1. VOICE AND VIDEO OVER IP
VOIP, RTP, RSVP

2. Can also handle voice and video
TCP/IP Protocols
Designed for data
Can also handle voice and video

3. Representation
Voice and video must be converted between analog and digital forms
Typical device is codec (coder / decoder)
Example encoding used by phone system is Pulse Code Modulation (PCM)
Note: 128 second audio clip encoded in PCM requires one megabyte of memory
Codec for voice, known as vocodec, attempts to recognize speech rather than just waveforms

4. Audio And Video Transmission And Reproduction
Conventional isochronous architecture
IP internet is not isochronous.
Datagrams can be duplicated, delayed, or arrive out of order.
Variance in delay is called jitter, and is especially pervasive in IP networks.

5. Illustration Of Jitter Buffer
Data arrives in bursts
Data leaves at steady rate

6. Real-Time Transport Protocol (RTP)
Internet standard to transmit digitized audio or video signals

7. RTP provides two key facilities:
A sequence number in each packet that allows a receiver to detect out-of-order delivery or loss
a timestamp that allows a receiver to control playback.

8. RTP Message Format

9. RTP can coordinate multiple data streams
Mixing
RTP can coordinate multiple data streams
Intended for combined audio and video
Up to 15 sources
Header specifies mixing

10. RTP is an application protocol RTP runs over UDP
RTP Encapsulation
RTP is an application protocol
RTP runs over UDP

11. RTP Control Protocol (RTCP)
Required part of RTP
Allows sender and receiver to exchange information about sessions that are in progress
Separate data stream
Uses protocol port number one greater than port number of data stream

12. RTCP Message Types

13. a sender report message that provides an absolute timestamp.
RTCP Message Types
receiver report messages that inform the source about conditions of reception.
a sender report message that provides an absolute timestamp.
synchronize multiple streams.

14. RTCP Message Types
Source description messages which provide general information about the user who owns or controls the source.
canonical name for the stream owner, a character string in the form:
host

15. IP telephony or Voice over IP (VoIP)
RTP used for encoding and transfer
Also need signaling protocol for
Dialing
Answering a call
Call forwarding
Gateway used to connect IP telephone network to Public Switched Telephone Network (PSTN)
PSTN uses SS7 for signaling

16. Standards For IP Telephony
SIP (Session Initiation Protocol)

17. H.323
ITU standard
Set of many protocols
Major protocols specified by H.323 include

18. How H.323 Protocols Fit Together

19. Session Initiation Protocol (SIP)
IETF standard
Alternative to H.323
Less functionality
Much smaller
Permits SIP telephone to make call
Does not require RTP for encoding

20. Session Description Protocol (SDP)
Companion to SIP
Specifies details such as
Media encoding
Protocol port numbers
Multicast addresses