1 Modeling Performance and QoS with Asynchronous Transfer Mode (ATM)

Why Discuss ATM?? ATM provides a good model to discuss various QoS offerings and high performance networking ATM provides a good model to discuss various QoS offerings and high performance networking ATM provides a good example of how circuit switching differs from packet switching (i.e., IP) ATM provides a good example of how circuit switching differs from packet switching (i.e., IP) ATM is deployed in some backbone networks as a “link layer” technology in the Internet Protocol stack (“IP- over-ATM” and wireless ATM) ATM is deployed in some backbone networks as a “link layer” technology in the Internet Protocol stack (“IP- over-ATM” and wireless ATM) The ATM QoS Model 2

3 Evolution ATM Forum (1991) ATM Forum (1991) Frame Relay Forum (1991) Frame Relay Forum (1991) ADSL (later DSL) Forum (1994) ADSL (later DSL) Forum (1994) MPLS Forum (2000) MPLS Forum (2000) Frame Relay Forum and MPLS Forum merge to form MPLS & Frame Relay Alliance (2003) Frame Relay Forum and MPLS Forum merge to form MPLS & Frame Relay Alliance (2003) ATM Forum merges to form MFA Forum (2005) ATM Forum merges to form MFA Forum (2005) DSL Forum merges to form Broadband Forum (2008) DSL Forum merges to form Broadband Forum (2008)

The ATM QoS Model 4 Introduction ATM Protocol Architecture ATM Protocol Architecture Logical connections Logical connections ATM cell structure ATM cell structure Service levels/categories Service levels/categories ATM Adaptation Layer (AAL) ATM Adaptation Layer (AAL)

The ATM QoS Model 5 ATM Protocol Architecture Fixed-size packets called cells Fixed-size packets called cells –“cell switching” like packet switching 2 primary protocol layers relate to ATM functions: 2 primary protocol layers relate to ATM functions: –Common layer providing packet transfers, logical connections (ATM) –Service dependent ATM adaptation layer (AAL) AAL maps other protocols to ATM AAL maps other protocols to ATM –like IP (AAL5)

The ATM QoS Model 6 Protocol Model has 3 planes User – provides for user/application data transfer and associated controls (flow control, congestion control) User – provides for user/application data transfer and associated controls (flow control, congestion control) Control – performs call control and connection control functions (signaling) Control – performs call control and connection control functions (signaling) Management – provides plane management and layer management and coordination functions Management – provides plane management and layer management and coordination functions

The ATM QoS Model 7 ATM Protocol Reference Model Various data rates ( Mbps, Mbps) over various physical media types (Fiber Optic, SONET, UTP, etc.) Framing, cell structure & Logical Connections Map data to the ATM cell structure

The ATM QoS Model 8 User Plane Layers AAL ATM User data AAL ATM PHY PHY ATM PHY ATM PHY … End system Network

The ATM QoS Model 9 User Plane Layers User information

The ATM QoS Model 10 Logical Connections VCC (Virtual Channel Connection): a logical connection analogous to a virtual circuit in X.25, or Frame Relay data link connection VCC (Virtual Channel Connection): a logical connection analogous to a virtual circuit in X.25, or Frame Relay data link connection –full-duplex flow between end users –user-network control signaling –network-network management/routing VPC (Virtual Path Connection): a bundle of VCCs with the same network end-points (not necessarily same end-users) VPC (Virtual Path Connection): a bundle of VCCs with the same network end-points (not necessarily same end-users) –switched along the same path

The ATM QoS Model 11 ATM Connection Relationships Virtual Channel: basic logical communications channel Virtual Path: groups of “common” virtual channels Physical Transmission Path: physical communications link

The ATM QoS Model 12 Advantages of Virtual Paths Simplified network architecture – allows separation of functionality into into individual logical connections and related groups of logical connections Simplified network architecture – allows separation of functionality into into individual logical connections and related groups of logical connections Increased network performance and reliability – network consists of fewer aggregated entities Increased network performance and reliability – network consists of fewer aggregated entities Reduced processing and short connection setup time – complex setup tasks are in virtual paths, simplifies setup of new virtual channels over existing virtual path Reduced processing and short connection setup time – complex setup tasks are in virtual paths, simplifies setup of new virtual channels over existing virtual path Enhanced network services – supports user- specified closed groups/networks of VC bundles Enhanced network services – supports user- specified closed groups/networks of VC bundles

The ATM QoS Model 13 Virtual Path/Virtual Channel Terminology Virtual Channel(VC) A generic term used to describe unidirectional transport of cells associated by a common unique identifier Virtual Channel Identifier (VCI) A unique numerical tag for a particular VC link Virtual Channel LinkA means of unidirectional transport of cells between the point where a VCI is assigned and where it is translated or terminated Virtual Channel Connection (VCC) A concatenation of VC links that extends between two connected ATM end-points

The ATM QoS Model 14 Virtual Path/Virtual Channel Terminology Virtual Path (VP) A generic term which describes unidirectional transfer of cells that are associated with a common unique identifier Virtual Path Identifier(VPI) Identifies a particular VP Virtual Path LinkA group of VC links identified by a common identifier between the point where the identifier (VPI) is assigned and where it is translated or terminated Virtual Path Connection (VPC) A concatenation of VP links that extends between ATM end- points where the VCIs are assigned and where they are translated or terminated

The ATM QoS Model 15 ATM VPC/VCC c ATM Sw 1 ATM Sw 4 ATM Sw 2 ATM Sw 3 a b d e VP3 VP5 VP2 VP1 a b c d e Sw = switch DCC = Cross-connect switch ATM DCC VP6

The ATM QoS Model 16 ATM Connection Relationships

17 ATM – Second Session

The ATM QoS Model 18 VPC/VCC Characteristics Quality of Service (QoS) provisioning Quality of Service (QoS) provisioning Switched and semi-permanent virtual channel connections Switched and semi-permanent virtual channel connections Cell sequence integrity Cell sequence integrity –i.e., cells are delivered in the order sent Traffic parameter negotiation and usage monitoring (policing) Traffic parameter negotiation and usage monitoring (policing) –average rate, peak rate, burstiness, peak duration, etc. (VPC only) virtual channel identifier restriction within a VPC (VPC only) virtual channel identifier restriction within a VPC –e.g., a channel reserved for network management

The ATM QoS Model 19 Call Establishment with Virtual Paths SignalingPhase Admission Control Phase Connection Setup Phase

The ATM QoS Model 20 ATM Cells Fixed size Fixed size –5-octet header –48-octet information field Small cells may reduce queuing delay for high-priority cells (essential for low delay) Small cells may reduce queuing delay for high-priority cells (essential for low delay) Fixed size facilitates more efficient switching in hardware (essential for very high data rates) Fixed size facilitates more efficient switching in hardware (essential for very high data rates)

The ATM QoS Model 21 ATM Cell Format (p. 98)

The ATM QoS Model 22 Header Format Generic flow control (more ->) Generic flow control (more ->) Virtual path identifier (VPI) Virtual path identifier (VPI) Virtual channel identifier (VCI) Virtual channel identifier (VCI) Payload type (3 bits: identifies cell as user data or network management cell, presence of congestion, SDU type) Payload type (3 bits: identifies cell as user data or network management cell, presence of congestion, SDU type) Cell loss priority (0: high; 1: low) Cell loss priority (0: high; 1: low) Header error control (more ->) Header error control (more ->)

The ATM QoS Model 23 Generic Flow Control Used to control traffic flow at user- network interface (UNI) to alleviate short-term overload conditions Used to control traffic flow at user- network interface (UNI) to alleviate short-term overload conditions –Note: not employed in network core When GFC is enabled at the UNI, two procedures are used: When GFC is enabled at the UNI, two procedures are used: –Uncontrolled transmission: not subject to flow control –Controlled transmission: flow control constraints (using GFC mechanism) are in force

The ATM QoS Model 24 Generic Flow Control (GFC) Field Coding

The ATM QoS Model 25 Header Error Control 8-bit field - calculated based on the other 32 bits in the header 8-bit field - calculated based on the other 32 bits in the header –CRC based on x 8 + x 2 + x + 1 -> generator is error detection error detection in some cases, error correction of single-bit errors in header in some cases, error correction of single-bit errors in header 2 modes: 2 modes: –Error detection –Error correction

The ATM QoS Model 26 HEC Operation at Receiver Based on recognition of fact that bit errors in fiber-based networks are single-bit or occur in large bursts.

The ATM QoS Model 27 ATM Service Categories Real-time service Real-time service –Constant bit rate (CBR) –Real-time variable bit rate (rt-VBR) Non-real-time service Non-real-time service –Non-real-time variable bit rate (nrt-VBR) –Available bit rate (ABR) –Unspecified bit rate (UBR) –Guaranteed frame rate (GFR)

The ATM QoS Model 28 ATM Bit Rate Service Levels

The ATM QoS Model 29 ATM Adaptation Layer (AAL) Support higher-level protocols and/or native applications Support higher-level protocols and/or native applications –e.g., PCM voice, LAPF, IP AAL Services AAL Services –Handle transmission errors –Segmentation/reassembly (SAR) –Handle lost and misinserted cell conditions –Flow control and timing control

The ATM QoS Model 30 ATM Adaptation Layer (AAL)

The ATM QoS Model 31 Applications of AAL and ATM Circuit emulation (e.g., T-1 synchronous TDM circuits) Circuit emulation (e.g., T-1 synchronous TDM circuits) VBR voice and video VBR voice and video General data services General data services IP over ATM IP over ATM Multiprotocol encapsulation over ATM (MPOA) Multiprotocol encapsulation over ATM (MPOA) LAN emulation (LANE) LAN emulation (LANE)

The ATM QoS Model 32 AAL Protocol and Services Basis for classification: requirement for a timing relationship between source and destinationrequirement for a timing relationship between source and destination requirement for a constant bit rate data flowrequirement for a constant bit rate data flow connection or connectionless transferconnection or connectionless transfer

The ATM QoS Model 33 AAL Protocols AAL layer has 2 sublayers: AAL layer has 2 sublayers: –Convergence Sublayer (CS) Supports specific applications/protocols using AAL Supports specific applications/protocols using AAL Users attach via the Service Access Point (like a port number) Users attach via the Service Access Point (like a port number) Common part (CPCS) and application service-specific part (SSCS) Common part (CPCS) and application service-specific part (SSCS) –Segmentation and Reassembly Sublayer (SAR) Packages data from CS into ATM cells and unpacks at other end Packages data from CS into ATM cells and unpacks at other end

The ATM QoS Model 34 AAL Protocols and PDUs

The ATM QoS Model 35 AAL Protocol Descriptions

The ATM QoS Model 36 Segmentation and Reassembly PDUs

The ATM QoS Model 37 AAL Type 1 Constant-bit-rate source Constant-bit-rate source SAR simply packs bits into cells and unpacks them at destination SAR simply packs bits into cells and unpacks them at destination One-octet header contains 3-bit SC field to provide an 8-cell frame structure One-octet header contains 3-bit SC field to provide an 8-cell frame structure No CS PDU structure is defined since CS sublayer primarily for clocking and synchronization No CS PDU structure is defined since CS sublayer primarily for clocking and synchronization

The ATM QoS Model 38 AAL Type 1

The ATM QoS Model 39 AAL Type 2 Intended for variable bit rate applications that generate bursty data and demand low loss Intended for variable bit rate applications that generate bursty data and demand low loss Originally, connectionless (AAL4) or connection (AAL3) oriented, now combined into single format (AAL 3/4) Originally, connectionless (AAL4) or connection (AAL3) oriented, now combined into single format (AAL 3/4) Provides comprehensive sequencing and error control mechanisms Provides comprehensive sequencing and error control mechanisms AAL Type 3/4 Intended for use with applications with variable bit-rate service on multiple channels (multiplexing), or low bit rate, short-frame traffic Intended for use with applications with variable bit-rate service on multiple channels (multiplexing), or low bit rate, short-frame traffic

The ATM QoS Model 40 AAL 3/4

The ATM QoS Model 41 AAL Type 5 Streamlined transport for connection oriented protocols Streamlined transport for connection oriented protocols –Reduce protocol processing overhead –Reduce transmission overhead –Ensure adaptability to existing transport protocols –primary function is segmentation and reassembly of higher-level PDUs (such as, perhaps, IP datagrams)

The ATM QoS Model 42 AAL5 Example e.g., IP datagram

The ATM QoS Model 43 AAL5