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Impact of Satellite Networks on Transport Layer Protocols
 

Impact of Satellite Networks on Transport Layer Protocols

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  • one or more TCP segments may not reach the otherend of the connection, and TCP uses timeout mechanisms to detect those missing segments.
  • allows routers to inform TCP senders about imminentcongestion without dropping segments

Impact of Satellite Networks on Transport Layer Protocols Impact of Satellite Networks on Transport Layer Protocols Presentation Transcript

  • Satellite Networking Principles and Protocols;Impact of Satellite Networks on Transport Layer Protocols
    Advisor: Dr. Nemaney pour
    Prepared By: Reza Ghanbari Maman
    December 2010
  • Outline
    Introduction
    TCP performance Analysis
    Slow Start Enhancement
    Loss recovery enhancement
    Enhancements using interruptive mechanisms
    Voice over IP
    Real-time transport protocol
  • Introduction
    Transport Communication Protocol
    The end to end protocol between processes in different hosts across internet networks.
    It is transparent to the internet.
    The most challenging task is to provide reliable and efficient transmission services without knowing anything about application above it or anything about the internet below it.
    Application
    Host parameters
    Configurations
    Channel
    TCP control
  • Introduction
    Application Characteristics
    Remote login
    File transfer
    World wide web and e-mail
    Client and server host parameters
    Process power
    Buffer sizes
    Speeds of NIC’s
    Round Trip Time (RTT)
    Satellite network configurations
    Assumption :
    Constraints: Long delay, Errors, Limited bandwidth, etc.
    Access networks and internetworking units are capable of dealing with traffic flows
    Application
    Host Parameters
    Configurations
    Channel
    TCP control
  • Introduction
    Application
    Host Parameters
    Configurations(Cont.)
    Channel
    TCP control
    Asymmetric satellite networks
    Forward direction : From satellite gateway station to user stations
    Return direction: User stations to satellite gateway station
    Data rate in the forward direction is larger than the return direction, because of limits on the transmission power and the antenna size at different satellite earth stations
    Receive-only broadcasting satellite systems:
    Unidirectional
    It can be used as non-satellite return path
    The nature of most TCP traffic is asymmetric with data flowing in one direction and acknowledgements in the opposite direction
    DVB-S, DVB-RCS and VSAT satellite networks
  • Introduction
    Application
    Host Parameters
    Configurations(Cont.)
    Channel
    TCP control
    Satellite link as last hop
    Provide directly service as opposed to satellite links located in the middle of a network, may allow for specialized design of protocols used over the last hop.
    Providers use;
    Satellite link as shared high-speed downlink to users with a lower speed
    Non-shared terrestrial link as a return link for requests and ACK’s
    Hybrid satellite networks
    Typical configuration
    Satellite links
    Locate at any point in the network topology
    Act as another link between two gateways
    Connection may be sent over terrestrial links (including terrestrial wireless), as well as satellite links
  • Introduction
    Application
    Host Parameters
    Configurations(Cont.)
    Channel
    TCP control
    Point-to-point satellite networks
    Pure Configuration
    Only hop is over the satellite link
    Multiple satellite hops
    Network traffic may traverse multiple hops between source and destination which aggravates the satellite characteristics
    Generic problem because of many more constraints due to long delay, error and bandwidth
    Constellation satellite networks
    Without Inter Satellite Links
    Wide coverage is achieved by multiple satellite hops
    With Inter Satellite Links
    wide coverage is achieved by ISL
    Problem:
    Dynamic network routing
    Variable end-to-end delay
  • Introduction
    Application
    Host Parameters
    Configurations
    Channel
    TCP control
    Internet consists of various topologies, bandwidth, delays and packet sizes
    TCP
    defined in RFC793, RFC1122, RFC1323
    It is a byte stream (Not a message stream)
    Message boundaries are not end to end preserved
    It is full-duplex connection and point to point
    It does not support multicasting or broadcasting
    The sending and receiving entities exchange data in the form of segments
    Segment of TCP
    Fixed 20-bytes header followed by zero or more data bytes
    Size limitations
    Each segment fit into 65,535 bytes IP/v4 payload and Maximum Transfer Unit (MTU)
  • Introduction
    Application
    Host Parameters
    Configurations
    Channel (Cont.)
    TCP control
    TCP and satellite channel characteristics
    Long Round Trip Time (RTT)
    Due to the propagation delay
    Determination of successfully received at the final destination may take a long time for a TCP sender
    Large Delay Bandwidth product
    Due to the bottleneck link
    It defines the amount of data a protocol should have data that has been transmitted but not yet acknowledged (called In-Flight)
    Variable Round Trip Times
    It is a variable propagation delay to and from the satellite in LEO constellations
    Affects to Retransmission Time Out (RTO)
    Alternate connectivity
    This may cause packet loss in non-GSO satellite orbit configurations
  • Introduction
    Application
    Host Parameters
    Configurations
    Channel (Cont.)
    TCP control
    TCP and satellite channel characteristics (Cont.)
    Asymmetric use
    Due to the expense of the equipment used to send data to satellites
    Situated that the uplink has less available capacity than the downlink for return channel
    May have an impact on TCP performance
    Transmission errors
    Bit Error Rate (BER)
    Satellite channels higher than typical terrestrial networks
    TCP assumes
    network congestion
    encloses to all packet drops
    Moderated by reduction of window size
    Avoided by assigning that the drop was due to it
  • Introduction
    Application
    Host Parameters
    Configurations
    Channel
    TCP control
    TCP Control
    Flow control
    To ensure
    the transmitted data is at a rate consistent
    Shared capacity of a link among the connections using it
    Result
    Most throughput issues are exhausted
    Congestion Control
    Used to avoid generating network traffic
    Mechanisms
    Slow start
    Congestion avoidance
    Fast retransmit before RTO expires
    Fast recovery to avoid slow start
  • Introduction
    Application
    Host Parameters
    Configurations
    Channel
    TCP control (Cont.)
    TCP Control
    Characteristics
    Congestion Window (cwnd)
    Higher priority to inject into the network before receiving an ACK
    The value is limited to the receiver’s advertised window size
    Slow Start Threshold (ssthresh)
    If cwnd < ssthresh then the Slow-Start Algorithm is used to increase the value of cwnd
    If cwnd >= ssthresh then Congestion Avoidance Algorithm is used
    The initial value is the receiver’s advertised window size and is set when congestion is detected
    Negative impact on the performance
    Because of slow probe to the network for additional capacity and wastes bandwidth
    It is true over long-delay satellite channels
    because of more time consumption to obtain feedback from the receiver
  • TCP performance analysis
    First Transmission
    Slow Start Trans.
    Congestion Avoidance Trans.
    Usage of satellite link as satellite networks
    Expensive
    Time consumption to implement
    Analysis and calculation of bandwidth utilization over a point-to-point satellite network as;
    First TCP Transmission
    TCP Transmission in Slow Start Stage
    TCP Transmission in Congestion Avoidance Stage
  • First Transmission
    Slow Start Trans.
    Congestion Avoidance Trans.
    : Data to transmit
    : Propagation Delay
    : Bandwidth capacity
    : Utilization
    First TCP Transmission
    Bandwidth Utilization
    Complete data transmission
    TCP transmission in slow start Stage
    Let where n is the total number of RTT
    Bandwidth Utilization
    TCP performance analysis
  • First Transmission
    Slow Start Trans.(Cont.)
    Congestion Avoidance Trans.
    : Data to transmit
    : Propagation Delay
    : Bandwidth capacity
    : Utilization
    TCP transmission in slow start Stage(Cont.)
    Complete data transmission
    General Transmitted date size where 0 ≤  < 1
    Link Utilization
    General Complete data transmission
    TCP performance analysis
  • First Transmission
    Slow Start Trans.
    Congestion Avoidance Trans.
    TCP transmission in congestion avoidance stage
    Transmitted data size where m is maximum size
    Link Utilization where 0 ≤ β < 1
    Window Size
    TCP performance analysis
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger initial window
    Slow-Start Termination
    Optimization of TCP performance
    Major problem of TCP
    Unknown total data size
    Unknown available bandwidth
    Unknown carry process of TCP segment
    Slow-start enhancement
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger initial window
    Slow-Start Termination
    Optimization of TCP performance (Cont.)
    Rules and parameters
    Increase minimum segment size of
    Limitations
    Slow-Start threshold
    Congestion window size
    Receiver buffer size
    Improve Slow-Start algorithm
    Limitation
    Slow transmission
    Improve ACK
    Limitation
    Buffer Space
    Detect packet loss due to transmission error
    Limitation
    ACKs transmitted at different paths
    Improve congestion avoidance mechanism
    Limitation
    Slow transmission
    Slow-start enhancement
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger initial window
    Slow-Start Termination
    TCP enhancement techniques
    For short request/response traffic, utilization affected by
    Connection set-up
    Using three-way handshake (with Synchronization number-SYN)
    Requiring 1 to 1.5 RTT
    Using TCP extensions to eliminate
    Connection close-down time
    Bandwidth utilization
    At small data size transactions
    Very low
    Improvement
    Ability to share the same bandwidth
    Slow-start enhancement
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger initial window
    Slow-Start Termination
    Slow start and delayed acknowledgement (ACK)
    Slow-Start algorithm
    Used by TCP to increase the size of congestion window
    Used to making safe against transmitting an inappropriate amount of data into the network when the connection starts up
    Waste network capacity due to large DB product
    Delayed ACK
    receivers refrain from acknowledging every incoming data segment
    Every second full-sized segment is acknowledged
    If it does not arrive within a timeout, then an ACK must be generated (Timeout <500 ms)
    by increasing of cwnd size, the number of ACKs slows the cwnd growth rate may decrease
    a second segment must arrive before an ACK is sent
    Note: The receiver is always forced to wait for the delayed ACK timer to expire before acknowledging the first segment which also increases the transfer time
    Slow-start enhancement
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger Initial Window
    Slow-Start Termination
    Larger Initial Window
    By increasing the initial value of cwnd
    More packets are sent during the first RTT of data transmission,
    More ACKs, allowing the congestion window to open more rapidly.
    By sending at least two segments initially
    First segment does not need to wait for the delayed ACK timer to expire as is the case when the initial size of cwnd is one segment
    Using a fixed larger initial congestion window
    decreases the impact of a long RTT on transfer time
    A mechanism is required to limit the effect of these bursts.
    Using delayed ACKs only
    Offers an alternative way to immediately ACK the first segment of a transfer
    Opens the congestion window more rapidly
    Note: The value of cwnd saves the number of RTT and a delayed ACK timeout
    Slow-start enhancement
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger Initial Window
    Slow-Start Termination
    Termination of Slow Start
    When TCP detects congestion
    When the size of cwnd reaches the size of the receiver’s advertised window
    When cwndgrows beyond a certain size
    When the cwnd reaches the reduced ssthresh
    Notes:
    TCP ends slow start and begins using the congestion avoidance algorithm when it reaches the slow-start threshold (ssthresh)
    Terminating at the right time is useful to avoid overflowing the network
    Avoiding multiple dropped segments
    Slow-start enhancement
  • TCP for trans.
    Slow-Start & Delayed ACK
    Larger Initial Window
    Slow-Start Termination(Cont.)
    Termination of Slow Start (Cont.)
    Packet-pair algorithm
    observes the spacing between the first few returning ACKs
    Determines the bandwidth of the bottleneck link
    Together with the measured RTT
    Determining DB product is determined
    Setting ssthresh the value
    Slow-start enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification
    Detecting corruption loss
    Congestion avoidance enhancement
    Loss Recovery Enhancement
    Satellite paths
    Higher error rates than terrestrial lines
    Causing errors in data transmissions to be retransmitted
    TCP typically interprets loss as a sign of congestion and goes back into the slow start
    Prevents TCP going to slow start unnecessarily when data segments get lost due to error
    NewReno TCP algorithm is used ,but independent from the availability of Selective ACK
    Note: we need to reduce the error rate to a level acceptable to TCP or find TCP knowing that datagram loss is due to transmission errors, not congestion
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification
    Detecting corruption loss
    Congestion avoidance enhancement
    Fast Retransmission and Fast Recovery
    TCP segments may not reach the other end connection, and TCP uses timeout mechanisms to detect those missing segments, hence TCP assumes that segments are dropped due to network congestion
    Result: ssthresh being set to half the current value of cwnd and its size is being reduced to the size of one TCP segment
    Avoids the unnecessary process of backward process of Slow Start when a segment fails to reach the intended destination
    Detects the loss of segments by using duplication of ACKs
    Used to retransmit the missing data segment
    Result: TCP can use to resume the normal transmission process via the congestion avoidance phase instead of slow start as before
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification
    Detecting corruption loss
    Congestion avoidance enhancement
    Selective Acknowledgement
    When multiple segments are lost within a single transmission window, TCP performs poorly
    Limitation
    TCP can only learn of a missing segment per RTT
    Lack of cumulative acknowledgements
    Reduction of TCP throughout
    Improves TCP performance
    Identifies missing TCP segments and retransmits within a single RTT
    Note:Due to occasional high bit-error rates (BER) of the channel, the sender is notified about which segments have not been received and need to be retransmitted by received sequence numbers
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification
    Detecting corruption loss
    Congestion avoidance enhancement
    SACK based enhancement mechanisms
    Algorithm starts after Fast Retransmit triggers the resending of a segment
    Algorithm reduces cwnd into half of the size when a loss is detected
    Algorithm keeps a PIPE variable
    Which is an estimate of the number of outstanding segments
    Which is decremented by one segment for each duplicate ACK that arrives with new SACK information
    Which is incremented by one for each new or retransmitted segment sent
    Algorithm recovers multiple segment losses in a window of data within one RTT of loss detection
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification
    Detecting corruption loss
    Congestion avoidance enhancement
    ACK congestion control
    In high asymmetric networks (VSAT)
    low-speed return link on a high-speed forward link
    If a terrestrial modem link is used as a reverse link, ACK congestion as the speed of the forward link is increased
    The flow of ACKs can be restricted on the low-speed link
    by the bandwidth of the link
    by the queue length of the router
    Note: The Current congestion control mechanisms are aimed at controlling the flow of data segments, but do not affect the flow of ACKs
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification
    Detecting corruption loss
    Congestion avoidance enhancement
    ACK Filtering
    It is designed
    to address the same ACK congestion effects
    to operate without host modifications
    It takes advantage of the cumulative ACK structure of TCP
    It is implemented by the modified bottleneck router in the reverse direction
    It is used to produce significant sender bursts by modification of Sender Adaption (SA)
    Explicit Congestion Notification (ECN)
    It allows routers to inform TCP senders about imminent congestion without dropping segments
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification (Cont.)
    Detecting corruption loss
    Congestion avoidance enhancement
    Explicit Congestion Notification (Cont.)
    Forms
    Backward ECN (BECN)
    BECN router transmits messages directly to the data originator informing it of congestion
    IP routers can accomplish this with an ICMP source quench message
    The arrival of a BECN signal may or may not mean that a TCP data segment has been dropped, but it is a clear indication that the TCP sender should reduce the value of cwnd
    Forward ECN (FECN)
    FECN routers mark data segments with a special tag when congestion is imminent, but forward the data segment
    The data receiver then shows the congestion information back to the sender in the ACK packet
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification (Cont.)
    Detecting corruption loss
    Congestion avoidance enhancement
    Detecting Corruption Loss
    Corruption Loss
    TCP should retransmit the damaged segment as soon as its loss is detected; there is no need for TCP to adjust its congestion window i.e. it should immediately reduce its congestion window to avoid making the congestion worse
    May be detected using the fast retransmit algorithm or by the expiration of TCP’s retransmission timer
    Problem
    It is more common than on terrestrial networks
    Solution
    Adding Forward Error Correction (FEC) to the data but it can not be universally applied
    Corrupted TCP segment
    Dropped by intervening routers
    Survive without detection until it arrives at the TCP receiving host
    Does not indicate congestion
    Loss recovery enhancement
  • Fast re-trans. & fast recovery
    Selective ACK
    SACK based enhancement
    ACK congestion control
    ACK filtering
    Explicit congestion notification (Cont.)
    Detecting corruption loss
    Congestion Avoidance Enhancement
    Congestion avoidance enhancement
    In the absence of loss, the TCP sender adds approximately one segment to its congestion window during each RTT
    Problem
    Unfair sharing of bandwidth when multiple connections with different RTTs traverse the same bottleneck link, with the long RTT connections
    Solution
    Deployment of fair queuing and TCP-friendly buffer management in network routers
    Policy changes
    The “constant-rate” increase policy attempts to equalize the rate at which TCP senders increase their sending rate during congestion avoidance
    The “increase-by-K” policy can be selectively used by long RTT connections in a heterogeneous environment
    Loss recovery enhancement
  • TCP Spoofing
    Cascading or Split TCP
    Perfect Solution
    Enhancements for satellite networks using interruptive mechanisms
    Interruptive Mechanism
    Enhancements using interruptive mechanisms
  • TCP Spoofing
    Cascading or Split TCP
    Perfect Solution
    TCP Spoofing
    Helps to improve TCP performance over satellite
    Problem
    The router must do a considerable amount of work after it sends an acknowledgement
    Spoofing requires symmetric paths:
    the data and acknowledgements must flow along the same path through the router
    Spoofing is vulnerable to unexpected failures
    If a path changes or the router crashes, data may be lost
    Spoofing does not work if the data in the IP datagram are encrypted
    Because the router will be unable to read the TCP header
    Enhancements using interruptive mechanisms
  • TCP Spoofing
    Cascading or Split TCP
    Perfect Solutions
    Cascading TCP or Split TCP
    TCP running over the satellite link can be modified, with knowledge of the satellite’s properties, to run faster
    Because each TCP connection is terminated, cascading TCP is not vulnerable to asymmetric paths
    Perfect Solutions
    Satellite Networking
    Should be able to meet the requirements of user applications,
    Takes into account the characteristics of data traffic
    Makes full use of network resources
    Enhancements using interruptive mechanisms
  • TCP Spoofing
    Cascading or Split TCP
    Perfect Solutions(Cont.)
    Perfect Solutions (Cont.)
    Solutions
    Based on the enhancement of existing TCP mechanisms have reached their limits as
    No knowledge about applications
    No knowledge about networks and hosts
    Finding new techniques to achieve multi-layer and cross-layer optimization of protocol architecture
    Enhancements using interruptive mechanisms
  • TCP Spoofing
    Cascading or Split TCP
    Perfect Solutions(Cont.)
    Perfect Solutions (Cont.)
    Solutions
    Based on the enhancement of existing TCP mechanisms have reached their limits as
    No knowledge about applications
    No knowledge about networks and hosts
    Finding new techniques to achieve multi-layer and cross-layer optimization of protocol architecture
    Enhancements using interruptive mechanisms
  • Gateway Decomposition
    Protocols
    Gatekeepers
    MMC
    Conference Control
    Based on RTP, IP telephony is becoming a mainstream application moving away from proprietary solutions to standards based solutions, providing QoS comparable to the PSTN and providing transparent interoperability of the IP and PSTN networks
    Gateway Decomposition
    The signaling gateway is responsible for signaling between end users on either network. On the PSTN side, an IP signaling protocol such as SIP or H.323, and transported across the IP network
    SAP
    Announces the session
    SDP
    Describes the call (or session)
    Voice over IP
  • Gateway Decomposition
    Protocols
    Gatekeepers
    MMC
    Conference Control
    Gateway Decomposition (Cont.)
    Media gateway
    Data, video and audio stream transfer responsibility once a call is set up
    On the PSTN side, media transport is by PCM-encoded data on TDM streams;
    On the IP network side, media transport is by PCM-encoded data on RTP/UDP
    Media gateway controller
    Controls one or more media gateways
    Protocols
    H.323 (s)
    Introduced by ITU
    Provide multimedia capability over the Internet
    RTP,RTSP, RTCP, Megaco, SIP and SDP
    Introduced by IETF
    Provide the foundation for standards based IP telephony
    Voice over IP
  • Gateway Decomposition
    Protocols
    Gatekeepers
    MMC
    Conference Control
    Gatekeepers
    Are responsible for addressing, authorization and authentication of terminal and gateways, bandwidth management, accounting, billing and charging
    Provide call-routing services
    Note: Terminal is a PC or stand-alone device running multimedia applications. Multipoint control units (MCU) provide support for conferences of three or more terminals.
    Voice over IP
  • Gateway Decomposition
    Protocols
    Gatekeepers
    MMC
    Conference Control
    Multimedia conferencing (MMC)
    One of the typical example applications based on IP multicast
    Components
    Voice provides packet audio in time slices, numerous audio-coding schemes, redundant audio for repair, unicast or multicast, configurable data rates
    Video provides packet video in frames, numerous video-coding schemes, unicast or multicast, configurable data rates
    Network Text Editor can be used for message exchanges
    Whiteboard can be used for free-hand drawing
    Voice over IP
  • Gateway Decomposition
    Protocols
    Gatekeepers
    MMC
    Conference Control
    Conference control
    provides functions and mechanisms for users to control how to organize, manage and control a conference
    Control function
    Floor control: Who speaks? Chairman control? Distributed control?
    Loose control: One person speaks, grabs channel
    Strict control: Application specific, e.g. lecture
    Resource reservation: Bandwidth requirement and quality of the conference
    Per-flow reservation: Audio only, video only, audio and video
    Voice over IP
  • Real-time transport protocol
    Internet protocols
    Specified for the transmission of raw data between computer systems
    The emergence of modern applications and mainly those based on real-time voice and video present new requirements to the IP protocol suite
    Products support streaming audio, streaming video and audio-video conferencing
    Basic of RTP
    Real time transport protocol
    Provides end-to-end network transport functions suitable for applications transmitting real-time data.
    RTP does not
    Address resource reservation
    Guarantee QoS for real-time services
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Basic of RTP(Cont.)
    RTCP(real-time transport control protocol):
    Allows monitoring of the data delivery in a manner scalable to large multicast networks
    Provides minimal control and identification functionality
    Applications run RTP on top of UDP:
    Make use of its multiplexing and checksum services.
    There are two closely linked parts:
    RTP, to carry data that has real-time properties
    RTCP, to monitor the quality of service and to convey information about the participants in an ongoing session
    Real-time transport protocol
    Basic of RTP(Cont.)
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Basic of RTP(Cont.)
    Property
    ability of one party to signal to one or more other parties and initiate a call
    Session Invitation Protocol
    a client-server protocol that enables peer users to establish a virtual connection between them and then refers to a RTP session carrying a single media type.
    Applications typically run RTP on top of UDP to make use of its multiplexing and checksum services
    Real-time transport protocol
    Basic of RTP(Cont.)
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
    IP header
    UDP header
    RTP header
    Data
  • Basic of RTP(Cont.)
    Components
    End system
    An application that generates the content to be sent in RTP packets and/or consumes the content of received RTP packets
    Mixer
    An intermediate system that receives RTP packets from one or more sources combines the packets in some manner and then forwards a new RTP packet
    Translator
    An intermediate system that forwards RTP packets with their synchronization source identifier intact
    Monitor
    An application that receives RTCP packets sent by participants in an RTP session, in particular the reception reports, and estimates the current QoS for distribution monitoring, fault diagnosis and long-term statistics
    Real-time transport protocol
    Basic of RTP(Cont.)
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Basic of RTP(Cont.)
    RTP header format
    V 2-bits, version number (=2)
    P 1-bit indicates padding
    X 1-bit indicates extension header present
    CC 4-bits, Number of CSRCs (CRSC count)
    M 1-bit, profile specific marker
    PT 7-bits, payload type, profile specific
    SSRC synchronization source
    CSRC contributing source
    Timestamp has profile/flow-specific units
    Real-time transport protocol
    Basic of RTP(Cont.)
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • RTP control protocol
    Based on the periodic transmission of control packets to all participants in the session, using the same distribution mechanism as the data packets
    Performance functions
    Primary function provides feedback on the quality of the data distribution
    RTCP carries a persistent transport-level identifier for an RTP source called the canonical name or CNAME
    The first two functions require that all participants send RTCP packets, therefore the rate must be controlled in order for RTP to scale up to a large number of participants
    Optional function is to convey minimal session control information
    Real-time transport protocol
    Basic of RTP
    RTP Control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Sender report (SR) packets
    The first section (header) consists of the following fields.
    Version (V)
    Padding (P)
    Reception report count (RC)
    Packet type (PT)
    Length
    SSRC
    The second section, the sender information, is 20 octets long and is present in every sender report packet.
    NTP timestamp
    RTP timestamp
    Sender’s octet count
    The third section contains zero or more reception report blocks depending on the number of other sources heard by this sender since the last report.
    Fraction lost
    Cumulative number of packets lost
    Extended highest sequence number received
    Inter-arrival jitter
    Last SR timestamp (LSR)
    Delay since last SR (DLSR)
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Receiver report (RR) packets
    The format of the receiver report (RR) packet
    the same as that of the SR packet except that the packet type field contains the constant 201 and the five words of sender information are omitted
    The same as SR packet except that the packet type field contains the constant 201 and the five words of sender information are omitted
    Source description (SDES) RTCP packet
    SDES packet
    A three-level structure composed of a header and zero or more chunks, each of which is composed of items describing the source identified in that chunk.
    Chunk
    Consists of an SSRC/CSRC identifier which carry information about the SSRC/CSRC
    Starts on a 32-bit boundary
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Source description (SDES) RTCP packet(Cont.)
    Item
    Consists of an eight-bit type field describing the length of the text and the text itself.
    System sends one SDES packet containing its own source identifier
    Mixer sends one SDES packet containing a chunk for each contributing source from which is receiving SDES information or multiple complete SDES packets
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet(Cont.)
    SAP & SIP protocols for SI
    SDS
  • SAP and SIP protocols for session initiations
    Session Announcement Protocol (SAP)
    Session creator merely multicasts packets periodically to a well-known multicast group carrying an SDP description of the session that is going to take place
    Gets a little more complex when we take security and caching into account
    Session Initiation Protocol (SIP)
    Works like making a telephone call
    Finds the person you are trying to reach and causes their phone to ring
    Able to call traditional telephone numbers
    Users may move to a different location
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • SAP and SIP protocols for session initiations(Cont.)
    A typical SIP call of initiate and terminate session
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI(Cont.)
    SDS
  • SAP and SIP protocols for session initiations(Cont.)
    A typical SIP call using a redirect server and location server
    A typical SIP call using a proxy server and location server
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI(Cont.)
    SDS
  • Session directory service (SDS)
    Multicast services growing and leading applications to some navigation difficulties
    Creation of a session directory service
    Functions
    A user creating a conference needs to choose a multicast address that is not in use
    By allocating addresses with respect to a Pseudo-Random strategy
    Multicasting the session information out and if it detects a clash from an existing SA, it changes its allocation
    Users need to know what conferences there are on the multicast backbone (Mbone), what multicast addresses they are using, and what media are in use on them
    Real-time transport protocol
    Basic of RTP
    RTP control protocol
    Sender Report
    Receiver Report
    SDES-RTCP packet
    SAP & SIP protocols for SI
    SDS
  • Thanks
    Any Question?