Broadband ISDN 3BA33 David Lewis 3BA33 D.Lewis 2007 1 B-ISDN Model has 3 planes User Control Management 3BA33 D.Lewis 2007 3 Broadband ISDN Was Expected to be the Universal Network of the future Takes multi-service approach of N-ISDN to broadband speeds Designed to handle data, voice and new media e.g. Video, HDTV, VR etc Bandwidth-on-Demand up to very high speeds Variety of physical layers using optical fibre, copper, wireless WAN and LAN Telecoms style signalling Extension to SS7 Fundamental Technology is Asynchronous Transfer Mode (ATM) aka cell-relay, fast-packet etc. 3BA33 D.Lewis 2007 2 ATM Outline ATM Protocol Architecture Logical connections ATM Cells Service categories ATM Adaptation Layer (AAL) Text: High-Speed Networks and Internets, William Stallings, ch 5 3BA33 D.Lewis 2007 4
ATM Protocol Architecture Fixed-size packets called cells Streamlined: minimal error and flow control Designed for fast switching 2 protocol layers relate to ATM functions: Common layer providing packet transfers Service dependent ATM adaptation layer (AAL) AAL maps other protocols to ATM E.g. TCP/IP, Q.93b signalling Standardised by ITU-T and ATM Forum Latter now the MPLS, Frame Relay and ATM Forum (MFA Forum) 3BA33 D.Lewis 2007 5 Standards Terminology terminology 3BA33 D.Lewis 2007 7 Logical Connections VCC (Virtual Channel Connection): a logical connection analogous to virtual circuit in X.25 VPC (Virtual Path Connection): a bundle of VCCs with same endpoints 3BA33 D.Lewis 2007 6 Advantages of Virtual Paths Simplified network architecture Provides a level of VC aggregation Increased network performance and reliability Reduced processing and short connection setup time Don t need to find routes for every VCC Enhanced network services User-defined VP-based VPNs or VCC bundles 3BA33 D.Lewis 2007 8
VCC Uses Between end users Carrying user data Between an end user and a network entity Signalling or network embedded service, e.g. video conf server Between 2 network entities Traffic management, in-network signalling and routing 3BA33 D.Lewis 2007 9 VPC/VCC Characteristics Quality of Service (QoS) Switched and semi-permanent virtual channel connections Switched requires call control signalling Cell sequence integrity Traffic parameter negotiation and usage monitoring (VPC only) virtual channel identifier restriction within a VPC 3BA33 D.Lewis 2007 11 Setting up a VCC 3BA33 D.Lewis 2007 10 Control Signaling A mechanism to establish and release VPCs and VCCs 4 methods for VCCs: Semi-permanent VCCs (no call control signalling needed) Meta-signaling channel User-to-network signaling virtual channel User-to-user signaling virtual channel 3BA33 D.Lewis 2007 12
Control Signaling 3 methods for VPCs Semi-permanent Customer controlled Network controlled 3BA33 D.Lewis 2007 13 Header Format Generic flow control Virtual path identifier (VPI) Virtual channel identifier (VCI) Payload type Cell loss priority Header error control 3BA33 D.Lewis 2007 15 ATM Cells Fixed size 5-octet header 48-octet information field Small cells reduce delay for high-priority cells Fixed size facilitate switching in hardware 3BA33 D.Lewis 2007 14 Figure 5.4 3BA33 D.Lewis 2007 16
Generic Flow Control Control traffic flow at user-network interface (UNI) to alleviate short-term overload conditions When GFC enabled at UNI, 2 procedures used: Uncontrolled transmission Controlled transmission 3BA33 D.Lewis 2007 17 Processing Error in Cell Header 3BA33 D.Lewis 2007 19 Header Error Control 8-bit field calculated based on remaining 32 bits of header error detection in some cases, error correction of single-bit errors in header 2 modes: Error detection Error correction 3BA33 D.Lewis 2007 18 Service Categories Real-time service Constant bit rate (CBR) Real-time variable bit rate (rt-vbr) Non-real-time service Non-real-time variable bit rate (nrt-vbr) Available bit rate (ABR) Unspecified bit rate (UBR) Guaranteed frame rate (GFR) 3BA33 D.Lewis 2007 20
Co-existence of Service Categories 3BA33 D.Lewis 2007 21 Applications of AAL and ATM Circuit emulation (e.g., T-1 synchronous TDM circuits) VBR voice and video General data services IP over ATM Multiprotocol encapsulation over ATM (MPOA) LAN emulation (LANE) 3BA33 D.Lewis 2007 23 ATM Adaptation Layer (ATM) Support non-atm protocols e.g., PCM voice, IP AAL Services Handle transmission errors Segmentation/reassembly (SAR) Handle lost and misinserted cell conditions Flow control and timing control 3BA33 D.Lewis 2007 22 AAL Protocols AAL layer has 2 sublayers: Convergence Sublayer (CS) Supports specific applications using AAL Segmentation and Reassembly Layer (SAR) Packages data from CS into cells and unpacks at other end 3BA33 D.Lewis 2007 24
AAL Layers and PDUs 3BA33 D.Lewis 2007 25 AAL Type 5 Streamlined transport for connection oriented protocols (TCP/IP, signalling) Reduce protocol processing overhead Reduce transmission overhead Ensure adaptability to existing transport protocols 3BA33 D.Lewis 2007 27 AAL Type 1 Constant-bit-rate source SAR simply packs bits into cells and unpacks them at destination One-octet header contains 3-bit Sequence Count field to provide an 8-cell frame structure No CS PDU since CS sublayer primarily for clocking and synchronization 3BA33 D.Lewis 2007 26