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David Large, James Farmer, in, 2009 10.1 IntroductionNetwork architecture is the logical and physical interconnection of all elements between a signal's generation and its termination. Chapter 9 dealt with ways of measuring architecture-related parameters and the needs of various types of services.
This chapter will first delineate each of the elements from which an architecture is constructed and then present some examples of high-level HFC distribution networks that have been proposed or built. Fiber-deep architectures will be covered in Chapter 11; the relationship between network architecture and service reliability and availability will be dealt with in Chapter 12. Zoned Trust TopologyThe firewalls inside the LAN provide accountability, protection, and encryption of sensitive data.
To access a resource on the protected side (i.e., inside) of the firewall you must create a virtual private network (VPN) connection. The VPN connection will generate a log entry in your syslog server, which will also show all failed as well as successful access attempts. This VPN connection ensures that all data from the firewall endpoint to the desktop is encrypted against packet capture on the inside of the unsecure portion of the network. If anyone attempts to map the network with a PING sweep and port scan program such as Nmap or SuperScan, these software packages cannot show the resources behind the firewall, therefore keeping these resources invisible to attackers.The two types of devices that you will find frequently in both flat topology LAN and zoned trust topology layouts are routers and switches.
If you set up your switches with only their default settings, you will be leaving a lot of well-known vulnerabilities wide open to attackers. To prevent this from happening, Cisco switches enable users to set port-level security at a variety of different levels, which we will cover in the following chapters. Meanwhile, how to prevent a direct attack from outside the network on Cisco routers on the perimeter of the network is well documented, but for routers deployed internally you need a subtler approach—you need to be monitoring the internal syslog servers to see what activities are occurring on the routers and switches so that you can identify when breaches and incidents occur. One of the best tools available for doing this is a free utility from Microsoft, called Log Parser. Log Parser uses Structured Query Language (SQL)–style queries to get information from log files; users can then present that information in reports or on XML Web pages and send it to another database for future reporting. Network Layout Used in This BookIn this layout, the Internet enters through a perimeter router that connects to the firewall. From the firewall we connect to servers in the Demilitarized Zone (DMZ).
In the DMZ, we place servers that need to be accessed by resources outside the network (public resources). On the core switch, you will find the distribution switches and servers that are in the internal network. At the distribution layer, you will find the workstations and the WAPs that support wireless kiosks and laptops.
Even though you see a separate firewall in Figure 3, the router and the firewall are one device. Sassan Ahmadi, in, 2011The WiMAX network architecture is a non-hierarchical end-to-end all-IP framework for mobile WiMAX systems that is based on maximal use of non-proprietary standard IP protocols, and is compatible with external service enablers such as IP Multimedia Subsystem. A distinctive feature of WiMAX network architecture is decoupling of access, connectivity, and service networks to allow combination of multi-vendor implementations of physical network entities, as long as they comply with the normative protocols and procedures across applicable interfaces that are defined in the WiMAX network specification.Chapter 2 provides a top-down systematic description of WiMAX and 3GPP evolved packet core network architecture, starting at the most general level and working toward details or specifics of the network components and their interconnections. Jean Walrand, Pravin Varaiya, in, 2000 13.2.1 ArchitectureThe network architecture provides a framework for organizing the functional elements needed for the global network. The elements must be modular (that is, specified independently of each other) so that different implementations can realize those elements in ways that encourage the use and development of technological innovations. The modularity of the Internet and OSI architectures has permitted the immediate incorporation into networks of higher-speed computers, links, and switches.However, as we have often stressed, many applications, particularly multimedia applications, demand dedicated resources at the physical layer.
Meeting such demands may create a dependence between the application layer and the physical layer of the architecture. The architecture must be carefully designed so that such dependence does not compromise modularity. An equally important requirement on the architecture is that it must accommodate existing networks.We are concerned primarily with technological challenges to global networking, but economic and social challenges must be overcome as well. Access to the global network must be sufficiently cheap if it is going to be global. (In many developing countries today, large numbers of people do not have access to telephone service.) And the global network must be deployed in ways that contribute to social progress.
Garg, Yih-Chen Wang, in, 2005 6.1 Computer Network ArchitectureComputer network architecture refers to a set of rules that allow for connectivity among a large number of computers. This set of rules is also called communication protocols. To simplify the complexity of network design, the communication functions are divided into several levels of abstractions. Each level or layer of the protocol is designed in such a way that the change to one layer normally does not affect adjacent layers.
The services of higher layers are implemented to use the services provided at lower layers. There are two interfaces at each layer. One is the peer-to-peer protocol between two computers. The other is the service interface to its adjacent layers on the same computer.
Peer-to-peer protocol between two computers mostly regards indirect communication, and the direct communication only occurs at the lowest layer or hardware level. Each higher layer of protocol adds its own header information to the data message it receives from its higher layer of protocol before it passes the data message to its lower layer. This process is called encapsulation. The receiving system reverses the process, called decapsulation, by removing the header at each layer before passing the data message to its upper layer. Two prevalent network architectures are described in this section. 6.1.1 Open System Interconnection. Open System Interconnection (OSI) is an International Standard Organization (ISO) standard that defines computer communication network architecture.
It is a well-defined network architecture, but the implementation of its network protocols is very rare. When its draft standard came out in 1985, many predicated that the implementation of network protocols would predominate in the industry. The prediction was incorrect due to the wide use of Internet protocols in 1985. However, OSI represents a very powerful network reference model to which all communication technologies refer their architecture (see Figure 6.1). This also includes the most popular TCP/IP architecture. OSI divides the communication functions into seven layers of which functions are described in the following list.Physical layer: This layer is responsible for activating and deactivating physical connections upon request from the data link layer and transmitting bits over a physical connection in a synchronous or asynchronous mode.
It also handles very limited error control, like single-character parity checking.Data link layer: This layer is responsible for establishing and releasing data link connections for use by the network layer.Network layer: Responsibilities of this layer include providing the data integrity transmission for a point-to-point connection so that data will not be lost or duplicated. The layer accomplishes this task by maintaining a sequential order of frames that are transmitted over a data link connection and detecting and correcting transmission errors with retransmission of the frames, if necessary. The other important function in the data link layer is to provide flow control, which is a way to allow the receiving station to inform the sending station of stopping transmission for a moment so that the receiver will not overload its buffers.Network (packet) layer: Two major functions in the network layer are routing control and congestion control. Routing control is the process for maintaining a routing table and determining optimum routing over a network connection. Congestion control is needed when there are too many packets queued for a system and there is no space to store them. This is normally happens in a datagram-type of connection, where the network resources for a connection are not preallocated. The network layer is also responsible for multiplexing multiple network connections over a data link connection to maximize its use.
Flow control is provided at the network layer as well.Transport layer: This layer provides error-free end user transmission. To improve the utilization, it multiplexes multiple transport connections over a network connection. It controls data flow to prevent from overloading network resources just like the flow control function provided at the data link and network layers.
This layer and layers above it are end-to-end, peer-to-peer protocols, for which their protocol data units (PDU) are processed between two end systems. The layers below the transport layers are the point-to-point, peer-to-peer protocol where the PDUs are processed only between two computer systems connecting together.Session layer: Providing management activities for transaction based applications, this layer ties these application streams, together to form an integrated application. For example, a multimedia application may consist of the transport of data, fax, and video streams that are all managed at the session layer as a single application.Presentation layer: This layer is responsible for performing any required text formatting or text compression. It negotiates the choice of syntax to be used for data transfer.Application layer: To provide an entry point for using OSI protocols is one task of this layer. This task can be accomplished by providing either the Application Programming Interface (API) or standard UNIX I/O functions, like open(0), close(0), read, and write functions.The layer also performs common application functions, such as connection management, and provides specific application functions, like file transfer using File Transfer and Access Management (FTAM), Electronic Mail (X.400), and Virtual Terminal Protocol (VTP). 6.1.2 TCP/IP Network Architecture.
The TCP/IP network architecture also refers to the Internet architecture. The Transmission Control Protocol (TCP) is a transport layer protocol, and the Internet Protocol (IP) is a network layer protocol. Both protocols were evolved from a earlier packet switching network called ARPANET that was funded by the Department of Defense.
The TCP/IP network has been the center of many networking technologies and applications. Many network protocols and applications are running at the top of the TCP/IP protocol.
For example, the Voice over IP (VOIP) and the Video Conference application using MBONE are the applications running over the TCP/IP network. The TCP/IP network has the corresponding five layers in the OSI reference model. Figure 6.2 shows the layers of the TCP/IP network and some applications that might exist on the TCP/IP networks.
The standard organization for the TCP/IP-related standard is the Internet Engineering Task Force (IETF), which issues Request-for-Comment (RFC) documents. Normally, IETF requires that a prototype implementation be completed before an RFC can be submitted for comments. Thomas Wilhelm, in, 2013 Network ArchitectureFrom a network architecture perspective, the De-ICE Network challenges have been designed to be as simple as possible.
In most cases, a single router will suffice for different challenges. However, as mentioned earlier, there are other hardware devices that should be learned about from a pentesting perspective, including IDSs/IPSs and firewalls. Configurations for each of these areas are currently available at HackingDojo.com/pentest-media/, and new challenges are being developed as well.Although the network architecture is intended to be fairly simplistic in its design, the actual challenge is representative of what is found in corporations around the world.
This gives users an opportunity to delve into the vulnerabilities found within networks without having to create massive, expensive networks themselves. Tammy Noergaard, in, 2010 4.2.3 Peer-to-Peer vs. Client–Server: The Network's Overall ArchitectureA network's architecture essentially defines the relationship between devices on the network. To date, the most common types of structures are modeled after client–server architectures, peer-to-peer architectures, or some hybrid combination of both architectures.A client–server architecture is a model in which one centralized device on the network has control in managing the network in terms of resources, security, and functions, for example. This centralized device is referred to as the server of the network.
All other devices connected to the network are referred to as clients. Servers can manage clients’ requests either iteratively, one at a time, or concurrently where more than one client request can be handled in parallel.
A client contains fewer resources than the server, and it accesses the server to utilize additional resources and functionality.On the flip-side, with a peer-to-peer architecture network implementation there is not one centralized device in control. Devices in a peer-to-peer network are more functionally independent and are responsible for managing themselves as equals. Berk Canberk, in, 2015 4 Software defined offloading mechanism 1The network architecture for SDN is represented in Figure 26.7 with two layers named Control and Data Plane. The Control Plane includes virtual representations of Data Plane components and the Controller processes data coming from the Virtualization layer that collects it from physical components. These two planes communicate by using special protocol named OpenFlow in the SDN approach.
4.1 Offloading Decision Algorithm. The Offloading Decision Algorithm processes the offloading strategy by using necessary data from the Entity sublayer. With this algorithm, the suitable offloading strategy for the system is defined. To do this, it uses a set of base stations M, a set of users N, and a satisfaction level of each mobile user.
Satisfaction level is calculated according to user types and is rated as Gold, Silver or Bronze. The Gold user has the least tolerance on alteration of service quality, whereas Bronze has the most tolerance. Silver is between these two types. According to these user types, the dissatisfaction ratio is calculated for each end-user. With these inputs, the algorithm runs according to the pseudocode provided in Algorithm 26.3. As seen in Figure 26.9, the pie charts show the offloaded user types for on-the-spot and SDWN controlled offloading strategies.
Due to having the least tolerance of change of quality of service, Gold users have higher priority than Silver users, and Silver users have higher priority than Bronze ones. Because the Offloading Decision Algorithm gives precedence to Gold users in offloading, the percentage of offloaded Gold users should be high in SDWN.
However, in the on-the-spot, the percentage of offloaded user types depends on topology, due to having a user-based offloading strategy. The percentage of Gold users in on-the-spot is 32%, whereas this is increased to 79% in SDWN. This means that the service quality of Gold users is enhanced by the controlled offloading strategy with global view. Originally network architecture was centralized, with all processing done on a mainframe. Remote users—who were almost always located within the same building or at least the same office park—worked with dumb terminals that could accept input and display output but had no processing power of their own.
The terminals were hard-wired to the mainframe (usually through some type of specialized controller) using coaxial cable, as in Figure 1.1. During the time that the classic centralized architecture was in wide use, network security also was not a major issue. The Internet was not publicly available, the World Wide Web did not exist, and security threats were predominantly internal.
▪ Figure 1-2. A modern centralized database architecture including LAN and WAN connections.From the point of view of an IT department, the centralized architecture has one major advantage: control. All the computing is done on one computer to which only IT has direct access. Software management is easier because all software resides and executes on one machine. Security efforts can be concentrated on a single point of vulnerability.
In addition, mainframes have the significant processing power to handle data-intensive operations.One drawback to a centralized database architecture is network performance. Because the terminals (or PCs acting as terminals) do not do any processing on their own, all processing must be done on the mainframe. The database needs to send formatted output to the terminals, which consumes more network bandwidth than would sending only the data.A second drawback to centralized architecture is reliability. If the database goes down, the entire organization is prevented from doing any data processing.The mainframes are not gone, but their role has changed as client/server architecture has become popular.
Hide And Seek is a horror graphic adventure in which you play a little girl that falls asleep inside a closet while playing hide and seek. When she gets out, she discovers there's no one home. Or maybe there is?The gameplay is the usual kind you’d find in a graphic adventure game: you can freely explore the surroundings, and interact with everything you find. The main character can pick up items like keys, which she'll need to use later on in a different location.You can save the game with the hourglasses scattered throughout the mansion, and you better do it as often as you can, because there will be plenty of near-death situations. Even opening a door that you shouldn't can lead to a quick death in this game.Hide And Seek is a graphic adventure game with some elements of RPG. It features an interesting story, and really beautiful graphics.
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