US 14913: EXPLAIN THE PRINCIPLES OF COMPUTER NETWORKS …

FETC: Information Technology Technical Support NQF 4: SAQA ID 78964

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Page 1 of 17 IT TECH NQF 4 – IT TECH – LG 2 – US 14913 Issue 3: 01-01-2020

US 14913: EXPLAIN THE PRINCIPLES OF COMPUTER NETWORKS NQF Level 3 Credits 5

Purpose This unit standard is intended:

to provide fundamental knowledge of the areas covered

for those working in, or entering the workplace in the area of Data Communication & Networking

As additional knowledge for those wanting to understand the areas covered.

Learning assumed to be in place The credit value of this unit standard is calculated assuming a person has the prior knowledge and skills to:

Demonstrate an understanding of fundamental mathematics (at least NQF level 3).

Demonstrate PC competency skills (End-User Computing unit Standards, at least up to NQF level 3.)

Demonstrate competence to resolve technical computer problems (SGB-ID=DC301/ 302).

Demonstrate an understanding of local and wide area networks, and their installation.

Unit standard range N/A Specific Outcomes and Assessment Criteria

Specific Outcome 1: Describe data communication.

Assessment Criteria The description explains the roles of key elements in data communication. .

The description differentiates between LAN’s and WAN’s.

Specific Outcome 2: Demonstrate knowledge of main features of LANs.

Assessment Criteria The demonstration identifies the uses of LAN’s with respect to current practice. .

The demonstration identifies the main types of LAN media.

The demonstration describes the main LAN configurations.

The demonstration describes LAN bandwidth.

The demonstration describes LAN protocols.

Specific Outcome 3: Demonstrate knowledge of main features of WANs.

Assessment Criteria The demonstration explains the uses of WAN’s with respect to current practice.

The demonstration explains the uses, hardware requirements and advantages of WAN’s. Critical Cross-field Outcomes (CCFO)

Unit Standard CCFO Working: Work effectively with others as a member of an organisation.

Unit Standard CCFO Organizing: Organise and manage him/herself and his/her activities

responsibly and effectively.

Unit Standard CCFO Collecting: Collect, analyse, organise, and critically evaluate information.

Unit Standard CCFO Science: Use science and technology effectively and critically, showing

responsibility towards the environment and health of others.

Unit Standard CCFO Demonstrating: Demonstrate an understanding of the world as a set of

related systems by recognising that problem solving contexts do not exist in isolation.

Unit Standard CCFO Contributing: Contribute to his/her full personal development and the social

and economic development of the society at large by being aware of the importance of: reflecting on and exploring a variety of strategies to learn more effectively, exploring education and career opportunities and developing entrepreneurial opportunities.


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SECTION 1: DATA COMMUNICATION Outcomes

Describe data communication. Assessment Criteria

The description explains the roles of key elements in data communication.

The description differentiates between LAN’s and WAN’s.

Key Elements in Data Communication

Networks are designed to increase productivity.

Without a network, the ability to share files would be limited to "sneaker-net," copying files onto external media, such as a CD, and carrying the disk from computer to computer. By making data available over a network, several people have easy access to data and user communication is improved through network services such as electronic mail. A network improves security. Physical data security is increased by allowing users to store data files in a central location that is backed up regularly. Security is also improved through access control. Most networks allow administrators to limit who can use the network and to what resources they will have access. Networking computers can simplify a technician's job. It is easier to support one or two operating systems and network applications than dozens of computers that follow no standards. Network-based management and troubleshooting utilities allow technicians to correct many system problems without having to physically visit the system. To have an actual network you will need two or more machines, and they need to be connected to each other. When these machines are connected, they are able to communicate with each other. If we look at an example, one user needs to send a document to another user, the sending user’s machine would serve as the sender and the receiving user’s machine would serve as the receiver. Once the sender has sent the message, it travels over a cable to the receiver and is called transmission media, which is normally measured in bits per second (bps).

Differentiate between LAN’s and WAN`s Although networks vary in size and complexity, each can be generally described as either a local area network (LAN) or wide area network (WAN). The primary difference between the two is the network's geographic scope. . Networks can also be categorised by security model. Security models include workgroup, client/server, domain-based and directory-based. There is no direct correlation between a network's physical and security models. A LAN or WAN can be configured as a workgroup, client/server, domain-based or directory-based network. The determining factor for the security model is the network software that is used and how that software is configured.

LAN (Local Area Network)

A Local Area Network (LAN) is a network that is confined to a relatively small geographic area such as an office, school, or building.

Note The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines.

Computers connected to a network are broadly categorised as servers or workstations. Servers

are generally not used by humans directly, but rather run continuously to provide "services" to the other computers (and their human users) on the network. Services provided can include printing and faxing, software hosting, file storage and sharing, messaging, data storage and retrieval, complete access control (security) for the network's resources, and many others.

Workstations are called such because they typically do have a human user which interacts with the network through them.

We usually thought of workstations as a desktop, consisting of a computer, keyboard, display, and mouse, or a laptop, with integrated keyboard, display, and touchpad. Now, with the tablet computer, and the touch screen devices such as iPad and iPhone, our definition of workstation is quickly changing to include those devices, because of their ability to interact with the network and utilize network services.


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Servers tend to be more powerful than workstations, although configurations are guided by needs.

For example, a group of servers might be located in a secure area, away from humans, and only accessed through the network. In such cases, it would be common for the servers to operate without a dedicated display or keyboard. However, the size and speed of the server's processor(s), hard drive, and main memory might add dramatically to the cost of the system. On the other hand, a workstation might not need as much storage or working memory, but might require an expensive display to accommodate the needs of its user. Every computer on a network should be appropriately configured for its use.

On a single LAN, computers and servers may be connected by cables or wirelessly.

Wireless access to a wired network is made possible by wireless access points (WAPs). These WAP devices provide a bridge between computers and networks. A typical WAP might have the theoretical capacity to connect hundreds or even thousands of wireless users to a network, although practical capacity might be far less. Nearly always servers will be connected by cables to the network, because the cable connections remain the fastest. Workstations which are stationary (desktops) are also usually connected by a cable to the network, although the cost of wireless adapters has dropped to the point that, when installing workstations in an existing facility with inadequate wiring, it can be easier and less expensive to use wireless for a desktop.

WAN (Wide Area Network)

Note Wide Area Networks (WANs) connect networks in larger geographic areas, such as Johannesburg, Gauteng, or the world.

Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of global network. Business and government entities utilise WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations. In essence this mode of telecommunication allows a business to effectively carry out its daily function regardless of location. Using a WAN, businesses in for example Johannesburg can communicate with places like Tokyo in a matter of seconds, without paying enormous phone bills. Two users a half-world apart with workstations equipped with microphones and a webcam might teleconference in real time. A WAN is complicated. It uses multiplexers, bridges, and routers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN.

Note: The Internet is an example of a worldwide WAN. You might not think of it as such since most users access the Internet through standard ADSL lines or Broadband.


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The textbook definition of a WAN is a computer network spanning regions, countries, or even the world. However, in terms of the application of computer networking protocols and concepts, it may be best to view WANs as computer networking technologies used to transmit data over long distances, and even between different LANs. WANs are used to connect LANs and other types of networks together, so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organisation's LAN to the Internet.

SECTION 2: MAIN FEATURES OF LAN’S

Outcomes

Demonstrate knowledge of main features of LANs. Assessment Criteria

The demonstration identifies the uses of LAN’s with respect to current practice.

The demonstration identifies the main types of LAN media.

The demonstration describes the main LAN configurations.

The demonstration describes LAN bandwidth.

The demonstration describes LAN protocols.

The Uses of LAN’s One of the greatest benefits of LAN’s today is data sharing. We have come a long way from sneaker net where users had to save for example a document to a floppy and physically walk to the person they want to share the information with and hand over the disk. The receiver then had to copy the document from the floppy onto their machine. Today we use local sharing. You can stay at your desk and simply send the document via the LAN to the receiver and you are done. You can also share more than just a document with a user. More advanced users are able to share programmes as well. Another great benefit is share peripherals. A great example of this is something like a printer. If an organisation has 30 employees who does admin work, you would have to buy each one of them a printer, which isn’t very cost effective. With a LAN, one printer can be connected to the network for, let’s say every 10 employees (depending on the amount of print work each employee has every day) and they can all share the same printer! This saves and organisation 26 printers that they would have had to buy if we haven’t discovered LAN’s yet.

The Main Types of LAN Media

In this section, we will look at 4 different types of media used to connect machines to one another in a LAN.

The first is twisted pair cables. Twisted-pair is a common type of cable that has been extensively

used for telephone systems. One pair of insulated wires twisted together forms a Twisted-Pair (TP)

Cable Grade Use Bandwidth

Category 1 Voice and data transfer 1Mbps

Category 2 Data (slow token ring) 4Mbps

Category 3 Data (Ethernet) 10Mbps

Category 4 Data (Fast token ring) 16Mbps

Category 5 Data (Fast Ethernet and 100VGAnyLAN)

100Mbps

Category 5e Data (LAN speed for ATM) 155+ Mbps


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and one or more twisted-pairs (normally two-pair or four-pair) form a twisted pair cable. Usually, the twisted-pair consists of two insulated 22 to 26 American Wire Gauge (AWG) copper wires. The pairs

are twisted to reduce external interference and crosstalk. Crosstalk is a phenomenon whereby one wire causes interference in another as a result of their close

proximity. Twisting the wires ensures the emitted signals from one wire are cancelled out by the emitted signals from the other and it also protects the wires from external interference. Each pair is twisted at a different rate to ensure the pairs do not interfere with each other. The distance between twists is defined by the cable category. Twisted pair cable is implemented as unshielded twisted pair (UTP) and shielded twisted pair (STP). Twisted pair cable is inexpensive and easy to install and maintain. UTP has two or more twisted pairs with an insulating cover. It is the least expensive type of cable, but it is somewhat susceptible to electromagnetic interference (EMI). UTP cable must be routed to avoid EMI sources. STP has two or more twisted pairs surrounded by a foil or braided wire shield that provides protection against EMI interference, making it the preferred choice when EMI sources cannot be avoided. Some network specifications require STP cable. It is more expensive than an equivalent UTP cable. Twisted pair cable is rated by category that describes its bandwidth. The higher the category number,

the higher its potential bandwidth. Common telephone lines are an implementation of category 1 twisted pair.

Category 1 is not considered an acceptable media for network data transmissions, but does support low-speed serial communications such as connections to dial-up lines. Category selections are made according to network data transmission requirements.

Coaxial Cable

Coaxial cable (coax) takes its name from its physical characteristics. Coax has a central conductive core that carries the data signal. This core is surrounded by an insulator, then a foil or braided mesh shield, which also acts as the signal ground. The entire cable is then covered with an insulating cover. The conductor and shield are on a common axis, or a coaxial configuration. Coax is relatively inexpensive to use. The shielding makes the cable resistant to communication problems caused by electromagnetic interference (EMI). At one time, coax was the most common LAN cabling option. Several types of coaxial cable are used in network implementations. Cable types are specific to network implementations. Be sure to purchase the correct cable type for your network. You will notice an impedance value listed for each of the cable types in the table. Impedance is a measure of a cable resistance to a changing signal. You will most commonly see RG-58/AU or RG-58/CU cable used in LAN applications. You will sometimes see RG-8 and RG-11 used in some older LANs. RG-62 cable was used in some legacy LAN configurations.

Cable type Usage Impedance

RG-8 Thick Ethernet 50 Ohms

RG-11 Broadband LANs 75 Ohms

RG-58 Thin Ethernet 50 Ohms

RG-59 Television 75 Ohms

RG-62 ARCnet 93 Ohms


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Fibre Optic

Fibre optic cable is made of a glass or plastic cylinder enclosed in a tube, called cladding. An insulating sheath covers the core and cladding. The cable carries optical light pulses by laser or light-emitting diodes (LEDs). The glass cladding is used to reflect light back into the core. Fibre-optic cable is used in high-speed network implementations. One advantage of fibre optic cable is its high bandwidth and low attenuation. These factors allow data transmissions over long distances, with implementation specifications up to 2 km. The physical limit of high-qualify fibre optic cable can be 20 km or more. Also, because data is transmitted by light, EMI interference does not present a concern. However, fibre optic cable does present some inherent disadvantages. It is more expensive and difficult to install than other cable types. It is also fragile and easily damaged.

Wireless

Wireless media uses either radio broadcast signals or infrared light to communicate. Wireless media is sometimes referred to as unbounded media. Wireless media can be used when using a physical cable is impractical. Wireless media is also used in some long-range, high-volume communication applications. Infrared communication is relatively easy to implement. It is often used as a supplement to other network communication media rather than as a primary communication method. For example, you might use infrared to provide network support to laptop users who need infrequent access to the network. One of the biggest drawbacks to infrared communication is that it is a line-of site communication method. A clear path between the sending and receiving systems is required. Communication can sometimes be degraded by strong light sources, as well. Other wireless communication methods that are gaining popularity in specialised applications are microwave and satellite communication methods. One of the more common uses of microwave systems is terrestrial microwave, a point-to-point communication method requiring a microwave antenna at each end. Terrestrial microwave can be a cost-effective solution for linking two sites when a wire-based communication method could prove more expensive over time. For example, you can sometimes find microwave links used between two offices in the same metropolitan area. Satellite systems transmit signals from the transmitting antenna to a satellite in space, back to a

receiving antenna. To use a satellite system, you need to launch your own satellite or lease a service from a company offering these services. Due to the costs involved, you will seldom see satellite links used except in specialised applications. All radio frequency broadcast wireless communication methods, including microwave and satellite links, are susceptible to weather and other environmental influences. It can be difficult to justify the expense required in setting up these systems unless an organisation is willing to take a very long-term outlook for cost justification.

Main LAN Configurations

Network topology describes a network's physical layout, or how cables, nodes and connection devices are linked together. PC networks are usually wired as a bus, ring or star topology.

Bus

A bus topology has the simplest structure and was, at one time, the most commonly used method for connecting computers. All nodes are connected to a central line and, in theory, have equal access to the network. A bus topology transmission is sent to all of the nodes on the network, but only the node with the correct address accepts the data. All other nodes reject the data. Only one node at a time can send data across the network. Due to this limitation, adding nodes to a bus network will eventually cause slower network performance.


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The data signal is broadcast along the entire central line, travelling the trunk from end to end. If the signal is not interrupted, it continues to travel or bounce on the trunk, keeping other computers from communicating. To eliminate bounce, each end of the cable is terminated with a resistor. The terminator stops the bouncing signal, thereby clearing the cable so other computers can continue to communicate. Bus topology networks are typically wired with coaxial cabling. They are relatively simple and inexpensive to implement; these two factors helped make this the most popular topology for PC networks for several years. Some potential disadvantages are inherent in a bus topology network. Traffic levels increase with the number of nodes supported and can reach levels at which network performance is severely impaired. Attenuation may present a problem if you attempt to run a cable segment longer than allowed by specifications. Also, a failure anywhere along the central cable or with either terminator results in a failure of the entire cable segment. Locating, isolating and repairing cable faults can be very difficult.

Cable use specifications vary with different network access methods and access protocols (data link protocols).

Ring

The ring topology connects nodes in a circle. Packets travel around the circle and through each computer before moving on to the next one. Because the electronic signal travels around a circle, there are no ends to terminate. Because each system will receive and rebroadcast each packet, attenuation tends to be less of a concern in a ring network. Most ring configurations also have a built-in level of fault tolerance to recover from a failing node and sometimes even from a break in the ring. Current implementations of ring topology tend to be more expensive than bus or star network topologies. Most current ring networks also support lower bandwidths, making them potentially less appropriate to high-volume applications. Ring networks are most commonly wired in a fashion that causes them to appear as if they are star networks.

Note: A trade-off exists in ring topology implementations. Token ring networks are relatively cost-effective, but slower than other LAN technologies. FDDI is a fibre optic-based access protocol that uses a ring topology to provide high-speed communication, but at a high cost.

Ring Network

Star

In the star topology, cables run from each node into a central hub device. Electronic signals are sent from the node, to the hub, and then on to the remaining computers on the network. The network is expanded with the addition of more hubs. Star topology networks are easy and relatively inexpensive to implement. Connections from hubs to nodes and between hubs are made using twisted pair cabling and, in most cases, standard modular connectors. Failure of a single node or cable typically does not affect the rest of the network. When problems do occur, it is usually easy to locate and isolate the failing component. There is a potential problem in that each hub represents a central point of failure. A failing hub can impact several nodes.


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LAN Bandwidth Think of bandwidth as a pipe through which your information flows. The larger the pipe, the faster the information can move. When the pipe starts to fill up or become constricted in some way, the information begins to slow down. In theory, a higher bandwidth indicates faster data transfer capabilities. In actual practice available bandwidth is more important to speed than bandwidth capacity alone. For example: Assume you are driving in rush hour traffic on a four-lane interstate highway. Although you have four traffic lanes available, your circumstances (rush hour) dictate that you may not be travelling very fast. In fact, if a collision happens in front of you, you may not travel at all. In contrast to driving in rush hour, imagine driving an isolated two-lane country road on a Sunday afternoon. Chances are, few other vehicles are on the road and your speed is limited by the posted speed limit or road conditions. This is similar to what can happen on a network. You may have a potential bandwidth of 100 Mbps on an Ethernet bandwidth, but collisions can significantly reduce your available bandwidth during peak use times. Two options can be used to increase available bandwidth:

increase the base bandwidth

reduce the amount of traffic Increasing the base bandwidth can be expensive, because it typically means replacing network cabling and connection devices, and may also require replacement of most or all of your network adapters. A more cost-effective solution is to reduce network traffic.

You need to understand the sources of network traffic before you can reduce it. Your task may include having to reduce the number of communication protocols installed on each computer or replacing applications that generate unnecessarily high levels of network traffic. More often, your solution for reducing network traffic will be to segment the network. To do so, you will need to identify the systems that communicate with each other regularly and set them up in semi-isolated groups. You will most commonly use bridges or routers to segment network traffic.


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The computers are not restricted from communicating with other segments or sub-networks, but local traffic will be kept local. This isolation can lead to significant improvement in traffic levels and network performance.

Note: You might find that traffic problems are being caused by users playing network-based multiplayer games over the company network. Graphic-intensive games can sometimes cause noticeable performance problems.

LAN Protocols

In this section we will look at Ethernet, Token Ring and TCP/IP

Ethernet Communication Ethernet networks use an access method called Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Check the chart for the description of terms. Collisions are a problem inherent in Ethernet communication. In an active network, two or more systems will often be waiting for the cable to become available so that they can transmit. As soon as the cable is available (that is, no other system is transmitting) any systems that are waiting will try to transmit. This attempt causes a collision.

CSMA/CD Term

Description

Carrier Sense All nodes monitor the cable to determine if another node is communicating. A node will not attempt to communicate unless no another nodes are communicating

Multiple Access In theory all nodes have equal access to the cable. All are connected to the cable at the same time.

Collision Detection Collisions occur when two nodes attempt to communicate at the same time. This event requires both nodes to retransmit.

When collisions occur:

All transmitting systems will wait a semi-random interval

After its timeout, a system will check to see if the cable is available

Each system will attempt to retransmit Collisions can become a problem on large, active Ethernet networks. The process of waiting and retransmitting slows network performance.

A common solution is to separate the LAN into smaller sub-networks, segmenting the traffic and

reducing traffic levels on each of the segments. 10Base2 10Base2 or "thinnet" Ethernet was the most common networking solution for many years. It is still sometimes used in new installations, but is most commonly found in legacy networks.

10Base2 uses a bus topology wired with RG-58/AU or RG-58/CU coaxial cable.

Cable specifications are as follows: The maximum segment length is 185 m.

As many as five segments may be connected by repeaters.

The maximum network length, for all segments, is 925 m.


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A 50-ohm termination is needed at each end of the cable.

A maximum of 30 nodes per segment is required. The cable technical specifications can be somewhat misleading, because only three of the segments can support connected nodes, limiting the network to 90 nodes. A node's connection is made using

BNC T-connectors, inserted inline in the cable that connects directly to the node's network adapter.

There must be at least .5 m between any two T-connectors.

The coax centre conductor is considered pin 1 and carries the data signal.

The metal sheath acts as signal ground and provides EMI protection. 10Base5

10Base5 or "thicknet" Ethernet is found in some legacy networks, but many implementations have

been replaced by other technologies. One common use of thicknet was as a backbone cable in larger LANs. 10Base5 uses a bus topology wired with either RG-8 or RG-11 coaxial cable. Cable technical specifications are given below:

The maximum segment length is 500 m.

As many as five segments may be connected by repeaters.

The maximum network length is 2,500 m.

A 50-ohm termination is needed at each end of the cable.

The maximum number of nodes (transceivers) per segment is 100.

The minimum distance between any two transceivers is 2.5 m.

A maximum of 1,024 devices per network is required.

Connections are made to the network through transceivers. The transceiver connects to the coaxial

cable. The transceiver can connect directly to a computer or other device, or to a terminal server or fan-out unit that supports multiple device connections through a single transceiver connection. The maximum transceiver cable length is 50 m. Device connections are made through a standard DB-15 connector,

called an AUI or DIX connector. For pin definitions see Reference section AUI pin-outs. Legacy Ethernet network adapters usually included both a DB-15 AUI connector and a BNC connector. Both were included so the adapters could be used with thinnet or thicknet networks. 10/100BaseT 10BaseT and 100BaseT Ethernet networks use twisted pair cable for communication between devices. Depending on environmental conditions, either UTP or STP cable can be used to wire the network. Except for the cable category required and bandwidth, the two specifications are essentially the same. Connections between devices are made through central hubs or switches. Devices are wired using a star topology. 10BaseT networks will be wired using Category 3 or Category 5 cable. Category 5 cable is specified for 100BaseT networks. The network can be expanded when additional hubs are connected. A separate backbone cable is sometimes used to connect hubs, as shown in the figure.

Note: Some manufacturers have stated that Category 3 cable can be used for 100BaseT implementations. Category 3 cable will work in some situations, but is a potentially unreliable choice for 100BaseT networking.

Cable specifications for a 10/100BaseT network are given below:

The maximum cable length to the hub is 100 m (328 ft.).

The minimum cable length to the hub is 0.6 m (2 ft.).

One device may be used per cable.

The maximum number of network devices is 1,024.


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Most hubs are unintelligent devices. Connections in a simple hub are tied together to a single line,

making the connections electronically equal, as if they were bus topology connections. Intelligent hubs are also available and provide additional features such as traffic buffering to reduce collisions.

Device connections are made using an RJ-45 connector. Differential data signals are used so that

each signal has a + and a - signal. For pin assignments, see Reference section RJ-45 pin assignments.

Note: Most new Ethernet adapters are 10/100 adapters. Therefore, the adapter is compatible with both 10BaseT and 100BaseT networks. The adapter will sample traffic on the network when it comes online and will select the appropriate bandwidth

automatically.

Token Ring

Token ring networks are based on the IEEE 802.5 standard and control communication through token passing. The standard was originally developed by IBM, but soon became a public standard.

A token ring network is a logical ring, but is often physically wired to resemble a star topology.

A token is a packet that passes from system to system.

The following steps describe the basics of how data is passed in a token ring network:

An empty token is received by a computer.

The computer loads the token with data and a destination address.

The token is passed to the network computer in the ring.

Each system passes the token to the next system in line until the recipient is reached.

The receiving system removes the data and adds an acknowledgement to the token.

The token is passed back around the network until it reaches the sending system.

The sending system removes the acknowledgement and passes on an empty token. Token ring communication is tightly controlled. Collisions cannot occur in a Token ring network, but communication can be interrupted by hardware failures in the ring.

When a ring failure is detected, the system detecting the error will be transmitting beacon frames. The beaconing frames are used to determine:

The system detecting the error.

The nearest active upstream neighbour (NAUN) which is the operational system nearest the error.

All systems between the detecting system and the NAUN. After the NAUN has been determined, the NAUN will remove itself from the network and perform a self-test. If the self-test fails, the NAUN will remain detached from the network.


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If, after waiting a timeout period, ring communications have not recovered, the detecting station will remove itself from the ring and run a self-test. If the self-test fails, the system will remain detached from the network. If the error cannot be corrected when these systems are removed from the ring, manual repair measures must be implemented. Multiple Access Unit (MAU)

Device connections are made through MAUs. Standard MAUs support eight connections, but 16-node MAUs are available. When a device is connected to a MAU, it is added to the ring. If no device

is connected to a port, the data signal is passed directly to the next MAU port. Multiple MAUs can be

connected by connecting the Ring Out connection of one MAU to the Ring In connection of the

next. If a ring has only one MAU, Ring Out and Ring In are connected internally to complete the ring.

Note: Token ring networking can also be supported with fibre optic cable. When fibre optic cable is used, the maximum distance (by token ring specification) between a MAU and a repeater is 1.5 km and the maximum network length is 4 km.

Token Ring Specifications The two standards for token ring communications are 4 Mbps and 16 Mbps. A ring will operate at one or the other, but not both. UTP or STP can be used with 4-Mbps token Ring. STP is required for 16-Mbps token ring.

Token ring cables are typically referenced by IBM cable types. Later we will discuss IBM cable types. Token ring connection specifics are as follows:

The maximum distance from MAU to computer is 45 m.

The maximum length for cable between two MAUs is 120 m.

The maximum length from MAU to repeater is 600 m.

The maximum network length is 750 m (with IBM type 1 cable).

The maximum number of MAUs per ring is 12.

The suggested maximum number of nodes per ring is 72. Attempting to support more than 72 nodes in a single ring typically degrades performance.

Note: Token ring networking can also be supported with fibre optic cable. When fibre optic cable is used, the maximum distance (by token ring specification) between a MAU and a repeater is 1.5 km and the maximum network length is 4 km.


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Token ring connections are most commonly made using RJ-45 modular connectors. IBM data connectors, DB-9 connectors and, to a lesser extent, RJ-12 and RJ-14 connectors are also used. For

the pin-out for a RJ-45 token ring connector, see Reference section RJ-45 Token ring connector. The IBM data connector is a four-wire connector. Pins 1 and 2 are used for the Transmit - and Transmit + signals. Pins 3 and 4 are used for the Receive - and Receive + signals. When a DB-9 connector is used for token ring connections, pins 1, 5, 6 and 9 are the only pins used. The remaining pins are not

connected. For descriptions of the DB-9 pin-outs see Reference section Token ring DB-9 assignments in the glossary. J-12 and RJ-14 connectors can be used for token ring connections, but

are rarely used. An RJ-14 is a six-pin modular connector, similar to RJ-12 and RJ-45 connectors. For signal assignments

see Reference section RJ-12 and RJ-14 token ring assignments in the glossary.

Note: You will sometimes see RJ-12 connections documented as RJ-11 connections. RJ-11 and RJ-12 use the same physical connection, but RJ-11 is technically a two-wire connection. Four-wire connections are more accurately called RJ-12 connections.

Cabling for token ring applications is typically documented by IBM standard cable types rather than the standard categories. See the table below for the cable types to reveal the gauge and description for

that type. Gauge values are given as American Wire Gauge (AWG) values.

Cable type Gauge Description

Type 1 22 STP cable with two twisted pairs. Suitable for use in 4 Mbps and 16 Mbps token ring applications.

Type 2 22 STP cable with four twisted pairs. Typically used for telephone service and RS-232 data communications. Can be for used for 4 Mbps or 16 Mbps token ring, but not typically recommended for those applications

Type 3 24 UTP with four twisted pairs. Suitable for telephone and 4 Mbps token ring.

Type 6 26 UTP with two twisted pairs. Typically used for patch panel and network adapter cable applications.

Note: There is also an IBM fibre optic cable, Type 5, which is used for fibre optic-based token ring. The cable contains two fibre optic conductors.


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Fibre Distributed Data Interface (FDDI) FDDI is based on the ANSI X3T9.5 standards, and is used primarily for high-speed communication over long distances. FDDI communicates over a fibre optic ring, or more accurately, a dual fibre optic ring. A token passing access method is used with tokens passed on both rings, but in opposite directions. This configuration is referred to as using dual counter-rotating rings. Should either ring fail; the FDDI network can continue communicating over the remaining ring. FDDI supports a 100 Mbps bandwidth. You can have up to 2 km between FDDI stations and up to 1000 stations. Total network length is limited to no more than 200 km. Because stations are typically implemented as Class A stations (connected to both rings) you are effectively limited to 500 stations.

Note: The 100 Mbps limit is set by the FDDI specification. In theory, a fibre optic network can support a bandwidth of up to 4 Gbps with a single segment of 20 km or more.

TCP/IP

The TCP/IP suite is the current de facto standard for both local and wide area networking. Most operating systems include TCP/IP support as a default selection when installing and configuring network support, including current Windows family operating systems. In addition to being used as a communication protocol on private networks, TCP/IP is required for Internet access. TCP/IP is used as the primary or sole communication protocol on nearly all new PC network installations. In addition, most existing PC networks either have converted or are converting to TCP/IP. TCP/IP is a routable protocol that can be used in nearly any LAN or WAN networking configuration. TCP/IP Suite TCP/IP is a protocol suite, meaning that it includes several specialised protocols, network services and network support utilities. An overview of some of the more commonly used suite components is provided in the chart. Many of these components, such as the specific protocols, operate in the background and are never seen directly by the users. Others, such as the ping utility, are executed from a command line when they are needed.

TCP/IP Components

Components Description

Internet Protocol (IP) Connectionless protocol that operates as the underlying protocol for both connectionless and connection-orientated delivery servers between computer systems.

Transmission Control Protocol (TCP) Provides connection-orientated delivery services between computer systems.

Address resolution Protocol (ARP) Determines a system’s MAC address when its host address is known.

Reverse Address resolution Protocol (RARP) Determines a system’s host address when its MAC address is known.

Telnet TCP/IP connection utility that supports remote terminal emulation applications

File Transfer Protocol (FTP) File transport protocol used for transferring files between computers with dissimilar file systems

Ping Creates a shortcut icon for the printer on the desktop

Tracert/Traceroute Documents will be entered into the printer queue, but not printed. You can select to print the document later.

Ipconfig/Winipcfg Deletes the printer. You will also be prompted to delete the printer’s device driver file.


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Two terms that need additional explanation are "connectionless protocol" and "connection-oriented protocol."

A connectionless protocol does not provide a guaranteed delivery. In other words, there is

no guarantee that a packet will be received by the destination system.

A connection-oriented protocol provides packet acknowledgment and sequencing.

Acknowledgement means that the receiving system will respond to the sending system when the

packet is received.

Packet sequencing means that if packets are received out of order, the receiving system will place them in the proper order and reconstruct the data.

SECTION 3: MAIN FEATURES OF WAN’S

Outcomes

Demonstrate knowledge of main features of WANs. Assessment Criteria

The demonstration explains the uses of WAN’s with respect to current practice.

The demonstration explains the uses, hardware requirements and advantages of WAN’s.

Uses of WAN’s with Respect To Current Practice A WAN is a collection of LANs, typically connected through public carriers such as standard telephone lines or high-speed digital lines. The geographic scope of a WAN will be determined by an organisation's communication requirements. Some WANs are limited to one city or province, and others cross international boundaries. The best known WAN (for its use and popularity) today is the internet. The Internet is an example of a worldwide WAN. You might not think of it as such since most users access the Internet through ADSL lines or Broadband. ADSL is often a component of private WANs, as well. A great use of the internet is downloading programmes. Technically someone or an organisation is sharing the programme with you or gives you the option to pay them to download it, but still it stays a great advantage instead of having to drive to a vendor, the software you are looking for is at the tip of your fingers.

Remote Communication

Remote communication takes place when a remote user accesses a network through ADSL that connect to a remote access server on that network. The user connects as if connecting directly to the network, but at a much lower bandwidth. A solution that has gained a great deal of recent popularity is providing access to remote users through the Internet. This access is usually accomplished through the use of a virtual private network (VPN) that uses the Internet as the WAN backbone. VPN connections can be used to connect individual remote users or remote LANs. One of the biggest concerns about using the Internet for remote network connections is security. Protection devices, such as firewalls, need to be provided to restrict access into your network and to encrypt data that is being passed through the Internet.

Note: Two other topologies that are used, but that you will probably not see in a LAN, are mesh and cellular topologies.

A mesh topology is sometimes used as a WAN topology. A cellular topology is sometimes used with unbounded communication media.

Uses, Hardware Requirements and Advantages of WANs

A network includes both hardware and software components. The figure illustrates how a network is often graphically represented. Unless otherwise specified, figures used in this lesson do not necessarily represent a network's physical configuration.


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Network hardware includes: Network Adapter

Communication Media (network cable)

Network Communication Devices (bridges, routers, etc.)

A communication protocol can be thought of as the language that a computer uses when passing data across the network.

\For two computers to be able to communicate, they must have at least one communication protocol in common. The communication protocols you are most likely to see used on a PC network are:

NetBIOS Extended User Interface (NetBEUI)

Internet Packet Exchange/Sequenced Packet Exchange (IPX/SPX, implemented by Microsoft as NWLink)

Transmission Control Protocol/Internet Protocol (TCP/IP) For example, you could have NetBEUI and NWLink installed on one system and NWLink and TCP/IP installed on a second system. The two systems would be able communicate because they have NWLink in common. Here is an example of what you would need to build a WAN:

Now, in terms of communication, I would like us to focus mostly on Frame Relay. Devices attached to a Frame Relay WANs fall into the following two general categories:

Data terminal equipment (DTE)

Data circuit-terminating equipment (DCE) DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer. In fact, they may be owned by the customer. Examples of DTE devices are terminals, personal computers, routers, and bridges. DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to provide clocking and switching services in a network, which are the devices that actually transmit data through the WAN. In most cases, these are packet switches. The Figure below shows the relationship between the two categories of devices.


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DCEs Generally Reside Within Carrier-Operated WANs

The connection between a DTE device and a DCE device consists of both a physical layer component and a link layer component. The physical component defines the mechanical, electrical, functional, and procedural specifications for the connection between the devices. One of the most commonly used physical layer interface specifications is the recommended standard (RS)-232 specifications. The link layer component defines the protocol that establishes the connection between the DTE device, such as a router, and the DCE device, such as a switch. Advantages

One of the advantages of WANs is VoIP (Voice over IP) Internet Voice, also known as Voice over Internet Protocol (VoIP), is a technology that allows you to make telephone calls using a broadband Internet connection instead of a regular (or analogue) phone line. Some services using VoIP may only allow you to call other people using the same service, but others may allow you to call anyone who has a telephone number - including local, long distance, mobile, and international numbers. Also, while some services only work over your computer or a special VoIP phone, other services allow you to use a traditional phone through an adaptor. VoIP allows you to make telephone calls using a computer network, over a data network like the Internet. VoIP converts the voice signal from your telephone into a digital signal that travels over the internet then converts it back at the other end so you can speak to anyone with a regular phone number. When placing a VoIP call using a phone with an adapter, you'll hear a dial tone and dial just as you always have. VoIP may also allow you to make a call directly from a computer using a conventional telephone or a microphone. VoIP lets you make toll-free long distance voice and fax calls over existing IP data networks instead of the public switched telephone network (PSTN). Today businesses that implement their own VoIP solution can dramatically cut long distance costs between two or more locations. Let’s go back to see the history: For the past 100 years’ people have relied on the PSTN (Public Switched Telephone Network) for voice communication. During a call between two locations, the line is dedicated to the two parties that are using it. No other information can travel over the line, although there is often plenty of bandwidth available. Later, as data communications emerged, companies paid for separate data lines so their computers could share information, while voice and fax communications were still handled by the PSTN. But this is no longer a problem now as today, with the rapid adoption of IP, we now have a far reaching, low-cost transport mechanism that can support both voice and data. A VoIP solution integrates seamlessly into the data network and operates alongside existing PBXs, or other phone equipment, to simply extend voice capabilities to remote locations. The voice traffic essentially “rides for free” on top of the data network using the IP infrastructure and hardware already in place.