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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.