ccna protocols pdf

ccna protocols pdf.BroadcastA broadcast is a data link layer frame sent to each network device in the current network segment. An example broadcast is shown at the bottom of Figure 2.4. In this example, PC-A sets the destination address field of the data link layer frame to a broadcast address. all bits of the MAC broadcast address are 1, so its hexadecimal representation is FF:FF:FF:FF:FF:FF. next, PC-A places the frame on the cable. Notice that in this example, PC.B, PC.C and PC.D receive this frame and process it.Broadcast is used in two main situations. First, when information needs to be sent to all devices, broadcasting is more efficient than unicasting. If unicast is used, a frame must be created for each device in the network segment; with broadcast, only one frame is created. Second, broadcasts are used to discover the unicast address of a device. For example, when you boot up a PC, it does not know the MAC address of any devices in the network. To learn the MAC addresses of these devices, broadcasts can be used, since they all process broadcast frames. In TCP/IP, the Address Resolution Protocol (ARP) uses this method to learn the MAC addresses of other devices; ARP is discussed in Chapter 5. Other protocols that use broadcasts include Dynamic Host Configuration Protocol (DHCP) and NetBIOS oCommon Layer 2 troubleshooting tools include ARP (discussed in Chapter 5), Cisco Discovery Protocol (CDP, discussed in Chapter 16), switch port address tables (discussed in Chapters 4 and 11), and protocol analyzers (out of the scope of this book).2.2.7 Layer 1: Physical LayerLayer 1 (the lowest layer) of the osi reference model is the physical layer. The physical layer is responsible for the physical mechanisms of network connectivity, including :. The types of interfaces used by network devices .. . the type of cable used to connect the devices; . The connectors that terminate the cables; . The pin layout of the cable; . Signal encoding of messages, i.e., conversion of binary bits to a physical representation based on the type of medium, such as electrical signals in copper cables,optical signals in optical fiber or radio waves in wireless communications. The interface (often called the NIC) can be a plug-in card that plugs into a computer, female 0lOBaseT Ethernet NIC, or a fixed interface on a router, such as the Gigabit Ethernet port on a Cisco 1921 router.The physical layer also defines how to convert between binary information and physical layer signals. For example, when using copper cable as a transmission medium, the physical layer defines how the binary numbers 1 and 0 are converted to electrical signals using different levels, while when using fiber optic cable as a transmission medium, the physical layer defines how light emitting diodes or laser emitters use different optical frequencies to represent 1 and 0 binary will be discussed in Chapter 6.