計畫主持人：許蒼嶺 ( 國立 中山大學 電機工程學系 ) 授課教師 ：萬欽德 ( 國立高雄第一科技大學 電腦與通訊工程系 )

1. 教育部補助「行動寬頻尖端技術跨校教學聯盟第二期計畫--行動寬頻網路與應用--小細胞基站聯盟中心」EPC核心網路系統設計課程單元 08：Session Management 與 Mobility 計畫主持人：許蒼嶺 (國立中山大學 電機工程學系) 授課教師：萬欽德 (國立高雄第一科技大學 電腦與通訊工程系)

2. IP Connectivity Enables Session Management • In conjunction with the evolution of the access networks provided with LTE, it • provides a common packet core with appropriate policy, security, charging, and mobility • provides end-users with ubiquitous access to network services across different access networks • provides them with session continuity across various access technologies.

3. IP Connectivity • IPv4 or IPv6 • QoS

4. IP Connectivity (continued; 2/8) • APN ( corresponding PDN) : • user’s subscription profile in the HSS (if not, default) • PDN GW • EPS concerns: • PDN connection layer • associated functions such as IP address management, QoS, mobility, charging, security, policy control, etc.

5. IP Connectivity (continued; 3/8) • The user IP connection (the PDN connection) is separate from the IP connection between the EPC nodes (the transport layer). • Transport network in the EPC provides IP transport: • Using different technologies such as MPLS, Ethernet, wireless point-to-point links, etc. • Not aware of the PDN connections.

6. IP Connectivity (continued; 4/8) Trusted Non-3GPP Accesses

7. IP Connectivity (continued; 5/8) • IP Addresses • Can be purely private IP network • IPv4 or IPv6 • A terminal with a PDN connection in EPS may request an IPv4 address, an IPv6 prefix, or both • Two alternative ways ( both methods to coexist in EPC) • IPv4 address to the UE during the attach procedure (E-UTRAN) or PDP context activation procedure (GERAN/UTRAN) • DHCPv4 • Stateless IPv6 address auto configuration (SLAAC)

8. IP Connectivity (continued; 6/8) • IP Address Allocation in Other Accesses • Trusted Non-3GPP Accesses • Untrusted Non-3GPP Accesses

9. IP Connectivity (continued; 7/8) Trusted Non-3GPP Accesses

10. IP Connectivity (continued; 8/8) Untrusted Non-3GPP Accesses

11. Session Management, Bearers, and QoS Aspects • The basic functions in EPS to manage the user-plane path between the UE and the PDN GW • EPS bearer in E-UTRAN and EPS • for providing the IP connection • for enabling QoS

12. Session Management, Bearers, and QoS Aspects (continued; 2/13) • Default bearer • associated with a default type of QoS • Dedicated bearers • Additional EPS bearers • activated on demand • for example, when an application is started with a specific guaranteed bit rate or prioritized scheduling

13. Session Management, Bearers, and QoS Aspects (continued; 3/13) • User-Plane Aspects • The UE and the PDN GW (for GTP-based S5/S8) or Serving GW (for PMIP-base S5/S8) use packet filters to map IP traffic onto the different bearers • Each EPS bearer is associated with a so-called Traffic Flow Template (TFT)

14. Session Management, Bearers, and QoS Aspects (continued; 4/13) • This packet filter information is typically an IP 5-tuple defining the source and destination IP addresses, source and destination port, as well as protocol identifier (e.g. UDP or TCP).

15. Session Management, Bearers, and QoS Aspects (continued; 5/13) • The filter information may contain the following attributes: • Remote IP Address and Subnet Mask • Protocol Number (IPv4)/Next Header (IPv6) • Local Address and Mask (introduced in Release 11) • Local Port Range • Remote Port Range • IPSec Security Parameter Index (SPI) • Type of Service (TOS) (IPv4)/Traffic Class (IPv6) • Flow Label (IPv6).

16. Session Management, Bearers, and QoS Aspects (continued; 6/13) • GTP-U header contains: • a field that allows the receiving node to identify the bearer the packet belongs to • A user-plane packet encapsulated using GTP-U

17. Session Management, Bearers, and QoS Aspects (continued; 7/13)

18. Session Management, Bearers, and QoS Aspects (continued; 8/13)

19. Session Management, Bearers, and QoS Aspects (continued; 9/13) • How the UE, PDN connection, EPS bearer, TFT, and packet filters within the TFT relate to each other

20. Session Management, Bearers, and QoS Aspects (continued; 10/13) • Control-Plane Aspects • To activate, modify, and deactivate bearers, to assign QoS parameters, packet filters, etc., to the bearer. • Dedicated bearer • network-requested secondary PDP context activation procedure • If the default bearer is deactivated the whole PDN connection will be closed.

21. Session Management, Bearers, and QoS Aspects (continued; 11/13) • Bearers in PMIP- and GTP-Based Deployments • GTP designed to support • all functionality required to handle the bearer signaling • the user plane transport, • PMIP designed by IETF to only handle • functions for mobility and forwarding of the user plane.

22. Session Management, Bearers, and QoS Aspects (continued; 12/13) • When PMIP-based S5/S8 is used: • Packet filters are needed to map the downlink traffic onto the appropriate bearer

23. Session Management, Bearers, and QoS Aspects (continued; 13/13)

24. Session Management for EPS and GERAN/UTRAN Accesses (1/3) • The SGSN provides the mapping between PDP context and EPS bearer procedures, and maintains a one-to-one mapping between PDP contexts and EPS bearers. • By using PDP context procedures between UE and SGSN, the UE can use similar ways to connect when the 2G/3G access connects to EPC. • By using the EPS bearer in the EPC also for 2G/3G access, it is easier for the PDN GW to handle mobility between E-UTRAN and 2G/3G.

25. Session Management for EPS and GERAN/UTRAN A ccesses (2/3)

26. Session Management for EPS and GERAN/UTRAN A ccesses (3/3) • SGSN using S4 maps “the UE-initiated PDP context procedures over GERAN/UTRAN” into “corresponding EPS bearer procedures towards the Serving GW” • For example, when the UE is using GERAN/UTRAN and has requested activation of a secondary PDP context, the PDNGW must activate a new EPS bearer corresponding to the PDP context

27. Subscriber Identifiers and Corresponding Legacy Identities (1/3) • Permanent Subscriber Identifiers • Structure of IMSI

28. Subscriber Identifiers and Corresponding Legacy Identities (2/3) • Temporary Subscriber Identifiers • stored in an MME (or SGSN in the 2G/3G case) • The GUTI (Globally Unique Temporary ID) is a worldwide unique identity that points to a specific subscriber context in a specific MME. • The S-TMSI is unique within a particular area of a single network.

29. Subscriber Identifiers and Corresponding Legacy Identities (3/3)

30. Relation to Subscription Identifiers in 2G/3G

31. Mobility Principles • EPS • complete realization of multi-access convergence: • a packet core network that supports full mobility management • access network discovery • and selection for any type of access network. • The functionality of mobility management • the network can “reach” the user • a user can initiate communication towards other users or services • ongoing sessions can be maintained as the user moves

32. Mobility within 3GPP Family of Accesses • Cellular Idle-Mode Mobility Management • Not be practical to keep track of a UE in idle mode every time it moves between different cells. • Not practical to search for the UE in the whole network for every terminating event (incoming call) • Cells are grouped together into “registration areas”

33. Cellular Idle-Mode Mobility Management (1/7)

34. Cellular Idle-Mode Mobility Management (2/7) • Base stations broadcast registration area information. • UE compares the broadcasted registration area information with its own information

35. Cellular Idle-Mode Mobility Management (3/7) • In EPS the registration areas are called Tracking Areas (TAs). • As long as the UE moves within its list of allocated TAs, it does not have to perform a tracking area update. • Periodic updates are used to clear resources in the network for UEs that are out of coverage or have been turned off.

36. Cellular Idle-Mode Mobility Management (4/7) • In GSM/WCDMA there are two registration area concepts: • the PS domain (Routing Areas, RAs) • the CS domain (Location Areas, LAs). • The Routing Areas are a subset of the Location Areas and can only contain cells from the same LA.

37. Cellular Idle-Mode Mobility Management (5/7) • A summary of the idle mobility procedure in EPS: • A TA consists of a set of cells • The registration area in EPS is a list of one or more TAs • The UE performs TA Update when moving outside its TA list • The UE also performs TA Update when the periodic TA Update timer expires. • An outline of the Tracking Area Update procedure is shown in the figure of next slide.

38. Cellular Idle-Mode Mobility Management (6/8)

39. Cellular Idle-Mode Mobility Management (7/7) • Paging is used to search for Idle UEs and establish a signaling connection.

40. References • M. Olsson, Shabnam Sultana, Stefan Rommer, Lars Frid, and C. Mulligan, “EPC and 4G Packet Networks,” Second Edition: Driving the Mobile Broadband Revolution, Elsevier, 2013