wireless convergence architecture: a case study using gsm and wireless lan

Wireless Convergence Wireless Convergence Architecture: A Case Study Architecture: A Case Study Using GSM and Wireless Using GSM and Wireless

LANLANNIKOS A. NIKOLAOUNIKOS A. NIKOLAOUKONSTANTINOS G. VAXEVANAKIS, SOTIRIOS I. MAKONSTANTINOS G. VAXEVANAKIS, SOTIRIOS I. MANIATIS and IAKOVOS S. VENIERISNIATIS and IAKOVOS S. VENIERISNICHOLAS A. ZERVOSNICHOLAS A. ZERVOS

通訊所簡精政通訊所簡精政

AbstractAbstract

The evolution of wireless networks has motivated The evolution of wireless networks has motivated the expansion of the static business environment to the expansion of the static business environment to a mobile and wireless one.a mobile and wireless one.

This paper presents the Wireless Convergence This paper presents the Wireless Convergence Architecture (WCA) that incorporates different Architecture (WCA) that incorporates different wireless interfaces under the same mobile terminal.wireless interfaces under the same mobile terminal.

A specific implementation is presented, based on A specific implementation is presented, based on two complementary wireless technologies – in two complementary wireless technologies – in terms of coverage area – an IEEE 802.11-terms of coverage area – an IEEE 802.11-compliant in the short local and a GSM in the wide compliant in the short local and a GSM in the wide area.area.

OutlineOutline

IntroductionIntroduction

Wireless Convergence Architecture overviewWireless Convergence Architecture overview SupervisorSupervisor Resource RepositoryResource Repository IP Mobility Enhancement Client, ServerIP Mobility Enhancement Client, Server Abstract Socket Layer and Communication ManagerAbstract Socket Layer and Communication Manager

Reference network environmentReference network environment

Experimental resultsExperimental results

ConclusionsConclusions

1. Introduction(1/4)1. Introduction(1/4)

The trend in network evolution favours the presencThe trend in network evolution favours the presence of various network technologies that reveal differee of various network technologies that reveal different characteristics, in terms of coverage area, underlnt characteristics, in terms of coverage area, underlying physical medium, medium access control (MAying physical medium, medium access control (MAC), available bandwidth and delay.C), available bandwidth and delay.At the same time, various wireless technologies, witAt the same time, various wireless technologies, with different pros and cons, are becoming more populh different pros and cons, are becoming more popular, as they eliminate the disadvantage of having the ar, as they eliminate the disadvantage of having the user restricted in a particular location.user restricted in a particular location.in the near future, the expansion of the working envin the near future, the expansion of the working environment to a global one will be based on different ironment to a global one will be based on different wireless access technologies, interworking with eacwireless access technologies, interworking with each other transparently.h other transparently.


Current wireless networks provide connectivity, Current wireless networks provide connectivity, targeting specific environments that pose targeting specific environments that pose restrictions in terms of available bandwidth, restrictions in terms of available bandwidth, coverage area and cost.coverage area and cost.A common difficulty faced by mobile users, which A common difficulty faced by mobile users, which actually contradicts their “mobile” nature, is that actually contradicts their “mobile” nature, is that they are constrained by the coverage area of the they are constrained by the coverage area of the wireless technology used.wireless technology used.This paper introduces the This paper introduces the Wireless Convergence Wireless Convergence Architecture Architecture (WCA) that caters for the (WCA) that caters for the aforementioned requirements, introducing new aforementioned requirements, introducing new software components, both at the terminal and the software components, both at the terminal and the local Intranet.local Intranet.


Seeking for complementary technologies that could Seeking for complementary technologies that could provide connectivity for both indoors and outdoors, provide connectivity for both indoors and outdoors, two specific wireless technologies have been two specific wireless technologies have been selected, namely the IEEE 802.11 Wireless LAN selected, namely the IEEE 802.11 Wireless LAN and the Global System for Mobile communications.and the Global System for Mobile communications.

Taking into account this specific implementation, a Taking into account this specific implementation, a reference network environment has been reference network environment has been determined and experiments were performed using determined and experiments were performed using standard and proprietary networking applications.standard and proprietary networking applications.

2. Wireless Convergence 2. Wireless Convergence Architecture overview(1/4)Architecture overview(1/4)

In order to free the mobile user from location restrictions the In order to free the mobile user from location restrictions the mobile terminal must be equipped with multiple wireless netmobile terminal must be equipped with multiple wireless network adapters.work adapters.

Following the distinction between indoors and outdoors comFollowing the distinction between indoors and outdoors communications, it seems reasonable that two adapters – one fomunications, it seems reasonable that two adapters – one for each case – would be sufficient.r each case – would be sufficient.

There are two major issues that must be sufficiently resolveThere are two major issues that must be sufficiently resolved, namely the location transparency and the resilience to ted, namely the location transparency and the resilience to temporal wireless link disconnection.mporal wireless link disconnection.


To adequately address them, new software components To adequately address them, new software components have to be incorporated both at the terminal and the network have to be incorporated both at the terminal and the network side (local Intranet), as shown in figure 2.side (local Intranet), as shown in figure 2.

As far as the network side is concerned, all the As far as the network side is concerned, all the modifications are introduced in a dedicated machine called modifications are introduced in a dedicated machine called Gateway/ProxyGateway/Proxy..

Location transparency involves the automatic switching from Location transparency involves the automatic switching from one wireless interface to the other, when moving from one wireless interface to the other, when moving from indoors to outdoors and vice-versa.indoors to outdoors and vice-versa.

IPMEC(IP Mobility Enhancement Client)IPMEC(IP Mobility Enhancement Client) IPMES(IP Mobility Enhancement Server)IPMES(IP Mobility Enhancement Server)


A separate pair of modules has been introduced, A separate pair of modules has been introduced, consisting of the consisting of the Abstract Socket Layer Abstract Socket Layer (ASL) and (ASL) and the the Communication Manager Communication Manager (CM), placed at the (CM), placed at the mobile terminal and the Gateway/Proxy, mobile terminal and the Gateway/Proxy, respectively.respectively.

Two more components have been identified and Two more components have been identified and introduced in the terminal side, namely the introduced in the terminal side, namely the Supervisor Supervisor and the and the Resource Repository Resource Repository (RR).(RR).

2.1 Supervisor2.1 Supervisor

The Supervisor is responsible for monitoring The Supervisor is responsible for monitoring the connectivity status of the underlying the connectivity status of the underlying wireless adapters.wireless adapters.

Supervisor continuously examines the signal-Supervisor continuously examines the signal-to-noise ratio (SNR) of the active interface.to-noise ratio (SNR) of the active interface.

Supervisor takes into account predefined Supervisor takes into account predefined priorities among the available wireless priorities among the available wireless interfaces, to resolve conflicts where more interfaces, to resolve conflicts where more than one wireless adapter is operational.than one wireless adapter is operational.

2.2 Resource Repository2.2 Resource Repository

The Resource Repository (RR) is used for The Resource Repository (RR) is used for storing critical information for the proper storing critical information for the proper operation of the mobile terminal.operation of the mobile terminal.

RR provides an interface through which RR provides an interface through which registered modules or user-applications are registered modules or user-applications are asynchronously notified when the value of a asynchronously notified when the value of a specific parameter changes.specific parameter changes.

All the information is organized in tree-like All the information is organized in tree-like structure, thus, making future extensions easy.structure, thus, making future extensions easy.

2.3 IP Mobility Enhancement Client, 2.3 IP Mobility Enhancement Client, Server(1/2)Server(1/2)

The IP Mobility Enhancement Client and Server team up The IP Mobility Enhancement Client and Server team up with the IP protocol to achieve location transparency and with the IP protocol to achieve location transparency and hide mobility from higher layer protocols and, eventually, hide mobility from higher layer protocols and, eventually, applicationsapplications

IPMEC is mainly responsible for redirecting IP packets over IPMEC is mainly responsible for redirecting IP packets over the correct underlying wireless interface.the correct underlying wireless interface.

IPMEC does not determine by itself which wireless interface IPMEC does not determine by itself which wireless interface is active or inactive.is active or inactive.

The Supervisor, through RR’s asynchronous notification The Supervisor, through RR’s asynchronous notification mechanism, conveys this kind of information to IPMEC.mechanism, conveys this kind of information to IPMEC.

2.3 IP Mobility Enhancement Client, 2.3 IP Mobility Enhancement Client, Server(2/2)Server(2/2)

When switching occurs, the terminal’s IP addWhen switching occurs, the terminal’s IP address is not modified.ress is not modified.

This is one of the prerequisites that enables tThis is one of the prerequisites that enables the terminal to switch between interfaces, withe terminal to switch between interfaces, without having the active transport connections hout having the active transport connections terminated.terminated.

IPMES component resides in the Gateway/PrIPMES component resides in the Gateway/Proxy and implements the complementary funcoxy and implements the complementary functionality of IPMEC.tionality of IPMEC.

2.4 Abstract Socket Layer and 2.4 Abstract Socket Layer and Communication Manager(1/3)Communication Manager(1/3)

The Abstract Socket Layer (ASL) and Communication Manager (CM) pair of modules provide application resiliency to wireless link disruptions.

The basic idea behind the operation of those two modules is to split an end-to-end TCP session into three consecutive parts – Application-ASL, ASL-CM and CM-Server – as shown in figure 3.

In this manner, the wireless part of the communication is isolated and the possible side effects of a temporal wireless link disconnection can be absorbed.

ASL resides at the mobile terminal side and provides a socket-like Application Programming Interface (API).


Whenever an interruption occurs, ASL re-establishes transpWhenever an interruption occurs, ASL re-establishes transport connections to CM, and, subsequently, re-associates sesort connections to CM, and, subsequently, re-associates sessions with physical connections.sions with physical connections.

以下圖解說明以下圖解說明 ASLASL 和和 CMCM 間的運作。間的運作。

3. Reference network 3. Reference network environment(1/4)environment(1/4)

It accommodates two wireless networks, based on different tIt accommodates two wireless networks, based on different technologies, namely the IEEE 802.11 Wireless LAN and the echnologies, namely the IEEE 802.11 Wireless LAN and the GSM.GSM.

Wireless terminal is equipped with a WLAN NIC, for indoors Wireless terminal is equipped with a WLAN NIC, for indoors communication, and a combined GSM/PSTN adapter, for oucommunication, and a combined GSM/PSTN adapter, for outdoors communication.tdoors communication.

Gateway/Proxy maintains the control of a pool-of-modems aGateway/Proxy maintains the control of a pool-of-modems also maintains the control of a poolof-modems, providing acclso maintains the control of a poolof-modems, providing access through the public GSM/PSTN network.ess through the public GSM/PSTN network.


When it moves towards the boundaries of WLAN and the When it moves towards the boundaries of WLAN and the Wireless LAN SNR drops below a predefined threshold, the Wireless LAN SNR drops below a predefined threshold, the system switches to GSM.system switches to GSM.

The selection of the aforementioned wireless interfaces has The selection of the aforementioned wireless interfaces has been triggered mainly by two factors.been triggered mainly by two factors. First of all, the GSM technology is mature, well established First of all, the GSM technology is mature, well established

and used by millions of people in a daily basis.and used by millions of people in a daily basis. The second reason is correlated with the requirement to have The second reason is correlated with the requirement to have

two different wireless interfaces that can be used in a two different wireless interfaces that can be used in a complementary manner.complementary manner.

WLAN and GSM are a perfect match, because they provide WLAN and GSM are a perfect match, because they provide wireless communication for indoors and outdoors, wireless communication for indoors and outdoors, respectively.respectively.


The coverage area of WLAN is a sub-area within thThe coverage area of WLAN is a sub-area within the GSM coverage, but, whenever it is feasible, the e GSM coverage, but, whenever it is feasible, the WLAN must be favoured over the GSM.WLAN must be favoured over the GSM.The transition from GSM to WLAN implies that morThe transition from GSM to WLAN implies that more bandwidth becomes available for the running apple bandwidth becomes available for the running applications.ications.Through that API user-level applications are informThrough that API user-level applications are informed about the bandwidth capabilities of the active wired about the bandwidth capabilities of the active wireless interface and warned when a switching is goieless interface and warned when a switching is going to be performed.ng to be performed.

4. Experimental results(1/6)4. Experimental results(1/6)

The implementation of the mobile terminal componThe implementation of the mobile terminal components, presented in section 2, has been realized in tents, presented in section 2, has been realized in two different Operating Systems (OS), including Winwo different Operating Systems (OS), including Windows NT 4.0 and Linux (SuSE 6.1).dows NT 4.0 and Linux (SuSE 6.1). The former was selected because it has a largebase of eThe former was selected because it has a largebase of e

nd-users and, at the time of the decision, it was themost nd-users and, at the time of the decision, it was themost stable among the various clones of MS Window OSs.stable among the various clones of MS Window OSs.

The Linux OS was considered so as to prove the implemThe Linux OS was considered so as to prove the implementation feasibility and the generality of WCA.entation feasibility and the generality of WCA.


The testing scenarios were based on standard The testing scenarios were based on standard networking applications, including Telnet, Web networking applications, including Telnet, Web browsing (Internet Explorer for Windows NT and browsing (Internet Explorer for Windows NT and Netscape for Linux) and videoconference Netscape for Linux) and videoconference (NetMeeting for Windows NT).(NetMeeting for Windows NT).

Two testing scenarios were used, depicted in figure Two testing scenarios were used, depicted in figure 5:5:


This happens because as soon as Windows NT detects that the GSM (PSTN) link is down, it releases all resources referring to the Point-to-Point protocol, with the imminent result of terminating any previously active TCP connection.


Based on the results, we have concluded that the switching Based on the results, we have concluded that the switching between different wireless interfaces, while maintaining TCP between different wireless interfaces, while maintaining TCP sessions intact, is accomplished successfully in almost all sessions intact, is accomplished successfully in almost all the experiments, apart from the cases restricted by the the experiments, apart from the cases restricted by the operating system’s limitations.operating system’s limitations.

Moreover, measurements collected during the execution of Moreover, measurements collected during the execution of the testing scenarios revealed that the average time to set the testing scenarios revealed that the average time to set up the GSM link is about 20 s.up the GSM link is about 20 s.

ASL and CM gave a good solution to this problem, provided ASL and CM gave a good solution to this problem, provided that the networking applications do not utilize the standard that the networking applications do not utilize the standard socket API, but the one offered by ASL.socket API, but the one offered by ASL.

Although ASL and CM provide resiliency to wireless link Although ASL and CM provide resiliency to wireless link breaks, they also introduce extra delay.breaks, they also introduce extra delay.

5. Conclusions(1/2)5. Conclusions(1/2)

Wireless communications seem to be more Wireless communications seem to be more appealing than wiredappealing than wired

Combining the capabilities of different wireless Combining the capabilities of different wireless interfaces, a working environment can be built-up interfaces, a working environment can be built-up for both indoors and outdoors communications, for both indoors and outdoors communications, allowing the user to move seamlessly in the allowing the user to move seamlessly in the resulting resulting virtual virtual worldworld

Seamless and uninterrupted connectivity cannot be Seamless and uninterrupted connectivity cannot be achieved by simply installing some network achieved by simply installing some network interfaces on a mobile host.interfaces on a mobile host.

5. Conclusions(2/2)5. Conclusions(2/2)

Another major concern regarding WCA is the Another major concern regarding WCA is the support of a large number of mobile hosts support of a large number of mobile hosts connecting to the home Intranet through the connecting to the home Intranet through the Gateway/Proxy.Gateway/Proxy.Scalability problems may arise, as a result of the Scalability problems may arise, as a result of the simultaneous existence of multiple active TCP/IP simultaneous existence of multiple active TCP/IP flows from various mobile hosts.flows from various mobile hosts.In spite of the fact that there are many open points In spite of the fact that there are many open points regarding the provision of seamless handoff regarding the provision of seamless handoff between different wireless mediums, WCA offers a between different wireless mediums, WCA offers a realized and tested paradigm of the feasibility of realized and tested paradigm of the feasibility of uninterrupted connectivity.uninterrupted connectivity.

wireless convergence architecture: a case study using gsm and wireless lan

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