Business Data Communications,
Fourth Edition
Chapter 6: Protocols
Learning Objectives
• Describe the role of software in a data
communications network
• Define a protocol and how it is used in a
network
• Explain the Open Systems Interconnection
(OSI) model
• List the types of protocols
• Differentiate between wide area and local
area network protocols
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Learning Objectives
• List and explain Internet protocols
• Describe the difference among characteroriented, byte-count-oriented, and bitoriented protocols, H.323, and X.25
protocols
• Describe the protocols and standards
used in wireless networks
• Describe the protocols used for Apple
Macintosh networks
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Introduction
• Early networks consisted of equipment
from one manufacturer
• Modern networks are made up of different
equipment from different manufacturers
• Rules are needed to allow the equipment
to communicate over a network
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The Role of Software in a
Network
• Software is made up of programs that
control data transmission
• All devices run some type of software
• Computers (servers), controllers, clients
(including terminals) all use software in a
WAN
• Servers and clients use software in a LAN
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Protocols
• Set of rules that defines how devices
communicate
– Translates codes within the devices
• Three key elements of protocols
– Syntax – format of data, transmission coding
schemes
– Semantics – control information
– Timing – controlling flow of data on network, match
device speeds on the network, provides sequencing
for data
• Early protocols were proprietary
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Protocols
• Open Systems Interconnection (OSI) Model
– A standard for communications systems
– Composed of seven layers
• Application layer – allows user access to the
network
• Presentation layer – defines format of the data
• Session layer – establishes and maintains network
connection
• Transport layer – maintains connections between
networks
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Protocols
• Open Systems Interconnection Model
– 7 Layers (cont.)
• Network layer – creates packets, adds address
and routing information
– Route is the path data takes
– Adaptive versus dynamic routing
– Routing tables
• Data link layer – establishes and controls physical
path, creates frames
• Physical layer – concerned with hardware, makes
the physical connection
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Types of Protocols
• Introduction
– Different types for mainframe computers,
personal computers, wireless networks
– No standard set of protocol for all devices
– Communications developed in an atmosphere
of competition
– Data link protocols – rules for implementing
the data link layer
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Wide Area Network Protocols
• Mainframe Computer Protocols
– Character-Oriented Protocols
•
•
•
•
Binary Synchronous Communications (BSC)
Data sent as blocks of characters (synchronous)
Used only for half-duplex transmission
Uses special characters for control
– Byte-Count-Oriented Protocols
• Adds the number of characters instead of special control
characters
• Digital Data Communication Message Protocol (DDCMP)
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Figure 6-6. BSC data with control characters.
Figure 6-7. Format for byte-count-oriented protocol.
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Wide Area Network Protocols
• Mainframe Computer Protocols
– Bit-Oriented Protocols
•
•
•
•
Data and control information put in frames
Different protocols created by many companies
SDLC – IBM
HDLC – ISO Standard
Figure 6-8. HDLC, SDLC frame format.
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Wide Area Network Protocols
• Mainframe Computer Protocols
– Systems Network Architecture (SNA)
• Originally used on IBM mainframe networks
• Now used in other networks as well
• Uses a layered model
– Old model – 5 layers
– Modern model – 7 layers
– More compatible with OSI model
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Figure 6-9. Comparison among old SNA, new SNA, and OSI layered Model.
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Wide Area Network Protocols
• Mainframe Computer Protocols
– H.323 Protocol
• Real-time audio, video, and data
communications on packet-switched
networks
• Multimedia presentation over a network
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Wide Area Network Protocols
– Mainframe Computer Protocols
• X.25 Protocol
– Packet switching protocol
– Uses only the bottom 3 layers of the OSI
model
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Internet Protocols
• Transmission Control Protocol/Internet
Protocol (TCP/IP)
– Developed in 1973 for ARPANET
– The first Wide Area Network protocol
– Five layer model
– Data broken up in to packets
• TCP segment
• IP datagram
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Internet Protocols
• Internet Protocol Version 6 (IPv6)
– AKA Internet Protocol next generation (IPng)
– Address length increased to 128 bits
– Allows the addition of more Internet Web sites
– Allows for growth for the Internet
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Internet Protocols
• Other Internet Protocols
– File transfer protocol (ftp)
– Hypertext transfer protocol (http)
– Electronic Mail Protocols
• X.400 (e-mail standard)
• X.500 (public e-mail directory standard)
• Post Office Protocol 3 (POP3) – e-mail downloaded to user’s
computer
• Internet Message Access Protocol (IMAP) – e-mail stored on
server, even after it is read
• Simple Mail Transfer Protocol (SMTP) – used for sending
only
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Local Area Network Protocols
• Local Area Network
– Limited area
• X.PC
– Converts asynchronous data for transmission on a packet
switching network
• Ethernet
– Contention access method
– Carrier Sense Multiple Access with Collision Detection
(CSMA/CD)
– Fast Ethernet (100 Mbps)
– Gigabit Ethernet (1 Gbps)
– 10-Gigabit Ethernet (10 Gbps)
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Local Area Network Protocols
• Token Passing
– Token
– Token ring
– 4Mbps or 16Mbps
– Uses Multistation Access Unit (MAU)
– Fast token ring (high-speed ring) (100 Mbps)
– Fiber Distributed Data Interface (FDDI)
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Local Area Network Protocols
• Internetwork Packet Exchange/Sequenced
Packet Exchange (IPX/SPX)
– Used on Novell LANs
– Incorporates features of discontinued Xerox
Network System (XNS)
– Uses lower 3 layers of OSI model
– Data link layer divided
• Logical Link Control (LLC)
• Media Access Control (MAC)
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Wireless Protocols and Standards
• Cellular Digital Packet Data (CDPD)
– AKA Wireless IP protocol
– Used on wireless packet switched networks
– Uses radio frequencies, up to 19.2 Kbps
– Allows multicast messages
– Connects to the wired network as well
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Wireless Protocols
• Wireless Application Protocol (WAP)
– Allows wireless devices to have Internet
access
– Browser exists on hand-held device
– Server software is at the wireless service
provider
– Devices that adhere to the protocol are called
“WAP-enabled”
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Wireless Protocols
• Infrared Data Association (IrDA)
– Provides point-to-point link
– PDAs, keyboards, mouse
– Limitations on length of signal
– Line of sight transmission
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Wireless Protocols
• Third Generation (3G) of Mobile
Communications
– Technology for future wireless applications
– Proposes standards
– Voice and data communications technologies
of the future
– Propose to put W-CDMA on an IP network
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Wireless Protocols
• Bluetooth
– Short-range radio links
– Printers, mouse, keyboard connected to PC
without wires
– Bluetooth networks
• Piconet – point-to-point between two devices
• Scatternet – Two or more piconets communicating
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Wireless Protocols
• Enhanced Data Rates for Global Evolution
(EDGE)
– Standard for GSM and TDMA networks
– Transmission up to 384 Kbps
– Part of the evolution to 3G
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Wireless Protocols
• SyncML
– Common language for synchronizing data on
mobile devices
– XML protocol
– Mobile devices need to communicate with
networks so synchronization is needed
– Over 300 companies involved in developing
SyncML
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AppleTalk Protocol
•
•
•
•
Used with Macintosh computers
Uses CSMA/CA
Uses a 7-layer model
Interfaces with other LANs
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Summary
• Networks made up of
hardware and software
• Software exists on every
network device
• Protocols are rules for
communications
• OSI is a model for
protocol standards
• Mainframe computer
protocols differ from
personal computer
protocols
Chapter 6: Protocols
• Multimedia networks use
the H.323 protocol
• X.25 used on packet
switching networks
• Internet protocols include
TCP/IP, IPv6, and several
e-mail protocols
• Local area network
protocols include X.PC,
Ethernet, and token ring
• Wireless networks
include CDPD and WAP
• Macintosh networks use
AppleTalk
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