miscellaneous questions, bandwidth and vlan

[sarahr202]

Hi every body.

1)Let say we have two host,h1 and h2  both are connected by fastethernet duplex link (100Mbps)

.

h1--------------------------h2

how do we interpret bandwidth of 100Mbps?   Do we look at bandwidth as the maximum number of bits that can be put on the medium in one second,If yes, that means that bandwidth(.100Mbps) put the upper limit on max transmission rate of frame by a host.  If a frame size is 1518 bytes,  then host1 can transmit  100 EE 6/ 1518*8=8234 (approx).

Is my understanding correct?

2)  For our discussion, a delay  includes propagation delay+ processing delay( ignoring the queues delay for simplicity)

One link I visited says there is no connection between delay and bandwidth.  I believe there might not be direct relation but depending upon the protocol in use e.g udp or tcp,  or data link protocol such as frame relay , delay will affect the bandwidth .  For example in case of frame relay,  a bit can be set to indicate congestion and that  sending node should slow its transmission rate.In case of tcp, window gets reduced which in turn determines the actual bandwidth of the network.

3)  While discussing the motivations for using vlans on switches, my book lists one of the reason as follows:

"  To reduce the workload for stp by limiting a vlan to a single access switch"

The book is implying that vlan should be limited to an access switch that is one vlan per switch.  Is it  just ideal design model?

thanks  and have a great weekend.

[speculor_cisco · Accepted solution]

Hello sarahr202.

Ideal design model is not a simple topic.

I would suggest you the text "Designing Cisco Network Service Architectures" by Hutton, Schofield and Teare.

You can find that when it is possible limiting a vlan to a single access switch, then this design is ideal for many reasons.

When it is not possible limiting a vlan to a single access switch, as in a server farm with dual attached servers, then there is a suboptimal design more

difficult to understand but well explained in the text.

But If you want really understand all these design problems, you have to know STP, RSTP, HSRP, GLBP, VRRP and routing protocols.

[speculor_cisco]

Hello sarahr202.

About the first point, you are right even if 100 Mbps is a bit rate rather then a bandwidth.

Bit rate and bandwidth are linked together but different concepts.

Have you got any math knowledge about Fourier transformation of a signal?

About the second point, the link you visited is right because it considers the bit rate of a link as how many bits the

phisical layer can put onto the wire in a second, the delay instead the time spent by the signal for the propagation in the medium or

spent in order to be processed by a switch or a router. Everyway, if the communication is experimenting a strong delay and this is a

symptom of a future congestion, then some dispositive could change the bit rate of a link in order to not miss informations but, after

the bit rate change, we consider bit rate and delay independent as in the first case.

I have the impression that you use the term bandwidth as synonymous of speed of communication.

This is the commercial and marketing use of the term but things are more complex.

I suggest you Tanenbaum's text and Kurose-Ross's text about networking.

You can find important explanations without too many mthematical details.