Packet core fundamentals: From 2G/3G PS to 4G EPC

Explore the evolved packet core (Epyc) of 4G networks, its role as the gateway to IMS, and how LTE evolved from GSM/UMTS to an IP-based architecture using OFDMA.

Trace the evolution of 3gpp standards from 2g to 4g, outlining the shift from circuit switching cores to the evolved packet core and all-ip 4g networks.

Trace the evolution from gsm to lte, noting gsm's voice, sms, and data services, cs and ps in umts, and lte's packet switching for data and voice over ip.

Trace the evolution from 2G to 4G by examining access networks—GSM radio access network, UMTS terrestrial radio access network, and E-UTRAN—and core networks from CS/PS to EPC and IMS.

Explain the e-utran architecture of 4G LTE, detailing eNodeB, Uu, X2 and S1 interfaces, and how eNodeB connects to the EPC, and handles handover, self-organizing networks, resource management, and encryption.

Explore the evolved packet core (epc) in LTE, detailing the MME, home subscription server, SSE gateway, PDM gateway, and PCRF, and how control and user planes flow.

Learn how the evolved packet core supports LTE with five nodes—MME, HSS, SGW, PGW, and PCRF—and separates signaling from the user plane while enabling bearer management, roaming, and QoS.

Explore how 4g epc interfaces and protocols move signaling and user data, covering eps, apc, s1 u plane, s1 me, s3, s12, se5, gcs, rex, and v interfaces.

The lecture explains LTE and EPC identifiers, including IMSI, MCC/MNC, and GUTI, and how GUTI is used after attach; it covers PMN, tracking areas, TAC, ECI, and eNodeB IDs.

Explain how the 4G EPC PDN connectivity service lets a subscriber access internet and IMS networks via APN attachment and IP address allocation, using bearers with QoS.

Describe how pdn addresses are assigned for eps bearers, contrasting dynamic ips from apn pools with static ips from subscription, via create session requests between mms, pe gateway, and ue.

Explain the difference between default and dedicated bearers in LTE: default bearer provides a dynamic IP and QoS profile; dedicated bearer offers distinct QoS on the same IMS APN.

Gateway assigns QoS to each bearer, shaping traffic by delay, loss, and priority, with ERP, QCA, GBR, MBR, APN aggregated maximum bitrate, and UE aggregate maximum bitrate.

Explain how QCI quality of service class identifiers govern traffic flow with priority, packet loss, and delay budgets, including guaranteed and non guaranteed bitrate.

Learn how the ARP allocation and retention priority assigns an r.p value to each QoS flow, guiding resource access under congestion and enabling preemption of lower-priority users with higher values.

Explore how EPS bearers, including the EPS radio access bearer (ERAB) and default versus dedicated bearers, shape end-to-end QoS for traffic like voice over IP and web browsing.

Explain how traffic flow templates in the user equipment and PDM gateway assign service data flows to dedicated or default bearers for uplink and downlink, including Skype and WhatsApp traffic.

Examine the EPS bearer and UE contexts stored across gateways, including default and dedicated bearers, APN, PDN address, QoS per APN, mobility management, security parameters, and tunnel endpoint IDs.

Explain the 4g lte attach procedure, including the attach request, authentication and security, location update, and eps bearer establishment to enable packet data exchange, using IMSI or GUTI.

Explore how 4g lte networks authenticate subscribers and the network, ensure integrity, and encrypt traffic using master, cipher, and integrity keys to casm and nas encryption for eNodeB and ue.

Explain how EPS bearer establishment works, linking radio bearers from user equipment to the network and S5/S1 tunnel bearers between gateways to route traffic to the external packet data network.

Explore the epc call flow after authentication, including mobile identity checks, blacklist/whitelist decisions, and the update location process that cancels old contexts and bearer sessions.

Detach procedures explain how a user equipment or network nodes trigger detach, delete the EPS bearers and context, and terminate the EPS session to enable new network attachment.