Benefits of VoIP

Lower operational cost – single infrastructure, free additional features (caller ID & conference call). Flexibility – more than one call over single broadband connection. Security – encrypt/authenticate IP stream. Integration – video conversation, data file exchange & audio conference.  

Corporate Users

Many large companies have extensive data communications networks internally and across sites. No need to spend extra for voice services, use existing network for VoIP services. Advantages: Migrating from copper-wire to VoIP over data network Better use of bandwidth Lower cost – no duplicating services Unified communication systems – single infrastructure to manage Dual-mode phones – use VoIP on internal […]

Consumer Market

Available since 2004. Delivered by existing broadband connection. Behaves much like standard Public Switched Telephone Network (PSTN). Requires equipment: Dedicated VoIP phone, or Adaptor for standard analog phone, or Software and headset/web cam Benefit for home users is ability to make free phone calls, especially when making long distance calls. Most common provider is Skype.

SIP Messages

SIP protocol defines several messages: INVITE: inviting user to call BYE: terminating connection between two end points ACK: reliable exchange of invitation messages OPTIONS: get information about capabilities of call REGISTER: passes user location information to SIP registration server CANCEL: terminates search for user

SIP Components

User Agents: End system acting on behalf of user e.g. client & server. Initiates SIP request & server receives requests and returns responses on behalf of user. Network Servers: Three types available: Registration server – receives client location updates. Proxy server – forwards receiving request to next-hop server. Redirect server – determines next-hop server, returns address of next-hop server to […]

SIP Functions

SIP has following functions: User Location: determination of end system to use for communications Call Setup: ringing & establishing call parameters by both called and calling parties User Availability: determination of willingness of called party to engage in communications User Capabilities: determination of media and media parameters to use Call Handling: transfer & termination of calls

Session Initiation Protocol (SIP)

Distributed architecture for creating, modifying and terminating sessions with one or more participants. Controls communications sessions. Standardised under IETF. Covers video conferencing, audio conferencing and one-to-one telephone calls. Stack independent, usually run over TCP or UDP. Uses request/response model similar to HTTP – client sends a request and gets a response from server. Requests/responses in plain text with SIP borrowing […]


ITU-T’s (International Telecommunications Union) standard – vendors need to comply to supply VoIP. Encompasses point to point communications & multipoint conferences. Consists of four components: Terminals Endpoint host systems providing real time, two way comms. Can communicate with another H.323 terminal, H.323 gateway or MCU. Gateways Endpoint providing communication between terminal or another gateway. Translates transmission formats e.g audio an […]