Thursday, December 9, 2010

Qos Interview Questions?

1. What is QOS and why it is required?
2. What is layer2 qos and layer3 qos?
3. What is tail drop?
4. Describe methods of QOS?
5. What is hardware QOS and Software QOS?
6. Difference between a policer and a shaper?
7. What is token bucket algorithm?
8. Where to define the markings?
9. Does QOS increase the load of the equipment?
10. What is TOS and IP DSCP?
11. what are the different classes available?
12. How to calculate the decimal value of classess?
13. What is the difference between priority and bandwidth command?
14. What is low latecy queueing?
15. what is class based weighted fair queuing?
16. What is first in first out queue (FIFO)?
17. What is fair queue?
18. If I give teh ip precendence five to data traffic, what will happen?

Other Useful Questions
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Wednesday, December 8, 2010

NodeB To RNC Communication Over MPLS Cloud

I am mulling on the current 3G network which doesn't give much room to the MPLS technology. But MPLS could be used to delivery nodeB traffic to RNC over MPLS cloud down the year. In the depicted figure, 3rd party MPLS network is used instead of single aggregator router

By adding 3rd party MPLS network or own MPLS network; providers can get the benefits of Traffic Engineering, QOS and Fast Reroute. The PWE3 again plays a vital role to deliver the services over MPLS cloud.  

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Tuesday, December 7, 2010

How nodeB communicates to RNC in 3G network?

In the previous post, a aggregator router is added to reduce the cost and the same router is also responsible for making communication possible between the nodeB and RNC side. As in the depicted diagram, ch-STM port is used towards nodeB aggregation and un Ch-STM port is used at RNC side. The reason for using un Ch-STM port at RNC side, to overbook the bandwidth. In case of ch-STM overbooking is not possible.

NodeB is allocating more than 2 E1s and to aggregate the nodeB bandwidth IMA groups are being used. The IMA group from ch-STM port is carried over PWE3 circuit towards the un Ch-STM port. By doing this we can aggregate more IMA groups towards the RNC side. This all calculation depends on the number of user and traffic. 

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Sunday, December 5, 2010

Adding Aggregator Between NodeB and RNC in 3G

In my previous post of common backhaul, I have given a high level design of for the common backhaul used by the operators to serve 3G. But with that design, RNC need to be equipped with n*E1 links to serve the nodeB. We have the following disadvantages with design:-

1. As the nodeB traffic will increase, operator need to increase the E1 ports on RNC.
2. Adding E1 ports on RNC is really an expensive solution.
3. More operations and manageability.
4. Number of more physical links.
5. TDM means end to end E1 will be blocked whether traffic runs over it or not.

To address the above mentioned issues, operators need to add an aggregator router which would serve nodeB traffic towards the RNC and vice versa. By adding an aggregator router, operators can drastically reduce the cost of the network without making much change in the network.

What operators need to know before adding an aggregator router:-
1. An aggregator must support channelize STM port towards nodeB side.
2. An aggregator must support UN-channelize STM port towards RNC side.
3. Option to create an IMA group on aggregator.
4. Must support PWE3.
5. Static routing if require dynamic routing also. 

So the new design will look like after adding an aggregator router:-

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