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LTE QoS (Part 2) - LTE QoS Parameters (QCI, ARP, GBR, MBR and AMBR)
October 15, 2013 | By Dr. Michelle M. Do (tech@netmanias.com)
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42

We will look a little bit further into LTE QoS that we discussed last time, and learn what QoS parameters are for.  

 

 

There are two types of EPS bearers: default and dedicated. In the LTE network, the EPS bearer QoS is controlled using the following LTE QoS parameters:
 
  ▶ Resource Type: GBR or Non-GBR
  ▶ QoS Parameters

  • QCI
  • ARP
  • GBR
  • MBR
  • APN-AMBR
  • UE-AMBR

Every EPS bearer must have QI and ARP defined. The QCI is particularly important because it serves as reference in determining QoS level for each EPS bearer. In case of bandwidth (bit rate), GBR and MBR are defined only in GBR type EPS bearers, whereas AMBR (APN-AMBR and UE-AMBR) is defined only in Non-GBR type EPS bearers. 
 
Below, we will explain the LTE QoS parameters one by one.

 

Resource Type = GBR (Guaranteed Bit Rate)


For an EPS bearer, having a GBR resource type means the bandwidth of the bearer is guaranteed. Obviously, a GBR type EPS bearer has a "guaranteed bit rate" associated (GBR will be further explained below) as one of its QoS parameters. Only a dedicated EPS bearer can be a GBR type bearer and no default EPS bearer can be GBR type. The QCI of a GBR type EPS bearer can range from 1 to 4.

 

Resource Type = Non-GBR


For an EPS bearer, having a non-GBR resource type means that the bearer is a best effort type bearer and its bandwidth is not guaranteed. A default EPS bearer is always a Non-GBR bearer, whereas a dedicated EPS bearer can be either GBR or non-GBR. The QCI of a non-GBR type EPS bearer can range from 5 to 9.

 

QCI (QoS Class Identifier)


QCI, in an integer from 1 to 9, indicates nine different QoS performance characteristics of each IP packet. QCI values are standardized to reference specific QoS characteristics, and each QCI contains standardized performance characteristics (values), such as resource type (GBR or non-GBR), priority (1~9), Packet Delay Budget (allowed packet delay shown in values ranging from 50 ms to 300 ms), Packet Error Loss Rate (allowed packet loss shown in values from 10-2 to 10-6. For more specific values, search on Google for "3GPP TS 23.203" and see Table 6.1.7 in the document. For example, QCI 1 and 9 are defined as follows:
 
QCI = 1
: Resource Type = GBR, Priority = 2, Packet Delay Budget = 100ms, Packet Error Loss Rate = 10-2 , Example Service = Voice
QCI = 9
: Resource Type = Non-GBR, Priority = 9, Packet Delay Budget = 300ms, Packet Error Loss Rate = 10-6, Example Service = Internet
 
QoS to be guaranteed for an EPS bearer or SDF varies depending on the QCI values specified.
QCI, though a single integer, represents node-specific parameters that give the details of how an LTE node handles packet forwarding (e.g. scheduling weights, admission thresholds, queue thresholds, link layer protocol configuration, etc). Network operators have their LTE nodes pre-configured to handle packet forwarding according to the QCI value.
 
By pre-defining the performance characteristics of each QCI value and having them standardized, the network operators can ensure the same minimum level QoS required by the LTE standards is provided to different services/applications used in an LTE network consisting of various nodes from multi-vendors.    
 
QCI values seem to be mostly used by eNBs in controlling the priority of packets delivered over radio links. That's because practically it is not easy for S-GW or P-GW, in a wired link, to process packets and also forward them based on the QCI characteristics all at the same time (As you may know, a Cisco or Juniper router would not care about delay or error loss rate when it processes QoS of packets. It would merely decide which packet to send first through scheduling (WFQ, DWRR, SPQ, etc.) based on the priority of the packets (802.1p/DSCP/MPLS EXP)). 

 

ARP (Allocation and Retention Priority)


When a new EPS bearer is needed in an LTE network with insufficient resources, an LTE entity (e.g. P-GW, S-GW or eNB) decides, based on ARP (an integer ranging from 1 to 15, with 1 being the highest level of priority), whether to:

  • remove the existing EPS bearer and create a new one (e.g. removing an EPS bearer with low priority ARP to create one with high priority ARP); or
  • refuse to create a new one. 

So, the ARP is considered only when deciding whether to create a new EPS bearer or not. Once a new bearer is created and packets are delivered through it, the ARP does not affect the priority of the delivered packet, and thus the network node/entity forwards the packets regardless of their ARP values.
One of the most representative examples of using the ARP is an emergency VoIP call. So, an existing EPS bearer can be removed if a new one is required for a emergency 119 (911 in US, 112 in EC, etc) VoIP call. 

 

GBR (UL/DL)


This parameter is used for a GBR type bearer, and indicates the bandwidth (bit rate) to be guaranteed by the LTE network. It is not applied to a non-GBR bearer with no guaranteed bandwidth (UL is for uplink traffic and DL is for downlink traffic).

 

MBR (UL/DL)


MBR is used for a GBR type bearer, and indicates the maximum bit rate allowed in the LTE network. Any packets arriving at the bearer after the specified MBR is exceeded will be discarded.

 

APN-AMBR (UL/DL)


As you read the foregoing paragraph, you may wonder why a non-GBR type bearer does not have a "bandwidth limit"? In case of non-GBR bearers, it is the total bandwidth of all the non-GBR EPS bearers in a PDN that is limited, not the individual bandwidth of each bearer. And this restriction is controlled by APN-AMBR (UL/DL). As seen in the figure above, there are two non-GBR EPS bearers, and their maximum bandwidths are specified by the APN-AMBR (UL/DL). This parameter is applied at UE (for UL traffic only) and P-GW (for both DL and UL traffic).

 

UE-AMBR (UL/DL)


In the figure above, APN-AMBR and UE-AMBR look the same. But, please take a look at the one below.
A UE can be connected to more than one PDN (e.g. PDN 1 for Internet, PDN 2 for VoIP using IMS, etc.) and it has one unique IP address for each of its all PDN connections. Here, UE-AMBR (UL/DL) indicates the maximum bandwidth allowed for all the non-GBR EPS bearers associated to the UE no matter how many PDN connections the UE has. Other PDNs are connected through other P-GWs, this parameter is applied by eNBs only.

 

 

 

Boby 2014-08-21 15:59:14

SDF will deceide QOS and QCI,so these SDF will give PCRF at the time of provisoning. But SDF will different for INTERNET, SDF will different for SKYPE and SDF will different for IMS. SO my query is  how PCRF know this packet is came from Inetrnet,this packet is from IMS,this packet is from SKYPE(so based on this packets only SDF will decide right).

Abhi1103 2015-08-27 02:36:25

If Skype  and Internet has to have 2 different QoS, then PCEF shall get 2 different PCC rules one for each and its PCEF who has to decide  which rule has be applied, based on SDF filters configured.

SDF 1 for Skype  and SDF2 for Internet which will be configured in PCEF. SDF's are IP flows where multiple IP flows can have single SDF or single IP flow can have single SDF ,its completely operator driven.  


Tarun 2015-01-30 18:32:54

Nice and good description of QoS; Thank you very much.. i have below doubt, could you please

addrss it.

What is the difference between SDF and TFT, please give example if possible?

Joao Nuno 2015-04-16 21:55:02

Hello NetManias,

Thanks for the presentation..

 

I would like to know what the role of eNB in all this QoS process? is there any requirement from the eNB in order to keep the balance with what is pre-defined at Core level?

 

If we have a VIP User, how eNB knows that some specific QCI must be assign to that user? Are all the definitions/rules coming or set from the PCRF(PCC)?

 

BR

Joao

Peeyush 2015-05-01 00:50:49

Hi Tarun,

 

As per my understanding TFT for a bearer is one. This term is basically used on the S5/S8 interface.

It can contain multiple SDF (Service Data Flow) which are realted to a particular service.

 

A single bearer can have multiple SDF which are mapped to different service. The packet filters which we send in a PCC rules are usually considered as SDF. Term SDF is usually used on the Gx interaface,

 

I hope it helps.

 

Regards,

Peeyush

Gary Casagrande 2015-10-08 01:30:43

Hope someone can help. I am trying to understand what levers QCI manipulates to impact latency, packet loss, etc. Is it ARP? Secondary question. Why is QCI 6 better for video than QCI 7 (or the opposite). This goes to the base of the question... what are the levers that QCI is manipulating for the different levels of QCI. Thank you.

jamee dade 2016-06-08 09:26:55

Excellent comments ! I was fascinated by the specifics - Does someone know if my company could access a template DS-11 form to type on ?

CHARISSE LIPTON 2016-06-10 07:38:32

Greetings Jamee! my assistant saw a blank DS-11 form at this site http://pdf.ac/5gMlzi

nidhishankaryadav@gmail.com 2016-10-19 15:44:11

I would like to know what the role of eNB in all this QoS process? is there any requirement from the eNB in order to keep the balance with what is pre-defined at Core level?

 

If we have a VIP User, how eNB knows that some specific QCI must be assign to that user? Are all the definitions/rules coming or set from the PCRF(PCC)?

berseek 2016-11-18 15:55:20

Hello

 

 if GBR/MBR qos paramter of the specific flow (data flow)  are set to GBR bearer.  so that tuple of Bandwidth is below like

 MBR> bandwidth of the specific flow > GBR ,  am I right?  

 

 

Raj 2016-11-30 20:39:32

Thank you for such great information.....

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