Presentation on theme: "國立清華大學資訊系黃能富教授 1 All rights reserved. No part of this publication and file may be reproduced, stored in a retrieval system, or transmitted in any form."— Presentation transcript:
國立清華大學資訊系黃能富教授 1 All rights reserved. No part of this publication and file may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior written permission of Professor Nen-Fu Huang (E-mail: firstname.lastname@example.org). ATM Networks
國立清華大學資訊系黃能富教授 2 An Overview of ATM ATM is Asynchronous Transfer Mode. A technology for multiplexing fixed-length (53 octets) cells from a variety of sources to a variety of remote locations. Capable of moving data at a wide range of speeds. Capable of handling data from a variety of media (e.g. voice, video, and data) using a single interface. ATM is a connection-oriented protocol. Connections are established between ATM service users, (e.g. a workstation with an ATM interface or a call setup process running on an ATM switch).
國立清華大學資訊系黃能富教授 3 An Overview of ATM Connections can be switched (SVC), or permanent (PVC). Signaling procedures are used to set up calls(Q.2931). Permanent connections are established through administrative procedures. Each ATM connection operates at a certain quality of service (QoS) which is characterized by such parameters as cell loss rate, cell delay, delay jitter, bandwidth, peak rate, average rate, duration, etc. The QoS is negotiated between the user and the network when the connection is established.
國立清華大學資訊系黃能富教授 4 ATM operates on a best effort basis. ATM guarantees that cells will not be misordered. Two types of connections: Point-to-point Multipoint (Multicast) Four Types of Services: CBR (Constant Bit Rate) VBR (Variable Bit Rate) ABR (Available Bit Rate) Flow Control, Rate-based, Credit- based UBR (Unspecific Bit Rate) No Flow control. Aggregate Bandwidth vs. Shared Medium (FDDI, Fast Ethernet). An Overview of ATM
國立清華大學資訊系黃能富教授 5 ATM Network Structure ATM LAN ATM WAN UNI NNI UNI: User-Network Interface (UNI 4.0) NNI: Network-Network Interface (PNNI) UNI End Station ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch ATM Switch End Station
國立清華大學資訊系黃能富教授 6... Fore ASX-200 Newbridge VIVID DEC OC-3c (OC-3c x 4) (TAXI x 6) (OC-3c x 12) (OC-3c x 8) 電通中心 （綜二館 7F ） 清大計算機中心 ( 綜二館 3F) 資訊系 2F 資訊系 3F 電機系 4F WS WWW Servers ATM/FDDI (DEC Alpha Station x 8) 清華大學高速網路實驗平台 (1998) 遠距教學教室 OC-3c FDDI FORE ASX-200 交大計算機中心 SW T1/T3 OC-3c T1/T3 NII 網路 OC-3c (SUN) WS 電機系 6F TAXI (TAXI x4) VoD Server Clients VoD Clients, Video Conference Video Conference (OC-3c x 12) FORE ASX-200 FORE ASX-200 FORE ASX-100 FORE ASX-200 高速電腦中心 OC-3c WS ATM/Ethernet Hub Ether-Switch TAXI ATM/Wireless Bridge
國立清華大學資訊系黃能富教授 7 ATM Cell Format 酬載 48 Octets GFC VPI VCI PTI CLP HEC 4 8 16 3 1 8 位元 酬載 48 Octets VPI VCI PTI CLP HEC 12 16 3 1 8 位元 (a) UNI Cell format (b) NNI Cell format GFC: Generic Flow Control (4 bits). Used by the flow control mechanism at the UNI. VPI: Virtual Path Identifier (8 bits). Used for directing cells within the ATM network. VCI: Virtual Channel Identifier (16 bits). PTI: Payload Type Identifier (3 bits). Identifies the type of data being carried by the cell. CLP: Cell Loss Priority (1 bit). 1 = low priority. HEC: Header Error Correction (8 bits). Generated and inserted by the physical layer. For first 4 octets. Correct single-bit errors and detect some Multiple-bit errors.
國立清華大學資訊系黃能富教授 10 ATM Layer Service Transparent transfer of 48-octet data unit Deliver data in sequence on a connection Two levels of multiplexing Three types of connections Point-to-point Point-to-Multipoint Multipoint-to-Multipoint Transport is best-effort Network QoS negotiation Traffic control and congestion control
國立清華大學資訊系黃能富教授 11 ATM Layer Functions Cell multiplexing and switching Cell rate decoupling Cell discrimination based on pre-defined VPI/VCI Quality of Service (QoS) Payload type characterization Generic flow control Loss priority indication and Selective cell discarding Traffic shaping
國立清華大學資訊系黃能富教授 12 Pre-assigned VPI/VCI Values Unassigned Cell Indication (VPI = 0, VCI = 0) Meta signaling (VCI=1) Meta signaling is the bootstrap procedure used to establish and release a signaling VC. Not used for PVC setup. General broadcasting signaling (VCI=2) OAM F4 flow indication -- segment and end-to- end (VCI=3 and VCI=4) Point-to-Point Signaling (VCI=5) Carriage of Interim Local Management Interface (ILMI) messages (VPI=0, VCI=16)
國立清華大學資訊系黃能富教授 13 Cell Rate Decoupling and Cell Discrimination Cell Rate Decoupling ATM sending entity adds unassigned cells to the assigned cell stream in order to adjust to the cell rate acquired by the payload capacity of the physical layer (R). Cell Discrimination Meta signaling General broadcast signaling Point-to-point Signaling Segment OAM F4 flow cell End-to-end OAM F4 flow cell ILMI message User data
國立清華大學資訊系黃能富教授 15 Virtual Channels v The virtual channel (VC) is the fundamental unit of transport in a B-ISDN. Each ATM cell contains an explicit label in its header to identify the virtual channel. a Virtual Channel Identifier (VCI) a Virtual Path Identifier (VPI) v A virtual channel (VC) is a communication channel that provides for the transport of ATM cells between two or more endpoints for information transfer. v A Virtual Channel Identifier (VCI) identifiers a particular VC within a particular VP over a UNI or NNI. v A specific value of VCI has no end-to-end meaning.
國立清華大學資訊系黃能富教授 16 Virtual Paths v A Virtual Path (VP) is a group of Virtual Channels that are carried on the same physical facility and share the same Virtual Path Identifier (VPI) value. v The VP boundaries are delimited by Virtual Path Terminators (VPT). v AT VPTs, both VPI and VCI are processed. v Between VPTs associated with the same VP, only the VPI values are processed (and translated) at ATM network elements. v The VCI values are processed only at VPTs, and are not translated at intermediate ATM network elements.
國立清華大學資訊系黃能富教授 17 Why Virtual Paths and Virtual Channel ? A B (1) VCI OP (1) 2 (2) New VCI (127) 2 (35) 0 1 255 0 1 (2) (3) (127) (35) (255) (208) (254) (38) (208) 2 (254) 0 1 255 Assume the identification field contains 8 bits. All used as VCI. Then the size of the mapping table is 256. VCI OP (2) 1 (3) New VCI (35) 1 (255) (254) 1 (38) 0 1 255
國立清華大學資訊系黃能富教授 18 Why Virtual Paths and Virtual Channels ? 0 1 7 0 1 7 0 1 7 (0/1) (7/1) (1/1) (1/31) (0/31) (7/25) (1/25) (7/25) 0 1 31 0 1 0 1 7 VPI OP (0) 2 (7) New VPI (1) 2 (0) 0 1 (7) 2 (1) VPI OP (7) 1 (1) New VPI (0) 1 (0) 0 1 (1) 1 (7) 7 Assume VPI takes 3 bits and VCI takes 5 bits. Then the size of the mapping table is 8.
國立清華大學資訊系黃能富教授 19 Virtual Channels Examples 1 A D 1 C B (300,10) (100,20) (300,20) (100,10) (300,10) (200,20) (200,10) (100,10) (100,20) 2 3 1 2 2 4 2 VPI/VCI OP (100,10) 2 (200,10) New VPI/VCI (100,20) 2 (200,20) VPI/VCI OP (200,10) 3 (300,20) New VPI/VCI (200,20) 2 (300,10) VPI/VCI OP (300,20) 2 (100,20) New VPI/VCI VPI/VCI OP (200,10) 4 (300,10) New VPI/VCI a b c d Port (a,1) Port (c,2) Port (d,1) Port (b,1) VPI/VCI OP (100,10) 4 (200,10) New VPI/VCI Port (b,2) 4 1 (100,20) VPI/VCI 1 (300,10) VPI/VCI 1 (300,10) VPI/VCI 1 (100,10) VPI/VCI 連線 1 (100,10) VPI/VCI 輸出連線 2 (100,20) (200,10) 輸出連線 輸入連線 連線
國立清華大學資訊系黃能富教授 20 ATM Adaptation Layers (AAL) AAL Reference Structure AAL Type 1 AAL Type 2 AAL Type 3/4 AAL Type 5 SAAL (Signaling AAL)
國立清華大學資訊系黃能富教授 21 AAL Reference Structure Service Specific CS (SCCS) (may be Null) Common Part CS (CPCS) SAR(Common) AAL Convergence Sublayer (CS) SAR SAP Primitives
國立清華大學資訊系黃能富教授 23 AAL Functions FunctionsParameters Error DetectionCRC, length, correlation tags Framing of user data unitsPayload type/segment type Cell sequence indicationCell sequence count field Multiplexing Message ID (MID) Error CorrectionFEC, retransmission Flow Control Credit window Timing RecoveryTime stamp
國立清華大學資訊系黃能富教授 24 ATM Adaptation Layers (AAL) In order to carry data units longer than 48 octets in ATM cells, an adaptation layer is needed. The ATM adaptation layer (AAL) provides for segmentation and reassembly of higher-layer data units and for detection of errors in transmission. Since the ATM layer simply carries cells without concern for their contents, a number of different AALs can be used across a single ATM interface. The AAL maps the user, control, or management protocol data units into the information field of the ATM cell and vice versa. To reflect the spectrum of applications, four service classes have been defined by CCITT.
國立清華大學資訊系黃能富教授 25 CCITT Services Classifications Timing between source and destination Class A Class B Class C Class D Required Not required Bit Rate Constant Variable Connection mode Connection oriented Connectionless Circuit Emulation Packetized voice/video Connection Oriented Data Datagram Attribute Examples: Class A: 64kbps digital voice Class B: Variable bit rate encoded video Class C: Frame Relay over ATM, File Transfer (Telnet, FTP, TCP),... Class D: IP over ATM, MPOA,... Class X: Raw Cell Service (e.g., proprietary AAL)
國立清華大學資訊系黃能富教授 26 AAL Service Classification Timing between source and destination Class A Class B Class C Class D Required Not required Bit Rate Constant Variable Connection Mode Connection oriented Connectionless Circuit Emulation Packetized voice/video Connection Oriented Data Datagram Attribute AAL1 AAL2 SAAL AAL 5 AAL 4 AAL 3 Signalling (Q.93B)
國立清華大學資訊系黃能富教授 27 AAL Types Five AALs have been accepted for consideration by the CCITT. AAL 1 is meant for constant-bit-rate services (voice). AAL 2 is meant for variable-bit-rate services with a required timing relationship between source and destination (audio and video). AAL 3 was originally meant for connection-oriented variable -bit-rate services without a required timing relationship; it has now been merged with AAL 4. AAL 3/4 and 5 are meant for connectionless services (e.g. connectionless data). Only AALs 3/4 and 5 are of interest for IP networking.
國立清華大學資訊系黃能富教授 28 AAL 1 (Constant Bit Rate - CBR) Functions Emulation of DS1 and DS3 Circuits Distribution with forward error correction Handle cell delay for constant bit rate Transfer timing information between source and destination Transfer structure information (structure pointer) Provide indication of unrecoverable lost or errored information Header SN SNP 47 Octets Payload SAR PDU CSI Seq Count EP CRC 1 3 3 1
國立清華大學資訊系黃能富教授 29 AAL 2 Protocol Data Unit (PDU) Header SN IT 47 Octets Payload LI CRC SAR PDU ATM PDU SN: Sequence number IT: Information Type:BOM,COM,EOM,SSM Length Indicator
國立清華大學資訊系黃能富教授 30 AAL 3/4 The variable bit rate (VBR) adaptation layer, defined in CCITT recommendation I.363, is defined for services (e.g. data) that require bursty bandwidth. Comprises two sublayers: the convergence sublayer (CS) the segmentation and reassembly sublayer (SAR)
國立清華大學資訊系黃能富教授 31 AAL 3/4 CS and SAR PDU Structures CS-PDU Header 4 Octets CS-PDU User Information <= 65,535 Octets CS-PDU Trailer 4 Octets PAD 0-3 Octets Common Part Indicator BTag BASize Alignment CS User Infor. Length ETag 1 1 2 CPI:00000000 Btag/Etag: Beginning/Ending Tag -- 256 increment counters BAsize: receiving side maximum buffering requirement (>= CPCS-PDU) Pad: make CPCS-PDU on 32-bit boundary AL(Alignment): make trailer 32-bit aligned Length: CPCS-PDU size
國立清華大學資訊系黃能富教授 32 AAL 3/4 SAR Sublayer SAR-PDU Header 2 Octets Segmentation Unit,SAR-PDU Payload 44 Octets SAR-PDU Trailer 2 Octets SAR Type Length SAR SN MID SAR-PDU CRC 2 4 1 9 6 10 p ST: COM(00),BOM(10),EOM(01),SSM(11) SN: Modulo 16 sequence counter P(Priority): 1- Priority CS-PDU, 0- Normal CS-PDU MID (Multiplexing ID) -- Multiplexing multiple CPCS connections on a single ATM connection LI: Length <=44 CRC on Cell Header, SAR-PDU payload and LI
國立清華大學資訊系黃能富教授 33 AAL 5 PDU Structure The Simple and Efficient Adaptation Layer (SEAL), attempts to reduce the complexity and overhead of AAL 3/4. It eliminates most of the overhead of AAL 3/4. AAL 5 comprises a convergence sublayer and a SAR sublayer, although the SAR is essentially null. CS-PDU User Information <= 65,535 Octets CS-PDU Trailer 8 Octets PAD 0-47 Octets Protocol Control CRC Length 2 2 4
國立清華大學資訊系黃能富教授 34 AAL 5 Segmentation and Reassembly CPCS-PDU Payload (CPCS-SDU) <= 65,535 Octets CS-PDU Trailer 8 Octets PAD 0-47 Octets Control CRC-32 Length 2 2 4 User SDU User Data More = T User Data More = T Data T More = F... Control CPCS-UU -- CPCS User-to-User Indication (1 octet). Transparently transfer CPCS user to user information CPI -- Common Part Indicator (1 octet). Align trailer to 64 bits. Possible identification of layer management message. 48 octets ATM cell
國立清華大學資訊系黃能富教授 35 AAL 5 A datagram is converted to a CS-PDU by adding the pad (if necessary) and trailer. The CS-PDU is breaked into 48-octet SAR- PDUs and transmitted in an ATM cell. Since there is no AAL 5 SAR header, an end-of- frame indication in the ATM cell header is required: SDU type of 1 (binary value 0X1) in the PTI field. The receiver simply concatenates the received cells, watching for the end-of-frame indication. The higher layer is responsible for ignoring or using the PDUs with CRC errors.
國立清華大學資訊系黃能富教授 36 SAAL Structure Service Specific Coordination Function (SSCF) Service Specific Connection Oriented Peer-to-Peer Protocol (SSCOP) Common Part AAL Peer-to-Peer Protocol (CP-AAL) Service Specific Convergence Sublayer Common Part Peer-to-Peer Message Peer-to-Peer Message Primitives
國立清華大學資訊系黃能富教授 37 SAAL v Reside between Q.93B and ATM Layer. v SAAL is used to provide reliable transport of Q.93B messages between peer Q.93B entities. v SAAL CP-AAL uses AAL5 Common Part Protocol. v SSCOP can be used for any reliable service.
國立清華大學資訊系黃能富教授 38 Interconnection with Legacy LANs LAN Emulation IP-Over-ATM Multiple Protocol Over ATM (MPOA) IP Switching
國立清華大學資訊系黃能富教授 39 Summary of ATM Networks Switching-Based Network Architecture Connection-Oriented Protocol QoS Guaranteed Services Aggregated Bandwidth Multiple Data Rates and Interfaces