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Computer networks and internets (Sixth edition): Part 2

(BQ) Continued part 1, the document Computer networks and internets (Sixth edition): Part 2 has contents: Wireless networking technologies; repeaters, bridges, and switches; networking technologies past and present, datagram forwarding,. and other contents. Invite you to refer. | www.downloadslide.net 15 Wired LAN Technology Ethernet And 802.3 15.1 Introduction Chapters in this part of the text describe packet switching networking technologies. Chapter 13 presents the IEEE 802 model used in LANs and the division of layer 2 into Logical Link and MAC sublayers. The chapters also discusses the 48-bit addressing scheme that forms a significant part of the Logical Link sublayer. Chapter 13 focuses on the MAC sublayer and considers protocols for medium access. This chapter continues the discussion of Local Area Networks by focusing on wired LAN technologies. The chapter shows how concepts from previous chapters form the basis of Ethernet the wired LAN technology that has proceeded to dominate all others. 15.2 The Venerable Ethernet Recall from Chapter 14 that Ethernet is a LAN technology originally invented at Xerox PARC and later standardized by Digital Equipment Corporation Intel and Xerox. Ethernet has survived for thirty years. Although the hardware devices cabling and media used with Ethernet have changed dramatically the basic packet format and addressing scheme have remained constant. One of the most interesting aspects of Ethernet evolution concerns the way newer versions of Ethernet remain backward compatible a new version can sense an older form and automatically adapt to accommodate the older technology. 287 www.downloadslide.net 288 Wired LAN Technology Ethernet And 802.3 Chap. 15 15.3 Ethernet Frame Format The term frame refers to a layer 2 packet and the term frame format refers to the way a packet is organized including details such as the size and meaning of individual fields. The main reason that older versions of Ethernet have remained compatible with newer versions arises from the frame format which has remained constant since the DIX standard was created in the 1970s. Figure 15.1 illustrates the overall Ethernet frame format and the details of the frame header. Figure 15.1 Illustration of the Ethernet frame format and header .