Category Archives: Bandwidth/Latency/TCP/UDP

Basics of Reliability, TX & RX

“The overall reliability or load of an interface at a given point in time can be measured by the txload/rxload a fractional ( 255/255 = 100% ) calculation over a default average of 5 minutes. This 5 minute time interval is the default on most if not all Cisco devices, however it can be changed or tuned if necessary. We always want to see the overall reliability at 255/255 which basically means all is good. The thing to remember with regards to txload/rxload reliability is that they both make up the same 255. For example you wouldn’t see the txload at let say 200/255 and the rxload 60/255 that would equal an overall reliability of 260.”

The total load on a given interface can be measured by a the txload/255 + rxload/255 together never exceeding 255 or 100% of the overall interface. For example lets say we had an interface that was completely saturated at 100% capacity over a given period of time. Let’s say that during this given period of time the rxload was at 124/255 or 49% of the received interface utilization. Due to the fact that the interface is currently at 100% capacity this would mean that the txload would have to be ( 255 – 124 = 131 ) 131/255 or 51% of the total transmit interface utilization.

( 255 – 124 = 131 ) 131/255 = 0.513 or roughly 51%.

Note: Keep in mind that the bandwidth command modifies only the perceived bandwidth of the interface: it has no effect on the actual speed at which packets are transmitted or received.

## Modifying default interval.
Router#configure terminal
Router(config)#interface gigabitethernet0/0
Router(config-if)#load-interval 30



3 major network performance indicators / Base for network troubleshooting:
– Latency is the time required to vehiculate a packet across a network.
Latency may be measured in many different ways: round trip, one way, etc…
Latency may be impacted by any element in the chain which is used to vehiculate data: workstation, WAN links, routers, local area network, server… and ultimately it may be limited, for large networks, by the speed of light.

– Throughput is defined as the quantity of data being sent/received by unit of time.

– Packet loss reflects the number of packets lost per 100 of packets sent by a host.