Interview Questions.

Question 1. What Is Sip?

Answer :

The Session Initiation Protocol (SIP) is a signaling, presence and instantaneous messaging protocol advanced to installation, modify, and tear down multimedia sessions, request and supply presence and immediate messages over the Internet. SIP is a text-encoded protocol.

Question 2. What Is Request-uri?

Answer :

The Request-URI is a special form of SIP URI and shows the aid to which the request is being despatched, also referred to as the request goal.

C Interview Questions
Question three. What Is The Significance Of The Via Header Field?

Answer :

Each SIP device that originates or forwards a SIP message stamps its very own address in a "Via" header discipline, usually written as a number name that may be resolved into an IP cope with the use of a DNS query. The Via header subject consists of the SIP version range (2.0), a “/”, then UDP for UDP delivery, a space, then the hostname or address, a colon, then a port variety. And also comprise "branch" parameter.

Question four. Where The Branch Parameter Is Used And What Is Its Significance?

Answer :

A "department" parameter is used in "Via" header area. It is signified because the transaction identifier used to correlate the reponses to the request.

C Tutorial
Question five. What Is The Significance Of Max-forwards Header Field?

Answer :

Max-Forwards header area is used for simple loop detection. It is initialized to a few large integer and decremented by means of each SIP server which receives and forwards the request.

Linux Interview Questions
Question 6. What Are The Significance Of To And From Header Fields?

Answer :

To and From header fields display the originator and destination of the SIP request.

Question 7. Why The Name Labels Will Be Used In To And From Header Fields?

Answer :

When a call label is used, the SIP URI is enclosed in brackets and used for routing the request.The call label might be displayed at some point of alerting, but isn't always used by the protocol.

Linux Tutorial Linux Embedded systems Interview Questions
Question eight. What Is The Sigificance Of The Call-identity Header Field?

Answer :

The Call-ID header discipline is an identifier used to maintain song of a selected SIP session. The originator of the request creates a locally particular string, then commonly adds an “@” and its host call to make it globally precise. In addition to the Call-ID, every birthday party inside the consultation also contributes a random identifier, precise for every call. These identifiers, known as tags, are blanketed inside the To and From header fields as the consultation is mounted.

The user agent that generates the preliminary INVITE to set up the session generates the particular Call-ID and From tag. In the reaction to the INVITE, the consumer agent answering the request will generate the To tag. The aggregate of the local tag (contained in the From header subject), remote tag (contained in the To header field), and the Call-ID uniquely identifies the hooked up session, referred to as a “dialog.” This dialog identifier is used by both events to perceive this call due to the fact they may have more than one calls set up among them. Subsequent requests inside the established session will use this dialog identifier.

Question nine. What Is Dialog Identifier?

Answer :

The aggregate of the nearby tag (contained within the From header subject), faraway tag (contained inside the To header field), and the Call-ID uniquely identifies the established consultation, called a “conversation.” This conversation identifier is used by each parties to become aware of this name due to the fact they might have a couple of calls installation among them. Subsequent requests within the hooked up consultation will use this dialog identifier.

Telecommunication Project Management Interview Questions
Question 10. When The Cseq Header Field Value Will Be Incremented? Or What Is The Significance Of Cseq Header Field?

Answer :

CSeq or Command Sequence consists of a number followed with the aid of technique name.This quantity is incremented for every new request despatched.

Linux Embedded systems Tutorial
Question eleven. What Are The Minimum Required Header Fields In Any Sip Message? Or What Are The Mandatory Header Fields In Sip Message?

Answer :

Via, Max-Forwards, To, From, Call-ID and CSeq are the minimal required header fields.

Voice Over Internet Protocol (VOIP) Interview Questions
Question 12. What Is The Significance Of Contact Header Field?

Answer :

Contact header subject incorporates the device-URI where the originator of request or response may be immediately reached. Usually consists of IP cope with of the tool which generated the request or reaction.

C Interview Questions
Question 13. What Is Received Parameter And In Which Header Field It Will Be Appeared?

Answer :

Usually the received parameter can be discovered in Via header discipline of the response message. This parameter contains the literal IP deal with that the request became acquired from, which commonly is the identical cope with that the URI in the Via resolves the usage of DNS.

Unix/Linux Tutorial
Question 14. Is The To And From Header Fields Define The Direction Of The Sip Message?

Answer :

No, the To and From header fields in SIP are defined to signify the route of the request, not the route of the message.

Question 15. Is The Branch Parameter In Via Header Field Of The Ack Sent For 200ok Would Be Same As That Of Invite In A Session?

Answer :

No, department parameter in Via header area of the ACK might be specific than the INVITE message of that session due to the fact ACK despatched to renowned the 200OK is taken into consideration as a seperate transaction.

Unix/Linux Interview Questions
Question sixteen. Is The Branch Parameter In Via Header Field Of The Bye Message Would Be Same As Ack Sent For 200ok And That Of Invite In A Session?

Answer :

No, due to the fact BYE message is considered as a new transaction.

LTE Tutorial
Question 17. What Is Dialog?

Answer :

A dialog is a peer-to-peer SIP courting among two UAs that persists for a while.  A dialog is established with the aid of SIP messages, including a 2xx response to an INVITE request.  A conversation is identified through a name identifier, local tag, and a remote tag.  A dialog turned into formerly called a name leg in RFC2543.

LTE Interview Questions
Question 18. What Is A Session?

Answer :

A multimedia consultation is a fixed of multimedia senders and receivers and the information streams flowing from senders to receivers. A multimedia convention is an example of a multimedia session.

Linux Interview Questions
Question 19. What Is The Difference Between Dialog And Session?

Answer :

A conversation is a sip relationship. A consultation is a media courting. Dialog mean a "call has already been setup" in the signaling experience, whilst a session imply the "media has already been setup" inside the media experience.

Telecom Billing Tutorial
Question 20. What Does "component Of A Dialog" Mean? Are "invite", "ack" And The Responses Considered "part Of A Dialog"?

Answer :

Dialog represents country, which incorporates collection numbers, path sets, and URIs. A request sent as part of a conversation manner that it consists of direction headers from the route set of the conversation, and uses the next maximum series number within the dialog.'

Voip Telephony Interview Questions
Question 21. What Does "outdoor The Dialog" Mean Then? Is A Request Is Outside The Dialog, Does It Still Affect Or Change Anything "interior The Dialog" Then?

Answer :

Outside the dialog approach that it is not within the context of a dialog. It doesnt use the callid, cseq, or direction sets of any current dialogs, and whilst such a reuqest is set, it has no effect on the kingdom of an existing conversation.

Question 22. What Is The Difference Between Transaction, Dialog And Session?

Answer :

A transaction refers to a essential unit of message trade. It basically consists of a request-response cycle. 

A Dialog represents a peer-to-peer courting between  consumer dealers.It is typically created thru technology of "non-failure" responses to request. 

A session refers back to the trade of media among  or more Endpoints. Also, there can be dialogs without SIP classes.

Question 23. What Is The Advantage Of Using Sip Uris? Over Ip Address?

Answer :

A request routed the usage of best IP addresses will attain handiest one end point—handiest one tool. Since communique is normally person-to-person instead of device-to-device, a extra useful addressing scheme could allow a specific person to name any other unique user, which might result in the request accomplishing the goal person irrespective of which he is currently the use of, or if he has more than one gadgets.SIP URI is a name that is resolved to an IP address by using the usage of SIP proxy server and DNS lookups at the time of the decision.

Telecom Billing Interview Questions
Question 24. What Is Sip Uri?

Answer :

SIP URI is a call that is resolved to an IP address by using the use of SIP proxy server and DNS lookups on the time of the call.

Linux Embedded systems Interview Questions
Question 25. What Is Sip Proxy Server?

Answer :

A SIP proxy server sits inside the center of SIP message change, receives messages and forwards them, however it does not set up or terminate sessions. A proxy server generally has get admission to to a database or a place service to useful resource it in processing the request (figuring out the subsequent hop). Databases may want to incorporate SIP registrations, presence statistics, or some other kind of facts about where a consumer is positioned.

Question 26. What Is Stateful Proxy?

Answer :

A stateful proxy server maintains track of requests and responses received in the beyond and uses that records in processing destiny requests and responses. For example, a stateful proxy server starts a timer while a request is forwarded. If no response to the request is received within the timer length, the proxy will retransmit the request, relieving the consumer agent of this assignment. A stateful proxy normally sends a a hundred Trying response whilst it receives an INVITE.

Question 27. What Is Stateless Proxy?

Answer :

A stateless proxy server methods each SIP request or response most effective based at the message contents. Once the message has been parsed, processed, and forwarded or responded to, no statistics approximately the message is stored—no dialog information is saved. A stateless proxy never retransmits a message, and does not use any SIP timers.A stateless proxy by no means sends a one hundred Trying response.

Telecommunication Project Management Interview Questions
Question 28. What Is Transaction Stateful Proxy?

Answer :

A transaction stateful proxy continues state approximately a transaction but handiest for the length that the request is pending. For example, a transaction stateful proxy could keep kingdom whilst it gets an INVITE request till it acquired a 200 OK or a very last failure response (e.G., 404 Not Found). After that, it would destroy the nation facts. This allows a proxy to perform useful search services however reduce the amount of state garage required.

Question 29. How The Proxy Server Is Different From A User Agent Or Gateway?

Answer :

A proxy server is different from a gateway or person agent in three key ways:

A proxy does not issue request, it only responds to requests from person marketers. (A CANCEL request is an exception to this rule)
A proxy server has no media abilties.
A proxy server does no longer parse message bodies, it relies completely on message header fields.
Question 30. What Is Outbound Proxy Server?

Answer :

The proxy server to which the consumer agent sends the SIP request is referred to as the outbound proxy server. This proxy server will authenticate the user agent and may pull up a profile of the user and practice outbound routing services.

Question 31. What Is Inbound Proxy Server?

Answer :

The proxy server from which the consumer agent recieves the SIP request is called the inbound proxy server.

Question 32. What Is Forking Proxy Server?

Answer :

a proxy server that gets an INVITE request, then forwards it to some of locations on the same time. This “forking” proxy server maintains track of every of the amazing requests and the reaction to each. This is useful if the area service or database research returns a couple of viable locations for the referred to as party that want to be attempted. For example forking proxy F1 is obtained from UA1 which forks to two consumer dealers UA2 & UA3. Each consumer agent starts offevolved alerting and sending lower back  provisional resposes(one hundred eighty Ringing) to F1. The  responses are identical except for having one of a kind To tags and Contact URIs. Finally, one of the  UAs answers and sends a 200 OK reaction. The forking proxy server sends a CANCEL to the second UA to stop that phone alerting. If each UAs had replied, the forking proxy might have forwarded both 200 OK responses again to the caller who then would have had to select which one, probably accepting one and sending a BYE to the opposite one.

Question 33. Explain About Session-expires Header Field?

Answer :

A SIP consultation timer has been proposed to restrict the time period over which a stateful proxy should hold state records. In the initial INVITE request, a Session-Expires header field indicates a timer c programming language and then stateful proxies may discard kingdom records about the session. User retailers have to tear down the decision after the expiration of the timer. The caller can ship re-INVITEs to refresh the timer, allowing a “hold alive” mechanism for SIP. This solves the problem of how long to shop nation data in cases in which a BYE request is misplaced or misdirected.

Voice Over Internet Protocol (VOIP) Interview Questions
Question 34. What Is Redirect Server?

Answer :

A redirect server is a type of SIP server that responds the requests however does not forwards the requests. Like proxy server, a redirect server uses a database or area provider to look up a user. The location records, however, is sent returned to the caller in a redirection elegance response (3xx), which, after the ACK, concludes the transaction.

Question 35. Is The Ack Sent To Non-2xx Final Response Is Considered To Be Part Of The Same Transaction As Invite?

Answer :

Yes, the ACK despatched to non-2xx final response is considered to be a part of the equal transaction as INVITE. ACK request reuses the same department ID as INVITE. Only an ACK despatched in reaction to a two hundred OK is considered a separate transaction with a unique branch ID. Also an ACK to a non-2xx very last response is a hop-by way of-hop reaction, no longer an give up-to-stop reaction.

Question 36. How Would You Describe Its Potential?

Answer :

Henderson -IMS, with its accepted attraction to both wireline and wi-fi vendors, will shape the idea for achieving the closing aim of telecommunication service operations: a single better services structure for turning in any service, using any media, to reach any patron, no matter how they connect with the community.

Longhenry -It is very possibly that IMS will be deployed, in some style, via maximum foremost companies over the subsequent 5 years. It is the only standards-based method of addressing the essential assignment with which providers warfare whilst thinking about utility roadmaps. That is, the way to decrease the price of recent utility deployments that allows you to profitably cope with the possibilities available in micro-segments of their subscriber base.

McCracken -The capacity for IMS is one of simplification for the service company and stop purchaser. Simplification for the provider company lies within the fact that IMS will establish a horizontal set of skills that may be carried out to all the networks they run and to all the services they need to set up. For well hooked up service companies, reaching this capability will now not occur overnight due to the fact it can not make enterprise sense to take existing offerings and migrate them to IMS. But IMS will help new services pretty. Customers will experience a simplified communications revel in due to the fact they will have a single profile to manipulate and they will revel in the equal services throughout any network and device, in an effort to attention at the project to hand, instead of figuring out the era.

Hluchyj -The capability for IMS is vast, as it basically adjustments the communications paradigm. Voice, facts, and video can all be converged in an IMS landscape. From a service company perspective, the delivery version is far more green and dynamic. From a subscriber perspective, they have got access to an revel in this is truely now not available with present day legacy era. 

Burger -IP will remain a disruptive era to traditional telecom operators for years to come and assist to convert operator enterprise models from voice-driven to carrier-driven agencies. Operators require greater programs to fulfill aggressive threats and will want a better environment for creating and deploying excessive cost multimedia offerings. IMS addresses this want.

Scott Erickson, President, IMS Service Delivery Solutions, Telcordia -IMS has the potential to trade communications as we understand it. Carriers now have the possibility to solid themselves freed from the highly-priced underlying network hardware and exert direct and flexible manage over their offerings through software. IP-based communications provide vendors with the ability and openness to quickly offer new revenue producing offerings, at the same time as allowing carriers to lower their overall value of doing business, growth their sales capacity, understand better productiveness and decrease churn.

Marinho -Lucent’s primary marketplace studies indicated a pent up demand for the sort of blended life-style services that IMS can permit. For example, U.S. Carrier companies have a capacity marketplace for converged services really worth an expected $10 billon dollars, with that figure being potentially reached five years after such services are delivered to the customer and corporation markets.

Gray -Ubiquity believes that IMS can have giant capacity primarily based on the improved offerings it's going to allow. It has potential to enrich the personal lives of consumers and potential to enhance the productiveness of commercial enterprise and agency users, converting the arena of communications as we understand it. This alternate has the potential to drive new economic growth in our enterprise.

Unix/Linux Interview Questions
Question 37. What Are Some Potential “killer Apps” That Ims Might Enable?

Answer :

Henderson -IMS will facilitate new multimedia offerings, accelerate the migration of legacy TDM offerings to IP, and make any telecom provider greater seamless and ubiquitous the usage of any kind of get entry to device. Services concerning multimedia, presence, and comply with-me functions will not have the technical barriers between get admission to networks that existed before IMS.

Longhenry -There are not any authentic “killer apps” for IMS, as any utility that may be introduced over IMS can also be added through a stand by myself proprietary utility server. Rather, the “killer ROI case” is that IMS can enable vendors to install ten packages from a common standardized (i.E., value competitive) platform, in place of from ten wonderful platforms requiring ten separate integration efforts.

McCracken -Some of the most compelling programs might be ones that capitalize at the potential of IMS networks to carry voice, video, and information streams collectively to supply so known as “rich media services” across a couple of access networks and devices. These services will deliver those historically separate skills collectively and permit more compelling man or woman-to-person communications than have been ever possible on separate networks. IMS presents a commonplace framework that can be leveraged across all of the get entry to methods and devices that human beings want to use for his or her private and business communications. It breaks down the proprietary “provider silos” which have existed for years.

Hluchyj -It does not surely remember what the subsequent “killer app” is -this is some thing this is continually going to alternate. What’s amazing approximately IMS is that it employs a allotted version where software creation mirrors Web application improvement. In the vintage telecom world, introducing new offerings changed into steeply-priced and unstable. In an IMS world, the price of experimentation is driven way down, and while the fee of experimentation is diminished, the opportunity for innovation expands exponentially. The next killer app will usually be right across the corner.

Burger -IMS is all approximately SIP-primarily based packages. Potential applications include audio and video conferencing, video messaging, hosted offerings, multi-participant gaming, and ubiquitous offerings/customized content material. By supplying a trendy communications infrastructure primarily based on IP, IMS permits multimedia application convergence

Scott Erickson, President, IMS Service Delivery Solutions, Telcordia -For vendors, the real ‘killer app’ is the potential to offer a myriad of thrilling IP-enabled subsequent technology services quickly, including push-to-video, cellular TV, multi-party gaming, presence and region-based services, TV Caller ID, and converged VPNs. IMS offers carriers with the agility, flexibility and speed-to-shipping this is vital for them to pressure expanded revenue from these new offers and cozy their future growth and viability.

Marinho -The look for the “killer app” may not be applicable to a large market, as we historically might assume. The secret is identifying the “right” aggregate of offerings that addresses demand in particular marketplace segments. IMS-based totally services, as an instance, can enable friends to devise a night out in real-time, which include discussing the possibilities, viewing a movie trailer and shopping tickets, picking a restaurant and making the reservation, and receiving custom guidelines to the restaurant.

Gray -IMS not only enables the killer app, but it allows the “Killer Capability”, that means that multiple packages or mixed applications are enabled via IMS. Given Ubiquity’s role in permitting application improvement and fast provider introduction, we see “Instant Multimedia Sharing” programs inclusive of song, video, and voice being widely adaopted.

Question 38. Who Stands To Benefit The Most From Ims? Carriers? Equipment Manufacturers? End Users?

Answer :

Henderson -IMS is a tremendous for the complete telecommunications industry. Carriers, and subsequently corporation companies, will gain from unified carrier structure. Equipment producers becomes greater efficient, focusing sources on a unmarried IMS product line, rather then distinct products for one-of-a-kind markets. End customers, mainly business customers, will benefit from seamless services, no matter access or device.

Longhenry -End users will in the end advantage maximum from IMS, as they will advantage access to exponentially greater programs will be commercially viable in a non-IMS global. The satisfactory analogy is probably the person enjoy to be had from DoCoMo and iMode, as 1/3 birthday celebration programs can be speedy developed, included, and brought to a fad-orientated subscriber base. IMS enables this in a standardized fashion. 

McCracken -The ones who will benefit maximum are the provider providers and the quit clients. Service companies could have a core community that sooner or later separates consultation manage from the bearer course and the offerings. This creates an structure extra suitable to bringing new packages to market greater quickly, and reduces lots of traditional duplication. End customers will benefit because they'll have simplified communications so that it will be customized across any network and tool. They will be capable of revel in a far richer multimedia communications experience in an effort to now not be dependent on a particular access method tied to a selected device. Equipment manufacturers will face more competition as proprietary architectures are broken apart with IMS, beginning up new opportunities for nimble corporations to polish with innovative services.

Hluchyj -The benefits without a doubt extend across the enterprise. By standardizing the one of a kind community additives, carrier providers can pick the portions we want and producers can consciousness on their core competency regions. The end result is lower fee infrastructure and a much extra type of services that can be rapidly deployed, which advantages the purchasers.

Burger -If everyone can conform to standardize on IMS, then the entire industry advantages. Carriers could be capable take benefit of all the blessings of open structures gadget, such progressed ROI, quicker time to deployment, and fine of breed solutions. End users will gain from new and innovative personalised services, handy whenever and everywhere. Equipment producers will benefit from imparting merchandise that permit the deployment of recent services

Scott Erickson, President, IMS Service Delivery Solutions, Telcordia -Carriers. Wireless vendors will velocity new offerings to marketplace. Wireline vendors can be able to boom customer pride via bundled gives. MVNOs will release themselves greater unexpectedly into niche markets at the same time as simplifying provider introduction. MSOs will evolve by using using IMS to compete with both wireline and wireless providers. All will enjoy the delivered sales from new services and accelerated client delight.

Marinho -End customers advantage from an advanced communications experience geared to their personal desires and necessities. Carriers benefit from the pent up call for, marketplace opportunity, and “stickiness” of IMS offerings. Manufacturers benefit from the adoption of the era and improved community ability call for that is pushed via IMS primarily based services.

Gray -Many stakeholders will advantage from IMS. First, and primary, End Users will gain via having new offerings, more services, and more preference in services. Moreover, End Users will benefit via the private and professional productiveness provided with the aid of enhanced offerings. Once a success enterprise models are mounted, the pull thru impact will benefit companies, gadget carriers, and application builders.

Question 39. What Is The Timeline For Real Commercial Deployments Of Ims?

Answer :

Henderson -Carriers are already purchasing IMS-well suited additives and systems, and realizing early benefits from IMS structure standards in small pilot deployments and unique services. However, completely interoperating, standards-based, multi-vendor IMS answers are probably still a few years out.

Longhenry -IMS deployments might be taking place throughout the telecommunications surroundings nowadays if IMS customer architecture changed into on par with IMS server infrastructure. Unfortunately, the idea of an IMS customer has not but received sufficient momentum within the standardization system and, consequently, advanced client-server IMS programs cannot but be seamlessly added to subscribers. As that is addressed within the next 24 months, IMS deployments will unexpectedly boost up.

McCracken -Technically, there are industrial deployments today for a few initial IMS components, like a barebones CSCF (Call Session Control Function) in assist of push-to-communicate services, however these deployments are simplest starting to whet the appetite for what’s to come back later in 2006 and into 2007. Once SIP-primarily based session manage is used for greater services than PTT, that’s while other factors, like a Home Subscriber Server (HSS), will begin to show their cost. IMS will co-exist with these days’s networks for decades to return, and offerings might be migrated because the business evolves. Ironically, IMS may see faster deployment via constant carrier vendors due to the fact they could leverage their broadband get right of entry to networks and more effective gadgets to supply a number of the multimedia abilities sooner than wi-fi vendors.

Hluchyj -Some solutions are IMS-ready today, and network operators are already laying the groundwork of their IMS deployments. That stated, we expect that the delivery of more suitable applications constructed on IMS might be a 2007/2008 occasion.

Burger -Early commercial deployments are definitely taking place now. Brooktrout/Excel labored with TMN, the biggest provider in Portugal, to deliver one of the first live 3G video messaging offerings. The aim changed into to deliver real-time video services in time for the European football championships. For TMN, this changed into an opportunity for a brand new revenue-producing service, due to the fact that voice is swiftly becoming a commodity.

Scott Erickson, President, IMS Service Delivery Solutions, Telcordia -IMS is already seeing sizeable worldwide momentum. Some providers have already all started to make inroads in IMS-geared up deployments. The beauty of IMS is that vendors can proceed on the tempo that is proper for them, their commercial enterprise, and their clients, based totally on their existing community investments and customers’ needs.

Marinho -We expect to see industrial offerings primarily based on IMS answers start to roll out later this yr, and the momentum will select up in 2007.

Gray -Based on reviews and lab trials, we'd anticipate to peer actual deployments in the next 12 – 24 months. Ubiquity is involved now in helping providers plan, increase and installation new services, even pre-IMS, to recognise sales and offerings today in order to be IMS-geared up while IMS networks are deployed, regardless of the time-frame.

Question forty. What Is The Significance Of Update Method?

Answer :

The UPDATE approach is used to modify the state of a consultation with out changing the kingdom of the conversation. A session is set up in SIP the usage of an INVITE request in an offer/answer way. Typically, a session provide is made in the INVITE and a solution made in a response to the INVITE. In a longtime session, a re-INVITE is used to replace consultation parameters. However in pending consultation (INVITE sent but no final reaction obtained) UPDATE is used to replace consultation parameters. Basically UPDATE is used to perform QoS and negotiate give up-to-quit attributes previous to session establishment.

LTE Interview Questions
Question forty one. What Is The Significance Of Prack Method?

Answer :

The PRACK technique is used to acknowledge receipt of reliably transported provisional responses (1xx). The reliability of 2xx, 3xx, 4xx, 5xx, and 6xx responses to INVITEs is finished using the ACK technique. However, in instances in which a provisional reaction, inclusive of a hundred and eighty Ringing, is crucial in determining the decision country, it may be essential for the receipt of a provisional reaction to be confirmed. The PRACK method applies to all provisional responses besides the a hundred Trying reaction, that's never reliably transported. A PRACK is generated by a UAC while a provisional response has been acquired containing a RSeq reliable collection variety and a Supported: 100rel header. The PRACK reproduction the quantity within the RSeq and the CSeq of the response in a RAck header.

Question 42. What Is The Significance Of Info Method?

Answer :

The INFO method is utilized by a consumer agent to ship name signaling records to every other person agent with which it has an established media consultation. This isn't like a re-INVITE since it does no longer change the media traits of the call. The request is give up-to-give up, and is in no way initiated by proxies. A proxy will usually forward an INFO request—it's miles as much as the USAto check to see if the conversation is valid. INFO requests for unknown dialogs get hold of a 481 Transaction/Dialog Does Not Exist reaction.

Voip Telephony Interview Questions
Question 43. What Is The Significance Of Message Method?

Answer :

The MESSAGE technique is used to transport immediate messages (IM) the usage of SIP. IM typically consists of short message exchanged in close to-actual time via participants engaged in a "communication." MESSAGEs can be sent inside a conversation or out of doors a conversation, but they do no longer set up a conversation by means of themselves.

Question forty four. What Is The Significance Of Notify Method?

Answer :

The NOTIFY approach is utilized by a user agent to convey records approximately the occurrence of a selected event. A NOTIFY is constantly despatched within a dialog while a subscription exists between the subscriber and the notifier. A NOTIFY request usually gets a 200 OK reaction to signify that it's been acquired. If a 481 Dialog/Transaction Does Not Exist response is received, the subscription is automatically terminated and no greater NOTIFYs are despatched. NOTIFY requests incorporate an Event header discipline indicating the package and a Subscription-State header field indicating the present day kingdom of the subscription.

Question 45. What Is The Significance Of Subscribe Method?

Answer :

The SUBSCRIBE method is used by a user agent to set up a subscription for the purpose of receiving notifications (thru the NOTIFY method) about a selected event. A a hit subscription establishes a conversation among the UAC and the UAS. The subscription request carries an Expires header area, which indicates the preferred duration of the life of the subscription. After this time period passes, the subscription is robotically terminated. The subscription can be refreshed with the aid of sending some other SUBSCRIBE inside the conversation earlier than the expiration time.

A server accepting a subscription returns a 2 hundred OK reaction additionally containing an Expires header subject. The expiration timer can be the same as the request, or the server can also shorten the c programming language, but it is able to not prolong the c program languageperiod. There is no "UNSUBSCRIBE" approach used in SIP—as a substitute a SUBSCRIBE with Expires:zero requests the termination of a subscription and as a result the conversation. A terminated subscription (either due to timeout out or a termination request) will result in a final NOTIFY indicating that the subscription has been terminated.

Question forty six. What Is The Significance Of Refer Method?

Answer :

The REFER approach is used by a person agent to request some other consumer agent to access a URI or URL useful resource. The aid is recognized by a URI or URL within the required Refer-To header subject. A REFER request can be sent either internal or outdoor an present dialog.

Question 47. What Is The Significance Of Options Method?

Answer :

The OPTIONS technique is used to query a consumer agent or server about its capabilities and find out its cutting-edge availability.

Question 48. What Is The Significance Of Cancel Method?

Answer :

The CANCEL technique is used to terminate pending searches or call tries. It can be generated by way of both user retailers or proxy servers provided that a 1xx response containing a tag has been received, but no very last reaction has been received. The department ID for a CANCEL matches the INVITE that it's miles canceling. A CANCEL best has which means for an INVITE in view that simplest an INVITE may additionally take several seconds (or mins) to complete. All other SIP requests complete at once. A person agent confirms the cancellation with a 200 OK reaction to the CANCEL and replies to the INVITE with a 487 Request Terminated response.

Question 49. What Is The Significance Of Ack Message?

Answer :

The ACK technique is used to well known final responses to INVITE requests. Final responses to all other requests are in no way acknowledged.An ACK may additionally incorporate an application/sdp message frame. This is allowed if the initial INVITE did not contain a SDP message frame. If the INVITE contained a message body, the ACK may not comprise a message frame. For 2xx responses, the ACK is stop-to-quit, however for all other very last responses it's far done on a hop-with the aid of-hop basis while stateful proxies are involved. A hop-via-hop ACK reuses the identical branch ID because the INVITE given that it's far taken into consideration part of the equal transaction. An stop-to-cease ACK uses a extraordinary department ID as it is taken into consideration a brand new transaction.

Question 50. What Is The Significance Of Bye Message?

Answer :

The BYE method is used to terminate a longtime media consultation. A BYE is despatched simplest by means of person sellers participating within the session, never by proxies or different 1/3 parties. It is an give up-to-quit technique, so responses are best generated by way of the other person agent.

Question 51. How To Cancel All The Registrations Using A Single Register Message?

Answer :

The touch header area is same to * and Expires: 0

Question fifty two. What Is Third Party Registration?

Answer :

If the UA sending the registration request on behalf of other UA it is known as third celebration registration. In this case, the From header will comprise the URI of the birthday party submitting the registration on behalf of the party recognized inside the To header.

Question fifty three. What Is The Significance Of The Expires Header In Register Message?

Answer :

The presence of an Expires header sets the expiration of Contacts without a expires parameter. If an expires parameter is gift, it sets the expiration time for that Contact handiest.

Question fifty four. What Is The Registration And Why It Is Required?

Answer :

The registration creates a transient binding among the Address of Record (AOR) URI inside the To header and the tool URI within the Contact header.The binding of  Registration isn't always required to enable a consumer agent to apply a proxy server for outgoing calls. It is necessary, however, for a user agent to sign up to acquire incoming calls from proxies that serve that domain until a few non-SIP mechanism is used by the area carrier to populate the SIP URIs and Contacts of end-points.

Question 55. What Is The Significance Of The Register Message?

Answer :

The REGISTER approach is utilized by a user agent to notify a SIP community of its current Contact URI (IP cope with).

Question 56. What Is The Significance Of Invite Message?

Answer :

The INVITE approach is used to set up media periods between user retailers. An INVITE commonly has a message body containing the media data of the caller. If an INVITE does not include media facts, the ACK includes the media facts of the UAC. If the media statistics contained in the ACK is not suitable, then the referred to as birthday party need to send a BYE to cancel the session—a CANCEL cannot be despatched due to the fact the session is already established.

Question fifty seven. What Is The Significance Of The Expires Header In An Invite Message?

Answer :

An Expires header in an INVITE shows to the united stateshow lengthy the call request is valid. For instance, the U.S.Could depart an unanswered INVITE request displayed on a display screen during unique inside the Expires header. Once a session is hooked up, the Expires header has no which means—the expiration of the time does not terminate the media session. Instead, a Session-Expires header can be used to vicinity a time limit on a longtime session.

Question fifty eight. If The Re-invite Is Failed Or Refused, Will The Call/consultation Discontinued?

Answer :

No, If a re-INVITE is refused or fails in any way, the consultation continues as if the INVITE had in no way been sent.

Question fifty nine. Can You List Out The Sip Methods?

Answer :

The INVITE, REGISTER, BYE, ACK, CANCEL, and OPTIONS techniques are the original six methods in SIP. The REFER, SUBSCRIBE, NOTIFY,MESSAGE, UPDATE, INFO, and PRACK strategies are defined in separate RFCs.

Question 60. What Is Turn Protocol?

Answer :

Traversal Using Relay NAT (TURN) protocol lets in a client to gain a transport IP address and port that it can acquire packets sent from a single IP deal with inside the public Internet. For some NAT topologies which include a patron at the back of a symmetric NAT, using a relay located inside the public Internet is the handiest approach that lets in verbal exchange to take place.