Download 4. Data-link layer

Chapter 1, Networking Basics
The outline presents only the key points from the course textbook. It’s not intended
to be a complete recap of the textbook content presented in outline form.
Where demonstrations are suggested or recommended, it’s assumed that the
instructor will know the procedures for the demonstration or will find them in the
course textbook. Some of the demonstrations require other equipment or network
setup in addition to your class presentation computer. You should review each
chapter outline before class to ensure that you have the proper equipment and
connections in the classroom and that you know the correct procedure to perform
the suggested demonstrations.
The outlines are not included on the Student CD-ROM for this course. However,
you can certainly make them available to your students, as a study aid, if you
wish. If you do so, you might want to edit the file to remove some of the
Instructor Notes before giving the outline to your students.
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Chapter Overview
A.
B.
Network Communications
The OSI Reference Model
Chapter 1, Lesson 1
Network Communications
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1.
Signals and Protocols
A.
B.
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C.
D.
E.
A data network is a group of computers connected by a network
medium.
1.
Network media: cables of various types or wireless technologies
The network medium carries signals between computers, including the
following types:
1.
Electric currents
2.
Light pulses
3.
Infrared
4.
Radio waves
Signals reduce complex information to the simplest possible form.
Computers communicate by using a language called a protocol.
Protocols can provide the following services:
1.
Packet acknowledgment. The transmission of a return message by the
recipient to verify the receipt of a packet or packets
a.
A packet is the fundamental unit of data transmitted over a local area
network (LAN).
2.
Segmentation. The division of a lengthy data stream into segments small
enough to transmit over the network inside packets
3.
Flow control. Messages sent by a receiving system that instruct the
sending system to speed up or slow down its transmission rate
4.
5.
6.
7.
2.
Protocol Interaction
A.
B.
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C.
D.
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3.
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A.
C.
D.
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Computers on a network use many different protocols.
The protocols on a networked computer are arranged in a stack.
1.
The protocol stack ranges from the application running on the computer
to the network medium (the network interface adapter providing the
connection to the network).
2.
The protocols at each layer of the stack provide services to the layers
above and below.
Direction of data flow
1.
Complex information originating from the transmitting computer at the
top of the stack is reduced to simple signals by the time it reaches the
bottom.
2.
The process by which data travels down the protocol stack on a
transmitting computer is reversed on the receiving computer.
The protocols at the same layer of the stack on different computers
communicate with each other.
Local Area Networks and Wide Area Networks
B.
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Error detection. The inclusion of special codes in a packet that the
receiving system uses to verify that the content of the packet was not
damaged in transit
Error correction. Messages sent by a receiving system that inform the
sender that specific packets were damaged and must be retransmitted
Data compression. A mechanism for reducing the amount of data
transmitted over a network by eliminating redundant information
Data encryption. A mechanism for protecting the data transmitted over a
network by encoding it with a key already known by the receiving
system
E.
A local area network (LAN) is a collection of computers located in a
relatively small area and connected by a common medium.
1.
Typically located in the same room, floor, or building
2.
Each computer or communicating device on the LAN is called a node.
The pattern in which the computers in a LAN are connected is called
the topology.
Types of LAN topologies
1.
Bus
2.
Star
3.
Ring
The defining protocols for a LAN are the data-link layer protocols, such
as Ethernet.
Wide area networks (WANs) are long-distance connections that nearly
always use an external network provider (such as a telephone
company).
1.
Are usually point-to-point connections, whereas LANs can connect
many systems
Outline, Chapter 1
Network+ Certification, Second Edition
2.
F.
4.
Broadband and Baseband
A.
B.
C.
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D.
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5.
6.
B.
C.
7.
Half-duplex communication. Signals travel in one direction only.
Full-duplex communication. Signals travel in both directions
simultaneously.
Segments and Backbones
A.
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A baseband network transmits a single signal at a time.
A broadband network simultaneously transmits multiple signals over a
single medium.
Packet switching enables computers to share a baseband medium.
1.
In a packet-switching network, data is split into discrete units that are
transmitted individually and are reassembled at the destination.
A circuit-switched network is one in which two communicating systems
establish a connection that remains open until all of the data is
transmitted.
Half-Duplex and Full-Duplex Communications
A.
B.
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WAN links can connect two LANs, a computer to a LAN, or a computer
to a computer.
Two or more networks connected together are called an internetwork.
The term “segment” is typically synonymous with LAN.
1.
A cable segment does not necessarily refer to a single length of cable.
A well-designed internetwork uses a backbone network to connect the
LANs.
When all of the segments are connected to a single backbone,
internetwork traffic never has to pass through more than two routers,
and no through traffic passes over the segments.
Client/Server and Peer-to-Peer Networking
A.
B.
C.
On a client/server network, computers function as either clients or
servers.
1.
Server. A computer or an application running on a computer that
provides a service to other computers
2.
Client. A computer that uses the services provided by servers
On a peer-to-peer network, computers can function as both clients and
servers.
Most network operating systems used today, including Microsoft
Windows and all forms of UNIX, use the peer-to-peer model.
1.
Only Novell NetWare is a pure client/server operating system.
Chapter 1, Lesson 2
The OSI Reference Model
1.
Standards
A.
The OSI reference model is based on standards published by the
International Organization for Standardization (ISO) and the
Outline, Chapter 1
Network+ Certification, Second Edition
3
B.
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C.
D.
2.
Data Encapsulation
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A.
B.
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C.
3.
B.
C.
D.
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Protocols at the various layers provide services to the layer above.
Data encapsulation is the process by which a protocol adds a header
(and possibly a footer) to data received from the layer above.
1.
The header consists of fields containing information specific to the
protocol functions.
2.
The footer contains error detection information.
3.
Data encapsulated at one layer becomes the payload for the layer below.
The protocol data units (PDUs) created at the various OSI model layers
have different names at different layers.
1.
Application layer: message
2.
Transport layer: segment or datagram
3.
Network layer: datagram
4.
Data-link layer: frame
5.
Any layer: packet
a.
Packet is a generic term for the data unit created at any layer.
The Physical Layer
A.
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Telecommunication Standardization Sector of the International
Telecommunication Union (ITU-T).
The OSI model divides a computer’s networking functions into seven
layers.
1.
The top of the model interfaces with the application running on the
computer.
2.
The bottom of the model represents the interface to the network, such as
a network interface adapter (also known as a network interface card, or
NIC).
The protocols used today predate the OSI reference model.
None of the protocol stacks in common use conform strictly to the
layers of the model.
Defines the hardware elements of the network, including
1.
The network medium
2.
How the network is installed
3.
The type of signaling the devices use
Physical layer elements
1.
Cables
2.
Network interface adapters (also called network interface cards, or
NICs)
3.
Hubs
The physical layer elements are usually dictated by which data-link
layer protocol you select.
Most physical layer installations should conform to the Commercial
Building Telecommunications Cabling Standard, also known as EIA/TIA
568A.
Outline, Chapter 1
Network+ Certification, Second Edition
1.
4.
The Data-Link Layer
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A.
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B.
C.
D.
E.
5.
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Published jointly by the American National Standards Institute (ANSI),
the Electronics Industry Association (EIA) and the Telecommunications
Industry Association (TIA)
Data-link layer protocols
1.
Ethernet
2.
Token Ring
3.
Fiber Distributed Data Interface (FDDI)
4.
Serial Line Internet Protocol (SLIP)
5.
Point-to-Point Protocol (PPP)
Data-link layer protocol components
1.
Frame format
2.
Media Access Control (MAC) mechanism
3.
Physical layer specifications
Data-link layer protocols are implemented on a computer in its network
interface adapter and the adapter driver.
Data-link layer functions
1.
Hardware addressing (also called MAC addressing)
2.
Error detection and correction
3.
Network-layer protocol identification
Data-link layer protocols are only capable of carrying traffic to other
computers on the same network.
The Network Layer
A.
B.
C.
Network layer protocols
1.
Internet Protocol (IP)
2.
Internetwork Packet Exchange (IPX)
3.
NetBIOS Extended User Interface (NetBEUI)
4.
AppleTalk
Responsible for end-to-end communications
Network layer functions
1.
Addressing
a.
Network layer addresses and data-link layer addresses may identify
different computers.
b.
Network layer addresses can be self-contained (like IP addresses) or
borrowed (like IPX node addresses).
2.
Fragmenting
a.
Different networks support different packet sizes.
b.
The network layer protocol splits the datagram into pieces small
enough for the data-link layer protocol to transmit.
3.
Routing
a.
Is the process of using the most efficient path possible to direct a
datagram from its source to its destination
4.
Transport layer protocol identification
Outline, Chapter 1
Network+ Certification, Second Edition
5
6.
The Transport Layer
A.
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B.
C.
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7.
The Session Layer
A.
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B.
C.
8.
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The two most important services at this layer are dialog control and
dialog separation.
Dialog control
1.
Selects the mode that systems will use to exchange messages
2.
Systems can choose between two-way alternate (TWA) and two-way
simultaneous (TWS) mode.
Dialog separation is the process of creating checkpoints in a data
stream to enable systems to synchronize their functions.
The Presentation Layer
A.
B.
C.
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Transport layer protocols
1.
Transmission Control Protocol (TCP)
2.
User Datagram Protocol (UDP)
3.
NetWare Core Protocol (NCP)
4.
Sequenced Packet Exchange (SPX)
Transport layer functions
1.
Packet acknowledgment
2.
Data segmentation
3.
Flow control
4.
Error detection
5.
Application layer protocol identification
Some transport-layer protocols are connection-oriented (CO) and
others are connectionless (CL).
1.
CO protocols require a preliminary exchange of control messages, called
a handshake; CL protocols do not.
2.
CO protocols have larger headers and more overhead than CL protocols
do.
3.
CO protocols provide additional services, such as packet
acknowledgment, data segmentation, flow control, and end-to-end error
detection and correction.
4.
CO protocols acknowledge transmitted packets and are therefore called
reliable protocols.
a.
CL protocols do not use acknowledgments and are therefore
technically described as not reliable.
Has only one function: translating syntax between different systems
1.
Enables systems to negotiate a common syntax for network
communications
The transmitting system converts its abstract syntax to transfer syntax.
1.
Abstract syntax. Native form of communication
2.
Transfer syntax. Alternative syntax that the two systems have in
common
The presentation layer translation process
Outline, Chapter 1
Network+ Certification, Second Edition
1.
2.
3.
9.
The Application Layer
A.
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B.
Is the layer that programs use to access the OSI model and use
network resources
Application layer protocols
1.
File Transfer Protocol (FTP)
2.
Hypertext Transfer Protocol (HTTP)
3.
Simple Mail Transfer Protocol (SMTP)
4.
Post Office Protocol, Version 3 (POP3)
5.
Internet Mail Access Protocol (IMAP)
6.
Simple Network Management Protocol (SNMP)
7.
Domain Name System (DNS)
8.
Dynamic Host Configuration Protocol (DHCP)
Chapter Summary
A.
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The sender translates its abstract syntax to transfer syntax.
The sender transmits data to the receiver.
The receiver translates the transfer syntax to its own abstract syntax.
B.
Lesson 1: Network Communications
1.
Computers communicate by using languages called protocols.
2.
Protocols provide services to other protocols operating above and below
them.
3.
A LAN uses a common network medium to connect computers in a
relatively small area.
4.
A WAN uses an external network provider to connect LANs.
5.
Broadband networks carry multiple signals at once, while baseband
networks carry only one signal.
6.
A backbone network connects segments together, forming an
internetwork.
7.
Most operating systems today use the peer-to-peer model, which allows
computers to function as both clients and servers.
Lesson 2: The OSI Reference Model
1.
The physical layer defines the hardware elements and structure of the
network installation.
2.
The data-link layer provides addressing, data encapsulation, and media
access control.
3.
The network layer provides end-to-end routing and addressing.
4.
The transport layer provides packet acknowledgment, flow control, and
error detection.
5.
The session layer provides dialog control and dialog separation.
6.
The presentation layer translates syntaxes between different systems.
7.
The application layer provides an interface to applications running on
the computer.
Outline, Chapter 1
Network+ Certification, Second Edition
7