MOS - Mean Opinion Score

What is Mean Opinion Score?

In voice and video communication, quality usually dictates whether the experience is a good or bad one. Besides the qualitative description we hear, like 'quite good' or 'very bad', there is a numerical method of expressing voice and video quality. It is called Mean Opinion Score (MOS). MOS gives a numerical indication of the perceived quality of the media received after being transmitted and eventually compressed using codecs.

MOS is expressed in one number, from 1 to 5, 1 being the worst and 5 the best. MOS is quite subjective, as it is based figures that result from what is perceived by people during tests. However, there are software applications that measure MOS on networks, as we see below.
The Mean Opinion Score Values

Taken in whole numbers, the numbers are quite easy to grade.

5 - Perfect. Like face-to-face conversation or radio reception.
4 - Fair. Imperfections can be perceived, but sound still clear. This is (supposedly) the range for cell phones.
3 - Annoying.
2 - Very annoying. Nearly impossible to communicate.
1 - Impossible to communicate

The values do not need to be whole numbers. Certain thresholds and limits are often expressed in decimal values from this MOS spectrum. For instance, a value of 4.0 to 4.5 is referred to as toll-quality and causes complete satisfaction. This is the normal value of PSTN and many VoIP services aim at it, often with success. Values dropping below 3.5 are termed unacceptable by many users.
How Are MOS Tests Conducted?

A certain number of people are sat and are made to hear some audio. Each one of them gives a rating from within 1 to 5. Then an artihmetic mean (average) is calculated, giving the Mean Opinion Score. When conducting MOS test, there are certain phrases that are recommended to be used by the ITU-T. They are:

You will have to be very quiet.
There was nothing to be seen.
They worshipped wooden idols.
I want a minute with the inspector.
Did he need any money?

Factors Affecting Mean Opinion Score

MOS can simply be used to compare between VoIP services and providers. But more importantly, they are used to assess the work of codecs, which compress audio and video to save on bandwidth utilization but with a certain amount of drop in quality. MOS tests are then made for codecs in a certain environment.

There are however certain other factors that affect the quality of audio and video transferred, as mentioned in that article. These factors are not supposed to be accounted for in MOS values, so when determining the MOS for a certain codec, service or network, it is important that all the other factors are favorable to the maximum for a good quality, for MOS values are assumed to be obtained under ideal conditions.
Software Automated Mean Opinion Score Tests

Since the manual/human MOS tests are quite subjective and less than productive in many ways, there are nowadays a number of software tools that carry out automated MOS testing in a VoIP deployment. Although they lack the human touch, the good thing with these tests is that they take into account all the network dependency conditions that could influence voice quality. Some examples are AppareNet Voice, Brix VoIP Measurement Suite, NetAlly, PsyVoIP and VQmon/EP.

Text from voip.about.com, all rights to the author.

List Of SIP response codes

SIP responses are the codes used by Session Initiation Protocol for communication. They complement the SIP Requests, which are used to initiate action such as a phone conversation. Note that the Reason Phrases of the responses listed below are only the recommended examples, and can be replaced with local equivalents without affecting the protocol.
Contents


* 1 1xx—Informational Responses
* 2 2xx—Successful Responses
* 3 3xx—Redirection Responses
* 4 4xx—Client Failure Responses
* 5 5xx—Server Failure Responses
* 6 6xx—Global Failure Responses
* 7 External links

1xx—Informational Responses

* 100 Trying

extended search being performed may take a significant time so a forking proxy must send a 100 Trying response

* 180 Ringing
* 181 Call Is Being Forwarded
* 182 Queued
* 183 Session Progress

2xx—Successful Responses

* 200 OK
* 202 accepted: It Indicates that the request has been understood but actually can't be processed
3xx—Redirection Responses

* 300 Multiple Choices
* 301 Moved Permanently
* 302 Moved Temporarily
* 305 Use Proxy
* 380 Alternative Service

4xx—Client Failure Responses

* 400 Bad Request
* 401 Unauthorized (Used only by registrars or user agents. Proxies should use proxy authorization 407)
* 402 Payment Required (Reserved for future use)
* 403 Forbidden
* 404 Not Found (User not found)
* 405 Method Not Allowed
* 406 Not Acceptable
* 407 Proxy Authentication Required
* 408 Request Timeout (Couldn't find the user in time)
* 409 Conflict
* 410 Gone (The user existed once, but is not available here any more.)
* 412 Conditional Request Failed
* 413 Request Entity Too Large
* 414 Request-URI Too Long
* 415 Unsupported Media Type
* 416 Unsupported URI Scheme
* 417 Unknown Resource-Priority
* 420 Bad Extension (Bad SIP Protocol Extension used, not understood by the server)
* 421 Extension Required
* 422 Session Interval Too Small
* 423 Interval Too Brief
* 424 Bad Location Information
* 428 Use Identity Header
* 429 Provide Referrer Identity
* 433 Anonymity Disallowed
* 436 Bad Identity-Info
* 437 Unsupported Certificate
* 438 Invalid Identity Header
* 480 Temporarily Unavailable
* 481 Call/Transaction Does Not Exist
* 482 Loop Detected
* 483 Too Many Hops
* 484 Address Incomplete
* 485 Ambiguous
* 486 Busy Here
* 487 Request Terminated
* 488 Not Acceptable Here
* 489 Bad Event
* 491 Request Pending
* 493 Undecipherable (Could not decrypt S/MIME body part)
* 494 Security Agreement Required
5xx—Server Failure Responses

* 500 Server Internal Error
* 501 Not Implemented: The SIP request method is not implemented here
* 502 Bad Gateway
* 503 Service Unavailable
* 504 Server Time-out
* 505 Version Not Supported: The server does not support this version of the SIP protocol
* 513 Message Too Large
* 580 Precondition Failure
6xx—Global Failure Responses

* 600 Busy Everywhere
* 603 Decline
* 604 Does Not Exist Anywhere
* 606 Not Acceptable


From Wikipedia, the free encyclopedia

Fone

Novas Rides - Tarifação telefonica no Brasil.

Novas regras para DDD entre cidades próximas passam a valer em 120 dias (27/01/2011)

Regulamento foi publicado no Diário Oficial da União (27/01/2011).

Entram em vigor em até 120 dias as novas regras que permitirão realizar chamadas telefônicas a custo de ligação local entre municípios de uma mesma região metropolitana ou de região integrada de desenvolvimento que contenham continuidade geográfica e o mesmo código nacional de área (DDD), de acordo com informações da Agência Nacional de Telecomunicações (Anatel).

O novo Regulamento sobre Áreas Locais para o Serviço Telefônico Fixo Comutado destinado ao Uso do Público em Geral (STFC) foi publicado na quinta-feira (27/01) no Diário Oficial da União, e, por isso, o prazo começará a ser contado a partir dessa data.

Cerca de 68 milhões de consumidores serão beneficiados com uma decisão aprovada na última quinta-feira (20) pelo Conselho Diretor da Anatel, que converte ligação de longa distância (DDD) em ligação local para cerca de 560 municípios brasileiros, o que reduzirá o valor da conta de telefone para os usuários de telefonia que vivem nessas áreas.

A proposta faz parte do novo regulamento sobre áreas locais para o Serviço Telefônico Fixo Comutado (STFC), que amplia os critérios de definição de áreas locais, que passa a abranger o conjunto de municípios pertencentes a uma região metropolitana ou região integrada de desenvolvimento (Ride) que tenham continuidade geográfica e pertençam a um mesmo código nacional de área (DDD).

Como região metropolitana, a Anatel considerou o agrupamento de municípios limítrofes, instituída legalmente, que tem como finalidade integrar a organização, o planejamento e a execução de funções públicas de interesse comum. O conceito de Ride adotado pela agência foi o de complexo geoeconômico e social, instituído legalmente, que tem o objetivo de articular a ação administrativa da União visando seu desenvolvimento e a redução das desigualdades regionais. Como áreas com continuidade urbana, a Anatel considerou o resultado da fusão de duas ou mais localidades, que constitui um todo urbanizado, podendo, entretanto, ocorrer descontinuidades de mil metros ou por motivo de acidente aquático, como rio, lago, baía ou braço oceânico.

Depois do prazo de adequação de até 120 dias, contados a partir da data da publicação do regulamento, a nova configuração permitirá a realização de chamadas telefônicas a custo de ligação local entre todos os municípios de uma mesma região metropolitana ou de região integrada de desenvolvimento que contenham continuidade geográfica e o mesmo código nacional de área (DDD). O regulamento contempla 39 regiões metropolitanas e 3 três regiões integradas de desenvolvimento.

O novo regulamento também estabelece que as novas situações que se enquadrem na definição de áreas com continuidade urbana ou em decorrência de solicitação fundamentada por parte da concessionária de telefonia fixa na modalidade do serviço local serão revistas anualmente. As revisões de configuração da área local resultante da criação ou da alteração de regiões metropolitanas ou de Rides ocorrerão junto com as revisões quinquenais dos contratos de concessão.

Veja relação de regiões:

RM Agreste (AL):
Arapiraca, Belém, Campo Grande, Coité do Nóia, Craíbas, Estrela de Alagoas, Feira Grande, Girau do Ponciano, Igaci, Jaramataia, Junqueiro, Lagoa da Canoa, Limoeiro de Anadia, Olho D’Água Grande, Palmeira dos Índios, São Brás, São Sebastião, Tanque D’Arca, Taquarana, Traipu

RM Maceió (AL):
Barra de Santo Antonio, Barra de São Miguel, Coqueiro Seco, Maceió, Marechal Deodoro, Messias, Paripueira, Pilar, Rio Largo, Santa Luzia do Norte, Satuba

RM Manaus (AM):
Autazes, Careiro, Careiro da Várzea, Iranduba, Itacoatiara, Itapiranga, Manacapuru, Manaquiri, Manaus, Novo Airão, Presidente Figueiredo, Rio Preto da Eva, Silves

RM Macapá (AP):
Macapá, Santana

Ride Petrolina/Juazeiro (BA):
Casa Nova, Curaçá, Juazeiro, Sobradinho

RM Salvador (BA):
Camaçari, Candeias, Dias D’Ávila, Itaparica, Lauro de Freitas, Madre de Deus, Mata de São João, Pojuca, Salvador, São Francisco do Conde, São Sebastião do Passé, Simões Filhos, Vera Cruz

RM Fortaleza (CE):
Aquiraz, Cascavel, Caucaia, Chorozinho, Eusébio, Fortaleza, Guaiúba, Horizonte, Itaitinga, Maracanaú, Maranguape, Pacajus, Pacatuba, Pindoretama, São Gonçalo do Amarante

RM Cariri (CE):
Barbalha, Caririaçu, Crato, Farias Brito, Jardim, Juazeiro do Norte, Missão Velha, Nova Olinda, Santana do Cariri

Ride DF/Entorno (DF):
Brasília (localidades: Brasília, Brazlândia, Ceilândia, Condomínio Asa Branca, Condomínio Morado Nobre, Cruzeiro, Gama, Guará, Núcleo Bandeirante, Núcleo Rural Capão Seco, Núcleo Rural DVO, Paranoá, Planaltina, Rajadinha II, Rajadinha III, Recanto das Emas, Riacho Fundo, Samambaia, Santa Rita, São Sebastião, Sobradinho, Taguatinga)

RM Grande Vitória (ES):
Cariacica, Fundão, Guarapari, Serra, Viana, Vila Velha, Vitória

Ride DF/Entorno (GO):
Água Fria de Goiás, Mimoso de Goiás, Águas Lindas de Goiás, Cabeceiras, Cidade Ocidental, Cristalina, Formosa, Luziânia, Novo Gama, Padre Bernardo, Planaltina, Santo Antônio do Descoberto, Valparaíso de Goiás

RM Goiânia (GO):
Abadia de Goiás, Aparecida de Goiânia, Aragoiânia, Bela Vista de Goiás, Bonfinópolis, Brazabrantes, Caldazinha, Caturaí, Goianápolis, Goiânia, Goianira, Guapó, Hidrolândia, Inhumas, Nerópolis, Nova Veneza, Santo Antônio de Goiás, Senador Canedo, Terezópolis de Goiás, Trindade

Ride DF/Entorno (GO):
Abadiânia, Alexânia, Cocalzinho de Goiás, Corumbá de Goiás, Pirenópolis

RM Sudoeste Maranhense (MA):
Buritirana, Davinópolis, Governador Edison Lobão, Imperatriz, João Lisboa, Montes Altos, Ribamar Fiquene, Senador La Rocque

RM Belo Horizonte (MG):
Baldim, Belo Horizonte, Betim, Brumadinho, Caeté, Capim Branco, Confins, Contagem, Esmeraldas, Florestal, Ibirité, Igarapé, Itatiaiuçu, Jaboticatubas, Juatuba, Lagoa Santa, Mário Campos, Mateus Leme, Matozinhos, Nova Lima, Nova União, Pedro Leopoldo, Raposos, Ribeirão das Neves, Rio Acima, Rio Manso, Sabará, Santa Luzia, São Joaquim de Bicas, São José da Lapa, Sarzedo, Taquaraçu de Minas, Vespasiano

RM Vale do Aço (MG):
Coronel Fabriciano, Ipatinga, Timóteo

Ride DF/Entorno (MG):
Buritis, Cabeceira Grande, Unaí

RM Vale do Rio Cuiabá (MT):
Cuiabá, Nossa Senhora do Livramento, Santo Antonio do Leverger, Várzea Grande

RM Belém (PA):
Ananindeua, Belém, Benevides, Marituba, Santa Bárbara do Pará, Santa Isabel do Pará

RM Campina Grande (PB):
Alagoa Nova, Areial, Aroeiras, Barra de Santana, Boa Vista, Boqueirão, Campina Grande, Caturité, Esperança, Fagundes, Gado Bravo, Ingá, Itatuba, Lagoa Seca, Massaranduba, Matinhas, Montadas, Pocinhos, Puxinanã, Queimadas, Riachão do Bacamarte, Roça, Serra Redonda

RM João Pessoa (PB):
Alhandra, Bayeux, Caaporã, Cabedelo, Conde, Cruz do Espírito Santo, João Pessoa, Lucena, Mamanguape, Pitimbu, Rio Tinto, Santa Rita

Ride Petrolina/Juazeiro (PE):
Lagoa Grande, Orocó, Petrolina, Santa Maria da Boa Vista

RM Recife (PE):
Abreu e Lima, Araçoiaba, Cabo de Santo Agostinho, Camaragibe, Igarassu, Ilha de Itamaracá, Ipojuca, Itapissuma, Jaboatão dos Guararapes, Moreno, Paulista, Recife, São Lourenço da Mata

Ride Grande Teresina (PI):
Altos, Beneditinos, Coivaras, Curralinhos, Demerval Lobão, José de Freitas, Lagoa Alegre, Lagoa do Piauí, Miguel Leão, Monsenhor Gil, Teresina, União

RM Curitiba (PR):
Adrianópolis, Agudos do Sul, Almirante Tamandaré, Araucária, Balsa Nova, Bocaiúva do Sul, Campina Grande do Sul, Campo Largo, Campo Magro, Cerro Azul, Colombo, Contenda, Curitiba, Doutor Ulysses, Fazenda Rio Grande, Itaperuçu, Lapa, Mandirituba, Pinhais, Piraquara, Quatro Barras, Quitandinha, Rio Branco do Sul, São José dos Pinhais, Tijucas do Sul, Tunas do Paraná

RM Maringá (PR):
Bom Sucesso, Cambira, Jandaia do Sul

RM Londrina (PR):
Bela Vista do Paraíso, Cambé, Ibiporã, Jataizinho, Londrina, Rolândia, Sertanópolis,Tamara

RM Maringá (PR):
Ângulo, Astorga, Atalaia, Doutor Camargo, Floraí, Floresta, Flórida, Iguaraçu, Itambém, Ivatuba, Lobato, Mandaguaçu, Marialva, Maringá, Munhoz de Melo, Ourizona, Paiçandu, Presidente Castelo Branco, Santa Fé, São Jorge do Ivaí, Sarandi

RM Rio de Janeiro (RJ):
Belford Roxo, Duque de Caxias, Guapimirim, Itaboraí, Itaguaí, Japeri, Magé, Maricá, Mesquita, Nilópolis, Niterói, Nova Iguaçu, Paracambi, Queimados, Rio de Janeiro, São Gonçalo, São João de Meriti, Seropédica, Tanguá

RM Natal (RN):
Ceará-Mirim, Extremoz, Macaíba, Monte Alegre, Natal, Nísia Floresta, Parnamirim, São Gonçalo do Amarante, São José de Mipibu, Vera Cruz

RM da Capital – Roraima (RR):
Boa Vista, Cantá

RM Central – Roraima (RR):
Caracaraí, Iracema

RM do Sul do Estado – Roraima (RR):
Caroebe, São João da Baliza, São Luiz

RM Porto Alegre (RS):
Alvorada, Araricá, Arroio dos Ratos, Cachoeirinha, Campo Bom, Canoas, Capela de Santana, Charqueadas, Dois Irmãos, Eldorado do Sul, Estância Velha, Esteio, Glorinha, Gravataí, Guaíba, Ivoti, Montenegro, Nova Hartz, Nova Santa Rita, Novo Hamburgo, Parobé, Portão, Porto Alegre, Santo Antonio da Patrulha, São Jerônimo, São Leopoldo, Sapiranga, Sapucaia do Sul, Taquara, Triunfo, Viamão

RM Vale do Itajaí (SC):
Apiúna, Ascurra, Benedito Novo, Blumenau, Botuverá, Brusque, Doutor Pedrinho, Gaspar, Guabiruba, Ilhota, Indaial, Luiz Alves, Pomerode, Rio dos Cedros, Rodeio, Timbó

RM Chapecó (SC):
Águas de Chapecó, Águas Frias, Arvoredo, Caxambu do Sul, Chapecó, Coronel Freitas, Cunhataí, Faxinal dos Guedes, Guatambú, Itá, Marema, Nova Erechim, Nova Itaberaba, Paial , Palmitos, Pinhalzinho, Planalto Alegre, Quilombo, São Carlos, Saudades, Seara, União do Oeste, Xanxerê, Xavantina, Xaxim

RM Carbonífera (SC):
Araranguá, Balneário Arroio do Silva, Balneário Gaivota, Cocal do Sul, Criciúma, Ermo, Forquilhinha, Içara, Jacinto Machado, Lauro Muller, Maracajá, Meleiro, Morro da Fumaça, Morro Grande, Nova Veneza, Passo de Torres, Praia Grande, Santa Rosa do Sul, São João do Sul, Siderópolis, Sombrio, Timbé do Sul, Treviso, Turvo, Urussanga

RM Florianópolis (SC):
Águas Mornas, Alfredo Wagner, Angelina, Anitápolis, Antônio Carlos, Biguaçu, Canelinha, Florianópolis, Garopaba, Governador Celso Ramos, Leooberto Leal, Major Gercino, Nova Trento, Palhoça, Paulo Lopes, Rancho Queimado, Santo Amaro da Imperatriz, São Bonifácio, São João Batista, São José, São Pedro de Alcântara, Tijucas

RM Norte/Nordeste Catarinense (SC):
Araquari, Balneário Barra do Sul, Barra Velha, Campo Alegre, Corupá, Garuva, Guaramirim, Itaiópolis, Itapoá, Jaraguá do Sul, Joinville, Mafra, Massaranduba, Monte Castelo, Papanduva, Rio Negrinho, São Bento do Sul, São Francisco do Sul, São João do Itaperiú, Schroeder

RM Lages (SC):
Anita Garibaldi, Bocaina do Sul, Bom Jardim da Serra, Bom Retiro, Campo Belo do Sul, Capão Alto, Cerro Negro, Correia Pinto, Curitibanos, Frei Rogério, Lages, Otacílio Costa, Painel, Palmeira, Ponte Alta, Ponte Alta do Norte, Rio Rufino, Santa Cecília, São Cristovão do Sul, São Joaquim, São José do Cerrito, Urubici, Urupema

RM Tubarão (SC):
Armazém, Braço do Norte, Capivari de Baixo, Grão Pará, Gravatal, Imaruí, Imbituba, Jaguaruna, Laguna, Orleans, Pedras Grandes, Rio Fortuna, Sangão, Santa Rosa de Lima, São Ludgero, São Martinho, Treze de Maio, Tubarão

RM Aracaju (SE):
Aracaju, Barra dos Coqueiros, Nossa Senhora do Socorro, São Cristóvão

RM Campinas (SP):
Americana, Artur Nogueira, Campinas, Cosmópolis, Engenheiro Coelho, Holambra, Hortolândia, Indaiatuba, Jaguariúna, Monte Mor, Nova Odessa, Paulínia, Pedreira, Santa Bárbara D’Oeste, Santo Antônio de Posse, Sumaré, Valinhos, Vinhedo

RM Baixada Santista (SP):
Bertioga, Cubatão, Guarujá, Itanhaém, Mongaguá, Peruíbe, Praia Grande, Santos, São Vicente

Asterisk Security

How to make your asterisk safer:


Asterisk Security

Quick Start


Hardware Firewall


Most Asterisk boxes should be located behind a hardware firewall. Configure the firewall to block traffic from anyone that doesn't need to connect to you. Allow your VoIP provider, any remote phones/users, and others that may need to connect, but keep the restrictions as tight as possible. If you do have remote users, lock your firewall down to only allow those users to connect if possible, rather than opening it to the entire internet. If you have mobile users this may not be an option however.

Other services, such as SSH should be blocked by the hardware firewall.

Software Firewall


Implement a software firewall if possible, using Linux IP Chains. The rules should be similar to the hardware firewall, with the possible addition of additional rules to protect against attacks originating on the local LAN.

Fail2Ban


Implement Fail2Ban to prevent denial of service attacks (password guessing can cause excessive CPU utilization).

Strong Passwords


All remote users should have strong, alpha-numeric passwords. These should be long. They should NEVER be the same as the username or based on the user's extension.

Default Context


Your default context in extensions.conf should be empty. This context is used when other contexts might not match a peer. You should explicitly refer to a non-default context for remote SIP calls.

sip.conf configuration


In the general section, define:


[general]
...
context=bogus
allowguest=no
alwaysauthreject=no
...


The context line will refer to a context (which you *must define* in extensions.conf!) that should handle "default" SIP calls. This should go to a context with nothing in it (unless you want to play with them - then, if you have the bandwidth, feel free to play a recording or such!). Obviously if you want to accept anonymous SIP calls, send them to the proper context (but *never* a context that can dial out!).

The "allowguest" line disables anonymous SIP calls to your PBX. Some SIP providers connect as a guest user, however, so this may be inappropriate for your situation. Also, if you want to accept anonymous SIP calls, this line would block them, so you wouldn't want that. But it is listed here because it is the safest configuration.

The "alwaysauthreject" line is important. This causes a hacker to get the same response from your PBX when they try to guess passwords whether or not they guessed a valid username. This also has the side-effect of making poorly written scanning scripts (the vast majority of hacker scripts seem to be poorly written) take less resources on your Asterisk box, as even if they scan a valid username, they'll think it doesn't exist.

In addition to these, verify that all peers listed in sip.conf are valid and have strong passwords.

iax.conf


(I'm hoping others will fill in this section - I block IAX)

Dialplan


Do your users need to be able to dial internationally? If not, make sure your dialplan blocks international calls (in the US, these calls start with a 011 typically, although some countries "look like" US numbers - so also block calls to area codes that don't correspond to areas you call). You may be able to request your provider also blocks international calls. If you only have SOME users that need to call internationally, place them in a different context than the rest of your users.

Logs, CDR


Review your logs and CDR at least daily. Even one day of illegitimate calls can add up to tons of money quickly.

Tons de progresso da telefonia brasileira.

* Tom de discar - sinal senoidal contínuo de 425 Hz - informa ao usuário para iniciar a discagem.

* Tom de controle de chamada - sinal senoidal intermitente de 425Hz, com duração de 1s e interrupção de 4s sucessivamente. Informa ao usuário que originou a ligação, que o telefone do usuário para o qual a ligação foi direcionada esta "tocando".

* Tom de ocupado - sinal senoidal intermitente de 425 Hz, com duração de 250ms e interrupção de 250ms sucessivamente. Informa ao usuário que originou a ligação que o telefone do usuário para o qual a ligação se destina está ocupado.

* Tom de número inacessível ou inexistente - sinal senoidal intermitente de 425Hz com durações alternadas de 750ms e 250ms em intervalos de 250ms, sucessivamente. Informa ao usuário que efetuou a ligação que o número discado não existe ou esta inacessível naquele momento.

* Tom de toque de chamada - sinal elétrico senoidal intermitente de 25Hz e tensão de 75Volts com duração de 1s e intervalo de 4s. - possibilita que o telefone toque.

Sip Messages Structure

Format

All SIP messages are either requests from a server or client or responses to a request. The messages are formatted according to RFC 822, "Standard for the format of ARPA internet text messages." For all messages, the general format is:

* A start line

* One or more header fields

* An empty line

* A message body (optional)

Each line must end with a carriage return-line feed (CRLF).
Requests

SIP uses six types (methods) of requests:

* INVITE—Indicates a user or service is being invited to participate in a call session.

* ACK—Confirms that the client has received a final response to an INVITE request.

* BYE—Terminates a call and can be sent by either the caller or the callee.

* CANCEL—Cancels any pending searches but does not terminate a call that has already been accepted.

* OPTIONS—Queries the capabilities of servers.

* REGISTER—Registers the address listed in the To header field with a SIP server.

Responses

The following types of responses are used by SIP and generated by the Cisco SIP Proxy Server:

* SIP 1xx—Informational Responses

* SIP 2xx—Successful Responses

* SIP 3xx—Redirection Responses

* SIP 4xx—Client Failure Responses

* SIP 5xx—Server Failure Responses

* SIP 6xx—Global Failure Responses

The Registration Process

A registration occurs when a client needs to inform a proxy or redirect server of its location. During this process, the client sends a REGISTER request to the proxy or redirect server and includes the address (or addresses) at which it can be reached.
The Invitation Process

An invitation occurs when one SIP end point (user A) "invites" another SIP endpoint (user B) to join in a call. During this process, user A sends an INVITE message requesting that user B join a particular conference or establish a two-party conversation. If user B wants to join the call, it sends an affirmative response (SIP 2xx). Otherwise, it sends a failure response (SIP 4xx). Upon receiving the response, user A acknowledges the response with an ACK message. If user A no longer wants to establish this conference, it sends a BYE message instead of an ACK message.

SIP is a new protocol developed by the Internet Engineering Task Force (IETF) Multiparty Multimedia Session Control (MMUSIC) Working Group as an alternative to the ITU-T H.323 specification. SIP is defined by RFC 2543 and is used for multimedia call session setup and control over IP networks.

Retirado de:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_programming_reference_guide_chapter09186a0080087357.html

Todos os direitos ao autor.