Internet, Data Communication and Broadband Services
What this domain covers
The syllabus tests layering, addressing and the broadband access technologies a subscriber actually buys - plus the protocols and ports that make the internet work.
Core rules
- OSI has seven layers (physical, data link, network, transport, session, presentation, application); TCP/IP collapses these into four (network access, internet, transport, application).
- TCP is connection-oriented and reliable (sequence numbers, acknowledgements, retransmission); UDP is connectionless and used where latency matters more than perfect delivery.
- IPv4 is 32-bit dotted decimal; IPv6 is 128-bit hexadecimal. Private ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. 127.0.0.1 is loopback; 169.254.x.x is link-local (APIPA).
- Ports to remember: 80 HTTP, 443 HTTPS, 21 FTP, 25 SMTP, 110 POP3, 53 DNS, 67/68 DHCP, 22 SSH.
- DNS resolves names to addresses; DHCP leases addresses; neither routes packets.
- Broadband access: ADSL (asymmetric, on copper), cable (DOCSIS), FTTH/GPON, leased line, VSAT, 4G/5G fixed wireless. India's regulator has defined broadband as an always-on connection of at least 512 kbps, with consultations to raise the floor.
Worked example
Find the subnet of 192.168.1.100/26. A /26 mask is 255.255.255.192, block size 64, so subnets begin at .0, .64, .128, .192. The host lies in 192.168.1.64; usable range .65 to .126; broadcast .127; usable hosts = 64 − 2 = 62. Reasoning: subtract network and broadcast addresses from the block size.
Traps
- Swapping TCP and UDP characteristics.
- Writing port 80 for HTTPS - HTTPS is 443.
- Using a public address inside a LAN instead of a private range.
- Believing DNS performs routing.