Interview questions.

Networking interview questions.

1. Benefits of OSPF over RIP?
2. What will happen when a new switch boots?
3. Why VLAN is required?
4. How STP works?
5. Why Area 0 is required in OSPF conecpt?
6, ARP purpose.

Sip interview questions:

1.What do you mean by a sip session?
2. explain a simple call flow
3.Draw the call flow for music on hold
4.What is the use of address of record in REGISTER messages.
5.what is record route.
6.Difference between strict routing and loose routing.
7.stateless, stateful and superstateful proxies.
8.what all components are used in a call.

9.use of contact header.
Answer:

The Contact header field describes the SIP or SIPS URI that the originating UA can be contacted at. This is used  both in a request establishing a dialog, registrations and redirects. The Contact header must be present in INVITE messages and be globally unique and accessible. 

10.difference of usage of contact header and connection information in SDP.
Answer:

The  c= field  contains  information  about  the  media  connection.  The  field contains: c=network-type address-type connection-address. The network-type parameter is defined as IN for the Internet. The address type  is  defined  as   IP4 for  IPv4  addresses,  IP6 for  IPv6  addresses.  The  connection-address is the IP address that will be sending the media packets, which could  be  either  multicast  or  unicast.  If  multicast,  the  connection-address  field contains:connection-address=base-multicast-address/ttl/number-of- addresses where ttlis the time-to-live value, and number-of-addressesindicateshow  many  contiguous  multicast  addresses  are  included  starting  with  the base-multicast-address.

11.Use of subscribe and Notify. Real time example.
Answer:

NOTIFY requests simply relay information related to the configured event package to the subscriber.  Since there is no SIP call state change, the subscriber usually responds with a “200 OK”.  There are a few situations in which a subscriber  may want to respond to a NOTIFY request with something other than a “200 OK” response message; those  situations  are  considered  error  states  and  are  not  part  of  this  particular  test.      This  test  requires  that  theNOTIFY request be part of the same dialog that the initial SUBSCRIBE request created.  Since this group of tests explicitly  evaluates  the  SUBSCRIBE/NOTIFY  functionality,  and  therefore  assumes  that  the  subscription  state  is installed via a SUBSCRIBE request.  It is possible that the subscription state would be established out of band, in which case the NOTIFY message would NOT be part of a dialog.

USAGE: Automatic call back

12.Explain Attended Transfer?
13.what is early media and why it is needed?
Answer:

Early media is used to avoid voice slicing. Basically with ISDN to sip gateways , a media path will be established before 200 OK. So the caller at the sip side will get access to any informations like call busy tones, network busy tones. Also this helps to avoid voice chopping because the caller may start to speak without the actual start of the session.

14.What is delayed media?
Answer:

Media negotiation happens in 200 Ok.

Usage: Music on Hold Scenarios

15.DNIS, DID and ANI-details?
Answer:

DNIS: Dialed Number Information Service.

DID: Direct Inward Dialing--> Number used for Dialing.

ANI: Caller ID

16.RTP, RTCP. How Voice Quality metrics are measured.
17.How will you put a call on HOLD? the methods and their explanation.
18.what is DTMF buffer?
19.How will you debug a sip call. What all parameters you will look on.
20.What are the parameters you configure in a gateway?


Reasoning questions:
1. http://brainteaserbible.com/interview-brainteaser-matches-in-a-knockout-tournament
2. http://datagenetics.com/blog/july22012/index.html