By network layer
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the four layer Internet Protocol Suite model. In practice, the great majority of networks use the Internet Protocol (IP) as their network layer. Some networks, however, are using IP Version 6 IPv6, usually in coexistence with IPv4. IPv6 use is often experimental. it is an interconnection of a group of computers in other words.
A network as simple as two computers linked with a crossover cable has several points at which the network could fail: either network interface, and the cable. Large networks, without careful design, can have many points at which a single failure could disable the network.
When networks are critical, the general rule is that they should have no single point of failure. The broad factors that can bring down networks, according to the Software Engineering Institute [4] at Carnegie-Mellon University:
Attacks: these include software attacks by various miscreants (e.g., malicious hackers, computer criminals) as well as physical destruction of facilities.
Failures: these are in no way deliberate, but range from human error in entering commands, bugs in network element executable code, failures of electronic components, and other things that involve deliberate human action or system design.
Accidents: Ranging from spilling coffee into a network element to a natural disaster or war that destroys a data center, these are largely unpredictable events. Survivability from severe accidents will require physically diverse, redundant facilities. Among the extreme protections against both accidents and attacks are airborne command posts and communications relays[5], which either are continuously in the air, or take off on warning. In like manner, systems of communications satellites may have standby spares in space, which can be activated and brought into the constellation.
Dealing with Power Failures
Computer networks may be classified according to the network layer at which they operate according to some basic reference models that are considered to be standards in the industry such as the seven layer OSI reference model and the four layer Internet Protocol Suite model. In practice, the great majority of networks use the Internet Protocol (IP) as their network layer. Some networks, however, are using IP Version 6 IPv6, usually in coexistence with IPv4. IPv6 use is often experimental. it is an interconnection of a group of computers in other words.
A network as simple as two computers linked with a crossover cable has several points at which the network could fail: either network interface, and the cable. Large networks, without careful design, can have many points at which a single failure could disable the network.
When networks are critical, the general rule is that they should have no single point of failure. The broad factors that can bring down networks, according to the Software Engineering Institute [4] at Carnegie-Mellon University:
Attacks: these include software attacks by various miscreants (e.g., malicious hackers, computer criminals) as well as physical destruction of facilities.
Failures: these are in no way deliberate, but range from human error in entering commands, bugs in network element executable code, failures of electronic components, and other things that involve deliberate human action or system design.
Accidents: Ranging from spilling coffee into a network element to a natural disaster or war that destroys a data center, these are largely unpredictable events. Survivability from severe accidents will require physically diverse, redundant facilities. Among the extreme protections against both accidents and attacks are airborne command posts and communications relays[5], which either are continuously in the air, or take off on warning. In like manner, systems of communications satellites may have standby spares in space, which can be activated and brought into the constellation.
Dealing with Power Failures
One obvious form of failure is the loss of electrical power. Depending on the criticality and budget of the network, protection from power failures can range from simple filters against excessive voltage spikes, to consumer-grade Uninterruptible Power Supplies(UPS) that can protect against loss of commercial power for a few minutes, to independent generators with large battery banks. Critical installations may switch from commercial to internal power in the event of a brownout,where the voltage level is below the normal minimum level specified for the system. Systems supplied with three-phase electric power also suffer brownouts if one or more phases are absent, at reduced voltage, or incorrectly phased. Such malfunctions are particularly damaging to electric motors. Some brownouts, called voltage reductions, are made intentionally to prevent a full power outage.
Some network elements operate in a manner to protect themselves and shut down gracefully in the event of a loss of power. These might include noncritical application and network management servers, but not true network elements such as routers. UPS may provide a signal called the "Power-Good" signal. Its purpose is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present, the computer shuts down. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself
To help standardize approaches to power failures, the Advanced Configuration and Power Interface (ACPI) specification is an open industry standard first released in December 1996 developed by HP, Intel, Microsoft, Phoenix and Toshiba that defines common interfaces for hardware recognition, motherboard and device configuration and power management.
By scale
Computer networks may be classified according to the scale: Personal Area Network (PAN), Local Area Network, Campus Area Network, Metropolitan area network (MAN), or Wide area network (WAN). As Ethernet increasingly is the standard interface to networks, these distinctions are more important to the network administrator than the end user. Network administrators may have to tune the network, based on delay that derives from distance, to achieve the desired Quality of Service (QoS).
Controller Area Networks are a special niche, as in control of a vehicle's engine, a boat's electronics, or a set of factory robots.
By connection method
Computer networks may be classified according to the hardware technology that is used to connect the individual devices in the network such as Ethernet, Wireless LAN, HomePNA, or Power line communication.
By functional relationship
Computer networks may be classified according to the functional relationships which exist between the elements of the network, for example Active Networking, Client-server and Peer-to-peer (workgroup) architectures.
By network topology
Main article: Network Topology
Computer networks may be classified according to the network topology upon which the network is based, such as Bus network, Star network, Ring network, Mesh network, Star-bus network, Tree or Hierarchical topology network, etc.
Network Topology signifies the way in which intelligent devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a Bus Topology. In this regard the visual and operational characteristics of a network are distinct.
By protocol
Computer networks may be classified according to the communications protocol that is being used on the network. See the articles on List of network protocol stacks and List of network protocols for more information
No comments:
Post a Comment