Chapter 4 Network Acess

Synchronous:

Data signals are sent along with a clock signal which occurs at evenly spaced time durations referred to as the bit time.

Controlled access:

: Each node has its own time to use the medium

Amplitude modulation (AM):

A transmission technique in which the amplitude of the carrier varies in accordance with the signal.

Rollover

A Cisco proprietary cable used to connect to a router or switch console port.

Data:

Contains the frame payload (i.e., packet header, segment header, and the data).

Control:

Identifies special flow control services.

Three common types of fiber-optic termination and splicing errors are

Misalignment: The fiber-optic media are not precisely aligned to one another when joined. End gap: The media does not completely touch at the splice or connection. End finish: The media ends are not well polished or dirt is present at the termination.

Wireless NIC adapters

Provides wireless communication capability to each network host.

Lucent Connector (LC)

Sometimes called a little or local connector, is quickly growing in popularity due to its smaller size. It is used with single-mode fiber and also supports multimode fiber.s

Standard IEEE 802.15:

Wireless Personal Area Network (WPAN) standard, commonly known as "Bluetooth", uses a device pairing process to communicate over distances from 1 to 100 meters.

Carrier sense multiple access with collision avoidance (CSMA/CA):

The end device examines the media for the presence of a data signal. If the media is free, the device sends a notification across the media of its intent to use it. Once it receives a clearance to transmit, the device then sends the data.

Non-Return to Zero (NRZ):

This is a common means of encoding data that has two states termed "zero" and "one" and no neutral or rest position. A 0 may be represented by one voltage level on the media and a 1 might be represented by a different voltage on the media.

Type

Used by the LLC to identify the Layer 3 protocol.

Frame start and stop indicator flags:

Used by the MAC sublayer to identify the beginning and end limits of the frame.

Addressing:

Used by the MAC sublayer to identify the source and destination nodes.

Long-Haul Networks

Service providers use long-haul terrestrial optical fiber networks to connect countries and cities. Networks typically range from a few dozen to a few thousand kilometers and use up to 10 Gb/s-based systems.

Manchester encoding:

A 0 is represented by a high to low voltage transition and a 1 is represented as a low to high voltage transition. This type of encoding is used in older versions of Ethernet, RFID and Near Field Communication.

Hub and Spoke

A WAN version of the star topology in which a central site interconnects branch sites using point-to-point links.

Frequency modulation (FM):

A method of transmission in which the carrier frequency varies in accordance with the signal.

Pulse-coded modulation (PCM):

A technique in which an analog signal, such as a voice, is converted into a digital signal by sampling the signal's amplitude and expressing the different amplitudes as a binary number.

Contention-based access:

All nodes compete for the use of the medium but have a plan if there are collisions.

IEEE 802.11ad

Also known as "WiGig". It uses a tri-band Wi-Fi solution using 2.4 GHz, 5 GHz, and 60 GHz and offers theoretical speeds of up to 7 Gb/s.

Straight-Tip (ST):

An older bayonet style connector widely used with multimode fiber.

Ethernet Crossover:

An uncommon cable used to interconnect similar devices together. For example to connect a switch to a switch, a host to a host, or a router to a router.

Half-duplex communication

Both devices can both transmit and receive on the media but cannot do so simultaneously. Ethernet has established arbitration rules for resolving conflicts arising from instances when more than one station attempts to transmit at the same time.

Full-duplex communication

Both devices can transmit and receive on the media at the same time. The data link layer assumes that the media is available for transmission for both nodes at any time.

Cable Internet installations

Cable service providers are currently converting their one-way systems to two-way systems to provide Internet connectivity to their customers. To provide these services, portions of the coaxial cable and supporting amplification elements are replaced with fiber-optic cable.

Wireless installations:

Coaxial cables attach antennas to wireless devices. The coaxial cable carries radio frequency (RF) energy between the antennas and the radio equipment.

Standard IEEE 802.16:

Commonly known as Worldwide Interoperability for Microwave Access (WiMAX), uses a point-to-multipoint topology to provide wireless broadband access.

Wireless Access Point (AP):

Concentrates the wireless signals from users and connects, usually through a copper cable, to the existing copper-based network infrastructure, such as Ethernet. Home and small business wireless routers integrate the functions of a router, switch, and access point into one device as shown in the figure.

Multimode fiber (MMF):

Consists of a larger core and uses LED emitters to send light pulses. Specifically, light from an LED enters the multimode fiber at different angles. Popular in LANs because they can be powered by low cost LEDs.

Single-mode fiber (SMF):

Consists of a very small core and uses expensive laser technology to send a single ray of light. Popular in long-distance situations spanning hundreds of kilometers such as required in long haul telephony and cable TV applications.

Core:

Consists of pure glass and is the part of the fiber where light is carried.

Crosstalk

Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire. In telephone circuits, crosstalk can result in hearing part of another voice conversation from an adjacent circuit.

Asynchronous:

Data signals are transmitted without an associated clock signal. The time spacing between data characters or blocks may be of arbitrary duration, meaning the spacing is not standardized. Therefore, frames require start and stop indicator flags.

Cancellation

Designers now pair wires in a circuit. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Therefore, the two magnetic fields cancel each other out and also cancel out any outside EMI and RFI signals.

Electromagnetic interference (EMI) or radio frequency interference (RFI)

EMI and RFI signals can distort and corrupt the data signals being carried by copper media. Potential sources of EMI and RFI include radio waves and electromagnetic devices such as fluorescent lights or electric motors as shown in the figure.

Encoding

Encoding or line encoding is a method of converting a stream of data bits into a predefined "code". Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the received. In the case of networking, encoding is a pattern of voltage or current used to represent bits; the 0s and 1s.

Subscriber Connector (SC):

Sometimes referred to as square connector or standard connector. It is a widely adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion. This connector type is used with multimode and single-mode fiber.

Enterprise Networks

Fiber is used for backbone cabling applications and interconnecting infrastructure devices.

FTTH and Access Networks:

Fiber-to-the-home (FTTH) is used to provide always-on broadband services to homes and small businesses. FTTH supports affordable high-speed Internet access, as well as telecommuting, telemedicine, and video on demand.

Submarine Networks

Special fiber cables are used to provide reliable high-speed, high-capacity solutions capable of or surviving in harsh undersea environments up to transoceanic distances.

Error Detection:

Included after the data to form the trailer, these frame fields are used for error detection

Start Frame field

Indicates the beginning of the frame.

Source and Destination Address fields

Indicates the source and destination nodes on the media.

Type field:

Indicates the upper layer service contained in the frame.

IEEE 802.11n

Operates in the 2.4 GHz and 5 GHz frequency bands. The typical expected data rates range from 150 Mb/s to 600 Mb/s with a distance range of up to 70 meters.

IEEE 802.11b

Operates in the 2.4 GHz frequency band and offers speeds of up to 11 Mb/s.

IEEE 802.11g

Operates in the 2.4 GHz frequency band and offers speeds of up to 54 Mbps. Devices implementing this standard therefore operate at the same radio frequency and range as 802.11b but with the bandwidth of 802.11a.

IEEE 802.11ac

Operates in the 5 GHz frequency band providing data rates ranging from 450 Mb/s to 1.3 Gb/s (1300 Mb/s.) It is backward compatible with 802.11a/n devices.

Physical topology:

Refers to the physical connections and identifies how end devices and infrastructure devices such as routers, switches, and wireless access points are interconnected.

Logical topology:

Refers to the way a network transfers frames from one node to the next. This arrangement consists of virtual connections between the nodes of a network. These logical signal paths are defined by data link layer protocols.

Carrier sense multiple access with collision detection (CSMA/CD):

The end device monitors the media for the presence of a data signal. If a data signal is absent and therefore the media is free, the device transmits the data. If signals are then detected that show another device was transmitting at the same time, all devices stop sending and try again later.

Cladding:

The glass that surrounds the core and acts as a mirror. The light pulses propagate down the core while the cladding reflects the light pulses. This keeps the light pulses contained in the fiber core in a phenomenon known as total internal reflection.

Ethernet Straight-through

The most common type of networking cable. It is commonly used to interconnect a host to a switch and a switch to a router.

Physical Components

The physical components are the electronic hardware devices, media, and other connectors that transmit and carry the signals to represent the bits. Hardware components such as network adapters (NICs), interfaces and connectors, cable materials, and cable designs are all specified in standards associated with the physical layer.

Signaling

The physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. The method of representing the bits is called the signaling method. The physical layer standards must define what type of signal represents a "1" and what type of signal represents a "0".

Point-to-Point:

This is the simplest topology which consists of a permanent link between two endpoints. For this reason, this is a very popular WAN topology.

Media Access Control (MAC):

This lower sublayer defines the media access processes performed by the hardware. It provides data link layer addressing and delimiting of data according to the physical signaling requirements of the medium and the type of data link layer protocol in use.

Mesh:

This topology provides high availability, but requires that every end system be interconnected to every other system. Therefore the administrative and physical costs can be significant. Each link is essentially a point-to-point link to the other node.

Logical Link Control (LLC)

This upper sublayer defines the software processes that provide services to the network layer protocols. It places information in the frame that identifies which network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6, to utilize the same network interface and media.

Varying the number of twists per wire pair:

To further enhance the cancellation effect of paired circuit wires designers vary the number of twists of each wire pair in a cable. UTP cable must follow precise specifications governing how many twists or braids are permitted per meter (3.28 feet) of cable. Notice in the figure that the orange/orange white pairs are twisted less than the blue/white blue pair. Each colored pair is twisted a different number of times

Jacket

Typically a PVC jacket that protects the core and cladding. It may also include strengthening materials and a buffer (coating) whose purpose is to protect the glass from scratches and moisture.

Standard IEEE 802.11:

Wireless LAN (WLAN) technology, commonly referred to as Wi-Fi, uses a contention or non-deterministic system with a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) media access process.

IEEE 802.11a:

perates in the 5 GHz frequency band and offers speeds of up to 54 Mb/s. Because this standard operates at higher frequencies, it has a smaller coverage area and is less effective at penetrating building structures.