Voice over IP, Data Communication & Networking
- 1. Voice over IP PREPARED BY:- SHIVANGI SINGH DATA COMMUNICATION & NETWORKING (2171008) E.C DEPT.
- 2. Voice over IP (Internet telephony) The idea is to use the Internet as a telephone network with some additional capabilities. Instead of communicating over a circuit-switched network, this application allows communication between two parties over the packet-switched Internet. Two protocols have been designed to handle this type of communication: SIP and H.323.
- 3. SIP The Session Initiation Protocol (SIP) was designed by IETE It is an application layer protocol that establishes, manages, and terminates a multimedia session (call). It can be used to create two-party, multiparty, or multicast sessions. SIP is designed to be independent of the underlying transport layer; it can run on UDP, TCP, or SCTP. SIP is a text-based protocol, as is HTTP. SIP, like HTTP, uses messages.
- 4. Messages
- 5. Each message has a header and a body. The header consists of several lines that describe the structure of the message, caller's capability, media type, and so on. We give a brief description of each message. Then we show their applications in a simple session. The caller initializes a session with the INVITE message. After the callee answers the call, the caller sends an ACK message for confirmation. The BYE message terminates a session. The OPTIONS message queries a machine about its capabilities. The CANCEL message cancels an already started initialization process. The REGISTER message makes a connection when the callee is not available.
- 6. Addresses In a regular telephone communication, a telephone number identifies the sender, and another telephone number identifies the receiver. SIP is very flexible. In SIP, an e-mail address, an IP address, a telephone number, and other types of addresses can be used to identify the sender and receiver. However, the address needs to be in SIP format (also called scheme)
- 7. Simple Session A simple session using SIP consists ofthree modules: establishing, communicating, and terminating.
- 8. Establishing a Session: Establishing a session in SIP requires a three-way handshake. The caller sends an INVITE message, using UDP, TCP, or SCTP to begin the communication. If the callee is willing to start the session, she sends a reply message. To confirm that a reply code has been received, the caller sends an ACK message. Communicating: After the session has been established, the caller and the caller can communicate by using two temporary ports. Terminating the Session: The session can be terminated with a BYE message sent by either party.
- 10. When a caller needs to communicate with the callee, the caller can use the e-mail address instead ofthe IP address in the INVITE message. The message goes to a proxy server. The proxy server sends a lookup message (not part of SIP) to some registrar server that has registered the callee. When the proxy server receives a reply message from the registrar server, the proxy server takes the caller's INVITE message and inserts the newly discovered IP address of the callee. This message is then sent to the callee.
- 11. H.323 H.323 is a standard designed by lTV to allow telephones on the public telephone network to talk to computers (called terminals in H.323) connected to the Internet.
- 12. A gateway connects the Internet to the telephone network. In general, a gateway is a five-layer device that can translate a message from one protocol stack to another. The gateway here does exactly the same thing. It transforms a telephone network message to an Internet message. The gatekeeper server on the local area network plays the role of the registrar server, as we discussed in the SIP.
- 13. Protocols H.323 uses a number ofprotocols to establish and maintain voice (or video) communication. H.323 uses G.71 or G.723.1 for compression. It uses a protocol named H.245 which allows the parties to negotiate the compression method. Protocol Q.931 is used .for establishing and terminating connections. Another protocol called H.225, or RAS (Registration!Administration!Status), is used for registration with the gatekeeper.
- 15. Operation of a telephone communication using H.323
- 16. The steps used by a terminal to communicate with a telephone 1. The terminal sends a broadcast message to the gatekeeper. The gatekeeper responds with its IP address. 2. The terminal and gatekeeper communicate, using H.225 to negotiate bandwidth. 3. The terminal, gatekeeper, gateway, and telephone communicate by using Q.931 to set up a connection. 4. The terminal, gatekeeper, gateway, and telephone communicate by using H.245 to negotiate the compression method. 5. The terminal, gateway, and telephone exchange audio by using RTP under the management of RTCP. 6. The terminal, gatekeeper, gateway, and telephone communicate by using Q.931 to terminate the communication.
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