GATE CSE 2019 | Question: 49

Question

Consider that $15$ machines need to be connected in a LAN using $8$-port Ethernet switches. Assume that these switches do not have any separate uplink ports. The minimum number of switches needed is ______

Comments

What is meant by :-

 “switches do not have any separate uplink ports” ?

Edit: Found the answer to the question:-

When a device, such as a switch, is said to not have any separate uplink ports, it means that it does not have any ports that are specifically designated for connecting to other devices, such as routers. Instead, all of the ports on the device can be used to connect to other devices or devices can be daisy chained together using one of the device's ports.

 In networking, an uplink port is a port that is used to connect one device to another device at a higher level in the network hierarchy. For example, an uplink port on a switch might be used to connect the switch to a router, while an uplink port on a router might be used to connect the router to a broadband modem. Uplink ports are typically used to expand the capabilities of a network by adding additional devices or to connect a network to the internet.

Ref: Networking ALL-IN-ONE 7th Edition by Doug Lowe, Uplink Port vs Normal Port on Network Switch

---

GREAT EXPLAINATION THANKS ALOT @Abhrajyoti00 FOR CLEAR THE QUESTION.

---

@Abhrajyoti00 Just looking Like Waw…..

Answer 1

Answer is $3.$ 

Using $3$ switches we can connect maximum $20$ machines together.

∴ We require at least $3$ switches to connect $15$ machines.

Comments

@ankitgupta.1729

Ankit Bhai tell me something about this question?

I am  not able to get it.

---

@Tuhin Dutta

I have read that part from the Furouzon and it has nothing to do with this topic according to me.

Why do you think the question is related to that in any way?

 

---

We can further extend it,

With $n$ such switches, we can connect $6n+2$ machines.

In other words, for $m$ machines, we will need $\lceil\frac{m-2}{6}\rceil$ such switches.

Answer 2

There are 15 devices. And there are 8 ports in 1 Ethernet switch. So it's obvious that one switch is not sufficient. So one more switch is required. So in 1st switch only 7 ports are connected to 7 devices and 8th one is used for connecting to another switch. Now come to second switch. Only 7 ports are left as 1st port is used for connecting to 1st switch. Those 7 ports can be connected to 7 devices. But there are total 15 devices and so 1 would be left. So we need another switch. So now, in second switch we connect 6 devices to 6 ports and last port to third switch. And in the last switch 1st port is connected to 2nd switch and two ports to two left devices.So we require 3 switches in total.

Comments

Finally, I understood from this answer.

Thanks.

---

Great explanation. Thank you.

Answer 3

Given :- A switch with $8$ ports and we require to connect $15$ machines together.

Using $1$ switch we can connect only $8$ machines together.

 

Using $2$ switches we can connect only $14$ machines together.

 

Using $3$ switches we can connect $20$ machines together.

 

$\therefore$ We require atleast $3$ switches to connect $15$ machines together.

Comments

@jeet even i have problem with this topic..

correct me if i am wrong here:

Here it is given in the question that 15 computers need to be connected.. we can connect all 15 computers as shown in fig.a.

But we need to connect as shown in the figure.b attaining the same functionality as shown in figure a.

It is given that switch has 8 ports and it is given that there are no uplink ports. So all 8 ports can be used for connecting other devices.

we can connect  8 devices to a single switch .In that way ,we can connect 15 computers with 2 switches. but these 2 switches need to be connected so that all the devices are connected.

So we have to dedicate 1 port to connect with other switch..

Now you can refer satbir's answer.

---

Yeah I understood this basically, it is like this way:

M1

M2

M3

M4

M5

M6

M7

$\color{Red}{\mathbf{Ethernet-port1- out}}$

 

$\color{red}{\mathbf{Ethernet-port1- In}}$

M8

M9

M10

M11

M12

M13

$\color{red}{\mathbf{Ethernet-port2- out}}$

 

$\color{red}{\mathbf{Ethernet-port2- In}}$

M14

M15

M16

M17

M18

M19

M20

 

---

@chirudeepnamini

Thanks.

Answer 4

$\frac{15}{7}=2.1$

So, Answer is $3$

Comments

is this question for 1 mark or 2 marks?

---

2 marks