This chapter introduces the general functions of the Data Link layer and the protocols associated with it.
Media is the physical copper cable, optical fiber, or atmosphere through which the signals travel. A physical network is different from a logical network.
Two fundamental concepts in networking are the difference between the logical and the physical network.
At each hop along the path, an intermediary device accepts the frames (encapsulated packet) from a medium, decapsulates the frame, and then forwards the packets in a new frame appropriate to the medium of that segment of the physical network.
Each frame type has three basic parts: header, data and trailer.
The Data Link layer is often divided into two sub-layers.
Data Link layer protocols are generally not defined by Request for Comments (RFCs). Although the Internet Engineering Task Force (IETF) maintains the functional protocols and services for the TCP/IP protocol suite in the upper layers, IETF does not define the functions and operation of that model's Network Access layer.
The topology of a network is the arrangement or relationship of the network devices and the interconnections between them. Network topologies can be viewed at the physical level and the logical level.
There are benefits to using a layered model to describe network protocols and operations.
A physical point-to-point connection.
A logical point-to-point connection between two nodes may not necessarily be between two physical nodes at each end of a single physical link.
Each frame type has three basic parts: header, data and trailer.
The field names above are non-specific fields listed as examples. Different Data Link layer protocols may use different fields from those mentioned.
IPv6 features
Technology is determined by the size of the network – in terms of the number of hosts and geographic scope – and the services provided by the network. Difference in bandwidth normally results in the use of different protocols for LANs and WANs.
The following assumptions are made for this communication. All routing tables are converged ARP tables are complete A TCP session is already established between client and server DNS lookup for the www server is already cached at the client PPP has already established a physical circuit and has established a PPP session
Consider an internetwork that requires three subnets.
Consider this example with five LANs and a WAN for a total of 6 networks.
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