/99/$10.00 (c) 1999 IEEE

(1)

A. Ganz, A. Phonphoem, N. Llopis, I. Kim, K. Wongthavarawat Multimedia Networks Laboratory, ECE Department

University of Massachusetts, Amherst, MA 01003 [email protected]

Z. Ganz

AIM Engineering, [email protected] Abstract-We have developed and implemented novel

so-lutions that provide Quality of Service (QoS) support for voice, video and data applications in wired and wireless LANs that can also follow standards such as Ethernet IEEE 802.3 or wireless IEEE 802.11. Since our solutions can transform existing legacy LANs to an environment that provides the bandwidth, time-delay and other requirements needed to provide users satisfactory quality, the LAN users can achieve signicant productivity increase and cost sav-ings. The limited bandwidth wireless segments are partic-ularly important since wireless devices, such as cordless IP telephones, will be part of future networks. Our solutions can also manage the often limited bandwidth pipeline that connects the LAN to the backbone network or internet ser-vice provider.

In this paper we report initial successful results of our solutions on a Windows based testbed consisting of wired and wireless LAN segments. Our testbed that incorporates a novel software framework provides a research and devel-opment platform for implementing , debugging and testing various MAC policies and their QoS provision for multime-dia applications in wired and wireless LANs. The devel-oped testbed is built using Windows operating system, o-the-shelf wired and wireless network interface cards, and standard applications.

The testbed we introduce in this paper is the rst phase in the ongoing process of having a testbed comprised of a number of wired and wireless segments interconnected through routers, switches, bridges, and T1 lines which pro-vide the interconnection to the Internet.

I. INTRODUCTION

Future networks will need to support multimedia ap-plications such as voice, data and video apap-plications. By converging multimedia applications into a single network, users can achieve signicant productivity increase and cost savings. Users are expected to use a diverse range of multimedia applications: groupware applications , video streaming, video conferencing, teleconferencing, remote learning and other. The problem is that current lead-ing LANs cannot support the Quality of Service (QoS) re-quirements of such multimedia applications. This support problem is especially critical when bandwidth is limited and expensive, such as in a wireless network, or when users demands exceed network capacity. The general expecta-tion is that demand will increase and surpass network ca-pacity since more users become aware of the productivity increase due to multimedia, the in ux of new multimedia applications, and the constant desire to increase picture

quality and size.

Thereby, the requirement to provide QoS support arises in LANs as well as WANs. Our current solutions focus is on LANs and the pipeline that connects such LANs to the backbone network. Such pipelines are often limited in their bandwidth capacity and the expectation is that such capacity will not reach comparable speeds of future wired LANs. This limitation is due to technology and available infrastructure. For example, cable modems speed of 10 Mbps compared to switched Ethernet of 100 Mbps.

Our solution which is implemented in software and runs on each PC in the LAN, will manage network load as well as manage the bandwidth allocated to dierent applica-tions. The principle of our solution: one station in the LAN is assigned the role of the arbiter that manages the network resources, admission control, signaling to other computers a permission to transmit, and other MAC func-tionality. The signaling mechanism is a result of an adap-tive mechanism that learns the network conditions as well as the applications temporarily needs. The rest of the stations have a non-arbiter role and transmit packets only when requested by the arbiter station.

To conduct research in quality of service support, we must have access to a tightly controllable, highly portable, and exible environment that mimics the real world envi-ronments. Such an experimental testbed, in conjunction with well developed modeling and simulation techniques, can be useful for gaining valuable insight into developing better quality of service solutions. To date, there has been signicant work in both modeling and simulations to sup-port the development of techniques that provide quality of service support techniques in LANs [7], yet much work is still needed in experimentation of such techniques. We believe that by developing an experimental testbed envi-ronment, we can facilitate investigations and evaluations that contribute to the development of QoS supporting so-lutions.

The Multimedia Networks Laboratory at the Univer-sity of Massachusetts at Amherst and AIM Engineering, Inc., have developed a number of research and develop-ment platforms on which to design and impledevelop-ment dier-ent aspects of Quality of Service support in Local Area Networks (LANs). Our preliminary prototypes have been

(2)

reported by the authors in [3]and [4].

In the testbed we describe in this paper, we have devel-oped and implemented a novel software architecture that is integrated in Windows protocol stack, below TCP/IP and above the network interface card driver (see Fig. 1). This architecture allows us to have control on each packet that travels between the network and the application. Therefore, we will be able to easily implement quality of service algorithms that control the trac ow to the net-work according to the quality of service required by the application, network conditions, etc.

Our testbed has several features that distinguishes it from other testbeds, for example, [1], [2], [5], and [6]:

can be easily recongured to wired, wireless and hy-brid LANs

can use any commercial o-the-shelf application soft-ware

can use any commercial o-the-shelf wired and wire-less network interface cards

uses Windows PCs

allows easy protocol development, implementation and testing

connection to a backbone network consisting of routers, high speed connections and wireless point to point links.

Through this work we hope to gain insight into support-ing QoS in LANs that are either independent or connected via some links to a backbone network. Using this insight we will pursue the development of solutions that eec-tively address the variety of quality of service problems that occur in today's networks.

We plan to use the testbed to implement and test a number of QoS related topics such as: QoS support in wired LANs, QoS support in wireless LANs, QoS support in hybrid networks, QoS support in multiple LAN seg-ments interconnected through routers and/or bridges and QoS support in the pipeline that interconnects the LAN to the WAN.

The paper is organized as follows. In the next section we introduce an overview of our QoS intelligence. Section 3 introduces the Software Framework that we have de-veloped. Section 4 presents the testbed and preliminary results and Section 5 concludes the paper.

II. QOS INTELLIGENCE

The intelligence that we have developed is composed of two main modules: The Media Access Control (MAC) and the Resource Manager (RM). The RM provides ad-mission control and allocates initial bandwidth. Since this initial bandwidth allocation is static, we have developed in the MAC a just-in-time, adaptive bandwidth allocation mechanism that leads to an ecient system with QoS dif-ferential service. The RM is based on mathematical pro-gramming tools that are capable to eectively consider multiple parameters and constraints. The MAC is based

on a polling mechanism based on a state machine with learning capabilities. Our MAC has a build-in queuing mechanism that allows it to dierentiate among several classes and provides service according to the pre-dened QoS.

In our solution we implement the MAC on top of an ex-isting or native MAC (e.g., IEEE 802.3 and IEEE 802.11) which is implemented on the network interface card (NIC). Actually, our MAC-on-MAC solution uses the native MAC as a transmit/receive (wired or wireless) engine only. The media arbitration is performed only in our MAC. The na-tive MAC acknowledgment and retransmissions are dis-abled since 1) we use broadcast at the existing MAC layer (disabling all acknowledgement mechanisms at the native MAC) and 2) our MAC only allows one station to trans-mit at any given time (there will be no collisions, and therefore no retransmissions at the native MAC).

A. Media Access Control

The arbiter station polls sessions frequently enough to sustain the assigned communication rates for those ses-sions, but does not poll substantially more often than re-quired to sustain the assigned rates. This polling approach avoids use of bandwidth with the overhead of unnecessary polling.

Sessions belong to one of multiple classes. For simplic-ity of explanation we assume only two classes. The rst class includes quality-of-service requirements. This class is referred to as the QoS class. The other class of ses-sions is the non-QoS class. The arbiter station allocates resources to QoS sessions in preference to non-QoS ses-sions. In polling, the QoS sessions are polled to satisfy their QoS requirements while non-QoS sessions are polled as a second priority.

Our MAC has a build-in queuing mechanism that allows it to dierentiate among several classes and provide service according to the pre-dened QoS. Each class is assigned a unique pre-determined queue. The MAC also includes an adaptive mechanism that is used to adjust the polling pattern for a session in response to that session's actual data transmissions. If a session does not have data ready for transmission when polled, that session may not require polling as often in the future to support it's actual data rate. The learning mechanism is using a state machine for each session in the network. The frequency of the polls is proportional to the current state. Transition rates between the states are determined by the actual trac of the specic session.

B. Resource Manager

The Resource Manager accepts a quality of service re-quirement from a user for a session either by the user ex-plicitly specifying the requirement for the session, such as by specifying a minimum data rate, or by choosing from

(3)

a pre-determined set of classes of sessions (e.g., as dened by the MMCF forum). Such classes can be dened by a number of quality of service metrics, such as a maximum and minimum data rate, or any other communication re-lated parameters. Another way of obtaining the applica-tion parameters is to communicate with transport layer protocols such as RTP or RSVP (recall that our software is located below the TCP/IP). The Resource manager also maintains network statistics, e.g. retransmission rate esti-mates for each pair of stations. For each admitted session, the resource manager computes the necessary bandwidth and associated polling rate. Note that these adjusted rates may change in future reallocations as the retransmission rate estimates change. If the RM cannot nd a feasible set of assigned rates, then it removes one or more sessions from the set of sessions polled during the rst phase of each cycle.

III. SOFTWARE FRAMEWORK

The design guidelines driving the software framework: card independence, i.e., use of the software on any

LAN (wired or wireless)

application independence, i.e., use the software with any o-the-shelf application

easy to plug in modules that control the packets TCP/IP compliant, i.e., no changes are requested in

the existing protocol stack

We chose to work with Windows operating system. We will brie y describe the software architecture that we have designed and implemented.

Packets that are generated by network applications fol-low the folfol-lowing path in Windows protocol stack:

1. Winsock (1 or 2). 2. TCP/IP, UDP/IP

3. NDIS network interface card device driver. 4. Wireless or wired network interface card (NIC). Our software framework and intelligent modules are im-plemented between steps 2 and 3 dened above. Both these Windows protocol stack modules and our software modules are depicted in Fig. 1.

User Applications:

The user may open real-time

multimedia applications, such as video-conferencing, and non-real-time applications, such as le transfer. This user may open several applications in parallel.

Graphical User Interface (GUI):

The GUI is

de-veloped at the user level. There are two types of GUI: user GUI and QoS developer GUI. The user GUI is de-signed to allow user interaction with the multimedia QoS support mechanism. Such input may include the ability to modify QoS default parameters, negotiate relaxed QoS service, and other advanced features. The user may also get output such as network statistics. The QoS developer GUI shown in Fig. 2 allows the developer to easily debug the QoS intelligence modules implemented in the software framework. Upper Layer Framework GUI Applications NETWORK User Level Kernel Level WINSOCK TCP/IP NIC driver Lower Layer Framework Network Statistics Module Association/ Disassociation Module Medium Access Control Module Resource Manager Module Other Modules Existing Module Framework Testbed Module Qos Intelligence Module

Fig. 1. Software Architecture

The software framework that is shown in Fig. 1 is com-posed of two main layers: lower layer framework (VxD) and upper layer framework.

Upper Layer Framework:

The major task of the

upper layer framework is to act as a switching board. It accepts packets from the lower layer framework and directs it to the modules (e.g. the MAC, the RM) connected to it and vice versa. It also interfaces with the GUI that displays debugging and status messages (see Fig. 2) and gets input from the user to the testbed.

Lower Layer Framework

: this layer is inserted in

the Windows protocol stack and bound to higher proto-col stack such as TCP/IP and to the network card de-vice driver. The main purpose of this layer is to intercept any packet from TCP/IP, before passing it to the net-work card, and from netnet-work card, before passing to the TCP/IP. It also performs the interface and address trans-lation functions to and from the higher layer. Using this method, the software is independent of the network card. This lower framework is implemented as Virtual Device Drivers (VxD) in Windows.

The framework we created allows us to:

1. Control the sending and receiving of all packets 2. Integrate all the modules together

3. Easy relocate the dierent modules 4. Work with dierent network cards

5. Test and debug the system at various stages.

Intelligence Modules:

The intelligence modules that

govern the QoS in the network are: the MAC module and the RM module.

(4)

Fig. 2. Testbed GUI

IV. OUR TESTBED

We will start with the testbed software and hardware description and continue with a brief description of pre-liminary experiments that we have conducted.

A. Testbed Setup

Hardware: The choice of a hardware platform is driven by the following goals:

Easy to install (hardware and software)

Easy to recongure (switch between the wireless, wired and mixed environments)

Reasonable cost (leverage the economy of scale of desktop and laptop PCs)

Easy to expand

Can run a large range of commercial applications Multimedia hardware support (sound card, speakers,

etc.)

To meet the above goals we have chosen the following hardware platform:

Desktop and laptop PCs with multimedia capabilities Networking equipment: 10-Mbps PCMCIA Ether-net cards, 2-Mbps PCMCIA Harris Wireless cards, 10Base-T Network hubs, Wireless to wired access points.

The testbed hardware setup is shown in Fig. 3a, 3b and 3c for Ethernet, Wireless LAN, and mixed medium (hybrid), respectively. To ease the reconguration process between the wired and wireless platforms, we chose to use PC card slot which is installed on each computer and also use PCMCIA wireless and wired network interface cards (NIC). This choice allows us to easily recongure between

PC PC PC PC Hub PC PC PC ,, ,, PC ,, ,, PC ,, ,, PC ,, ,, PC ,, PC ,, Hub Access Point , a) b) c)

Fig. 3. Testbed setup for a) Ethernet b) Wireless LAN c) Hybrid

Simulated T1 connection 1.544 Mbps ,,Simulated Microwave, Ethernet 10 Mbps Simulated Fractional T1 connection 64 Kbps Simulated T1 connection 1.544 Mbps 10 BT 10 BT ,, ,, Access Point , , , , Hub , Access Point , , , Hub 10 BT Hub Internet

Ethernet over Fiber 10 Mbps

Router Cisco 2500 Router: Cisco 2500 Router: Cisco 4000 Router: Cisco 2500

Bridge

10 BT

Fig. 4. Testbed Expansion (in progress)

the media: just plug in a new PCMCIA NIC and reboot the computer and you get a new LAN.

We are currently in the process of expanding the testbed to include a number of wired and wireless segments inter-connected through CISCO routers, switches and bridges, and T1 lines which interconnect us to the Internet as shown in Fig. 4.

Software: Windows 95

We rst create data les, audio and movie clips with various bandwidth requirements. These les are in-stalled at the stations chosen to be ftp or http servers. Applications: ftp and http servers, media player, ftp

client, netscape browser.

Network connectivity/monitoring/debugging/testing tools: 1) EtherPeek from AG Group that performs trac monitoring by capturing all trac on the LAN,

(5)

2) NetMedic for PC for network trac monitoring, 3) SoftICE: we monitor each packet that is sent from our lower layer software framework to the network inter-face card, 4)The GUI that we have developed (see Fig. 2): this GUI monitors and displays all messages that arrive at the upper layer software framework. B. Preliminary Experimental Results

Our test goal is to demonstrate QoS support for multi-media applications in wired and wireless LANs in which we have installed our software, and contrast it to LANs on which our software is not installed and that do not provide multimedia support.

Experiment 1:

use 4 computers in the testbed

intercon-nected through a 10 Mbps Ethernet hub.

1. Run Mpeg player to retrieve and display the prepared movie clip remotely (from the http server). Observe the quality of the picture. Quality is very high.

2. Run a number of non-real time trac streams such as ftp. Add one connection at a time. Observe the qual-ity of the movie. With 3 ftp sessions we observed severe quality degradation of the video clip: the video and audio stop very frequently. We observed intense collisions in the Ethernet hub (using the collision light integrated in the hub).

Experiment 2:

intercon-nected through a 10 Mbps Ethernet hub.

1. Activate the framework with the new MAC module 2.Run Mpeg player to retrieve and display the prepared movie clip remotely (from the http server). Observe the quality of the picture. Quality is very high.

3. Run a number of non-real time trac streams such as ftp. Add one connection at a time. Observe the quality of the movie. We have not observed any degradation of the video quality in spite of intense competition from ftp applications. We have observed that there are no colli-sions in the network by checking the collision light in the Ethernet hub. We observe that ftp applications get less bandwidth than in Experiment 1.

Experiment 3:

intercon-nected through a 2 Mbps IEEE 802.11 compliant Harris wireless PC card.

1. Run audio player to retrieve and play the prepared audio clip remotely (from the http server). Observe the quality of the sound. Quality is very high.

2. Run a number of non-real time trac streams such as ftp. Add one connection at a time. Observe the quality of the sound. With 3 ftp sessions we observed severe quality degradation of the audio clip.

Experiment 4:

intercon-nected through a 2 Mbps IEEE 802.11 compliant Harris wireless PC card.

1. Activate the framework with the new MAC module 2. Run audio player to retrieve and play the prepared

audio clip remotely (from the http server). Observe the quality of the sound. Quality is very high.

3. Run a number of non-real time trac streams such as ftp. Add one connection at a time. Observe the quality of the sound. The quality of the sound is maintained in spite of intense data trac. We observe that ftp applications get less bandwidth than in Experiment 3.

V. DISCUSSION

In summary, our preliminary test results show that the media access control module that we have implemented provides quality of service support in a wired and wire-less LANs. We have observed that with our software framework, the multimedia applications' quality is main-tained in spite of intense competition from a number of ftp streams. Without our software framework, in Ether-net and in the wireless LAN these multimedia applica-tions' quality is severely degraded when a number of ftp sessions are active.

We plan to continue experimentation to validate the quality of service techniques we develop. We need to ex-pand the set of applications, quality of service solutions, and make full use of the mixed media environment of the testbed.

ACKNOWLEDGEMENT

We would like to thank Harris Semiconductor Corp. rep-resented by Steve Andrezyk for their technical support in setting up the current testbed and John Jackson for his technical assistance in our testbed expansion eorts.

REFERENCES

[1] Shih-Fu Chang, Alexandros Eleftheriadis, Dimitris Anas-tassiou, Stephen Jacobs, Hari Kalva and Javier Zamora, \Columbia's VoD and Multimedia Research Testbed with

Het-erogeneous Network Support," Columbia University, New York,

Multimedia Tools and Applications 5, p 171-184, 1997. [2] Shuang Deng, Alan R. Bugos, and Paul M. Hill, \Design and

Evaluation of an Ethernet-Based Residential Network,"IEEE Journal on Selected Area in Communications, Vol.14, No.6, August 1996.

[3] A. Ganz, D. Awduche, J. Euh, I. Kim, E. Haslett, S.H. Park, A. Phonphoem, Z Ganz, \ Multimedia Wireless LAN Prototype",

3rd Telecommunications R&D conference in Massachusetts, Lowell, MA, November 1997.

[4] A. Ganz, Z. Ganz and S. Andrezyk, \ Multimedia Wireless LAN Architecture", 3rd Telecommunications R&D conference in Massachusetts, Lowell, MA, November 1997.

[5] William E. Johnston, \BAGNet: A High Speed, Metropolitan Area, IP over ATM Network Testbed," http://george.lbl.gov /BAGNet.html#tech, Lawrence Berkeley Laboratory,

Univer-sity of California, Berkeley, CA, 94720.

[6] Michael J. Katchabaw, Hanan L. Luyya, and Michael A. Bauer, \A Quality of Service Management Testbed," Proceed-ings of the IEEE Third International Workshop on Systems Management, Newport, RI, p 57-66, 1998

[7] Andrew Tanenbaum, \Computer Networks", Third Edition,