Last Updated on 2013-06-23.
You have to wait up to ~30 seconds to obtain an IP from your DHCP server – or even if you have configured a static IP, you cannot ping a host in your network for a long time after resume from standby.
Maybe your DHCP server does various checks (Ping, DNS, …) before he gives the IP to the client.
But in many cases, a network switch setting is the problem: STP (Spanning Tree Protocol). Disable it, or leave it enabled but set the Port Fast mode for all ports.