Learning content.
Chapter 4 Local Area Networks and Metro Networks.
It mainly explains the related technologies of LAN and metro network, including IEEE protocol on LAN, working mechanism of LAN CSMA CD protocol, high-speed Ethernet and VLAN basic content. There is also a technical brief on metro networks.
There are 5 knowledge modules in this chapter, with a total of 24 knowledge points.
4.1 Introduction to LAN Technology.
4.2 Logical link control sub-layer.
4.3 ieee802.3 standards.
4.4 LAN interconnection.
4.5 Metro.
Today's learning content.
4.1 Introduction to LAN Technology.
4.2 Logical link control sub-layer.
4.3 ieee802.3 standards.
Past past papers. 1.The CSMA CD protocol is a ( ) protocol.
a.Physical layer
b.Media access layer
c.Logical link sublayer
d.Network layer.
Answer: b
Analysis: CSMA CD protocol corresponds to 8023. Media access control sub-layer.
2.The Ethernet protocol can use three monitoring algorithms: non-persistent, persistent, and p-persistent. In the following description of these 3 algorithms, the correct one is ( ).
a.Persistent listening algorithms have a low probability of collision, but may introduce excessive channel delay.
b.The non-persistent listening algorithm has a low probability of collision, but it may waste channel bandwidth.
c.The pPersistence monitoring algorithm is simple to implement and provides the best performance.
d.The non-persistent listening algorithm can preempt the channel in time and reduce the transmission delay
Answer] B Learning Summary:
There are three types of Ethernet listening algorithms:
Non-persistent listening algorithm: If the channel is busy, the system gives up the listener and backs for a random period of time before trying to retransmit it. This approach has a low probability of re-collision, but can introduce excessive channel delay and waste the channel's bandwidth.
Persistent listening algorithm: If the channel is busy, the system continues to listen until the channel is free and can be sent. This approach has a high probability of conflict, but can reduce sending delays.
pPersistent listening algorithm: If the channel is busy, the system will continue to listen with probability p, or give up the listening with probability 1-p, back a random period of time, and then try to retransmit. This method has the advantages of the above two methods, but the algorithm is complex, and the size of the p-value has a great impact on the performance of the network.
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