The document describes the LTE random access procedure and attach process. It involves the following key steps: 1) The UE synchronizes with the eNB by receiving synchronization signals and acquiring system information. 2) The UE selects a random preamble and transmits it to the eNB to initiate the random access procedure. 3) The eNB responds with a random access response assigning resources for the UE to transmit an RRC connection request message. 4) Once connected, the UE can complete the attach procedure by transmitting an attach request message through the MME to the HSS for authentication and location update.

1. OFDM Allocates users in time & frequency domain
OFDMA- each subcarrier carries information related to one specific symbol
SC-FDMA-each subcarrier carries information related to allsymbols
LTE RANDOM ACCESS PROCEDURE:
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PSS is transmitted at the start and middle of the 10ms frame and the SSS is also
transmitted every 5ms( subframe 0 and subframe 5)
PSS & SSS provides the aquisition of cell timing & identity during cell search
PSS is a CAZAC(Constant Amplitude Zero Auto Correlation) Signal
SSS is modulated with BPSK
1) UE synchronizes with eNB
UE downloads PSS & SSS
2) UE downloads the system information
UE decodes the MIB(PBCH) and aquires system information
MIB is 24 Bit Codes consisits of
~sequence frame number
~BW information
~PHICH confiuration
UE is tuned to PDCCH to download the DCI, and SIB1
SIB1 contains DCI and Sheduling for other SIB's
UE is assigned with a SI-RNTI
3) UE downlaods the SIB2 on DL-SCH
SIB2 download contains parameters neded for intial access transmission
4) UE selects a random pramble1 and transmits to eNB on RACH Channel
RA_RNTI is implicitily specified by the timing of the pramble transmission.
The eNB detects the preamble transmission
The eNB estimates the uplink transmission timing of the UE
The eNB derives the RA-RNTI from the time slot number in which the preamble
is received.
A temporary C-RNTI is assigned to the UE, This address is used to address the
UE in subsequent messages
The eNB assigns the resources via PDCCH, the PDCCH message is addressed by
RA-RNTI that is assigned to a UE
5) The eNB transmits the RA responce on DL-SCH, this message consists of timing
and uplink rsource allocation for the pramble
this message also includes the back off indicator MAC header for controlling
the backoff duration in the event of a random access procedure
6) UE sends the rrc connection request on UL-SCH with a temporary identity and
starts a timer T300
7) eNB send the RRC conncetion setup on DL-SCH to UE
8) UE sends RRC connection setup comple on UL-SCH to eNB.
LTE ATTACH:
===========
Random Access Procedure
-----------------------
Randomly select a preamble for sending a RACH
UE picks one of the 64 RACH preambles available in an LTE cell. The preambles
are generated from Zadoff-Chu sequences.
Random Access Preamble (RACH,Preamble,RA-RNTI)(UE-------->eNB)
The terminal initiates a new session with the randomly selected preamble. The
message identifies the UE with RA-RNTI.

2. -(UE--->eNB)RACH: Random Access Preamble (RA-RNTI): UE initiates a session to
the eNodeB using a random RA-RNTI
~The UE pickups a random preamble and sends to eNB, The Preambles consists
Zadoff-chu sequences
~The Preamble consists of Cyclic prefix and sequence
~The sequence identifies the UE that is initiating the random access, it
contains the type of the UE and the UE ID value are included in the msg
~RA-RNTI is used as a temporary identifier during the random access
procedure
~Random Access Preamble contains Cyclic prefix + Sequence
~sequence contains UE ID/RNTI Type + UE ID/RNTI Type
~UE ID/RNTI Type contains RA-RNTI
Random Access Response (DL-SCH,RA-RNTI,Timing Advance,Uplink Resource
Grant,Temporary C-RNTI)(eNB-------->UE)
The eNodeB responds to the preamble with the "Random Access Response" message on
the DL-SCH. The message addresses the UE with a RA-RNTI but the message also
assigns a Temporary C-RNTI.The message also sends a timing adjustment to correct
the uplink timing from the UE. Optionally, the message may assign resources to
the
terminal for uplink transmission.
-(eNB--->UE)DL-SCH: Random Access Response (RA-RNTI, C-RNTI, Timing): eNodeB
assigns a C-RNTI and adjusts timing
~The eNodeB responds with a Random Access Response on the DL-SCH channel
~The UE is addressed with the RA-RNTI that was sent in the Random Access
Preamble
~The message carries a Timing Advance that is used to adjust the UE
transmitter timing
~This adjustment will synchronize the UE transmitter so that the
transmissions from the UE are received within the receive timing window
~The message may carry an uplink resource assignment
~The message also assigns a C-RNTI that will be used to address the UE
~ Random Access Responce will contain UE ID/RNTI Type + RA-RNTI
Value + Timing Advance Value +Uplink Grant Resources +Temporary C-RNTI
~ UE ID/RNTI Type will contain RA-RNTI
RRC Connection Establishment
----------------------------
RRC Connection Request(UL-SCH,C-RNTI,UE-Identity = S-TMSI,Establishment Cause
=mo-Signalling)(UE-------->eNB)
~The UE uses a UL-SCH allocation to send the RRC Connection Request message.
The UE is identified by the C-RNTI that was assigned in the Random Access
Response message. The message contains a UE identity (typically S-TMSI:
MMEC+M-TMSI). The message also includes the establishment cause for the RRC
connection.
-(UE--->eNB)UL-SCH: RRC Connection Request (C-RNTI, M-TMSI, Establishment
Cause): UE requests an RRC connection via the UL-SCH.
~The UE has received the Random Access Response based on the RA-RNTI.
~The Random Access Response assigns a C-RNTI and resources for
transmission of the RRC Connection Request
~The message identifies the UE with the C-RNTI
~The message contains the UE-Identity
~IMSI is sent in the message if this is the first attach to the network
~If the terminal had attached previously, the S-TMSI is included in the
message
~The message also contains the establishment cause.
~In this example, the RRC Connection Request is sent with “Mobile
Originated Signaling“ cause.
~Note that the eNodeB may optionally send a contention resolution message
on receipt of this message
~RRC Connection Request contains UE ID/RNTI Type + RA-RNTI Value +
UE-Identity +Establishment Cause

3. ~UE ID/RNTI Type will contain RA-RNTI
~UE-Identity will contain S-TMSI
~Establishment Cause will contain mo-Signalling
~S-TMSI will contains MMEC & M-TMSI
~Establishment cause having 5 Types Emergency,High Priority Access,
mt-Access, mo-signalling, mo-data
RRC Connection Setup(DL-SCH,C-RNTI,SRB Identity,DL AM RLC,UL AM RLC,UL-SCH
Config,PHR Config,Uplink Power Control)(eNB-------->UE)
~eNodeB responds with an RRC Connection Setup message on the DL-SCH. The
message creates the signaling radio bearer (SRB) in Acknowledged mode. The
message also contains configuration parameters for uplink RLC, UL-SCH,
Power Head Room (PHR) and Uplink Power Control.
-(eNB--->UE)DL-SCH: RRC Connection Setup (SRBs, DRBs, UE Specific
Configuration) : Network establishes the SRBs and DRBs based on the
establishment cause.
~he message identifies the signaling radio bearer (SRB) ~The
configuration parameters carried in the message are described in the next two
slides
Attach and Authentication
-------------------------
RRC Connection Setup Complete + NAS Attach Request(UL-SCH,Selected PLMN
Identity,Old TAI,Old GUMMEI,Old GUTI,Selected PLMN Identity)(UE-------->eNB)
~The UE signals the setup of the RRC connection. The message is also used to
initiate the Attach procedure by sending the Attach Request as
NAS Payload. The attach message contains the old GUTI (Globally Unique
Temporary Identifier).
~Identify the MME from the Old GUMMEI (Globally Unique MME Identifier)
reported by the UE.
-(UE--->eNB)UL-SCH: RRC Connection Complete (PLMN id, Dedicated NAS Info): UE
acknowledges the setup of SRBs and DRBs.
~UE sends this message on receipt of the RRC Connection Setup message
~“Dedicated Info NAS“ is used to transfer UE specific NAS layer
information between the network and the UE. The RRC layer is transparent for
this information.
~The message may optionally contain registered MME
~The RRC Connection Setup Complete may also carry octets for a NAS message
exchanged between the UE and the MME
~RRC Connection Setup contains Selected PLMN Identity+Registered MME
(Optional)+Dedicated Info NAS
~Registered MME contains PLMN Id+MMEGI+MMEC
~Dedicated Info NAS contains Octets carrying NAS message
S1AP Initial UE Message [Attach Request + PDN Connectivity Request](id = eNB UE
S1AP ID,Tracking Area Id = TAI+Cell Id,EPS Attach Type = EPS Attach,Identity =
Old GUTI,EPS Encryption and Integrity Algorithms,Selected Network)
(UE-------->new MME)
~The Attach message is sent in the Initial UE message to the MME over the S1AP
interface. The "Attach Request" is embedded in the Initial UE Message. The
message also includes the PDN Connectivity Request message. The Tracking
Area Identify (TAI) and E-UTRAN Cell Global Identifier (ECGI) are also included.
Note that the eNodeB uses the eNB-UE-S1APID to uniquely identify the UE.
~Initial UE Message is the first message sent to the MME to establish a
connection
~The eNode uses the eNB-UE-S1AP-ID to uniquely identify the UE
~EPS attach type may be:
~EPS Attach: UE is attaching only to the 4G LTE network
~Combined EPS/IMSI Attach:
~The UE identity is specified is:
~IMSI: If the UE has is not registered with the network
~Old GUTI: Subsequent attach requests identify the UE with the Old GUTI

4. Identification Request [Attach Request] Old GUTI(new MME-------> old MME)
~Since the UE identified itself with GUTI and the MME has changed since
detach, the new MME uses the GUTI received from the UE to derive the old MME,
and send an Identification Request (old GUTI, complete Attach Request
message) to the old MME to request the IMSI.
Identification Response(old MME-------> new MME)
~The old MME responds with Identification Response (IMSI, unused EPS
Authentication Vectors, KSIASME, KASME)
Authentication Info Request(new MME-------> HSS)
~MME updates the UE location with the HSS
~Origin and Destination are specified as Host and Realm (domain)
~The user name in the request is set to IMSI
~The Radio Access Technology is specified in the RAT Type
~It will be set to EUTRAN for LTE access
~The Visited PLMN is also included in the message
Authentication Info Answer(HSS----------> new MME)
~The HSS accesses the database and responds with user information to the
MME
~The Aggregate Maximum Bit Rate (AMBR) occurs twice in the message:
~The first occurrence specifies the maximum bit rate for the default PDP
context
~The second occurrence specifies the data maximum data limit via the APN.
These limits are specified by the PDN
~APN configuration also includes:
~IP address of the PDN Gateway. This address is used to determine the
default route for the traffic towards the Internet
~IP address assigned to the UE (Served Party IP Address)
Ciphered Options Request(new MME---------->UE)
~Since the UE has set the Ciphered Options Transfer Flag in the Attach Request
message, the ciphered Options i.e. PCO or APN or both, shall now be retrieved
from the UE.
Ciphered Options Response(UE--------->new MME)
Update Location Request(Origin,Destination,User Name = IMSI,Visited PLMN Id)
(new MME-------->HSS)
~Since the MME has changed since the last detach, the MME sends an Update
Location Request message to the HSS. The MME capabilities indicate the MME's
support for regional access restrictions functionality. Update Type
indicates this is Attach procedure.
Cancel Location(IMSI,Cancellation Type)(HSS--------->old MME)
~The HSS sends Cancel Location to the old MME. The old MME acknowledges with
Cancel Location Ack and removes the MM and bearer contexts.
Cancel Location Ack(IMSI)(old MME--------->HSS)
Update Location Request Answer(IMSI,Aggregate MBR (DL and UL),MSISDN,APN = PDN
GW Address, QCI, Charging, Aggregate MBR (DL, UL))(HSS-------> new MME)
~The HSS acknowledges the Update Location message by sending an Update
Location Answer message to the new MME. The Subscription
Data contains PDN subscription contexts. Each PDN subscription context
contains an 'EPS subscribed QoS profile' and the subscribed
APN-AMBR . The new MME validates the UE's presence in the (new) TA. If all
checks are successful then the new MME constructs a context
for the UE.
Default Radio Bearer Setup
--------------------------

5. GTP Create Session Request(Sender F-TEID for Control
Plane,ARP,QCI,MSISDN,TAI,PGW IP Address,PDN IP Address,APN,IP Address Assigned
to UE)(new MME-------->SGW)
~MME initiates the default route establishment by asking the SGW to create a
GTP tunnel. The APN specified by the UE is used for default bearer activation.
The IP Address assigned to the UE is also included along with the downlink
and uplink maximum data rates allowed at the APN level.
Create a new entry in EPS Bearer table
Map from APN to PDN Gateway
~MME initiates the default route establishment by asking the SGW to create
a GTP tunnel
~The source is identified by the fully qualified endpoint identifier with
the Tunnel Endpoint Identifier (TEID) and the MME IP Address
~The IP Address assigned to the UE is also included along with the
downlink and uplink maximum data rates allowed at the APN level
~The TAI and ECGI (E-UTRAN Cell Group Identifier) information identify the
current location of the user
Create Default Bearer Request(IMSI,MSISDN,APN,Serving GW Address)(SGW-------
>PGW)
~Serving Gateway sends Create Default Bearer Request message to the PDN GW.
Create a new entry in its EPS bearer context table and generates a Charging
Id
The new entry allows the P GW to route user plane PDUs between the SGW and
the packet data network, and to start charging.
Create Default Bearer Request(PDN GW User Plane address,PDN GW TEIDs User and
Control Plane,EPS Bearer Identity and QoS)(PGW------>SGW)
Downlink Data
~Serving Gateway receives the first downlink data block. This block is
buffered at the Serving GW".
Create Default Bearer Request(SGW---------->new MME)
Initial Context Setup Request [Attach Accept, Activate Default Bearer Request]
(new MME-------->eNB)
~MME responds back to the eNodeB with a message containing three messages:
SIAP Initial Context Setup Request, NAS Attach Accept and Activate Default
Bearer Request.
~The message is identified by the S1AP id that was sent in the initial UE
message. The message contains maximum bit rate information for the
UE.Quality of service information for the new eRAB is also specified (QCI,
maximum bit rate downlink and uplink). The information received
in this message will be used to setup radio resources for the eNodeB.
~The message is extracted from the NAS payload of the Initial Context Setup
Request message. It signals the successful completion of attach.
The message contains the GUTI and the TAI list. This message will be sent to
the NAS layer on the UE.
~The message is extracted from the NAS payload of the Initial Context Setup
Request message. The message contains quality of service information for the
default RAB. The Access Point Name (APN) and PDN Address are also included.
This message will be sent to the NAS layer on the UE.
~The next message from the MME is really a three-in-one. The message
contains:
~SIAP Initial Context Setup Request
~A request to establish a context between the MME and eNodeB
~The message contains SGW tunneling information
~NAS Attach Accept
~This message acknowledges the successful Attach to the UE.
~The eNodeB will pass this message to the UE
~Activate Default Bearer Request
~The message initiates the default bearer setup on the UE

6. ~The eNodeB will pass this message to the UE
RRC Connection Reconfiguration [Attach Accept](EPS Radio Bearer Identity,RLC
Mode,PDCP Sequence Number)(eNB-------->UE)
~The RRC Connection Reconfiguration message is sent to activate the default
radio bearer. The message also carries the Attach Accept message as NAS Payload.
RRC Connection Reconfiguration Complete(UE------->eNB)
~UE replies back to the eNodeB.
Initial Context Setup Response(eNB---------->new MME)
~The eNodeB sends the Initial Context Response message to the new MME. This
Initial Context Response message includes the TEID of the eNodeB and the address
of the eNodeB used for downlink traffic on the S1_U reference point.
Direct Transfer [Attach Complete](UE--------->eNB)
~The UE sends a Direct Transfer message to the eNodeB, which includes the
Attach Complete (EPS Bearer Identity, NAS sequence number, NAS-MAC) message.
Attach Complete(eNB---------->MME)
Uplink Data(UE------------>PGW)
Update Bearer Request(EPS Bearer Identity,eNodeB address,eNodeB TEID)(new
MME------>SGW)
~Upon reception of both, the Initial Context Response message and the Attach
Complete message, the new MME sends an Update Bearer Request message to the
Serving GW.
Update Bearer Response [EPS Bearer Identity] (SGW---------> new MME)
~The Serving GW acknowledges by sending Update Bearer Response message to the
new MME. The Serving GW can then send its buffered downlink packets.
Downlink data(SGW-------->UE)
~Buffered downlink data is forwarded to the UE.