GTE Laboratories
GBN?95
April 2, 1995

In-Service Monitoring of QOS in ATM Networks

Thomas Chen, Steve Liu, Vijay Samalam
GTE Laboratories, Inc
40 Sylvan Road
Waltham, Mass 02254
email: tmc0@gte.com
tel: 617-466-2758

GTE Laboratories
GBN?95
April 2, 1995

Introduction

? ATM networks support voice, video, and data services over CBR/ VBR connections with guaranteed quality of service (QOS)
? QOS can be degraded by congestion, faults, etc.
? network providers need to detect and diagnose troubles quickly to
minimize their effect on users

? Out-of-service testing:
? performance measurements under controlled traffic conditions
? service is interrupted

? In-service QOS monitoring:
? continuous performance measurements with actual user traffic
? no service interruption

GTE Laboratories
GBN?95
April 2, 1995

Management Cells for In-Service QOS Monitoring

? Cannot use ATM user cells for QOS monitoring
? ATM protocol is streamlined to move data quickly
? no cell header fields to detect cell loss or measure cell delays

? Propose ?management cells?
? class of ATM cells
? identified by particular VCI or PT field codes
? carry measurement data in cell payload
? processed by network nodes

? Generalization of OAM cells
? management cells can provide more capabilities than currently
standardized OAM

GTE Laboratories
GBN?95
April 2, 1995

Monitoring Procedures

? Monitor cell delays
? assume ATM switches can measure cell delays from input to output
? switch records input-to-output delay in passing management cells
? management cells can record delays experienced along a
connection

? Monitor cell loss
? assume ATM switches can measure number of cells lost at switch
? record this number in passing management cells
? management cells can record number of cells lost along a
connection

GTE Laboratories
GBN?95
April 2, 1995

Trade-Offs

? Advantages
? In-service monitoring
? Accurate and detailed QOS measurements along a connection
? More general than currently standardized OAM

? Disadvantages
? switches must monitor their own performance
? switches must process and write performance data into passing
management cells