1 / 35

CS 4594 Broadband Communications

CS 4594 Broadband Communications. ATM. ATM. ATM = Asynchronous Transfer Mode Asynchronous - in contrast to SONET/SDH in which large frames of data are sent on a completely regular basis, completely synchronized.

glyn
Télécharger la présentation

CS 4594 Broadband Communications

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CS 4594 Broadband Communications ATM

  2. ATM • ATM = Asynchronous Transfer Mode Asynchronous - in contrast to SONET/SDH in which large frames of data are sent on a completely regular basis, completely synchronized. • Purpose: Convey voice, video, and data service over the same channel. Each service has different timing requirements. • ATM was developed to meet the new telephone network model called Broadband ISDN = Integrated Services Digital Network

  3. ATM Layers • ATM has three major layers: AAL, ATM, Physical. AAL • AAL provides network services. Converts user data into fixed length cells (53 bytes) • ATM handles switching, traffic management, etc. • Physical connects to a variety of different media ATM Physical

  4. ATM Cells • ATM transports data in small packets called cells. • Each cell is 53 bytes long with a 5 byte header and a 48 byte payload.

  5. ATM Cell Header • The ATM cell header has two different forms: • UNI = User-Network Interface - as the cell enters the network • NNI = Network-Network Interface - as it moves through the network.

  6. ATM Cell Header – Fields • Labeling – Cell ID • GFC = Generic Flow Control – 4 bits for UNI, not present in NNI, misnamed, now used for multiplexing user channels • VPI = Virtual Path Identifier – 8 bits for UNI, 12 bits for NNI • VCI = Virtual Channel Identifier – 16 bits • Cell Management • PTI = Payload Type – 3 bits • CLP = Cell Loss Priority • Error Control and Framing • HEC = Header Error Control – 8 bits, CRC check on header

  7. ATM – Virtual Circuits • VPI/VCI form a label for the cell that determines how the cell will be handled in the next switch. • Each switch has a number of inputs and outputs, each with a identifying number. • When a cell enters a switch, its VPI/VCI is input into a table look-up that returns the output identifier and a new VPI/VCI.

  8. ATM – Virtual Circuit Types • PVC = Permanent Virtual Circuit – set up manually by programming each switch along the route • SVC = Switched Virtual Circuit – set up dynamically by signaling procedures.

  9. AAL = ATM Adaptation Layer • ALL is the top layer among ATM layers AAL ATM Physical

  10. Role of AAL • Provides interface between application layers and ATM network itself • Implemented in endpoint devices (at edge of network) • Supports a number of different service classes • Shields ATM layer from knowing anything about user data

  11. Classical AAL Classes

  12. Modern Service Categories • CBR = Constant Bit Rate • rt-VBR = Real Time Variable Bit Rate • nrt-VBR = Non Real Time Variable Bit Rate • ABR = Available Bit Rate • UBR = Unspecified Bit Rate • GFR = Guaranteed Frame Rate

  13. Traffic Contract • Agreement between user and network • Contains • Traffic descriptors – specifying ATM cell flow • QoS parameters – specifing timing and error qualities • Conformance checking rules

  14. Traffic Parameters • PCR = Peak Cell Rate • SCR = Sustainable Cell Rate • MBS = Maximum Burst Size • MCR = Minimum Cell Rate

  15. QoS Parameters • Timing • Cell Transfer Delay (CTD) • Cell Delay Variation (CDV) • Errors • Nonegotiable • Cell Error Ratio (CER) • Cell Misinsertion Rate (CMR) • Severely-Errored Cell Block Ratio (SECBR) • Negotiable • Cell Loss Ratio (CLR) • Cell Misinsertion Rate (CMR)

  16. AAL Sublayers Service specific convergence sublayer (SSCS) Common part convergence sublayer (SSCS) Segmentation and reassembly sublayer (SAR)

  17. Sublayers of AAL • CS = Convergence Sublayer (CS) • Performs functions such as end-to-end synchronization, traffic control and monitoring, cell loss control • Sublayers • Service Specific (SSCP) – application dependent • Common Part (CPCS) – common to all users of a service • Segmentation and Reassembly (SAR) • Performs repackaging between convergence layer packets and ATM cells

  18. AAL Types • Designed to handle the different service types • Specify architectural details, traffic parameters, packet formats and procedures

  19. AAL-0 • Unofficial • Designed to send ATM cells directly from ATM-cell based application to ATM cell • Has empty CS and SAR

  20. AAL-0 Operations Higher Layers ATM Cell ATM Cell ATM Cell ATM Cell AAL Layers ATM Layer ATM Cell ATM Cell ATM Cell ATM Cell

  21. AAL-1 • Designed for Class A= CBR • Transports a constant stream of bits with timing • Applications: circuit emulation, uncompressed voice and video. • May handle: • segmentation and reassembly (SAR) • handling cell delay variation (buffering) • handling cell delay • handling lost and mininserted cells • clock management • recovery of source data framing • monitoring and correction of error in user data

  22. AAL-1 PDU • SAR header • SN (4 bits): sequence number • CSI (1 bit): Convergence layer indicator (can be used for clock) • Sequence number (3 bits) • SNP (4 bits): sequence number protection • 3-bit CRC • 1 bit parity

  23. H H H H 1 1 1 1 47 47 47 47 H H H H ATM Cell ATM Cell ATM Cell ATM Cell 5 5 5 5 48 48 48 48 AAL-1 Operations Higher Layers Bit Stream 47 47 47 47 (bytes) CS AAL Layers SAR ATM Layer

  24. AAL-2 • Designed to handle Class B, rt-VBR • Transfers multiplexed streams of bits and timing • Handles errors or indicates when errors have occurred • Two layers: packet and PDU (cell)

  25. 3 3 3 3 H STF STF H H H STF STF 47 1 1 1 1 47 47 47 H H H H ATM Cell ATM Cell ATM Cell ATM Cell 5 5 5 5 48 48 48 48 AAL-2 Operations Higher Layers User 1 User 2 User 3 User 1 packet AAL 2 Layers PDU ATM Layer

  26. AAL-2 CPS Packet • CPS-PH (3 octets) common part sublayer packet header • CID (8 bits): channel id for multiplexing • LI (6 bits): length indicator for number of octets in variable payload structures • UUI (5 bits): user-to-user information • HEC (5 bits): error control for packet header

  27. AAL-2 CS-PDU • STF (8 bits): start field • OSF (6 bits): offset • SN/P (2 bits): error correction and detection for start field • Payload data (47 bytes) • PAD (padding as needed for real-time)

  28. AAL-3/4 • Designed for Class C and Class D (nrt-VBR) connection and connectionless • Can do multicasting (network-based distribution) • Can do multiplexing (multiple streams through same service) • Designed to be highly reliable • CRC check on cells • SAR support • Sequencing • Mux id • Beginning and end tags • HEC • Multiple modes of operation (assured and non assured delivery)

  29. 4 4 4 75 75 75 5 5 5 4 4 4 H H H P P P T T T 2 2 2 2 44 44 44 44 2 2 2 2 H H H H T T T T 48 48 48 48 H H H H ATM Cell ATM Cell ATM Cell ATM Cell 5 5 5 5 48 48 48 48 AAL-3/4 Operations Higher Layers packet packet packet 75 75 75 (bytes) SSCS CPCS AAL Layers SAR ATM Layer

  30. AAL-3 structures CPI BT BA size User Data PAD AL ET Length Header (1+1+2) Trailer (1+1+2)

  31. AAL-3/4 CPCS-PDU • Header (4 octets) • CPI (1 octets): Common Part Indicator – defines how the other parts are encoded • BT (1 octet): Beginning Tag • BA size (1 octet): Buffer Allocation size • User Data (1-65,535 octets) • PAD: padding to keep PDU length a multiple of 4 octets • Trailer (4 octets) • AL (1 octet): Alignment to make CPS trailer 4 octets • ET (1 octet): Ending Tag • Length (2 octets) of entire PDU

  32. AAL-3/4 SAR-PDU • Header (2 octets) • ST (2 bits): Segment Type: BOM 10, COM 00, EOM 01 • SN (4 bits): Sequence Number • MUX-ID (10 bits): multiplexing id • SAR-PDU Payload (44 octets) segment of CPCS-PDU • Trailer (2 octets) • LI (6 bits): length indicator • CRC (10 bits): CRC check on segment

  33. AAL-5 • Designed for Class C and Class D (nrt-VBR) connection and connectionless • Simplified (lightweight) version of AAL-3/4 • No overhead in cells

  34. 75 75 75 13 13 13 8 8 8 P P P T T T 48 48 48 48 48 48 48 48 H H H H ATM Cell ATM Cell ATM Cell ATM Cell 5 5 5 5 48 48 48 48 AAL-5 Operations Higher Layers packet packet packet 75 75 75 (bytes) SSCS CPCS AAL Layers SAR ATM Layer

  35. AAL-5 SDUs • CPCS-PDU • User Data: 1-65,535 octets • PAD: 0-47 octets • CPCS-PDU trailer • CPCS UU: 1 octet • CPI: 1 octet • CPCS-PDU length: 2 octets • CRC: 4 octets

More Related