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The internet multimedia conferencing architecture - Coggle Diagram
The internet multimedia conferencing architecture
The Internet Layered Architecture
Transport Layer Protocols
User Datagram Protocol (UDP)
Unreliable datagram delivery
Demultiplexing, checksum
Stream Control Transmission Protocol (SCTP)
Newly developed, less available
Transmission Control Protocol (TCP)
Reliable, in-sequence transport of byte-streams between hosts
Time-outs, retransmissions, sequence numbers
Flow control, error detection
Real-Time Services in the internet
Internet Multimedia Conferencing Architcture
Multimedia services
Specific protocols for multimedia services
Delay sensitive
Streaming and interactive
Four layers implemented on top of the physical layer
Multicast
Routing Towards Many Receivers
many-to-many communication
Multicast Address
Group of host receive the IP that will be transmitted.
Any host in the network can send data to a multicast address, but it must belong to the multicast group in order toreceive data.
Advantages of Multicast
Scalable
Data traverses each link only once
intelligent use of network resources
The end systems do not need to know who the members of the multicast group are in order to send data.
Multicast Routing Protocols
Dense Mode Multicast Routing Protocols
Used in networks where most of the hosts are members of the multicast group. Number of hosts receiving multicast data is high
shortest-path tree
different distribution tree depends
where the data comes from
Sparse Mode Multicast Routing Protocols
Used in networks the proportion of hosts receiving multicast traffic is low
implement a meeting point
Shared tree that will be used by all the sources
The Mbone
Portion of Internet that supports multicast
Mbone routers are par of Internet and are enabled for
Unicast and Multicast traffic.
When a group or routers are not directly connected to Mbone, IP tunnels are used between them and the rest of Mbone
Internet Group Management Protocol (IGMP)
Hosts send requests for joining or leaving a particular group.
If subnetwoork doesn't has no members, it remove itself from the distribution tree by multicast routing protocol,
if a host in its subnetwork wishes to become a member of the multicast group, that router will be added to the distribution tree again.
Transport of Real-Time Data: RTP
Jitter and Sequencing of Datagrams
Jitter = variation in delay
If the jitter is high it can cause out-of-sequence packets
RTP solves this by assigning
Timestamps
Sequence numbers
Real-Time Transport Control Protocol
Associate timestamps and a real-time clock
Every RTP session has a parallel RTCP session
Reports how many packets the network dropped during the session
QoS Provisioning: IntegratedServices and DifferentiatedServices
Integrated services
Services available
Controlled-load services
Packets are given priority over best-effort traffic
Ensures that packets get superior treatment
guaranteed services
Provides a certain bandwidth and a delay bound for a particular flow
State information stored in the network
As integrated services work with different treatment for different flows, the network stores state information to differentiate datagrams properly
Soft states
Store state information temporarily
Needs to be refreshed periodically
Once it expires the resources reserved in the router will be released
RSVP
Protocol used to reserve resources in the network
Differentiated services
Defines several traffic classes with different priority levels
Packets are tagged
Scales better than integrated services
Session Announcement Protocol (SAP)
Session Descriptions
Following the IETF various
protocols besides SAP can be used to describe sessions.
When a system fails to
understand an SAP it has no recourse
SDP serves as the common protocol for
session description, and all applications must support SDP
Distributes information about multicast sessions among potential receivers
SAP announcements are unreliable and
must be retransmitted periodically.
SAP announcements use a fixed amount of bandwidth
Session Description Protocol (SDP)
SDP Syntax
An SDP session description consists of a set of lines of text of the form:
Type = value
The type field is always one character long and the format of the value field depends on which type it applies.
The session-level section always starts off with v=0, where v is the type and 0 is the value.
An SDP description contains session-level information and media
Media-level sections begin with an m line. The lines below it, provide information about that particular media stream
SDP Next Generation (SDPng)
New contexts, as well as a number of future applications that
might need a session description mechanism, put new requirements on the successor of SDP
This is called SDP next generation (SDPng) and is being developed in the Multiparty Multimedia Session Control (MMUSIC) working group.
SDP specifies how the information necessary to describe a session should be encoded
An SDP description is a chunk of information that a system can use to join a multimedia session
It includes, IP addresses, port numbers,
and times and dates when the session is active.
They
can be distributed using SAP, or they can be sent inside an e-mail
SIP also carries session descriptions in its
messages.
Real-Time Streaming Protocol (RTSP)
RTSP is used to control multimedia servers
Typically for streaming applications
RTSP can be used, to implement a distributed answering machine, or record an event that is being multicast on the Internet.
Usage Example of the Internet Multimedia Conferencing Toolkit
Multicasting a film over the internet
End user session description elaboration using SDP
SDP session distributed via SAP to potential recievers
End user properly configures media tools to watch the film
Session controller uses RSTP to alert the multimedia server to multicast using the SDP session description
Media server multicasts RTP packets with audio and video, RTCP packets to store statistics, and RSVP for QoS
