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Difference between attach and service request message ?

+5 votes
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Difference between attach and service request message ?
posted Nov 12, 2014 by Neeraj Mishra

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My general thought is when UE(mobile device)first time attach with base station(EnodeB1).this is attach request.
Same UE going to new base station(EnodeB2) that time its need all information about UE.here ue send service request message.

3 Answers

+1 vote

Both the messages come under LTE NAS protocol but the objective of both messages are quite different.
Attach request message is sent by UE to MME when it want to register with network for example: when an UE switch on and a lte cell is available in that particular location.
Service request or Extended service request message is sent from UE to MME when UE want to send/receive data and UE is already registered with network.
I think you got the answer. If you have still any doubt please ask.

answer Nov 13, 2014 by Harshita
0 votes

Difference between attach and service request message is -
1. when UE is in EMM-DeRegistered state and want to move in EMM-Registered state then UE needs to perform attach procedure.
2. In EMM-Registered state UE can be in ECM-connected, RRC-connected state or ECM-Idle, RRC-Idle state. If UE is in ECM-idle, RRC-Idle state during EMM-Registered state and UE has data to send in UL/getting paging for MT data then UE sends service request to move in ECM-connected,RRC-connected mode.

answer Nov 13, 2014 by Veer Pal Singh Yadav
best answer
0 votes

On behalf of Bart (https://www.facebook.com/groups/LTE.Professionals/ )
Long story short Attach is to obtain the IP where Service Request happens after attach when UE goes out from emm-idle to establish NAS

answer Nov 13, 2014 by Salil Agrawal
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+1 vote

I was looking into NAS header. First four bits are used for security header type. Few values I understood but one value I could not understand which was 1100 saying "security header for service request message". I could not understand why such thing is defined only for service request message not for the other messages ?

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