How does the RNC Admission Control works ? How do the ulHwAdm and dlHwAdm parameters impact new call attempts ?

Network: WCDMA

Node: CPP RNC

Service: W-RAN

High MP Load due to Admission

Hot to disable or enable RBS Hw Admission Control

How do the Utrancell::ulHwAdm and Utrancell::dlHwAdm parameters impact new call attempts ?

What type of calls are given priority; 911, handovers, speech calls etc ?

What is the implication of setting ulHwAdm and dlHwAdm parameters to 92 ? to 99 ?

What are the implications if we set dlHwAdm and ulHwAdm parameters to different values ?

What is the recommended value of setting to have minimum impact on the MP load and still allow emergency calls ?

When an RNC Module P CPU load reaches 85%, it discards new traffic requests. What happens to a emergency call in this case ?

How does the RNC Admission Control works ? How do the ulHwAdm and dlHwAdm parameters impact new call attempts ?

For more How To solutions see WRAN/CPP "How to" KCS Solutions

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See the following FIX statements :

1- How do the Utrancell::ulHwAdm and Utrancell::dlHwAdm parameters impact new call attempts ? 2- What type of calls are given priority; 911, handovers, speech calls etc. ?

3- What is the implication of setting ulHwAdm and dlHwAdm parameters to 92 ? to 99 ? 4- What are the implications if we set dlHwAdm and ulHwAdm parameters to different values ? 5- What is the recommended value of setting to have minimum impact on the MP load and still allow emergency calls ? 6- When an RNC Module P CPU load reaches 85%, it discards new traffic requests. What happens to a emergency call in this case ?

SOLUTION:

CONDITIONS:

1- How do the Utrancell::ulHwAdm and Utrancell::dlHwAdm parameters impact new call attempts?

PROCEDURE:

The Admission Control function monitors three main resource categories; Cell resources, RBS HW resources and IubLink resources. The Admission

Control function prevents congestion to occur, provides a possibility to secure mobility (handovers) and, to some extent, prioritises certain services (RABs).

The Admission Control function is called before any traffic access procedure that may increase the monitored resource usage is executed.

When a request for a new call (RRC Connection Request) is received in the RNC, the Resource Manager (RM) adds the requested resource increase to the current utilisation and makes a comparison with load and overload control limits. The requests are judged according to their ARP attributes, request class (guaranteed, non-guaranteed) and admission class (handover, non-handover). Each RM will either admit or reject the request. A reject can be either conditional or unconditional.

If the Reject is conditional, soft congestion will be triggered and the RNC will attempt to release some RBS or Iub link resources to accommodate the new request. If the Reject is unconditional, an RRC Connection Reject will be returned to the UE. This also happens if it is not possible to release resources by soft congestion actions when the request is conditional rejected.

Admission Control will be disabled in the RNC when ulHwAdm and dlHwAdm are set to 100. When it is so, the RNC will not do any of the calculations mentioned above when new RRC Connection Request are received and they will always be accepted. It will then be up to the RBS to reject or accept the request. If the RBS does have enough HW resources on UL/DL, then the RBS will send an NBAP Failure message and the RNC will reject the new request.

When Admission Control is disabled, soft congestion is never triggered in the RNC Module and it will not waste CPU cycles trying to accommodate the new request. This will help reduce the ModMP CPU load. This can help significantly when one or several sites trigger soft congestion on RNC, lead to high ModMp CPU load affecting many modules and consequently rejecting further access requests because of the high load (which will trigger more access requests, etc.).

SOLUTION:

CONDITIONS:

2- What type of calls are given priority; 911, handovers, speech calls etc?

PROCEDURE:

The Resource Manager (RM) in the Module MP that receives a request for a new call (RRC Connection Request) adds the requested resource increase to the current utilisation and makes a comparison with load and overload control limits. The requests are judged according to their ARP attributes, request class (guaranteed, non-guaranteed) and admission class (handover, non-handover) and according to their priorities. Emergency calls have the highest priority and will never be targeted by soft congestion.

Emergency calls have a higher priority than speech handovers which have higher priority than new speech calls (because RAB is already established in case of handovers). PS traffic RABs have the least priority.

SOLUTION:

CONDITIONS:

3- What is the implication of setting ulHwAdm and dlHwAdm parameters to 92 ? to 99 ?

PROCEDURE:

By setting it to 92 (%), the ModMp accept new requests up to 92% of RBS HW resources usage, any new request that will increase resource usage above 92% will trigger soft congestion.

Increasing the parameters to 99 (%) instead of 92 will only delay the trigger for soft congestion but soft congestion will eventually occur anyways and the ModMp will use the Soft Congestion algorithm to try to release resources and that can increase ModMp CPU load. Sometimes it helps to delay soft congestion on sites where the load is very high and where HW capacity is not under dimensioned.

SOLUTION:

CONDITIONS:

4- What are the implications if we set dlHwAdm and ulHwAdm parameters to different values ?

PROCEDURE:

RBS HW Monitoring can be deactivated in UL and DL independently using parameters dlHwAdm and ulHwAdm parameters. The two are independent of each other and can be set to different values. It all depends on the DL and UL HW capacity and operator's desire of when is a good time to trigger soft congestion.

SOLUTION:

CONDITIONS:

5- What is the recommended value of setting to have minimum impact on the MP load and still allow emergency calls?

PROCEDURE:

There is no recommended value that avoids using soft congestion.

By definition, soft congestion implies poor network dimensioning. It means that the customer has not allowed enough HW resources on a NodeB on Ul or DL or on its Iub link. They did not dimension RAN to support the amount of traffic that sites are getting. Soft congestion is triggered on the RNC as the RNC tries to release some of the used resources by downgrading users for example to try to accommodate as many users as possible while prioritizing emergency traffic and handovers. The best way out of this problem is for the customer to add more HW resources on the sites that have very high traffic demands.

SOLUTION:

CONDITIONS:

6- When an RNC Module P CPU load reaches 85%, it discards new traffic requests. What happens to an emergency call in this case ?

PROCEDURE:

The question is twofold :

a) Is an emergency call rejected due to high MP load?

Emergency calls are never targeted by any admission or congestion control so no matter what is the MP load, they will always be accepted. The RNC will release other resources to make sure it can handle emergency traffic.

b) How are emergency calls handled when UL/DL HW control is activated/de-activated ?

If UL/DL HW Admission is activated (dlHwAdm and ulHwAdm are different than 100), emergency call will always be allowed. The RNC will release other resources to accommodate that.

If UL/DL HW Admission is de-activated (dlHwAdm and ulHwAdm are set to 100) then all new admission requests are granted by the RNC and reject depends only on the RBS and transport function.

Case I: A user attempts to make a new emergency call, the RRC connection request will be received by the RNC, the RNC will grant admission and outcome depends on the following: If RBS has resources, the call will proceed. If RBS does not have resources, the RBS will send NBAP Failure message to the RNC and call fails.

Case II: An emergency call is already established (RAB is already established), the call will never be released because emergency calls are not targeted/filtered by any congestion/admission control functionality.

Note : There is a feature called Redirection of Emergency Calls to GSM that the customer can use whenever they want to disable UL/DL HW Admission control. So that all new RRC Connection Request calls with establishment cause "Emergency call" will be handed over to GSM. They need to guarantee that their GSM network can handle emergency calls and GSM network has localization. In some countries, the operators are forced by law to be able to determine location of emergency calls.