MINT - A Mobile Internet Router

Transcription

1 MINT - A Mobile Internet Router Anders Klemets, Gerald Q. Maguire2, Frank Reichert, and Mark T. Smith3 Teleinformatics at Royal Institute of Technology, Stockholm, Sweden komputer Science at Columbia University, New York NY, USA 3Media Technology Lab at Hewlett Packard Laboratories, Palo Alto CA., USA Abstract Tohy, mobility of portable computers and workstations is not transparent to users. lky adjust to reduced services as long as they have no connection to a supporting infrastructure. The goal of the Walkstation project is to realize a user transparent mobile IP router (MINT) for wireless links (infrared and radio) operating at 1-10 Mbiv sec. For the study of user behavior and system characteristics a campus wide testbed (ERIC) with stations is planned to demonstrate the new solutions found in the Walkstation II project. 1. Introduction A fundamental shift is occurring which is moving computing and communication together in to one synergistic activity. New technologies have paved the way, and their continuing rapid introduction will accelerate the rate of this change. Due to the existence of portable phones and portable computers, user have now become accustomed to being able to communicate and compute independent of their location. However, they have not usually been able to have their computers communicate independent of location. Thus with the exception of serial line operation via (cellular) phone modems, low data rate paging services, and low rate packet radio communication - users have been forced to attach their computer via umbilical cords to the local wired infrastructure. The AT&T Personal Communicator [8] is one of the first commercial examples of a small sized personal communication device combining computation and communication. The recent introduction of HP Omnibook 300 and the introduction in of an Notebook with an integral radio modem shows that this trend is moving from research to commercial products. This project builds upon the existing work on Mobile- IP protocols for TCP/IP which has already been done at Columbia University [l]. This Mobile-IP work is the result of the earlier Student Electronic Notebook project which showed that mobile workstations with a full UNIX and X-windows environment were feasible and that many users found them to be useful. The current project seeks to go beyond the level of tens of machines to find out more about correlated traffic effects, the effects of scaling wireless network to thousands of users, how to achieve high transmission rates at low cost, how to construct cellular spread spectrum radios, etc. While it is now possible to add a radio modem to a portable computer, for example via the increasingly common FCMCIA interface, it is not easy to utilize this interface to provide either a seamless interconnection or to automatically provide the correct wireless interface. The user is faced with (a) determining the correct interface to use, (b) plugging it in, (c) configuring the software to use this interface, and (d) using this interface via software which is typically very aware of which specific interface is being used. If the user changes location, or in some cases if the environment around them changes, the user must select a new interface and repeat the above process. In order to provide user transparent mobility, we have adopted a different approach, we have placed all of the facilities needed for mobility into a Mobile INTemet (MINT) Router. Utilizing this separate router, the user simply attaches their portable machine to this single device which provides all of the hardware and sofhvare needed to support tetherless mobility. 2. Communication protocols The integration of mobile stations into existing networks is being addressed by an Internet Working Group for Mobile IP. It was established officially in June 1992 with milestones for posting an Internet Dtdt (November 1992) and a new,, protocol in March, 1w3. It has not yet (as of October, 1993) produced such a draft. However four working drafts had been submitted by X/93 $ IEEE 70

2 November 1992 by Columbia University and Xerox PARCPI, IBM [41, [SI, SONY [61, and Matsushita 171. We have chosen the Columbia mobile IP protocol ( Mobile*IP ) [3] as the basis for our routing software. In this protocol the network consists of mobile hosts (MH) and mobile support routers (MSRs) which are attached to the wireless and fixed LAN. All MHs have a peamanent address on a virtual network (e.g., mobile.kth.se in Fig. 4). The virtual network covers a whole campus (which in the case of the KTH will involve two physically separated campuses), but appears to the outside world as a single network. The virtual network is in reality composed of many physical cells.the MSRs execute a distributed algorithm to heal the partitions in this virtual network and give the effect of providing a single network. MOBILE.KTH.SE n TDS.KTH.SE RADIO.KTH.SE IT.KTH.SE Fig. 1. Columbia Mobile*IP Scenario By having each MINT act as a Mobile Support Router (MSR) we modify the network diagram shown in the above figure, into that shown below. By running all of the protocols which are concerned about mobility on the separate MINT router, we hope to provide the facilities of mobile IP available in the Student Electronic Notebook project [3] without having to design and construct a new notebook, which is a very difficult engineering task.. 3. The Mobile Internet Router - MINT As a first step in providing mobility of personal computers and workstations in a transparent fashion to users we have proposed moving all of the software and hardware for this mobility and communication to a separate device - MINT. This approach has some major advantages: it localizes all specific hardware and software efforts in to a separate device which is compatible with most host computers, the operating system in the host computers need not require modifications in order to support basic mobility, and the MINT can be optimized independently of the attached host. While transparent mobility has many desirable MOBILE.KTH.SE I TDS.KTH.SE RADIO.KTH.SE IT.KTH.SE Fig. 2. Columbia Mobile*IP Scenario with MINTS properties, we recognize that we can only provide functionally transparent mobility - since the performance of the different interfaces may vary. Thus a user need not see any functional difference between the use of their computer when in their office or in another location within the supporting radio infrastructure. They may see some performance differences based on the changes in competing traffic (note that this is due both to competition for radio bandwidth and competition for traflic through the base stations) and varying radio channel characteristics. Our primary focus has been on interfaces which can allow us to realize a user transparent TCPAP router for wireless links (infrared and radio) operating at 1-10 MbiVsec. While studying the scenario in Fig. 3, we realized that the wireless communication device (shown as? in the diagram) for the mobile host and for the basestations could be realized by the same kind of hardware. While the communication hardware is symmetric, we have chosen to use an asymmetric software configuration which puts a greater portion of the communication for the distributed protocol onto the device attached to the wired network. However, we also permit mobile-to-mobile communication, thus two or more mobiles can communicate even though they are isolated from a wired infrastructure. It should be noted that this method of implementing the base stations turns Fig. 4 into the configuration shown in Fig. 4. The MSR now consists of the MINT hardware with the addition of the MSR software. The MINT hardware has three major parts (Fig. 3, one for the connection to the host (or the backbone Ethernet in the case of the MINT acting as an MSR), one for connecting to the mobile network (wireless LAN (radio or infrared) or point-to-point wired network), and a processing part for executing the communication protocols. Thus a MINT serves as much more than a 71 I

3 ETHERNET Fig. 3. Wireless Communication Scenario DUAL PORT Serial Parallel Fig. 5. Basic components of a MINT 4. Wireless interfaces Fig. 4. MSRs implemented with MINTS mobile modem, it actually routes packets over potentially multiple paths with varying connectivity and quality. Essential to the construction of such a router is that it must support many interfaces - since by the above definition it should provide the ability to interface to any external network or communication system. Our current prototype supports the following interfaces: two serial ports, two ethemets (both with AUI connectors, and one with a built-in Thin-LAN connector), 1 parallel port, 1 SCSI port, and a prototyping area to add other interfaces. By using one of the etbemet interface as the connection to the existing departmental network, it should not be necessary to install special purpose wiring dedicated to mobile communication. Instead the existing network, which normally is globally available, is simply used as a backbone for base stations Initially each MINT will execute a MACH kernel on top of which we will use the Columbia Mobile*IP protocol. The MINT hardware has been developed in conjunction with HP Labs (Palo Alto) while the software is the responsibility of the KTH collaborators. There exists a spectrum of wireless interface needs. There are at least two axes to this spectrum, bandwidth and coverage area. At one end of this spectrum are wireless data networks based on DECT or other wireless PBX technology. This approach can be used to eliminate cables within an office environment while providing low data rats (up D 4OOkbit/sec) to a small number of users. At the other end of the performance spectrum are local area radio networks, such as the Telesystems ARLAN, NCR WaveLan [4], and Motorola Altair [I]. These systems offer high data rates (0.5 - lombit/sec), to a larger number of users within a limited area, but currently consume too much power and space to fit into a portable computer. Problems of the DECT and existing radio LAN products have been previously described[21. Along the other axis we see a range of devices such as the GFdEricsson Mobidem and cellular phones combined with modems providing low data rates (8kbiVsec) over very large geographic areas. These devices have the advantages or large manufacturing volumes, small size (with some PCMCIA versions now coming to market), relatively low power, and low purchase cost. There is a question about the operational costs, as they generally utilize an infrastructure provided by a local operating company and thus users generally are charged a basic fee, plus a per packet charge. A number of manufacturers are 72

4 defining a cellular data packet protocol to answer the needs of this market (this will allow interoperability of equipment interconnected across the infrastructure). We have taken a different approach to providing wireless interfaces. For use in local settings requiring high data rates and low cost we have developed a lombit/sec infrared interface which can simply be attached to the AUI connector and provides all the functionality of an ethemet MAU, except for collision detection - which must be handled by the processor in software. Although the current costs of IR emitters for operation at this high speed are expensive (-$300 in quantity one) it is expected that with increased volume these prices wili fall. For high speed operation over the local campus Daniel Kerek in the Electronic Systems Design Department of the Royal Institute of Technology is developing a high speed (2 Mbiusec) spread-spectrum radio which will feature multiple receivers, so that although the user can only transmit using a single spreading code, they are able to receive with multiple spreading codes, thus facilitating listening for new base stations while listening to an existing base station. A prototype of this system, constructed using 3 Xilinx chips for the receiver and 1 for the transmitter, is currently operating at 500kbiVsec. The next version of this radio will also include the ability to receive GPS signals, in order to allow the MINT to determine its physical location. In the interim, while these new interfaces are being developed we will add a number of PCMCIA slots to the MINT and use existing single function cards to add additional existing interfaces. However, in order to provide users with mobility and universal connectivity (i.e., if there exists any wireless infrastructure the user should be able to utilize it) we need to consider not only what additional interfaces should be provided but how we might provide them. As is becoming increasingly clear [91, the performance of general purpose processors has reached a sufficient level that we can synthesize specific YO devices on the fly, i.e., if we need a modem we can execute the DSP software on the main processor. Thus we are now in the process of planning how to add a number of additional interfaces using this method. It should be noted that the circuitry of the current prototype radio interface can be modified by simply reloading the Xilinx FPGAs with a new bit string, the major problem is to calculate what this bit string should be. Clearly a number of different radios could be precomputed and these precomputed personalities downloaded as necessary. It is not yet clear if this is the best method of providing a number of interfaces or if a better method is to make an ASIC which has one section per interface and simply power these sections on and off. 5. Evolution to a Walkstation Once the initial MINTS and their software are completed we will next expand them into Walkstations, i.s., add the additional interface to support display(s), audio input and output, pen interfaces,.... Until these devices are constructed we will utilize existing notebook computers for the user interface and location to execute user software. 6. The Walkstation II Project The Walkstation I1 project will not only investigate wireless networks but a complete radio based cellular system for interactive mobile multimedia applications including aspects of VLSI design, radio communication, network protocols and mobile application services. In order to realize this environment we will combine the mobile internet routers (MINT) and our experimental infrared transceivers to construct a testbed called ERIC (Electrum Radio based network for Interactive multimedia Communication). The existence of this testbed will enable research on distributed applications, radio link and network protocols, network measurements, and bow to integrate the electronics and algorithms into custom designed VLSI chips in order to achieve low power systems. In order to evaluate the overall system for multimedia applications we must address topics such as: robust mobile file systems, distributed databases, disconnected operations, and layered audiohide0 compression. These services are the basis for demonstration of two sample applications: distributed education, and bedside computers for hospital environments. Experience from the Student Electronic Notebook project [l] shows that user traffic is partly coherent. Studies of user behavior and correlated traffic will result in new application based communication methods and thus bandwidth can be saved by distributing the same information to different users at the same time. 7. Summary The MINT router realizes user and host communication software transparency by locating all specific hardware and software efforts in a local device which is compatible with most host computers. The operating system in the host computers need not require modifications in order to support basic mobility. Thus a user need not see any functional difference between the use of their computer when in their office or in another location within the supporting radio infrastructure. To further exploit the characteristics of mobility there will need to be operating system and application level 73

5 changes. Extensive studies will need to be made on how to adapt these higher levels to truly exploit rather than simply tolerate the varying bandwidth and connectivity of radio channels. We are proposing the creation of a mobility applications programming interface to define what this information is and how applications can determine the characteristics of the communication channel or be notified of changes. In conclusion, we believe that the existence of a ubiquitous network infrastructure will also cause the creation of new applications which can utilize their mobility and exploit knowledge of their location. The authors can be reached by electronic mail at: klemets 8 it.kth.se, maguire 8 cs.columbia.edu, reichert@it.kth.se, msmith@hplren2.hpl.hp.com. 8. References [I] 121 D. Duchamp, S. Feiner, G. Maguire, Software technology for Wireless Mobile Computing, IEEE Network Magazine, Nov R. Hager, A. Klemets, G.Q. Maguire Jr., M.T.Smith, and F. Reichert, MINT - A Mobile Internet Router, IEEE Vehicular Technology Conference, May [3] J. Ioannidis, D. Duchamp, G. Maguire, S. Deering, Protocols for supporting Mobile IP hosts, Internet Draft available from parcftp.xerox.com ( ) in pubhobile-ipl, June [4] Y. Rekhter, Ch. Perkins, Optimal Routing for mobile hosts using IP s Source Route option, Internet Draft available from parcftp.xerox.com ( ) in pub/ mobile-ip/. October [SI Y. Rekhter, Ch. Perkins, Support for Mobility for Connectionless Network Layer Protocols, Internet Draft available from parcftp.xerox.com ( ) from avalon.mpce.mq.edu.au:/dist, January [6] F. Teraoka, M. Tokoro, VIP: Host Migration Transparency in IP Networks: The VIP Approach, Computer Communication Review, Vol. 23, No. 1, January [7l H. Wada, T. Yozawa. T. Ohnishi, T. Tanaka, Mobile Computing Environment Based on Internet Packet Forwarding, USENIX Winter 1993 Technical Conference. January [8] B. Ryan, Communications Get Personal, Byte Magazine, Vol. 18, no. 2, February [9] Lawrence C. Stewart, Andrew C.Payne, and Thomas M. Levergood, Are DSP Chips Obsolete? Digital Equipment Corporation, Cambridge Research Lab, CRL Report 92/10, November 16,