H.323

1
H.323

• An International Telecommunications Union (ITU)
  standard.
• Architecture consisting of several protocols
• o G.711 Encoding and decoding of speech (other
  protocols are supported as well)
• o H.245 Negotiates what type of compression to
  use as well as the bitrate
• o RTP/RTCP (Real Time Transport Protocol)
  Handles the actual voice communication
• o Q.931 Standard telephony functions (connection
  establishment, dial tones, ringing)
• o H.225 PC to Gatekeeper function that utilizes
  the Registration/Admission/Status (RAS) channel

2
Voice over IP (3)

• Logical channels between the caller and callee
  during a call.

3
Voice over IP (2)

• The H323 protocol stack.

4
Voice over IP

• The H323 architectural model for Internet
  telephony.

5
Making a call with H.323

• 1. Locate the Gatekeeper by broadcasting a UDP
  discover packet to port 1718. Gatekeeper
  responds with its IP address.
• 2. Register with the Gatekeeper via RAS.
• 3. Request bandwidth to be allotted for the call
  via RAS
• (call setup begins since telephone
  communication is connection oriented, TCP is used
  instead of UDP)
• 4. Client sends a SETUP request with the number
  being called
• Gatekeeper sends a CALL PROCEEDING signal back to
  the client
• Gatekeeper forwards the SETUP request to the
  Gateway
• Gateway makes an ordinary telephone call to the
  desired number
• The end office of the destination number sends
  back an ALERT signal to signify that the call was
  successful (phone is ringing)
• When the call is answered the end office sends a
  CONNECT signal
• At this point, the gatekeeper is bypassed and all
  packets are sent directly the gateway. H.245
  determines the capabilities of both sides and
  communication commences via RTP.

6
SIP The Session Initiation Protocol

• Designed by the IETF
• Text-based protocol modeled on HTTP
• Works well with existing Internet Applications
• SIP URL
• siprob_at_cs.wku.edu
• Handles the setup of a call while actual data
  transfer is handled by a protocol like RTP.

7
SIP The Session Initiation Protocol

• The SIP methods defined in the core specification.

8
SIP (2)

• Use a proxy and redirection servers with SIP.

9
Comparison of H.323 and SIP