Knowing Link Quality by RTT

In the telecommunication world, we can know link quality using RTT parameters.

Round Trip Times required for a network communication to travel from source the destination and back. RTT is used by something routing algorithms to aid in calculating optimal routes and measured in milliseconds or microseconds.



For example, we want to compare which provide that we have to choose before we make contract .

From the picture we assume one company want to choose provider A or provider B. Network Administrator configure HQ and branch with EIGRP. (No matter you use what kind of routing protocol)


HQ Configuration

interface Serial0/0/0
description .: Provider A :
bandwidth 512
ip address 192.168.10.4 255.255.255.252
frame-relay lmi-type ansi
frame-relay interface-dlci 102

interface Serial0/0/1
description .: Provider B :
bandwidth 512
ip address 192.168.11.4 255.255.255.252
frame-relay lmi-type ansi
frame-relay interface-dlci 103


Branch Configuration

interface Serial0/0/0
description .: Provider A :
bandwidth 512
ip address 192.168.12.4 255.255.255.252
frame-relay lmi-type ansi
frame-relay interface-dlci 102

interface Serial0/0/1
description .: Provider B :.
bandwidth 512
ip address 192.168.13.4 255.255.255.252
frame-relay lmi-type ansi
frame-relay interface-dlci 103


Now, we want to calculate Provider A RTT
Step 1 :

Make sure there’s no traffic through both of interface by applying delay command at HQ and Branch Interface

HQ Configuration :

interface Serial0/0/0
description .: Provider A :.
bandwidth 512
ip address 192.168.10.4 255.255.255.252
frame-relay lmi-type ansi
frame-relay interface-dlci 102
delay 100000

Branch Configuration
interface Serial0/0/0
description .: Provider A :
bandwidth 512
ip address 192.168.12.4 255.255.255.252
frame-relay lmi-type ansi
frame-relay interface-dlci 102
delay 100000


Step 2 :

Do Ping test, by command :

Ping 192.168.12.4 sou rce 192.168.10.4 size 36 repeat 100

For size : 36 – 18024 datagram size
For repeat : 1-2147483647 repeat count

And will get the result :

Success rate is 100 percent (100/100), round-trip min/avg/max = ms

You also can calculate Provider B Link quality by doing same steps.

Finally,

You can decide which the best link quality. Of course, the small time result RTT is better than big result.