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.
EPC

3. IP Connectivity
IPv4 or IPv6
QoS
EPC

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.
EPC

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.
EPC

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

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)
EPC

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

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

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

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
EPC

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
EPC

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)
EPC

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).
EPC

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).
EPC

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
EPC

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

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

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
EPC

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.
EPC

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.
EPC

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
EPC

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

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.
EPC

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

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
EPC

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

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.
EPC

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

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

31. Mobility Principles EPS The functionality of mobility management
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
EPC

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”
EPC

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

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
EPC

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.
EPC

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.
EPC

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.
EPC

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

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

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
EPC