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International Journal ofIntelligent Engineering & Systems

http://www.inass.org/

Monitoring Network through SNMP-based System

Jianqing Liu∗, Rongkai Lu

School of Information Technology Engineering,Tianjin University of Technology and Education, Tianjin, China

∗ Corresponding author’s Email: [email protected]

Abstract: SNMP-based system for monitoring network is equipped with network management, monitoring systemand statistic analysis of the network in it. It not only contains the function like network information capture thatnormal network devices have, but also has the ability to extend such applications as CPU usage rate, traffic flowinformation of interfaces and memory usage rate through plug-in mechanism. Simplifying the basic network man-agement tasks by centering on auto-topology mechanism and making a tradeoff between usability and extensibility,the auto-topology control which is implemented and designed independently could support almost networking deviceswith better flexibility. Completely supporting to capture TrapV1, TrapV2 and partial TrapV3 (limited by protocol)with embedded database to facilitate backend storage, the software has become a green-software except depending on.NET Framework 4.

Keywords: SNMP; Automatic Topology; Weight Priority.

1. Introduction

SNMP is widely used for the monitoring, manage-ment and controlling of the network devices. Now inits third release, SNMP has become the de facto stan-dard for network management since its developmentin 1987 [1]. Thus, it is a full-fledged network manage-ment protocol [2]. As we know, different network de-vices need to be supported by different programs; forexample, Literature [3, 4, 5] focus on single functionlike traffic monitoring or topology display regardlessof the scalability and generality of the system based onSNMP; so the SNMP-oriented matured framework ofnetwork management system is few and far between.Cisco Company is at the leading edge of supportingSNMP [6]. It not only provides fully support to thedefinition of MIB-2 in RFC1213, but also supportsRMON of RFC2819 and RFC2021 embraced withinsome devices. Therefore, it is of significance to de-velop extensible SNMP-based network framework to

support the prevalent Cisco devices.Two basic and important problems are confronted to

software development when talked to programming;they are generality and scalability respectively. Gen-erality can assure devices’ basic functions to performwell in most networking environment while scalabil-ity can guarantee their special functions on the condi-tion that the generality of software is well conducted,which makes the job designing general framework mu-ch more difficult.

How to simplify the network management tasks catc-hes more attention. This is mainly because the oper-ating behavior can be affected by the working way ofsoftware selected. C/S pattern or pure single-structuredsoftware no doubt has powerful graphic presentationwhile B/S pattern can show its merits on scalabilityand cross-platform. A tradeoff and efficiency alterna-tive is to implement generality and cross-platform onthe level of framework while different solution can beadopted on this presentation.

International Journal of Intelligent Engineering and Systems, Vol.5, No.1, 2012 1

2. System Analysis

2.1 Key issuesSince the supports to networking devices furnished

by SNMP are different between devices, developingsome general functions attached in software, whichare compatible with most of networking equipment, ischallengeable. On the basis of topology as its blueprint,the common network management tasks can be ful-filled properly. Therefore, no matter what diverse thenetworking equipments are, and how complicated theenvironment supported by SNMP is, automatic net-work topology discovery is undoubtedly an indispens-able and core function. Thus, how to extend functionon common compatible equipment becomes the focusof our research.

2.1.1 Compatible with most of existing equipmentRather than realizing compatibility, it would be bet-

ter to implement the functions backed by most hard-ware. One solution to it is to utilize MIB-2, the func-tional groups defined by RFC1213, which releases theroutine objects in networking administration and gainsthe general acceptance from most devices.

2.1.2 Obtain network topology through SNMPThere are no objects in functions relevant to SNMP

which can be directly used to obtain network topol-ogy. But they can be found in some MIB which is inthe possession of the private where Cisco can be takenan example. Some objects related to CDP (Cisco Dis-covery Protocol) from Cisco conduct such functionsof getting the topology immediately. However, it posesvery sticky requirement on network environment andthe equipment for CDP must be used in pure networkCisco-based, although a few non-Cisco start to givesupport to CDP. Thus, it is not a solution for generalpurpose.

To keep the compatibility between network equip-ment, the conservative objects should be the priorityto implement the core functions. And the automatictopology discovery can be deployed until we importemphasis on the MIB-2. The scheme is to find out theaddress translation table with the information about IPof PC among it. With these IP, the SNMP testing onPCs can be employed; consequently, the SNMP-basednetwork is well-supported.

Figure 1 Domain for Transformation

2.2 Difficulty in software design2.2.1 Layout of topology

Once the mechanism of topology is confirmed, anintractable issue, the layout of devices and devices’links, blocks the way to further the job. It is too hardto draw the topology the same as the physical structuretotally by software.

During the course of developing software, the strat-egy pattern is adopted to abstract the layout algorithm,so we can do some substitution manually.

2.2.2 Mapping from domain model to storage mo-del

The domain model is regarded as conceptual modelof a system, which is used to describe the relationshipbetween entities and their relations visually. For anapplication system based on SNMP, the domain modelis its main entity. Additional extensive function, man-aging the network devices, is associated with such ap-plication as assets appraisal, devices accounting, andmaintenance.

3. Framework Design

3.1 Logic design of domainThe main logic of Software to interact with SNMP

network is dependent on the SNMP object data trans-mission by SNMP protocol; meanwhile SNMP ob-jects are dependent on the relevant MIB to describe itscharacteristics and structure. Software needed logic ismainly concentrated on the operation of the SNMPentity, but not friendly to the program, that is, notthrough the smooth operation of API to make use ofthe software for SNMP.

So it is necessary to design domain logic to con-vert specific domains of SNMP into program friendlydomains. Now consider the domain transformationshown in Figure 1.


Figure 2 Model with DSL Characteristics

From the figure above, SNMP operating primitive isconverted into the corresponding programming con-cepts, so that the domain of SNMP completely turnsinto the programming domain. This provides the basisfor the expansion of AOP programming and storagemodel.

3.2 DSL expressive forceDSL is a Domain-Specific Language [7], according

to Martin Fowler’s view; DSL is also a tool which canhelp users abstract a certain part from a system.

SNMP protocol itself is designed as an associatenetwork management tool, so it is a pity that if thisproperty is abandoned and a new administrative modelis developed from the beginning. Starting from a spe-cific language and using this feature of SNMP, AOP(aspect-oriented programming) model is made to achi-eve the specific features of DSL, which keeps the lan-guage and the framework itself easy to use and sim-plifies programming.

The benefits of using DSL features is obvious, fordata with strong type could be employed in the designstage, and the introduction of caching strategy andparallel optimization in later design step can becomeeasy by using excellent AOP framework. A relativelysimple example of using AOP with SNMP features isshown in Figure 2.

Store SNMP-related data into metadata and obtainSNMP entity through reflection, which not only hidesthe SNMP communication at the bottom, but also getsthe “shallow buffer”. This is the expression force ofDSL.

3.3 Scalability and flexibilityMatured framework is often evolved on the basis of

the continuous evolution, and a reasonable design isthe premise of this kind of smooth evolution. Soft-

Figure 3 Measurement Result of Code

ware takes the strategy of the incremental evolution–every time a small iteration to design and implementthe software framework–this makes framework main-tainable in later, meanwhile, better performance canalso be shown in scalability and flexibility.

The framework’s basic extension point lies in the in-cremental expansion of plug-in applications with cen-tered as topology, implementing the function of soft-ware extensions on the whole. Through the AOP modelimplemented and the application of the plug-in mech-anisms, the software has great flexibility in the func-tion and the maintainability for “upgrade” with no sideeffects available. The following Figure 3 shows mea-surement results of parts of code.

From the figure above, SNMP operating primitive isconverted into the corresponding programming con-cepts, so that the domain of SNMP completely turnsinto the programming domain. This provides the basisfor the expansion of AOP programming and storagemodel

The “maintainability index” 57 is the value of SMan-age project, the most top-level application, accord-ing to Robert C. Martin’s point of view, the top-levelapplication and framework of the maintainability in-dex is often pyramid-shaped distribution. The main-tainability index of core framework–Framework andTopology Control are respectively 89 and 87, whichbasically reaches the maintenance needs later.

3.4 Storage modelStorage model can provide the persistence mecha-

nism for the relevant extension applications; mean-while, it plays the essential role for statistic and anal-ysis which request the comparison of history data. Atthe earlier stage of our design, a work model calledsynchronous engine was put forward, which could syn-chronously store the MIB-2 information of found de-vices into storage model in fixed time. The work modelof Sync engine is illustrated in Figure 4.

However, when synchronous engine was tested, the


Figure 4 Working Model of Synchronous Engine

discovery from test revealed that it wrote and readstorage model more frequently and the increasing amountof data was higher than before after every update. Sothe sync engine was discarded finally. From the angleof cost and deployment, the selectable database prod-ucts like Microsoft SQL Server Express, MicrosoftSQL CE, MongoDB, NoSQL, MongoDB, and NoSQLcan solve the problem of persistence. Combined withthe performance, Microsoft SQL CE is an alternative.

3.5 TestabilityAgile development declaration says:The individual and interaction is more important than

process and tools;Working software is more important than detailed

documentation;Corporation with Clients is more important than con-

tract negotiations;Prompt response to changes is more important than

following a plan.The rapid response to changes reflects the software’s

capabilities in scalability, maintainability, robustnessand so on. And the key technology of quick respond-ing to changes is the continuous integration and TDD(Test Driven Development).

In response to rapid changes in software, as well astaking into account the development cycle which doesnot allow much time to do the test and consider otherfactors, the software following up the part of the prin-ciple of “agile development” puts forward three prin-ciples to help software sustainable evolution: (1) Us-ing Microsoft Visual Studio Team Foundation Serverfor source code version management and continuousintegration; (2) give priority to the use of “ink test”,the core mechanism of “white box”; (3) add a smallincremental iterative function.

Software easy to test is rooted in the clear respon-sibilities of “class”. Through continuous reconstruc-tion [11], the software refines the core mechanism ofthe abstraction level; for example, Figure 5 shows theAOP abstracts model part of the interface, which makesit easier to test.

Figure 5 Public Interfaces Provided by Framework

Figure 6 Process of Auto Topology Discovery

4. Detailed Design

4.1 Automatic topology controlThe automatic topology Control is the core of SNMP-

based system which is the starting point of other ex-tensions. This control also provides functions such asadjusting topology, storing topology, loading topol-ogy and storing images. More details about imple-menting the function of automatic topology controlare involved.

4.1.1 Operating modeObtaining topological graph is a high-cost and time-

consuming process. Asynchronous discovery avoid-ing the congestion of UI threads is the best choice. Inthe mechanism of topological graph discovery, a spe-cial “hook” is added in. This is the observer pattern[8, 9, 10] which is normally employed in design field.When a station is found, mechanism will notify thesubscriber of this event. The station will be shown asan image corresponding to it in the software picture.

When topological mechanism finds a device, it willreport this event. The automatic topology control sub-scribing this event will receive the report that standsfor a device. Then automatic topology control willcheck the device which this report stands for. Initial-ization will be started until the checkup is finished.Initialization will complete a series of job to the cor-responding devices. Context Menu extension Mecha-nism is added in at this time. After initialization, thealgorithm of locating device will be conducted to lo-cate devices. Finally, the device discovered is added


into the visual panel. Thus, the addition of device isfinished.

4.1.2 Double buffersThe links among devices of topology graph are drawn

by GDI +. An obvious problem is that topologicalgraph will blink when we adjust topological graphmanually. This problem has nothing to do with .NETplatform, but it is caused by the efficiency of the GDI+tool. Double buffers can reduce the frequency of draw-ing in order to speed up the drawing rate, which cansolve the drawing blink.

If DirectX is used to draw the topology, another dif-ficulty, interoperation of COMs, is brought in. Study-ing API related to Windows no doubt increases thecost of technique with a bit higher efficiency than GDI+.

Selecting GDI+ leads to the efficiency of itself. Thereason of using double buffers is that speeding up therate of drawing and reducing the blink may slow downthe drawing frequency.

A buffer container should be ready for the usage ofdouble buffers. This software adopts the default im-plementation provided by .NET. For instance, the fol-lowing code will start double buffers.

var bu f f eredGraphics = Bu f f eredGraphicsManager

.Current.Allocate(graphic,DisplayRectangle);

Then, the buffer can be used to draw pictures.

bu f f eredGraphics.Graphics.DrawLine(Pens.Black,

p1, p2);

Finally, pictures in buffers are drawn into visual panelafter all the drawing is done.

Double buffers decrease the blink but lead to an-other problem–transparency of the control, which bringsabout bad experience to users.

4.1.3 Smoothing modeDouble buffers can eliminate the drawing blink, but

there is still one more problem; that is unbeautifulgraph interface. Of course, a line with aliasing is ugly.Smoothing mode can be employed to clear the alias-ing, which is called anti-aliasing.

In terms of drawing, there is no difference betweenthe utilization of buffer container and GDI +. Thus,the setup of smoothing model is as same. Drawingcurve using smoothing model needs to set the Smooth-ing Mode property of Graphics before drawing.

Usually it is enough for system to only set the prop-erty Smoothing Mode. The other properties appear in

the occasion where there are many curves. However,the more properties are set, the more cost the diagramdrawn by GDI+ will take.

4.1.4 Synchronization contextEvent mechanism supporting asynchronous discov-

ery solves the problem of real-time response. But an-other serious problem occurs. The thread used to dis-cover topology is not the same one as UI thread. Ifthey are the same, the asynchronous model cannot beimplemented.

Topology mechanism will notify the subscriber onceit finds device(s), and at that time the functions, whichhave registered the events, are evoked. But the evok-ing thread is still the thread itself discovered by topol-ogy, not the one of UI threads. If there is no specialmechanism to tackle it, the exception will be thrownout.

An unofficial solution to it is to explicitly shut downthe checkup of thread in the constructors of UI achiev-ing this effectiveness by setting the property of Con-trol.CheckForIllegalCrossThreadCallsas false. How-ever, it is not safe to operate UI through cross-threadsfor it can invoke deadlock. Therefore, a mechanismtransferring UI operation to its own threads is in theurgent need.

.NET platform provide a mechanism to guaranteethe synchronization, which is called SynchronizationContext [12]. Synchronization Context has many ver-sions, such as Windows Forms Synchronization Con-text fit for Win FormDispatcher Synchronization Con-text used for the technique of WPF and Silverlight,ASP.NET Synchronization Context for ASP.NET andSynchronization Context based on threads. All of themhave common in unified abstract, though the imple-mentation of them are different from each other.

Since UI of the system is implemented by Win Form,Windows Forms Synchronization Context is the prior-ity.

Retile Searching implements the interface of ITopol-ogyStrategy, so the events subscribed from Found Sta-tion, found during the topology discovery can controlasynchronous present.

4.1.5 SerializabilityTopology structure as a structure of software is stored

in the memory of host, and its presentation is a struc-ture of Collection¡Station¿. The main tasks of stor-ing and loading topology are to store or restore thisstructure into persistence mechanism or memory. Themapping from data structure to persistence mechanism


Figure 7 Working Process of Serialization

needs a mapping, but the programming is very time-consuming. The topology stored in form of a file is agood choice because it can be used conveniently andeasily.

Take all the above into account, serialization is theright scenario and .NET provides the function of se-rialization. What we need to do is to mark “serializ-able” on the data structure that needs to be serialized.The process of serialization is illustrated as Figure 7.

Auto-topology control forwards the request of save/loadto the class LoadSaveHelper, then LoadSaveHelperconverts it into the structure of StationInofo instead ofdirectly serializing it into Controls set of AuTopology.StationInofo keeps such information as IP address, co-ordinates, and links and so on. The real serializationis conducted in Serialize Formatter.

Serialize Formatter is classified into many types, suchas binary serialization, XML serialization and openstandard SOAP serialization. Since the interoperationbetween platforms is temporally not involved, binaryserialization with higher efficiency is a priority.

Topology is saved into a file with the suffix .tpg bydefault under the default directory Data. When thesystem starts, it will check up the directory Data. Ifthere are files with suffix .tpg, a dialogue box will ap-pear to enquire if the last topology is loaded. If thereis a topological file, the system will make a new topol-ogy according to the creating time of the files.

4.2 Device managementFor every found device, SNMS can check its infor-

mation and generate an exclusive hash code whichidentifies the device. SNMS is in charge of the fol-lowing information.

1) Location information: The logical location in topo-logical graph is not the physical location. SNMS should

Figure 8 The Intermediate Layer of Trap

hold the physical location of the devices.2) Device parameter: The statistic of device param-

eters can be helpful for maintaining the devices at laterstage.

3) Information of equipment: Assets appraisal al-ways involves the records of purchase, providers, andother relevant information, which is the starting pointof maintenance and statistic.

4) Maintenance record: It is important for networkadministrator to know the running state of the net-working equipment. The system provides users withthis function regarding to adding or updating mainte-nance records.

4.3 Trap detectionThere are many versions of traps. In order to be no-

tified when events occur, the system needs a kind ofmechanism which can receive trap and unify the dif-ferent versions of traps. The system uses intermedi-ate layer to act as an agent shown in Figure 8. Exceptmultiple versions, the multiple types of traps make thesoftware analysis a time-consuming job. SNMS couldnot predict the emerging traps with new definition be-cause of its scalability. Modeling trap, abstracting itscore into an expandable and configurable mode andimplementing it by XML file can make SNMP suit-able for different environment and easy deployment.

Filtering useful trap plays another import role, whichis determined by the management property of soft-ware. Filtering mode, white list and black list, is usedin filtration. White list shows the traps matching therules in the list while the traps mismatching the rulesin the list are in black list.

4.4 The application extension of context menuAs a major method of extending software, the con-

text menu of devices expresses itself in this way. Sincethe extension mechanism is added into topology dis-covery, the extension of the context menu behaves glob-ally. The system carries three extension functions it-


Figure 9 Definition of interface IDevice&ITopology

self used for network routine tasks, which are pro-vided by the form of plug-in.

Every device has its unique identification to supportContext Menu. Thus, the system framework offers theinterface IDevice and designs the interface ITopologyfor assistance to topology mechanism. Figure 9 givesthe definitions of mentioned two interfaces.

IDevice, as the core interface of Context Menu, isimplemented by all the devices, so the plug-in can re-extend surrounding to IDevice. Compared with IDe-vice, ITopology interface supports the conversion be-tween different devices.

IDevice only provides the basic function in the earlysoftware making period, and it does not offer func-tions like grouping and extending icon, which will beconsidered in later development by gradually extend-ing more controls on this interface.

4.5 Algorithm of automatic topologyThe algorithm called weight circular distribution is

mainly due to introducing the weight of devices inthe network. As the goal of layout is to distribute themajor devices in reasonable and correct places in thescreen, this kind of topology layout make the findingof devices with highest weights as its first task. If sortand locate them in the weight orderthis algorithm iscomprised of four steps as follows:

The first step is to sort devices by weight. The sys-tem is routers and switches oriented. Therefore, themost sensitive information within topology is so rel-evant to routers. A device is regarded as a core one,which is always equipped with a wealth of routingscompared with others. Though the case like above iscontended to be absolute, it is the fact in most of thetime. Generally speaking, the number of devices withmore routings is not so much than the one with lessroutings. Consequently, the ones called core devicesshould be definitely placed on the core location, andthis is what the second step will do.

Locating by weight priority is the second step. Once

Figure 10 Distribution of satellite devices

the core devices have been settled down as well as thedevice group according to the weight, the first step isterminated. Then the ones in first group, the most cru-cial devices, averagely distribute on the circle sharedthe same length of radius and centered as the midpointof the screen. To define the radius often needs somesteps as follows. The more devices there are, the big-ger the value of radius is. When the devices locatingis done, the angle of the midpoint of the screen for thecorresponding device is confirmed. The angle, thus,becomes the starting point of next step.

Here comes the third step–“satellite” devices distri-bution. The devices adjacent to the core devices arenamed and classified into satellite devices. In thisalgorithm the conception of aggregation is not takeninto account, but the satellite devices used take theplace of it. Now an example is taken of the algorithmfor the distribution of satellite devices.

Assume that there are n core devices. The satellitedevices for every core device can only be within thesector of 360/n. Illustrated in the figure below.

There are three core devices shown in the picturewhich is divided into three sectors. Herein, take R2as an example. Its three satellite devices are well-distributed in the sector B according to the angle of 6 θand the radius can be adjusted following the amountof the satellite devices. Another correcting algorithmcan be like this. Observe if devices in other sectorsare apparently less than the ones in current sector ornot. If they are, distributing satellite devices will in-vade into the adjacent sectors in order to utilize thespace of screen to the full. Then, the satellite devicesof satellite devices distribute their topology using thesame algorithm.


Figure 11 Drawing Links

Figure 12 Adjust for topology

The fourth one is to draw the links. The intersec-tion is permitted for links to core devices as there arealmost no possibilities to be not intersected. The prob-lem of intersection cannot become severe because ofthe guarantee furnished by annual distribution of de-vices. The links between core devices and satellitedevices can be directly connected. However, if theconnections happen to satellite devices, the layout ofsatellite devices should be slightly adjusted so that theoverlaps can be avoided. See the figure below.

Currently, if there are connections between device Xand device Z, the slight adjustment will be conductedin accordance with the space of the screen. Thus, thedistribution of links from X to Z seems much morereasonable as shown in the figure.

The direction of devices moving follows their upperdevices, of course, which is determined by the spaceof screen. That is, near to the upper or away from the

Figure 13 Simulation Testing

upper.Another moving is longitudinal. For example, when

Y is going to connect to R3, R2 is in the way obvi-ously. The adjustment to y is neither next to R2 noraway from R2, but in the direction of coordinate axisY . Consequently, further judgment should be made tocorrect the links and the best correctness is to move ydown shying from R2.

There is still one problem needing to be solved, thatis to set a value of a pixel, for instance, 50px, whichcan be used to adjust when the correctness should bedone if the distance from current link to the device inthe way is too small. If the distance is smaller than50 pixels, adjust the location of devices, and then thetopology is changed accordingly.

5. Testing and Deployment

5.1 TestingFirst, simulation testing is conducted under the Cisco-

simulating environment with matured simulation soft-ware. Figure 13 shows the system’s performance with10 devices in the LAN.

Second, the real environment testing is conducted.Medium-sized data exchange network of routing typeis used as testing environment. It consists of 5 Cisco7200 routers and 7 Cisco 3640 switches. After theconfiguration of the routing protocols, the SNMS issetup as well as the trap function. The real topologyof the mentioned network is illustrated as Figure 14before the test is done.

Using the system SMNS (SNMP-based MonitoringNetworks System), the testing result is displayed as


Figure 15 Testing Result

Figure 14 Topology of Network

Figure 15.The discrepancy between original topology and test-

ing result is caused by the switch’s transparent role inthe network, which influences the judgment of topol-ogy logic. But the problems can occur until the topol-ogy happens to the computers.

5.2 Deployment1) Compile: SNMS aiming to serve network man-

agement could probably be run on X64 platform. There-fore, the guarantee that SNMS can be properly uti-lized on the platforms with the architecture of X64 orX86 should be taken into account. The best optionfor compiling the applications on different platformsis the compiling way-AnyCPU as one of the inherentattributions of .net to make compiling easy.

2) Installer: SNMS depends on the .NET Frame-work, so the computer without .NET Framework in-stalled could not run SNMS properly. Packing .NET

Framework together with SNMS facilitates the users.The software package should also include WindowsInstaller.

3) Running platform: One advantage of .NET plat-form is independent of running platform. .NET is alay of abstracting between SNMS and OS. Differentplatforms, such as Linux, Mac OS, IOS, and Androidcan run on the core framework of SNMP.

6. Conclusion and Future Work

As a kind of software used in upper application basedSNMP, SNMS not only implements the core mecha-nism of topology discovery, but also perfects the soft-ware frame, which makes it fit to develop different up-per application. The ideal evolution of software is tomake a basic framework based on SNMP, thus, otherapplications can be extended on it continuously. Dueto the maturity of SNMP, this kind of frame has greatpotential to share the future marketing.

The design of framework is an evolutionary process.This requires that back compatibility should be con-sidered when the increment and deletion of every APIis done. The first edition of SNMS only provides con-servative APIs for upper applications. With the evo-lution of frame, more APIs and functions will be pro-vided so as to simplify the difficulty of developing up-per applications.

The future direction to develop SNMS is to extend


its transversal functions, but not application functions.Performance and buffer are the major direction to work.For example, the introduction of parallel concept canspeed up 5∼10 times in auto topology control, of course,the complexity of developing job will rise up.

Acknowledgment

This work was sponsored by the Scientific ResearchFoundation for the Returned Overseas Chinese Schol-ars, State Education Ministry. This work was also sup-ported by Tianjin Research Program of ApplicationFoundation and Cutting-Edge Technologies Grant 10J-CYBJC26100.

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