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LTE Identification III: EPS Session/Bearer Identifiers
August 26, 2013 | By Netmanias (tech@netmanias.com)
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47
SUMMARY
As the third document for LTE Identification, this document (Part III, LTE Identification III) covers EPS Session/Bearer ID groups related to user traffic delivery. Session/Bearer IDs such as Packet Data Network (PDN) ID (Access Point Name (APN)), EPS bearer ID, E-RAB ID, Data Radio Bearer (DRB) ID, Tunnel Endpoint Identifier (TEID) and Linked EPS Bearer Identity (LBI) are described, followed by a summary of the characteristics of these IDs. Finally, all the LTE IDs covered in the three LTE Identification documents are listed.
Page 1 of 5
 
     

Table of Contents  

1. Introduction
2. EPS Session and EPS Bearer: Overview
3. Identifiers for EPS Session/Bearer (Session/Bearer IDs)

4. Summary: Table of LTE Identifiers

5. Closing and References  

 

 

1. Introduction

 

We have learned about the LTE ID groups such as UE and ME IDs, and Network Equipment (NE) and UE location identifier (location) IDs in LTE Identification 1 [1] and LTE Identification II [2], respectively.

 

This document, as the third document of the LTE Identification series, describes EPS Session/Bearer IDs related to user traffic delivery. E2E sessions that include application entities are out of the scope of this document, and hence only EPS sessions that provide users with PDN connectivity will be covered herein. In Table 1, EPS Session/Bearer IDs to be discussed herein are shown in the last row with a gray background.

 

Table 1. Classification of LTE Identification [1]


 

The LTE IDs that we have learned in [1] and [2] are used to identify a different UE, ME and NE in an LTE network, whereas EPS Session/Bearer IDs are used in a UE1. This means, since more than one EPS session and bearer can be established in a UE concurrently, IDs are needed to identify them.

 

 

 

Page 1 of 5
sdkdsftg 2014-01-09 19:19:52
good
Frededick 2014-04-18 10:26:44
Hi,

How are an EPS bearer and an EPS session different?
Netmanias 2014-04-18 15:49:18
Hi Frededick,

A session refers to user traffic (an IP flow) while a bearer refers to a path that user traffic (IP flows) uses when passing an LTE transport network (between UE and P-GW). In other words, an EPS bearer is a pipe that carries session(s), and hence more than one session can use the same EPS bearer.

Both the session and bearer are related to user traffic delivery, but in different ways: Sessions are about WHO uses WHAT service while bearers are about HOW user traffic is delivered in the LTE network. Bearers only care about “how to deliver user traffic to its destination?”, and not about “who uses what service?”. This is why, when user traffic is delivered through bearers, user IP addresses are not shown, and only the information about the pipe that carries the user traffic, such as DRB ID or GTP tunnel (i.e. S1 or S5 bearer) IP address, is shown.

But, once arrived at P-GW (or UE), different sessions carried by the bearer are identified and processed individually.
Walter 2016-08-09 11:14:41

Hi, Netmanias Team.

Thanks for your good response.

 

One question:

About "more than one session can use the same EPS bearer. ":

One session means one PDN connection. Is it right?

If so, different session may not use same EPS bearers as each EPS bearers can only have one LBI. In other words, each beaer is linked to only one PDN. Maybe I am wrong if one session does not mean one PDN connection.

Jack Lin 2017-02-17 10:08:06

1. Thanks for the good work from Netmanias team.

2. I do have the same doubt about this. Different PDN connections will setup different default EPS bearers, how can an EPS session use the same EPS bearer if one EPS session means one PDN connection?  

Vimal Tewari 2014-05-07 03:21:04
Hello Sir,
First of all Thankyou for such wonderful presentations. Its a delight to study these documents.
In the presentation you have mentioned "The E-RAB ID is assigned by an eNB, generally with the same value as the EPS bearer ID". Is the E-RAB ID not assigned by the MME. Spec 36.413 says that ERABList ( in InitialContextSetupRequest or E-RAB Setup Request ) is sent by MME to eNB and one of the mandatory parameters of this list is E-RAB Id. Moreover, eNB would never know what EPS Bearer ID is because it is generated by MME and sent to UE in NAS message. It is not part of S1ap Message sent to eNB.
Please correct me if I am wrong and Thankyou again.
곽권섭 2014-05-07 13:07:04
Hi Vimal,
Thanks for your comment. i just want to clarify some of your comment. basically, E-RAB interface is between UE and SGW which is NAS. Furthermore, E-RAB establishment should be done by EPC Side. I agreed with your this point. but, according to E-RAB Procedure, EPC (MME is part of EPC) send E-RAB Setuprequest to eNB with e-RAB ID after PDN connectivity request from UE side through NAS signaling. after that, if eNB send back to EPC with "E-RAB Setup response" after eNB performed RRC-Reconfiguration complete. and then finally, E-RAB will be established.
Here is some of clarificaiton from myside for your concern and hopefully NETMANIAS can response for our query.
1. E-RAB ID Allocator is not eNB.
2. eNB would know E-RAB ID. (If you are familiar with S1 - signaling, then you can verify by yourself)
Thanks, Bred
Netmanias 2014-05-08 02:04:07
Hi Vimal and Bred,

Thank you for your comments and clarifications. As you pointed out, E-RAB ID is allocated by MME. The error has been corrected on the post and the attached file.

The below is our understanding of “E-RAB ID allocator” and “whether eNB knows EPS bearer ID”.
- E-RAB ID allocator: MME
E-RAB ID is allocated by MME (TS 23.401, 5.2.1) and the value of E-RAB ID is the same as the value of EPS bearer ID (TS 36.300, 8.2).
- Whether eNB knows EPS bearer ID:
When an eNB receives S1 signaling (e.g. Initial Context Setup Request message or E-RAB Setup Request message) from MME, the eNB can know E-RAB ID i.e., EPS bearer ID. When the eNB establishes a DRB, the EPS bearer ID and the corresponding DRB ID are sent to UE through RRC Signaling (e.g. RRC Connection Reconfiguration).

Thanks again for your kind notice.
Vimal Tewari 2014-05-08 14:21:48
Hello Sir,
Thanks for your prompt response and for making things so clear.
Netmanias is one of the best things that has happened to people trying to learn LTE. Thanks again and please keep up the good work.

Vimal
Netmanias 2014-05-08 18:42:56
Thank you for the encouragement. We will try our best, and hope you do as well.
Dirk Van Aken 2014-10-03 17:54:30

I think there is a tiny mistake in this excellent paper:

 

Namely:

An APN is a combination of a network ID and an operator ID. The network ID is used when identifying PDNs such as Internet or cooperate VPNs or identifying services like IMS that the PDN provides.

 

Should read:

 

An APN is a combination of a network ID and an operator ID. The network ID is used when identifying PDNs such as Internet or Corporate VPNs or identifying services like IMS that the PDN provides.

Netmanias 2014-10-10 17:38:19

Hi,

Thank you for your kind comment. The typo has been corrected (as Corporate VPNs) on the post and the attached file. 

 

Rintho Sihotang 2014-11-21 07:01:23

Hello NetManias,

 

Excellent documentation. 

Do you have any plan for VoLTE Technical Documents? Thank you.

 

 

---

rintho

Wei 2015-01-07 23:42:13

Hello, experts,

 

Thanks for the good paper.

I have one stupid question: what's the difference between the EPS sessions and IP flows?

Thanks.

 

Wei

Chris 2015-01-08 09:58:06

Hello, Wei,

I'd expect you can find answer in link below:

http://www.netmanias.com/en/?m=view&id=techdocs&no=5908 (LTE QoS: SDF and EPS Bearer QoS)


In my understanding,

- EPS session = PDN connection

- An EPS session can have single or multiple EPS bearers

- EPS bearer is transmission path between UE and P-GW to deliver user traffic (IP flows) with specficied QoS

- An EPS bearer can have single or multiple IP flows

Wei 2015-01-09 10:17:55

Hi, Chris,

 

Thanks for your explanation. I'll check the paper you recommended.

Thanks.

 

BR

Wei

kibrom 2015-01-18 23:33:25

Dear guys,

can we think of gtp load balancing between eNB and S-GW.

I really need it.

Thank you

Tom 2015-04-10 16:34:55

Hi Netmanias,

  I love your answers, especially this one:"whether eNB knows EPS bearer ID". Thank you!

Arjun 2015-05-05 16:53:29

Hi Netmanias,

 

Why do have concept of ERABID and EPS Bearerid when there is 1 to 1 mapping b/w two and also there value is always same. We could have used any one of the IDs.

 

Regards,

Arjun

Daniel 2015-05-12 02:00:43

Refer to the TS 23.401 as shown below:

 

5.2.1    EPS bearer identity
An EPS bearer identity uniquely identifies an EPS bearer for one UE accessing via E-UTRAN. The EPS Bearer Identity is allocated by the MME. There is a one to one mapping between EPS RB and EPS Bearer, and the mapping between EPS RB Identity and EPS Bearer Identity is made by E-UTRAN. The E-RAB ID value used at S1 and X2 interfaces to identify an E-RAB is the same as the EPS Bearer ID value used to identify the associated EPS Bearer.

Lajos Pajtas 2015-07-03 17:56:42

The description is perfect and well structured, as always.
Keep up the good work!
 

vineetagr1975 2015-08-07 21:33:16

If say GTPU and PDCP on eNB are not on same system (dis-integrated stack), for DL traffic after GTPU decapsulation when UE IP clear packet is submitted for PDCP prorcessing, what is the best way to identify DRB in PDCP leayer? Can we assume UE IP address and ToS value in IP header is unique for every DRB?

Melih Tiftik 2015-10-06 20:09:30

Hi,

 

In Figure 4. Bearer IDs allocators, I think P-GW should be responsible for S5 TEID DL allocation, not UL. S5 TEID UL allocation is done by S-GW which is already indicated there.

 

Regards,

Melih

saurabh 2016-02-11 16:54:48

Can a single APN have two IP-CAN sessions for a UE? 

Rahil Khan 2016-04-27 19:07:22

Thanks for the explanation. It inc. my basic understanding

 

huy hung 2016-07-15 17:05:29

Hi, 

when you do sizing for EPC, how many bearer per user you used? Tks

 

chaithanya 2016-08-10 18:49:54

What happens to the dedicated bearers when the linked default bearer is deactivated ? If the dedicated bearer will also gets deactivated, then how will it be done ? how will dedicated bearer comes to know that default has been deactivated ? What action does it take ? Whats the procedure ?

TianMing 2016-10-21 18:29:11

Hi, there is one thing confuse me that what is the relationship between the Eps and SRB(singling ridio bearer)。 thank you

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