323 standard Session Initiation Protocol(SIP) Supporting protocols . availability. limitations Main issues How to protect against risks H. compressed and converted to IP packet CONTENTS • VOIP configurations • • • • • • Requirements.What is VoIP • • • • • • It is a form of communication Can make phone calls over broadband internet connection Can make calls over traditional landline numbers Uses IP to transmit voice as packets over IP n/w Voice – digitized.

VoIP configurations • • • • Dedicated routers – Traditional phones are connected to cable/DSL modems. – Once configured. it require no special software Adapters(USB) – Can use traditional phones – It is slightly larger than normal USB Software controlled VoIP – Softphone software – Need a computer with necessary equipements – Less cost Dedicated VoIP phone – It connects directly to a computer network – Consist of a phone and a base station that connects to the internet .

Availability and Limitations • • • Requirements – A connection to the internet through ISP – VoIP service to reach traditional landlines – VoIP software Availability – Need power source – Need high speed broadband internet connection Threats/Risks – SPIT(SPam over Internet Telephony).VoIP data travels unencrypted over internet .telemarketing – Spoofing.an attacker can masquerade as another VoIP caller – Confidentiality.Requirements.

• Identify. • Configure your web browser(s) securely. • Use a firewall. • If you are using a software VoIP application. • Do not divulge personal information to people you don’t know. back-up. consider using encryption software for both your installation and for those you wish to talk to. • Patch and update your application software. • Be cautious about opening files attached to email messages or instant messages.How to protect against risks • Use and maintain anti-virus and anti-spyware programs. and secure your personal or financial data. . • Verify the authenticity and security of downloaded files and new software. • Create and use strong passwords.

Main issues • • • • • Quality of Service – IP was designed for carrying data – VoIP can provide best effort service only Interoperability – It needs to work with different vendor in a public network environment Security – Anyone can capture the packets in the data since it is in plain format Integration with PSTN – It need to cooperate with Public Switched Telephone Network Scalability – VoIP may grow to large user market .

Standards • H.323 vs SIP .323 • SIP – Components of SIP – SIP messages – SIP operation • H.323 standard – Components of H.323 protocol stack – Call setup in H.323 – H.

H.323 • ITU standard for VoIP communication (International Telecommunication Union) • No QoS is provided • Components – Terminals – Gateways – Gatekeepers – Multipoint Control unit .

for call signaling and setting up call • RTP(Real time Transport Protocol). Admission Status).carries voice packets • RAS(Registration.to interact with gate keeper • Gateway – Interface between LAN/endsystem with PSTN – They perform translation b/w different formats – Put voice data from PSTN in public n/w and vice versa . • Q 931.• Terminals – Endpoints which makes a call – Should support some protocols • H.245 – for allowing the usage of channels.

• Gatekeeper – acts as a manager – Central point for all calls from its zone – Functionalities • • • • • • Address Translation Admissions Control Call signaling Call Authorization Bandwidth Management Call Management • Multipoint Control Units (MCU) – provides the capability for three or more terminals and gateways to participate in a multipoint conference – Multipoint Controller and Multipoint Processor .


H.323 Protocol Stack .

Call Setup in H. retrasmits the request Registration of the endpoint with its gatekeeper – Endpoint sends Registration request(RRQ) to gatekeeper – Gatekeeper sends Registration Confirmation(RCF) or Registration Reject(RRJ) – Unregister Request(URQ) – endpoint/gatekeeper can cancel its request – Unregister Confirmation(UCF) .323 • Discovering a gatekeeper – Discovers the gatekeeper to which the endsystem shoutld register – Multicasts Gatekeeper Request message(GRQ) – Replies with either • Gatekeeper Confirmation (GCF) message with its transport address • Gatekeeper Reject(GRJ) message • – Endpoint may choose any one gatekeeper – If timeout.

.• Endpoint enters the call setup phase – To determine contact information – Issue Location Request(LRQ) message – Location Confirmation(LCF) with contact information • The capability exchange – To provide admission control and bandwidth management functions – Admission Request(ARQ) – Admission Confirm(ACF) – Bandwidth Change Request(BRQ) • The call is established – After call establishment. it can terminate the call. media control protocol will be executed • • • • Determining master/slave Capability exchange Media Channel Control Conference Control • When the endpoint is done.

SIP(Session initiation Protocol) • IETF standard for VoIP • Application layer control protocol • Client sends request. server process the request • SIP depends on Session Description Protocol(SDP) .

– CANCEL: for terminating the search for a user .determines the next-hop server and returns the address of next-hop to client instead of forwarding Messages – INVITE: for inviting a user to a call – BYE: for terminating a connection between the two end points – ACK: for reliable exchange of invitation messages – OPTIONS: for getting information about the capabilities of a call – REGISTER: gives information about the location of a user to the SIP registration server.forwards request to next hop server • Redirect server.• • Components – User agent : end system for client .updates current locations of user • Proxy server. server – Network servers • Registration Server.

SIP Operation .

SIP Invitation – The INVITE request asks the callee to join a particular conference – Callee response by sending an ACK request Locating a User – locations can be dynamically registered with the SIP server Changing an Existing Session – This is done by re-issuing the INVITE message .• • • • • • SIP Addressing – SIP hosts are identified by a SIP URL Locating a SIP server – client can send the request to a SIP proxy server SIP Transaction – A request together with the responses triggered by that request make up a SIP transaction.

H.323 vs SIP .

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