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Q1(d) · UDP applications

2023-11-22 · Final 2023-24 / Re-exam 2022-23

Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.

Q1(d). UDP would make a good candidate as a transport protocol if reliability is not of primary importance. Justify this statement with any 5 applications of UDP. [5 marks]

Answer

User Datagram Protocol (UDP) provides connectionless, message-oriented process delivery. One send creates a datagram; message boundaries are retained. UDP has an 8-byte header, carries ports and length, and offers checksum-based corruption detection. It does not itself guarantee delivery, ordering, duplicate suppression, retransmission, flow control or congestion control.

Swipe across the diagram to read its labels ↔
UDP header: each row contains 32 bits
Diagram: UDP header: each row contains 32 bits. Labels: UDP header: each row contains 32 bits | UDP header: each row contains 32 bits | Source port · 16 | Destination port · 16 | Length · 16 | Checksum · 16 | Total 8 bytes. Length = header + UDP payload.
UDP fixed header: four 16-bit fields, eight bytes total.
UDP fieldWidthPurpose
Source port16 bitsSending endpoint; a zero value can indicate no reply port when unused
Destination port16 bitsReceiving application endpoint
Length16 bitsUDP header plus UDP payload; minimum 8 bytes
Checksum16 bitsError detection over UDP and an IP pseudo-header; not retransmission

Operation and services

  1. The application chooses the destination IP/port and supplies a message. UDP adds its header and passes the datagram to IP without a connection handshake.
  2. The receiving UDP layer validates the length/checksum as applicable and uses the destination endpoint to deliver the datagram.
  3. A corrupt or undeliverable datagram may be discarded; UDP does not recover it. Any reliability or rate-control policy must come from the application or a protocol above UDP.
  4. UDP checksum zero can mean checksum omitted in IPv4. IPv6 ordinarily requires the UDP checksum; specialized exceptions are outside this syllabus.

Yaad rakho: UDP datagram preserve; reliability automatic nahi.

Five suitable application examples

ApplicationWhy UDP can suit it
DNS queriesSmall request/reply; application retries if necessary. DNS also supports TCP.
DHCPA host without an assigned address can use UDP broadcasts to obtain configuration.
Real-time audio/video using RTPLate packets are often less useful than timely packets; application handles loss/jitter.
Online game state updatesA newer position can replace a stale one; application-specific reliability can protect critical events.
NTPSmall timestamp exchanges; a fresh later measurement can replace a lost exchange.

These are examples of applications that can use UDP, not a claim that every implementation of each application always uses UDP. Applications must still manage congestion responsibly.