This lecture briefly describe on data link layer issues. Network hardware can be categorized into two types: Circuit-switched (telephone) and Packet-switched (Ethernet, ATM etc.). Here also explain advantages and disadvantages of Data Link Layer Issues. Disadvantages are: Circuit-switched, Packet-switched and Advantages are: after the first message, routing is faster, Messages do not arrive out of order etc. Finally explain Circuit-Switching, Datagram Packet-Switching and types of Packet-Switching.