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Mar 20, 2014

Bootstrapping server function (BSF) in LTE

Recently I faced question about role of Bootstrapping Server Function (BSF) function in the LTE network, this made me thinking and digging. On the end I decided to share this woit you in case anyone has ever wondered about that. So what is the role of BSF in LTE?


The BSF queries the Subscriber Locator Function (SLF) over Dz interface, which is Diameter based,  to get the name of the HSS containing the required subscriber specific data.

It's similar to Zh or Zh' (Z-h-prim), dont remember it right now, interface used by BSF to connect to HLR to fetch authentication information.



Check the 3GPP 33.220 for more details http://www.3gpp.org/ftp/specs/archive/33_series/33.220/

Jan 15, 2014

Resource: SIM Card Forensics - Introduction

Just few moments ago I have found quite interesting article that covers in details how the SIM card is build and works. Maybe for Terminal-side guys this is obvious but myself I found few new things for myself.
As the title says this is just introduction, more information could be coming.

SIM Structure and File Systems

A SIM card contains a processor and operating system with between 16 and 256 KB of persistent, electronically erasable, programmable read-only memory (EEPROM). It also contains RAM (random access memory) and ROM (read-only memory). RAM controls the program execution flow and the ROM controls the operating system work flow, user authentication, data encryption algorithm, and other applications. The hierarchically organized file system of a SIM resides in persistent memory and stores data as names and phone number entries, text messages, and network service settings. Depending on the phone used, some information on the SIM may coexist in the memory of the phone. Alternatively, information may reside entirely in the memory of the phone instead of available memory on the SIM.
Fig. 1. SIM Card File System

follow the link to get more - resource.

Source:
Internet

Jan 14, 2014

Combined Attach in LTE/4G

Some time ago I'v covere the Attach Procedure, from then many times I saw questions about the Combined Attach.
So here it is, the Combined Attach himself.

First it has to be addressed what is the Combined Attach and why it's so different from Attach procedure already covered.

What Combined Attach is?

It's attach for both EPS and non-EPS services, or both EPS services and "SMS only".
The combined attach procedure is also used by a UE in CS/PS to attach for EPS services if it is already IMSI attached for non-EPS services.

How Combined Attach is triggered?

When the UE initiates a combined attach procedure, the UE shall indicate "combined EPS/IMSI attach" in the EPS attach type IE.


If the UE is in EMM state EMM-DEREGISTERED, the UE initiates the combined attach procedure by sending an ATTACH REQUEST message to the network, starting timer T3410 (More about EMM timers? Check the EMM timers or ESM timers article) and entering state EMM-REGISTERED-INITIATED.

If timer T3402 is currently running, the UE shall stop timer T3402. If timer T3411 is currently running, the UE shall stop timer T3411.

Jan 2, 2014

New year, another year online!

Hi everyone!,
It has been 2 years since the blog is up and running, or it will be in exactly 4 days from now. ;-)

Few things has changed during this time in my private life, I have definitely moved forward with what I'm doing for living, and definitely running this blog helped me to evolve.

Your comments and inputs to whatever I'm posting keeps me up to speed and motivated. Anyone of them is important to me, thanks for everything. With few of you I'm having conversations on telecom topics on monthly basis. Thanks for your trust in me.
Thanks for all your questions and for the opportunities to help in problems you had. Solving those also pushed me forward.

If you have any questions or propositions I could take into consideration to write about simply let me know.

Hope you will stick with me next 2 years or even longer.

Wish you all great 2014, success at work and ample of energy to self improve.

Regards, Cheers!,
Bart Barton

Nov 30, 2013

S-TMSI usage and allocation process

During which procedure the S-TMSI  (SAE-Temporary Mobile Subscriber Identity) is allocated?

Answer could be put as a one-liner, during the Attach procedure.

Going little bit deeper into the details..
At the time of initial attach (so I would say IMSI not GUTI attach, what is the difference? Check here What is GUTI and IMSI attach) procedure, the UE sends Att Req with IMSI to the Network to process the Request. If it's successful the MME will reply with Attach Accept message which contain the GUTI as one of the IE (Information Element).

Based on article IMSI, TMSI and GUTI - how they are created (and 3GPP Specs) we know that GUTI consist from MCC, MNC, MME Group ID, MME Code and M-TMSI.

What is M-TMSI (MME-Temporary Mobile Subscriber Identity)?
M-TMSI represents a TMSI in MME area.


Last statement on allocation topic is left to say that S-TMSI is being created from MME Code and M-TMSI. The S-TMSI represents the TMSI in MME pool area.

During the Attach process MME creates the UE Context and assigns the S-TMSI to it. Later this UE Context holds user subscription information fetched from HSS in Authentication process. The local (in MME) storage of subscription allows faster execution of procedures such as bearer establishment because it removes the need to consult the HSS each time.


Source(s):
own experience,
3GPP Spec

DIAMETER based interfaces in EPC, UMTS and IMS

Recently I've seen question regarding on which interface in LTE or UMTS the DIAMETER protocol is used.

Basically DIAMETER is an Authentication, Authorization & Accounting (AAA)  protocol. That is why any of you will see DIAMETER used for these functions.

                    S6a - Authentication, more in TS 29.272
                    Gy - Prepaid charging, more in TS 23.203, TS 32.299;
                    Gz - Postpaid charging;
                    Gx - QoS/Policy, more in TS 29.211, TS 29.212;
                    Rf - Charging, more in TS 32.299;
                    Ro - Charging, more in TS 32.299;
                    Rx - QoS/Policy, more in TS 29.214;
                    S6d - Authentication;
                    S9 - QoS/Policy;
                    Sh - Subscriber Profile;
                    Cx - Subscriber Profile;
                    e2 - Location.
But also few others specific to IMS

Nov 9, 2013

Resource: Basic LTE call flows and tutorials

Found this when surfing the web, maybe any of you will find it useful.
Most of the topics I've covered here, but this looks good for a Radio/Device reference.

Follow the link to get more, resource


Source:
LinkedIn, Internet

Nov 4, 2013

Extended Service Request procedure

The Extended Service Request and Service Request are same procedure just used for different purposes.
To make it simple, the below are color-coded. The cases when the Extended Service Request are triggered are marked light blue, the cases in black trigger Service Request procedure.

 Service Request triggers

a)    the UE in EMM-IDLE mode receives a paging request with CN domain indicator set to "PS" from the network;
b)    the UE, in EMM-IDLE mode, has pending user data to be sent;
c)    the UE, in EMM-IDLE mode, has uplink signalling pending;
d)    the UE in EMM-IDLE or EMM-CONNECTED mode is configured to use CS fallback and has a mobile originating CS fallback request from the upper layer;
e)    the UE in EMM-IDLE mode is configured to use CS fallback and receives a paging request with CN domain indicator set to "CS", or the UE in EMM-CONNECTED mode is configured to use CS fallback and receives a CS SERVICE NOTIFICATION message;
f)    the UE in EMM-IDLE or EMM-CONNECTED mode is configured to use 1xCS fallback and has a mobile originating 1xCS fallback request from the upper layer;
g)    the UE in EMM-CONNECTED mode is configured to use 1xCS fallback and accepts cdma2000® signalling messages containing a 1xCS paging request received over E-UTRAN;
h)    the UE, in EMM-IDLE mode, has uplink cdma2000® signalling pending to be transmitted over E-UTRAN;
i)    the UE, in EMM-IDLE or EMM-CONNECTED mode, is configured to use 1xCS fallback, accepts cdma2000® signalling messages containing a 1xCS paging request received over cdma2000®  1xRTT, and the network supports dual Rx CSFB or provide CS fallback registration parameters; or
j)    the UE, in EMM-IDLE or EMM-CONNECTED mode, has uplink cdma2000® signalling pending to be transmitted over cdma2000® 1xRTT, and the network supports dual Rx CSFB or provide CS fallback registration parameters.


Sep 26, 2013

LTE EPS mobility management timers - EMM timers

Lately many times I had to reach towards the EPS Mobility Management (EMM) timers, because it took me some time to google them here you go. Hope any one will find them as useful I did. 
In the two tables you can easily find the times name it's default or suggested value, what is triggering it and what happens in case it will finally expire.