Telecommunication Networks and Transmission Media
This domain tests how networks are layered and how the physical medium limits distance, speed and immunity to interference. Questions mix OSI/TCP-IP layer matching with practical cable selection and structured-cabling rules.
Core rules
- OSI layers: physical, data link, network, transport, session, presentation, application. TCP/IP maps to application, transport, internet and network access.
- Encapsulation produces segments at transport, packets at network and frames at data link.
- UTP categories: Cat5e supports 1 Gbps to 100 m; Cat6 supports higher rates over shorter runs. The 100 m channel is 90 m horizontal cable plus 10 m of patch cords.
- Coax is 75 Ω for TV/CATV; fibre suits long distance and EMI-heavy routes; radio provides mobility.
- Star topology dominates LANs; mesh is resilient; bus and ring are legacy. A hub shares a collision domain; a switch separates it.
- Attenuation, crosstalk and duplex mismatch are common impairments. TIA-568 and ISO/IEC 11801 govern structured cabling.
Worked example
A desktop is 78 m of cable route from the IDF. Allow 3 m slack at each end and 2 m patch cords at each end: 78 + 6 + 4 = 88 m, inside the 100 m UTP channel limit. A second desk is 96 m route distance; with the same allowances it reaches 106 m, so the design must add an intermediate switch or use fibre, not a longer patch cord.
Traps
Assuming a switch divides collision and broadcast domains equally; calling a hub a switch; using Cat6 as a licence for 150 m; forgetting patch cords count in the 100 m; confusing MAC at data link with IP at network; ignoring EMI near power cables.