Review In which of the topology a dedicated link connect a device to a central controller? 2022

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Domain 4: Communication and Network Security (Designing and Protecting Network Security)

Eric Conrad, … Joshua Feldman, in CISSP Study Guide (Third Edition), 2022

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Domain 4: Communication and Network Security (Designing and Protecting Network Security)Exam WarningDefining a VPNStar TopologyStar TopologyNetwork FundamentalsThe Star Topology (Hierarchical)25.2 Network topologiesLoRaWAN protocol: specifications, security, and capabilities3.3.1 LoRaWAN star topology with receive diversity is the key to scaling in an unlicensed spectrumSecurity in low-power wide-area networks: state-of-the-art and development toward the 5G17.1.1 Low-power wide-area architectureCloud Data Center Networking TopologiesDesign considerations and network architectures for low-power wide-area networks2.4.1 Low-power wide-area network topologiesVideo liên quan

Star

Star topology has become the dominant physical topology for LANs. The star was first popularized by ARCNET, and later adopted by Ethernet. Each node is connected directly to a central device such as a hub or a switch, as shown in Figure 5.17.

Figure 5.17. Star Topology

Exam Warning

Remember that physical and logical topologies are related, but different. A logical ring can run via a physical ring, but there are exceptions. FDDI uses both a logical and physical ring, but Token Ring is a logical ring topology that runs on a physical star, for example. If you see the word ring on the exam, check the context to see if it is referring to physical ring, logical ring, or both.

Stars feature better fault tolerance: any single local cable cut or NIC failure affects one node only. Since each node is wired back to a central point, more cable is required as opposed to bus (where one cable run connects nodes to each other). This cost disadvantage is usually outweighed by the fault tolerance advantages.

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Defining a VPN

In Firewall Policies and VPN Configurations, 2006

Star Topology

In a star topology configuration, the remote branches can communicate securely with the corporate headquarters or central site. However, intercommunication between the branches is not permitted. Such a configuration could be deployed in a bank network so that compromise of one branch will not immediately lead to the compromise of a second branch without being detected. To gain access to a second branch, the attacker would have to first compromise the central network that would hopefully be able to detect such an attack. A star topology configuration is shown in Figure5.6. Star topologies provide an inherent advantage that a new site can be added with ease; only the central site will have to be updated.

Figure5.6. Star VPN Deployment Topology

In star topology, the central site plays an important role; if it fails, all the connections will go down. Performance of the central hub dictates the performance of the connection. For a star topology, it may happen that two nodes might be closed to each other; however, they will have to communicate via central node.

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Networks

Jeremy Faircloth, in Enterprise Applications Administration, 2014

Star Topology

A star topology is a network that is designed to look very similar to a star with a central core and many systems connected directly to that core. The systems in a star topology do not connect to each other, but instead pass messages to the central core that, in turn, passes the message to either all other systems or the specific destination system depending on the network design. This topology works well for many smaller networks and works around many of the detriments associated with bus or ring topologies. You can see the general design of this topology in Figure 2.3.

Figure 2.3. Star topology.

A star topology does have its own limitations but there are effective ways of working around them. In reality, you can only connect so many systems to the same star network before you begin to run into physical limitations, such as cable length or the number of ports available on the hardware used for the network. The star topology handles this by being easily extended into multiple stars with a central core in the middle. This design can be seen in Figure 2.4, where there are multiple distinct star networks connected into a central core. In networking terminology, this core could be considered the backbone of the overall network. Messages intended for each system are transferred from the initiating system, to its star, into the core and then back out to the appropriate star and destination system.

Figure 2.4. Star topology with backbone.

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Network Fundamentals

Naomi J. Alpern, Robert J. Shimonski, in Eleventh Hour Network+, 2010

The Star Topology (Hierarchical)

In a star topology, computers aren’t connected to one another but are all connected to a central hub or switch. When a computer sends data to other computers on the network, it is sent along the cable to a central hub or switch, which then determines which port it needs to send the data through for it to reach the proper destination. Characteristics of a star topology are as follows:

All cables run to a central connection point.

If one cable breaks or fails, only the computer that is connected to that cable is unable to use the network.

A star topology is scalable.

As the network grows or changes, computers are simply added or removed from the central connection point, which is usually a hub or a switch.

Because there is so much cabling used to connect individual computers to a central point, this may increase the cost of expanding and maintaining the network.

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Networks

William Buchanan BSc (Hons), CEng, PhD, in Computer Busses, 2000

25.2 Network topologies

There are three basic topologies for LANs, which are shown in Figure25.3. These are a star network, a ring network and a bus network. There are other topologies which are either a combination of two or more topologies or are derivatives of the main types. A typical topology is a tree topology, that is essentially a combined star and a bus network, as illustrated in Figure25.4. A concentrator (or hub) is used to connect the nodes to the network.

Figure25.3. Network topologies

Figure25.4. Tree topology

25.2.1 Star network

In a star topology, a central server switches data around the network. Data traffic between nodes and the server will thus be relatively low. Its main advantages are:

As the data rate is relatively low between central server and the node, a low-specification twisted-pair cable can be used to connect the nodes to the server.

A fault on one of the nodes will not affect the rest of the network. Typically, mainframe computers use a central server with terminals connected to it.

The main disadvantage of this type of topology is that the network is highly dependent upon the operation of the central server. If it were to slow significantly then the network becomes slow. In addition, if it were to become unoperational then the complete network would shut down.

25.2.2 Ring network

In a ring network, computers link together to form a ring. To allow an orderly access to the ring, a single electronic token passes from one computer to the next around the ring, as illustrated in Figure25.6. A computer can only transmit data when it captures the token. In a manner similar to the star network, each link between nodes is a point-to-point link and allows the usage of almost any type of transmission medium. Typically, twisted-pair cables to allow a bit rate of up to 16Mbps, but coaxial and fibre optic cables are normally used for extra reliability and higher data rates.

A typical ring network is IBM Token Ring. The main advantage of token ring networks is that all nodes on the network have an equal chance of transmitting data. Unfortunately it suffers from several problems; the most severe is that if one of the nodes goes down then the whole network may go down.

Figure25.5. Token passing ring network

25.2.3 Bus network

A bus network uses a multidrop transmission medium, as shown in Figure25.6. All nodes on the network share a common bus and all share communications. This allows only one device to communicate a time. A distributed medium access protocol determines which station is to transmit. As with the ring network, data frames contain source and destination addresses, where each station monitors the bus and copies frames addressed to itself.

Figure25.6. Bus topology

Twisted-pair cables give data rates up to 100 Mbps, whereas, coaxial and fibre optic cables give higher bit rates and longer transmission distances. A bus network is a good compromise over the other two topologies as it allows relatively high data rates. Also, if a node goes down, it does not affect the rest of the network. The main disadvantage of this topology is that it requires a network protocol to detect when two nodes are transmitting the same time. It also does not cope well with heavy traffic rates. A typical bus network is Ethernet 2.0.

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LoRaWAN protocol: specifications, security, and capabilities

Alper Yegin, … Nicolas Sornin, in LPWAN Technologies for IoT and M2M Applications, 2022

3.3.1 LoRaWAN star topology with receive diversity is the key to scaling in an unlicensed spectrum

LoRaWAN deployments use a star topology with a frequency reuse factor of 1. This simplifies network deployment and ongoing densification because there is no need for frequency pattern planning or reshuffling as more gateways are added to the infrastructure. It also facilitates seamless collaboration between public and private networks.

Compared to mesh technologies, the single-hop-to-network infrastructure minimizes power consumption because nodes do not have to relay communication from other nodes. Another advantage is that initial network deployment in sparse mode with low node density is possible, compared with a mesh that requires minimum node density.

However, the most important design feature of LoRaWAN is its receive diversity. As usage of unlicensed spectra grows, background radio noise known as the noise floor is increasing. Some experts predict that unlicensed networks will inevitably face increasing packet loss and therefore cannot guarantee quality of service (QoS) in the long term. But this is not in fact inevitable. LoRaWAN networks can adapt to noise by leveraging multiple reception gateways operating simultaneously for each end device. LoRaWAN networks uplink messages that can be received by any gateway (RX macro-diversity). Such uplink macro-diversity significantly improves network capacity and QoS because it is very unlikely that destructive interference will occur all antennas simultaneously. As a result, LoRaWAN networks are expected to cope with increasing noise much better than earlier mesh networks, where each node is managed by only one next-hop receiver a time, and which, on the contrary, suffer catastrophic degradation due to the cumulative effect of increasing packet loss each hop, as shown in Fig. 35.

Figure 35. Mesh versus LoRaWAN behavior with rising noise level.

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Security in low-power wide-area networks: state-of-the-art and development toward the 5G

Radek Fujdiak, … Petr Mlynek, in LPWAN Technologies for IoT and M2M Applications, 2022

17.1.1 Low-power wide-area architecture

Albeit the LPWA technology market is still very fragmented and composed of several dozen different technologies, the technical solutions underlying many of them have much in common. Specifically, many LPWA technologies feature the architecture similar to that illustrated in Fig. 171.

Figure 171. Typical architecture of an LPWA network.

A conventional LPWA network features the star-of-stars topology with three major actors:

The machines, which we term end devices (EDs)1 and which are typically represented by resource-limited radio-enabled machines such as, sensors and actuators. Among the most common limitations for LPWA EDs are their limited processing capabilities (due to the push for ED cost minimization) and their energy budget (for the EDs powered with batteries). Also, to address the scalability constraints, the LPWA network operators often limit the amount of uplink or downlink traffic for particular EDs (e.g., in the form of monthly uplink/downlink data traffic, the share of time the ED can operate in the channel, or the number of uplink/downlink packets transferred per a unit of time). The EDs typically communicate only with the GW, while communication between the individual EDs or between an ED and a third-party system is typically not supported.

The LPWA network core is typically composed of one or multiple GWs, which are connected through an Internet protocol (IP)-based backbone link to a server or cloud, which manages the LPWA network. Typically, a wired interface (e.g., Ethernet or optical fiber cable) is used as the physical layer for backbone, albeit there are also commercial solutions featuring the broadband wireless backbone. Also, the LPWA network core may encapsulate other elements such as the dedicated authorization server or the server storing the data and managing the access to the data by external systems and services. These may also be integrated with the network-managing server or, in some cases, even the GW. Most often, the elements of the LPWA network core are powered from mains and thus are not significantly restricted for their energy consumption.

The third component of an LPWA application is the various external systems and servicesend-users and subscribers, which communicate with the LPWA network core to obtain the data sent by EDs in the uplink or to inject the data that need to be delivered to EDs in the downlink. The communication between end-users and LPWA core are typically carried using the IP-based interfaces and using special application programming interfaces.

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Cloud Data Center Networking Topologies

Gary Lee, in Cloud Networking, 2014

ToR switch

The servers within the rack connect to a ToR switch using a star topology as shown in Figure 4.3. Here, every server has a dedicated link to the ToR switch and the ToR switch may forward data to other servers in the rack, or out of the rack through high-bandwidth uplink ports. Due to factors such as multiple VMs sharing the same network connection, 10Gb Ethernet is widely used as the link between the server shelf and the ToR switch in cloud data center networks. A typical rack may contain on the order of 40 or more servers, so many ToR switches contain up to 48 10GbE ports and four 40GbE uplink ports which are connected to aggregation switches. Although this is a 3:1 mismatch in server bandwidth (480Gbps) versus uplink bandwidth (160Gbps), data center traffic is very bursty in nature and it is rare for all the servers to be using their full allocation of 10Gbps bandwidth simultaneously.

Figure 4.3. Top of rack switch feeding an aggregation switch.

As we discussed in the previous chapter, switch silicon technology can place limitations on the maximum number of ports per switch chip. In the case of a ToR switch, a single switch chip can tư vấn all of the ports described above (48 10GbE plus four 40GbE) using todays technology. In the case of the 10GbE ports, lower cost, direct attach copper cabling can be used for the short distance between the servers and the ToR switches, which is less than a few meters. Optic modules are used for the ToR switch uplink ports as they need to drive longer distances and higher bandwidth to other switches that interconnect multiple server racks. The uplinks may be connected to aggregation switches which aggregate the traffic from multiple ToR switches into a core switch.

Each ToR switch contains a control plane processor that, among other things, configures the switch forwarding tables and monitors the health of the switch. This processor may run layer 2 or layer 3 forwarding protocols or simply process table update commands from an external centralized software defined networking (SDN) controller. Using traditional layer 2 or 3 networking protocols, each switch learns about its environment through exchange of information with other switches and servers in the network. Today, more direct approaches may be used where the network administrator configures and monitors all of the ToR switches in the network. In the near future, this network orchestration work will be performed in a more automatic manner using software defined networking.

The ToR may also act as a gateway between the servers and the rest of the network by providing functions such as tunneling, filtering, monitoring, and load balancing. To enable these features, the ToR needs to inspect packet headers and match various header fields using what are called Access Control List (ACL) rules. The result of a match can produce several actions such as route the packet, tunnel the packet, assign the packet to a load balancing group, count the packet, police the packet, drop the packet, or assign a traffic class to the packet for egress scheduling. By adding this capability to the ToR switch, the functions of the other network components can be simplified, reducing overall network costs.

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Design considerations and network architectures for low-power wide-area networks

Bharat Chaudhari, Suresh Borkar, in LPWAN Technologies for IoT and M2M Applications, 2022

2.4.1 Low-power wide-area network topologies

Prominent topologies are star and mesh. Generally, star or star-on-star topology is preferred for LPWAN over mesh network for preserving battery power and increasing the communication range. LPWANs long-range connectivity allows such single-hop networks access to a large number of nodes, thus reducing the cost. From coverage viewpoint, traditional wireless sensor technologies such as ZigBee, Bluetooth, and Wi-Fi are not designed for wide coverage and hence are not directly applicable as LPWAN technologies.

The simplest form of wireless network topology is a point-to-point network in which nodes communicate directly with a central node. It is often used for remote monitoring applications and can be useful in hazardous environments where running wires is difficult or dangerous. Such LPWAN technologies tư vấn a star topology, as shown in Fig. 22A. A star network consists of one gateway node to which all other nodes connect. Nodes can only communicate with each other via the gateway. Node messages are relayed to a central server via gateways. Each end node transmits the messages to one or multiple gateways. The gateway forwards the messages to the network server where redundancy, errors, and security checks are performed. Star networks are fast and reliable because of their single-hop feature. Faulty nodes can also be easily identified and isolated. But, if the gateway fails, all the nodes connected to it become unreachable. Since the end node sends messages to multiple gateways, there is no need for gateway-to-gateway communication. This simplifies the design as compared to networks where the end nodes are mobile.

Figure 22. (A) Star topology. (B) Mesh network topology.

Mesh topology network consists of a gateway node, sensor nodes, and sensor-cum-routing nodes connected, as shown in Fig. 22B.

All the nodes can connect directly to each other in a full mesh topology. In a partial mesh topology, some nodes are connected to some of the others, but others are only connected to those with which they exchange the most messages with.

Mesh networks have several advantages such as availability of multiple routes for reachability, simultaneous up/downstream transmissions, easy scalability of the network, and capability of self-healing. These networks have some disadvantages including complexity due to redundant nodes, added latency because of multihop communication, and increase in cost. Redundancy of nodes also compromises the energy efficiency of the network.

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