (XD) 4 Data Terminal Ready (DTR) 5. Signal Ground (SG) 6. Data Set Ready (=DCE) 7. Request To Send (RTS) 8. Clear To Send (CTS) 9. Ring Indicator (RI)

Signal attenuation What is it Why is it important Types of errors –extra bits –missing bits –flipped –set to zero/one

Common causes White noise (unavoidable) Impulse noise or spikes Cross talk from multiplexing Intermodulation noise from interference Echoes from inadequate termination Attenuation from too long cables Delay distortion (Sync. Freq. timings) Jitter (Imperfect digital -> analogue) Line outage

Error prevention Shielding Moving cables Changing multiplexing (cross talk) Improving connection quality Amplifiers Equaliser (syncs freq. timings) Conditioning (certified)