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Eboook Computer networking - A top down approach (6th edition): Part 2

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(BQ) Part 2 book "Computer networking - A top down approach" has contents: The link layer links, access networks, and LANs; wireless and mobile networks, multimedia networking, security in computer networks, network management. | CHAPTER 5 The Link Layer: Links, Access Networks, and LANs In the previous chapter, we learned that the network layer provides a communication service between any two network hosts. Between the two hosts, datagrams travel over a series of communication links, some wired and some wireless, starting at the source host, passing through a series of packet switches (switches and routers) and ending at the destination host. As we continue down the protocol stack, from the network layer to the link layer, we naturally wonder how packets are sent across the individual links that make up the end-to-end communication path. How are the network-layer datagrams encapsulated in the link-layer frames for transmission over a single link? Are different link-layer protocols used in the different links along the communication path? How are transmission conflicts in broadcast links resolved? Is there addressing at the link layer and, if so, how does the link-layer addressing operate with the network-layer addressing we learned about in Chapter 4? And what exactly is the difference between a switch and a router? We’ll answer these and other important questions in this chapter. In discussing the link layer, we’ll see that there are two fundamentally different types of link-layer channels. The first type are broadcast channels, which connect multiple hosts in wireless LANs, satellite networks, and hybrid fiber-coaxial cable (HFC) 433 434 CHAPTER 5 • THE LINK LAYER: LINKS, ACCESS NETWORKS, AND LANS access networks. Since many hosts are connected to the same broadcast communication channel, a so-called medium access protocol is needed to coordinate frame transmission. In some cases, a central controller may be used to coordinate transmissions; in other cases, the hosts themselves coordinate transmissions. The second type of link-layer channel is the point-to-point communication link, such as that often found between two routers connected by a long-distance link, or between a .