Dear Mohsen,

The size of a packet is dependent on a protocol. If you are interested in finding out the size of the packet at the network layer, then you don't need to worry about the time slots. Because it is the issue of a link layer MAC protocol. Standard routing protocols define the format of a packet.

At the network layer, packet delivery ratio can simply be determine by using the following formula.

∑ Number of packet receive / ∑ Number of packet send

The size of packet depends on the application as well as the protocol. Time slot based scheduling is taken care by MAC layer and not the routing protocol. Routing protocols determine the packet structure for data as well as route maintenance. number of packets at source network layer and receiver network layer can be counted to determine packet delivery

The packet size will be dependent on the type of the WSN. Most WSN datasheets specifies the packet size, so find out the type. This will also determine the protocol to use and even the deployment context

Got it ! thank you all friends.

There's also two types of packets data packet and control packet like hallo packet 

The PHY/MAC layer will determine the frame size, for instance IEEE 802.15.4 standard  says the frame size is 127 bytes (including headers, thus the payload is less!). In WSN, fragmentation (which is done by the network layer, e.g. by 6lowpan) will increase your energy consumption, since you have tro transmit more frames per packet generated on the application layer. You should consider your application profile to determine the data packet sizes (e.g., temperature readings have a couple of bytes).

read this paper:

Conference Paper An energy efficient long hop (LH) first scheduling algorithm...