Frame Relay question

I have a doubt regarding the following question :

Barney has got five sites, with routers connected to the same frame relay network. VCs have been defined between each pair of routers. Barney, wants the frame relay to be configured using point-to-point subinterfaces. What is the fewest subnets that barney could use on the frame relay network ?

according to me the no. of VCs should be 4 so 4 subnets must be used, but the correct answer is total of 10 VCs. With all of them configured on ppp subinterfaces, one VC per subnet.

can anyone tell me how is it possible ?
I am not able to understand the meaning of the word site over here. Does it mean the the number of routers with their local switches or something else.

any help would be appreciated.

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Comments

ziggy

WOW ! Kinda had me stumped on that one with an answer of "10"

I had to actually draw it out on paper with a diagram to see it.

With 5 sites all connected to each other with virtual circuits through a frame relay switch. The best way is to draw out a picture with a cloud in the center and the 5 sites surrounding it. Start drawing bidirectional paths from one site to the other thru the cloud, and you will see where you get 10 Virtual Circuits.

VC

PATH
1

1 to 2
2

1 to 3
3

1 to 4
4

1 to 5

2 to 1 (already built)
5

2 to 3
6

2 to 4
7

2 to 5

3 to 1 (already built)

3 to 2 (already built)
8

3 to 4
9

3 to 5

4 to 1 (already built)

4 to 2 (already built)

4 to 3 (already built)
10

4 to 5

I don't need to spell out the 5 to 1 and so on......as you can see everything is already connected to site no 5 with VC.

Hope this helps.....If I am wrong, I am sure someone else will help out

darkuser

5 sites

n * (n-1) /2

10 right ?

Undertow

Full mesh?

AceAll

Thank you ziggy and darkuser. I have still got a question.

I am not able to understand the meaning of the word "site" over here. Does it mean the the number of routers with their local switches or something else.

I guess it is a full mesh frame relay circuit.

ziggy

the meaning of the term "site"

I work for a telco company as a data installer. With my experience, the word site usually refers to a geographical location. Generally, a place of business with a network and a need for a WAN solution, ie frame relay.

Normally, a site will have minimum one router with one or more switches. I realize that some sites can have multiple routers. However, in this type of question, I believe that one would assume that there is one router per site.

johnnynodough

VCs have been defined between each pair of routers

Theres your indication that it is a full mesh.