Session Initiated sip

8/6/2019 Session Initiated sip

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SESSION INITIATED

PROTOCOL(SIP)

GC MUNEEB ILYAAS

GC HASSAN IRSHADGC AHMAD RAZA



What is SIP?

� An Application-layer control (signaling)

protocol for creating, modif ying and

terminating sessions with one or more

participants

� Text based , Model similar to HTTP.

� Sessions include Internet multimedia

conf erences, Internet telephone calls and

multimedia distribution.



SIP HISTORY

� Encompasses many protocols

� Missing part..sip

� Example



Session invitation protocol (sipv1)

� Mmcc (multimedia conf erence control)

� Used ccp

� One request , one response� Ccp used udp

� 1996, sipv1

� Used udp

� Text based



Scip

� Email identifiers

� Sipv2 evolved

� Incorporate f eatures of sipv1 and scip



Functionality provided by sip

� Session establishment, modification and

termination.

�

User mobility



Session establishment, modification

and termination

� Used to invite new members or to create

brand new sessions

�

Independent of multimedia session handledand the mechanism used to describe the

session.

� Sip distributes the session , can be used to

negotiate.



User mobility

� Cant deliver a session description until user hasbeen located.

� Sip urls (uniform resource locators)

� User name and a domain name

� E.g sip: [email protected]

� Consult sip server, anas url may be

sip:[email protected]� Register several locations with same server

or.



Registration

� User register their current location to a server

if they wish to be found.

�

Two modes of operation, redirect servers andproxy servers



Sip entities

� User agent (UA), interact with user and has an

interf ace towards the user.

�

Example:



Redirect servers

� Provide alternative locations of users to sip

UAs.

�

Example� return the address of another server..

� Return the list..



� Two redirect servers:

server with more knowledge



Proxy servers



Forking proxies(proxy servers)

� When a proxy server tries more than 1

location for a user, it is said to fork the

invitation.



Group addresses(proxy servers)



Registrars

� Ref ers to sip server accepting registrations

� Co-located with a proxy server or a redirect

server



Location servers

� A location server is used by a SIP redirect or proxy

server to obtain information about a called partys

possible location(s).

� Stores and returns possible location for users.

� Most registrars upload location updates to a

location server upon receipt.



SIP Negotiations:

The process of negotiating the

sessions extensions is conductedusing two headers

� Required header

�

Supported header



� The server decides which extensions will be used in the session based upon these twoheaders.

� The server lists the extensions that will be used in the required header and the ones it supports in the supported header.

�

In this way the server reciprocates the clientsinformation about which extensions it supports.



Example

� Bobs UA supports extensions foo1,foo2,foo3 andfoo4.Bob wants to use extension foo1 in the session , so he adds it to the required header of his INVITE.

� Laura wants to use extension foo2 as well . She knows it is supported by Bob so it is possible touse this extension.

� Therefore, she adds foo2 to the required header.

� However foo1,foo3 and foo 4 will not be used for session as they are supported by only one of the end systems.



Design principles for SIP extensions

Why principles are necessary ??

� Spirit of SIP is kept alive.

�It is used for the purpose it is developed

� Efficient working of SIP.

� Avoiding complex and huge protocol.



Do not break tool kit approach.

� Extensions to SIP should not broaden the

scope of SIP.� SIP should not be used for tasks that are

handled better by other internet protocols ,

even if at the moment , it appears SIP

would do the job.



Q uestion !!!

Using SIP to download web pages f rom

a server ??It wont be wise to use SIP for this purpose because :

� HTTP already exists for this purpose.

� It might do our work but protocol will become very complex and huge which is against the

Philosophy of IETF(Internet Engineering Task

Force).

� The IETF standardization process ensures that SIP

is kept simple and manageable.



Peer to peer relationship:

� SIP entities usually have a peer to peer relationship.

� When server receives a request f rom client it

performs some tasks and returns the response with the result of the request.

� Client does not tell server continuously telling it how to proceed.

� Thus,SIP is not really eff ective in a master/slave architecture where the master has a lot of controlover the slave.



Advantages of peer to peer

relationship:

� It makes the protocol highly suitable for inter-

domain communications.

�

Master/slave protocols have been provenineff ective for inter-domain communications

where domain owners typically want to

prevent the owner of a diff erent domain f rom

controlling their resources.



SIP security:

� Internet users protect their transmission against potential hackers in many ways . SIP users are noexception.

�

Encryption is used for SIP security� SIP security should not be confused with the security of a SIP enabled session.

� Muneeb can send an encrypted INVITE to Anas so that nobody knows what kind of session they are establishing but once the session is established , if they transmit unencrypted packets ,any potential hacker willbe able to hear the whole conversation .



Security measures:

� A ma jor aspect of security is authentication.

�

When Muneeb receives a SIP request f romsomebody claiming to be Anas , he wants to

be sure that Anas is really the one sending the

request.

� He needs a mechanism to check the identity

of caller.



1.Basic authentication

� In this scheme ,the client provides a user ID

and a password as credentials.

Drawback:

� Both user ID and password are sent in clear

text.

� Thus, anyone can readily obtain them just by

sniffing the network.



2.Digestion authentication

� It is also based on user IDs and passwords with the diff erence that they are never sent through the network.

� The server challenges the client sending a nonce value.

� The client calculates a checksum of the nonce value ,the request URI, the SIP method , the user

ID and password and sends it to server.� Server thus confirms the user ID and password

without ever exposing them.



End-to-end and hop-by-hop security:

� Headers need to be examined to route

requests and responses properly so ,they cant be encrypted end to end.

� Instead it is possible to use hop-by-hop

encryption.



� A secure channel can be established betweena UA and a proxy or between two proxies.

� Everything sent through this secure channel is

encrypted.

� However a UA using a secure channel towardsa SIP proxy cannot be sure that latter will use

another secure channel towards the next hop.� End-to-end and hop-by-hop security are

complementary and should be used together.

Session Initiated sip

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