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LTE QoS: SDF and EPS Bearer QoS
September 11, 2013 | By Netmanias (tech@netmanias.com)
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Page 2 of 6

 

     

Table of Contents  

1. Introduction
2. SDF and EPS Bearer
3. QoS Parameters of SDF and EPS Bearer

4. QoS Provisioning and Enforcement

5. An Example for SDF and EPS Bearer QoS

6. Closing  

 

 

2. SDF and EPS Bearer

 

Figure 1 illustrates SDFs and EPS bearers, and their relationship. In an LTE network, user traffic (IP flows or IP packets) is classified into SDF traffic (hereinafter referred to as “SDF”) and EPS bearer traffic (hereinafter referred to as “EPS bearer”). An SDF refers to a group of IP flows associated with a service that a user is using, while an EPS bearer refers to IP flows of aggregated SDFs that have the same QoS class.

 

Figure 1. SDFs and EPS Bearers

 

The SDF and EPS bearer are detected by matching the IP flows against the packet filters (SDF templates for SDFs or traffic flow templates (TFTs) for EPS bearers). These packet filters are pre-configured by network operators in accordance with their policy, and each of them typically consists of 5-tuple (Source IP address, Destination IP address, Source port number, Destination port number, and Protocol ID).

In other words, in the LTE network, IP flows with the same service characteristics that match the packet filters of a SDF template are designated a SDF. SDFs that match the packet filters of a TFT are mapped to an EPS bearer, to be finally delivered to a UE. SDFs with the same QoS class are delivered, as aggregated, through an EPS bearer, whereas ones with different QoS class are delivered through different EPS bearers. 

 

SDF    

User traffic using different services (or applications) has different QoS class. A SDF is an IP flow or an aggregation of IP flows of user traffic classified by the type of the service in use. Different SDFs have different QoS class and hence an SDF serves as a unit by which QoS rules1 are applied in accordance with Policy and Charging (PCC) procedure in the LTE network (See “LTE PCC” technical document for detailed PCC procedure). In Figure 1, IP flows heading to a UE are classified into different SDFs according to their service type by using the SDF template. Then, appropriate QoS policies (e.g. priority, bandwidth control, etc.) are applied to these SDFs before they are delivered to the UE. As QoS is provided by EPS bearers when the SDFs are delivered over the LTE network, each SDF is mapped by the P-GW to an EPS bearer that satisfies its QoS requirement, and then delivered to the UE.

 

EPS Bearer

There are two types of EPS bearers: default and dedicated (See [1]). When a UE attaches to the LTE network, an IP address to be used in a PDN (Packet Data Network) is assigned, connecting to a PDN2, and a default EPS bearer is established all at the same time. When a user who has been using a service through a default bearer (e.g. Internet) attempts to use a service which requires higher QoS that the current default bearer cannot provide (e.g. VoD), a dedicated bearer is established on demand3. Thus, the dedicated bearer is established with QoS different from the one already sent in the existing bearer. A UE can be connected to more than one PDN, which has one mandatory default EPS bearer and none to many optional EPS bearers. The number of EPS bearers a UE can have cannot exceed 11 (See [1]). 

   

Once the default bearer is established at the initial attach of a UE to the network, the establishment lasts even while no service is being used and until the UE detaches from the network. The default bearer is established one per each PDN. When a UE initially attaches to the network, the network (MME) needs information about how to establish a default bearer, such as which QoS to use and to which PDN to connect. This information is already provisioned to an HSS as subscription information. So, the MME can simply download the subscription information (default APN, EPS subscribed QoS profile, etc.), select a P-GW to connect a PDN from based on the APN, and activate a default bearer associated to the PDN based on the subscribed QoS profile.

 

SDFs and EPS Bearers in Figure 1

Figure 1 shows EPS bearers and SDFs when downlink IP flows are delivered to a UE through EPS. The IP flows arriving at a P-GW through a PDN are filtered to SDFs by using SDF templates (kind of packet filters). In the figure, IP flows 1, 2 and 3 are filtered to SDFs 1, 2 and 3, respectively while IP flows 4 and 5 are filtered to SDF 4. Different QoS policies are applied to each SDF and then the SDFs are mapped to EPS bearers as classified by using Traffic Flow Template (TFT). SDFs 1 and 2 are mapped to the default bearer and SDFs 3 and 4 are mapped to the dedicated bearer, all destined to the UE. Upon arrival at the UE, the IP flows are all sent to their destination applications.

 

Terms relating to EPS bearers and SDFs shown in Figure 1 are listed in Table 1. Out of the IP Connectivity Access Networks (IP-CANs) covered in 3GPP standards, this document discusses EPS only. So, all IP-CANs are referred to as EPS herein (e.g. IP-CAN Bearer = EPS Bearer).

 

Table 1. Terms relating to SDFs and EPS Bearers

 

 

Page 2 of 6
Vassilios Stefanidis 2014-04-14 20:19:19
Hello,

I noticed a misspelling in chapter EPS Bearer QoS Parameters at p.6 of the PDF document: in the first paragraph (near the end) the MRB should be MBR.

BR
Vassilis
Netmanias 2014-04-15 17:09:13
The typo was modified. Thank you for your kind noticing.
kimfeng 2014-04-25 21:01:56
A default bearer must be non-GBR while a dedicated bearer can be either GBR or non-GBR. So, in what kind of condition, a dedicated bearer will be allocated for non-GBR service?
Netmanias 2014-04-27 12:34:08
Hi kimfeng,

3GPP defines service characteristics in terms of priority packet delay budget and packet error loss rate.
Then according to the characteristics, it maps standardized QCI values to standardized characteristics and classifies GBR type and non-GBR type services. (please see Table 6.1.7 of 3GPP TS 23.203)

Though assigning a QCI to a service depends on operators' policy, QCI 9 is typically used as a default bearer and QCIs from 5 to 8 are used as a non-GBR type dedicated bearer.
For example, a dedicated bearer with a QCI value of 5 is used for IMS signaling when operators provide VoLTE services.
vh.valluru 2018-04-07 20:46:26

QCI is 5 for IMS signaling and is default bearer with unique ip adrs .. but here dedicated bearer is mentioned?? pls correct me if iam wrong.

ramakrishna 2014-05-02 00:00:19
Good presentation thanks
sharmapeeyush840 2014-06-06 14:00:34

Hi,

 

I have a doubt about QoS per SDF. I tried reading 23.203 as mentioned in your reference. However I could not find any information which says there should be a specific MBR value associated with a SDF in case of Non-GBR SDF.  If possible kindly guide me to a particular section from where I can draw this conclusion. 

 

Regards,

Peeyush Sharma

Netmanias 2014-06-17 07:33:09

Hi Peeyush,

 

A PCC rule defines the policy control information for a service data flow.
Table 6.3 lists PCC rule information (Rule ID, SDF detection, Charging, Policy control, ..). UL/DL-maximum bitrate and UL/DL-guaranteed bitrate are being defined as (part of) Policy control information. For non-GBR SDFs, UL/DL MBR is conditional, but can be used for rate policing. 

Thank you. (and sorry for late reply due to business trip..)
 

Vimal Tewari 2014-06-23 00:58:55

First of all Thankyou for such wonderful presentations.

Based on what is written in this document and in the relevant 3GPP specifications, I have developed an understanding why a distinction needs to be maintained between EPS Bearer Flow and SDF. The 3GPP specifications define EPS Bearer as "An EPS bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PDN GW ". All the LTE/EPC nodes work with an EPS Bearer and one EPS Bearer can have multiple services mapped to it. A guideline for mapping the different services to different QoS classes is also provided by the specifications. However the specifications do not talk about the bit rate values for individual services and assignment of bit rate is left to the individual operators. In the absence of SDF, this notion of working only with EPS bearer can lead to 2 problems:

  1. The different nodes (UE, eNB, SGW) map user traffic to EPS Bearer and accordingly enforce the QoS rules. However these nodes do not have any understanding of the individual services that this user traffic belongs to. Two services (e.g. email and ftp) might have the same QCI characteristics but their QoS requirements can be different (they may differ in their bit rate requirement). The QCI being same, these services will be mapped to same bearer and the different nodes will enforce the combined bit rate (Bitrate (email) + Bitrate (ftp)) on this EPS Bearer. It may happen that the combined bit rate for the EPS Bearer will be achieved but individual services end up not getting the correct bit rate.
  2. The second and more critical reason is related to billing. Two services might have same QCI characteristics and even same QoS requirements, but the operator may decide to charge the two services differently. This cannot be achieved if we cannot distinguish between the different services within an EPS Bearer.

Having the notion of SDF can effectively address both the above problems. If PGW can segregate the IP flows into different Service Data Flows, it can

  1. Enforce the correct data rate on that particular SDF. So any error in achieving the correct bit rate at other nodes can be corrected at PGW.
  2. The PGW can now apply correct billing policy on the SDF and charge accordingly.

Request you to kindly confirm if this understanding is correct.

Netmanias 2014-07-16 13:03:56

Hello Vimal,

 

Thanks for sharing your understanding! We are in agreement with your comments.

Peeyoosh 2014-10-03 18:12:11

Thanks NetManias for sharing such a nice information and thanks Vimal for sharing detailed understanding, it helped me to understand the sense of SDFs.

 

Regards,

Peeyoosh S

Michael Topouzas 2014-07-01 21:08:45

Hello,

 

Very nice presentation.

Just a small typo error : Service Date Flow should be Service Data Flow 

Netmanias 2014-07-11 17:48:30

Hi Michael, 

 

We have corrected the typo. Thank you for noticing.

Shafali 2014-07-08 20:35:04

Hi,

 

Thanks for the useful information & nice presentation. Can anyone please tell the exact difference between SDF Template and TFT?

 

Thanks!!

 

Saurabh Thukral 2014-09-18 20:38:29

Please refer Table 5. Description for MBR.

It is wrongly mentioned that this QoS parameter applies for non-GBR bearers.

raghu(GESL) 2014-12-22 15:04:32

SDF(service data flow) are used to map packets  to the TFT(traffic flow template) based on 5 tuples and TFT is responsible for maping packet to the respective bearer which matches the QOS of bearer and the packet.

Is it correct?

Netmanias 2015-02-07 17:57:56

SDF template vs. TFT

 

An SDF template consists of IP packet filters, and each IP packet filter has a set of filter rules (5-tuple consisting of Source IP, Destination IP, Source Port number, Destination Port number, and Protocol ID). IP flows arriving at P-GW are identified by matching these packet filters (SDF template), one by one, and those that match the same filter rule are grouped together and classified as an SDF.

 

P-GW keeps traffic mapping information (TFT filters) that indicates which EPS bearer can support (QoS of) which SDFs, i.e. QoS the LTE network can support for UE.

 

Each SDF has a set of QoS parameters (e.g. QCI, ARP, MBR, GBR) and so does each EPS bearer (e.g. QCI, ARP, MBR, GBR, UE-AMBR, APN-AMBR). An EPS bearer has the same variety of QoS parameters that mapped SDF(s) have, except it has access system-dependent parameters as well. 
SDFs (or SDF aggregate) with the same QCI and ARP can be delivered through the same EPS bearer. If an SDF cannot be served at any of the currently available EPS bearers (e.g. if a new SDF, SDF 5 (GBR=500Kbps), arrives when SDF 3 (GBR=1Mbps) and SDF 4 (GBR=1Mbps) have already been delivered through EPS bearer 5 (GBR=2Mbps)), another EPS bearer can be created to serve the new SDF.

 

Sameer Gagneja 2015-05-28 22:16:36

Hi,

1>Please explain a bit on Protocol ID in SDF Template.

2>During downlink:how come PGW differentiate whether traffic is voice data (RTP), video streaming, voice signaling (SIP), two-way game, and Internet traffic. 

3>Like max number of EPS bearer for one UE can be 11 because of EBI bit value of 4.My question is where in your website i can have understanding of other bit values and there relative constraints.

James 2015-06-26 14:37:55

1. Protocol ID: In the IPv4 there is a field called "Protocol" to identify the next level protocol.  This is an 8 bit field (Protocol ID = 6 for TCP and 17 for UDP). In IPv6, this field is called the "Next Header" field.

 

2. PGW differentiates traffic type based on SDF filters (5-tuple based packet classification rule) and these fileters are part of PCC rule. PCC rule (SDF filters) can be provisoned by PCRF (dynamic PCC) or pre-configured on PGW (predefined PCC). Note that SDF filters are unidirectional, so detection is applied independently for downlink and uplink direction.

Probably,

- SDF filters for voice data (RTP) are provisioned by PCRF (IMS core -> PCRF -> PGW) whenever voice bearer (dedecated bearer) are established

- SDF filters for voice signalling (SIP) are predefined in PGW (TCP/UDP port = 5060 which means SIP)

- If it is not able to detect video streaming/two-way game traffic based on 5-tuple, DPI (Deep Packet Insepction) feature should be used (DPI supported PGW or external DPI box)

 

3. I cannot find any EBI value greater than 11 in this document.

Akash 2015-06-21 17:16:16

Hi ,


First of all Thank you for this wonderful presentation.


I have just 1 query,


In your example (5.1 QoS Operation in Downlink), you have written that when IP packets comes at PGW , for GBR SDF , PGW apply MBR DL policing .


My question is why not GBR DL policing ?


Thanks,

Akash


Amrendra 2015-07-14 20:09:45

Hi Netmanias,

 

Thanks a lot for wonderful explanation.

However there is one request while downloading it in pdf format, please include option to download comments too as they also contain sometimes valuable knowledge.

 

Thanks,

Amrendra

Sathish Kumar R 2015-09-10 23:19:16

Hi All,

 I am not able to understand how the SDF aggregation happens and how the sdf's mapping to EPS bearer ? My understanding in SDF aggregation is, For eg - 5.1 QoS Operation in Downlink

in that image SDF 1 and SDF 2 are GBR mapped to dedicated bearer, IS this called SDF aggregation or IP packet SDF 3 and SDF 3 marked in the image are going to SDF 3 this called SDF aggregation ? 


Thanks,
Sathish 

Sabyasachi Samal 2015-12-10 18:12:39

Hi,

Is there any document specifing the UE AMBR QOS values discussed for video calling during VoLTE?

 

Regards,

Sabyasachi

Sowmya 2016-05-16 15:11:44

For the downlink icmp packet, the icmp packet contains only the source address, destination address and protocol ID. But durinf SDF template filtering how the source port and destination port were mapped ? Please expain me in details.

vplazam 2016-06-24 12:14:25

Great document, this helps me to catch the idea that EPC/PGW is able to stablish dedicated EPS Bearer without using PCRF in the service set up. I thought before that PCRF is needed for stablishing dedicated bearer on this kind of scenarios. Many thanks

Netmanias 2016-06-27 16:04:19

We are glad you found it helpful. Stay tuned for more!

anandroni 2016-09-12 16:22:58

Hi,

 

Is the commeny by vplazam is correct ?.....we can understand atleast during Initial attach defualt bearer is setted up based on QOS parameters set by HSS....but how come a dedicated bearer can be setted up by PGW alone without PCRF ? .......For Dynamic PCC rules in the case of realm time traffic we need a PCRF provisioning PCC rules for different service data flows

 

Atleast i can guess a NON GBR dedicated bearer can be setted up without PCRF

 

please explain if i'm wrong.....

 

Best Regards

Anand R

 

Gaurav Gupta 2016-12-20 22:18:24

Hello There  

 

I had following query - What is the DL/UL Bearer mapping in EPC Network across below interface ( where it is 1:1 and where There is Only one bearer needed for UL and DL Traffic Both )  

a- UE<->eNodeB<->SGW<->PGW<->PDN 

b -How many maximum number of bearers that gets configured in EPC network for a UE in operator network .  Standards says 11 But at certain places I see at max - 3 bearer can be configured per UE ( 1 default + 2 dedicated bearer ) 

 

c- what is the service to UL/DL to bearer mapping at each Interface on   - 

 UE<->eNodeB<->SGW<->PGW<->PDN 

mostafa 2017-09-23 22:19:12

what about the reverse direction?

does the eNodeB apply TFT to the incoming IP flows from UE and genereate diffrent SDFs ,then aggregate simillar SDFs to EPS bearers?

thank you for clarification

Sebastiano Rametta 2018-04-18 22:25:35

Hello,

first of all my thanks for the wonderful pictures, explaining better than any text.

 

I suppose there is a typo error, in par EPS Bearer QoS Provisioning mentioning PDRF; supposed to be PCRF.

Thx

monisha patro 2018-09-09 11:38:32

Hi Netmanias,
In Table 5: EPS Bearer QoS Enforcement, MBR enforcements is applied for GBR Bearers only. 
So, I suppose it should be as below :

UL: Applied to only GBR bearers by UE and eNB
DL: Applied to only GBR bearers by S-GW and P-GW.
But in the above document I see it is mentioned that UL and DL should be applied to non-GBR bearers.
Correct me if i am wrong.

 

Thank you.

Sardar Sajid 2018-09-18 15:33:25

Wonderful ...

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