[Q3] Say a proxy P, is required to implement Hunt-me service (i.e. looking up the callee in multiple contacts). Which of the following statement is the CORRECT one?

a) It must be call Stateful. b) It must be transaction Stateful. c) It may be stateless. d) It does not matter what it is, since an App Server is needed anyways to implement such a service.

[Q4] Which of the following statements is the most accurate one? A registrar knows where to return the response for the REGISTER request based on:

a) The IP address (or FQDN) in the Via field. b) The source field in the IP header of the REGISTER request. c) The Contact header provided in the REGISTER request. d) Any of the above. e) Based on (b) in case of contradicting values of (a) and (b).

[Q5] Endpoint B receives from endpoint A an INVITE, which contains (among others) Contact, and Record-Route headers. A session is established. Later B wants to send BYE to A.

a) B must send the BYE to the last element on the Record-Route list. b) B must send the BYE to the first element on the Record-Route list. c) B MAY send the BYE to the IP address, which was indicated in the Contact header. d) B MUST send the BYE to the IP address, which was indicated in the Contact header.

[Q6] Endpoints A and B are having a normal two-way phone call (single two-way audio stream). The most appropriate way for A to put B on hold is by:

a) Sending it a Re-invite with a “sendonly” attribute in the SDP element. b) Sending it a Re-invite with port equal to zero in the SDP element. c) Sending it a Re-invite with an “inactive” attribute in the SDP element. d) None of the above

[Q7] Which one is the most CORRECT statement? The Branch-ID field in the Via header is used:

a) Only by proxies for loop detection. b) Only by proxies for loop detection and to match responses of forked requests. c) Only by proxies for loop detection and to match responses of forked requests, and as a transaction identifier. d) Must be used also by clients (which are 3261 compliant). e) It is not a must to be used by the UAC, but a stateful proxy should edit the Via line of the UAC and add a branch parameter if not there already.

[Q8] UAC sends an INVITE. It must start a request retransmission timer.

a) Only if it uses unreliable transport to the next hop element. b) For any type of transport. c) The default value of this timer is 50ms. d) (a) and (c) above are correct.

[Q9] UAC has its INVITE transaction in the “Proceeding” state:

a) It should not retransmit the request even if T1 has expired. b) It should retransmit the request, only if T1 has expired. c) It should not retransmit the request only if it saw at least one 1xx response while in this state. d) None of the above is true.

[Q10] The TO header field in any SIP request:

a) Can be modified by proxies. b) Shall never be modified by proxies. c) Can be modified by proxies only if they are stateful. d) Can be modified by proxies only if they are super stateful (i.e. call stateful).

[Q11] A UAS has received a SIP request over UDP transport with a payload greater than zero, but with no length field:

a) It shall reject the request by returning a 400 (bad request) error code. b) It shall reject the request by returning a 413 (request entity too large) error code. c) It shall accept the request and shall assume the data to the end of the pkt to be a payload. d) None of the above is correct.

Skipped...

[Q21] Which of the following statements is the correct one:

a) There are already SIP extensions, which support exchange of IPsec parameters between an endpoint and its outbound proxy. b) SIP does not need IPsec, as security is provided by the built-in authentication functionality (e.g. www-authenticate). c) IPsec might be a better choice than TLS in cases where UDP transport is desired (since IPsec does not mandate TCP). d) (a) and (c) are correct.

[Q22] Which of the following dialog related statements is the correct one:

a) INVITE is the only SIP method, which establishes a dialog. b) Under certain circumstances the OPTIONS request may establish a dialog too. c) In addition to INVITE, the REGISTER method establishes a dialog too, hence Call-ID has to be the same for all re-registrations. d) In addition to INVITE there is at least one more SIP method, which establishes a dialog. However, this method is not defined in RFC 3261.

[Q23] SIP endpoint, A, sent an OPTIONS request to SIP endpoint, B, via a stateful proxy, P. The transport between A and P is UDP. The transport between P and B is UDP as well. After 200 mili seconds B sent back 200-OK, which got lost.

a) A will never retransmit the request, since after timer T1 P will detect the loss, and will retransmit the request. b) There could be a situation in which A will have to retransmit the request. c) OPTIONS request is a non-INVITE request and thus never gets retransmitted regardless of the transport.

[Q24] SIP endpoint, A, sent an OPTIONS request to SIP endpoint, B, via a stateless proxy, P. The transport between A and P is UDP. The transport between P and B is UDP as well. After 200 mili seconds B sent back 200-OK, which got lost.

a) A will never retransmit the request, since after timer T1 P will detect the loss, and will retransmit the request. b) There could be a situation in which A will have to retransmit the request. c) A will obviously have to retransmit the request. d) OPTIONS request is a non-INVITE request and thus never gets retransmitted regardless of the transport.

[Q25] SIP endpoint, A, sent an OPTIONS request to SIP endpoint, B, via a stateful proxy, P. The transport between A and P is UDP. The transport between P and B is TLS. After 200 mili seconds B sent back 200-OK, which got lost.

a) A will never retransmit the request, since after timer T1 P will detect the loss, and will retransmit the request. b) P will never retransmit due to the reliable transport, thus after expiration of T1 A will retransmit the request. c) OPTIONS request is a non-INVITE request and thus never gets retransmitted regardless of the transport.

[Q26] Which of the following is the correct statement? In SIP registration...

a) The client specifies its contact address, but can not specify the transport to be used to reach it. b) The client must specify (also) the transport to be used in order to reach it. c) The client may specify the transport to be used in order to reach it. d) Technically SIP enables the client to specify the transport to be used to reach it, but recommends to leave it to the registrar to decide.

[Q27] Let's assume registrar policy, which allows expiration interval of any value between 10 to 120 minutes. A SIP UA has registered three contacts with expiration intervals of 15, 30 and 60 minutes respectively. After 10 minutes the UA decides to reset the expiration interval for the three contacts to a value of 12 minutes.

a) The UA can do that by sending SIP REGISTER request with the wildcard '*' and expiration val of 12. b) The UA can do that by sending SIP REGISTER request (with an Expires hdr set to that val), but it has to specify three separate contacts. c) The UA has to wait for the expiration of the first contact, and only then can re-register with the new expiration val. d) The UA has to wait for the expiration of the three contacts altogether, and only then can re-register with the new expiration val.

Skipped...

[Q38] Querying SIP registration contact list can be done:

a) Only by using outsdie-of-SIP-scope methods. b) By using a SIP REGISTER request with an empty contact list. c) By using a special query directive in the REGISTER request. d) By using an OPTIONS or INFO SIP request(s).

[Q39] The best/safe way to query capabilities of other SIP endpoints is:

a) Only by using out of SIP methods. b) By using the SIP OPTIONS request. c) By using the SIP CAPABILITIES-INFO request. d) By using the OPTIONS or INFO SIP request(s).

[Q40] A request path is consisted of UA1->P1->P2-UA2. UA1 sent an INVITE, which was proxied by P1 and P2 to UA2. UA2 returns 100-Trying response back to P2:

a) If P2 sees only itself in the Via list it should consume the response, otherwise it shall forward it upstream. b) P2 should always consume the response regardless of the Via list (i.e. shall not forward it upstream). c) If Via list has only one element, P2 shall discard the response as a bad formatted one. d) If Via list has only one element, P2 shall consume it, but shall also let UA2 know about the error by using ICMP.

[Q41] SIP element has received a request with an unknown protocol version:

a) The element should respond to the request with a 505 Version Not Supported error code. b) The element should respond to the request with a 400 Bad request error code. c) The element should ignore the "typo" if the rest of the request is understood. d) The element shall silently discard the request, as the sender may not be able to process responses correctly anyways.

[Q42] SIP invitation to a multicast conference:

a) Must be multicasted as well. b) Does not necessarily have to be multicasted. c) Has to be multicasted if there is no outbound proxy.