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LTE IP Address Allocation Schemes I: Basic
February 13, 2015 | By Netmanias (tech@netmanias.com)
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Page 2 of 5

 

2. Types of IP Address Allocation

 

When UE initially attaches to an LTE network, it requests for a PDN connection. Then a P-GW allocates an IP address (i.e. PDN address) to be used by the UE for the PDN, and forwards it to the UE while a default bearer connecting the two is being established. With this IP address, the UE can use services provided through the PDN.

 

A P-GW allocates IP addresses in two ways: dynamic or static IP address allocation. In case of dynamic allocation, it automatically assigns an IP address every time UE accesses the network. On the other hand, in case of static allocation, it assigns a designated IP address to UE upon its subscription, and then allocates the designated IP address every time it accesses the network. Figure 1 below compares the two types.

 

Figure 1. IP Address Allocation Schemes

 

In case of dynamic IP allocation, the network (e.g. P-GW) automatically selects an IP address for UE. The network operator has IP pool(s) provisioned at the P-GW in advance. Then later when UE initially attaches to the LTE network, the P-GW dynamically allocates an IP address to the UE. So, a new dynamic IP address is allocated to the same UE every time it initially attaches to the network.


However, in case of static IP allocation, the network operator allocates a permanent IP address to each UE upon their subscription to the network. The operator has an allocated static IP address provisioned for UE in the network (HSS) along with other subscription information. Then later when the UE initially attaches to the LTE network, the P-GW obtains the static IP address from HSS, and forwards it to the UE. So, this particular IP address is allocated to the UE every time it initially attaches from then on.

 

When requesting for a PDN connection during initial attach, UE can request for protocol data related with external protocol/application (e.g. configuration parameters) by using Protocol Configuration Options (PCO)2 parameters (e.g. request for DNS server address, P-CSCF address). This document will explain a case where DNS server addresses as well as an IP address are requested.

 

Page 2 of 5
Sachidananda 2015-02-13 23:14:02

Hello Team, Thanks for Superb and Detailed Explantion , I am unable to find part 2 of this document , can you provide the link for it.

 

 

Thanks

Kshirod 2015-02-15 13:26:05

Do we have part-2 please upload it.

I am great fan of this site.
I am sure all the documnet we have now in EPC side.
Can we put something in air interface side.

Following is the over protocal sequence being exchanged between UE and Network. Actually understanding all the details of these steps would be the goal of your whole LTE career.

1) <Cell Search and Detection>
2) MIB
3) SIB 1
4) <Check Cell Selection Criteria>
5) SIB 2 and other SIBs
6) RRC : PRACH Preamble
7) RRC : RACH Response   
8) RRC : RRC Connection Request
9) RRC : RRC Connection Setup

>>>>> Can we put something how 1-7 works.
      I mean what happens when somebody switchon the mobile.What happens in air interface side.
    Like cell search and RACH procedure.

10-14 is coverred in attach procedure.
 
10) RRC : RRC Connection Setup Complete + NAS : Attach Request + ESM : PDN Connectivity Request
11) RRC : DL Information Transfer + NAS : Authentication Request
12) RRC : UL Information Transfer + NAS : Authentication Response
13) RRC : DL Information Transfer + NAS : Security Mode Command
14) RRC : UL Information Transfer + NAS : Security Mode Complete

 

I am Kshirod and you can reach me in softkshirod@gmail.com

ZG 2015-02-24 05:29:48

I have 2 quick questions:

  1. APN has been shown as part of PDN. Is this correct or should it be part of P-GW?
  2. The above document is using IPv4. Would the procedure remain the same for IPv4v6 and IPv6. It seems that for IPv6 addressing, the UE can dynamically generate it's own IP addresses. Not absolutely certain though.
Dieter Busch 2015-07-10 16:37:12

A question on the sequence diagram differences of of fixed and dynamic address allocation:

 

In dynamic alloc. step 2 points to SGW whereas for static step 2 points to HSS. I do not quite understand if and how the MME distinguishes what to do. Is there just a shortcut in the dynamic sequence diagram? -meaning: the update location request and answers are also part in the complete diagram for dynamic, but these were skipped in the picture?

버너 2015-07-15 13:10:06

To Dieter Busch : 

When UE send "initial attach request" to MME, UE also includes GUTI (unique id of each MME) information within "initial attach request". 

After receiving "IAR" from UE, MME checks GUTI and

 - send ULR to HSS if GUTI is different with MME's own 

 - send CSR to SGW if GUTI is same as MME's own 

pls check "Figure 5.3.2.1-1" in TS.23.401 for more explanation 


To Netmanias : 

Please comment more detailly, example call flow has a potential to make a misunderstanding. 

ULR/ULA also can happen in "dynamic IP allocation" scenario. (in this case, HSS does not return any IP address information to MME)

gecuili 2016-03-17 16:15:42

To Dieter Busch,

in ts 23.401, ULR is sent when in following cases:

"If the MME has changed since the last detach, or

 if there is no valid subscription context for the UE in the MME, or

 if the UE provides an IMSI or

 the UE provides an old GUTI which doesn't refer to a valid context in the MME, or

 for some network sharing scenario (e.g. GWCN) if the PLMN-ID of the TAI supplied by the eNodeB is different from that of the GUTI in the UE's context, "

 

To 버너

I do not quit sure all the cases can be concluded into "if GUIT is different with MME' own"?

 

Sundar Ramaswamy 2017-04-13 15:07:54

What if a device executes PSM mode and goes to deep sleep state and wakes up to connect later. What will happen to the IP address? Also, in the case of dynamic IP allocation, is there a possibility that IP address can be changed? 

berry blacks 2017-07-02 05:03:25

in the following example, user 1 belongs to operator A. When he is on network A, the IP address is allocated by the P-GW of network A.

When he roams on network B, he may still be using the P-GW of network A which can allocate an IP address.

Question: can there be overlap of IP addresses, between a user 2 of Network B who get an IP address by P-GW(B), with user 1 on network B who got an address from P-GW(A)?
 

Srijan Singh 2017-09-26 16:46:24

@berry blacks:
As far as I know, there can be overlap of IP addresses in that P-GW of network A itself for different APNs in that PGW. What is done to overcome that is VLAN tagging at SGi interface. 

Roel Derksen 2019-02-04 22:54:07

As I understand it, the UE gets it's IP address and the DNS IP address if the device is known and reachable.

What happens to the bearer and IP address allocation of the UE when it is powered down or is no longer reachable? Are there timers on network side to re-allocate the used IP address? 

monisah 2019-02-18 21:41:21

Where do i search how many PDN connection does the UE have in wireshark

nirav kapoor 2019-04-09 17:41:46

Dear Netmanias Team,

I had referred to the material LTE IP Address Allocation Schemes I: Basic,  it seems only HSS subscription profile is mentioned for statis UE IP allocation, can you please elaborate on the PDN GW Allocation as well during static IP allocation.

Static UE IP can be allocated only if PDN GW is statically assigned to the particular user every time it attaches.

 

Regards,

Nirav Kapoor

Steven Yuan 2019-09-27 16:36:09

Is the IP address a common IP, can it be seen out of LTE network?

Jon Gettys 2020-04-29 21:26:47

Shouldn't starting address in IP pool be 1.1.0.1 and not 1.1.1.1?

Thanks

internet_user 2020-07-18 13:45:35
Mahmoud Maher 2020-07-21 19:50:59

Thanks for this comprehensive article ..

i need to know the cases inwhich the UE will be re-assigned with new IP address ? 

is it only when attaching to the LTE network , or it can be assigned with new IP address incase of inter rat ? 

 

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