ccna question bank pdf

ccna question bank pdf.The primary function of the components is to allow users to access applications and data, share resources such as printers and network storage, and connect to other networks when necessary.Currently, Ethernet is the most commonly used Layer 2 LAN protocol for corporate networks. The predecessor to Ethernet was invented by Xerox in 1973; in the late 1970s, DEC, Intel, and Xerox came together to standardize it and call it the Ethernet DIX implementation.1 This was named after the three founding vendors.2 The DIX version specified the use of a shared medium and a data transfer rate of 10 Mbit/soThe DIX was improved in 1982; the improved version now known as Ethernet II (version 2), is the version widely used today.The Institute of Electrical and Electronics Engineers (IEEE), a professional standardization organization, has been responsible for developing new standards for Ethernet since the mid-1980s. o The first two standards developed by IEEE were 802.3 and 802.2, with the former specifying physical layer functions and some data link layer functions, and the latter specifying advanced data link layer functions. o IEEE has been continually updating these Both DIX and IEEE standards are discussed in this chapter.3.1.1 How Ethernet worksEthernet is a LAN technology that operates at the data link layer. It uses a carrier listening multiple access/conflict detection (CSMA/CD) mechanism to send information in a shared environment. Ethernet was originally developed based on the idea that many devices would be connected to the same cable. The acronym CSMA/CD depicts how Ethernet works on a shared medium.1. carrier listening and multiple accessIn a traditional hub-based Ethernet environment, multiple NICs cannot send frames at the same time, but all NICs are able to listen for information on the cable. Before the Ethernet NIC places a frame on the cable, it will listen to the cable to make sure there are no other frames in it. The NIC can do this by checking the level if it is using a copper cable, or by checking the optical frequency if it is using a fiber optic cable.The reason the NIC must listen first is that the Ethernet media supports multiple access - another NIC may be sending frames over the cable. If no frame is detected on the cable, the NIC transmits its own frame; otherwise the NIC waits for the current transmission to end before transmitting its own frame.2. Conflict detectionIf multiple devices listen to the cable at the same time and no frames are detected, they all put their own frames on the cable and thus conflict occurs. In this case, the level on the copper cable or the optical frequency on the fiber optic cable will be a mess. For example, if two NICs add the same level to the cable at the same time, the final level will be different than if only one device does so. Basically, both original frames will be unrecognizable. After placing the frame on the cable, the NIC checks the status of the cable to make sure no conflict has occurred, which is the CSMA/CD detection mechanism.If a conflict is detected, the NIC must retransmit the frame. In this case, each NIC that was transmitting the frame when the conflict occurred generates a special signal one-by-one congestion signal on the cable; and waits for a random period of time before listening to the cable again. If there are no frames on the cable, the NIC will retransmit the frames it originally sent. the NIC waits for only a few microseconds, a delay that is imperceptible. In addition, the wait time is randomized to avoid another conflict when these NICs retransmit frames.