Link Layer Switching questions. What is the difference between a hub and a switc

Question

Link Layer Switching questions. What is the difference between a hub and a switch? Hub is used to connect segments of a LAN. Switch forwards packets a. List at least two functions of a link layer switch. b. Why are switches said to be "self learning? What are bridges and how do they know whether to forward frames? At what layer in the Internet Architecture do they operate? What are some of the advantages of a switch over broadcast links such as busses or hub-based star topologies? Compare and contrast a router and a switch. c. d. e.

Explanation / Answer

(a) Data link layer is the second layer in OSI reference model from below.
functions of link layer are :
1. Framing :
One of the most important funciton of link layer is framing the data. Frames are the streams
of bits received from the network layer into manageable data units.
2. Physical Addressing :
Data link layer provides physical address to the streams. It adds a header to the frame to
define physical address of the sender or the receiver of the frame, if the frames have to
be distributed to different systems on the network.
3. Flow control :
A flow control technique is used to prevents traffic jam at the receiver side. This control
mechanism is used to avoid a fast transmitter from running a slow receiver by buffering the
extra bit is provided by flow control.

(b) Switches are called "self learning" because it learns which hosts can be reached through
which interfaces when there is a records of sender/location pair in switch table or when a
frame is received, the switch "learns" the location of the sender.

(c) Bridges operates in data link layer(below network layer) in internet architecture.
Bridges is a device which is used to connect two seperate ethernet networks into one extended
network.It only forward packets between networks that are destined for the other network.
Bridges build a list of MAC addresses on either side of the bridge. Therefor it knows which packets
should be forwarded to the other side and which should not be.

d) Advantages of switch over broadcast links :
Broadcast links is a transmission technology. A broadcast links is shared by all the machines in the network.
In broadcast networks the packet is sent by any machine and recevied by all other machine.
Switch works in a physical star topology but it works as a logical bus on an ethernet networks. It increases
available network bandwidth on individual computer.

(e) Comparison between router and switch :
1. Router directs data in a network, it passes data between home computers and between computers and
modem whereas a switch allows to connect multiple device and port that can be managed.
2. Routers operates in network layer in the OSI model and switch operates at data link layer of the OSI model.
3. Routers transmits data in the form of packet. Switch transmits the data in ther form of frame(L2 switch) and
in ther form of packet(L3 switch).
4. Routers are used in LAN and WAN whereas switch is used in LAN.

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