📝 QoS definitions in computer networks (13 MCQs)
📖 From Data Communication and Networks • 30. Quality of Service • 13 questions available
What is QoS definitions in computer networks?
Quality of Service is defined as the set of technologies and mechanisms used in computer networks to manage data traffic by prioritizing critical applications and guaranteeing specific performance levels like throughput and latency for different types of communication.
📝 All QoS definitions in computer networks MCQs
Q1. Why is a blank line included between the header section and the body in a SIP message?
📖 Explanation: The blank line signals the end of the header block and the start of the message body. SIP parsers treat any text after this empty line as payload, typically SDP. Without the blank line the parser cannot reliably distinguish header fields from body content, leading to misinterpretation.
Q2. If a SIP request passes through multiple proxies, how does the Via header affect the path of the response?
📖 Explanation: Each proxy that forwards a request appends its own Via entry. When a response is generated, it traverses the Via list in reverse, ensuring the reply returns through the same set of proxies that handled the request. This mechanism guarantees proper routing and allows each proxy to perform necessary processing on the response.
Q3. What would likely happen if the Content-Length value in a SIP INVITE header is smaller than the actual size of the SDP body?
📖 Explanation: When the Content-Length does not match the true body size, the receiver cannot reliably parse the message. According to RFC 3261, this mismatch is treated as a malformed request, and the server must respond with a 400 Bad Request error, prompting the sender to correct the header and resend.
Q4. Which statement best describes the SIP start line compared to the HTTP start line?
📖 Explanation: A SIP start line begins with a method (e.g., INVITE), followed by the request‑URI and the SIP version (SIP/2.0). This mirrors HTTP’s request line but uses SIP‑specific methods and versioning. Unlike HTTP responses, SIP responses have a status line with a numeric code, making the start line structure a key distinguishing feature.
Q5. Evaluate the distinct roles of the Call-ID header and the From header in a SIP dialog.
📖 Explanation: The Call-ID header contains a globally unique identifier that distinguishes a particular SIP session, allowing both parties to correlate messages belonging to the same dialog. The From header, by contrast, specifies the logical address of the originator, which is used for routing and display purposes. Their functions are complementary, not interchangeable.
Q6. Differentiate the three parts of an SDP body based on their purpose.
📖 Explanation: SDP is organized into logical sections: the first (v=, o=) carries version and origin information essential for session identification; the second (s=, i=, u=, e=) supplies descriptive data that assists the user in deciding whether to join; the third (c=, t=, m=) offers concrete network and timing details required to establish the media stream.
Q7. Which SDP code provides the timing information for a session?
📖 Explanation: The \t=\ line in SDP specifies the start and stop times of the session, using a pair of numeric values (e.g., \t=0 0\ for an ongoing session). This timing information enables participants to know when the media session is intended to be active, distinguishing it from other SDP fields that describe version, connection, or subject.
Q8. Explain the relationship between the Content-Type header and the body format in a SIP message.
📖 Explanation: The Content-Type header tells the receiver how to interpret the payload. For SIP messages that carry SDP, the header is typically set to \application/sdp\. This informs the parser that the following body follows SDP syntax, enabling correct decoding of session parameters. Mismatched or missing Content-Type can cause the body to be misinterpreted.
Q9. Which of the following represents a correctly constructed SIP INVITE message for establishing an audio session?
📖 Explanation: A valid INVITE must contain routing headers (Via, From, To), identification headers (Call-ID, CSeq), contact information, and payload descriptors (Content-Type, Content-Length). The SDP body supplies session details: version (v=0), origin (o=...), session name (s=...), connection address (c=IN IP4 192.0.2.1), timing (t=0 0), and media description (m=audio 49170 RTP/AVP 0). This combination satisfies RFC 3261 and enables audio negotiation.
Q10. What does the 'v' code represent in an SDP description?
📖 Explanation: The \v=\ line is the first line of an SDP body and indicates the version of the SDP protocol being used. Currently, the version is always \0\, which signals compliance with the SDP specification. This line establishes a baseline for interpreting the remainder of the description.
Q11. Suppose a SIP REGISTER request includes an Expires header set to 0. What can be inferred about the client’s intent?
📖 Explanation: An Expires value of zero signals that the client wishes to remove its registration from the server. According to RFC 3261, a zero expiration causes the registrar to delete the existing binding for the address of record, effectively deregistering the user agent.
Q12. Compare the purpose of the 'c=' line and the 'm=' line in SDP.
📖 Explanation: The \c=\ line conveys the network address (IP) and type (unicast/multicast) that participants must join to receive media. The \m=\ line defines the media stream itself, including the media type (audio, video), transport protocol (RTP/AVP), and the port numbers. Both lines are essential for establishing a functional media path.
Q13. How does the ordering of SDP lines (v, o, s, i, u, e, c, t, m) affect the parsing and interpretation of a SIP INVITE?
📖 Explanation: RFC 4566 specifies a strict order for SDP lines. Parsers expect the sequence v→o→s→i→u→e→c→t→m. Deviating from this order can lead to parsing failures or misinterpretation of session parameters, because the parser may treat a later line as belonging to a different section. Maintaining the prescribed order ensures reliable negotiation.