LTE Attach Part 3: Attach Call Flow

The LTE attach call flow explained. From RRC (Radio Resource Control) Connection Establishment to IP address assignment.
ADDITIONS/ERRATA:
26:00 - There is another mechanism allowed by standards for UE to obtain IP address, which is provided to the UE as part of "Activate Default EPS bearer request" message (step 23). The UE in "Activate PDN Context Request" (step 5) states if it wants (a) IP address allocated via the NAS message or (b) will use DHCPv4 after the Attach procedure is completed. For (a) the PGW provides IP address as part of step 21 which is relayed to UE in step 23. (a) is the typical approach used by most UEs and network. Slides at: github.com/irfanalii/youtube_...

[@shubhamjain8389]

This is one of the best LTE training channels ever, it has to have many many subscribers

[@davedamerjian6035]

Fantastic set of videos as I just posted comment for the GTP Primer video. One thing I will say with regards to the DHCP used to give out UE IP address at end of this video, while maybe that it part of the spec, that is NOT the way I see our Cisco customers do it, every instance I see is the PGW's Create Session Response giving out the UE IP address (IPv4 and/or IPv6).

[@ramgollakota1225]

have been struggling with some of these concepts, and Irfan sir you have given lot of clarity and peace of mind to me.

[@aniruddhsrinivas4552]

This video is indeed an impeccable explanation of LTE Attach procedure one could ever find and understand. Thank you Irfan! Looking forward for more such videos.

[@seanwells1672]

I could kiss you for creating this! Been pulling my head reading online till I found your videos.

[@lt_cristian]

The finest LTE call flow explanation that I've seen, very fluent and compressive! Congratulations

[@mustakimdhanse1407]

The best & easiest explanation I have ever seen. Keep it up & keep posting more videos.

[@chinmaymarathe53]

Best LTE explanation I have ever seen. Really Appreciated

[@chotonrahman5959]

Thank you so much, one of the best trainings I've ever seen...

[@suman2110]

Really It's a good explanation from end to end, Thank you, Ifran Ali.

[@swarnban8634]

He really rocked at *2.04*

[@atahanaltuntas6164]

irfan, you are the best:))

[@jobanpreetsingh3880]

Please create the series for 5g too. You are a life saver

[@muditgoyal6910]

Thanx a lot Irfan. Such a perfect explaination, even a newbie like me could understand the explaination easily.

[@shivamkasaudhan9850]

Irfan Sir.. Thank you for the Best #LTE Session Rocks

[@manav6502]

wow this is impeccable explanation, really helpful!!

[@fatmaghandour9427]

Perfect explanation of attach procedure, thank you !

[@IrfanAli-nz7mb]

You are welcome.

[@abuismael4763]

Thank you it is perfect and clear explanation

[@abhishek-xv5ow]

Very Concise and clear..Thanks a Lot :)

[@IntroMaster2216y]

you are my hero

[@RuwanIndikaPrasanna]

Great video !

[@KamranKhan-hv5ti]

Excellent!

[@minkeshgupta1422]

great explanation helped alot thanks

[@harrison5758]

Thanks for your sharing!

[@lehlagaremogadime7494]

very informative

[@bibhubehera649]

Tysm :)

[@SachinSharma-vf5xh]

Authentication process goes like this: both the HSS and UE has a (K=master key) key which is used to authenticate the UE as well as the network, the MME asks (sends authentication token) both HSS and UE to derive a specific key using K key and sent it to me to which UE replies with RES and HSS with XRES (expected response), (since both have the same K key the RES and XRES should match), the MME compares the responses, if match UE is authenticated, else its an imposter
UE can derive the authentication token using the K key as well so that it can make sure the network is valid

[@arcert6743]

Hello Sir, you have explained the details in an excellent way. This is very helpful. Thank you and appreciate very much. I am looking for understanding on LTE roaming scenarios or call flows. Can you please guide me ? I have searched a lot on internet but didn't find any good info.

[@juanky1007]

what is the diference (talking about this messages call flow) between LTE Attach procedure and combined attach procedure?

[@HiteshKumar-bq8xy]

Hello Boss, One question, IF I am doing a CSFB and I have given priority to GSM but TAC AC mapping is still in 3g LAC so how CSFB will perform means how MT CSFB to GSM will happen where MME will send 3g LAC to MSC ?

[@amitsareen8326]

Hi Irfan.....thanks for this information. I have a doubt. If IP address is not being used by the network (UE to PGW) then what is the need to transfer the IP address to the UE. P-GW can simply allocate the IP by himself (allocate the IP with SIAPTEID) thus saving resources in the signalling.

[@adamrhaman5833]

Great video. One suggestion. Complete the messaging first and then go details inside msg.

[@sxndeepak]

UE send UE id in connection req and NW respond same in setup if it did not match UE dropped it . this is not happen in CBRA ?

[@rathig007]

This training is really good, can avoid random names like Ashok in between to keep it professional and can use the actual names to keep the context intact.. Thanks :)

[@abhishek-xv5ow]

But Ashok is not a random Name :)

[@mohiteric]

Hi Irfan, can you explain a bit about SGW n PGW selection and DNS queries

[@shahidHussain-ie4hh]

Why HLR is HSS in EPC?

[@temirlankessikov3345]

How about PCC architecture included during initial attach

[@Santana198]

Thanks for the in depth explanation. Had a few questions
1)Does not the Attach Accept message actually provide the UE with the IP ?

[@IrfanAli-nz7mb]

Standards allow options: (i) UE can request for IP address allocation via attach or (ii) IPv4 address allocation via DHCPv4. In case (i) IPv4 and/or IPv6 address is provided to the UE along with the attach accept message (the IP address is in the PDN Address IE of the ESM NAS message "Activate Default EPS Bearer Request" shown in Step 23 of the slide and not the Attach Accept message itself). In case (ii) UE will request IPv4 address via DHCPv4 after attach is completed. For most of the traces I have seen in the market, IP address is allocated using (i), i.e. in the activate Default EPS bearer request message sent along with Attach Accept message.

[@Santana198]

Irfan Ali Thank you!. Great videos...

[@anandhebbali4813]

Hi Irfan, Could you please tell who are Mehmet and Ayse?

[@shaikyaseen3210]

Sir more Videos please

[@joanlim5634]

Hi Irfan Ali, is this the same for lte data?

[@narenderreddy5031]

Hi

[@simpsonmathew1361]

Hi Irfan,
What is the concept of SRBs in LTE. Why SRB is required in LTE?
Thanks in advance

[@IrfanAli-nz7mb]

Signaling Radio Bearers are for sending control messages called Radio Resource Control RRC (please see the LTE Radio Primer series part 6-7) between UE and eNB. The RRC messages are grouped into two groups: (a) those that are sent early on and are not provided with RLC retransmission (SRB0), and (b) those that are provided with RLC retransmission (ack mode) (SRB1 and SRB2). SRB1 and SRB2 are used to differentiation priorities for messages, SRB1 are messages that require higher priority and these are direct messages between UE and eNB and SRB2 are lower priority and can take longer delays, which are NAS messages between UE and MME. Hope this answers your question.

[@simpsonmathew1361]

@@IrfanAli-nz7mb Yes. Thanks for the detailed explanation.

[@nitin007verma]

Sir can we get this slides??

[@IrfanAli-nz7mb]

Hi Nitin. The slides are available at slideshare: www.slideshare.net/aliirfan04/lte-architecture-and-lte-attach

[@vishalzacharias3732]

hi sir can you tell me total how many call flows in LTE?

[@vishalzacharias3732]

can you give all call flows please

[@shivamkasaudhan9850]

Irfan Sir.. Thank you for the Best #LTE Session Rocks