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Data Communications - IM3 Network Components

When signals from a NIC must travel a long distance over coaxial cable...

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Electronics Engineering (CR 061)

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LESSON CONTENT

Network Interface Controller (NIC)

A network interface controller (NIC) provides the I/O interface between each node on a network and the network wiring. In older PCs, these were printed circuit cards that are plugged into the PC bus. Today the NIC is one or more ICs that are integrated into the motherboard of the PC and provide connectors at the rear of the computer for attaching the cable connectors. NICs perform a variety of tasks. For example, when the PC wishes to transmit information over the network, it takes data stored in RAM to be transmitted and converts it to a serial data format. This serial information is usually stored within RAM on the NIC. Logic circuitry in the NIC then groups the information into frames or packets, the format of which is defined by the communication protocol used by the LAN. Once the packet or frame has been formed, the binary data is encoded, normally by using the Manchester code, and then sent to a logic-level converter, which generates the proper binary 0 and binary 1 voltage levels that are sent over the coaxial or twisted-pair cables

Upon reception, the destination NIC recognizes when it is being addressed, i., when data is being sent to it. The NIC performs logic-level conversion and decoding, recovering the serial frame or packet of information; performs housekeeping functions such as error detection and correction; and places the recovered data in a buffer storage memory. The data is then converted from serial to parallel, where it is transferred to the computer RAM and used by the software.

Repeaters

When signals from a NIC must travel a long distance over coaxial cables or twisted-pair cables, the binary signal is greatly attenuated by the resistance of the wires and distorted by the capacitance of the cable. In addition, the cable can pick up noise along the way. As a result, the signal can be too distorted and noisy to be received reliably.

A common solution to this problem is to use one or more repeaters along the way (see Figure 1). A repeater is an electronic circuit that takes a partially degraded signal, boosts its level, shapes it up, and sends it on its way. Over long transmission distances, several repeaters may be required.

Repeaters are small, inexpensive devices that can be inserted into a line with appropriate connectors or built into other LAN equipment. Most repeaters are really transceivers—bidirectional circuits that can both send and receive data. Transceiver repeaters can receive signals from either direction and transmit them in the opposite direction

Figure 1. Concept of a Repeater

Hubs

A hub is a LAN accessory that facilitates the interconnections of the cables to the nodes. Whether the network topology used by a LAN is bus, ring, or star, the wiring usually resembles a star. This is so because the cabling for most networks today is permanently installed in walls, ceilings, and

plenums. Bus and ring topologies, where cables logically run between individual PCs, are not convenient for plenum wiring, as they do not provide an easy way to modify the network to add or remove nodes in different parts of the office or building.

The device that facilitates such wiring is the hub, a central connecting box designed to receive the cable inputs from the various PC nodes and to connect them to the server (see Figure 2). In most cases, hub wiring physically resembles a star because all the cabling comes into a central point, or hub. However, the hub wiring is such that it can logically implement either the bus or the ring configuration. That is, inside the hub the wiring connects the nodes into a miniature ring or bus.

Hubs are usually active devices containing repeaters. Hubs amplify and reshape the signal and transmit it to all connection parts. Hubs are available with 8, 12, 16, 24, 32, and 48 ports. All signals received at the hub are repeated to all nodes connected to the hub.

Figure 2. A hub facilitates interconnections to the server

Bridges

A bridge is a network device that is connected as a node on the network and performs bidirectional communication between two LANs (see Figure 3).

A bridge can also be used when one LAN becomes too big. Most LANs are designed for a maximum upper limit of nodes. The reason for this is that the greater the number of nodes, the longer and more complex the wiring. Furthermore, when many individuals attempt to use a LAN simultaneously, performance deteriorates greatly, leading to network delays. One way to deal with this problem is to break a large LAN into two or more smaller LANs. First it is determined which nodes communicate with other nodes the most, and then a logical breakdown into individual LANs is made. Communication between all users is maintained by interconnecting the separate LANs with bridges. The result is improved overall performance.

A bridge is generally designed to interconnect two LANs with the same protocol, e., two Ethernet networks. However, there are bridges that are able to accomplish protocol conversion so that two LANs with different protocols can converse.

Remote bridges are special bridges used to connect two LANs that are separated by a long distance. A bridge can use the telephone network to connect LANs in two different parts of the country, or can connect two LANs on a large campus or the grounds of a big military base through a fiber-optic cable or wireless connection.

Figure 4. An Ethernet switch speeds up the network and provides security

The switch identifies each PC by its media access control (MAC) address. The MAC address is a 48bit number unique to each PC. The MAC address is made up of 6 bytes or octets identified by its hexadecimal code in the following format:

00:A0:C9:14:D3:

The first 3 bytes identify the manufacturer of the NIC or PC, such as Intel, Dell, or Cisco; the last 3 bytes are special to the PC or other device. The MAC address is hardwired into each NIC or PC when it is built and is used as the source or destination address in the Ethernet protocol frame. Ethernet switches use the MAC address to route the data from the source to the desired destination. The switch actually “learns” the addresses as the network is used and creates a MAC address lookup table in its memory. It also learns which ports each PC is connected to. The lookup table is updated each time a message is sent or received.

Routers

Like bridges, routers are designed to connect two networks. The main difference between bridges and routers is that routers are intelligent devices that have decision-making and switching capabilities.

The basic function of a router is to expedite traffic flow on both networks and maintain maximum performance. When many users access a network at the same time, conflicts occur and speed performance is degraded. Routers are designed to recognize traffic buildup and provide automatic switching to reroute transmissions in a different direction, if possible. If transmission is blocked in one direction, the router can switch transmission through other nodes or other paths in the network.

Some routers are a combination of a bridge and a router. There are many different types of routers for the wide variety of networks in use. They can switch, perform protocol conversion, and serve as communication managers between two LANs or between a LAN and the Internet.

Gateways

A gateway is another internetwork device that acts as an interface between two LANs or between a LAN and a larger computer system. The primary benefit of a gateway is that it can connect networks with incompatible protocols and configurations. The gateway acts as a two-way translator that allows systems of different types to communicate.

Figure 5 shows a typical gateway system, one designed to interconnect one or more PC-based LANs to a mainframe. There are many different types of gateways available depending upon the equipment and protocols involved. Most gateways are computers and are sometimes referred to as gateway servers.

As the number of companies that provide hardware increases, the functions of each device vary and devices labeled as routers may perform the functions of the switch, router, and gateway.

Figure 5. A gateway commonly connects a LAN to a larger host computer

Modems

Modems are interfaces between PCs and communications systems, such as the telephone or cable TV networks. They convert the binary signals of the computer to analog signals compatible with the telephone or cable TV system and, at the other end, convert the analog signals back to digital signals.

Modems are widely used in home networking to connect to an Internet service provider (ISP), which provides services such as Internet access and e-mail.

CSUs/DSUs

A Channel Service Unit/Data Service Unit (CSU/DSU) acts as a translator between the LAN data format and the WAN data format. Such a conversion is necessary because the technologies used on WAN links are different from those used on LANs. Some consider a CSU/DSU as a type of digital modem; but unlike a normal modem, which changes the signal from digital to analog, a CSU/DSU changes the signal from one digital format to another. Figure 6 shows how a CSU/DSU might fit into a network.

Figure 8. An internal network adapter

Installing an external ISDN adapter is simple because, like an external modem, an external ISDN adapter plugs in to the serial port of the system and thus uses its resources. You need drivers for an ISDN terminal adapter, so be sure to visit the manufacturer’s website and download the latest available drivers. An internal ISDN terminal adapter requires a little more effort: You must make sure that you have physical and logical system resources to accommodate it.

Wireless Access Point (WAP)

Wireless access points, referred to as either WAPs or wireless APs, are a transmitter and receiver (transceiver) device used for wireless LAN (WLAN) radio signals. A WAP is typically a separate network device with a built-in antenna, transmitter, and adapter. WAPs use the wireless infrastructure network mode to provide a connection point between WLANs and a wired Ethernet LAN. WAPs also typically have several ports allowing a way to expand the network to support additional clients.

Depending on the size of the network, one or more WAPs may be required. Additional WAPs are used to allow access to more wireless clients and to expand the range of the wireless network. Each WAP is limited by a transmissions range, the distance a client can be from a WAP and still get a useable signal. The actual distance depends on the wireless standard being used and the obstructions and environmental conditions between the client and the WAP. Figure 9 shows an example of a WAP in a network configuration.

Figure 9. WAPs connect WLANs and a wired Ethernet LAN

As mentioned, a WAP is used in an infrastructure wireless network design. Used in the infrastructure mode, the WAP receives transmissions from wireless devices within a specific range and transmits

those signals to the network beyond. This network may be a private Ethernet network or the Internet. The transmission range a WAP can support and number of wireless devices that can connect to it depends on the wireless standard being used and the signal interference between the two devices. In infrastructure wireless networking, there may be multiple access points to cover a large area or only a single access point for a small area such as a single home or small building. Figure 10 shows an example of an infrastructure wireless network using a WAP.

Figure 10. An infrastructure wireless network uses a WAP

Transceivers

The term transceiver does not necessarily describe a separate network device but rather an integrated technology embedded in devices such as network cards. In a network environment, a transceiver gets its name from being both a transmitter and a receiver of signals, such as analog or digital. Technically, on a LAN the transceiver is responsible to place signals onto the network media and also detecting incoming signals traveling through the same cable. Given the description of the function of a transceiver, it makes sense that that technology would be found with network cards.

Although transceivers are found in network cards, they can be external devices as well. As far as networking is concerned, transceivers can ship as a module or chip type. Chip transceivers are small and are inserted into a system board or wired directly on a circuit board. Module transceivers are external to the network and are installed and function similarly to other computer peripherals, or they may function as standalone devices.

There are many types of transceivers: RF transceivers, fiber-optic transceivers, Ethernet transceivers, wireless (WAP) transceivers, and more. Though each of these media types is different, the function of the transceiver remains the same. Each type of the transceiver used has different characteristics such as the number of ports available to connect to the network and whether fullduplex communication is supported.

Firewalls

Today, firewalls are an essential part of a network’s design. A firewall is a networking device, either hardware or software based, that controls access to your organization’s network. This controlled access is designed to protect data and resources from outside threat. To do this, firewalls are

allow or permit certain types of network traffic. In small offices and for regular home use, a firewall is commonly installed on the local system and configured to control traffic. Many third-party firewalls are available.

Hardware firewalls are used in networks of all sizes today. Hardware firewalls are often dedicated network devices and can be implemented with very little configuration and protect all system behind it from outside sources. Hardware firewalls are readily available and often combined with other devices today. For example, many broadband routers and wireless access points have firewall functionality built in. In such a case, the router or WAP may have a number of ports available to plug systems into.

Data Communications Hardware

A data communications system is comprised of three basic elements: a transmitter (source), a transmission path (data channel), and a receiver (destination). For two-way communications, the transmission path would be bidirectional and the source and destination interchangeable. Therefore, it is usually more appropriate to describe a data communications system as connecting two endpoints (sometimes called nodes) through a common communications channel. The two endpoints may not possess the same computing capabilities; however, they must be configured with the same basic components. Both endpoints must be equipped with special devices that perform unique functions, make the physical connection to the data channel, and process the data before they are transmitted and after they have been received. Although the special devices are sometimes implemented as a single unit, it is generally easier to describe them as separate entities. In essence, all endpoints must have three fundamental components: data terminal equipment, data communications equipment, and a serial interface.

14 Data Terminal Equipment

Data terminal equipment (DTE) can be virtually any binary digital device that generates, transmits, receives, or interprets data messages. In essence, a DTE is where information originates or terminates. DTEs are the data communications equivalent to the person in a telephone conversation. DTEs contain the hardware and software necessary to establish and control communications between endpoints in a data communications system; however, DTEs seldom communicate directly with other DTEs. Examples of DTEs include video display terminals, printers, and personal computers.

Over the past 50 years, data terminal equipment has evolved from simple on-line printers to sophisticated high-level computers. Data terminal equipment includes the concept of terminals, clients, hosts, and servers. Terminals are devices used to input, output, and display information, such as keyboards, printers, and monitors. A client is basically a modern-day terminal with enhanced computing capabilities. Hosts are high-powered, high capacity mainframe computers that support terminals. Servers function as modern- day hosts except with lower storage capacity and less computing capability. Servers and hosts maintain local databases and programs and distribute information to clients and terminals.

14 Data Communications Equipment

Data communications equipment (DCE) is a general term used to describe equipment that interfaces data terminal equipment to a transmission channel, such as a digital T

carrier or an analog telephone circuit. The output of a DTE can be digital or analog, depending on the application. In essence, a DCE is a signal conversion device, as it converts signals from a DTE to a form more suitable to be transported over a transmission channel. A DCE also converts those signals back to their original form at the receive end of a circuit. DCEs are transparent devices responsible for transporting bits (1s and 0s) between DTEs through a data communications channel. The DCEs neither know nor do they care about the content of the data.

There are several types of DCEs, depending on the type of transmission channel used. Common DCEs are channel service units (CSUs), digital service units (DSUs), and data modems. CSUs and DSUs are used to interface DTEs to digital transmission channels. Data modems are used to interface DTEs to analog telephone networks. Because data communications channels are terminated at each end in a DCE, DCEs are sometimes called data circuit-terminating equipment (DCTE).

Data Communications Circuits

A data modem is a DCE used to interface a DTE to an analog telephone circuit commonly called a POTS. Figure 1 shows a simplified diagram for a two-point data communications circuit using a POTS link to interconnect the two endpoints (endpoint A and endpoint B). As shown in the figure, a twopoint data communications circuit is comprised of the seven basic components:

DTE at endpoint A
DCE at endpoint A
DTE/DCE interface at endpoint A
Transmission path between endpoint A and endpoint B
DCE at endpoint B
DTE at endpoint B
DTE/DCE interface at endpoint B

Figure 12. Multipoint data communications circuit using POTS links

Line Control Unit

As previously stated, a line control unit (LCU) is a DTE, and DTEs have several important functions. At the primary station, the LCU is often called a FEP because it processes information and serves as an interface between the host computer and all the data communications circuits it serves. Each circuit served is connected to a different port on the FEP. The FEP directs the flow of input and output data between data communications circuits and their respective application programs. The data interface between the mainframe computer and the FEP transfers data in parallel at relatively high bit rates. However, data transfers between the modem and the FEP are accomplished in serial and at a much lower bit rate. The FEP at the primary station and the LCU at the secondary stations perform parallelto-serial and serial-to-parallel conversions. They also house the circuitry that performs error detection and correction. In addition, data-link control characters are inserted and deleted in the FEP and LCUs.

Within the FEP and LCUs, a single special-purpose integrated circuit performs many of the fundamental data communications functions. This integrated circuit is called a universal asynchronous receiver/transmitter (UART) if it is designed for asynchronous data transmission, a universal synchronous receiver/transmitter (USRT) if it is designed for synchronous data transmission, and a universal synchronous/asynchronous receiver/transmitter (USART) if it is designed for either asynchronous or synchronous data transmission. All three types of circuits specify general-purpose integrated-circuit chips located in an LCU or FEP that allow DTEs to interface with DCEs. In modern-day integrated circuits, UARTs and USRTs are often combined into a single USART chip that is probably more popular today simply because it can be adapted to either

asynchronous or synchronous data transmission. USARTs are available in 24- to 64-pin dual in-line packages (DIPs).

UARTS, USRTS, and USARTS are devices that operate external to the central processor unit (CPU) in a DTE that allow the DTE to communicate serially with other data communications equipment, such as DCEs. They are also essential data communications components in terminals, workstations, PCs, and many other types of serial data communications devices. In most modern computers, USARTs are normally included on the motherboard and connected directly to the serial port. UARTs, USRTs, and USARTs designed to interface to specific microprocessors often have unique manufacturerspecific names. For example, Motorola manufactures a special purpose UART chip it calls an asynchronous communications interface adapter (ACIA).

16 UART

A UART is used for asynchronous transmission of serial data between a DTE and a DCE. Asynchronous data transmission means that an asynchronous data format is used, and there is no clocking information transferred between the DTE and the DCE. The primary functions performed by a UART are the following:

Parallel-to-serial data conversion in the transmitter and serial-to-parallel data conversion in the receiver
Error detection by inserting parity bits in the transmitter and checking parity bits in the receiver
Insert start and stop bits in the transmitter and detect and remove start and stop bits in the receiver
Formatting data in the transmitter and receiver (i., combining items 1 through 3 in a meaningful sequence)
Provide transmit and receive status information to the CPU
Voltage level conversion between the DTE and the serial interface and vice versa
1. Provide a means of achieving bit and character synchronization

Transmit and receive functions can be performed by a UART simultaneously because the transmitter and receiver have separate control signals and clock signals and share a bidirectional data bus, which allows them to operate virtually independently of one another. In addition, input and output data are double buffered, which allows for continuous data transmission and reception.

Figure 13 shows a simplified block diagram of a line control unit showing the relationship between the UART and the CPU that controls the operation of the UART. The CPU coordinates data transfer between the line-control unit (or FEP) and the modem. The CPU is responsible for programming the UART’s control register, reading the UART’s status register, transferring parallel data to and from the UART transmit and receive buffer registers, providing clocking information to the UART, and facilitating the transfer of serial data between the UART and the modem.

A specific range of voltages for transmit and receive signal levels
Limitations for the electrical parameters of the transmission line, including source and load impedance, cable capacitance, and other electrical characteristics.
Standard cable and cable connectors
Functional description of each signal on the interface

In 1962, the Electronics Industries Association (EIA), in an effort to standardize interface equipment between data terminal equipment and data communications equipment, agreed on a set of standards called the RS232 specifications (RS meaning “recommended standard”). The official name of the RS- 232 interface is Interface Between Data Terminal Equipment and Data Communications Equipment Employing Serial Binary Data Interchange. In 1969, the third revision, RS-232C, was published and remained the industrial standard until 1987, when the RS-232D was introduced, which was followed by the RS232E in the early 1990s. The RS-232D standard is sometimes referred to as the EIA- standard. Versions D and E of the RS-232 standard changed some of the pin designations. For example, data set ready was changed to DCE ready, and data terminal ready was changed to DTE ready.

The RS-232 specifications identify the mechanical, electrical, functional, and procedural descriptions for the interface between DTEs and DCEs. The RS-232 interface is similar to the combined ITU-T standards V (electrical specifications) and V (functional description) and is designed for serial transmission up to 20 kbps over a maximum distance of 50 feet (approximately 15 meters).

17 RS-232 Serial Interface Standard

The mechanical specification for the RS-232 interface specifies a cable with two connectors. The standard RS-232 cable is a sheath containing 25 wires with a DB25Pcompatible male connector (plug) on one end and a DB25S-compatible female connector (receptacle) on the other end. The DB25Pcompatible and DB25S-compatible connectors are shown in Figures 14a and 14b, respectively. The cable must have a plug on one end that connects to the DTE and a receptacle on the other end that connects to the DCE. There is also a special PC nine-pin version of the RS-232 interface cable with a DB9Pcompatible male connector on one end and a DB9S- compatible connector at the other end. The DB9Pcompatible and DB9S-compatible connectors are shown in Figures 4c and d, respectively (note that there is no correlation between the pin assignments for the two connectors). The nine-pin version of the RS-232 interface is designed for transporting asynchronous data between a DTE and a DCE or between two DTEs, whereas the 25- pin version is designed for transporting either synchronous or asynchronous data between a DTE and a DCE.

Figure 14. RS-232 serial interface connector: (a) DB25P; (b) DB25S; (c) DB9P; (d) DB9S

Figure 15 shows the eight-pin EIA-561 modular connector, which is used for transporting asynchronous data between a DTE and a DCE when the DCE is connected directly to a standard two-wire telephone line attached to the public switched telephone network. The EIA561 modular connector is designed exclusively for dial-up telephone connections.

Figure 15. EIA-561 modular connector

Although the RS-232 interface is simply a cable and two connectors, the standard also specifies limitations on the voltage levels that the DTE and DCE can output onto or receive from the cable. The DTE and DCE must provide circuits that convert their internal logic levels to RS-232-compatible values. For example, a DTE using TTL logic interfaced to a DCE using CMOS logic is not compatible. Voltageleveling circuits convert the internal voltage levels from the DTE and DCE to RS-232 values. If both the DCE and the DTE output and accept RS-232 levels, they are electrically compatible regardless of which logic family they use internally. A voltage leveler is called a driver if it outputs signals onto the cable and a terminator if it accepts signals from the cable. In essence, a driver is a transmitter, and a terminator is a receiver. Table 1 lists the voltage limits for RS-232-compatible drivers and terminators. Note that the data and control lines use non–return to zero, level (NRZ-L) bipolar encoding. However, the data lines use negative logic, while the control lines use positive logic.

Table 1. RS-232 Voltage Specifications

From examining Table 1, it can be seen that the voltage limits for a driver are more inclusive than the voltage limits for a terminator. The output voltage range for a driver is between +5 V and +15 V or between -5 V and -15 V, depending on the logic level. However, the voltage range in which a terminator will accept is between +3 V and +25 V or between -3 V and - V. Voltages between ±3 V are undefined and may be interpreted by a terminator as a high or a low.

Figure 16. RS-232 logic levels and noise margin: (a) driver and terminator voltage ranges; (b) noise margin with a +10 V high and -10 V low; (c) noise violation

17.1 RS-232 electrical equivalent circuit. Figure 17 shows the equivalent electrical circuit for the RS- 232 interface, including the driver and terminator. With these electrical specifications and for a bit rate of 20 kbps, the nominal maximum length of the RS232 interface cable is approximately 50 feet.

Figure 17. RS-232 Electrical specifications

17.1 RS-232 functional description. The pins on the RS-232 interface cable are functionally categorized as either ground (signal and chassis), data (transmit and receive), control (handshaking and diagnostic), or timing (clocking signals). Although the RS-232 interface as a unit is bidirectional (signals propagate in both directions), each individual wire or pin is unidirectional. That is, signals on any given wire are propagated either from the DTE to the DCE or from the DCE to the DTE but never in both directions. Table 2 lists the 25 pins (wires) of the RS-232 interface and gives the direction of signal propagation (i., either from the DTE toward the DCE or from the DCE toward the DTE). The RS-232 specification designates the first letter of each pin with the letters A, B, C, D, or S. The letter categorizes the signal into one of five groups, each representing a different type of circuit. The five groups are as follows:

A—ground B—data C—control D—timing (clocking) S—secondary channel

Because the letters are non-descriptive designations, it is more practical and useful to use acronyms to designate the pins that reflect the functions of the pins. Table 3 lists the EIA signal designations plus the nomenclature more commonly used by industry in the United States to designate the pins.

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Data Communications - IM3 Network Components

Course: Electronics Engineering (CR 061)

95 Documents

Students shared 95 documents in this course

University: Samar State University

Was this document helpful?

LESSON CONTENT

1. Network Interface Controller (NIC)

A network interface controller (NIC) provides the I/O interface between each node on a network and

the network wiring. In older PCs, these were printed circuit cards that are plugged into the PC bus.

Today the NIC is one or more ICs that are integrated into the motherboard of the PC and provide

connectors at the rear of the computer for attaching the cable connectors. NICs perform a variety of

tasks. For example, when the PC wishes to transmit information over the network, it takes data

stored in RAM to be transmitted and converts it to a serial data format. This serial information is

usually stored within RAM on the NIC. Logic circuitry in the NIC then groups the information into

frames or packets, the format of which is defined by the communication protocol used by the LAN.

Once the packet or frame has been formed, the binary data is encoded, normally by using the

Manchester code, and then sent to a logic-level converter, which generates the proper binary 0 and

binary 1 voltage levels that are sent over the coaxial or twisted-pair cables

Upon reception, the destination NIC recognizes when it is being addressed, i.e., when data is being

sent to it. The NIC performs logic-level conversion and decoding, recovering the serial frame or

packet of information; performs housekeeping functions such as error detection and correction; and

places the recovered data in a buffer storage memory. The data is then converted from serial to

parallel, where it is transferred to the computer RAM and used by the software.

2. Repeaters

When signals from a NIC must travel a long distance over coaxial cables or twisted-pair cables, the

binary signal is greatly attenuated by the resistance of the wires and distorted by the capacitance of

the cable. In addition, the cable can pick up noise along the way. As a result, the signal can be too

distorted and noisy to be received reliably.

A common solution to this problem is to use one or more repeaters along the way (see Figure 1). A

repeater is an electronic circuit that takes a partially degraded signal, boosts its level, shapes it up,

and sends it on its way. Over long transmission distances, several repeaters may be required.

Repeaters are small, inexpensive devices that can be inserted into a line with appropriate

connectors or built into other LAN equipment. Most repeaters are really transceivers—bidirectional

circuits that can both send and receive data. Transceiver repeaters can receive signals from either

direction and transmit them in the opposite direction

Figure 1. Concept of a Repeater

3. Hubs

A hub is a LAN accessory that facilitates the interconnections of the cables to the nodes. Whether

the network topology used by a LAN is bus, ring, or star, the wiring usually resembles a star. This is

so because the cabling for most networks today is permanently installed in walls, ceilings, and

Data Communications - IM3 Network Components

Electronics Engineering (CR 061)

Samar State University

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LESSON CONTENT

00:A0:C9:14:D3:

16 UART

Data Communications - IM3 Network Components

Course: Electronics Engineering (CR 061)

University: Samar State University

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