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PA-A2 ATM CES Port Adapter Installation and Configuration
OL-3460-01
Chapter 1 Overview: PA-A2 ATM CES Port Adapter
Circuit Emulation Services Overview
Implementing adaptive clocking is simple and straightforward, because it does not require network clock
synchronization services, a PRS, or the advance planning typically associated with the development of
a logical network timing map. However, adaptive clocking does not support structured CES services,
and it exhibits relatively high wander characteristics.
Summary of Clocking Modes
Table 1-1
summarizes the characteristics of the three clocking modes available for handling CBR traffic
in an ATM networking environment. Although the wander and jitter characteristics of these clocking
modes differ, each mode preserves the integrity of the user’s CBR data, ensuring its error-free transport
from source to destination.
Other Network Factors Relevant to CES Operations
The following factors affect the functioning of CES circuits:
•
The intended source and destination nodes for CES circuits.
•
The clocking mode that best suits your particular network topology and timing requirements for the
handling of CBR data.
Although synchronous clocking is the recommended (default) clocking mode for CES operations,
this fact does not preclude other clocking modes from consideration.
•
The cell delay variation (CDV) characteristics of the network, measured in microseconds.
•
Each end-to-end CES circuit exhibits delay characteristics, based on the following factors:
–
The delay characteristics of the individual devices participating in the CES circuit. Each
network device contributes some increment of delay, reflecting that device’s unique electrical
characteristics.
Table 1-1
Clocking Modes for CBR Traffic
Clocking Mode
Advantages
Limitations
Synchronous
Supports both unstructured (clear
channel) and structured CBR traffic.
Exhibits superior wander and jitter
characteristics.
Requires network clock
synchronization services.
Ties the CES interface to the network
clock synchronization services clocking
signal (PRS).
SRTS (synchronous
residual time stamp)
Conveys externally generated user
clocking signal through ATM
network, providing independent
clocking signal for each CES circuit.
Requires network clock
synchronization services.
Supports only unstructured (clear
channel) CBR traffic.
Exhibits moderate wander
characteristics.
Adaptive
Does not require network clock
synchronization services.
Supports only unstructured (clear
channel) CBR traffic.
Exhibits poorest wander characteristics.
