Table of Contents
To use LTE services, a user must purchase an LTE device, sign up for an account with his mobile operator, and then select the service types and plan he wants. Then, to support and manage the selected services, the operator configures a subscription profile based on his subscription information. When the user uses LTE services, an EPS session is established (or modified) to each Access Point Name (APN) associated with different services selected. In the meantime, the network determines a policy on how network resources are to be allocated and how services are to be charged when an EPS session is established or modified. Then, it applies the policy to the EPS session while the session remains active. This procedure is called Policy and Charging Control (PCC), and is mainly taken care of by entities like Policy and Charging Control Function (PCRF) and Policy and Charging Enforcement Function (PCEF)1.
When an EPS session is established or modified, PCRF determines a PCC rule for each Service Data Flow (SDF) based on the operator’s policy (e.g. QoS policy, gate status, charging methods, etc.). PCEF (P-GW) detects an SDF, and applies a PCC rule that is specific to the particular SDF to the user packets in it. It also binds the SDF QoS and bearer QoS, and applies the bearer QoS to the EPS bearer(s). That is, EPS bearer contexts are set or modified at EPS entities (UE, eNB, S-GW, P-GW, and MME).
Establishment, modification and termination of an EPS session are performed in accordance with the PCC procedure. EPS session modification procedure may include establishment, modification or termination of an EPS bearer. During this procedure, EPS bearer contexts between UE and MME are processed by EPS Session Management (ESM) function in NAS layer.
This document discusses PCC rules and procedures, and is organized as follows:
Chapter 2 defines PCC rules, and describes how PCC rules are provisioned over the Gx interface for different service types.
Chapter 3 explains PCC procedures required for EPS session establishment and modification, along with ESM procedures.
Chapter 4 explores how IP packet flows are handled when policy control is applied, and
Chapter 5 summarizes information related to policy control held by EPS entities.
Thanks Netmanias, truly appreciate your efforts in preparing this document.
Any update on Online and Offline charging. (OCS and CGF)???
Who assigns the Dedicated bearer ID ? not clear from document. Is it MME or PGW
@Raj, MME assigns the EPS Bearer ID (EBI) for both default and dedicated bearer.
refer Figure 4.
An important parameter missing in the call flow for voice call modification procedure i.e setup of dedicated bearer is LBI. Please add this parameter
Thank you for the comment. We have added EPS bearer related IDs to Figure 3 and 4 (Default Bearer ID in Figure 3, and Dedicated Bearer ID and LBI in Figure 4), and the related STEPs have been modified (STEP 2) in Section 3.1, and STEPs 6) ~ 7) in Section 3.2).
We omitted EPS Bearer IDs and LBI to simplify the figures because the IEs are mentioned often in other LTE TRs. But, as you pointed out, LBI is important parameter when a dedicated bearer is created, so it seems better to add them. Thank you for your careful comment.
Thank you so much for sharing wonderful document which made me to understand about default and dedicated bearer. If you can plz share about messages like ASR STR clearly
Thank you so much for this excellent document.
What is unclear to me is, in case of PCC rule with closed gating status, whether or not the gating-status is delivered to SGW and/or UE as part of TFT template. I'd like to understand where the blocked uplink packets are discarded. (PGW or SGW or UE?)
First of all, congratulations for all these amazing LTE technical documents. They are really clear and helpful in order to understand the complexities of LTE, in addition to a nice quick reference. Thanks a lot for sharing.
I have a question about figure 6. The Bearer ID for both Default bearers is 5, is that correct or is it a typo? Is it possible to reuse the Bearer ID for different APNs?
According to TS 23.401 clause 5.2.1, "An EPS bearer identity uniquely identifies an EPS bearer for one UE accessing via E-UTRAN"
Is there any limitation on the number of Default Bearers that can be stablished, apart from the 11 Bearer IDs available?
It’s typo error. As you have mentioned, different bearer id is allocated to each bearer for an UE. We have corrected the typo in Figures 6 and 7 and updated this post and pdf file. Thank you for letting us know that.
We are not sure about the maximum number of default bearers for an UE, but it may depends on the number of PDNs the UE can be connected to. Some eNBs/femto APs have been implemented to support only a limited number of PDNs.
Thank you for this informative document.
I have a question concerning the dedicated bearer creation. Can two bearers with the same QCI values but different ARP values exist at the same time? For example, concider the following scenario. A new PCC rule is authorized with a certain QCI and ARP values. If a bearer with the same QCI but with a different ARP value already exist, can the PCC rule be mapped into this bearer or is a new bearer with same QCI but different ARP value created?
No, Bearer is uniquely identified by the combination of QCI and ARP. So even if ARP is different, dedicated bearer creation will be triggered by PCEF.
How does the PCRF store the PCC Rules (based on what index). I mean lets say same QOS is applied
for two Applications (mapped to SDF1 and SDF2, both mapped to dedicated bearer id 1.
So lets say the App related to SDF#1 is stopped. Then PCRF needs to delete PCC Rule related to SDF#1.
But the rule is still valid for SDF#2. Any pointers on how this is implemented in PCRF.
It will be great if you can give some practical example (with just 1 or two rules in PCRF) .
Also what will be sent in the Diameter messages esp in Gx interface... Also may be bit about Rx interface ?
Thanks for such detailed documentions, I guess there is a typo in Figure 6. For PF1 of Deafult bearer (DL), SDF id is written as SDF2 which should be changed to SDF1.
I have some doubts related to section 3.1.
1. Suppose UE have configured multiple apns (internet.apn.com, ims.com) for internet and ims services. UE is switched on, shall it create eps session with both the apns or any of default apn (internet) and eps session with ims once UE attempt any voip call?
2. Suppose there is only single apn (ims.com) is configured in UE, Is pdn connectivity request need to send from UE to MME or attach shall be sufficent?
3. As per my understanding, there is one eps session for each apn. Shall the eps sessions share the same GTP tunnel or mutiple gtp tunnel shall be created per eps session?
regarding to 1)
After UE is switched on, two default eps bearers are created and kept alive.
- Default eps session for internet APN which can be removed
if you enable WiFi instead of LTE data service at the UE
- Default eps session for IMS APN which is used
for initial / periodic registration to IMS (SIP REGISTER to CSCF)
and also for receiving call (waiting of SIP messages from IMS, e.g. SIP INVITE)
- Dedicated eps bearers for IMS APN to carry RTP will only be created and maintained
while VoLTE calling
Sorry, I don't understand your question, "pdn connectivity request" is used for initial attachment.
If you are considering about creation of dedicated bearers for IMS APN, dedicated bearers are created only by IMS
- Initiated by CSCF -(Rx)-> PCRF -(Gx)-> PGW -(S5)-> SGW -(S11)-> MME -(S1)-> eNB/UE
- Yes if "multiple PDN" is not used
(As I know "mutiple PDN" is defined but not serviced by any operators)
- A GTP tunnel can not be shared by several eps sessions
- One EPS bearer is made up of one GTP tunnel and several SDF templates
- Please see following articles
Thanks a lot Netmanias, it is truely an excellent informative site.
I have one quiery, As we understood, we need a default bearer and dedicated bearer to IMS for the voice call, how many bearer we need for a normal internet usage ? As internet will be a separate PDN/APN.
I got the answer for my query...I didnt read all the pages while asked this query..
May I know the difference between EPS bearer QOS and subscriber's allowed QOS?
Thanks for your useful posts.
I had a question about "Default Bearer Establishment" (Section 3.1, Figure 3). In step 10 and 11 the MME and UE are informed about QoS parameters (such as QCI), however, the S-GW and eNodeB are not informed by anyone. As I know S-GW and eNodeB are envolved in policy enforcement process, so how they are informed about policy?