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Network Design Process

  1. Logical Design Phase
  2. Physical Layer
  3. Internetworking Devices
  4. Optimizing WAN Performance
  5. Network Management with SNMP and RMON
  6. TCP/IP Addressing
  7. Security
Network Development Process
"Waterfall Cycle"
  1. Analyze
  2. Design
  3. Build
  4. Test
  5. Deploy
Process Phases
  1. Requirements Gathering
  2. Analysis of the Existing Network
  3. Logical Design(also refered to as Conceptual Design)
  4. Physical Design(also refered to as Final Design)
  5. Installation and Maintenance
Installation and Configuration WAN Networks
HDLC data link layer information is transferred between the primary("master" node) and secondary("slave"node)stations.
(ie.combined station sends or accepts commands and response). HDLC frames are used to communicate between two communicating devices. HDLC fields in the HDLC header include:Flag(1 byte), Address(1 or 2 bytes), Control(1 or 2 bytes), Information("l" field), Frame Check Sequence (FCS, 2 bytes), Flag (1 byte).

SDLC session (unbalanced) command and response sequence to connect:
  1. Primary Station: Set Normal Response Mode(SNRM)sent
  2. Secondary Station:Unnumber Acknowledgement(UA)returned
  3. Primary Station: Receiver Ready(RR)sent

  4. Information transferred between devices until communication session completed.
  5. Primary Station: Disconnect(DISC)sent
  6. Secondary Station: Unnumber Acknowledgement(UA & DM)returned

The format of Point-to-Point Protocal(PPP) frame is similar to a HDLC frame. There are three formats of a PPP frame depending on whether its carring data or control information. The PPP information Frame fields in the PPP header include:Flag(1 byte), Address(1 bytes), Control(1 byte), Protocal (2 bytres), Information("l" field), Frame Check Sequence (FCS, 2 bytes), Flag (1 byte). A link control protocal can be used to specify certain data link options. Negotiiates not having to send a flag or address byte and reduce the size of the protocal field from two bytes to one for more efficent line use. The third format of a PPP frame is used to negotiate things such as header compression. This protocal is used to dynamically negotiate the IP address es for each end of the link.

HDLC Command Table
Field Type


Exchange User Data(Data from the Network Layer)
Reciever Ready - Positive Acknowledgement
Reciever Not ready - Positive Acknowledgement
Reject - Negative Acknowledgement, go Back N Frames
Selective Reject - Negative Acknowledgement
Selective Repeat
Disconnect - Terminate Connection
Disconnect Mode - Secondary Disconnect
Frame Reject
Set Asynchronous Balance Mode
Set Asynchronous Response Mode
Set Initialization Mode
Set Normal Response Mode
Unnumbered Acknowledgement
Request Initilzation Mode
Request Disconnect
Unnumbered Information
Unnumberd Poll
Exchange Identification

Selection of WAN Services Frame relay network provides a data communications alternative to private lines. It is a data only service, providing connection-orientated frame transport service. Frame relay services available today are permanent virtual circuits(PVC) based. Speed(56 Kbps to 1.544 Mbps)

Frame relay implemented as a private networking solution.
  1. Purchasing routers and establishing point-to-point connections between these two routers.
  2. Using Frame Relay Switches
Corporations can access a public Frame Relay network by:
  1. Installing a software upgrade to the route or bridge
  2. Purchasing a FRAD
  3. Connecting an access line between the carrier and the corporation's data service unit/channel service unit (DSU/CSU).
  4. Ordering the frame relay interface from a telephone carrier offering the services
LEC:Local Exchange Carrier
IEC:Inter Exchange Carriers

Frame Relay Network Design
  1. Determine the Points Of Connectivity( 5 or more)
  2. Establish Traffic Characteristics
  3. Select Frame relay service parameters based on networking requirements
  4. Select products or services meeting these requirements
Note: Identifying the number and location of sites is critical because each site location involves screening to determine if it qualifies for connection in the event the service providers have not deployed Frame Relay nodes. Each site pairing will require a seperate permanent virtual circuit(PVC)

Traffic Characteristics
  • File Transfer
  • Web Based Traffic
  • E-Mail
  • Database Manipulation

The committed information rate(CIR) is the gauraranteed capacity available to the user. To calculate the (CIR)
  1. Estimate the average data rate needed to support each of the site-to-site virtual circuits. This is done by estimating the leased line capacity
  2. A CIR is calculated for each connection supported from a given site. An access rate for the site can be determined.
  3. Carriers or private network equiptment vendors will generally recomnmed a ratio between the aggregate CIR of all PVC's on the trunk and trunk speed. The committed burst rate must be determined.
  4. Select products and services that meet the requirements

Network Devices
(Hubs, Switchs, Routers)
  • Switch :A switch (layer 2) segments a network with a goal of providing additional bandwidth and provides a high level of performance for a significantly lower cost per port then a router. Cost becomes an important factor as network managers purchase increasing numbers of internetworking devices to further segment their networks. Second a switch offers wirespeed forwarding across all ports at all times. The performance of intermediate network devices becomes a critical issue as clients and servers are placed in different segments, eroding the traditional 80/20 rule of network design. As a larger percentage of traffic must pass through a greater number of internetworking devices, the latency and the throughput of each device is a critical factor in the successful operation of the network. Because the impact of high-speed technologies will most likely be felt first in the backbone and data center , workgroup switchs must accomidate these technologies to provide a smooth migration path as networks grow. Third , a sitch is simpler then a router. A hardware intensive switch is easier to configure, manage, and trouble shoot than a software-heavy router
  • Router:A router (layer 3 ) segments a network with the goal of limiting broadcast traffic and providing security, control, and redundency between individual broadcast domains. Routing functionality will always be required in a large switched enviroment to isolate and define broadcast domains.

Network Security

Network Security begins with investment in your technical staff to manage security risks in a way that can be explained in the board room and actually withstand daily pounding from competent attackers all the while keeping various parts of your business functioning. Modern security technology, especially intrusion prevention can help immensley in defense if you want to ensure you have the technical skills and the business vision to keep your organization safe . iNet Model .Com

  • Security Management
  • A security system should allow for oversight and control by a human authority. Any system that uses authentication requires some centeral authority to verify identities wether it be the /etc/password file on a unix host, a Windows NT domain controller, or a Novell Directory Servicews(NDS)server. The ability to see histories and attempts to breach a firewall can provide invaluable information to those charged with protecting information assets

    Management consoles or functions themselves represent another potential point of failure for a security system. It is therefore important to ensure that these systems are physically secured and that authentication is in place for any logon to a management console.

    A comprehensive design process should specify security services and implementations. Security-related information is conceptually stored in the MIB of a network managementt system. This ensures that every collection of managed network security systems has a single , common security policy. The security policy may be null (if the administrator never enables security), or it may contain an extensive set of rules controling the communication conditions of all managed elements in the network. Network management security goals must include cofidentiality, integrity, and availibilty.

  • Firewall Considerations
  • The stance of a firewall system describes the fundamental security philosophy of the organization. An internet firewall may take one of two diametrically opposed stances

    Everything Not Specifically Permitted Is denied

    This stance assumes a firewall should block all traffic, and each desired service or application should be implemented on a case-by-case basis. This isn the recommended approach. It creates a very secure enviroment because only carefully selected services are supportrd. The disadvantage is that it places security ahead of ease of use, limiting the number of options availible to the user community.

    Everything Not Specifically Denied Is Permitted

    This stance assumes a firewall should forward all traffic, and each potentially harmful service should be shut off on a case-by-case basis. This approach creates a more flexible enviroment,with more services availible to the user commiunity. This disadvantage is that it puts ease of use ahead of network security, putting the network adminiostrator in a reactive mode and making it increasingly difficult to provide security as the size of the protected network grows.


A typical firewall is composed of one or more of the following building blocks to build an effective internet firewall system


Packet Filtering Router
Application Level Gateway (or Proxy Server)
Circuit Level Gateway

Hybrid Firewall

A hybrid firewall contains features of both the network Layer firewall and application firewall. These firewalls are
reffered to as dynamic packet filtering firewalls. " A hybrid firewall records the identity and allows communication between internal and external hosts, but only if the internal host initiates the session.

Intergrated Software Enviroment Development

  • Xilinx ISE
  • Xilinx ISE Overview The Integrated Software Environment (ISE?) is the Xilinx? design software suite that allows you to take your design from design entry through Xilinx device programming.

    • Design
    • Design entry is the first step in the ISE design flow. During design entry, you create your source files based on your design objectives. You can create your top-level design file using a Hardware Description Language (HDL), such as VHDL, Verilog, or ABEL, or using a schematic. You can use multiple formats for the lower-level source files in your design. Note If you are working with a synthesized EDIF or NGC/NGO file, you can skip design entry and synthesis and start with the implementation process.

    • Simulation
    • You can verify the functionality of your design at several points in the design flow. You can use simulator software to verify the functionality and timing of your design or a portion of your design. The simulator interprets VHDL or Verilog code into circuit functionality and displays logical results of the described HDL to determine correct circuit operation. Simulation allows you to create and verify complex functions in a relatively small amount of time. You can also run in-circuit verification after programming your device.

    • Synthesis
    • After design entry and optional simulation, you run synthesis. During this step, VHDL, Verilog, or mixed language designs become netlist files that are accepted as input to the implementation step.

    • Implementation
    • After synthesis, you run design implementation, which converts the logical design into a physical file format that can be downloaded to the selected target device. From Project Navigator, you can run the implementation process in one step, or you can run each of the implementation processes separately. Implementation processes vary depending on whether you are targeting a Field Programmable Gate Array (FPGA) or a Complex Programmable Logic Device (CPLD).

    • Configuration (iMPACT)
    • After generating a programming file, you configure your device. During configuration, you generate configuration files and download the programming files from a host computer to a Xilinx device.

    Software Development

    • MicroSoft Visual Studio Version 7.0
      • Planning
        • Design User Interface (Storyboard)
        • Plan the Properties
        • Basic Code(Pseudocode)
      • Programming
        • Create User Interface
        • Set Properties
        • Program Application

    • MacroMedia
      • Flash
      • Dreamweaver
        • Design the User Enviroment (Storyboard)
        • Plan the Architecture (Flow Chart)
        • Code (Pseudocode)/Program

    Web Site Development

    (Visual Studio 7.0, MacroMedia Flash/Dreamweaver, Frontpage 6.0)

    The design process from the top down: Define and design the look and feel of the site and then conform user interaction to the particular design is not used. Site design process is in reverse. The scenerio developement process is centered on identifying desired system behaviors in response behaviors for a web site. Each of these desired behaviors brings possible scenarios to be considered. They first provide you with a clear image of the project scope.

    A team approach to Web Developement is critical. Expertise in the following areas should be represented in any well rounded web design team.

    Web Design Team

    • Project Management
    • Graphic Design
    • Technology
    • Marketing
    • Writing and Editing
    • Information Architecture
    • Conceptualization
    • Design Visualization
    • Analysis
    • Production
    • Evolution
    Web Site Project (Three-Step Process) Sign-off Stages
    1. Design the User Enviroment (Storyboard)
    2. Plan the Architecture (Flow Chart)
    3. Basic Code (Pseudocode)

    Java EJB 3.0

    EJB 3.0 is a "sea of changes from the previous versions of EJB technology in that the programming and the deployment is very different."(Mastering EJB 3.0 4th Edition). The ability to use POJO(plain old Java object)) style entities with enterprise beans is a much sought after feature. A powerful concept introduced is the ability for any enterprise information system effectively sending any type of messages to a message-driven bean endpoint via EE connector architecture-based resource adapters. Because JAX-RPC does not support asynchronous messaging, connector architecture-based message providers/resource adapters can be extremly handy.

    Java 2 Enterprise Edition Applications

    J2EE is used to build extensible, scalable, reliable, timeliness systems for enterprise applications. Using the Model-View-Controller pattern provides an overall structure for web applications in J2EE. While the idea of using JavaBeans as a Model, Servlets, and JSP for the View for the controller is not a requirement, it is a good rule of thumb. It's far more important to understand how the seperation between Model, View, and the Controller makes an application extensible and maintainable. Most web application frameworks implement at the MVC pattern, and many even claim to be "pattern-based". In general, frameworks force applications written to them to conform to certain patterns. Recognizing these patterns can be a big help in designing applications that work well in a given framework. Jakarta Struts is probably the best-known web application framework(a part of the Apachie Project). It is based on what they call a "Model 2" approach, an implementation of MVC in which you write the model and view componenets, and Struts provides the controller. The struts controller is based on the Service to Worker pattern, featuring a front controller, a dispatcher configured via XML files, and a s2w code framework  for embedding application logic into actions. Struts also includes a number of utility classes and tag libaries, including Tiles, an implementation of the Composite View pattern

    • Reliability
    • Corporate software projects are subject to specific quality requirements, and reliability is usually first among these. Most large software teams have one or more people in a Quality Assurence role, or they make use of services of a dedicated QA team or department. Large projects, particularly in regulated industries such as health care, are subject to validation processes and audits. A software audit can include every aspect of the development cycle, from initial requirements gathering through design, up to final testing and release procedures.

      • Design Patterns
      • Design patterns play a major role in ensuring reliability and can be validated at a high level and incorporated early on in the design process. This type of planning makes the validation process simpler, and generally produces code that is easier to audit in the first place.

        • UML
        • UML supports all aspects of the software design development cycle, from requirements gathering to design to deployment. In particular, The UML can be extremely important(helpful) in documenting the object structure underlying an application, known as the domain model; but UML models can represent use cases, class structures, program interactions, process flows, physical deployments, packages, and more.

          Often simply creating UML diagrams uncovers subtle flaws in system design.

          UML also provides an excellent way to describe design patterns, both in terms of class structures and program processes. UML is complex. The specification itself is dense, and as a result much of the available literature must address the complexities in detail.

          Most teams find a comfortable middle ground in which modeling, via UML, or other methods, serves the teams underlying goals rather then becoming a end in itself.

          • Class Diagrams
          • Class diagrams show the relationships between classes in system. Since object oriented design blurs the line between data objects and executable application logic, a UML class diagram documents both. UML actually supports both class diagrams and object diagrams.

            The distinction between a class and an object:A class is a framework containing methods and data that can be instantiated into one or more objects, which contain actual data items. UML class diagrams show the relationship between the frameworks, and object diagrams show the state of a system with actual objects, containg actual values.

            Class diagrams can be used to build conceptual pictures of an application's domain model, which can then be used to develop more specific system designs that eventually map to code.

            In real life a client class could include persistence methods, cryptographic algorythms, message transports, or anything that might need to be done consistently in more then one way.

        Design patterns can also be misapplied, making simple problems more complex then necessary, or encourging code-first design later developemnt cycles as developers assume that the presence of patterns(with their promise of easy extensibility and maintenence.) allow requirements to be dealt with as they come up.

        To be useful, design patterns need to be expressed. While there are a varity of ways to do this, a UML diagram is a part of most of them. The diagram can make broad concepts and implemention details clear in a langauge-independent way that doesn't require working through large chunks of sample code. There are relatively few programming patterns that don't lend themselves to some sort of UML representation.

        Coupling modeling with design patterns has a number of advantages. The model provides context for choosing the right design patterns, although the presence of effective design patterns will also, perhaps somewhat recursively, influence the developement of the model. In most circumstances, the result is a simpler smaller, more manageble software.

        Software validation efforts can be time-consuming and require clear documentation at the design and implementation levels--and in some cases proveable correctiveness.

    • Scalability
    • Scalability and performance are closely intimate but are not the same thing. Scalability can broadly be defined as the ability of an application to maintain performance as the number of requests increase. The best possible scenerio is a constant response time, where the time it takes to process a request stays the same regardless of the load on the server.

      • Linear Scalability
      • Linear Scalalibility is when the time it takes to process n requests is equal to ntimes the time to process one request. So if one user gets a reponse in 1 second, 10 simultaneous users will have to wait 10 seconds, as each second of processing time is divided 10 ways.

    • Extensibility
    • The one constant in software development is that requirements always change. In general, the extensibility of software determines how easily changes can be accommodated. While objects must interact with each other in order for a program to do anything, the number of dependencies should be limited. Using clear interfaces separates an objects implementation from its interactions. This makes the specific implementation independent of the rest of the application, allowing implementations to be fixed, changed, or replaced at will. In an extensible program interfaces are kept as tight as possible to make sure they interact in well known ways.

      • Model-View-Controller Pattern

      • Click View Code Tutorial

        Using the Model-View-Controller pattern provides an overall structure for web applications in J2EE. Providing an architecture for the entire presentation tier that cleanly seperates state, presentation, and behavior.

        MVC breaks the interface into three distinct pieces: model, view, and controller. The model stores the application state. A view interpets data in the model and presents it to the user. The controller processes user input, and either updates the model or displays a new view.

        A controller is the first point of contact for a request. An application may have multiple controllers, each responsible for a certain area of an application. The model stores application state. Application state is data stored anywhere: databases, JavaBeans, files, network services or just in memory. The models job is to manage access to this state, providing the controller and view with a uniformed interface. The model does not simply copy the information. It is an abstraction of the data, and may implement and enforce rules on how the data may be accessed or combine muiltiple fields of data into a single logical field. The view reads from the model and uses the data to generate a response. The view itself is a stateless component that simply transforms values from the model into a format that clients will find useful.

        Building a Center Controller, the first point of contact for a request. Is the place where we have the most programming and design freedom. Unlike the model, which is shaped by the underlying data, the controller is designed from start to finish as a part of the presentation tier. And unlike the view , which is stateless and generally focused on presentation, we are free to perform as much complicated logic as we like.

      • Front Controller Pattern
      • Pattern's combined allow us to dynamically add functionality to the front controller, creating an extensible presentation tier. .................
        FrontController Servlet
        FrontController Class
        UML Diagram
        UML Diagram
        UML Diagram
        UML Diagram

        While decorators represent a fairly simple way to extending an object's functionality, aspect-oriented programming (AOP) is a programming methodolgy centered around dynamically extending objects. An aspect in AOP represents a common concept that cuts across multiple classes, like the ideal of logging. An aspect encapsulates the code to perform an action (like logging) as well targets it applies to(the front controller) and the conditions for which it should apply (whenever a get request is recieved), all in one construct. Whenever its conditions are met the code in an aspect is exicuted.

        The Model-View-Controller Pattern gives an architecture for enterprise applications that seperates the application into functional pieces with a clear interfaces. The Front Controller Pattern extends this architecture, describing a central controller that performs common functions on each request. Finally the Decorator Pattern shows how to dynamically add functionality to the front controller. Used together , these patterns create an extensible presentation tier.


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