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Network-Based Multimedia (INT338) Final Exam Questions and Answers

What is QoS (Quality of Service)?

Network provides application with level of performance needed for application
to function.

What are the multimedia performance requirements?

Deliver data in timely manner. Interactive multimedia requires short end-end
delay while streaming multimedia needs timely arrival for smooth playout. 100%
reliability not always required.

What is the simplest internet multimedia approach?

Audio/video stored in file, transferred as HTTP object, received entirely at
client then passed to player. No pipelining, long delays until playout.

How does streaming multimedia approach work?

Browser GETs metafile, launches player which contacts server. Server streams
audio/video to player. Uses separate control and data connections.

Why is client buffering needed in streaming?

To equal for network delay and delay jitter. Buffered video allows
constant bit rate playout despite variable network delay.

What is RTSP and its purpose?

Real Time Streaming Protocol (RFC 2326) for user control: rewind, fast-forward,
pause, resume. Uses out-of-band protocol with separate ports for control and
media, and using TCP and UDP for control MSG connection.

What is delay jitter?

Variation in packet arrival times caused by network congestion, routing changes
or processing delays. For example in real-time applications like video conferencing.

What are the components of QOS guarantees?

Available bandwidth for flows, delay bounds, low jitter (variation in delay),
and packet loss.

What are service provider QoS goals?

Traffic classes for differential pricing, service level agreements (SLAs) about
bandwidth/delay, and admission control to manage network usage.

Why new service models needed?

To maximize user satisfaction (utility) rather than just bandwidth/latency.
Different applications have different utility vs bandwidth needs.

What are elastic applications?

Tolerate delays and losses, adapt to congestion (e.g., email, web). Best-effort
service works for them.

What are inelastic applications?

Require performance limits (e.g., VoIP, video conferencing). Lower/upper bounds
on acceptable performance. Don't adapt well to congestion.

How to improve QoS in IP networks?

Differentiated Services (DiffServ): traffic prioritization. Integrated Services
(IntServ): resource reservations. RSVP: signaling for reservations.

What is IntServ?

Integrated Services provides guaranteed service by reserving network resources
(bandwidth, buffer space) end-to-end via signaling like RSVP.

What is RSVP?

Resource Reservation Protocol exchanges messages to request/allocate resources
for specific flows, maintaining soft state refreshed periodically.

What is DiffServ?

Differentiated Services classifies traffic into aggregated classes (e.g., AF,
EF) using DSCP values, prioritizing without per-flow reservations.

How to reconstruct DPCM sequence +4 +2 +3 -2 +3 -1 +1 +1?

Start with accumulator zero. Add each value: 4, 6, 9, 7, 10, 9, 10, 11.

How does Lempel-Ziv compression work?

Builds dictionary of variable-length strings, replacing repeated strings with
shorter dictionary indexes during compression.

How to compress "AAACCCCCCBCCCCDDDDAAAABBB" with run-length?

Replace runs with count+symbol: 3A6C1B4C5D4A3B. Compression rate 26/14 ≈ 1.86.

Can web server and media server run on different machines?

Yes. Protocol defines server as application-level process. Can be same or
different machines.

Why RTP needs UDP/TCP under it?

RTP lacks socket addresses for multiplexing. Relies on UDP/TCP for this while
adding multimedia features like timestamps.

What are three QoS measurement ways?

Packet loss rate, end-to-end delay, jitter (variation in delay).

Compare IntServ, RSVP and DiffServ for multimedia:

IntServ: per-flow guarantees via RSVP signaling. DiffServ: scalable class-based
prioritization. Choice depends on network size and app needs.

What's RTP's role in multimedia streaming?

Provides sequence numbers, timestamps, payload IDs for proper ordering/timing
over UDP's connectionless delivery.

How RTP works with other protocols?

Over UDP for low overhead. RTCP for QoS feedback. SIP/H.323 for session
management while RTP handles media delivery.

What's in RTP header for loss detection?

Sequence numbers let receiver detect gaps from lost/out-of-order packets.

What's RTCP's function?

Provides QoS feedback (packet loss, jitter) and participant info, enabling
adaptive streaming/quality monitoring.

What's SIP's layer and function?

Application layer. Call setup, finds callee IPs, negotiates codecs. Works with
TCP/UDP/RTP.

Why TCP unsuitable for streaming?

Timely delivery more crucial than reliability. Retransmissions cause
unpredictable delays. Apps handle congestion better at their level.

What's mistake in setting buffer = RTT?

Buffer should be based on jitter, not RTT. Short RTTs may have higher jitter
causing missed frames.

Why late packet considered lost?

Arriving after playout deadline means it can't be used, so effectively lost
despite physical arrival.

What's acceptable delay for VoIP?

150ms ideal, up to 400ms tolerable. Higher delays impair human interaction.

Why receiver needs buffer in streaming?

To store packets arriving with jitter, releasing them at constant rate for
smooth playback.

What's RTSP's role in streaming?

Governs server-client interaction (play/pause/stop). Works with TCP/UDP/RTP
transport.

Compare proxy caching vs CDN:

Both replicate content closer to users. Proxy: passive/pull-based. CDN:
proactive/push-based with global deployment.

What UDP header lacks for loss detection?

No sequence numbers. RTP adds these to detect gaps in received packets.

What RTCP reports can sender use?

Packet loss rate and delay info. Sender can reduce encoding rate or increase
error resilience.

Why multicast hard at network layer?

Requires router changes difficult to deploy globally, though efficient for
routing.

Why HTTP streaming beats UDP?

Works through firewalls, adapts to bandwidth, no separate control server
needed.

What TCP does but RTP/UDP doesn't?

Retransmissions, acknowledgments, flow/congestion control. Causes more delay.
RTP/UDP better for real-time.

Why combine data/control channels?

Lower overhead but may reduce control responsiveness if mixed with bulk data.

What's playout buffer tradeoff?

Larger buffers reduce packet loss from jitter but increase initial playback
delay.

How sockets handle UDP datagrams?

Identified by destination IP+port only. Different source IPs/ports can use same
socket if dest matches.

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before:./study_network_l2.mj