Table of Contents Link to heading

• OSI Physical Layer
• Frame Delivery Process
• Data-Carrying Capacity
  • Theoretically as Bandwidth
  • Practically as Throughput
  • Qualitatively as Goodput
  • Example
• LAN Network Components
  • Network Interface Controllers/Cards (NICs)
    • Types of NICs
  • Wireless Access Points (APs)
  • Physical/Network/Transmission Media
    • Unshielded Twisted-Pair (UTP) Cables
      • Twisting of Pairs Explanation
      • Categories of UTP Cables
      • Types of UTP Cables
      • Types of UTP Interfaces
    • Shielded Twisted-Pair (STP) Cables
    • Coaxial (Coax) Cables
    • Copper Media Safety
  • Fibre Media
    • Types of Fibre-Optic Cables
    • Fibre-Optic Connectors
    • Use Cases
  • Wiring/Physical Media Comparison
  • Wireless Media
    • Areas of Concern
    • IEEE Wireless Media Standards
    • Wireless LANs (WLANs)
    • Performance Level
    • Wi-Fi Range Extender/Expander
  • Network Media Comparison
• Device Interfaces
• LAN Physical Areas

OSI Physical Layer Link to heading

The data-link frame that comes down to the physical layer contains a string of bits representing application, presentation, session, transport, and network information.

The delivery of frames across the local media requires the following physical layer elements:

1. The physical media and associated connectors
2. A representation of bits on the media
3. Encoding of data and control information
4. Transmitter and receiver circuitry on the network devices

Frame Delivery Process Link to heading

1. The source node’s transport layer segments the user data, which is then placed into packets by the network layer and further encapsulated into frames by the data link layer.
2. The physical layer encodes the frames and creates the electrical, optical, or radio wave signals that represent the bits in each frame.
3. These signals are then sent on the media one at a time.
4. The destination node’s physical layer retrieves these individual signals from the media, restores them to their bit representations, and passes the bits up to the data link layer as a complete frame.

Data-Carrying Capacity Link to heading

Each type of medium carries data at a different speed. There are three different ways to analyse the transfer speed of data (bits per second - bps) on a medium.

Theoretically as Bandwidth Link to heading

The bandwidth measurement takes into account the physical properties of the medium and the signalling method applied to it.

Practically as Throughput Link to heading

In a multiaccess network, such as Ethernet, nodes are competing for media access. Therefore, the throughput of each node is degraded as the media usage increases.

Many factors influence throughput, including:

1. The amount of traffic
2. The type of traffic
3. The number of network devices encountered on the network being measured

Qualitatively as Goodput Link to heading

Example Link to heading

Consider two hosts on a LAN transferring a file. The bandwidth of the LAN is 100 Mbps. Due to sharing and media overhead, the throughput between the computers is only 60 Mbps. With the overhead of the encapsulation process of the TCP/IP stack, the goodput received by the destination computer is only 40 Mbps.

LAN Network Components Link to heading

To connect a end-user device to a LAN, several network components (both hardware and software components) are required.

Network Interface Controllers/Cards (NICs) Link to heading

Every NIC or device having a NIC has a unique identifier called a MAC address, which is used by the network to direct data to the correct device.

Types of NICs Link to heading

1. Ethernet/Wired NIC - offers a physical interface port.
   • Provides connectivity to a wired network (e.g., Token Ring or Ethernet).
   • Also known as a network interface card, network adapter, LAN adapter, or physical network interface.
2. Wireless NIC (WNIC) - is built into the motherboard and uses an antenna to provide a radio transceiver that enables the device to receive and transmit radio signals.
   • Provides wireless communication capability to a wireless network (e.g., Wi-Fi, Bluetooth, cellar).
   • May be implemented as an expansion card and connected using PCI [Express] bus or connected via USB, PC Card, ExpressCard, Mini PCIe, or M.2.
3. USB NIC - uses a USB port to connect to a network.
   • Provides connectivity to a device that does not have an Ethernet port or a wireless adapter.
   • Usually plug-and-play and can support speeds up to 1 Gbit/s.
4. Fibre optic NIC - uses a fibre optic cable to connect to a network.
   • More expensive and require special equipment, but offers higher bandwidth and lower latency than Ethernet NICs.
   • Supports speeds up to 100 Gbit/s2.

An end-user device may include one or many types of NICs. For example:

• An old printer only has an Ethernet NIC and therefore must connect to the network using an Ethernet cable.
• Many embedded devices, such as an MP3 player, only feature a WNIC and therefore must use a wireless connection.
• Most modern PCs come with a NIC and a built-in WNIC, providing both wired and wireless connection.

Wireless Access Points (APs) Link to heading

Wireless networks require cabling, at some point, to connect devices such as access points to the wired LAN.

Physical/Network/Transmission Media Link to heading

The design of the physical layer differs from that of upper layers in that it deals with the physical and electrical properties of the media rather than the logical processes.

Unshielded Twisted-Pair (UTP) Cables Link to heading

UTP consists of eight wires twisted into four colour-coded pairs and then wound inside a cable jacket.

UTP is mostly installed using a Registered Jack 45 (RJ-45) connector. The RJ-45 is an eight-wire connector used commonly to connect computers onto a LAN, especially Ethernet.

Twisting of Pairs Explanation Link to heading

A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk - the noise generated by adjacent pairs. When electrical current flows through a wire, it creates a small, circular magnetic field around the wire. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Thus, the two magnetic fields cancel each other out. They also cancel out any outside magnetic fields.

Twisting the wires can also enhance cancellation effect, which allows twisted-pair cables to limit signal degradation caused by electromagnetic interference (EMI) and radio frequency interference (RFI).

The higher the number of twists in the wire pairs, the further the crosstalk between the pairs in UTP cable can be reduced.

Categories of UTP Cables Link to heading

Types of UTP Cables Link to heading

Types of UTP Interfaces Link to heading

1. Medium-dependent interface (MDI) - uses the normal Ethernet pinout. Pins 1 and 2 are used for transmitting, and pins 3 and 6 are used for receiving.
   • Often found in end stations, such as computers, servers, or routers.
   • Uses a straight-through cable to connect devices of different types (MDI-MDIX).
2. MDI crossover (MDIX) - an MDI variant that uses pins 1 and 2 are used for receiving, and pins 3 and 6 are used for transmitting.
   • Often found in devices that provide LAN connectivity, usually hubs or switches.
   • Uses a crossover cable to connect the devices of the same type (MDI-MDI or MDIX-MDIX).

There are three ways to configure the UTP Ethernet port to be MDI or MDIX, depending on the features of the device:

1. On some devices, ports can have a mechanism that electrically swaps the transmit and receive pairs. The port can be changed from MDI to MDIX by engaging the mechanism.
2. As part of the configuration, some devices allow selecting whether a port functions as MDI or as MDIX.
3. Most devices now support the automatic crossover (auto-MDIX) feature. This feature allows the device to automatically detect what type of port is connected on the other end (MDI or MDIX) and swap the transmitting and receiving pins accordingly.
   • Therefore, either a crossover cable or a straight-through cable for connections to a copper 10/100/1000 port on a switch is usable.
   • The auto-MDIX feature is enabled by default on switches running Cisco IOS Release 12.2(18)SE or later.
   • However, the feature can be disabled; thus, it is important to use the correct cable type and should not rely on this feature.
   • Auto-MDIX can be [re]enabled using the mdix auto interface configuration command

Shielded Twisted-Pair (STP) Cables Link to heading

STP combines the techniques of shielding, cancellation, and wire twisting.

STP usually is installed with STP data connector, which is created especially for the STP cable. However, STP cabling also can use the same RJ connectors that UTP uses.

STP can still be useful in installations where electromagnetic interference (EMI) is an issue, but it is much more expensive than other available cable.

Coaxial (Coax) Cables Link to heading

Coax has a single, coated copper wire centre and an outer metal mesh that acts as both a grounding circuit and an electromagnetic shield to reduce interference. The outer layer is the plastic cable jacket.

The most common connectors used with Thinnet are BNC, short for British Naval Connector or Bayonet Neill Concelman, connectors.

Copper Media Safety Link to heading

1. The separation of data and electrical power cabling must comply with safety and codes.
2. Cables must be connected correctly.
3. Installations must be inspected for damage.
4. Equipment must be grounded correctly.

Fibre Media Link to heading

Whereas copper cable uses electrical voltage to represent data on the wire, fibre-optic uses light pulses conducted through special glass conductors to carry data. The cable is engineered to be as pure as possible and to allow reliable light signals to traverse the medium.

Advantages:

1. Offer the greatest bandwidth among other media
2. Run much farther than cable without needing a signal enhanced
3. Address safety issues
   • It does not carry voltage and current, so it is immune to the earth ground and lightning concerns.

Disadvantages:

1. Higher cost of fibre-optic cables and connectors
2. Great care is required when troubleshooting or installing the cable.
   • Light emitting diodes (LEDs) and lasers used in fibre-optic cables (to convert the data to light pulses) can be intense and can damage the human eye.
   • Incorrect termination of fibre-optic cables will result in diminished signalling distances or complete transmission failure.

When terminating fibre-optic cable, it is important to have the ends properly aligned, fused, and polished so that signalling remains strong and dispersion is at a minimum.

Types of Fibre-Optic Cables Link to heading

Fibre-Optic Connectors Link to heading

Fibre-Optic cable can carry light in only one direction, so fibre cables usually bundle up two optical fibre cables and terminate them with a pair of standard single fibre connectors. Since there is a dedicated medium for each direction (transmit and receive data), it allows for full-duplex communication.

Fibre-optic connectors come in a variety of types:

1. Straight Tip (ST) for multimode and Subscriber Connector (SC) for single-mode are two of the most common types in use.
2. Lucent Connector (LC) is gaining popularity and can adapt to both single-mode and multimode cables.

Use Cases Link to heading

Fibre-Optic cables are now being used in four types of industry:

Wiring/Physical Media Comparison Link to heading

Wireless Media Link to heading

Open areas are best for wireless connections.

Wireless frequencies range from 3 kilohertz (kHz) to 300 gigahertz (GHz). The data-transmission rates range from 9 kbps to as high as 54 Mbps.

Areas of Concern Link to heading

The wireless signal is susceptible to radio frequency interference (RFI) from small appliances, microwave ovens, fluorescent lighting, and household wireless devices (e.g., phones and Bluetooth devices).

A wireless connection is usually slower than a wired connection, and because the medium is open to anyone with a wireless receiver, it is more susceptible to security breaches than other media.

WLANs require half-duplex communication since they use a shared medium (the air) to transmit and receive data and that all stations must contend for use of that single channel to transmit frames. The more users accessing the WLAN simultaneously, the less bandwidth received for each user.

IEEE Wireless Media Standards Link to heading

The following data communications standards that have been defined to apply to wireless media.

Other wireless technologies, such as satellite communications, provide data network connectivity for locations without another means of connection. Protocols including GPRS enable data to be transferred between earth stations and satellite links.

Wireless LANs (WLANs) Link to heading

The IEEE have defined the following data communications standards that apply to WLANs:

Performance Level Link to heading

Although wireless is supporting huge increases in bandwidth, it has limitations in distance and power consumption.

Wireless device will experience degradation in performance based on its distance from an WAP. The further the device is from the WAP, the weaker the wireless signal it receives. This can mean less bandwidth or no wireless connection at all. Alternatively, a wired connection will not degrade in performance no matter how far the device is from the AP.

All wireless devices must share access to the airwaves connecting to the WAP. This means slower network performance may occur as more wireless devices access the network simultaneously. A wired device does not need to share its access to the network with other devices. Each wired device has a separate communications channel over its Ethernet cable.

Wi-Fi Range Extender/Expander Link to heading

It is situated in between a base router or WAP and a client that is not close enough to receive acceptable service or one that is on the other side of a barrier.

A WAP can also be used to extend the range of a wireless network. In this case, not only can the WAP receive or transmit traffic to other WAPs, but it can also be connected via a cable to the main network.

Network Media Comparison Link to heading

Each media type has its advantages and disadvantages. Consider the following factors when choosing a network media to suit your need:

Device Interfaces Link to heading

1. FastEthernet interface: A network interface that supports speeds up to 100 Mbps and uses an RJ-45 connector. It is used to connect routers to LANs or WANs.
2. Serial interface: A network interface that supports various speeds and protocols, such as Frame Relay, T1, T3, etc. It uses a V.35 or RS-232 connector and requires a clock rate on the DCE side.
3. Console interface: A local interface that allows direct access to the router’s configuration mode using a console cable and a terminal emulator program. It is used for initial setup, troubleshooting, and password recovery.
4. Auxiliary interface: A remote interface that allows dial-in access to the router using a modem and a phone line. It is used for backup, disaster recovery, or out-of-band management.

LAN Physical Areas Link to heading

1. Work area: The space where the end users and their devices are located. It includes the telecommunications outlet, which is the connection point for the horizontal cabling, and the work area equipment, such as computers, phones, printers, etc.
2. Telecommunications room: The space where the horizontal cabling from the work areas terminates at the patch panels, which are used to connect the devices to the network. It also contains the telecommunications equipment, such as switches, routers, servers, etc.
3. Horizontal cabling: The cabling that runs from the telecommunications room to the work area, following a star topology. It consists of four pairs of twisted-pair copper wires, which can support data rates up to 10 Gbps over distances up to 100 metres.
4. Backbone/Vertical cabling: The cabling that connects the telecommunications rooms to each other and to the equipment room, which is the central point of the network. It can use either copper or fiber-optic cables, depending on the distance and bandwidth requirements.
   • Backbone cabling is also used to interconnect LANs between buildings and is sometimes routed outside the building to the WAN connection or ISP.