Chapter 8- Physical Layer

Modified by Profs. Chen and Cappellino

Objectives In this chapter, you will learn to:

Explain the role of Physical layer protocols and services in supporting communication across data networks.

Describe the purpose of Physical layer signaling and encoding as they are used in networks.

Describe the role of signals used to represent bits as a frame is transported across the local media.

Identify the basic characteristics of copper, fiber, and wireless network media.

Describe common uses of copper, fiber, and wireless network media.

OSI Physical Layer - Purpose Accepts a complete frame from the Data Link

layer and _______________________ signals that are ______________________________

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

The physical _____________________________ A __________________________ on the media ____________________________________________________________________________

on the network devices Purpose of ___________________________

_________________________________________________________________ in each frame.

At the ___________________, the Physical layer _________________________ from the media, ______________________________, and pass the bits up to the Data Link layer as a complete frame.

Good summary of what we’ve seen so far…

Physical Layer - Operation The media ______________________, to

represent the bits that make up the frame. Three basic forms of network media:

______________ For copper cable media, the signals are patterns of ____________________

_________ For fiber, the signals are ____________. ________________ For wireless media, the signals

are patterns of _____________________________

End of one frame and beginning of the next is generally handled by what layer?

In many technologies, the Physical layer may add its own signals to indicate the beginning and end of the frame

Physical Layer - Standards The Physical layer consists of

hardware, in the form of _____ ___________________________

Standards set for by electrical and communications engineering organizations.

By comparison, the upper OSI layers are performed by software and are designed by software engineers.

The services and protocols in the TCP/IP suite are defined by the Internet Engineering Task Force (IETF) in RFCs.

Review of standard making body to the right…

Physical Layer standards define… Physical and electrical properties of the media Mechanical properties (materials, dimensions,

pinouts) of the connectors __________________ by the signals (encoding) Definition of control information signals And also hardware components such as ________

_____________________________________, etc

Three Physical Layer Fundamental Principles are…

The What are they?

Encoding is a _______________________________________

_____________________________________________Codes are groupings of bits recognized by both the sender and

receiver Codes used to indicate the data as well as control purposes such as

identifying the beginning and end of a frame.

What digits represent the signaling on the media?Depending on the type of media, how are those signals

represented?The Physical layer standards define what type of signal represents

a "1" and a "0". Example: A change in the level of an electrical signal or optical pulse or

a more complex signaling method.

Signaling Bits for the Media The transmission of the frame across the media occurs as

a stream of bits sent one at a time. Each signal placed onto the media has a ____________

_____________________________ called its _________Successful delivery of the bits requires some ____________________

between transmitter and receiver accomplished by the use of a clock

In LANs, each end of the transmission maintains its own clock.

Signals are processed by the receiving device and returned to its representation as bits.

The bits are then _____________________________ ______________ to determine a complete frame has been received.

The _________________________________________ to the Data Link layer.

Signaling Methods cont… Bits are represented on the medium by changing

one or more of the following characteristics of a signal:

AmplitudeFrequencyPhase

Signaling methods to represent bits on the media can be complex so we will focus on two basic types for example:

____________________________ where:A 0 may be represented by one voltage level on

the media during the bit time A 1 might be represented by a different voltage on

the media during the bit time. ___________________________ where:

A 0 is represented by a high to low voltage transition in the middle of the bit time.

A 1 is a low to high voltage transition in the middle of the bit time.

Next slide contains graphics

NRZ and Manchester Encoding graphics…

NRZ– suited for slow speed data links

Manchester Encoding – also best used at lower signaling speeds

Ethernet Encoding-- FYI

10BaseT uses Manchester encoding

100BaseT uses 4B/5B encoding

1000BaseT uses 8B/10B encoding.

Encoding – Grouping Bits __________________________________ being presented to the media.

_______________ before the signals are placed on the media ______________ ______________________________

Allows more ________________________________________ The Physical layer of a network device needs to be able to detect legitimate

data signals and _________________________________ that may also be on the physical medium.

Each frame with a pattern of signals representing bits that the Physical layer recognizes as denoting the _____________________________

Another pattern of bits will signal the ________________________________ Signal bits not framed in this manner are ignored by the Physical layer standard

being used.

Encoding – Code Groups Encoding techniques at the Physical layer

use _____________________________. A ___________________________________ ______________________ that are interpreted and mapped as data bit patterns.

Used to ________________________________ ______________________________

Used as an intermediary encoding technique for higher speed LAN technologies.

For example, code bits 10101 could represent the data bits 0011.

Although using code groups introduces overhead in the form of extra bits to transmit, they improve the robustness of a communications link.

Code Groups 4B/5B Example

In this technique, 4 bits of data are turned into 5-bit code symbols for transmission over the media system. These symbols represent the data to be

transmitted as well as a set of codes that help control transmission on the media.

Data Carrying Capacity

Different physical media support the transfer of bits at different speeds.

Data transfer can be measured in three ways as described on the following slides: BandwidthThroughputGoodput

More to come…

Data Carrying Capacity: ________ _______________________________________

______________________ of information that can flow from one place to another in a given amount of time.

Bandwidth is typically measured in kilobits per second (kbps) or megabits per second (Mbps).

Bandwidth is determined by a combination of factors: The __________________________________________

Some media just is not made to have a high bandwidth The ___________________________________ and detecting

network signals.The _________________________________

What is a nibble?

Data Carrying Capacity: _________ The __________________________________

across the media over a given period of time. Throughput __________________ to bandwidth

Why? the the the ___________________________________________ on the

network being measured.

Throughput _____________________________ of the path from source to destination.

It will only take one segment in the path with low throughput to create a bottleneck

Data Carrying Capacity: _________ A third measurement- goodput- has been

created to _____________________________ ___________________________________

measure that is of most interest to network users. ___________________________________________________

______________________________________________ Measured from Application layer of source to Application layer of

destinatin

As an example, consider two hosts on a LAN transferring a file.

The bandwidth of the LAN is 100 Mbps. Due to the 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 actual rate of the data received by the destination computer, goodput, is only 40Mbps.

Types of Physical Media The Physical layer is concerned with network

media and signaling. This layer produces the representation and groupings of bits as voltages, radio frequencies, or light pulses.

Standards for copper media, for example, are defined as follows:

Type of copper cabling used Bandwidth of the communicationType of connectors usedPinout and color codes of connections to the mediaMaximum distance of the media

See summary charts that follow…

Chart summaries

Copper Media ______________________ for data

communications _____________ consists of a ____________

__________________ that form circuits dedicated to specific signaling purposes.

_______________________ that runs through the center of the cable with insulation surrounding the copper core

Copper media can be used to connect nodes on a LAN to intermediate devices, such as routers and switches.

Also used to connect WAN devices to a data services provider such as a telephone company.

___________________________ is used widely in LANs with one type of media and in some WANs with another media type.

Copper Media: External Signal Interference Data is transmitted on copper cables as ______________.

These __________________________________________ from outside the communications system which can _____________ _______________________ being carried by copper media.

Potential sources of interference:

Minimize/limit signal degradation due to electronic noise… With __________________________________________ By selecting the _______________________________________

in a given networking environmentDesigning a cable infrastructure to ________________________

_____________________________________________Using cabling techniques that include the __________________

__________________________________________________

Copper Media: Unshielded Twisted Pair (___) cable __________________________ used

in Ethernet LANs Consists of _____________________

that have been twisted together and then encased in a flexible plastic sheath.

The ________________________ _________________________________

_______________________ is the ______________________________________________________________________________ in the cable.

Signal transmitted on one wire creates interference in another wire

The cancellation resulting from _________ the wires also ______________________

The different pairs of wires that are twisted in the cable use a different number of twists per meter to help protect the cable from crosstalk between pairs.

Unshielded Twisted Pair cont… The UTP cabling conforms to the standards established

jointly by the Telecommunications Industry Association (TIA) and the Electronics Industries Alliance (EIA).

________________A stipulates the commercial cabling standards for LAN installations such as:

________________________________________________________________________________________________

The electrical characteristics of copper cabling are defined by the Institute of Electrical and Electronics Engineers (______________).

Category 5 (Cat5) cable is used commonly in 100BASE-TX. Enhanced Category 5 (______) cable and Category 6 (_______).

Cables in As new gigabit speed Ethernet technologies are being developed

and adopted, Cat5e is now the minimally acceptable cable type

Unshielded Twisted Pair cont… Different situations require UTP

cables to be _____________ ________________________

The following are main cable types:

Ethernet Ethernet

Using a crossover or straight-through cable incorrectly between devices may not damage the devices, but connectivity and communication between the devices will not take place.

Should be the ______________ _____________________________________________________

• Crossover-

• Straight-through-

Copper Media: Shielded Twisted-Pair (___) STP uses four pairs of wires

___________________________________________

_______________________ ____________________ within the cable

Also ___________________ pairs.

STP __________________ __________ than UTP cabling

More expensive than UTP Not as popular as UTP

Copper Media: Coaxial (_________) Cable Consists of a _________________________

_________________________________ Over this insulating material is a ________

_______________________ the amount of outside electromagnetic ________________.

Coax used to be used in Ethernet installationsUTP replaced Coax in LAN installations

Coax is an important type of cable that is ______________________________________________________________

Coax cables are used to attach antennas to wireless devices.

Cable carries radio frequency (RF) energy between the antennas and the radio equipment.

Cable providers are currently converting their one-way systems to two-way systems using a combination of fiber and coax referred to as hybrid fiber coax (HFC).

Copper Media Safety Electrical Hazards

A potential problem with copper media is that the ___________________________________________________________________

Present undesirable voltage levels when used to connect devices that have power sources with different ground potentials.

Copper cabling _____________________ caused by lightning strikes to network devices.

Fire Hazards________________________________________ or produce toxic fumes when heated or burned.

__________________ is coated with a _________________ (usually Teflon) so that in case of a fire it does not give off toxic gasses and smoke as it burns.

Minimize hazards with __________________ ___________________________________ etc

Fiber Media _________________________________________

__________________ from source to destination. The bits are encoded on the fiber as _______________. Has very ___________ raw data bandwidth rates.

Advantages of Fiber Compared to Copper CablingFiber is ___________________________________ and will not conduct unwanted electrical currents.

Optical fibers are thin and have relatively low signal loss, they can be _________________________________ (many kilometers) than copper media.

Optical fiber is often ________________________ for high-traffic connections and for the interconnection of buildings

Fiber Media Disadvantages of Fiber Compared to Copper

CablingGenerally __________________ than copper media over the same distance (but for a higher capacity)

Different ___________________________ ____________________ the cable infrastructure

Harder to terminateMore careful handling than copper media

Fiber Media cont…

Cable Construction ____________________________ surrounding the glass or plastic

fiber is also _______________________________ from the fiber. Because light can only travel in one direction over optical fiber,

_____________________________________________________ Process of _____________________________

Either ______________________________ that are used to represent the transmitted data on the media.

Electronic semi-conductor devices _____________________ ___________________________ that can then be reconstructed into data frames.

Note: The laser light transmitted over fiber-optic cabling can damage the human eye

Avoid looking into the end of fiber

Fiber optic cables classified into two basic types: _______________________

Carries a _______________ of light Generally ___________________

Can transmit optical pulses for _____________________________

_______________________Typically uses ___________ emitters Light from an LED _________________

__________________________ and therefore takes different amounts of time to travel down the fiber

Travels _______________________________________________________ fiber

Wireless Media Wireless media carry ____________________

______________________________ that represent the binary digits of data communications.

Wireless data communication technologies work well in ______________________________

________________________ caused by:_____________________, certain _______________, microwave ovens, etc

Certain construction material, _____________ etc ____________________________________

network administration.Requires no access to a physical cable

Wireless Media- 4 common standards IEEE ___________ - Commonly referred to as Wi-Fi

WLAN technology using CSMA/CA media access process. IEEE ____________ - Known as “________________“

Wireless Personal Area Network (_______________) __________ able to communicate over distances from 1 to 100 meters.

IEEE __________________ - known as __________ (Worldwide Interoperability for Microwave Access)

Uses ______________________ to provide wireless broadband access.

Global System for Mobile Communications (_____) – uses General Packet Radio Service (GPRS) protocol to provide data transfer over ________________________________

Other wireless technologies such as satellite communications provide data network connectivity for locations without another means of connection.

The Wireless LAN A wireless LAN requires the

following network devices:_________________ (AP) - ______________________ and generally ____________ _______________________

______________ adapters - ___________________________________________ to each network host.

IEEE 802.11 in more detail… IEEE _________________ - Operates in the _____

frequency band and offers speeds of up to _________Has a smaller coverage area and is less effective at penetrating building

structures than 802.11b but has __________________________It is __________________________________________________

IEEE _________________ - Operates in the ________ frequency band and offers speeds of up to ___________

Longer range and are better able to penetrate building structures than devices based on 802.11a.

IEEE ________________ - Operates in the __________ frequency band and offers speeds of up to ___________

Operate at the same radio frequency and range as 802.11b but with the bandwidth of 802.11a.

IEEE _____________ - Currently in draft form but proposed standard defines ___________________________ with expected ________________________________ with a ______________ range of up to ___________________

Media Connectors Media connectors may look the same but may be

wired differently according to the Physical layer specification for which they were designed.

Punch block- ____________________ ________________________________________________________________

•One side has a place for each RJ-45 plug

•The back side has the punch down blocks that provide connectivity

Socket found in wall receptacle

•One side has a place for each RJ-45 plug

• Other ________________________ ___________________________

Correct Connector Termination When copper cabling is

terminated, there is the possibility of signal loss and the introduction of noise to the communication circuit.

If __________________ cable is a potential source of Physical layer ____________________________

Proper termination is essential to ensure optimum performance with current and future network technologies.

Common Optical Fiber Connectors: Straight-Tip (____) - widely used with

_____________________________ Subscriber Connector (_____) - This connector

type is widely used with ___________________ Lucent Connector (____) - A small connector for

use with ____________________ and also __________________________

Terminating and splicing fiber-optic cabling requires skill

Incorrect termination- such as: Misalignment End gap where the cable does not completely touch

the connection Etc

will result in diminished signaling distances or transmission failure.

____________________ and finding any faults can be done with an Optical Time Domain Reflectometer (_________________)

Or- a basic test with a bright flashlight and observing if light passes to the other end of the cable.