IPv6 Communication between LTE Nodes 


 • P-GW allocates the IPv6 address to UE.
 • This address allocation done through the Router Advertisement message.
 • The Router Advertisement message will carry both Prefix and Interface ID for an UE.
 • UE makes the FULL IPv6 address by using both Prefix and Interface ID
 • There will be no DAD(Duplicate Address Detection) for IPv6 UE address as the UE IPv6 address is globally unique.
 • As UE is in air interface and there is no IP Connectivity so there will be no DAD(Duplicate Address detection)
 • But in between eNB-MME-SGW-PGW, DAD is available as there is a chance of duplicate Address. So DAD is applicable here.

1. UE initiate Attach Request towards eNB to attach in the LTE network.
 2. eNB derives the MME and sends Attach Request to MME in S1-MME Initial UE Message.
 3. MME selects the SGW and sends Create Session Request towards SGW with EPS bearer information for default Bearer.
 4. SGW creates the EPS bearer context and sends Create session Request to PGW with default EPS bearer information. Note: PGW selection done by MME and shared with SGW in Create session Request from MME. PDN GW performs an IP-CAN Session Establishment with PCRF. The PCRF may modify the APN-AMBR and the QoS parameters (QCI and ARP) associated with the default bearer in the response to the PDN GW.
 5. PGW creates EPS Bearer Context table and generates Create Session Response towards SGW. PGW initiates the Charing activities for the EPS bearer. PGW also obtain the prefix from the external PDN through Diameter and shares the prefix info and Interface ID for an UE in the PAA(PDN Address) Informational Element of Create Session Request. Now PDN can sends the downlink packet for an UE but as the eNB information is not available the packet will get buffered at SGW. SGW might initiates Downlink indication towards MME.
 6. SGW confirms the Default bearer creation and sends the Create Session Request with MME. SGW shares the prefix info and Interface ID for an UE in the PAA(PDN Address) Informational Element of Create Session Request.
 7. MME creates the Bearer Context and sends Attach Accept in S1-MME Intial Context Setup Request to eNB. In the Attach Accept message, the MME does not include the IPv6 prefix within the PDN Address but shares the UE Interface ID to eNB.
 8. eNB sends RRC Reconfiguration Request message to UE. If the UE receives an IPv6 interface identifier, it may wait for the Router Advertisement from the network with the IPv6 prefix information or it may send a Router Solicitation if necessary.
 9. UE sends RRC Reconfiguration Complete message to eNB.
 10. eNB sends the Initial Context Setup Response message to MME with eNB’s TEID(Tunnel Identifier) and IP address for downlink packet.
 11. UE sends a Direct Transfer message to the eNodeB.
 12. eNB sends the Attach Complete towards MME.
 13. As UE knows the UL bearer information, now UE can sends the UL traffic. So UE initiates the Router Solicitation message towards network to get the Full IPv6 address. This packet is same as UL traffics.
 14. MME initiates the Modify Bearer Request towards SGW to share the eNB’s information i.e. eNB’s TEID and IP address for downlink packet.
 15. SGW updates the eNB information and sends Modify Bearer response towards MME.
 16. Now SGW has the information of eNB, so the downlink packet can be delivered to UE. So the PGW response back with Router Advertisement message for a Router Solicitation message initiated by UE. The Router Advertisement message will have IPv6 prefix in it to make the Full IPv6 address. This Router Advertisement Message is carried as a DL packet. Now UE can make the full IPv6 address by using the Interface ID shared before by PGW and the IPv6 prefix shared in Router Advertisement message. •

References: – http://tools.ietf.org/html/draft-sarikaya-v6ops-prefix-delegation-09
– 23.402 (LTE Over View) 3gpp specification
 – 29.274 (GTPv2-C) 3gpp specification

TFT filtering rule in LTE network

TFT

TFT is set of all packet filter associated with an EPS bearer. A packet filter may be associated with a protocol. A packet filter Identifier shall be used to identify a packet filter. For eg: lets say we have http traffic. Now we all know that destination port in Http is 80. So a packet filter can be created indicating destination port to 80 and this packet filter may associate with a ID which is nothing but packet filter ID. Now several packet filters can be combined to form a Traffic Flow Template.

One EPS bearer is established when UE connects to PDN and that remains lifetime of that PDN connection to provide UE with always on IP connectivity to PDN. This is default bearer. Any additional bearer that is established to the same PDN is referred as dedicated bearer.

Up Link Traffic Flow Template (UL TFT) : - Set of uplink packet filters in TFT
Downlink Traffic Flow Template (DL TFT) : - Set of downlink packet filters in TFT
Every dedicated EPS bearer is associated with TFT.

The following way we can define the TFT filtering rule for a bearer.

-       IP Network based

-       Port range base

-       Protocol base

-       Direction base

1. IP Network Base:

If each bearer will have distinct IP network then in this case the IP network base filtering can be used.

2. Port range Base:

If the network is same for the entire bearer then this can be used for TFT filtering.

3. Protocol Base:

This can be used to filter some protocol based TFT.

4. Direction Base:

This is a filtering rule for UL/DL direction.

Default_Dedicated_bearer_Creation in LTE network

This document will explain about the new bearer allocation on top of default bearer.

First we will cover the default bearer creation and then we will cover the allocation of dedicated bearer.

Default Bearer Creation:

Here I will elaborate more on GTP perspective for creating default bearer. Please refer the following points when attach request initiated by UE,

1.       UE initiate a “Attach Request” towards eNB with the UE information such as IMSI, UE Core Network Capability, Attach Type, NAS information, RRC parameters etc.

2.       ENB derives MME from RRC parameter and forward the “Attach Request” i.e. S1-MME message (Initial UE Message) towards MME with the Selected Network, CSG ID (Common subscriber group), and TAI+ECGI information.

3.       MME will initiate a GTP-C signaling message towards S-GW to proceed with attach. This will help the EPS (Evolved Packet system) to create default bearer in the network. MME initiates Create Session Request with the following important information

a.       IMSI

b.      MME’s F-TEID for control plane (MME IP + TEID (Tunnel ID)). This will be used for future communication with MME.

c.       PGW’s G-TEID for Control plane (P-GW IP + TEID (here it will be zero)). This will be used by S-GW to communicate with P-GW.

d.      Bearer Context to be created. This is the bearer information to be created at MME. This will include the default bearer ID with TFT, QOS.

e.      APN

f.        Recovery

4.       S-GW will process the “Create Session Request” initiated by MME and create the UE, eNB, and MME context and modify the Create session Request and send it to P-GW. Create session Request from S-GW will have the following important information

a.       IMSI

b.      S-GW’s F-TEID for control plane (S-GW IP + TEID (Tunnel ID)). This will be used for future communication with S-GW.

c.       Bearer Context to be created. This is the bearer information to be created at S-GW. This will include the default bearer ID with TFT, QOS, S-GW user plane F-TEID

d.      APN

e.      Recovery

5.       Once P-GW receives “Create Session Request” , it will create UE, S-GW context and communicate with PCRF for QOS and APN resolve. If that succeed, P-GW will respond back with “Create Session Response” towards S-GW. The Create Session Response will have following information:

a.       Cause. This value will be used for Success/failure for the Create Session Request.

b.      P-GW’s F-TEID for control plane (P-GW’s IP + TEID ). This information will be used for future signaling message communication with P-GW.

c.       PAA (PDN Address Allocation).

d.      Bearer Contexts Created. This information element will have Default EPS bearer ID, P-GW user plane F-TEID, TFT, Bearer Qos, Charging ID.

e.      Charging GW

f.        Recovery

6.       Once S-GW receives “Create Session Response”, it will create P-GW context and forward/process the “Create Session Response “with the following information.

a.        Cause. This value will be used for Success/failure for the Create Session Request.

b.      S-GW’s F-TEID for control plane (S-GW’s IP + TEID ). This information will be used for future signaling message communication with S-GW.

c.       PAA (PDN Address Allocation).

d.      Bearer Contexts Created. This information element will have Default EPS bearer ID, P-GW user plane F-TEID, TFT, Bearer Qos, Charging ID.

e.      Charging GW

f.        Recovery

7.       Now if downlink data comes from PDN it will get buffered in S-GW as user plane eNB information shared with S-GW.

8.       MME shares the eNB information as part of attach procedure with “Modify Bearer request” with the following information

a.       Bearer Contexts to be modified. This IE will have eNB’s user plane F-TEID.

9.       Once S-GW receives the “Modify Bearer request” with eNB information.  It will respond back with “Modify bearer Response”.

10.    Now downlink data can be sent to eNB because S-GW has the information of eNB.

11.   But uplink data can possible after step 6.

Dedicated Bearer Allocation:

Once the default bearer created the UE or network can opted for the dedicated bearer.  To get more service from network, UE or NW may initiate the dedicated bearer allocation.

1.      UE Initiated Dedicated Bearer Allocation:

a.       UE Request “Bearer Resource Allocation” message towards MME for allocating dedicated bearer.

b.      MME sends “Bearer Resource Command” with the default bearer ID to S-GW for a dedicated bearer allocation. That means MME commands to the P-GW to initiate a “Create Bearer Request” to start the dedicated bearer allocation. This command will provide the default bearer ID. This message will have the following information:

                                            I.            EBI i.e. Default EPS bearer ID.

                                          II.            PTI

                                        III.            TAD (TFT rule + TFT ID)

c.       Once S-GW receives the “Bearer Resource Command” then the SGW or the PGW will determine if the UE is requesting an Allocation operation of bearer resources for a traffic flow aggregate based on the TFT operation code and the packet filter ID value in the Traffic Aggregate (TAD) IE and/or the presence of the EPS Bearer ID IE.

d.      PCRF entity has to check the APN and QoS details for bearer approval.

e.      After P-GW received “Bearer Resource Command”, it will initiate “Create Bearer Request” towards S-GW for dedicated bearer allocation. This request will have the following information.

                                            I.            EBI i.e. Default EPS bearer ID.

                                          II.            Bearer Context. This IE will contain the dedicated bearer id with value “0” (as MME is going to allocate the bearer ID), TFT, P-GW user plane F-TEID etc.

f.        Once S-GW receives “Create Bearer Request”, it will propagate the message towards MME for dedicated bearer allocation.

g.       MME does a bearer setup request with eNB after receiving “Create Bearer request” from S-GW.

h.      Once the bearer setup request completes, MME sends back “Create Bearer Response” with the following information.

                                            I.            Cause. This is for success or failure.

                                          II.            Bearer Contexts. EBI. This ID will be assigned by MME with a value. eNB User plane F-TEID etc.

i.         Once S-GW receives “Create Bearer Response” then it update the UE,eNB and MME context for the dedicated bearer and sends the “Create Bearer Response” towards P-GW.

2.      NW Initiated Dedicated Bearer Allocation:

If the service provided by NW is not sufficient in a bearer then P-GW opted for dedicated bearer initiation.

a.       P-GW will initiate “Create Bearer Request” towards S-GW for dedicated bearer allocation. This request will have the following information.

                                            I.            EBI i.e. Default EPS bearer ID.

                                          II.            Bearer Context. This IE will contain the dedicated bearer id with value “0” (as MME is going to allocate the bearer ID), TFT, P-GW user plane F-TEID etc.

b.      Once S-GW receives “Create Bearer Request”, it will propagate the message towards MME for dedicated bearer allocation.

c.       MME does a bearer setup request with eNB after receiving “Create Bearer request” from S-GW.

d.      Once the bearer setup request completes, MME sends back “Create Bearer Response” with the following information.

                                            I.            Cause. This is for success or failure.

                                          II.            Bearer Contexts. EBI. This ID will be assigned by MME with a value. eNB User plane F-TEID etc.

e.      Once S-GW receives “Create Bearer Response” then it update the UE,eNB and MME context for the dedicated bearer and sends the “Create Bearer Response” towards P-GW.