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Chapter Overview
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Network Communications
The OSI Reference Model
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Signals and Protocols
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A data network is a group of computers
connected by a network medium.
The network medium carries signals between
computers.
Signals reduce complex information to the
simplest possible form.
Computers communicate by using a language
called a protocol.
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Protocol Services
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Packet acknowledgment
Segmentation
Flow control
Error detection
Error correction
Data compression
Data encryption
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A Protocol Stack
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Protocol Interaction
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Local Area Networks
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A local area network (LAN) is a collection of
computers located in a relatively small area
and connected by a common medium.
The pattern in which computers in a LAN are
connected is called the topology.
LAN topologies include bus, star, and ring.
The defining protocols for a LAN are the datalink layer protocols.
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Wide Area Networks
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Packet Switching
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Half-Duplex and Full-Duplex
Communications
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Backbone Network
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Client/Server and Peer-to-Peer
Networking
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On a client/server network, computers
function as either clients or servers.
On a peer-to-peer network, computers can
function as both clients and servers.
Microsoft Windows, UNIX, and Linux are
peer-to-peer operating systems.
Novell NetWare is a client/server operating
system.
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The OSI Reference Model
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Data Encapsulation
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PDU Names at Different OSI Layers
OSI Layer
Application
Protocol Data Unit
(PDU) Name
Message
Transport
Segment or datagram
Network
Datagram
Data-link
Frame
(Any layer)
Packet
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The Physical Layer
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Defines the hardware elements of the
network, including
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The network medium
How the network is installed
The type of signaling
Includes the following elements:
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Cables
Network interface adapters (also called network
interface cards, or NICs)
Hubs
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The Data-Link Layer
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Includes the following protocols:
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Ethernet
Token Ring
Fiber Distributed Data Interface (FDDI)
Serial Line Internet Protocol (SLIP)
Point-to-Point Protocol (PPP)
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The Data-Link Layer (Cont.)
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Includes the following protocol components:
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Frame format
Media Access Control (MAC) mechanism
Physical layer specifications
Performs the following functions:
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Hardware addressing
Error detection and correction
Protocol identification
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The Network Layer
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Includes the following protocols:
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Internet Protocol (IP)
Internetwork Packet Exchange (IPX)
NetBIOS Extended User Interface (NetBEUI)
AppleTalk
Performs the following functions:
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Addressing
Fragmenting
Routing
Protocol identification
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The Transport Layer
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Includes the following protocols:
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Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
IPX
NetWare Core Protocol (NCP)
Sequenced Packet Exchange (SPX)
Performs the following functions:
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Packet acknowledgment
Data segmentation
Flow control
Error detection
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Connection-Oriented and
Connectionless Protocols
Connection-Oriented (CO)
Protocols
Connectionless (CL)
Protocols
Require a handshake
Do not require a handshake
Have larger headers and more
overhead
Have smaller headers and less
overhead
Provide packet acknowledgments,
data segmentation, flow control,
and error detection and correction
Do not provide additional
services
Acknowledge transmitted packets,
so they are considered reliable
Do not acknowledge
transmitted packets, so they
are considered unreliable
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The Session Layer
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The two most important functions at this
layer are
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Dialog control
Dialog separation
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The Presentation Layer
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The presentation layer uses the following
translation process:
1. The sender translates its abstract syntax to
transfer syntax.
2. The sender transmits data to the receiver.
3. The receiver translates transfer syntax to it in
abstract syntax.
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The Application Layer
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Includes the following protocols:
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File Transfer Protocol (FTP)
Hypertext Transfer Protocol (HTTP)
Simple Mail Transfer Protocol (SMTP)
Post Office Protocol, Version 3 (POP3)
Internet Mail Access Protocol (IMAP)
Simple Network Management Protocol (SNMP)
Domain Name System (DNS)
Dynamic Host Configuration Protocol (DHCP)
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Lesson 1 Summary: Network
Communications
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Computers communicate by using languages called protocols.
Protocols provide services to other protocols operating above
and below them.
A LAN uses a common network medium to connect computers
in a relatively small area.
A WAN uses an external network provider to connect LANs.
Broadband networks carry multiple signals at once, while
baseband networks carry only one signal.
A backbone network connects segments together, forming an
internetwork.
Most operating systems today use the peer-to-peer model,
which allows computers to function as both clients and servers.
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Lesson 2 Summary: The OSI
Reference Model
OSI Model
Layer
Function
Physical
Defines the hardware elements and structure of the network
installation
Data-link
Provides addressing, data encapsulation, and media access
control
Network
Provides end-to-end routing and addressing
Transport
Provides packet acknowledgment, flow control, and error
detection
Session
Provides dialog control and dialog separation
Presentation
Translates syntaxes between different systems
Application
Provides an interface to applications running on the computer
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