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This document provides an overview of the key components and protocols in 3G and 4G mobile networks. It includes a high-level diagram of the overall 4G architecture and summaries of protocols like S1, X2, NAS, RRC. Key concepts covered include the PDCP, RLC, MAC and PHY layers, QoS classes, paging, attachment, handover procedures between eNodeBs and between 4G and 3G networks.
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Lte protocols
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- 2. Overall Architecture PCRFX2-UP S1-UP EP C S1-CP E-UTRAN S11 MME S-GW P-GW S5/S8 X2-CP P-CSCF S7/Gx Network & Service management OSS-RC EMA MM DNS/ENUM HSS S-CSCF I-CSCF IMS Control layer Platforms / Concepts TSP/NSP or TSP/IS DNS/ ENUM MGC MGW SUN IS A-SBG CPP / RBS6000 Juniper/Redback WPP GERAN UTRAN Broadband Wired Access GPRS Packet Core SGSN GGSN CDMA2000 HRPD (EV-DO) WLAN N-SBG Internet S6a CS Core MSC GWMSC PSTN PDSN S1-AP, X2-AP H.248 ISUP Diameter S3 S4 GTP-C Gxa S103 S2a RNC Other SIP/UDP or SIP/TCP Rx+ User data RTP/UDP GTP/UDP S101 IMS Connectivity layer Service Layer AS AS AS Application Servers MTAS S6d Uu eNodeB eNodeB
- 3. UE Protocol StackROHC/ Ciphering TM AM UM Physical Layer L2 PDCP RLC MAC RRC NAS Integrity/ Ciphering System Info Aquisition Cell Selection Paging Reception Mobility Management Session Management Connected Mode Mobility NAS Security IP Application AS Security RRC Connection RB Managementv Measurement Reporting Control/Report SAPs RA Control HARQ Control
- 4. Protocol interaction Segmentation,ARQ Ciphering Header Compr. Hybrid ARQ Hybrid ARQ MAC multiplexing Antenna and resrouce mapping Coding + RM Data modulation Antenna and resource mapping Coding Modulation Antenna and resource assignment Modulation scheme MAC scheduler Retransmission control Priority handling, payload selection Payload selection RLC # i PHY PDCP # i User #i User # j MAC Concatenation, ARQ Deciphering Header Compr. Hybrid ARQ Hybrid ARQ MAC demultiplexing Antenna and resrouce mapping Coding + RM Data modulation Antenna and resource demapping Decoding Demodulation RLC PHY PDCP MAC eNodeB UE Redundancy version IP packet IP packet EPS bearers E-UTRA Radio Bearers Logical Channels Transport Channels Physical Channels
- 5. Channel mapping UL-SCHDL-SCH Logical Channels “ type of information” (traffic/control) Transport Channels “ how and with what characteristics” (common/shared/mc/bc) Downlink Uplink Physical Channels “ bits, symbols, modulation, radio frames etc” MCH BCH -CQI -ACK/NACK -Sched req. -Sched TF DL -Sched grant UL -Pwr Ctrl cmd -HARQ info MIB SIB ACK/NACK PDCCH info Physical Signals “ only L1 info” -meas for DL sched -meas for mobility -coherent demod -half frame sync -cell id -frame sync -cell id group -coherent demod -measurements for UL scheduling PCH PCCH PDSCH MTCH MCCH BCCH DTCH DCCH DTCH DCCH CCCH PRACH RACH CCCH PUSCH PBCH PCFICH PUCCH PMCH PHICH PDCCH RS SRS P-SCH S-SCH RS
- 6. QCI Characteristics TS 23.203 p2p file sharing, progressive video, etc. 9 9 TCP-based (e.g., www, e-mail, chat, ftp, 8 8 Video (Buffered Streaming) 10 -6 300 ms 6 7 Interactive Gaming Video (Live Streaming) Voice, 10 -3 100 ms 7 Non-GBR 6 IMS Signalling 10 -6 100 ms 1 5 Real Time Gaming 10 -3 50 ms 3 4 Non-Conversational Video (Buffered Streaming) 10 -6 300 ms 5 3 Conversational Video (Live Streaming) 10 -3 150 ms 4 2 Conversational Voice 10 -2 100 ms 2 GBR 1 Example Services Packet Error Loss Rate Packet Delay Budget Priority Resource Type QCI p2p file sharing, progressive video, etc. 9 9 TCP-based (e.g., www, e-mail, chat, ftp, 8 8 Video (Buffered Streaming) 10 -6 300 ms 6 7 Interactive Gaming Video (Live Streaming) Voice, 10 -3 100 ms 7 Non-GBR 6 IMS Signalling 10 -6 100 ms 1 5 Real Time Gaming 10 -3 50 ms 3 4 Non-Conversational Video (Buffered Streaming) 10 -6 300 ms 5 3 Conversational Video (Live Streaming) 10 -3 150 ms 4 2 Conversational Voice 10 -2 100 ms 2 GBR 1 Example Services Packet Error Loss Rate Packet Delay Budget Priority Resource Type QCI
- 7. CN Initiated PagingTAC 1 S1AP Paging message RRC Paging message TAC 2 The MME sends the PAGING message to each eNode B with cells belonging to the tracking area(s) in which the UE is registered. Each eNode B can contain cells belonging to different tracking areas, whereas each cell can only belong to one TA. UEs use DRx when in idle mode in order to wake at regular intervals to check for paging messages. The paging response back to the MME is initiated on NAS layer and is sent by the eNB based on NAS-level routing information. MME
- 8. UE Attach MME7. INITIAL UE MESSAGE (Attach Request) 14. INITIAL CONTEXT SETUP REQUEST (EPS bearers, Attach Accept, Security) 22. INITIAL CONTEXT SETUP RESPONSE (EPS bearers) 1. System Information * 4. RRC CONNECTION REQUEST 5. RRC CONNECTION SETUP 15. RRC SECURITY MODE COMMAND 16.RRC SECURITY MODE COMPLETE 6. RRC CONNECTION SETUP COMPLETE (Attach Request) 2. Random Access Preamble 3. Random Access Response 20. RRC CONNECTION RECONFIGURATION (Bearer Setup) 21. RRC CONNECTION RECONFIGURATION COMPLETE 10.RRC DL INFORMATION TRANSFER (Authentication Request) 11. RRC UL INFORMATION TRANSFER (Authentication Response) DL NAS TRANSFER (Authentication) UL NAS TRANSFER (Auth. Response) 12. RRC DL INFORMATION TRANSFER (Security Mode Command) 13. RRC UL INFORMATION TRANSFER (Security Mode Complete) DL NAS TRANSFER (NAS SMC) UL NAS TRANSFER (NAS SMC) Cell Select * 23. RRC UL INFORMATION TRANSFER (Attach Complete)) UL NAS TRANSFER (Attach Complete) RRC IDLE RRC IDLE 8.RRC DL INFORMATION TRANSFER (UE Identity Request) 9. RRC UL INFORMATION TRANSFER (UE Identity Response) DL NAS TRANSFER (UE Identity Req) UL NAS TRANSFER (UEid Response) 17. RRC UE CAPABILITY ENQUIRY 18. RRC UE CAPABILITY iNFORMATION 19. UE CAPABILITY INFO INDICATION (UE Radio Capability) 24. UE CONTEXT RELEASE COMMAND 26. RRC CONNECTION RELEASE 25. UE CONTEXT RELEASE COMPLETE
- 9. Connection Reactivation OptionalMME 7. INITIAL UE MESSAGE (Service Request) 12. INITIAL CONTEXT SETUP REQUEST (EPS bearers, Security, UECap Request) 20. INITIAL CONTEXT SETUP RESPONSE (EPS bearers) 1. System Information * 4. RRC CONNECTION REQUEST 5. RRC CONNECTION SETUP 13. RRC SECURITY MODE COMMAND 14.RRC SECURITY MODE COMPLETE 6. RRC CONNECTION SETUP COMPLETE (Service Request) 2. Random Access Preamble 3. Random Access Response 18. RRC CONNECTION RECONFIGURATION (Bearer Setup,Measurement conf)) 19. RRC CONNECTION RECONFIGURATION COMPLETE 8.RRC DL INFORMATION TRANSFER (Authentication Request) 9. RRC UL INFORMATION TRANSFER (Authentication Response) DL NAS TRANSFER (Authentication) UL NAS TRANSFER (Auth. Response) 10. RRC DL INFORMATION TRANSFER (Security Mode Command) 11. RRC UL INFORMATION TRANSFER (Security Mode Complete) DL NAS TRANSFER (NAS SMC) UL NAS TRANSFER (NAS SMC) Cell Select * Optional 15. RRC UE CAPABILITY ENQUIRY 16. RRC UE CAPABILITY iNFORMATION 17. UE CAPABILITY INFO INDICATION (UE Radio Capability) RRC IDLE RRC CONNECTED Optional
- 10. Data flow inDL PDCP SDU Higher Layer Payload header H PDCP (Header Compression & Ciphering) PDCP header Higher Layer PDU Radio Bearer 1 RLC SDU MAC (multiplexing) MAC SDU CRC PHY Transport Block MAC header Higher Layer Payload header Higher Layer Payload header Higher Layer PDU Radio Bearer 1 Higher Layer PDU Radio Bearer 2 H H PDCP SDU PDCP header PDCP SDU PDCP header RLC header RLC header RLC SDU RLC header RLC SDU MAC SDU MAC header CRC Transport Block RLC PDU RLC PDU RLC PDU MAC PDU MAC PDU RLC (segmentation & concatenation) PDCP SDU Higher Layer Payload header H PDCP (Header Compression & Ciphering) PDCP header Higher Layer PDU Radio Bearer 1 RLC SDU MAC (multiplexing) MAC SDU CRC PHY Transport Block MAC header Higher Layer Payload header Higher Layer Payload header Higher Layer PDU Radio Bearer 1 Higher Layer PDU Radio Bearer 2 H H PDCP SDU PDCP header PDCP SDU PDCP header RLC header RLC header RLC SDU RLC header RLC SDU MAC SDU MAC header CRC Transport Block RLC PDU RLC PDU RLC PDU MAC PDU MAC PDU RLC (segmentation & concatenation)
- 11. X2 Handover MMERRC CONNECTED S-GW Source eNB Target eNB 1. RRC CONNECTION RECONFIGURATION (Bearer Setup,Measurement conf)) 2. RRC Measurement Report (Event A3) 3. HO Decision 4. X2 HANDOVER REQUEST 5.Admission Control 6. X2 HANDOVER REQUEST ACKNOWLEDGE 10. RRC CONNECTION RECONFIGURATION (Handover Command,Measurement conf) 7. X2 SN STATUS TRANSFER 8. Start Data forwarding 9. Buffer Forwarded Data 11 MAC: CFRA Random Access Preamble 12. MAC Random Access Response (UL allocation + TA) 13. RRC CONNECTION RECONFIGURATION COMPLETE (Handover Complete) 15. S1 PATH SWITCH REQUEST 16. S5 USER PLANE UPDATE REQ 18. S5 USER PLANE UPDATE RSPONSE 19. S1 PATH SWITCH RESPONSE 20. X2 UE CONTEXT RELEASE RRC CONNECTED 14.Data Transfer in Target 21. Forward if any Data in transition and release T304 TRELOCprep Regenerate Security Keys 17.Data Transfer in Target
- 12. S1 Handover RRC CONNECTED S-GW Source eNB Target eNB 1. RRC CONNECTION RECONFIGURATION (Bearer Setup,Measurement conf)) 2. RRC Measurement Report (Event A3) 3. HO Decision 4. S1 HANDOVER REQIRED ( Source to Target Transparent Container ) 8. Admission Control 9. S1 HANDOVER REQUEST ACKNOWLEDGE 12. RRC CONNECTION RECONFIGURATION (Handover Command,Measurement conf) 13 MAC: CFRA Random Access Preamble 14. MAC Random Access Response (UL allocation + TA) 15. RRC CONNECTION RECONFIGURATION COMPLETE (Handover Confirm) RRC CONNECTED T304 TS1RELOCprep Regenerate Security Keys 17.Data Transfer in Target MME MME S-GW Target Target 5. S10 FORWARD RELOCATION REQUEST 6. S11 CREATE BEARER REQ/RES 7. S1 HANDOVER REQUEST 10. S10 FORWARD RELOCATION RESPONSE 12. S1 HANDOVER COMMAND 18.S10 FORWARD RELOCATION COMPLETE/ ACK Source Source 19. S1 UE CONTEXT RELEASE COMMAND (Cause: Successful Handover ) UP Forwarding Source eNB Target eNB Source Source eNB Target eNB Target Source Source eNB Target eNB Source Target Source Source eNB Target eNB Target Source Target Source Source eNB Target eNB 11. S11 CREATE BEARER REQ/RES 16. S1 HANDOVER NOTIFY
- 13. LTE to 3GHandover RNC MME source S - GW PDN - GW target S - GW 1 1. Handover Required 2. Forward Relocation Request 3. Create PDP Context Request 4. Create PDP Context Response 5. Relocation Request 6. Relocation Request Ack 7. Update PDP Context Request 8. Update PDP Context Response 9. Forward Relocation Response 10. Create Bearer Request 11. Create Bearer Response 12. HO Command 13. HO from E - UTRAN Command 14. HO to UTRAN Complete 15. Relocation Complete 16. Forward Relocation Complete 17. Forward Relocation Complete Ack 18. Update PDP Context Request 19. Update Bearer Request 20. Update Bearer Response 21. Update PDP Context Response 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 SGSN SGSN RNC MME SGSN
- 14. LTE to 3GCell-reselection RNC MME PDN - GW S - GW 1a. Routing Area Update Request 1b. Routing Area Update Request 2. Context Request 3. Context Response 4. Context Acknowledge 5. Update Bearer Request 6. Update Bearer Request 7. Update Bearer Response 8. Update Bearer Response 9. Routing Area Update Accept 10. Routing Area Update Complete 2 1b 3 1a 6 7 4 5 8 9 10 SGSN SGSN RNC MME SGSN
Editor's Notes
- #7 The EPS bearer QoS profile includes the parameters QCI, ARP, GBR and MBR. Each EPS bearer (GBR and Non-GBR) is associated with the following bearer level QoS parameters: - QoS Class Identifier (QCI); - Allocation and Retention Priority (ARP) (NOTE: not supported in first release). A QCI is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.), and that have been pre-configured by the operator owning the access node (e.g. eNodeB) The ARP shall contain information about the priority level (scalar), the pre-emption capability (flag) and the pre-emption vulnerability (flag). The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected in case of resource limitations (typically available radio capacity in case of GBR bearers). The priority level information of the ARP is used for this decision to ensure that the request of the bearer with the higher priority level is preferred. In addition, the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during exceptional resource limitations (e.g. at handover). The pre-emption capability information of the ARP defines whether a bearer with a lower ARP priority level should be dropped to free up the required resources. The pre-emption vulnerability information of the ARP defines whether a bearer is applicable for such dropping by a pre-emption capable bearer with a higher ARP priority value. Once successfully established, a bearer's ARP shall not have any impact on the bearer level packet forwarding treatment (e.g. scheduling and rate control). Such packet forwarding treatment should be solely determined by the other EPS bearer QoS parameters: QCI, GBR and MBR, and by the AMBR parameters. The ARP is not included within the EPS QoS Profile sent to the UE. NOTE 2: The ARP should be understood as "Priority of Allocation and Retention"; not as "Allocation, Retention, and Priority". NOTE 3: Video telephony is one use case where it may be beneficial to use EPS bearers with different ARP values for the same UE. In this use case an operator could map voice to one bearer with a higher ARP, and video to another bearer with a lower ARP. In a congestion situation (e.g. cell edge) the eNB can then drop the "video bearer" without affecting the "voice bearer". This would improve service continuity. NOTE 4: The ARP may also be used to free up capacity in exceptional situations, e.g. a disaster situation. In such a case the eNB may drop bearers with a lower ARP priority level to free up capacity if the pre-emption vulnerability information allows this. Each GBR bearer is additionally associated with the following bearer level QoS parameters: - Guaranteed Bit Rate (GBR); - Maximum Bit Rate (MBR). The GBR denotes the bit rate that can be expected to be provided by a GBR bearer. The MBR limits the bit rate that can be expected to be provided by a GBR bearer (e.g. excess traffic may get discarded by a rate shaping function). See clause 4.7.4 for further details on GBR and MBR. Each APN access, by a UE, is associated with the following QoS parameter: - per APN Aggregate Maximum Bit Rate (APN-AMBR). The APN‑AMBR is a subscription parameter stored per APN in the HSS. It limits the aggregate bit rate that can be expected to be provided across all Non‑GBR bearers and across all PDN connections of the same APN (e.g. excess traffic may get discarded by a rate shaping function). Each of those Non‑GBR bearers could potentially utilize the entire APN‑AMBR, e.g. when the other Non‑GBR bearers do not carry any traffic. GBR bearers are outside the scope of APN‑AMBR. The P‑GW enforces the APN‑AMBR in downlink. Enforcement of APN‑AMBR in uplink is done in the UE and additionally in the P‑GW. NOTE 5: All simultaneous active PDN connections of a UE that are associated with the same APN shall be provided by the same PDN GW (see clauses 4.3.8.1 and 5.10.1). Each UE in state EMM-REGISTERED is associated with the following bearer aggregate level QoS parameter: - per UE Aggregate Maximum Bit Rate (UE-AMBR). The UE‑AMBR is limited by a subscription parameter stored in the HSS. The MME shall set the UE‑AMBR to the sum of the APN‑AMBR of all active APNs up to the value of the subscribed UE‑AMBR. The UE‑AMBR limits the aggregate bit rate that can be expected to be provided across all Non‑GBR bearers of a UE (e.g. excess traffic may get discarded by a rate shaping function). Each of those Non‑GBR bearers could potentially utilize the entire UE‑AMBR, e.g. when the other Non‑GBR bearers do not carry any traffic. GBR bearers are outside the scope of UE AMBR. The E‑UTRAN enforces the UE‑AMBR in uplink and downlink. The GBR and MBR denote bit rates of traffic per bearer while UE-AMBR/APN-AMBR denote bit rates of traffic per group of bearers. Each of those QoS parameters has an uplink and a downlink component. On S1_MME the values of the GBR, MBR, and AMBR refer to the bit stream excluding the GTP-U/IP header overhead of the tunnel on S1_U Each Service Data Flow (SDF) is associated with one and only one QoS Class Identifier (QCI). The QCI is scalar that is used as a reference to node specific parameters that control packet forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.) and that have been pre-configured by the operator owning the node (e.g. eNodeB). Standardized QCI values describe the packet forwarding treatment that an SDF receives edge-to-edge between the UE and the PCEF in terms of the following performance characteristics: 1 Resource Type (GBR or Non-GBR); 2 Priority; 3 Packet Delay Budget; 4 Packet Error Loss Rate. The Resource Type determines if dedicated network resources related to a service or bearer level Guaranteed Bit Rate (GBR) value are permanently allocated (e.g. by an admission control function in a radio base station). GBR SDF aggregates are therefore typically authorized "on demand" which requires dynamic policy and charging control. The Packet Delay Budget (PDB) defines an upper bound for the time that a packet may be delayed between the UE and the PCEF. For a certain QCI the value of the PDB is the same in uplink and downlink. The purpose of the PDB is to support the configuration of scheduling and link layer functions (e.g. the setting of scheduling priority weights and HARQ target operating points). The PDB shall be interpreted as a maximum delay with a confidence level of 98 percent. Services using a Non-GBR QCI should be prepared to experience congestion related packet drops, and 98 percent of the packets that have not been dropped due to congestion should not experience a delay exceeding the QCI's PDB. This may for example occur during traffic load peaks or when the UE becomes coverage limited. Services using a GBR QCI and sending at a rate smaller than or equal to GBR can in general assume that congestion related packet drops will not occur, and 98 percent of the packets shall not experience a delay exceeding the QCI's PDB. Exceptions (e.g. transient link outages) can always occur in a radio access system which may then lead to congestion related packet drops even for services using a GBR QCI and sending at a rate smaller than or equal to GBR. Packets that have not been dropped due to congestion may still be subject to non congestion related packet losses (see PELR below). Every QCI (GBR and Non-GBR) is associated with a Priority level . Priority level 1 is the highest Priority level. The Priority levels shall be used to differentiate between SDF aggregates of the same UE, and it shall also be used to differentiate between SDF aggregates from different UEs. Via its QCI an SDF aggregate is associated with a Priority level and a PDB. Scheduling between different SDF aggregates shall primarily be based on the PDB. If the target set by the PDB can no longer be met for one or more SDF aggregate(s) across all UEs that have sufficient radio channel quality then Priority shall be used as follows: in this case a scheduler shall meet the PDB of SDF aggregates on Priority level N in preference to meeting the PDB of SDF aggregates on Priority level N+1. The Packet Error Loss Rate (PELR) defines an upper bound for the rate of SDUs (e.g. IP packets) that have been processed by the sender of a link layer protocol (e.g. RLC in E‑UTRAN) but that are not successfully delivered by the corresponding receiver to the upper layer (e.g. PDCP in E‑UTRAN). Thus, the PELR defines an upper bound for a rate of non congestion related packet losses. The purpose of the PELR is to allow for appropriate link layer protocol configurations (e.g. RLC and HARQ in E‑UTRAN). For a certain QCI the value of the PELR is the same in uplink and downlink. NOTE 4: The characteristics PDB and PELR are specified only based on application / service level requirements, i.e., those characteristics should be regarded as being access agnostic, independent from the roaming scenario (roaming or non-roaming), and independent from operator policies.
- #8 Explain TRacking Area Concept!!!!!