23. LTE- operator benefit:
• Higher Data Rates (DL: ~300Mbps, UL:
~75Mbps).
• Low Latency as number of nodes are
reduced.
• Spectral Efficiency due to use of OFDMA
• Cost Effective Network in long term
• Better user experience.
25. MME:
• Selection of SGW and PDN Gateway
• Triggering and enabling Authentication
• Saving the subscriber profile to HSS
• Idle mobility Management
• Default Bearer Setup
Serving Gateway:
• Manages UP between Inter eNB HO and Inter-
RAT HO
• UP/Bearer path of a UE is managed by SGW.
26. PDN Gateway:
• Allocates IP address to UE
• Policy enforcement like QoS and traffic packet
rules/filtering.
HSS:
• Authorization of Users
• User database contains subscription related
information of users. It is like HLR in legacy
networks.
28. Interfaces:
LTE-Uu: UE<->eNB
• Air-interface is named as LTE-Uu
• DL: OFDMA, UL: SC-FDMA
S1-MME or S1-AP: MME<->eNB
• It is the control plane interface where all
signalling is carried out
29. S1-U: SGW<->eNB
• It is the user plane interface.
• Handles Inter eNB user plane path switching
during HO.
S5: SGW<->PDN Gateway
• It is the user plane interface.
• Handles Inter eNB user plane path switching
during HO.
30. S11: SGW<->MME
• Used for control information between MME
and Signalling Gateway
S4: SGW<->SGSN
• Used for user plane information exchange for
Inter-RAT scenario.
S3: MME<->SGSN
• Used for control plane information exchange
for Inter-RAT scenario.
31. S6a: HSS<->MME
• Based on Authentication, Authorization and
Accounting(AAA) protocol.
• Used to exchange subscriber information
between MME and HSS.
X2: eNB<->eNB
• Interface between two eNBs
83. Bibliography
• LTE PPT - Amit Kumar (Aricent-Vodafone MTS
Radio)
• LTE: User Identifiers - IMSI and GUTI
(www.netmanias.com)
• EM Spectrum -
http://www2.lbl.gov/MicroWorlds/ALSTool/E
MSpec/EMSpec2.html
84. Additional reference
For signalling and other material on CSFB refer:
• http://3g4g.blogspot.co.uk
• http://lteinwireless.blogspot.co.uk
• http://wired-n-wireless.blogspot.co.uk
• http://lteworld.org/blog/
• http://3g4g.blogspot.co.uk/2013/01/lte-epc-signalling-training-
from.html
• www.google.com
http://emfguide.itu.int/emfguide.html
FM bands
WiFi bands
Cellular bands
Channel or Lane
TV
Walkie Talkie
Cellular/cell phone
https://www.soneticscorp.com/technology/dect-vs-two-way-radios/
PDCCH Carries both DL and UL allocation information.
This information is encoded on the PDCCH using DCI( DL Control Information) elements.
DCI( DL Control Information) element carries both DL and UL allocation information for a UE.
DCI format varies depending upon the allocation is carried for DL or UL and how eNB is allocating resources.
DCI includes: No. of Resource blocks used, Modulation scheme used and MIMO status(for DL only), C-RNTI/SI-RNTI/RA-RNTI etc.( to identify UE).
Primary Sync Signal(PSS): Carries 3 unique code to identify beginning of a slot.
Secondary Sync Signal(SSS): Carries 2 binary sequences to identify beginning of a frame.
Total 504 possible unique code sequences are possible.
3 possible code sequences are for PSS.
168 possible codes sequences are for SSS.
Timing Adjustment: It is done to avoid UE collision in the uplink channel.
It is calculated by comparing the symbol arrival time of other UEs.
LTE controls and is responsible for setup of EPS bearer.
External bearer works on standard IP QoS concept.
MSISDN
Max 50 users can receive data at a time in a frame.
DRBs are created when data session is to be started.
SRB2 is used for all the NAS messages once established, SRB1 will not be used for NAS messages then.
NAS messages can also be piggybacked(attached) with RRC messages.
e.g. While sending RRC Connection Setup Complete, UE can piggyback NAS Attach Request and NAS PDN Activation Request message into it.
SIB1 and SIB2 are most important others are optional.
Contains cell access information and SIB schedules
Contains common channel configuration parameters
After successful RRC connection setup, UE will be in RRC Connected mode.
It leads to setting up S1-MME bearer.
Authentication:
HSS sends AUTN(Authentication Key), RAND(random key) and XRES(expected response from UE) to MME.
UE responds with RES in the Authentication Response.
MME compares RES with XRES, if they are same then UE is authenticated.
NAS Security:
1. MME selects the integration and encryption algorithm to be used.
2. Integrity procedure starts at the MME with transmission of NAS Security Mode Command.
3. Integrity and encryption procedure starts at UE with transmission of NAS Security Mode Complete.
4. Integrity and encryption procedure starts at MME after reception of NAS Security Mode Complete.
5. RRC Messages are explicitly used for NAS message transfer. In this procedure, NAS messages are not piggybacked with RRC messages.
RRC Security Procedure/AS(Access Stratum) Security.
After this procedure, Attach is assumed to be complete.
Next step is to activate PDN for data transfer.
PDN Activation for Data session or Default Radio Bearer Setup:
UE already had sent PDN Activation Request piggybacked with RRC Connection Setup Complete, so after both NAS and AS Security is successful, MME selects the default APN configured for that UE from HSS and initiates PDN Activation process. This is the Default EPS Bearer configured for the UE.
MME also selects the S-GW and P-GW.
P-GW allocates IP address to the UE.
If the new Dedicated Bearer is GBR then eNB will apply admission control.
eNB piggyback NAS Activate Dedicate Bearer Context Request message to be used for dedicated bearer in the RRC Connection Reconfiguration message.
UE also does the same.
Traffic Flow Template: It is used to map IP packets to bearers.
The TFT incorporates from one to eight packet filters;
a unique packet filter identifier identifies each filter. Filtering can be based on one or more of the following filter attributes:
• Source address (with subnet mask)
• IPv4 protocol number
• Destination port range
• Source port range
• IPSec Security Parameter Index (SPI)
• Type of Service (TOS) (IPv4)
UE starts sending data on PUSCH after 4ms of the frame carrying UL Grant on PDCCH.
MME does not remove Control/User plane for following interfaces:
S11-Control Plane between MME <-> S-GW
S5-Control/User plane between S-GW <-> P-GW
MME also maintains UE context.
The reason for keeping it is in case some data from PDN comes for the UE then it will be buffered at S-GW.
After a threshold, S-GW will initiate connection towards UE via MME.
MME uses paging in this case.
UE sends current GUTI, old and new TAI, defined but dormant EPS bearers and security parameters.
MME will match the EPS bearer list sent by UE with the one defined in HSS.
In case of discrepancy, MME tear down all the EPS bearers that are not active in the UE.
If T3450 expires then UE can release the RRC connection and return to RRC IDLE state.
MME will start timer after sending paging and will stop it when Paging response is received.
UE will send old KSI(Key Set Identifier for Authentication) and last NAS Message sequence number.
Explanation:
1. The source eNB configures the UE measurement procedures according to the area restriction information. UE sends MEASUREMENT REPORT by the rules set by i.e. system information, specification etc.
2. Source eNB makes decision based on MEASUREMENT REPORT and RRM information to hand off UE and issues a HANDOVER REQUEST message to the target eNB passing necessary information to prepare the HO at the target side.
3. Admission Control may be performed by the target eNB dependent on the received E-RAB QoS information to increase the likelihood of a successful HO. The target eNB configures the required resources according to the received E-RAB QoS information.
4. Target eNB prepares HO with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB. The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE as an RRC message to perform the handover.
5. The UE receives the RRCConnectionReconfiguration message with necessary parameters (i.e. new C-RNTI, target eNB security algorithm identifiers, and optionally dedicated RACH preamble, target eNB SIBs, etc.) and is commanded by the source eNB to perform the HO.
6. The source eNB sends the SN STATUS TRANSFER message to the target eNB to convey the uplink PDCP SN receiver status and the downlink PDCP SN transmitter status of E-RABs for which PDCP status preservation applies (i.e. for RLC AM).
7. After receiving the RRCConnectionReconfiguration message including the mobilityControlInformation , UE performs synchronisation to target eNB and accesses the target cell via RACH.
8. The target eNB responds with UL allocation and timing advance.
9. UE sends the RRCConnectionReconfigurationComplete message (C-RNTI) to confirm the handover to the target eNB to indicate that the handover procedure is completed for the UE. The target eNB verifies the C-RNTI sent in the RRCConnectionReconfigurationComplete message. 10. The target eNB can now begin sending data to the UE.
11. The target eNB sends a PATH SWITCH message to MME to inform that the UE has changed cell.
12. The MME sends an UPDATE USER PLANE REQUEST message to the Serving Gateway.
13. The Serving Gateway switches the downlink data path to the target side. The Serving gateway sends one or more "end marker" packets on the old path to the source eNB and then can release any U-plane/TNL resources towards the source eNB.
14. Serving Gateway sends an UPDATE USER PLANE RESPONSE message to MME.
15. The MME confirms the PATH SWITCH message with the PATH SWITCH ACKNOWLEDGE message.
16. By sending UE CONTEXT RELEASE, the target eNB informs success of HO to source eNB and triggers the release of resources by the source eNB. The target eNB sends this message after the PATH SWITCH ACKNOWLEDGE message is received from the MME.
17. Upon reception of the UE CONTEXT RELEASE message, the source eNB can release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue.
Explanation:
1. The source eNB configures the UE measurement procedures according to the area restriction information. UE sends MEASUREMENT REPORT by the rules set by i.e. system information, specification etc.
2. Source eNB makes decision based on MEASUREMENT REPORT and RRM information to hand off UE and issues a HANDOVER REQUEST message to the target eNB passing necessary information to prepare the HO at the target side.
3. Admission Control may be performed by the target eNB dependent on the received E-RAB QoS information to increase the likelihood of a successful HO. The target eNB configures the required resources according to the received E-RAB QoS information.
4. Target eNB prepares HO with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source eNB. The HANDOVER REQUEST ACKNOWLEDGE message includes a transparent container to be sent to the UE as an RRC message to perform the handover.
5. The UE receives the RRCConnectionReconfiguration message with necessary parameters (i.e. new C-RNTI, target eNB security algorithm identifiers, and optionally dedicated RACH preamble, target eNB SIBs, etc.) and is commanded by the source eNB to perform the HO.
6. The source eNB sends the SN STATUS TRANSFER message to the target eNB to convey the uplink PDCP SN receiver status and the downlink PDCP SN transmitter status of E-RABs for which PDCP status preservation applies (i.e. for RLC AM).
7. After receiving the RRCConnectionReconfiguration message including the mobilityControlInformation , UE performs synchronisation to target eNB and accesses the target cell via RACH.
8. The target eNB responds with UL allocation and timing advance.
9. UE sends the RRCConnectionReconfigurationComplete message (C-RNTI) to confirm the handover to the target eNB to indicate that the handover procedure is completed for the UE. The target eNB verifies the C-RNTI sent in the RRCConnectionReconfigurationComplete message. 10. The target eNB can now begin sending data to the UE.
11. The target eNB sends a PATH SWITCH message to MME to inform that the UE has changed cell.
12. The MME sends an UPDATE USER PLANE REQUEST message to the Serving Gateway.
13. The Serving Gateway switches the downlink data path to the target side. The Serving gateway sends one or more "end marker" packets on the old path to the source eNB and then can release any U-plane/TNL resources towards the source eNB.
14. Serving Gateway sends an UPDATE USER PLANE RESPONSE message to MME.
15. The MME confirms the PATH SWITCH message with the PATH SWITCH ACKNOWLEDGE message.
16. By sending UE CONTEXT RELEASE, the target eNB informs success of HO to source eNB and triggers the release of resources by the source eNB. The target eNB sends this message after the PATH SWITCH ACKNOWLEDGE message is received from the MME.
17. Upon reception of the UE CONTEXT RELEASE message, the source eNB can release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue.
