SGSN Selection procedure

As I said the last time, all points of the list below will be covered.
Until now I've covered the MME Selection, PGW and SGW Selection - both can be found through links.
So Now I will start with SGSN Selection (5th point on the list below), and later today will try also to publish the idea of HSS Selection.

Anniversary 40 years of mobile calls

I'm a little bit late, but still I think this is bigger or smaller anniversary for all of us and because of that all the best to all of you telecom-interested and/or telecom-engineers mates!

"The first mobile phone call was made 40 years ago today, on 3 April 1973."
more: http://www.bbc.co.uk/news/technology-22013228

Some other LTE resource

Just noticed that someone (Bandwidther thaks for sharing links mate!) put links to this blog on his forum. I went there and it looks like guy(s) are creating community which is worth participate in.
I did not read through, but on the first sight there are many sections including the LTE but also 2G, 3G and even the US version of 3G ;-)

Check it on your own

Bandwidther - Wireless Communication forum

 

What is GUTI and IMSI attach

Just found this as a way that someone joined this blog.
Because I always wanted to start like that..   

Dear wanderer..

If you would ask me to put it simple and shallow way, which I'm trying doing right now, I would say:

Difference between those two is very simple and answer to this question is what really GUTI is and why we are using GUTI in general.

So, GUTI (Globally Unique Temporary UE Identity), is used more or less is to hide "real identity" of the subscriber which is called  IMSI. The less you use IMSI the safer you can feel. Period.

Please keep in mind that it's simple and shallow explanation, and that the GUTI is used in more cases than the one mentioned above.

For more info please refer to LTE Attach article as well to article that cover the IMSI TMSI and GUTI topic.

You could be also interested in Combined Attach information

Source:
from my own experience

PGW and SGW Selection procedures in LTE

Last time it was about MME Selection, and today I will cover the PGW and SGW selection as well.
All other points will cover in details in few next days. Also, I'm aware that good example is worth few thousands words, that's why will provide a iDNS configuration as a separate article with all those NAPTR and so on explained.

Possible selection scenarios

As last time, same list of selection scenarios in which EPS Nodes send the DNS Query message to the Internal DNS (iDNS) for the selection of EPS nodes.

Periodic Tracking Area Update (TAU) - T3412 timer

Today I was asked about the Periodic Tracking Area Update. Question was what is happening when the UE is in one place cell or TA in general.

So here is what the Spec Rel 9. is saying about it.

Periodic TAU

Periodic tracking area updating is used to periodically notify the availability of the UE to the network. The procedure is controlled in the UE by the periodic tracking area update timer (timer T3412). The value of timer T3412 is sent by the network to the UE in the ATTACH ACCEPT message and can be sent in the TRACKING AREA UPDATE ACCEPT message. The UE shall apply this value in all tracking areas of the list of tracking areas assigned to the UE, until a new value is received.

No Periodic TAU case

If the timer T3412 received by the UE in an ATTACH ACCEPT or TRACKING AREA UPDATE ACCEPT contains an indication that the timer is deactivated or the timer value is zero, then the timer T3412 is deactivated and the UE shall not perform periodic tracking area updating procedure.

This part is a small change in Spec comparing to Rel 8. I feel this is because Machine to Machine (M2M) communication will take more part in overall. Because what else could be a reason to resign from (Periodic) TAUs?

Timer's behavior

The timer T3412 is reset and started with its initial value, when the UE goes from EMM-CONNECTED to EMM-IDLE mode. The timer T3412 is stopped when the UE enters EMM-CONNECTED mode or EMM-DEREGISTERED state.

How MME is selected - MME Selection procedure

It's beed a while from last time, but here we go. Many times I saw people accesing this site looking for MME seletcion, or how LTE pick MME/SGW/PGW nodes. Hope the below clarifies.


In each LTE network the Internet Domain Name System (DNS) is widely used to handle the Dynamic Peer selection of the PDN-GW, SGW, MME, SGSN and HSS within the network. We could use statistic assingments but, hey! belive me, DNS is much easier if handled properly.

In a few days I will try to cover the details of DNS config for points mentioned below - stay tunned.

EPS Nodes sends the DNS Query message to the Internal DNS (iDNS) for the selection of EPS nodes for the following uses cases.

1. As part of the UE Attach the eNB will query the iDNS Server using the TAI for the address of the MME it should provide to that UE.
2. During UE attach the MME query the iDNS Server to select the PDN-GW (Packet Data Network Gateway, PGW) where a requested (subscribed) PDN connectivity (APN) is located. Selection can be based on the information provided to the MME, when the UE attaches to the network.
3. Following the PGW selection, the MME query the DNS Server to select an available SGW to serve the UE using the TAC, which in most cases is based on network topology and the location of the UE within the network, so that the best SGW is selected.
4. SGSN will query the DNS Server to resolve the Old MME using LAC, and RAC (taken from Old GUTI received from UE) during LTE to 3G/2G Handover.
5. MME will query the DNS Server to resolve the Old SGSN using NRI, LAC, and RAC (taken from P-TMSI received from UE) during 3G/2G to LTE Handover.
6. During attach the MME is configured to support the HSS Peer Service and Interface Associations towards the Diameter proxy/edge agent. These are static configurations in the MME towards the Diameter Proxy and no DNS query is initiated by the MME to select the Diameter Proxy.

Today it will about two of them referring to MME Selection, and the list above will be copied few times more when covering the SGW, PGW, SGSN and HSS selection.

Happy New Year!

To you all - Happy New 2013!
All the best in New Year, for you, your families and close ones.


Have a good time. Regards,
Bart Barton

P.S. Come back for more of LTE/EPC shortly ;-)

Resource: filtering, principles, measurements durring HO, and more on Radio part

Yesterday I found good resource on multiple LTE Radio topics covered by one site.
To Whom it may concern.

Enjoy!

Multiple LTE Radio topics

• How Handover Filtering by UE in LT?
• Handover principles and Handover measurements in LTE
• Handover Algorithm and Procedure in LTE
• What is AMC & its Algorithm in LTE  
• How UE Switch to Service types in LTE?
• PLMN selection in “IDEL Mode” for LTE-UE
•   
• and much more from radio side
http://www.teletopix.org/category/4g-lte

EPS Mobility Management (EMM) and Connection Management (ECM) states

The EPS Mobility Management (EMM) states describe the Mobility Management states that result from the mobility management procedures e.g. Attach and Tracking Area Update procedures.
There are two EMM states described in Specs:

• EMM-DEREGISTERED
• EMM-REGISTERED

The EPS Connection Management (ECM) states describe the signalling connectivity between the UE and the EPC.
There are two ECM states described in Specs:

• ECM-IDLE
• ECM-CONNECTED

In general, the ECM and EMM states are independent of each other. Transition from EMM-REGISTERED to EMM-DEREGISTERED can occur regardless of the ECM state, e.g. by explicit detach signalling in ECM-CONNECTED or by implicit detach locally in the MME during ECM-IDLE. However there are some relations, e.g. to transition from EMM-DEREGISTERED to EMM-REGISTERED the UE has to be in the ECM-CONNECTED state.