Ch 14 Connection-Oriented Networking and ATM Spring 2003

Motivation A single technology to fill both LAN and WAN roles Introduces the connection-oriented packet switching paradigm

Asynchronous Transfer Mode ( ATM ) Designed by phone companies Single technology meant to handle Voice Video Data Intended as LAN or WAN Goal: replacement for Internet

ATM Characteristics End-to-end (application to application) Connection-oriented interface: Establish “connection” Send data Close connection Performance guarantees (statistical) Uses cell switching

ATM Cell Fixed size packet (for highest speed electronics) Size chosen as compromise between voice (small) and data (large) 5 octet header 48 octet payload Note: size not optimal for any application

ATM Cell Header

ATM Switch Building block of ATM network Connections to Computers Other ATM switches Accepts and forwards cells

Cell Forwarding Performed directly by hardware Incoming cell sent to an outgoing interface Uses label in cell Motivation: highest speed

Label Switching ATM connection identified with 24-bit binary value Known as Virtual Path Identifier / Virtual Channel Identifier (VPI / VCI) Generically called label VPI / VCI rewritten at each switch

Example of VPI/VCI Rewriting

ATM Quality of Service Fine-grained (per connection) Specified when connection established Endpoint specifies Type of data transfer Throughput desired Maximum packet burst size Maximum delay tolerated

Type of Data Transfer Constant Bit Rate (CBR) Variable Bit Rate (VBR) Example: audio Variable Bit Rate (VBR) Example: video with adaptive encoding Available Bit Rate (ABR) Example: data Unspecified Bit Rate (UBR) Each type has detailed parameters (e.g., mean, max, burst duration)

Sending Data Over ATM Uses ATM Adaptation Layer (AAL5) Accepts and delivers large, variable-size packets AAL5 divides into cells for transmission Called segmentation and reassembly

Assessment of ATM Failed to deliver on promiscuousness Switches too expensive for LAN QoS impossible to implement

Summary ATM—a universal networking technology that handles voice, video, and data transmission Two types of ATM VCs PVC SVC Specifying QoS requirements when creating a VC ATM has not been widely accpeted Expense Complexity Lack of interoperability with other technologies