1. Ch 14 Connection-Oriented Networking and ATM
Spring 2003

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

3. 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

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

5. 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

6. ATM Cell Header

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

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

9. 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

10. Example of VPI/VCI Rewriting

11. 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

12. 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)

13. 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

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

15. 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