関連ワード:  explain network layer in osi model    what is network layer in osi model    define network layer in osi model    what is network layer in osi model with example    definition of network layer in osi model    purpose of network layer in osi model    what is the network layer in osi model responsible for    explain the role of network layer in osi model and its associated protocols    explain the function of network layer in osi model    what is function of network layer in osi model