Internet Engineering Task Force Yousuf Saifullah INTERNET-DRAFT Stefano Faccin Date: July 2000 Nokia Inc. Expires: December 2000 Common Radio Access Protocols Issues and Requirements < draft-saifullah-craps-issues-req-00.txt > Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Distribution of this memo is unlimited. Copyright (C) The Internet Society 2000. All Rights Reserved. Abstract This paper discusses some of the issues that need to be considered in defining the CRAPS protocol set. It also specifies a set of requirements, which can be useful in the development of CRAPS. The issues are in consideration of some of the functionalities an existing cellular radio access network is required to provide. The document also discusses the issues, which are related to the new functional aspects of CRAPS. Saifullah and Faccin [Page i] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 Table of Contents Status of This Memo . . . . . . . . . . . . . . . . . . . . . . . . i Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 3.1. Congestion Control and Load Balancing . . . . . . . . . . . 2 3.2. Paging Management . . . . . . . . . . . . . . . . . . . . . 2 3.3. Location Services . . . . . . . . . . . . . . . . . . . . . 3 3.4. Efficient and Economical Radio Resource usage . . . . . . . 3 3.5. Robust Header Compression . . . . . . . . . . . . . . . . . 3 3.6. User Identity and Location Protection . . . . . . . . . . . 4 3.7. A single handover protocol independent of the RF link . . . 4 3.7.1. Seamless and Lossless Handoff Procedure . . . . . . . . 4 3.7.2. Moving of a Session Context . . . . . . . . . . . . . . 5 3.7.3. QoS management during HO . . . . . . . . . . . . . . . 5 3.7.4. Addressing before and after Handoff . . . . . . . . . . 5 3.8. Soft Handoff . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Requirements for CRAPS . . . . . . . . . . . . . . . . . . . . . 6 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 Saifullah and Faccin [Page ii] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 1. Introduction The CRAPS BOF has the intention to charter a working group to provide a handover protocol between access points of different radio technology. The working group has also the intention to work on simplifying the radio network protocols by pushing all the radio-related functions downinto the BSs. This document discusses a set of issues which need to be resolved in achieving the above mentioned goals. The idea is to identify the challenges, so the CRAPS group as a whole can discuss the possible solutions. This document also identifies a set of requirements, which are inferred as a result of the consideration of the issues. These requirements can be utilized alongwith the requirements identified in [1]. 2. Terminology Mobile Terminal (MT) A user terminal with an IP client. Also called the Mobile Node or Mobile Station. Base Station (BS) A network element which comprises of radio transmission and reception devices. Also called the Base Transceiver Station (BTS) or Node-B. Radio Access Network (RAN) This is a wired network that connects MT and the core network. The RAN may comprise of RNC and BS. Also called the Base Station Sub-system (BSS). Radio Network Controller (RNC) This acts as a gateway to the RAN and provides control to a group of base stations. Also called the Base Station Controller (BSC). Soft handoff A process by which a moving CDMA MT is transferred between the BSs. In soft handoff, a connection between the MT and the network is established and may be maintained indefinitely with the two or more BS serving the session. Saifullah and Faccin [Page 1] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 Frame Selection/Distribution This function is responsible for selecting the best incoming air interface reverse link frame from the channel elements involved in the soft handoff. It also distributes forward air interface frames to all the channel elements involved in a call. Also called the macrodiversity combiner (MDC) or selection and Distribution Unit (SDU). Seamless Handoff A handoff procedure which does not result in any communication break noticeable by a user. This procedure has strict timing requirement for the execution and is tolerant to some packet loss. Lossless Handoff A Handoff procedure which does not result in any packet loss. This procedure is not allowed to loose any user data and is tolerant to some delay in the procedure execution. 3. Issues 3.1. Congestion Control and Load Balancing A centralized radio resource manager (RRM) is used in traditional RANs to manage the resources in its BSs in order to increase the call success rate. The RRM keeps track of the assigned/unassigned resources in all the BSs it manages and redirects call originations attempts to neighbor BSs when appropriate. This may happen due to radio congestion, equipment failure, etc. A centralized RRM also helps in avoiding congestion by performing non-imperative handovers to balance the traffic among different BSs. The CRAPS WG shall consider how to provide congestion control and load balancing without any centralized radio resource manager, and by achieving the same level of optimizatons possible with a centralized RRM. 3.2. Paging Management In cellular networks the concept of "paging area" (or location area) is defined. Paging areas are used to locate an MT in idle mode in order to deliver incoming calls. The MT in idle mode keeps the network informed of its location at the level of paging area, i.e. indicates its current Saifullah and Faccin [Page 2] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 paging area to the network any time there is a change in the paging area. A paging area usually encompasses more than a BS area, so that the MT does not drain its battery out by performing frequent paging area updates. At the same time, the size of paging areas shall be such that the signaling load resulting from paging is minimized. Paging area size is calculated optimizing the trade off between the two aspects described above. The challenge for CRAPS WG is to manage paging area without involving any radio specific functions above the BSs. 3.3. Location Based Services The Location Based Services are important feature of cellular networks. Moreover, the provision of the MT location during emergency calls is mandatory in some jurisdictions with a specified accuracy in location estimate. The location determination for a target MT is an essential part of the Location Based Services. The location determination function traditionally resides inside the RNC because it uses an overall co-ordination, collection and calculation functions based on the measurements received by the different BSs and the MT. The CRAPS WG needs to define a mechanism to allow the determination of the MT location, which does not need any function to be centrally located over BSs, and is also independent of the BS RF technology. 3.4. Efficient and Economical Radio Resource usage The frequency spectrum in commercial large scale cellular networks is limited and expensive, thus it is important for such radio networks to have radio resource management optimized for an efficient use of the available spectrum. In the existing cellular radio networks the optimization is performed in many ways. For instance, by assigning radio resource after terrestrial resource assignment in a call setup, by performing call audit between the BS and the call processing agent to release any stuck radio resources, etc. The CRAPS WG needs to consider efficient and economical radio resource management in the protocol set development. 3.5. Robust Header Compression The idea of IP transport over the wireless link allow full deployment of the end-to-end IP model and the adoption of IP applications in the MT. One main problem in this regard is the overhead over the wireless link Saifullah and Faccin [Page 3] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 due to the IP header, which is particularly significant for service such as voice. This problem is being solved by developing header compression schemes, e.g. [2]. It is important for the CRAPS WG to select header compression schemes which can sustain the air interface characteristics of errors and packet loss. The scheme should also be spectrum efficient during the handoffs. 3.6. User Identity and Location Protection In a session initiation, there is a period during which the MT has identified itself with the network but the network has not yet verified the credentails received from the MT, and for this reason no security mechanism can be applied to protect the exchange of information between the MT and the network. In that period, the MT has to identify itself to the network with its subscriber identity using a message in clear. A third-party could at this stage listen to this identity and can find out where a subscriber is at this particular moment, thus breaching the location confidentiality that is a well known requirement for cellular networks. In the existing cellular systems, the MT hides its real identity by using a temporary identity provided by the network during previous interactions. Moreover, during roaming and handovers, the location of an MT is kept securely in the network and is not revealed to the correspondent nodes. The CRAPS WG has to provide mechanisms to ensure user identity and location confidentiality over the air interface and to the correspondent nodes. 3.7. A single handover protocol independent of the RF link 3.7.1. Seamless and Lossless Handoff Procedure In cellular network, both seamless and lossless handoff procedures are defined. A user may need one or the other based on the service being used. A seamless handoff procedure is desired for conversational services, where any break in communication or degradation of service due to handoffs is perceived as bad quality. A seamless handoff has strict timing requirement for the completion of the procedure. On the other hand, a lossless handoff procedure is desired for the services where it is important not to loose any data packets during handoff (e.g. data services). The CRAPS WG needs to develop a seamless handoff procedure with the timing limitations comparable to the existing cellular systems. It Saifullah and Faccin [Page 4] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 also needs to develop a lossless handoff procedure. The mechanism for ensuring no packet loss should be preferably developed at the radio specific protocol layers, so the upper layer remains agnostic to the handoff. 3.7.2. Moving of a Session Context A handoff procedure moves the current context of the session from the source to the target radio network. The context includes parameters such as current settings of codecs, encryption, header compression, radio frames acknowledged state etc. The target radio network uses this information to initialize the relevant functions for the target radio bearer. Different RF technologies may have different types of context parameters or different possible values of a context parameter. The CRAPS WG has to harmonize the session context, which need to be moved during handoff, between different RF technologies. 3.7.3. QoS management during HO Due to the limited number of radio resources and support of bandwidth hungry services, it may not be possible to maintain the same QoS level, which was assigned originally for the session, after handoff. There is a need to have a QoS management function, which will ensure that the QoS is within the user expectation after handoff. The function will also ensure that any QoS degradation during a handoff does not adversely effect the network performances or the user data flow. 3.7.4. Addressing before and after Handoff The CRAPS WG has to resolve how the IP addressing of a MT will be handled during handoffs. After a handoff, it is necessary to determine if a new address needs to be assigned or if the the same address can be kept. If a new address needs to be assigned, then it is necessary to determine if the time needed to assign the address is short enough and the signaling efficient enough to meet the requirements for both the handoff timing and the signaling efficiency over the air interface. If an old address can be used, then it is necessary to determine how re-routing of traffic flows to the new location takes place after handoff. Saifullah and Faccin [Page 5] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 3.8. Soft Handoff The CDMA radio access networks consists of a RAN gateway connected to one or more base stations. The RAN gateway has a frame selection/distribution function, which combines/splits radio frames in executing soft handoff between base stations. A strict synchronization is needed between the base stations for the execution of soft handoff. A detailed discussion on this topic can be found in [3]. The issues for CRAPS are to determine the location of frame selection/distribution function in the absence of a RAN gateway, how to replace radio frames between BS and frame selection/distribution function with IP packets, and how to keep synchronization between BS with an open IP transport. 4. Requirements for CRAPS The following is a list of requirements: 1. CRAPS shall provide mechanisms for Congestion Control and Load Balancing, for increasing the call success rate by utilizing the available radio resources among different base stations. 2. CRAPS shall define the concept of paging area and a mechanism for paging area management within the network. 3. CRAPS shall devise a location determination procedure, without any centralized entity performing such function. The location determination procedure shall also be independent of the RF technologies. 4. CRAPS must consider efficient use of radio resources. The call block rate due to the unavailability of radio resources must not be higher than in the existing cellular systems. 5. CRAPS shall use a robust and efficient header compression scheme. The scheme shall have consistent performance during handoffs. 6. CRAPS shall provide location confidentiality by protecting the user identity over the air interface and not revealing to the correspondent nodes the location of the node. 7. CRAPS shall provide both seamless and lossless handoff procedures, selectable on a service basis. 8. CRAPS shall provide a mechanism for the session context relocation from the source to the target BS during handoff, independent of the Saifullah and Faccin [Page 6] INTERNET-DRAFT CRAPS Issues and Requirements 23 June 2000 RF technologies of the BSs. 9. CRAPS shall provide a QoS Management function to manage QoS during handoff. 10. CRAPS shall provide an addressing mechanism, which does not increase the handoff latency and also does not require any special routers in the network. 11. CRAPS shall determine the location of the frame selection/distribution function for soft handoffs. 12. For soft handoff, CRAPS shall determine how to replace radio frames transferred between BS and frame selection/distribution function with IP packets. 13. For soft handoff, CRAPS shall determine how to achieve synchronization between BS with an open IP transport. 5. References [1] Neumiller, Phillip D., et. al, Open Base Station Transport (OBAST) Requirement, draft-neumiller-req-00.txt (work in progress), June, 2000 [2] Le, Khiem, et. al., Adaptive Header ComprEssion (ACE) for Real- Time Multimedia, draft-ietf-rohc-rtp-ace-00.txt (work in progress), May, 2000 [3] Kempf, James, et. al., IP Mobility and the CDMA Radio Access Network: Applicability Statement for Soft Handoff soft handoff a statement, draft-kempf-cdma-appl-00.txt (work in progress), May, 2000. 6. Authors' Addresses Yousuf Saifullah 6000 Connection Drive, Irving, TX 75039 Phone: +1 972 894 6966 Email: yousuf.saifullah@nokia.com Stefano Faccin 6000 Connection Drive, Irving, TX 75039 Phone: +1 972 894 4994 Email: stefano.faccin@nokia.com Expires December, 2000 Saifullah and Faccin [Page 7]