UMTS Protocols
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The document provides a comprehensive overview of radio and core network protocols in UMTS, detailing the network architecture, OSI communication model, and various protocol stacks for circuit and packet switched control and user planes. It explains the structure and roles of various interfaces such as iu-cs, iu-ps, iub, and iur, along with their associated protocols and functionalities. The summary highlights how UMTS is organized into non-access and access strata, with a focus on the significance of the transport network layers transitioning from ATM to IP.
UMTS Protocols
- 1. Radio and Core Network Protocols in UMTS Presented by: Naveen Jakhar, ITS
- 2. Topics: UMTS Network Architecture OSI Communication model UMTS Protocol stack Circuit switched-control plane/user plane Packet switched-control plane/user plane Generic protocol model for UTRAN interfaces Iu-CS interface protocol structure Iu-PS interface protocol structure Iur interface protocol structure Iub interface protocol structure Summary 2
- 4. OSI Communication model • Each layer communicates only with two adjacent layers and its peer on the other side • Each layer receives services from the layer below and provides services to the layer above Page 4 • Intermediate communication nodes require layers 1 through 3 • Internal operation within each layer is independent of the internal operation in any other layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical LayerPhysical Layer Data Link Layer Network Layer Physical Medium Physical Medium Node A Node B Node C Peer to peer protocols • WCDMA interfaces described using OSI model • OSI = Open System Interconnect • Developed by ISO as a general model for computer communication • Used as a framework for development and presentation of most contemporary communication standards Note: WCDMA covers Layers 1-3 of OSI Model
- 5. 5 UMTS Protocol stack • First three layers of the protocol stack are part of UTRAN Note: SMS exists on both circuit switched and packet switched side
- 6. NAS or the Non Access Stratum is a set of protocols in the UMTS that is used to convey non-radio signalling between the User Equipment (UE) and the core network. From a protocol stack perspective, the NAS is the highest stratum of the control plane The NAS procedures consist of MM, CC, GMM, SM Access Stratum signalling is between UTRAN and the terminal. Eg. RRC Connection setup 6
- 7. UMTS CS protocols – control plane • RNC terminates the Access Stratum (AS) • RRC, RLC and MAC terminate at RNC • PHY terminates at Node B except for outer loop power control • RAN (access stratum) acts as transport for NAS 7 Note: UTRAN protocols are layered in an architecture that follows OSI model
- 8. RRC: RRC connection management(setup, release, reconfiguration), – Radio Bearers management(setup, release, reconfiguration), Management of radio resources for the RRC connection, RRC connection mobility functions, Paging/notification Radio Link Control (RLC): The RLC protocol offers logical link control over the radio interface for the transmission of higher layer-signalling messages and SMS. RLC is defined in TS 25.322. 8
- 9. UMTS CS protocols – user plane • User plane – caries user data • Application – end to end protocol • Access stratum the same for both control plane and user plane 9
- 10. UMTS PS protocols – control plane • Control plane for packet data • Very similar to control plane for PS • Identical access stratum 10
- 11. UMTS PS protocols – user plane • Additional protocol PDCP • PDCP – compression of IP headers • PDCP may or may not be used 11
- 12. • PDCP: – provides protocol transparency (wrt the underlying radio- interface protocols) for higher- layer protocols – support for e.g., IPv4, PPP and IPv6 (easy introduction of new higher layer protocols) – compression of control information (header compression) – no user data compression in Iu mode ■ RLC: – RLC protocol provides logical link control over the radio interface. ■ MAC – MAC protocol controls the access signaling (request and grant) procedures for the radio channel
- 13. Figure :Generic protocol model for UTRAN interfaces
- 14. The structure consists of two horizontal layers: 1)The Radio Network Layer and 2) The Transport Network Layer. The Radio Network Layer is concerned with application information to be carried either user data and control information. The Transport Network Layer is concerned with the transport technologies used for the UTRAN interfaces. The two layers are logically independent of each other. This makes it possible to change the Transport Network Layer without affecting Radio Network Layer, if required. In Release 99, the Transport Network Layer is based on ATM. In Release 5, IP is used. 14
- 15. •The user plane includes the user data between the UE and the network and the data bearers. The user data consists of data streams characterized by frame protocols specific to a UTRAN interface. •The control plane includes the application protocols and the signaling bearers, which transport the control information. The application protocols used at different UTRAN interfaces are: ■ Iu-CS: Radio access network application protocol (RANAP) ■ Iu-PS: RANAP ■ Iub: Node B application protocol (NBAP) ■ Iur: Radio network system application protocol (RNSAP) •The transport network control plane includes the access link control application protocol (ALCAP). ALCAP is used to set up transport bearers to carry user and control plane information. It is not visible to the Radio Network Layer. 15
- 16. Figure : Iu-CS interface protocol structure. 16
- 17. IUcs interface protocol structure • In UMTS, the interface between RAN and CN is Iu. •Iu-CS is the interface specified between the RAN and the 3G MSC. •The Iu-PS interface is defined between the RAN and the 3G SGSN. •In order to have uniformity, 3GPP specifies a single protocol at Radio Network Layer for the Iu-CS and the Iu-PS interfaces. The radio access network application protocol (RANAP) is the Radio Network Layer protocol for the Iu interface. The RANAP peer entities reside in 3G MSC/SGSN and the SRNC. The RANAP functions are specified in 3GPP TS 25.413 in detail. In summary, RANAP procedures support the following key functions: ■ Radio access bearer (RAB) management including RAB setup, modification, and release ■ Iu connection management ■ Facilitate general UTRAN procedures from the core network, e.g., paging requests from the CN to UE ■ Services to upper layers including the transportation of upper layer nonstratum protocols (i.e., call control, session management, and mobility management) messages between the UE and CN ■ Overload and error handling ■ SRNS relocation ■ UE location reporting 17
- 18. The Service Connection and Control Part (SCCP) offers both connectionless and connection-oriented services. Each active UE is assigned a separate logical link in case of connection-oriented service between two RANAP entities. The SCCP utilizes services provided by the lower layers to transport messages between two entities. Layer 3 Broadband Message Transfer Part (MTP3b) provides message routing, discrimination, and distribution. It also provides link management functions including load sharing between linksets. The SSCF-NNI(Service-Specific Coordination Function for Signaling at the Network Node Interface) maps the requirements of above layers to the requirements of SSCOP. The SSCOP (Service-Specific Connection-Oriented Protocol)provides the mechanism for the establishment and release of connections and the reliable exchange of signalling information between the signalling entities. In cases where the IP transport option is chosen, the services are provided by M3UA(MTP 3 User Adaptation Layer), SCTP (Stream Control Transmission Protocol) and IP. AAL5 (ATM Adaptation Layer 5)is used to adapt the upper layer protocol to the requirements of the lower ATM cells. 18
- 19. As described in the previous section, the purpose of the transport network control plane is to set up, maintain, and release bearers to transport the data via the user plane. The AAL2 signaling protocol capability set 1 (ALCAP), which is described in ITU-T specification Q.2630.1, is used. ALCAP(Access Link Control Application Part ) is a Layer 3 protocol. Its responsibility is to set up and manage ATM Adaptation Layer 2 (AAL2) connections. In the user plane, ATM Adaptation Layer 2 (AAL2) is used as the user data bearer. AAL2 has been specifically designed to transport short-length packets. 19
- 20. Figure: Iu-PS interface protocol structure. 20
- 21. IUps interface protocol structure The Iu-PS interface is specified between the RAN and the 3G SGSN. As described in the previous section, 3GPP specifies a single protocol at the Radio Network Layer for the Iu-CS and the Iu-PS interfaces, i.e., RANAP for the control plane and Iu for the user plane. No transport network control protocol is needed. Unlike GPRS, where the GTP tunnel ends at the SGSN, the GTP tunnel in UMTS extends up to RNC. The tunnel ID and IP address, which is required to establish a tunnel, is included in the upper layer protocols. Like GPRS, GTP-U uses UDP/IP. AAL5 is used to carry the packet- switched user traffic over the Iu-PS interface. 21
- 22. Figure :Iur interface protocol structure. 22
- 23. Iur interface protocol structure Iur is the interface between the RNCs. One of the RNCs assumes the controlling role and is termed the serving RNC (SRNC); the other RNC is termed the drifting RNC (DRNC). The Radio Subsystem Application Part (RNSAP) is a Radio Network Layer protocol used at the Iur interface. RNSAP includes procedures for network control signaling between two RNC nodes: ■ Radio link management and reconfiguration ■ Radio link supervision ■ Common control channel (CCCH) signaling transfer ■ Paging ■ Relocation execution 23
- 24. RNSAP uses the services of the Transport Layer for reliable transfer of signaling messages in both connectionless and connection-oriented modes. The SCCP allows a separate independent logical connection with individual UE. If the ATM transport option is chosen between two RNCs, the SCCP uses MTP3-B, SSCF-NNI, and SSCOP services for networking and routing of messages. In cases where the IP transport option is chosen, these services are provided by the M3UA, SCTP, and IP. 24
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- 26. Iub interface protocol structure Iub is the interface between the Node B and the RNC . The Node B application protocol (NBAP) is a Radio Network Layer control plane protocol at the Iub interface. NBAP includes the procedures to manage the logical resources at Node B. NBAP procedures support the following functions: ■ Cell configuration management ■ Radio link management and supervision ■ Common transport channel management ■ System information management ■ Configuration verification/alignment ■ Measurement of common and dedicated resources System network protocols 26
- 27. Summary •UTRAN in WCDMA covers Layers 1-3 of OSI Model •Complete UMTS architecture is divided into Non Access Stratum and Access Stratum •The application protocols used at different UTRAN interfaces are: ■ Iu-CS: Radio access network application protocol (RANAP) ■ Iu-PS: RANAP ■ Iub: Node B application protocol (NBAP) ■ Iur: Radio network system application protocol (RNSAP) •In order to have uniformity, 3GPP specifies a single protocol at Radio Network Layer for the Iu-CS and the Iu-PS interfaces. •UMTS protocol structure is divided into horizontal layers and vertical planes 1)Radio network layer 1)User Plane 2)Transport network layer 2)control plane 3) Transport Network control Plane •In Release 99, the Transport Network Layer is based on ATM. In Release 5, IP is used. •There is no Transport Network control Plane in Iu-PS interface •Unlike GPRS, where the GTP tunnel ends at the SGSN, the GTP tunnel in UMTS extends up to RNC. 27
- 28. 28 Thank You!