Tuesday, 16 October 2012

Extended Access Barring (EAB) in Release 11 to avoid MTC overload

M2M is going to be big. With the promise of 50 Billion devices by 2020, the networks are already worried about the overloading due to signalling by millions of devices occurring at any given time. To counter this, they have been working on avoiding overloading of the network for quite some time as blogged about here.

The feature to avoid this overload is known as Extended Access Barring (EAB). For E-UTRAN, in Rel-10, a partial solution was implemented and a much better solution has been implemented in Rel-11. For GERAN a solution was implemented in Rel-10. The following presentation gives a high level overview of EAB for E-UTRAN and GERAN.



In Rel-11, a new System Information Block (SIB 14) has been added that is used specifically for EAB. Whereas in Rel-10, the UE would still send the RRCConnectionRequest, in Rel-11, the UE does not even need to do that, thereby congesting the Random Access messages.

The following is from RRC 36.331 (2012-09)
***

–                SystemInformationBlockType14

The IE SystemInformationBlockType14 contains the EAB parameters.
SystemInformationBlockType14 information element
-- ASN1START

SystemInformationBlockType14-r11 ::= SEQUENCE {
    eab-Param-r11                        CHOICE {
       eab-Common-r11                       EAB-Config-r11,
       eab-PerPLMN-List-r11                 SEQUENCE (SIZE (1..6)) OF EAB-ConfigPLMN-r11
    }                                                  OPTIONAL, -- Need OR
    lateNonCriticalExtension             OCTET STRING          OPTIONAL, -- Need OP
    ...
}

EAB-ConfigPLMN-r11 ::=               SEQUENCE {
    eab-Config-r11                   EAB-Config-r11            OPTIONAL -- Need OR
}

EAB-Config-r11 ::=               SEQUENCE {
    eab-Category-r11                 ENUMERATED {a, b, c, spare},
    eab-BarringBitmap-r11            BIT STRING (SIZE (10))
}

-- ASN1STOP

SystemInformationBlockType14 field descriptions
eab-BarringBitmap
Extended access class barring for AC 0-9. The first/ leftmost bit is for AC 0, the second bit is for AC 1, and so on.
eab-Category
Indicates the category of UEs for which EAB applies. Value a corresponds to all UEs, value b corresponds to the UEs that are neither in their HPLMN nor in a PLMN that is equivalent to it, and value c corresponds to the UEs that are neither in the PLMN listed as most preferred PLMN of the country where the UEs are roaming in the operator-defined PLMN selector list on the USIM, nor in their HPLMN nor in a PLMN that is equivalent to their HPLMN, see TS 22.011 [10].
eab-Common
The EAB parameters applicable for all PLMN(s).
eab-PerPLMN-List
The EAB parameters per PLMN, listed in the same order as the PLMN(s) occur in plmn-IdentityList in SystemInformationBlockType1.

***

Here is my attempt to explain the difference in overload control mechanism in Rel-8, Rel-10 and Rel-11. Please note that not actual message names are used.





As usual, happy to receive feedback, comments, suggestions, etc.

8 comments:

Marcin Mikuszewski said...

Hi,

1. I though that if UE is barred than it is not allowed to send RRC Connection Request. At least it was like this for UTRAN.
2. Do you have some more information about barring regarding to UTRAN? I am asking becasue recently I found some problems with domain access class barring.

Lao Miao said...

Hi, I think some information in the last diagram for REL-11 EAB is not so accurate. First the EAB is not necessarily triggered by OverloadStart from MME, the eNB itself or OAM can turn on the EAB. Secondly the "low priority" and "subjected to EAB" are two separate attributes of device, "low priority" doesn't automatically mean it's subjected to EAB. The NAS will decide if the device should be subjected to EAB per access and informs the lower layer(RRC).

Anonymous said...

Does it apply to UTRAN?

Zahid Ghadialy said...

I am not sure if there is an EAB capability in UTRAN. There was a mention that EAB needs to be done for UTRAN as well as GERAN but I have not explored further.

Suresh said...

Thanks Zahid. Your Blogs are really helpful :).

It seems that EAB is to be supported by all 3GPP Radio Access Technologies. I found this in TS 22.011 cluase 4.3.4.1. Although I didn't check how it is done in UTRAN.

Suresh said...

EAB for UTRAN is defined in 25.331

Shuaib Ahamed said...

If you have a cell barred info in SIB1, Then y do we require EAB?

permagrinado said...

EAB is needed to bar access to delay tolerant devices / M2M devices only. You would first use EAB when in congestion, and if that isn't effective in controling load, then AB. From 22.011:

4.3.4.1 General
Extended Access Barring (EAB) is a mechanism for the operator(s) to control Mobile Originating access attempts from UEs that are configured for EAB in order to prevent overload of the access network and/or the core network. In congestion situations, the operator can restrict access from UEs configured for EAB while permitting access from other UEs.