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Chapter Overview

Network Communications The OSI Reference Model

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Signals and Protocols

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

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

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

data-link 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

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 (Open Systems Interconnection) Reference Model

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Data Encapsulation

Play Video

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PDU Names at Different OSI Layers

OSI Layer Protocol Data Unit (PDU) Name (A generic name

for the data constructions created by the protocols operating at various layers of the OSI model)

Application Message

Transport Segment or datagram

Network Datagram

Data-link Frame

(Any layer) Packet

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The Physical Layer Defines the hardware elements of the

network, including The network medium How the network is installed The type of signaling 

Includes the following elements: Cables Network interface adapters (also called

network interface cards, or NICs) Hubs

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The Data-Link Layer

Includes the following protocols: 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.)

Includes the following protocol components: Frame format Media Access Control (MAC) mechanism Physical layer specifications 

Performs the following functions: Hardware addressing Error detection and correction Protocol identification

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The Network Layer Includes the following protocols:

Internet Protocol (IP) Internetwork Packet Exchange (IPX) NetBIOS Extended User Interface (NetBEUI) AppleTalk

Performs the following functions: Addressing Fragmenting Routing Protocol identification

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The Transport Layer Includes the following protocols:

Transmission Control Protocol (TCP) User Datagram Protocol (UDP) IPX NetWare Core Protocol (NCP) Sequenced Packet Exchange (SPX) 

Performs the following functions: 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

The two most important functions at this layer are Dialog control Dialog separation

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The Presentation Layer

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

Includes the following protocols: 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 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

Application Provides an interface to applications running on the computer

Presentation

Translates syntaxes between different systems

Session Provides dialog control and dialog separation

Transport Provides packet acknowledgment, flow control, and error detection

Network Provides end-to-end routing and addressing

Data-link Provides addressing, data encapsulation, and media access control

Physical Defines the hardware elements and structure of the network installation