SIP FAQSubcategories: SIP BasicsSIP FunctionalitySIP Protocol OperationRelationship to Other Protocols Answers in this category: How do I show this FAQ as a single page RTP Issues [Add a New Answer in "SIP FAQ"] mailto:? Hgs@cs.columbia.edu? subject = SIP FAQ, mailto: islepchin@dynamicsoft.com subject = SIP FAQ, mailto:? jdrosen@dynamicsoft.com subject = SIP FAQ2001-Apr-24 9:00 pm SIP FAQ:? SIP BasicsBasic questions about SIP 2000-Jun-28 2:20 pm mailto: hgs@cs.columbia.edu subject = SIP FAQSubcategories:? Answers in this category: What is SIP Who is implementing SIP Where can I find more information about SIP What is RFC2543bis What is not described in???? THE SIP SPEC? There Are Lots of Sip Extensions. Will The Protocol EVER BE? How do you test Sip import for? What does 'BIS' Stand for? [Add A New Answer in "SIP Basics] 2001-OCT-01 7 : 21PM SIP FAQ: SIP Basics: What Is Sip? Sip Stands for session Initiation Protocol. SIP IS An Internet Proposed Standard Document Up, Controll . Ing and tearing down sessions in the Internet Sessions include, but are not limited to, Internet telephone calls and multimedia conferences 2000-Jun-28 2:22 pm mailto:. Hgs@cs.columbia.edu subject =?
SIP FAQSIP can initiate calls between regular telephones, if the switch is suitably equipped (so-called PINT mechanism) [Append to This Answer] 2000-Dec-15 10:29 pm SIP FAQ:. SIP Basics: Who is implementing SIP Lots of? People. Take a look at the partial list at http://www.cs.columbia.edu/sip/implementations.html http://www.pulver.com/sip/products.html, and http: // www. Sipforum.org/. at The Last Sip Bake-Off, There Were Approximately 60 Implementations. 2000-DEC-15 10:31 PM Mailto: Islepchin@dyNamicsoft.com? Subject = SIP FAQ, Mailto: hgs@cs.columbia.edu? Subject = SIP FAQ [Append to this answer] 2000-DEC-15 10:31 PM SIP FAQ: SIP Basics: WHERE CAN I FIND MORE INFORMATION ABOUT SIP?
The SIP home page contains additional information about SIP. Until September 1999, discussion about SIP took place on the MMUSIC mailing list. The working group and mailing list is still the appropriate place for discussions related to SDP, SAP and RTSP, among other topics. SIP standardization has now moved to the SIP working group, with its own mailing list The SIP Forum at http://www.sipforum.org also provides information about SIP 2000-Dec-15 10:33 pm mailto:.. islepchin @ dynamicsoft. COM? SUBJECT = SIP FAQ, MAILTO: HGS@cs.columbia.edu? Subject = SIP FAQ [Append to this answer] 2000-DEC-15 10:33 PM SIP FAQ: SIP Basics: What is RFC2543BIS? RFC2543BIS IS An Updated Version of SIP protocol that incorporates bug fixes and enhancements that have surfaced since RFC2543 was issued Most of the changes in RFC2543bis were discussed extensively on SIP mailing list;. hence, most of them are very likely to be included into the next official version of SIP. RFC 3261 Incorporates The Changes and Obsoletes RF C 2543. There are only minor changes between bis-09 and RFC 3261. The changes between RFC 2543 and RFC 3261 are described in an appendix in RFC 3261.The latest version of this document can be found at http: //www.cs .COLUMBIA.EDU / SIP2002-JUL-24 11:03 AM mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ, Mailto: hgs@cs.columbia.edu? Subject = SIP FAQ [Append to this answer] 2002-jul- 24 11:03 am SIP FAQ: SIP Basics: What is not described in the SIP spec The SIP specification describes what is necessary to create interoperable implementations It does not describe or limit the functionality offered by implementations or impose minimum functionality beyond request handling?.. Thus, SIP DOESN '
T tell you how to do any of the following: - the color of the phone; - what language is buy; - what snoud, if any, is used to indicate ringback or ringing; - whether a registrar, proxy or redirect server are implemented in one process, on one machine or distributed across a network; - which media types or codecs the SIP implementation supports; - which type of network SIP is used in; - what type of security measures are required to be used; - the GUI for SIP calls; - how to build a network of proxy servers; - whether a phone can make calls while it's in a call; - qualifications for human beings to make use of SIP softphones; - how generous an implementation should be in dealing with requests and responses that have mistakes and how much error detail information it should provide; - how many simultaneous calls the device can be in.- what parser generator tool, IF any, shouth be used by importation what threading model to use [Append to This Answer] mailto: hgs@cs.columbia.edu subject = SIP FAQ, mailto:?? islepchin@dynamicsoft.com subject = SIP FAQ2000-Dec-07 3:10 pm SIP FAQ: SIP Basics : There Are Lots of Sip Extensions. Will The Protocol Ever Be Stable? Innovation Will Not Stop, Since this isn '
t the phone system. However, the basic protocol has been stable for quite a while and is sufficient to implement all basic phone services. Enhancements tend to be for specialized services, such as ISUP interworking, QoS negotiation, liveness detection, caller preferences or presence / instant messaging. All of these are backward-compatible with the basic protocol, with extensions negotiated if both sides support them. Basic calls will succeed without the extensions.Note also that just because something is proposed does not mean it will ever become a (Only About 10% of Internet Drafts Ever Get Published As RFCS) [Append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2000-DEC-15 10:36 PM SIP FAQ: SIP Basics: How do you test SIP implementations? ETSI is preparing a test specification, both prose and TTCN-3, for SIP. This work is to be completed by November / December 2001. Anthony Wiles http://www.cs.columbia.edu/ ~ hgs/sip/anthony.wiles@etsi.fr can provide further details. Also, roughly every four months, the SIP interoperability test events (SIPit) offer opportunities for implementors to test interoperability with other implementations.The SIP call flows document also provides test cases [Append to This Answer] mailto:. Hgs@cs.columbia. EDU? SUBJECT = SIP FAQ2001-SEP-19 2:29 PM SIP FAQ: SIP Basics: What Does 'Bis' Stand for? The suffixes 'Bis' AND 'Ter' Are Off Used for Revisions of Standards. for Example, There IS V .42bis for modems and v.25Ter. 'Bis', while 'ter' stands for 'Three'. Seehttp://www.informalmusic.com/latinsoc/latnum.htmlfor Details. 2001- Oct-01 7:24 PM Mailto: HGS @
cs.columbia.edu?subject=SIP FAQ [Append to This Answer] 2001-Oct-01 7:24 pm SIP FAQ: SIP FunctionalityDescribes how to provide standard services with SIP Subcategories:. Answers in this category: Does SIP support the standard telephone features? How does SIP provide message waiting services? Why does CSeq not have a compact form? How does the location server communicate with a proxy? How does SIP support caller ID? How do I charge / bill for Internet telephony using SIP? How do prepaid calling cards work in a SIP network? does SIP do conference control? How do I put a call on hold? How does SIP do "call progress tones" or "ring back"? does SIP do admission control? does SIP administer bandwidth? How does SIP support multipoint conferences? How does SIP support text chat and instant messaging? does SIP support video or multimedia conferences? When do I use a proxy server vs. a redirect server? How do gateways register with a registrar? [Add a New Answer in "SIP FunctionALITY] 2002-JUL-24 10:58 AM SIP FAQ: SIP Functionality: Does SIP support the standard telephone features Yes SIP supports, among others: -?. Call forwarding unconditional, busy, ... - call transfer (call control spec) - caller ID- call hold- 3-way conferences and multiparty Conferencing (Call Control Spec) - CALL RETURN ("* 69"
) - call park (with NOTIFY) - follow-me- find-me- call waiting - IVR systems - multiple line presences - camp on - call queueing- automatic call distribution- do not disturb Some services, like repetitive dialing, station speed dialing , last number redial, and distinctive ringing, are implemented purely in the end system and require no support from the signaling protocol. The Telecommunications Industry Association (TIA) is working on a recommendation http://www.tiaonline.org/standards/ip . / for business PBX-style services and other Internet phone requirements [Append to This Answer] mailto: hgs@cs.columbia.edu subject = SIP FAQ2000-Jun-28 2:47 pm SIP FAQ:? SIP Functionality: How does SIP provide message waiting services? First, there may well be other protocols that are more appropriate to indicating that voice or email messages are available, for example POP or IMAP. In particular, once one moves beyond a simple message waiting light to indication of message counts, Urgency, Senders, etc., . It is likely that any SIP-based solution starts replicating POP or IMAP functionality A SIP-based solution has not been standardized yet Using SUBSCRIBE and NOTIFY appears to be the most appropriate approach [Append to This Answer] mailto:.. Hgs @ cs .columbia.edu subject = SIP FAQ2000-Jun-28 2:56 pm SIP FAQ:? SIP Functionality: Why does CSeq not have a compact form This was an oversight, as all other SIP mandatory headers have a compact form However, it's?. too late to change this since older implementations would not know what to do with the single-character form fortunately, the penalty is only three bytes [Append to This Answer] mailto:.. hgs@cs.columbia.edu subject =?
SIP FAQ2000-Jun-30 7:38 pm SIP FAQ: SIP Functionality: How does the location server communicate with a proxy Location server and proxy server are logical entities, not physical ones They can reside in one host or application or be distributed across?. . several hosts or applications The API or protocol used between them is not specified, as it is an implementation decision (Generally, most implementations combine a location server with a proxy.) [Append to This Answer] 2000-Jul-01 5.: 42pm SIP FAQ: SIP Functionality:? How does SIP support caller ID Caller-ID is provided by the From SIP header containing the caller's name and "number" The number would most likely be placed in the user field of a SIP URL or appear. in a tel:. URL Since the callee generally does not know or trust the callee's server, only cryptographic signatures can be used to ensure that the information is valid For example, the outgoing proxy might be operated by an ISP, enterprise or phone company. And Sign for the ID entity of the caller, using the signed-by parameter, with the identity of the company verified by a public key certificate similar to those used by web sites. See section 13.2 of RFC2543bis for encryption details. 2000-Jul-02 10:50 pm mailto :? islepchin@dynamicsoft.com subject = SIP FAQ [Append to This Answer] 2000-Jul-02 10:50 pm SIP FAQ: SIP Functionality: How do I charge / bill for Internet telephony using SIP This depends on whether you plan to? Charge for SIP Services Like Directory Look-Ups, Call Processing Or Mobility, for Gateway Services To the Pstn, or for Carrying Media Data:
SIP SERVICES
THE
Authorization Header Can Be Used to Indicate A Customer Identity That Associates a SIP Request with a Billage Entity.
Examples of Possibly Chargeable SIP Services include:
Directory Services Suokups; Customer Profile Management; SIP Server Operations Can Be Charged Based ON Server Logs OR, For Real-Time Billing, Via AAA.
Media Services
Media Services include Retrieving and Storing Voice Mail, AS Well As Transcoding of Media Streams. They Are Not Initiated by SIP, But, For Example, VIA
RTSP.
Gateway Services
Similar to SIP services. Care has to be taken to stop billing when (say) RTP voice data is no longer flowing through the gateway. The gateway will generate call detail records (CDRs) either directly or through RADIUS.
TRANSPORT (NetWork Services)
It seems unlikely that voice calls carried over a best-effort service will generate per-minute charges. When reserving bandwidth or guaranteeing other quality-of-service parameters, the resource reservation protocol or differentiated services are the appropriate mechanism for including charging. These reservation protocols will likely be used in applications that are not initiated by SIP, for example, audio / video on demand or VPNs. Actual accounting records may be generated by AAA protocols (eg, by policy enforcement points (PEP) or policy decision points (PDP .))).
Under some circumstances, a SIP proxy server may be useful to initiate such reservations or differentiated services treatment on behalf of a call, since it may be easier to authenticate the SIP request than the lower-layer reservation request or the end system may not be capable Of Making Reservations or Marking Packets. in Those Cases, The Sip Proxy Would I Resource Reservation and "Charge Back" The Caller Identified by The Sip Request.
Dean Willis wrote with regards to billing for SIP services: Why can not service providers make a living providing (at a fixed cost) access to "free services" Do carriers do per HTTP-transfer billing now How much should they charge for?? An Email? for a call, What parameters might be used? Bandwidth, Duration, Distance - The Big Factors of the Pots Bill - Are Not Issues That Sip is Concerned with.
2000-JUL-02 10:55 PM Mailto: Islepchin@dynamicsoft.com? Subject = SIP FAQ
[Append to this answer] 2000-jul-02 10:55 PM SIP FAQ: SIP FunctionAlity: How do prepaid calling cards Work in a Sip network? Note That, in General, Prepaid Calling CARDS Only Make Sense In an IP network if there is a special-purpose VoIP internet, calls traverse a IP-to-PSTN gateway or VoIP packets receive special treatment. The SIP requests are forced to traverse a stateful proxy or a back to back User Agent (B2BUA), which controls the Internet telephony gateway , router QOS function or firewall, depending on the architecture. When the time is used up, the B2BUA or gateway issues a BYE request to both parties, using the existing call ID. It also disables the gateway connection, turns off any special QOS treatment for the RTP packets or closes the firewall for that stream. This requires no additions to either caller or callee. Sending a BYE suffices only if at least one of the end systems can be trusted to actually terminate the call when a BYE is received. 2001 -JAN-22 10:57 PM Mailto: IS lepchin@dynamicsoft.com?subject=SIP FAQ, mailto:? jdrosen@dynamicsoft.com subject = SIP FAQ [Append to This Answer] 2001-Jan-22 10:57 pm SIP FAQ: SIP Functionality: Does SIP do conference control SIP? leaves conference control, such as the election of a chair or floor control, to other protocols. SIP can be used for non-conferencing applications and floor control may be used outside the scope of SIP-initiated calls, so it seemed best to separate the . functionality However, SDP may be used to indicate which media are subject to floor control and what tools and protocols are to be used Unfortunately, there is no IETF-standardized floor control protocol 2000-Jul-03 6:39 pm mailto:.. islepchin @ DYNAMICSOFT.COM? SUBJECT =
SIP FAQ [append to this answer] 2000-jul-03 6:39 PM SIP FAQ: SIP Functionality: How do i put a call on hold? The party Wishing to Put The Other Party on Hold Sends A (Re) Invite, with a SESSION Description Containing a null (0.0.0.0) Address. When Used with sdp, the "c" address field of one or more Media Types is set to zero. 2000-jul-03 7:07 PM mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ [Append to this Answer] 2000-JUL-03 7:07 PM Sip FAQ: SIP FunctionAlity: How does Sip do "Call Progress Tones" or "Ring Back"? The Sip Server Being Called, Such as an Internet Telephony Gateway, Can Return Any Number Of Province, THATI, THIS JUST 100 (RING), BUT A Server Could Produce ElaBorate Feedback Such AS
100 Message Received
100 looking up number
100 Found Number, Looking Up Carrier According to Profile
100 Finding Cheapest Carrier Which Doesn't Do Animal Testing
100 Found Carrier "AT & T"
100 DiAlation Number
180 ringing
182 Queued, 3 people in Front of You
182 Queued, 2 people in front of you
............. ..
A 183 (Session Progress) Status Response Will Appear in RFC2543bis. It can be used for Both Progress Tones As Well As Error Messages.
One Would Use the 183 Only if you:
Are able to determine that the audio being generated is something other than ringing (eg "comfort tone" or "pay tone" as defined in E.18x), or Are unable to definitively determine that alerting is occuring. This really should only happen with older CAS protocols. ISUP and ISDN have sufficient information to determine what is happening on the far end.One can also use 183 if the gateway is able to determine that an error has occured, but that there is a tone or announcement accompanying it (eg AN ACM WITH, THE GATEWAY CAN SEND A 183 TO SET UPETEMENT As The Text String, Wait For A Timer (on the order of 30 Seconds, and the send an appropriate SIP Error Message.
However, this sales is likely a human being, as sending 183 1010 Would Otherwise Only Delay Failure Handling.
Take a look at Draft-Ietf-SIP-183-00.txt for Some Details On Using 183 Responses for Early Media Announcements. 2000-JUL-03 7:23 PM Mailto: Islepchin@dynamicsoft.com? Subject = SIP FAQ
[Append to This Answer] 2000-Jul-03 7:23 pm SIP FAQ: SIP Functionality:?. Does SIP do admission control Since this offers no real security (calls could always bypass a server), admission control is not supported by SIP If an "outbound proxy" is used for outgoing calls, that proxy may control the firewall and thus restrict outgoing calls ans resources used 2000-Jul-03 7:51 pm mailto:. islepchin@dynamicsoft.com subject = SIP FAQ [Append to This? Answer] 2000-Jul-03 7:51 pm SIP FAQ: SIP Functionality:? Does SIP administer bandwidth No, that is the role of a resource reservation protocol There is no reason to assume that any Internet telephony signaling server (such as a proxy. ) would know the available bandwidth in real networks. Having such a central server would not scale. Administering bandwidth separately for each application is also likely to be difficult and inefficient. There is a proposal for an SDP extension that allows SIP INVITE requests and responses to Indicate That Resource Reserv . Ation must succeed before the callee is alerted Several proposals can also be found at http://www.cs.columbia.edu/~hgs/sip/drafts_qos.html 2000-Jul-03 7:55 pm mailto:. Islepchin @ dynamicsoft .com? Subject =
SIP FAQ [Append to This Answer] 2000-Jul-03 7:55 pm SIP FAQ: SIP Functionality: How does SIP support multipoint conferences SIP has four ways to do multiparty conferencing:? 1. Dialup conference bridge: call the bridge just like you . call a person Conference is identified by request URI Works with rfc2543 -. no extensions needed 2. Distributed multiparty conferencing -... no server Fully distributed This is what is described in the now-expired draft, and is work in progress (see . http://www.softarmor.com/sipwg/teams/callcontrol/index.html for some recent drafts) 3. multicast conferences - you can run your conference on multicast Simply INVITE the person to join the multicast session Works with.. Baseline Sip. in Fact, this Was The Initial Purpose of Sip. in this case, there is not a fulamed of sip signaling. 4. 3-Way with local mc / mp function: a and b area talking. A Wishes To Add C To The Call C, But Also Act As A Mixer, So That The Media It Sends To B Contains The A C media, and the media to C is the A B media. RTCP CSRC indicate who is in the conference. This also works with baseline SIP. It imposes additional burden on the UA, but otherwise provides this standard feature in a simple Way. There is no preferred Way. It depends on the particular application. (Jonathan Rosenberg) 2000-jul-06 9:16 PM mailto: islepchin@dynamicsoft.com? Subject =
SIP FAQ [Append to This Answer] 2000-Jul-06 9:16 pm SIP FAQ: SIP Functionality:? How does SIP support text chat and instant messaging Text chat can be supported as part of SIP sessions using the RTP text conversation payload format ( . RFC 2793) Typically, text is sent one character at a time, although almost any number of characters can be packed into a single RTP packet.Instant messaging (IM) differs from text chat in that: - messages are sent as a whole and can be in any format, such as HTML; - messages are independent of a session setup; - store-and-forward or translation to email are feasible; SIP can support IM through the use of the proposed MESSAGE method [Append to This Answer. ] mailto: hgs@cs.columbia.edu subject = SIP FAQ2000-Aug-21 11:18 am SIP FAQ:? SIP Functionality:? Does SIP support video or multimedia conferences SIP was designed to support multimedia conferences, including video conferences, from the Very beginning. It can use any media type, incruade one or more surrio, video, shared application or text chat streams. For multiple participants, SIP can be used for- dial-in-style conferences with a central "bridge" (MCU) or multicast- dial-out conferences with a central bridge or multicast- multicast conferences- full Or Partial Mesh Conferences, WHERE End Systems Replicate Media Streams. [Append to this answer] mailto: hgs@cs.columbia.edu? Subject =
SIP FAQ2000-Aug-22 12:13 pm SIP FAQ: SIP Functionality: When do I use a proxy server vs. a redirect server I believe the difference is fundmentally one of control.You use a proxy when you want to control processing of the? call from the point you receive it, and forward. A proxy can see the provisional and final responses to the request. It can record route so that it sees whats going on during the call. A redirect server, however, hands off control to the device that sent it the INVITE. It will never see the final response to the request, and not be contacted again for the remainder of the call. Its a one-shot deal.As such, redirect servers are really good for high volume, lookup . style transactions They can almost be considered a form of database query, albeit a SIP specific one Proxies are generally needed for services and more complex routing problems 2000-Nov-14 10:50 am mailto:.. jdrosen@dynamicsoft.com subject =? SIP FAQ [Append to this Answer] 2000-NOV-14 10:50 AM SIP FAQ: SIP FUNCT ionality: How do gateways register with a registrar In H.323, the entity can register to Gatekeeper as Terminal type or as Gateway type with a prefix In SIP, the working group decided that registering PSTN prefixes is not the right approach, as?. it is insufficiently flexible and does not fit into the precise-match registration lookup mechanism. Rather, proxies make routing decisions based on local policy mechanisms, eg, static tables, TRIP routing information, or SLP (with gateway registration template). [Append to This Answer] mailto: hgs@cs.columbia.edu? Subject =
SIP FAQ2002-Jul-24 11:05 am SIP FAQ: SIP Protocol OperationContains FAQ and clarifications on protocol operation Subcategories:. Answers in this category:? What does the [H14.17] in RFC 2543 stand for Do callers need to know the location of the Location Server? What is the difference between a call leg and a call id? What is the difference between tag and branch-id? How can one recognize a retransmitted, duplicate or looped request? What is the relationship between the From, Contact ?, Via and Record-Route / Route headers How are URLs compared What's the difference between the request URIs tel:? 12125551212 and sip:? 12125551212@gw.com Do I always need a proxy or redirect server How does a caller find? its local registrar? How do I ensure registrar reliability? are ACK requests retransmitted? How are BYE requests routed? Can I CANCEL requests other than the first INVITE? How does a caller find its proxy server? What's the difference between a stateless and a stateful Proxy Server? Why Can a forking SIP PR oxy not be stateless? How does a caller find the remote SIP client of the callee? How does SIP get through a firewall? Does SIP do keep-alive? Why does SIP not have a Content-Transfer-Encoding header? I want SIP to be more compact. What can I do? What are the different addresses in SIP? The BNF for header
MA UAC. I Sent An Invite, And The Decide I Want To Hang Up Before Getting A Final Response. Do I Send Bye or Cancel? I'm A Proxy, And i forked A Request, And Forwarded Multiple 200 OK Upstream. Now, I get an Ack. What do I do with it? If i get a new sdp body in the Ack, and I don't like the Media Type, How can I indeicate its unacceptable to me? Can a Sip Ua Register with Multiple Registrars ? Is it a call to itself, and how the result be two separate calls on the estuest-uri or to field to determine if a call is for it? How are SIP parsers implemented? Is it possible to use Hide with Record-Route? How does a proxy handle a method other than the standard INVITE, ACK, BYE, etc.?Why does a proxy server doing TCP need to be stateful? In computing the Content -Length, Does The Newline In A Body Count As One Byte Or Two (CR VS. CR-LF)? Can a Proxy Fork A Non-INVITE REQUEST? IF YES, What HAPPEN HAPPENS MULTIPLE RESPONSES? SHOULD RESPONSES B e sent to the host specified in Via? Is From ever used for sending responses? Once a SIP registrar gets a REGISTER request, how does it update the Location Server with the contact information? Is a SIP URI without a user name valid? Is there a specific order for header fields? When is a CANCEL used? What do I need to do to use SRV records? Why does SIP / SDP allow for multiple codecs to be used for the same media stream? What are spirals? Why does a proxy ? care What's the difference between loose and strict source routing [Add a New Answer in "SIP Protocol Operation"] mailto:?? islepchin@dynamicsoft.com subject = SIP FAQ, mailto: jdrosen@dynamicsoft.com subject = SIP FAQ,? Mailto: hgs@cs.columbia.edu? Subject =
SIP FAQ2002-MAR-07 6:53 PM Sip FAQ: SIP Protocol Operation: What Does The [H14.17] in RFC 2543 Stand for? This Is Explained in Section 3 of RFC 2543. IT Refers To The Section Number in The HTTP / . 1.1 specification [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 8:06 pm SIP FAQ:? SIP Protocol Operation: Do callers need to know the location of the Location Server The caller doesn? 't interact with the location server directly. A redirect or proxy server asks the location server (which may be co-resident with the SIP server or not) for "advice". The location server is just a logical abstraction to indicate where the SIP Server Gets ITS Information from. The Protocol Between Sip Server and Location Server is Beyond The Scope of Sip. Examples of Location Servers Include
Finger; LDAP / X.500; WHOIS, WHOIS ; Phid File Systems with registration on login; LOCAL SQL DATABASES Reached THRough TCP.
Also, Callers Don n't register with the location server.
[Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 8:11 pm SIP FAQ:? SIP Protocol Operation:? What is the difference between a call leg and a call id A call leg refers to THE-TO-One Signaling Relationship Between Two User Agents (UAS). The call-id is an identifier, carried in the Sip message, That ReferS to the call. a call is a collection of call legs. a uac starts by sending an INVITE;... because of forking, it may receive multiple 200 OKs from different UAs Each corresponds to a different call leg within the same call Call is thus a grouping of call legs In the call control spec, additional call legs are created through special mechanisms. Call legs refer to end-to-end connections between user agents, rather than any relationship with proxies. Within a call leg, there are numerous transactions in both directions. The request URI is not used in call leg identification. The to And from Field Relate to local and remote in the folloading way. When Ali ce sends a request on a call leg to Bob, the From field contains the local address (Alice), and the To field the remote address (Bob). When a request is received by Bob, the To field is matched to Bob's local address , and the From field to the remote address (Alice) The CSeq spaces in the two directions of a call leg are independent Within a single direction, the sequence number is incremented for each transaction [Append to This Answer] mailto:... islepchin @ dynamicsoft.com subject = SIP FAQ2000-Jul-03 8:19 pm SIP FAQ:? SIP Protocol Operation: What is the difference between tag and branch-id Branch IDs allow proxies to match responses to forked requests Without them, a proxy?. Wouldn '
t be able to tell which branch a response corresponds to. Tags, in To headers, are of no help here since they are not known until responses arrive. Tags are used by the UAC to distinguish multiple final responses from different UASs. A UAS has no reliable way of determining if the request has been forked or not Thus, to be safe it needs to add a tag Proxies only insert tags into the final responses they generate themselves;.. they never insert tags into requests or responses they forward Since. a request can be forked several times on its way to UAS, a single "tag" (or whatever you like to call it) added to the request by one of the proxies is not sufficient for the next forking proxy along the chain to match responses on its own branches; every proxy that forked the request would need to add its own unique IDs to the branches it created This is precisely what's being achieved by the branch parameter in the Via header [Append to This Answer] mailto: islepchin @.. Dynamicsoft.com?subject=si P FAQ2000-JUL-03 8:23 PM Sip FAQ: SIP Protocol Operation: How Can One Recognize a Retransmitted, Duplicate or Looped Request? Header Retransmitted Duplicate Matching Response
From same same
To Same Same Same, But Tag May Have Been Added
Call-id Same Same Same
Request Uri Same Same N / A
CSEQ Same Same Same
Via - - Must Be Local Host; Check for Branch Parameter To Identify Which Branch
Looped Request Are Recognized by One of The Following:
The server finds itself in the request's Via list, including any branch parameter. (The server should compute the branch parameter so that it depends on the request URI.) Take a look at sections 6.47.5 and 12.13.1 of RFC2543bis for details on . computing and matching branch parameter for loop detection The Via header added by the server prior to proxying the request is the same as one of the Via's in the Via list [Append to This Answer] mailto:. islepchin@dynamicsoft.com subject =? SIP FAQ2000-Jul-03 8:57 pm SIP FAQ: SIP Protocol Operation: What is the relationship between the From, Contact, Via and Record-Route / Route headers All these headers determine how requests and responses are routed in a network of SIP? . proxy servers Roughly, the distinction is: - from: Used for subsequent requests from the callee to the caller if there is no Contact or Record-Route header Eg, if Alice makes a call with from: Alice sip: alice @ example.. Org to Bob, An Invite Request from Bob To Alice Would Uses SIP: Alice @
example.org as the To header and Request-URI - Contact:. Determines the destination placed in the Request-URI for subsequent requests and can be used to bypass proxies _not_ enumerated in a Record-Route header Also used in responses by redirect servers. and in REGISTER requests and responses - Record-Route / Route:. The Record-Route header is inserted into requests by proxies that want to be in the path of subsequent requests for the same call-id It is then used by the user agent. . to route subsequent requests The mechanism is similar to a source-route, as the Record-route information is copied into a set of route headers The Request-URI is set to the first route header - Via:.. Via headers are inserted by servers into requests to detect loops and to allow responses to find their way back to the client. They have no influence on the routing of future requests (or responses). Generally, in short, requests should be sent to Route if present, Contact if There is no route, from if there is n . O Contact [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-06 1:03 am SIP FAQ:? SIP Protocol Operation: How are URLs compared Two SIP URLs are compared for equality according to the? following rules: -. the display name is ignored; - tags must match; - user, password, host, port and parameters of the URI must match If a component is omitted, it matches based on its default value - string comparisons are case. -Sensitive Except for the domain part; - Characters Other Than Those in the "reserved" and "unsafe" sets (see rfc 2396) Are Equivalent to their ""% "HEX HEX"
. Encoding - An IP address that is the result of a DNS lookup on a hostname does not match that hostname This is TBD [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 9..? : 11pm SIP FAQ: SIP Protocol Operation: What's the difference between the request URIs tel: 12125551212 and sip:? 12125551212@gw.com Non-SIP URLs, such as tel: 12125551212 for a telephone number, may be used as request . URIs in SIP INVITE requests This only makes sense if all outbound calls are handled by a proxy server in the case of a tel:. URL, the proxy server would then translate the request URL to a SIP URL of a gateway server, if it . is not handling the gateway duty itself The proxy server might use the Telephony Routing over IP protocol (TRIP) to find the appropriate next-hop SIP server The to header may always be a tel:. URL even if the Request-URI is a SIP URL, Althought, Alth That Request-Uri and To Start Out The Same. [Append to this Answer] MAILT o: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 9:14 pm SIP FAQ:? SIP Protocol Operation: Do I always need a proxy or redirect server No, two SIP user agents can contact each other directly [Append?. To this answer] mailto: islepchin@dynamicsoft.com? Subject =
SIP FAQ2000-Jul-03 9:14 pm SIP FAQ: SIP Protocol Operation:? How does a caller find its local registrar The local registrar is either manually configured or, more likely, the SIP client issues a multicast registration request to the sip.mcast .net standard multicast address, which all registrars listen to. Another possibility is to use SLP through an extensions defined in http://www.cs.columbia.edu/~hgs/sip/drafts/draft-kempf-sip-findsrv- . 00.txt [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 9:34 pm SIP FAQ:? SIP Protocol Operation: How do I ensure registrar reliability There are several techniques that can be? used to minimize the impact of registrar / proxy server failures for a server in a local area network: - Run several servers that all respond to the same multicast registration address ( "warm standby") As long as multicast requests are mostly reliable, this. Ensures a Consistent Registration Picture. - IF A Registration Server IS Rebooted and DO es not have complete knowledge of the local UA population, it could multicast any incoming INVITE requests -. Use some of the available hardware redundancy solutions For servers separated from their client by a wide-area network, use of multicast is not appropriate, so. . that these servers have to rely on traditional backup techniques to achieve reliability For example, the designated registrar could multicast registration updates within its local network to keep standby servers synchronized [Append to This Answer] mailto:. islepchin@dynamicsoft.com subject =?
SIP FAQ2000-Jul-03 9:19 pm SIP FAQ: SIP Protocol Operation:?. Are ACK requests retransmitted No An ACK is sent when a response retransmission is received Reliability is achieved because the response is retransmitted until an ACK arrives, and the ACK. .. is retransmitted on response retransmissions ACK is only used for INVITE [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 9:20 pm SIP FAQ:? SIP Protocol Operation: How are BYE requests routed ? Since a Contact header MUST be present in INVITE and 200, the BYE will go directly to the user agent if there is no Record-Route header. If there is a Record-Route, it will traverse the list of proxies indicated there. If the caller decides to send a BYE before receiving a 200 from the callee, the BYE is be handled by the proxies just as the corresponding INVITE was handled, ie, it may be forked 2000-Jul-03 9:21 pm mailto:. islepchin @ Dynamicsoft.com?subject=sip FAQ [Append to this answer] 2000-jul-03 9:21 PM SIP FAQ : SIP Protocol Operation:? Can I CANCEL requests other than the first INVITE Yes, any request can be cancelled before it has been executed by the UAS However, it is likely that this will only make sense in practice for the initial INVITE and subsequent. .. re-INVITEs In the latter case, the call remains, just any changes requests are cancelled [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 9:22 pm SIP FAQ:? SIP Protocol Operation:? How does a caller find its proxy server Calls typically proceed directly to the callee's domain for example, when calling alice@example.com, the INVITE request would be sent to the SIP server for the domain example.com, found via. DNS. If A "
local "(outbound) proxy is needed for outgoing calls, it currently needs to be manually configured, similar to the configuration of web proxies in browsers Another possibility is to use DHCP or SLP through one of the extensions listed in http:. // www . .cs.columbia.edu / ~ hgs / sip / drafts_dhcp.html [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 9:26 pm SIP FAQ:? SIP Protocol Operation: What's the difference between a stateless and a stateful proxy server? Stateless proxies forget about the SIP request once it has been forwarded. Stateful proxies remember the request after it has been forwarded, so they can associate the response with some internal state. In other words, stateful proxies maintain transaction state. Stateful implies transaction state, not call state. Stateless proxies scale very well, and can be very fast. They are good for network cores. Stateful proxies can do more (they can fork, for example, see the next question ) And Can Provide Services stateless ones can not (call forward busy, for example) They do not scale as much as stateless ones An admininstrator gets to decide which to use These are also logical entities;... a physical proxy is likely to act as a stateless proxy for some calls, stateful for others, and as a redirect server for even others. Neither stateful nor stateless proxies need to maintain call state, although they can, but will need to make sure that they are part of via the Record- subsequent transactions Route header. A proxy must be stateful if one of the following conditions Hold: 1. IT Uses TCP, 2. IT Uses Multicast, 3. It forks. [Append to this answer] mailto: islepchin@dynamicsoft.com? Subject =
SIP FAQ2000-Jul-03 9:37 pm SIP FAQ: SIP Protocol Operation: Why can a forking SIP proxy not be stateless A forking SIP proxy can not be stateless because it needs to perform a filtering operation, returning (in general) one response out? of the many it receives. For example, a forking proxy with three branches, that receives a 200-class, 400-class, and 500-class response on each branch respectively, should return only the 200-class response upstream. If the proxy were stateless, it would end up returning all three of the responses upstream (since it will not remember that it had received prior responses when it gets another one). The result of this is (1) response implosion at the client, and ( 2) inconsistent responses at the client. (In this example, depending on the order the responses received, the client might think that the call failed, just to get a success indication some time later.) Thus, a forking proxy must be stateful. Also Note That A Proxy That Uses TCP Must Be Stateful As W ell, whether it forks or not This has to do with reliability issues Why do you want state in a proxy Certain services (like forking) simply require it A sequential search proxy requires state;..?. sequential search is the heart of services like follow-me and personal mobility. It's at the discretion of the implementor whether to use a stateful or stateless proxy. You can even be "super stateful", and use the Record-Route header to allow a proxy to be on the signaling path of All subsequent Exchanges. This allows a stateful proxy to maintain call state in addition to transaction state. [append to this answer] mailto: islepchin@dynamicsoft.com? Subject =
SIP FAQ2000-Jul-03 9:48 pm SIP FAQ: SIP Protocol Operation: How does a caller find the remote SIP client of the callee The process is similar to the delivery of email:? The caller uses the SIP host name to look up the destination host, first trying a SRV record and then "regular" DNS, just like an email client (MTA) looks up the MX record. (SRV records are generalized MX records applicable to any network service, including, but not limited to, SIP And RTSP.) for Example, When Contacting Sip: Bell@cs.columbia.edu, The Client Finds A Srv Record Pointing To Erlang.cs.columbia.edu as The Sip Server for the domain cs.columbia.edu. as for email , a single domain name can resolve to multiple servers, allowing load sharing and redundancy The server located in this manner can then proxy or forward the call to another server [Append to This Answer] mailto:..? islepchin@dynamicsoft.com subject = SIP FAQ2000-JUL-03 9:51 PM Sip FAQ: SIP Protocol Operation: How does Sip Get Through a firewall? There is several possible approaches to SIP-capable firewalls. One of the difficulties is that, unlike for, say, HTTP, connections are originated both by hosts inside and outside the firewall. A likely arrangement is that a SIP proxy sits "on"
the firewall and relays SIP requests between the Internet and the intranet. Thix proxy would also open up the necessary ports in the firewall to let audio and video flow through, for example using Socks V5. As an alternative, if a firewall or NAT allows outgoing TCP connections, the inside client can open up a TCP connection to an outside proxy. All outgoing and incoming calls would then be handled by that TCP connection. (The client would still have to use SOCKS or similar mechanism to convince the firewall to let RTP packets through.) Take a look at the two dratfs at http://www.cs.columbia.edu/~hgs/sip/drafts_firewall.html for a more detaled discussion of getting SIP through firewalls and NATs. [Append to This Answer ] solepchin@dynamicsoft.com? Subject =
SIP FAQ2000-Jul-03 9:56 pm SIP FAQ: SIP Protocol Operation:?. Does SIP do keep-alive SIP itself does not have a keep-alive mechanism during the call It was felt that loss of connectivity would be detected rapidly by the absence of media packets, typically sent at a much higher rate than any signaling keep-alive messages could be sent. In addition, the signaling path is not needed during the conversation and may well be completely different (due to proxy and redirect servers) than the media path, so that keep-alives have a limited functionality. If it is desired to test the liveness of a signaling server, it is always possible to send either OPTIONS or (re) INVITE messages. However, knowing the call state might be useful for certain applications (eg, when billing is involved, when firewall permissions need to be set etc.). Session timer extension has been defined to solve this. The draft can be found at http://www.cs.columbia.edu / ~ hgs/sip/drafts/draft-ietf-sip-ession-timer-01.txt and . It basically allows the servers indicate a desired refresh interval The call is considered terminated if a re-INVITE is not received within that interval [Append to This Answer] mailto:. Islepchin@dynamicsoft.com subject =?
SIP FAQ2000-Jul-03 10:29 pm SIP FAQ: SIP Protocol Operation:? Why does SIP not have a Content-Transfer-Encoding header The Content-Transfer-Encoding header was primarily meant to allow message bodies to be transformed into formats that could be transferred on channels that were not 8 bit clean. HTTP, which makes use of many of the MIME headers, is 8 bit clean, and thus did not need Content-Transfer-Encoding. SIP followed suit, and so does not use it either . Content-Encoding is used for things like compression, which is different (J. Rosenberg) See also RFC 2616 (HTTP / 1.1), Section 19.4.5 [Append to This Answer] mailto:.. islepchin@dynamicsoft.com subject? = SIP FAQ2000-JUL-03 10:53 PM Sip FAQ: SIP Protocol Operation: I Want Sip to Be More Compact. What Can I Do? First, One SHOULD REALIZE THAT INEERAL, SIP Exchanges Are INLENERAL, SIP Exchanges Are Only Going to Be a Tiny Fraction of The Overall Session Bandwidth. A Typical Sip Call Setup Takes Less Than 1000 Bytes, or the Equivalent of One Second of Highly Compress ed (G.729) audio. Some additional space savings can be realized by using short headers. (A realistic example for an audio call setup takes a total of about 640 bytes, of which about 69 bytes are SIP headers.) In general, more substantive savings are possible by using either payload compression (RFC 2393) or link-layer compression, eg, at the PPP layer. For the example above, the total size is reduced to about 520 bytes with gzip compression. [Append to This Answer ] solepchin@dynamicsoft.com? Subject =
SIP FAQ2000-Jul-03 10:55 pm SIP FAQ: SIP Protocol Operation: What are the different addresses in SIP SIP INVITE requests involve three addresses:? 1.The host address where the request came from Responses are sent back to the same host. address, regardless of what the from header indicates. Note that different requests for the same call can come from different hosts. 2.The from address contains the logical source of the request. It remains unmodified as a SIP request traverses proxies, for example. The From address may not be the same as the host address that generated the SIP request, although that's the typical case. 3.The session description (eg, SDP) contains one or more addresses where the caller expects media data (audio, video) . to be sent For some services, this address may not be the same as the From address [Append to This Answer] mailto:. islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-04 11:12 pm SIP FAQ:? SIP Protocol Operation: The Bnf for Header
example.com, and the server for example.com is listening on 5061. The request URI might look like: INVITE sip: joe@example.com: 5061 SIP / 2.0this arrives at example.com Since the request is for that server. , it looks up joe in some database and translates the request URI (for example, to sip: joe@engineering.example.com). It looks up engineering.example.com in DNS, and finds an A record for that machine, forwarding the request to the given IP address The outgoing request URI looks like:. INVITE sip: joe@engineering.example.com SIP / 2.0Note that in this case, the presence of port 5061 in the request URI sent to example.com didn ' t make a difference. Thats because the example.com just translated the request URI. Whether it had contained the port number or not would have had no effect on processing.However, had the request instead been sent to a local outbound proxy instead of example .com, the port number would Need to be there. Thats Because The Local Outbound Proxy Won't Translate The Request UR I, it will example it, determine its not for itself, look up the domain in the request URI in DNS, and forward the request there. So, the request URI needs to contain this port so that the local outbound proxy knows to forward it to 5061 as opposed to 5060 at example.com.So, the rule of thumb is this: if you send a request to the server listed in the domain of the request URI, URI parameters like port, transport, ttl etc MAY be present but are not needed. If you send a request to a server which is nOT the one identified in the request URI, you MUST include these parameters if they are not the defaults. Always inclduing them, when not default, means you don '
t need to determine which is the case, and is always the safest bet [Append to This Answer] mailto:. jdrosen@dynamicsoft.com subject = SIP FAQ2000-Jul-06 11:25 am SIP FAQ:? SIP Protocol Operation: Transport in ViaIf a proxy sends a request by UDP (TCP), the spec currently does not disallow placing TCP (UDP) in the transport parameter of the Via field, which it should. If such a request is received, it should be responded to with a . 400 Bad Request The protocol used for the request should also be used for the response [Append to This Answer] mailto:. islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-06 9:03 pm SIP FAQ:? SIP Protocol Operation: What should I do if my re-INVITE fails Here is what you should _not_ do:? you should _not_ terminate the call re-INVITE failure means that the request to change the media was declined and you should keep using the old media codecs you. Negotiated previously. [append to this answer] mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ2000-JUL-06 9:02 PM Sip F AQ: SIP Protocol Operation: How long CAN SIP HOST NAMES BE? DNS (RFC 1035, Section 3.1) Limits Labels (Each Component of a host name) to 63 character length of a domain name (IE, Label Octets and Label length octets) is restricted to 255 octets or less. http://www.networksolutions.com/help/long-domains.html, however, claims that host names can be up to 80 characters long. Note, however, that SIP implementations MUST be prepared to handle host names of any length, subject to any maximum message size restrictions that are part of local policy [Append to This Answer] mailto:. hgs@cs.columbia.edu subject = SIP FAQ, mailto:? jdrosen @ Dynamicsoft.com?subject=
SIP FAQ2000-Jul-06 9:06 pm SIP FAQ: SIP Protocol Operation: Can a User Agent also act as a Registrar Being a UA is a logical role, as is a registrar If an entity accepts REGISTERs and stores location information, its?. A registrar. so, you can write a basce of code this is book a ua and a registrar if you want. (Append to this answer] mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ2000-JUL-06 9:19 PM Sip FAQ: SIP Protocol Operation: Can I Remove An M = LINE from SDP in response or re-invite? No. Once an "m =" LINE Made it Into SDP of a Request Or Response, IT Cannot Be Removed Until THE ONLY WAY TO DECLINE A Media Session Is by Setting ITS Port Number To 0. The Only Way To Offer A New Media Session Is By Add. The Reason for this Is That We NEED TO Ensure That It is always Possible To Match Media Sessions (IE, "M =" LINES) IN Requests and Responses. Consider An Invite with The Following SDP: ... C = In IP4 1.2.3.4
M = Audio 54678 RTP / AVP 0 1 3
M = Video 7346 RTP / AVP 28 31 (FACE)
M = Video 7880 RTP / AVP 26 28 (Presentation) If The Response Contained Something Like ...
C = in ip4 3.4.5.6
M = AUDIO 6540 RTP / AVP 0 1
m = video 6578 RTP / AVP 28 the caller would not be able to tell which of the two offered video streams was accepted [Append to This Answer] mailto:.? islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-06 11: 16PM SIP FAQ: SIP Protocol Operation: I Sent An Invite, And Then Decide I Want To HANG Up Before Getting A Final Response. Do I Send Bye or Cancel? If The Caller Wants To HANG Up A CALL, Buthan't Yet Received A Final Response, IT CAN Send A Cancel or A Bye. Sending a Bye Would ISUES. First Off, You Won't have gotten a tag yet from the uas, NOR WILL YOU have received Record-Route or Contact headers (obtained in the 200 OK response). This means the BYE will be routed "afresh" by proxies. Its possible that routing logic may have changed (perhaps there was some time of day routing or randomized routing ), in which case the Bye May Reach A Different Set of Particles Than Reached by the Original Invite. so, if The Original Invite forked, And Reached A And B, And the Bye Reaches B And C, B Will Send A 200 OK, And C A 481. The Forking Proxy Forwards The 200 OK Upstream, And The Caller Gets The 200 OK. However, A is Still Ringing, And Might Later send a 200 OK. This yield inconsistent call state, which will persist until the UAS times out, as it will never get an ACK. Sending CANCEL helps solve many of these problems. CANCEL will reach the same set of recipients as the original INVITE, And It Doesn't Need A Record-Route or Tag in It. The Drawback, However, IS That The Us Might Pass On The Wire. Thus, The Uac May Still Need To Ack The 200 Ok, and then send bye. The Other Drawback is this you would don '
t send CANCEL if the call was already established, you'd send BYE. Folks complained they did not want to have state-dependent mechanisms for hanging up. Given the unlikelihood of the problems with sending BYE, it seems reasonable to allow it. [Append to This Answer] mailto: jdrosen@dynamicsoft.com subject = SIP FAQ2000-Jul-07 12:12 am SIP FAQ:? SIP Protocol Operation: I'm a proxy, and I forked a request, and forwarded multiple OK 200 upstream , I get an attk. What do I do with it? Normal, Using Route Headers Which Should Be Present in the Ack. In The Bis Draft, The Final 200 Ok Response Must Contain A Contact Header. This Means That Either (1 ) the proxy record-routes, in which case the ACKs will each contain (different) route headers which tell the proxy where to send the request, or (2) the proxy does not record-route, in which case it gets sent directly To The UAS, Since There Was a Contact.that Aside, Should IT Arrive Anyway, The Ack Should Be Routed Just As Any Other New Request. AP ply routing logic, which presumably causes it to be forked to both locations The tags will help identify for which UAS the ACK is meant [Append to This Answer] mailto:.. jdrosen@dynamicsoft.com subject = SIP FAQ2000-Jul-08? 1:10 AM SIP FAQ: SIP Protocol Operation: I Get a New SDP Body In The Ack, and I don't like the Media Type, How can I indeicate it? IT DOESN'T WORK THAT WAY. You Should NOT GET A "New" SDP in The Ack. SDP Goes in Ack ONLY INSERE WAS NO SDP in INVITE, THEN SDP WAS INCLUDED IN THE 200 OK. This SDP SHOULD Represent A Subset of the Media "Offered"
In The 200 OK. in Other Words, A Normal Sip Transaction Has One SDP in 200 OK. Now, We Have The Same Two Phase Process, But The First SDP IS in The 200 OK, And The Second in . the ACK [Append to This Answer] mailto: jdrosen@dynamicsoft.com subject = SIP FAQ2000-Jul-11 4:16 pm SIP FAQ:? SIP Protocol Operation: Can a SIP UA register with multiple registrars Yes A SIP UA will?. register with registrars of any domain where it maintains an identity. For example, a UA belonging to Alice, with identities alice@big-company.com, alice@myportal.com and alice@home-isp.net will register with three different registrars [Append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2000-JUL-19 11:45 AM SIP FAQ: SIP Protocol Operation: Is It Possible for a Ua to make a call to itself, and since THE RESE SAME MACHINE? IF you have take, please to help, cans, you shop, call-id, cseq, you shop be sure to have the direction of there request (sent or received) as part of the key, or use separate transaction tables even for incoming and outgoing requests. If you have a table of calls by Call-ID only, you will run into problems as you may think this is a re -INVITE for the same call. you really want the incoming and outgoing messages to be associated with totally different calls. It can be distinguished as a separate call if, again, you allow for direction in your lookups. There are many ways to do this .; the easiest is to include your local address as part of the call key for incoming requests, the key is callID from, for outgoing, callID to [Append to This Answer] mailto: jdrosen@dynamicsoft.com subject =.?
SIP FAQ2000-JUL-21 1:29 AM SIP FAQ: SIP PROTOCOL OPERATION: Does a UAS USE The Request-Uri Or To Field To DETERMINE IF A CALL IS for IT? IT Uses The Request Uri. A UAS SHOULD BE PREPARED to Receive Calls with the request URI set to values that it has registered (and placed in the Contact header of REGISTER). It should also be prepared to receive calls with the request URI set to the value it placed in the to field of the REGISTER. Its not likely to see such a request URI, unless its receiving a direct client to client call [Append to This Answer] mailto:. jdrosen@dynamicsoft.com subject = SIP FAQ2000-Jul-21 11:58 am SIP FAQ:? SIP Protocol Operation: How are SIP parsers implemented? parsers can be implemented either directly from the ABNF or via parser-generator tools. Some tools that have been used include- http://www.gnu.org/software/flex/flex.html flex for lexical Analysis- bison (http://www.gnu.org/software/bison/bison.html) or lemon (http://www.hwaci.com/sw/lemon/) for Parsing.a Somew Hat Outdated grammar summary canbe be found at http://www.cs.columbia.edu/ ~ hgs/sipbolumbgrammar.html [append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2000-JUL -30 1:35 pm SIP FAQ: SIP Protocol Operation:?. Is it possible to use Hide with Record-Route No, only Via can be hidden Hiding a Record-Route header in the same manner is impossible because it would need to be decrypted by the upstream proxy for subsequent requests from the callee to the caller; however, the secret key would only be known to the server that encrypted the header [Append to This Answer] mailto: islepchin@dynamicsoft.com subject =.?
SIP FAQ2000-Aug-24 12:50 pm SIP FAQ: SIP Protocol Operation:. How does a proxy handle a method other than the standard INVITE, ACK, BYE, etc.?See SIP RFC, section 4.2 Proxies always forward requests, regardless of NOTHOD. A UAS RETURns 501 (Not Implement) If IT Does Not Support a Particular Request Method. [append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2000-SEP-13 2:28 PM SIP FAQ: SIP Protocol Operation: Why does a proxy server doing TCP need to be stateful The situation comes up in a proxy which is TCP on the upstream side and UDP in the downstream side (see diagram below) TCP UDP?.
UA1 -------- Proxy -------- UA2 Lets Assume That this proxy is stateless are not retransmitted over TCP. So, the UA1 sends its request, say an INVITE, just once over the TCP connection. The proxy receives this, and forwards it to UA2. Its lost. UA1 will not retransmit (since its TCP), and . neither will the proxy, since its stateless, thus, the message is lost [Append to This Answer] mailto:? jdrosen@dynamicsoft.com subject = SIP FAQ, mailto:? islepchin@dynamicsoft.com subject = SIP FAQ2000-Oct- 27 3:18 PM SIP FAQ: SIP Protocol Operation: In Computing The Content-Length, Does The Newline In A Body Count As One Byte Or Two (CR VS. CR V)? The content-length is always the number of bytes in The body. if The body is text and has newlines, a cr- of hass, while just a cr is one bytes, while just a cr is one byte. [append to this answer] mailto: jdrosen@dynamicsoft.com? Subje CT = SIP FAQ2000-NOV-03 2:59 AM SIP FAQ: SIP PROTOCOL OPERATION: CAN A Proxy Fork A Non-Invite Request? if Yes, What happensiffiffs ing it gets multiple responses? Yes, a proxy can fork a non-invite request . HOWEVER, IT Must Forward Only A Single Response Upstream, 200 Or Otherwise. Thus, Only A Single 200 Is Everwarded Upstream. This is in contrast to invite, WHERE ALL 200 '
s received are forwarded upstream. Why is that? The reliability mechanism of non-INVITE requests dictates that. Response retransmissions are triggered on request retransmissions. Thus, the client retransmits its request until it gets * a * response. So, upon receiving the first final response, the client would cease retransmitting the request, and then there would be no way to reliably send the other final responses.As a result of this, forking of non-INVITE requests is only useful when the method has semantics that meet certain criteria Spectally, (1) The Client Doesn't Care Which Server Gets The Request, (2) The Client Doesn't Care Which Server Sent The Response, or Even IF Multiple Servers Sent a Response, (3) The Service Provided by Each . server is identical In essence, forking of non-INVITE requests is useful only for an anycast type of service [Append to This Answer] mailto:. jdrosen@dynamicsoft.com subject = SIP FAQ2000-Nov-19 5:18 pm SIP FAQ? : SIP Protocol Operation: SHOULD RESP onses be sent to the host specified in Via? Is From ever used for sending responses? The rules for forwarding responses are explained in section 6.47.5 of 2543bis. Note that if you are a UAS, you are the entity responsible for adding "received "parameter to the top Via so you may want to interpret the last two rules in the section as requiring to send the response to the source address of the request [Append to This Answer] mailto:. islepchin@dynamicsoft.com subject =?
SIP FAQ2000-Dec-07 11:37 am SIP FAQ: SIP Protocol Operation: Once a SIP registrar gets a REGISTER request, how does it update the Location Server with the contact information This depends on whether the location server is co-located with the? SIP registrar or not. If it is, a functional interface (API) suffices to save the location information and any registration payload. If it is not, any protocol or middleware like CORBA, LDAP, RPC, or a database access protocol (eg, .. SQL over TCP), can be used The details are implementation-dependent and outside the scope of the protocol (Vijay Gurbani) [Append to This Answer] mailto: hgs@cs.columbia.edu subject = SIP FAQ2001-Jan-? 16 7:58 PM SIP FAQ: SIP Protocol Operation: Is A SIP URI WITHOUT A User Name Valid? SIP Request Uris Such As Sip: Phone123.example.com Are Valid if The Device Being Addressed Does Not Have A Notion of A 'User' GENERLY, BULD NOT To A Proxy, But a Proxy May Translate, For Example, Sip: Joe@example.com Into The Request Uri Sip: Phone123.example.com, if That Phone Has Registered with That Contact Address. [Append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2001-MAR-14 4:53 PM SIP FAQ: SIP Protocol Operation: Is there a specific order for header fields header fields can appear in any order, except within a header field type (a list of headers separated by a comma or several fields with the same name) for example, Route,?. Record-Route and Via need to be kept in order Responses can re-order header fields found in the request.HTTP / 1.1 says:. ". The order in which header fields with differing field names are received is not significant" "
The order in which header fields with the same field-name are received is therefore significant to the interpretation of the combined field value, and thus a proxy MUST NOT change the order of these field values when a message is forwarded. "If a set of fields is authenticated, proxies must not re-order or otherwise modify these field, as this would break the authentication [Append to This Answer] mailto:. hgs@cs.columbia.edu subject = SIP FAQ2001-Mar-14 5:11 pm? SIP FAQ: SIP Protocol Operation: When is a CANCEL used - A proxy has forked an INVITE request, and it receives a 200 or 600 response on one of the branches, the proxy CANCELs unanswered branches; - The time described in the Expires header? of the request has elapsed; - No response, including provisional, was ever received from downstream nodes; -. Internal logic determines its time to end the transaction (a CPL or sip-cgi script, for example) [Append to This Answer] mailto : hgs@cs.columbia.edu? Subject = SIP FAQ2001-Mar-21 11:55 PM SIP FAQ : SIP Protocol Operation: What Do I NEED TO DO TO USE SRV RECORDS? Any Bind Implementation After 4.9.5 Supports Srv Records, As Does Windows 2000. _SIP._TCP SRV 0 0 5060 SIP-Server.cs.columbia.edu.srv 1 0 5060 Backup.ip-provider.net.
_SIP._UDP SRV 0 0 5060 SIP-SERVER.CS.COLumbia.edu.
SRV 1 0 5060 backup.ip-provider.net.DNS SRV records are supported by BIND 4.9.6 and newer, generally installed as named. Configuring named for Linux is discussed in a HOWTO at http://www.linuxdoc.org/ HOWTO / DNS-HOWTO.HTMLCURRENTLY Registered Srv Records: Sip.tcp.cs.columbia.edu SRV 0 0 5060 Erlang.cs.columbia.edu
Sip.udp.sip-happens.com srv 0 0 5060 Sip.SIP-HAPPENS.COMUSE, for EXAMPLE, HOST -V -T SRV Sip.tcp.cs.columbia.eduhost -v -t srv sudp.cs. Columbia.edu
Host -v -t srv _sip._udp.cs.columbia.edu [append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2001-Mar-22 12:03 AM SIP FAQ: SIP Protocol Operation: Why does SIP / SDP allow for multiple codecs to be used for the same media stream? In the call setup procedures of SIP / SDP, the caller offers their list of codecs for a stream, and the called party responds with those amongst the set which can be supported. The result is that both sides agree on a set of codecs which can be used for that stream. Any of those codecs can be used at any time. The codec used for a packet is indicated in the payload type of the RTP packet .Why does sip do what? Why doesn '
t it restrict it to a single codec, and then do something like an H.323 open logical channel to change codecs mid call? The answer is twofold. First, it supports application adaptation. Network conditions will vary. To adapt to those conditions, the sender needs the ability to vary the encoding rate and type. It will need to change codecs rapidly. Therefore, SIP allows for multiple codecs to be in use for a single stream.The second reason is that different codecs might be used depending on the content of the encoded media. for example, rfc2833 defines an encoding of DTMF. It is very useful for the caller to use g.723.1 to send speech, and then, when a number on the dialpad is pressed, to transmit the tone in SIP using rfc2833 instead of g.723.1. This requires the sender to quickly change codecs mid-stream. Similarly, during a silence period, a comfort noise codec might be used instead of the main codec. This too, will require the sender to change codecs On The fly.there area Scenarios ere a participant can indeed support multiple codecs, but can not change them on the fly Work is underway in the mmusic group in IETF to add some basic capability negotiation to SDP for this purpose [Append to This Answer] mailto:.. jdrosen @ dynamicsoft. com subject = SIP FAQ2001-Apr-27 5:05 am SIP FAQ:? SIP Protocol Operation: What are spirals Why does a proxy care Sprials are defined in bis-03 They are requests that loop back to the same proxy, but??. For Which The Request Uri Has Changed. Classic Example: Joe@example.com Calls Bob@bigcompany.com. Goes to the bigcompany.com proxy. it proxies it to bob @
marketing.bigcompany.com. The marketing.bigcompany.com proxy invokes a CPL. The CPL has bob forwarding all his calls to jane@bigcompany.com. This request is then proxied to the bigcompany.com proxy. Now, this is a " loop ", in the sense that the request has hit the same server, but its a valid one Its valid because the request URI the second time around (sip: jane@bigcompany.com). is not the same as the first time around ( SIP: Bob@bigcompany.com). SO, The Proxy Should Accept this and process it. this case is caled a "spiral". Its called that since you can Think of a proxy network in two dimensions; one Dimension is the set of os elements, and the other is the r-uri. The request returns to the same point in the first axis, but a different point in the second. Much like a spiral in 3D space, which returns to the same point in the X, Y AXIS, But A Different One in the Z. Now, How does The Proxy Know This Was A Spiral, And NOT A LOOP? Using the branch-id. The branch-id is supposed to Contain A HA SH OF THE R-URI. SO, WHEN The Request Arrives Again At The Proxy, IT FINDS ITS Previous Via Entry (Because of the Host Name), And It Matches. Then, IT Computes The Hash of The R-URI in The incoming Request, And Compares It to the Hash In the Branch Id. if the is, it, ip. ip. [append to this answer] mailto: jdrosen@dynamicsoft.com? Subject? Subject = SIP FAQ2001-JUN-12 1:23 PM SIP FAQ: SIP Protocol Operation: What '
s the difference between loose and strict source routing? Both loose and strict routing use the Route header.Strict routing (with more than zero intermediaries) attempts to carry information about the request target and the next hop to be reached in the Request-URI. Loose routing leaves the request target in the Request-URI and the next hop in the Route header Loose routing is identified by a; lr parameter in the Route URI [Append to This Answer] mailto:.. hgs@cs.columbia.edu? subject = SIP FAQ2002-Mar-07 6:55 pm SIP FAQ: Relationship to Other ProtocolsAnswers commonly asked questions about relationship between SIP and other protocols Subcategories:. Answers in this category:? What is the relationship between MGCP and SIP What is SIP and how Does it Relate to Siphow Does Sip Compare To H.323? Can Do I Interconnect Q.931 (ISDN SIGNALING) AND SIP? How do I interconnect isup (SS7 SIGNALING) and SIP? WHERE Do i find description of sdp? can Sip be used for Internet telephony gateways (ITGs)? What is sip-cgi and how does it relate to CPL? Is there a SIP interoperability certification? How can I test interoperability with others? Why use SIP-T as opposed to tunneling SS7 using SCTP? How does SIP Carry DTMF (TOUCH TONES)? What is The Relationship of A "SoftSwitch" to Sip? How does Sip / SDP Relate to T.38 Fax Calls? Where is the use of sip defined in 3GP? What port Numbers Should i Use for RTP ?? sessions set up with SIP Why use SIP for presence and instant messaging [Add a New Answer in "Relationship to Other Protocols"] mailto: islepchin@dynamicsoft.com subject = SIP FAQ, mailto:?? jdrosen@dynamicsoft.com subject = SIP FAQ, MAILTO: HGS@cs.columbia.edu? Subject =
SIP FAQ2001-Jul-26 3:26 pm SIP FAQ: Relationship to Other Protocols: What is the relationship between MGCP and SIP The details of combining the two in a system are still being fleshed out MGCP is a device control protocol, where a?. SLAVE (Gateway) IS Controlled by A Master (MGC), Call Agent. Sip May Be Used Between Controllers, In a Peer-to-Peer Relationship. Note That To The Sip Side, The MGC Looks Like a node with a large number of connection the same as a "native"
. SIP device Similarly, the MG is completely unaware that the call between MGCs is established via SIP Only the MGC needs to understand both protocols Additional details provided by Tom Taylor:.. Sip_h323_mgcp.gif (28.1 K) The basic architecture assumed by the Megaco Working Group postulates two functional entities: a Media Gateway Controller (MGC), which owns the call model and is responsible for call signalling, and a Media Gateway (MG), responsible for manipulating (directing, transforming) media flows under the control of the MG. MGCP and Megaco / H.GCP are both protocols used between the MGC and MG when they are realized in separate physical elements. MGCP (Media Gateway Control Protocol) was a major source of the ideas in the current Megaco / H.GCP protocol draft, and is being deployed in a number of products being announced over the next few months. It is best suited for IP telephony gateway applications. The Megaco protocol is also called H.GCP because it is being developed cooperat ively between the Megaco WG and ITU-T Study Group 16. H.323 is a complete system specification, including call signalling protocols which would run between an MGC and another MGC or other H.323 entities (Gatekeepers, endpoints). SIP can also be used as a call signalling protocol, and can therefore be viewed as a competitor to H.323 Both protocols are capable of supporting multipoint multimedia conferences H.323 was first standardized in 1996 and has been improved since then..;
current standardization is focusing on networking aspects such as translations data exchange and interworking with legacy telephony signalling. SIP just reached Proposed Standard status, but has attracted wide interest which may speed its maturing stages. The Megaco / H.GCP protocol will complement both protocols by also providing support for multipoint, multimedia calls at the media level [Append to This Answer] mailto:.? islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-03 11:10 pm SIP FAQ: Relationship to Other Protocols: What is SIP and how does it relate to SIPSIP was a proposal by Level3 on how to extend SIP to interconnect two MGCs. This functionality is now being provided by various orthogonal SIP extensions, including the carriage of multipart MIME types, the INFO method and others. These are being Document. The name Sip is Obsolete and stay not be used to avoid control. [append to this answer] mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ2000-JUL-04 10: 51PM SIP FAQ: RELATIONSHIP TO Other Protocols: How does Sip Compare to h.323? See Sip vs. H.323 Comparison At http://www.cs.columbia.edu/ ~ hgs/sip/h323-comparison.html. The brief answer: The main advantage of SIP is its full integration with other Internet protocols and functions, such as email, web and instant messaging For example, it is very easy to "forward" calls to web pages or email;.
web pages can be included in responses to call attempts. SIP is also codec-neutral and has been used to set up anything from audio and video to Doom distributed games and screen sharing. There a number of open-standard programming interfaces, SIP servlets, sip-cgi and CPL, that are particularly suited to SIP-based devices. These programming interfaces make creating SIP-based services very similar to writing web scripts or web pages.It also supports a number of services, such as ACD and follow-me , That are much harder to import in h.323. [append to this answer] mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ, MAILTO: HGS@cs.columbia.edu? Subject = SIP FAQ2000-DEC-15 10 : 28pm SIP FAQ: Relationship to Other Protocols: Can H.323 and SIP be used together Yes SIP can locate the called party and determine its capabilities, including H.323 H.323 is then used to connect the two parties?... Unfortunately, There Is Currently No Standard On Translating Between The Two. Conversion is Made More Dif ficult by the multiple versions of H.323 (v1, v2, v3). However, there is at least one product (Lucent PacketStar IP) that allows SIP and H.323 terminals to call each other. There is an ongoing effort within SIP Working Group to define SIP-H.323 interoperation standard. Some details on the effort are available at http://www.softarmor.com/sipwg/teams/sip-h323/index.html. The group has produced an internet dratf that Can Be Found At http://www.cs.columbia.edu/ ~ hgs/sip/drafts/draft-sisH-SIP-H323-00.txt. [append to this answer] mailto: islepchin@dynamicsoft.com? Subject? Subject =
SIP FAQ2000-Jul-04 11:00 pm SIP FAQ: Relationship to Other Protocols:? How do I interconnect Q.931 (ISDN signaling) and SIP A gateway that initiates an ISDN call based on a SIP call or vice versa is reasonably straightforward, As Sketched Here: ISDN_SIP.PDF (8.7k) Some Additional Information and Links to Related Internet Drafts Can Be Found At http://www.softarmor.com/sipwg/teams/sipt/index.html.[Append to this answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-04 11:09 pm SIP FAQ:? Relationship to Other Protocols:? How do I interconnect ISUP (SS7 signaling) and SIP SIP can be used either between SS7 nodes or to trigger . a phone call in an SS7 network While all the details have not been worked out, the basic call flow is similar to the ISDN case:. sip_isup.pdf (7.0 K) Some additional information and links to related Internet Drafts can be found at http://www.softarmor.com/sipwg/teams/sipt/index.html.[Append to this answer] mailto: islepchin@dynamicsoft.com? Subject = SIP FAQ2 000-Jul-04 11:08 pm SIP FAQ: Relationship to Other Protocols:?. Where do I find description of SDP SDP (Session Description Protocol) specification can be found in RFC2327 SIP uses SDP to describe media capabilities of call participants and to negotiate The Common Media set Media for a call. Appendix b of rfc2543 Describes the usage of sdp in sip messages. [append to this answer] mailto: islepchin@dynamicsoft.com? Subject =
SIP FAQ2000-Jul-06 10:45 pm SIP FAQ: Relationship to Other Protocols:?. Can SIP be used for Internet telephony gateways (ITGs) Yes, in two ways First, it can indicate to the Internet-based caller that the callee is . reachable via an ITG, via the Contact header Secondly, two ITGs connecting parties on the PSTN can signal new calls to each other, with the destination phone number contained in the request URL [Append to This Answer] mailto:. islepchin @ dynamicsoft. COM? Subject =
SIP FAQ2000-Jul-04 11:16 pm SIP FAQ: Relationship to Other Protocols: What is sip-cgi and how does it relate to CPL Both are viewed as different approaches for creating VoIP services Both are written offline, and both are executed?. when messages arrive in order to execute features. CPL is an XML-based language, while sip-cgi is a mechanism for invoking scripts or programs written in any language. sip-cgi is very similar to web cgi scripts. in its current version, CPL is only invoked when INVITE requests and responses arrive, while sip-cgi can intercept any request. sip-cgi is designed to be used by SIP, while CPL can probably be used by a number of signaling protocols such as Q.931 or H .323. CPL and sip-cgi differ in their applicability. CPL is designed for end user service creation. It is intentionally limited in capabilities and is not a general purpose programming language. Its execution on a server is generally very fast. CGI is more Powerful - You Can do Nearly Anything. IT IS P rogramming language independent. It incurs a process-spawning overhead, so its less efficient than CPL. (CPL is usually executed in the same process as the server). As a service provider, I would not want to execute CGI scripts sent to me by . end users However, I would prefer to use CGI to develop my own services Note that CGI may be used as the execution environment for a CPL script (Jonathan Rosenberg) [Append to This Answer] mailto:.. islepchin@dynamicsoft.com? Subject = SIP FAQ2000-JUL-04 11:18 PM SIP FAQ: Relationship To other protocols: Is there? How can I Test Interoperability WITHERS?
There currently is no certification that attests to the functionality and compatibility of a SIP implementation. However, there are regular SIP bake-offs where implementors can test their work. Also, some sites have set up public SIP servers. [Append to This Answer] mailto: islepchin@dynamicsoft.com subject = SIP FAQ2000-Jul-04 11:27 pm SIP FAQ:? Relationship to Other Protocols:? Why use SIP-T as opposed to tunneling SS7 using SCTP Using SCTP (aka SIGTRAN) to send SS7 between softswitches works fine assuming that you know the terminating device is an SS7 enabled softswitch, and that you are not interested in services provided by SIP. by using SIP instead, a softswitch can talk the same call control protocol to other softswitches, PC clients, gateways , IP phones, and so on. Furthermore, the softswitch does not need to know the identity of the terminating device ahead of time. in real networks, it will be unlikely that the originating softswitch knows. Calls will terminate in networks owned by other providers, in which case the type of terminating device can not be known ahead of time. SIP-T is ideal in that the extra ISUP information carried is ignored by non-SS7 devices, so it works for all devices. [Append to This Answer] mailto: jdrosen@dynamicsoft.com subject = SIP FAQ2000-Jul-05 11:25 pm SIP FAQ:? Relationship to Other Protocols: How does SIP carry DTMF (touch tones) First, in most cases it is not clear that SIP? Is The Right Mechanism for this, Since DTMF Detection Is Being Done in Devices That Generate RTP, Not Sip.rtp Can Be Used To Carry DTMF, AS Described in RFC 2833. RFC 2833 Uses "Forward Error Correction"
, Retransmitting DTMF digits periodically. Thus, unless there are extremely long bursts of packet errors, digits are transmitted reliably. Retransmission by SIP, either at the application layer or via TCP, is based on exponential back-off, with delays of a few seconds after several consecutive losses. If a human generates the touch tone commands, it is possible that such long retransmission delays will cause the user to press the button again, resulting in duplicate digits.DTMF over RTP is also required to synchronize audio and touch tones at VoIP-to-PSTN gateways.Gateways that are only interested in detecting tones do not need to buffer audio and can simply forward the audio packets while doing playout buffering and DTMF detection locally.A number of proposals exist for carrying DTMF in SIP INFO messages, But The Working Group Has NOT DECIDED Which of the approaches, if any, to pursue. [append to this answer] mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2000-JUL-10 4: 11 PM SIP FAQ: Relat ionship to Other Protocols: What is the relationship of a "softswitch" to SIP The term "softswitch" is primarily a marketing term, with no well-defined technical meaning It is often used to designate a collection of software providing telephony interworking services?. , including a signaling gateway (SG), media gateway controller (MGC) and a SIP user agent (UA). It can use any number of protocols, depending on the particular application and network configuration, including ISUP, CAS, MGCP, Megaco, H.323 and Sip. Many "SoftSwitches" User Sip for Communicating Between SoftSwitches. [Append to this answer] mailto: hgs@cs.columbia.edu? Subject =
SIP FAQ2000-JUL-20 12:06 PM Sip FAQ: Relationship To Other Protocols: How Does Sip / SDP Relate to T.38 Fax Calls? An SDP Addition To Allow Sip / SDP To Set Up T.38 Fax Calls IS Specified in Annex D of Itu REC. T.38 ("SIP / SDP CALL ESTABLISHMENT Procedures"). It can also be found at ftp://standards.nortelnetworks.com/itu_to_ieetf/sg8/february00/ [append to this answer] mailto: hgs @ cs.columbia.edu subject = SIP FAQ2000-Jul-24 6:12 pm SIP FAQ:? Relationship to Other Protocols: Where is the use of SIP defined in 3GPP The exact signalling and call control protocols are defined in 3GPP Technical Specification 3G? TS 24.228: "Signalling flows for the IP multimedia call control based on SIP and SDP" and 3GPP Technical Specification 3G TS 24.229:. "IP Multimedia Call Control Protocol based on SIP and SDP" (Jack Yu) 3GPP documents can be found at http : //www.3gpp.org/the Draft Version for TS24.228 Is Available At http://www.3gpp.org/ftp/specs/laft_drafts/ The Draft Version for TS24.229 IS Available At http://www.3gpp.org/ftp/specs/latest_drafts/ Also the Current Version for TS23.228 is Available At http://www.3gpp.org/ftp/specs/2001-12/rel-5/23_series /Http://www.3gpp.org/tb/other/ietf.htm Lists the Ietf Documents That 3GPP Depends on, Include Many Sip Documents. [append to this answer] mailto: hgs@cs.columbia.edu? Subject =
SIP FAQ2002-JAN-08 10:17 AM SIP FAQ: RELATIONSHIP TO Other Protocols: What Port Numbers Should I Use for RTP sessions set up with sip? You will need an eve / oded port pair. The even port is for rtp, and the odd is for RTCP. Never use ports below 1024. It is strongly recommended that you avoid ports between 1024 and 49151, since these are assigned by IANA, and might be in use by some other protocol. It is highly recommended that you choose ports between . 49152 and 65534. The general algorithm for this is to choose a pair in this range, and request it If one or both are in use, try another pair until you obtain a free one [Append to This Answer] mailto:. jdrosen @ Dynamicsoft.com?subject=sip FAQ2001-APR-22 9:47 PM SIP FAQ: Relationship To Other Protocols: Why Use Sip for Presence and Instant Messaging?
SIP networks already provide presence information (via REGISTER) as it is needed for session intitiation; delivery of presence and notification messages to people is supported on top of existing proxy networks; instant messages are often best modeled as a session; presence and IM are both parts of a broader communications service that also includes voice, video, shared applications, etc., and it would be nice to smoothly integtrate those together, events are needed for a number of session-related functions, thus SIP needs event notification functionality in any event (events are a generalization of presence); a requirements analysis showed that much of what's needed for a scalable presence and IM protoco is already offered by SIP [Append to This Answer] mailto:.? hgs@cs.columbia.edu subject = SIP FAQ2001-JUL-26 3:30 PM SIP FAQ: How do I show this faq as a single page? Click ON [Show this entire category] at the bottom of the sip faq "front" page, in the gray bar. [Append To this answer] mail To: hgs@cs.columbia.edu? Subject = SIP FAQ2000-JUL-10 4:03 PM SIP FAQ: RTP Issuesrtp Faqs Are Covered At http://www.cs.columbia.edu/~hgs/rtp.in particular, a common mistake is to assume that RTP mandates a certain packetization interval, eg, 20 ms. This is * wrong *. While RFC 1890 recommends certain values and SDP allows to express a preference, implementations need to be able to handle all reasonable values. there is no constraint that G.711 or other sample-based formats is conveyed in multiples of a certain unit. Thus, an RTP packet with 123 samples of G.711 is perfectly legitimate and needs to be handled appropriately. [Append to This Answer ] Mailto: hgs@cs.columbia.edu? Subject = SIP FAQ2001-APR-24 9:01 PM
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