How to increase aruba network speed and avoid limited connection error and avoid traffic??

If it is a large network. you have to closely monitor the network traffic.

block the internet access to video streaming websites like youtube etc. 

if you have wireless access points or router make sure unauthorized mobile phone or devices are not eating your bandwidth. 

if you have DHCP try to monitor DHCP leased addresses list find out who are connected to your network.

try to block unauthorized wireless devices connecting to the network.