ccna 200-301 network simulator toolstation direct

ccna 200-301 network simulator toolstation direct.2.3.1 Physical Layer**1. Function of the Physical Layer (Physical Layer) The primary function of the Physical Layer is to accomplish the transfer of raw bit streams between adjacent nodes and to control how data is placed on the communication medium. Typical issues of concern for physical layer protocols are what physical signals are used to represent data "1s" and "0s"; how long the -bit lasts; whether data transmission can take place in both directions at the same time; how the initial connection how the initial connection is established and completed and how the connection is terminated after communication; how many pins are in the physical interface (plugs and sockets) andThe purpose of each pin, etc. The design of the physical layer is mainly concerned with the mechanical, electrical, functional and process characteristics of the physical layer interface, as well as the transmission medium to which the physical layer interface is connected, etc. The design of the physical layer also involves a number of issues within the field of communications engineering.2. The main network devices of the physical layer(1) RepeaterRepeater is a device that connects network lines and is often used for two-way forwarding of physical signals between two network nodes. Repeater is the simplest network interconnection device, mainly to complete the physical layer functions, responsible for the physical layer of the two nodes to pass information by bit, to complete the signal replication, adjustment and amplification functions, as a way to extend the length of the network. Due to the existence of losses, the signal power transmitted on the line will gradually decay, and the decay will cause signal distortion when it reaches a certain level, thus leading to reception errors. Repeaters are designed to solve this problem by completing the connection of the physical line and amplifying the attenuated signal to keep it the same as the original data. Normally, the repeater is connected to the same media at both ends, but some repeaters can also do the job of transferring different media. In theory the use of repeaters is unlimited and the network can therefore be extended indefinitely. In fact this is not possible, because the network standards have specific regulations on the delay range of the signal, and repeaters can only work effectively within this specified range, otherwise they will cause network failure.As mentioned earlier, the theoretical maximum transmission distance of twisted pair is 100m, if it exceeds 100m, it is difficult to ensure the correct transmission of information due to signal attenuation, so repeaters can be used to extend the transmission distance. Repeater is only applicable to Ethernet, which can interconnect two or more segments (using multiple repeaters) of Ethernet.(2) HubA hub is equivalent to a multi-port repeater, and can also shape and amplify signals and send them to all nodes. We know that in a ring network there is only one physical signal transmission channel, all through a transmission medium to transmit, so there is a conflict between the nodes compete for the channel, the transmission efficiency is low. After the introduction of the hub network equipment, each workstation is connected to the hub with its own dedicated transmission medium, there is no longer only one transmission channel between the nodes, the signal sent back by the nodes through the hub, the hub and then the signal shaping, amplification and sent to all nodes, so that at least in the uplink channel no longer appear collision phenomenon. However, the hub-based network is still a shared medium LAN, where the "shared" is actually the hub's internal bus, so there will still be signal collisions when the uplink channel and downlink channel send data at the same time. When a hub detects a collision on its internal ports, a collision-enforcement signal is transmitted to all ports connected to the hub. At this point, all data will not be sent successfully. We can illustrate this with an image of a realistic situation where there are cars coming from both directions at the same time on a single lane. We know that only one direction of traffic is usually allowed to pass on a single lane, but in small towns, where conditions are limited and there are usually no such regulations, it is quite possible to allow two directions of traffic to pass on a single lane, but only if they pass at different times. The same is true in a hub, although . Each node has its own separate channel to the hub, but there is only one common channel inside the hub, and both upstream and downstream data must be sent and received through this shared channel, so that it is possible that, like a single lane, a traffic jam may occur when both upstream and downstream channels have data to send at the same time.k 18