Troubleshooting › General Troubleshooting › Increase in Network Round Trip Time (NRTT)

Increase in Network Round Trip Time (NRTT)

Network Round Trip Time can be defined by the following equation:

NRTT = S_Delay + Q_Delay + R/SW_Delay + D_Delay + P_Delay

Where:

S_Delay

Serialization Delay - [(Frame size * 8)/(Access Rate)]

Q_Delay

Queue Delay - dependent on utilization and S_Delay

R/SW_Delay

Routing/Switch Delay - typically no greater than 1 ms per hop

D_Delay

Distance Delay - propagation delay due distance traveled. Typically 5ìs/km for fiber, 5.56ìs/km for copper, 3.3ìs/km satellite

P_Delay

Protocol Delay - delay added by transmission or higher level protocols

For example: CSMA/CD for shared Ethernet

Generally, increases in NRTT associated with an application are caused by an increase in any of the variables listed above. However, the typical reasons for an increase in NRTT are listed in the order they typically occur:

• Increase in Q_Delay caused by increased utilization of a circuit, thus deep network queues
• Increase in D_Delay because of carrier or enterprise fail-over to protected/redundant path that is longer in distance
• Increase in R/SW_Delay because of network errors
• Increase in S_Delay because of enterprise failover to redundant path with lower bandwidth

To determine if a network issue is limited to a single remote site, contrast and compare spikes in NRTT of the affected remote site with other sites that are comparable in terms of distance from server, bandwidth, and user count. If the NRTT increases or spikes among multiple sites at the same point in time, the issue could be carrier related or might be caused by instability in the routing protocol.