Example e World wide web replieSonthehttpprotocol Web browser Web server Layer 5 Http Http Layer 4 TCP TCP Layer 3 IP IP aver 2IEEE802.11 IEEE 802.3 IEEE IEee 802 3 Layer 1 802.1lg 1000BASE-SX 16
16 Example • World Wide Web —Replies on the HTTP protocol Web browser HTTP TCP IP IEEE 802.11 IEEE 802.11g Web server HTTP TCP IP IEEE 802.3 IEEE 802.3 Layer 1 1000BASE-SX Layer 2 Layer 3 Layer 4 Layer 5
Benefit of layering The most challenging problem: how to provide a reliable data transfer service on top of an unreliable data network? This problem is so important that today's operating Systems all provide such reliable service. The burden of network application developers has been reduced significantly! -Hence the application developers can simply focus on the application layer issues. -We can easily develop thousands of network applications 17
17 Benefit of layering • The most challenging problem: how to provide a reliable data transfer service on top of an unreliable data network? —This problem is so important that today’s Operating Systems all provide such reliable service. • The burden of network application developers has been reduced significantly! —Hence the application developers can simply focus on the application layer issues. —We can easily develop thousands of network applications
Physical Layer The job of physical layer is to send individual bits from one node to a directly connected node Address the communications issue The physical layer also covers the physical interface between a data transmission device(e. g computer) and a transmission medium or network It is concerned with specifying characteristics of the transmission medium the nature of the signals the data rate, and related matters Examples Ethernet has many physical layer protocols: one for twisted-pair copper wire another one for coaxial cable some others for optical fiber, and so on EEE 802.11b, 802.1la, 802.11g are different physical protocols for Wireless lan, each with different transmission capabilities 18
18 Physical Layer • The job of physical layer is to send individual bits from one node to a directly connected node. — Address the communications issue • The physical layer also covers the physical interface between a data transmission device (e.g., computer) and a transmission medium or network. • It is concerned with specifying characteristics of the transmission medium, the nature of the signals, the data rate, and related matters. • Examples: — Ethernet has many physical layer protocols: one for twisted-pair copper wire, another one for coaxial cable, some others for optical fiber, and so on. — IEEE 802.11b, 802.11a, 802.11g are different physical protocols for Wireless LAN, each with different transmission capabilities