Advanced Internet Technologies Chapter 2 ATM Dr.-Ing. Falko Dressler Chair for Computer Networks & Internet Wilhelm-Schickard-Institute for Computer Science University of Tübingen http://net.informatik.uni-tuebingen.de/ dressler@informatik.uni-tuebingen.de Advanced Internet Technologies, SS 2004 2.1
Chapter 2 ATM Basics of ATM Introduction Reference Model Higher Layers Signaling, Routing IP over ATM LAN over ATM Advanced Internet Technologies, SS 2004 2.2
B-ISDN and ATM The goal of broadband ISDN (1990) Worldwide consistently build high-performance network Transmission of data, audio, video Standardization via ITU (CCITT) ATM (Asynchronous Transfer Mode) was selected as the base technology for B-ISDN Therefore, ATM is part of the ITU specification of B-ISDN Advanced Internet Technologies, SS 2004 2.3
Introduction ATM: Asynchronous Transfer Mode Based on standardized protocols Integrated technology for multiple services Data Speech / Audio Video Usable in LAN and WAN areas Highly scalable Support for different connection qualities -> Real-time! Employment of asynchronous time multiplex technologies for flexibility in support of various transmission bandwidths Advanced Internet Technologies, SS 2004 2.4
Properties Data packets of fixed size, named cells ATM cells have a length of 53 byte (5 byte header, 48 byte payload) This allows a high speed processing including massive parallel hardware operations Connection oriented point-to-point point-to-multipoint Connections may have a fixed (reserved) bandwidth and guaranteed quality of service characteristics Centralized coordination of permissions to send (in contrast to token techniques or CSMA/CD) No shared medium Dedicated bandwidth Advanced Internet Technologies, SS 2004 2.5
Standardization ITU-T: International Telecommunications Union Telecommunications Standards Section (formerly CCITT) http://www.itu.ch/ ETSI: European Telecommunications Standards Institute http://www.etsi.fr/ ANSI: American National Standards Institute http://web.ansi.org/ ATM-Forum Development of industry standards allowing a fest development of new products http://www.atmforum.com/ Advanced Internet Technologies, SS 2004 2.6
ATM Layer Model User plane: information flow between the layers Control plane: connection setup, maintenance and termination Management plane: meta-signaling and OAM information flow Advanced Internet Technologies, SS 2004 2.7
Physical Layer Physical medium sends and receives a bit stream Bit timing Transmission convergence The physical layer adopts the ATM cells received from the ATM layer to the bit stream required by the physical layer (cell coding) Direct cell transmission Cell adaptation to existing transmission frames PLCP based cell adaptation HEC generation Information flow to the management and to the supervision at the physical layer (OAM) Advanced Internet Technologies, SS 2004 2.8
Physical Layer II Transmission speeds PDH (Plesiochronous Digital Hierarchy) Europe: 2,048 Mbit/s, 8,448 Mbit/s, 34,368 Mbit/s, 139,264 Mbit/s USA: 1,544 Mbit/s, 6,312 Mbit/s, 44,736 Mbit/s, 254,176 Mbit/s SDH (Synchronous Digital Hierarchy) OC-3: 155,520 Mbit/s OC-12: 622,080 Mbit/s Today: OC-48, OC-192, Advanced Internet Technologies, SS 2004 2.9
ATM Layer Transport of ATM cells between the communication end points Tasks of the user and control plane Connection setup, multiplexing/de-multiplexing and maintaining ATM connection Generation of ATM cell headers (but HEC) Negotiation of QoS parameters Traffic and overload control OAM cells (management plane) Meta-signaling Advanced Internet Technologies, SS 2004 2.10
ATM Cell Format 53 Byte 5 Byte Header 48 Byte Payload Advanced Internet Technologies, SS 2004 2.11
ATM Cell Types UNI/NNI cells: data communication Transmission of user data Transmission of signaling data (connection setup, maintenance, tear down) VP/VC OAM cells (F4 and F5) Idle cells: decoupling of the cell rate at the sender and the available bandwidth of the transmission medium Empty cells: contain VPI/VCI but no payload OAM cells: contain control and service information Reserved VCI/VPI values Function Meta signaling ILMI Point-to-point signaling PNNI VPI/VCI VCI=1, VPI=0 VCI=16, VPI=0 VCI=5 VCI=18, VPI=0. Advanced Internet Technologies, SS 2004 2.12
ATM Connections 2 Hierarchies: paths and channels Virtual Channels Virtual Path Transmission Path Advanced Internet Technologies, SS 2004 2.13
Properties of ATM Connections Start and end at higher layer functions Have associated service parameters (e.g. cell loss ratio, latency) Negotiation of transmission parameters before a connection is set up (provision of QoS) Preservation of the transmission order Unidirectional or bidirectional Symmetric or asymmetric bandwidth Permanent PVC: Permanent Virtual Channel Dynamic SVC: Switched Virtual Channel Signaling: connection setup and tear down (ATM Forum: UNI 3.1, UNI 4.0) Routing Protocols (ATM-Forum: P-NNI) Addressing Advanced Internet Technologies, SS 2004 2.14
Traffic and Overload Control Traffic Management 4.0 (ATM Forum) Connection admission control Verification if connection setup would be possible User/network parameter control (UPC/NPC) Supervision of transmission bandwidth by setting a cell loss priority and selectively discarding of cells Traffic shaping adjustment / smoothing of the transmission rate Early packet discard discarding of complete AAL PDUs if single cells are lost Advanced Internet Technologies, SS 2004 2.15
Call Admission Control Exchange of information during the connection setup Source traffic descriptor Peak cell rate (PCR): upper bound for the maximum cell transmission rate [c/s] Sustainable cell rate (SCR): upper bound for the average cell transmission rate [c/s] Maximum burst size (MBS): size of a buffer used for short bursts [c] Minimum cell rate (MC): lower bound for the cell transmission rate [c/s] Cell delay variation tolerance (CDVT): lower bound for the minimum distance between two cells (generated by multiplexing, OAM cells, ) QoS of the connection (QoS parameters) Successful completion of the CAC Traffic agreement is negotiated between the network and the end systems Advanced Internet Technologies, SS 2004 2.16
UPC/NPC Usage Parameter Control / Network Parameter Control Verification of Correctness of the VP/VC identifiers in the cell header Conformance of the cell stream (compliance with the negotiated traffic profile) Actions Cell passing Cell tagging (warning) Cell discarding (in overload situations) Generic cell rate algorithm (GCRA) For every cell, a theoretical arrival time (TAT) is calculated based on the assumption that the distance between all cells is equal If the actual arrival time corresponds with the TAT (taking a tolerance into account), the cell is conform Advanced Internet Technologies, SS 2004 2.17
UPC/NPC II UPC typically at the ingress of an ATM switch One or two leaky buckets depending on the service category Advanced Internet Technologies, SS 2004 2.18
Traffic Shaping Implementation using a leaky bucket Reduction of the burst size and removal of the cell delay variation (by increasing the delay) Important note: the order of the cells is not changed Advanced Internet Technologies, SS 2004 2.19
Early Packet Discard EPD buffer threshold to prevent overload situations If threshold is exceeded, complete AAL5 PDUs are dropped performance enhancement Advanced Internet Technologies, SS 2004 2.20
Quality of Service Parameter are negotiated at connection setup (ITU I.356/UNI4.0) Cell error ratio Severely errored blocks Cell loss ratio* Cell misinsertion ratio Cell transfer delay* Mean cell transfer delay Cell delay variation* *: currently unused Different classes (ATM-Forum) Constant bit-rate (CBR) Delay sensitive CBR cell stream Variable bit rate - real time (VBR-rt) Delay sensitive VBR cell stream Variable bit rate - non real time (VBR-nrt) Delay insensitive VBR cell stream Unspecified bit rate (UBR) Best effort Available bit rate (ABR) Dynamic bandwidth allocation if available Advanced Internet Technologies, SS 2004 2.21
Quality of Service II Attribute CBR VBR-rt VBR-nrt UBR ABR Traffic parameters PCR and CDVT(pcr) Specified Specified Specified Specified Specified SCR, MBS, CDVT(scr) n/a Specified Specified n/a n/a MCR n/a n/a n/a n/a Specified QoS parameters Peak-peak CDVT Specified Specified Unspecified Unspecified Unspecified maxctd Specified Specified Unspecified Unspecified Unspecified CLR Specified Specified Specified Unspecified Flow control Closed loop Unspecified Unspecified Unspecified Unspecified Specified Advanced Internet Technologies, SS 2004 2.22
ATM Adaptation Layer AAL (ATM Adaptation Layer): mapping data structures between higher layers and ATM cells Criteria: Time constraints Bit rate (constant, variable) Connection type (connection oriented / connection less) Convergence Sublayer (CS) Building CS-PDUs out of an application generated byte stream Segmentation and Reassembly Sublayer (SAR) Convert CS-PDUs into 48 byte fragments which fit in the payload of ATM cells Advanced Internet Technologies, SS 2004 2.23
ATM Adaptation Layer II Advanced Internet Technologies, SS 2004 2.24
ATM Adaptation Layer III AAL0: native ATM AAL1: constant bit rate (circuit emulation) AAL2: transmission of data streams with variable bit rates and well defined time constraints between sender and receiver AAL3/4: Variable bit rate without any time constraints AAL5: simplified AAL3/4 (no multiplexing of cells) SAAL: Signaling Advanced Internet Technologies, SS 2004 2.25
Convergence Sublayer Common part: to add / to remove header and trailer Unreliable transmission of data packets of variable length Connection setup between two CPCS end points Preservation of the order within a single CPCS connection Error detection and handling Handling of overload information Handling of cell loss priorities Dropping of incomplete CPCS PDUs Service specific: Q.SAAL (SSCS: specification for signaling channels) Advanced Internet Technologies, SS 2004 2.26
Segmentation and Reassembly Sublyaer Identification of the next SAP PDU to transmit PTI informs about start and end of a SAR PDU Handling of overload Handling of cell loss priorities Check for ordering of SAR PDUs Advanced Internet Technologies, SS 2004 2.27
SAAL SAAL: Adaptation layer for signaling meta signaling signaling AAL ITU Q.2100 Offers a reliable service for the higher layer signaling (Q.2931) Q.2931 has no error correction mechanisms SSCS sublayer: realizes SSCOP protocol (Service Specific Connection Oriented Protocol) Sequence continuity Error correction, retransmission Flow control Keep alive Connection control Exchange of status information between sender and receiver Advanced Internet Technologies, SS 2004 2.28
Operation, Administration and Maintenance Information flow for management and control Cells can be identified by the PT field Error control and localization Performance control 5 hierarchies: F1-F5 Physical layer: F1-F3 SDH encoding: F1, F2: section overhead, F3: path overhead PDH encoding: using PDH internal structures Indication of unavailability state, transport of defect information to the end system, MUX problems ATM layer: F4, F5 Fault management Transmission of defect information in both directions AIS - Alarm Indication Signal: sent upstream to indicate downstream failures RDI - Remote Indication Signal: sent downstream to indicate upstream failures Continuity check Loopback cells: monitoring, fault localization Performance management Advanced Internet Technologies, SS 2004 2.29
ATM Components ATM Hosts ATM Switches ATM Edge Devices Interconnection of ATM networks and non-atm networks ATM Interfaces (public/private) UNI (User Network Interface): defines protocols for the communication between hosts and switches NNI (Network to Network Interface): defines the interface between two network components Advanced Internet Technologies, SS 2004 2.30
Higher Layers Signaling, Routing UNI User Network Interface PNNI - Private Network-to-Network Interface ILMI - Integrated Local Management Interface Advanced Internet Technologies, SS 2004 2.31
User Network Interface Connection Setup Host A: specification of bandwidth, QoS and destination address Within the network: Verification of the available resources Acceptance / rejection of the request Reservation of the required resources Maintenance of the routing tables Host B: acceptance / rejection of the connection request Advanced Internet Technologies, SS 2004 2.32
User Network Interface Connection Release Host A: connection release message Within the network: Release of resources belonging to the connection Acknowledgement of the connection release message Host B: acknowledgement of the connection release message Advanced Internet Technologies, SS 2004 2.33
User Network Interface III ATM point-to-multipoint connections Extensions in UNI 4.0 Signaling Multicast (leaf initiated join) Frame discard Signaling of more QoS parameters (CLR, meanctd, maxctd, CDV,...) Advanced Internet Technologies, SS 2004 2.34
Private Network-to-Network Interface Protocol P-NNI: also known as Private Network Node Interface Protocol Setup of SVCs in networks with NSAP addressing in a multivendor environment Hierarchical routing structure, similar to OSPF Using topology and resource information to setup paths Phase 0: Inter-Switch Signaling Protocol (IISP) Signaling protocol for the communication between ATM switches (administratively configurable address prefixes) Phase 1: QoS support scalability and reachability Signaling is based on UNI3.1/4.0 with some extensions Advanced Internet Technologies, SS 2004 2.35
P-NNI - QoS CAC (connection admission control) Admission control at each node along the path Topology state protocol GCAC (generic CAC) Determination of the shortest path over all nodes which comply with the ABR and CLR Additionally, the path is versified using the QoS requirements (CDV, ) Source node creates a Designated Transit List containing the complete route Cranback: possibility for a rollback Advanced Internet Technologies, SS 2004 2.36
P-NNI - Hierarchy Scalability: hierarchical routing protocol Summary of the reachability information at each hierarchy Identification using NSAP addresses Problems: internetworking with other networks Complexity in route aggregation Advanced Internet Technologies, SS 2004 2.37
Integrated Local Management Interface Protocol for the bidirectional exchange of management information Monitoring of systems Management of systems Using SNMP (simple network management protocol) for the communication (without UDP/IP addressing) Fundamentals: data base (ATM-UNI-MIB) with well defined commands for accessing the data base: AAL encapsulated SNMP messages, community name ILMI Advanced Internet Technologies, SS 2004 2.38
ILMI - Address Registration Bidirectional address registration Dynamic exchange of address information between end systems and the network at the UNI The ATM host informs the switch about its ESI address The ATM switch provides the address prefix to the host Protocol for automatic address registration Benefits: There is no need to configure the prefix at each host There is no need for an additional address resolution protocol in the switches (all hosts register first) Advanced Internet Technologies, SS 2004 2.39
Applications Multimedia Video over ATM Benefits: guaranteed QoS parameters Low latency Resource sharing between multiple applications Drawbacks: Complexity in the maintenance of ATM networks Examples: M-JPEG codecs: 15Mbit/s, TV quality MPEG2 codecs: 3-40Mbit/s, DVD up to studio quality Lossless SDI: 270Mbit/s, uncompressed studio signals IP/LAN over ATM Classical IP, MPOA LAN Emulation Advanced Internet Technologies, SS 2004 2.40
Multiprotocol Encapsulation over AAL5 (RFC2684) RFC2684 LLC/SNAP encapsulation LLC data packets are encapsulated into AAL5 CPCS PDUs Transmission of a complete data stream in a single VC A special header informs about the encapsulated protocol All protocols based on Ethernet, FDDI, can be transported VC based multiplexing Communication end point in layer 3 Avoidance of special LLC headers by using separate VCs for each protocol More efficient than LLC encapsulation Advanced Internet Technologies, SS 2004 2.41
Classical IP Specification of a complete IP implementation for ATM Allows unicast communication only Very efficient Support for large MTU sizes Direct encapsulation of IP packets into AAL PDUs LIS: logical IP subnet ATMARP/InATMARP: protocol similar to ARP to resolve IP to ATM addresses InATMARP functions are provided by an ATMARP server There must be an ATMARP server in each LIS Advanced Internet Technologies, SS 2004 2.42
Classical IP II Each ARP client must register its IP/ATM address information at the ATMARP server or request an IP address from the ATMARP server Advanced Internet Technologies, SS 2004 2.43
LANE LAN Emulation: connecting LANs over ATM networks The properties of ATM are completely hidden Complete emulation of the LAN MAC layer Thus, no need to modify existing LAN software But, no special ATM features can be used, e.g. QoS Provisioning of a special broadcast mechanism, which is also used for multicast Translation of MAC to ATM addresses Transmission of LAN packets using AAL5 PDUs Modules: LANE client (LEC) LANE server (LES) LANE configuration server (LECS) Broadcast and unknown server (BUS) Advanced Internet Technologies, SS 2004 2.44
LANE II LEC (LANE client) Control functions Data exchange using the ATM interface Interface to the application as a standard LAN MAC interface LES (LANE server) Control and maintenance of an E-LAN (emulated LAN) Registration of LECs Mapping of MAC to ATM addresses BUS (broadcast and unknown server) Delivery of broadcast, multicast and unknown packets received from any LANE client All packets with a broadcast or multicast address Packets which cannot be delivered directly, e.g. because the corresponding ATM address cannot be resolved Sequential processing of the single messages (AAL5 does not allow the change of the order of PDUs) Advanced Internet Technologies, SS 2004 2.45
LANE III LECS (LANE configuration server) Management of the different emulated LANs and the associated LANE servers Configuration database allowing a LANE client to find the appropriate LANE server for a specific emulated LAN LECS address Statically configured in LES and LEC Well known address via ILMI Advanced Internet Technologies, SS 2004 2.46
LANE IV Advanced Internet Technologies, SS 2004 2.47