Mobile IPv6 and some issues for QoS
Kan Zhigang Jian MA Luo Jun,
Hu Jianping ABSTRACT: Billions of portable computing devices such as mobile phone, laptop and palmtop computers are becoming widely available at very affordable prices. Since these devices are wireless and therefore mobile, they will derive great benefit form Mobile IPv6. Mobile IPv6 was designed to be a natural outgrowth of Mobile IPv4, just as IPv6 itself was designed to be a natural outgrowth of IPv4. As reliance on Internet and web-based services increases, so do customer expectations for availability, reliability, and responsiveness of the services, especially in the Mobile IPv6 network environment. There are two issues which affect the QoS of Mobile IPv6, one is the mobility of mobile node and the other are the features of wireless links such as high loss, high delay and high jitter. In this paper, the advantages of IPv6 for mobility are given and the Mobile IPv6 protocol is overviewed. Then the paper introduces some issues about QoS support in mobile IPv6 such as fast handover, smooth handover and mobility managements.Since the provisions in the existed QoS architectures such as InterServ and DiffServ do not have any mechanism to consider about the quality of service (QoS) requirement of packet streams between MN and CN or between MN and HA, Finally, a new QoS architecture framework based on "QoS Object" and "QoS Agent" is presented. In this architecture some signalings based on the Binding Update and Binding Acknowledge for QoS negotiation are introduced. 1 Introduction Internet is now becoming its own victim of its own great success because the intrinsic limitation of the current internet protocol version 4. Among the problems that IPv4 had to face, the most serious one is that the addresses of IPv4 will be exhausted in the near future based on the current developing speed of the Internet. Current projections indicate that sometime within the year 2002, there will be a billion mobile wireless communication devices in the hands of consumers. To cater for the Internet’s rapid development and huge requirements of wireless computing devices, IETF begun the standard works for IPv6 which is also called IPng (IP next generation) in 1991 and most of the IPv6 RFCs have been published since 1996. IPv6 is the new version of IP and born out of the great success of IPv4. The huge address space of IPv6 will meet the requirements for rapid development of Internet easily. Mobility, security and QoS are now integrated in IPv6. It is considered that IPv6 is the important foundation stone for building the mobile information society and the future Internet. As we know, IPv4 does not provide any support for mobility. In the current IPv4 Internet, each computer is assigned a fixed IP address that is belonged to a network. If the computer changed the attachment point to a different network, the packets sent to it will be routed the former network and will be discarded because of the absence of the destination. Moreover, the mobile computing equipments such as the embeded devices, PDA, multi-purposed handset will require the mobility support in IP. It is an important milestone for mobile computing because of the naissance of the IPv6. The main features of IPv6 that are important for the future growth of mobile wireless network are as follows: sufficient number of IP address; mandated security header implementation; destination options for efficient rerouting; address autoconfiguration; avoidance of the ingress filtering penalty; error recovery without soft-state bottleneck [1]. The design of Mobile IP support in IPv6 (Mobile IPv6) represents a natural combination of the experiences gained from the development of Mobile IP support in IPv4 (Mobile IPv4) [2, 3, 4], together with the opportunities provided by the design and deployment of a new version of IP itself (IPv6) and the new protocol features offered by IPv6. In mobile IPv6 three operation entities are defined: mobile node (MN), correspondent node (CN), home agent (HA); four new IPv6 destination options are defined: binding update option, binding acknowledgement, binding request and home address option; two ICMP message are defined for ‘Dynamic Home Agent Address Discovery’: ICMP home agent address discovery request message and ICMP home agent address discovery reply message; two new IPv4 options for ‘Neighbor Discovery’: advertisement interval option and home agent information option.
2 Mobile IPv6 Protocol overview [5] The main goal of Mobile IP is that a mobile node is always addressable by its home address, whether it is currently attached to its home link or is away from home. Mobile IP enables applications running on an Internet node to survive physical reconnection by inserting a few additional features at the network layer. These features allow the mobile node to always be addressable at its home addresses. While a mobile node is attached to some foreign link away from home, it is also addressable by one or more care-of addresses, in addition to its home address. A care-of address is an IP address associated with a mobile node while visiting a particular foreign link. The association between a mobile node's home address and care-of address is known as a "binding" for the mobile node. A mobile node typically acquires its care-of address through stateless or stateful (e.g., DHCPv6) Address Autoconfiguration, according to the methods of IPv6 Neighbor Discovery or other methods such as static pre-assignment by the owner or manager of a particular foreign link. Mobile IPv6 requires at least the occasional assistance of a home agent that has to be located on the home network. While away from home, a mobile node registers one of its care-of addresses with a router on its home link, requesting this router to function as the "home agent" for the mobile node. The home agent has the responsibility to use proxy Neighbor Discovery to intercept any IPv6 packets addressed to the mobile node's home address (or home addresses) on the home link, and tunnels each intercepted packet to the mobile node's primary care-of address. To tunnel each intercepted packet, the home agent encapsulates the packet using IPv6 encapsulation, with the outer IPv6 header addressed to the mobile node's primary care-of address. It is possible that while a mobile node is away from home, some nodes on its home link may be reconfigured, such that the router that was operating as the mobile node's home agent is replaced by a different router serving this role. In this case, the mobile node may not know the IP address of its own home agent. Mobile IPv6 provides a mechanism, known as "dynamic home agent address discovery", that allows a mobile node to dynamically discover the IP address of a home agent on its home link with which it may register its care-of address while away from home. Mobile IPv6 also defines one additional IPv6 destination option. By including the Home Address option in each packet, the sending mobile node can communicate its home address to the correspondent node receiving this packet, allowing the use of the care-of address to be transparent above the Mobile IPv6 support level (e.g., at the transport layer). With IPv6, a mobile node can inform each of its corresponding nodes of its care-of address. This avoids the phenomenon of triangle routing. The Optimization functionality allows direct routing from any correspondent node to any mobile node, without needing to pass through the mobile node's home network and be forwarded by its home agent, and thus eliminates the problem of "triangle routing" present in the base Mobile IPv4 protocol. Since the population of the future Internet is expected to largely be composed of wireless mobile nodes, any such widespread improvement in routing efficiency may have a substantial effect on the continued scalability of the Internet. Here is the building blocks for Mobile IPv6 (see Figure1) and the base protocol refers to [5].
3 Handover Mobile IPv6 already offers a handover procedure, which is recognized to have sufficient in certain circumstances that makes it unsuitable for real-time applications. The purpose of studying handover is to define a solution that reduces handover latency, so that Mobile IPv6 is a better candidate for handling mobility for mobile nodes hosting real-time applications. Additional signaling procedures and optimizations may be proposed to be used in addition to the basic handover procedure specified in Mobile IPv6. Fast Handover is a kind of handover operation that minimizes or eliminates latency for establishing new communications paths to the mobile node at the new access router. Smooth Handover is a kind of handover operation that minimizes data loss during the time that the mobile node is establishing its link to the new access point. Moreover, Seamless Handover a handover that is both fast and smooth. Generally, handovers are considered to fall into one of two classifications: Network-Controlled, whereby some entity in the serving domain directs the establishment of a new link between the mobile node at some point of attachment determined by the network elements. Mobile-Controlled, whereby the mobile node is responsible for determining its new point of attachment and carries out the necessary protocol for making the determination as well as establishing the link at the new attachment point. Now there are some internet-drafts to present different methods for handover. [6] presented that fast handoffs involve anticipating the movement of MNs and sending multiple copies of the traffic to potential Mobile Node movement locations. Both flat and Hierarchical Mobile IPv6 models are considered in this draft. The Hierarchical MIPv6 mobility Management model in [7] already offered improvements to Mobile IP handoffs by providing a local Mobility Anchor Point (MAP) functionality. Some additions are made to the operation of this existing Hierarchical model to achieve Fast Handoffs. When a Mobile Node (MN) undergoes handover from one link to another, it needs to obtain a new care-of address at the New Router as soon as possible in order to be able to send and receive IP packets. [8] outlined a proposal to reduce the delay involved in forming a new CoA so that the mobile node can resume IP packet transmission quickly and the latency involved in forwarding packets to the mobile node until it successfully informs its mobility agent(s) and correspondent Node(s) when handovers are network-controlled. This draft requires that there is a network entity to instruct the mobile node to undergo handover from one access router to another. This network entity is assumed to know the IP addresses and network prefixes of those routers. Other draft [9] proposes a new handoff method using the Explicit Multicast (xcast) technique for the Small Group Multicast (SGM). On the wired section, control/user packets are multicasted by xcast to the Base Stations where MN can access, then packets are passed to the air-link activated between a BS and the MN. For smooth handovers, [10] specifies extensions to Mobile IPv6 which allow additional control structures enabling the transfer of the necessary state during handovers. This state transfer allows the applications running on the mobile node to operate with reduced latency, minimal disruption, and reduced packet loss during handovers. Moreover, Mobile IPv6 regional registration [11] reduces the binding update signaling latency and the signaling load for a mobile node moving within the same visited domain. The latency is reduced by localizing binding updates to the visited domain and the signaling load is reduced by using a regional-aware router for a proxy care-of-address, the regional care-of-address, as seen by hosts outside the visited domain. Registration registration can uses an Anycast Address for all regional routers, creates host routes for mobile node at relevant routers, allows arbitrary hierarchical topology without disclosing details to mobile nodes roaming from other domains, specifies an optimal method for forwarding and be compatible with smooth/fast handovers[12]. An important issue to consider when supporting real-time applications like VoIP in mobile networks is the capability to provide smooth handoffs. A critical requirement for smooth handoffs is to minimize packet loss as a mobile node (MN) transitions between network links. [13] defines a buffering mechanism for Mobile IPv6 by which an MN can request that the router on its current subnet buffers packets on its behalf while the MN completes registration procedures with the router of a new subnet. Once the registration is complete and the MN has a valid care-of address in the new network, the buffered packets can be forwarded from the previous router, thus reducing the possibility of packet loss during the transition. In networks with limited bandwidths, such as wireless cellular networks, compression of IP and transport headers may be employed to obtain better utilization of the available spectrum capacity. When header compression is used along with handoffs in such networks, the header compression context needs to be relocated from one IP access point (i.e., a router) to another in order to achieve seamless operation. [14] proposes a mechanism to achieve this compression context relocation using IPv6 and Mobile IPv6. 4 Qos for Mobile IPv6 As the Mobile Node changes its point of attachment with the Internet, the intermediate network domains traversed by its packets may change. So it is desirable to program appropriate QoS support for the MN's packets in these network domains, so that the performance of QoS-sensitive applications running on the MN is maintained at desired level. In [15] a new IPv6 option called "QoS Object" is introduced Depending on the context, the QoS Object is included as a Destination Option or a Hop-by-Hop Option in IPv6 packets carrying Binding Update and Binding Acknowledgment messages. When included as a Hop-by-Hop Option, QoS Object triggers certain QoS procedures at the intermediate network domains. This document describes these QoS procedures for the cases of best-effort, MPLS, DiffServ and IntServ domains, which practically cover all the cases of QoS enabled network domains that would be available in near future. QoS Object is included, depending on the context, either as a Destination Option or as a Hop-by-Hop Option along with the packets carrying Binding Update and Binding Acknowledgment options. The basic idea is to include QoS Object as a Hop-by-Hop option along with the binding message that travels in the same direction (HA to MN, CN to MN or MN to CN) as that of MN's QoS-sensitive packet stream. As this packet traverses different network domains in the end to end path, the QoS Object is examined at these network domains to program QoS support for the MN's data packets. As we know, there are essentially two types of QoS available: Resource reservation (integrated services): network resources are apportioned according to an application’s QoS request, and subject to bandwidth management policy. RSVP provides the mechanisms to do this [16]. Prioritization (differentiated services): network traffic is classified and apportioned network resources according to bandwidth management policy criteria. To enable QoS, classifications give preferential treatment to applications identified as having more demanding requirements. [17] provides this service. These types of QoS can be applied to individual application "flows" or to flow aggregates, hence there are two other ways to characterize types of QoS: Per Flow: A "flow" is defined as an individual, uni-directional, data stream between two applications (sender and receiver), uniquely identified by a 5-tuple (transport protocol, source address, source port number, destination address, and destination port number). Per Aggregate: An aggregate is simply two or more flows. Typically the flows will have something in common (e.g. any one or more of the 5-tuple parameters, a label or a priority number, or perhaps some authentication information). DiffServ possesses excellent scaling properties from the perspective of the network, but there is not a highly accurate service response to every clients application, so an application may not be aware whether a particular service state is being delivered to the application. Moreover, the lack of end-to-end signaling facilities makes such an approach one that cannot operate in isolation within any environment What appears to be required within the DiffServ service model is both resource availability signaling from the core of the network to the DiffServ boundary and some form of signaling from the boundary to the client application. So we extend the existing signalings such as Binding Update, Binding Acknowledge, Binding Request to build a response model for Mobile IPv6 in DiffServ environment. We are now studying "DiffServ for Mobile IPv6" based on the QoS architecture framework presented in [18]. In [18], a QoS architecture framework with preliminary protocol specifications for next generation wireless IP networks is presented. The architecture is based on differentiated services in that traffic are aggregated and forwarded in backbone network based on per hop behaviors. In the proposed architecture, there is at least one global server referred to as the Global QoS Agent (or GQA) and several local nodes referred to as local QoS nodes (or LQN) in each RAN in each administration domain. The main characteristic of this architecture is that the QGA is in control plane and QLNs are in transport plane. By retaining the global information in central server and separating control and transport, the architecture is flexible, easy to add new services, and more efficient for mobile environment. COPS[19] is used to communicate with GQAs and LQAs. Figure 2 shows the control plane of the architecture. Figure 3 shows that how to guarantee the end-to-end QoS in the proposed architecture. Other considerations about the Integration Mobile IPv6 and DiffServ such as Network provisioning in mobile environments, lack of dynamic configuration, definition and Selection of Service Level Agreements (SLAs), mobile Flow Identification and billing had been considered in the architecture. 5 Conclusions In this paper, the advantages of IPv6 for supporting mobility have been described and the Mobile IPv6 protocol is overviewed. Also the paper introduces the handover that is composed of fast handover and smooth handover. Finally, a new IPv6 option called "QoS Object" and a QoS architecture framework based on DiffServ are introduced. The architecture makes use of the advantanges of InterServ and DiffServ and the extended signaling of Mobile IPv6. Now we are researching on Diffserv for Mobile IPv6. We plan to use the QoS architecture framework based on DiffServ proposed in [18]. Some proposals have been presented and several useful signaling has been defined based on Mobile IPv6 and some simulations have been done. Mobile IPv6 has a lot of advantages over Mobile IPv4 because its design represents a natural combination of the experiences gained from the development of Mobile IP support in Mobile IPv4, together with the opportunities provided by the design and deployment of a new version of IP itself (IPv6) and the new protocol features offered by IPv6. We believe that Mobile IPv6 is the first protocol for the future Internet. References [1] Charles E. Perkins. Mobile IPv6 and Cellular Telephony. 2000 International Conference on Communication Technology Proceedings. [2] Charles Perkins. IP encapsulation within IP. RFC 2003, October 1996. [3] Charles Perkins, editor. IP mobility support. RFC 2002, October 1996. [4] Charles Perkins. Minimal encapsulation within IP. RFC 2004, October 1996. [5] D. Johnson and C. Perkins. Mobility Support in IPv6. Internet Draft, Internet Engineering Task Force. draft-ietf-mobileip-ipv6-12.txt. April 2000. [6] Karim El-Malki, Hesham Soliman. "Fast Handoffs in MIPv6", draft-elmalki-handoffsv6-01.txt (work in progress), November, 2000 [7] H. Soliman, C. Castellucia, K. El Malki and L. Bellier. "Hierarchical Mobile IPv6 and Fast Handoffs", draft-ietf-mobileip-hmipv6-00.txt (work in progress), September 2000 [8] Rajeev Koodli, Charles E. Perkins. "Fast Handovers in Mobile IPv6", draft-koodli-mobileip-fastv6-01.txt (work in progress), October 2000 [9] Yutaka Ezaki, Yuji Imai. "Mobile IPv6 handoff by Explicit Multicast", draft-ezaki-handoff-xcast-00.txt, November, 2000 [10] Rajeev Koodli, Charles E. Perkins. "A Framework for Smooth Handovers with Mobile IPv6", draft-koodli-mobileip-smoothv6-00.txt, 13 July 2000 [11] Jari T. Malinen, Charles E. Perkins. "Mobile IPv6 Regional Registrations", draft-malinen-mobileip-regreg6-00.txt, 14 July 2000 [12] Charles E. Perkins. "Mobile IPv6 for 3G Telephony", presentations in China IPv6 Workshop 2001, May, 2001 [13] Govind Krishnamurthi, Robert C. Chalmers, Charles E. Perkins. "Buffer Management for Smooth HandOvers in Mobile IPv6", draft-krishnamurthi-mobileip-buffer6-00.txt, 13 July 2000 [14] Rajeev Koodli, Manish Tiwari, Charles E. Perkins. "Header Compression State Relocation in IP Mobile Networks", draft-koodli-rohc-hc-relocate-00.txt, 13 July 2000 [15] H. Chaskar, R. Koodli. "A Framework for QoS Support in Mobile IPv6", draft-chaskar-mobileip-qos-00.txt, November 2000 [16]. IETF "Integrated Services" working group. See http://www.ietf.org/html-charters/ intserv-charter.html [17]. IETF "Differentiated Services" working group. See http://www.ietf.org/html-charters/diffserv-charter.html [18] Jyh-Cheng Chen, Anthony McAuley, Armando Caro, Shinichi Baba, Yoshihiro Ohba, Parameswaran Ramanathan. "QoS Architecture Based on Differentiated Services for Next Generation Wireless IP Networks", draft-itsumo-wireless-diffserv-00.txt, July 2000 [19] D. Durham, J. Boyle, R. Cohen, S. Herzog, R. Rajan, A. Sastry. The COPS (Common Open Policy Service) Protocol, RFC2478, January 2000 |