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Guide to Networking Essentials Fifth Edition


The way in which computers attached to a network share the cable must be defined ... Requires two of the four pairs bundled in a Category 5 twisted-pair cable ... – PowerPoint PPT presentation

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Title: Guide to Networking Essentials Fifth Edition

Guide to Networking EssentialsFifth Edition
  • Chapter 7
  • Network Architectures

  • Compare and contrast media access methods used in
    network architectures
  • Describe the operation of Ethernet
  • Differentiate between Ethernet standards and
  • Explain the four Ethernet frame types and how
    they are used

Objectives (continued)
  • Describe the token ring architecture and its
  • Describe the AppleTalk network architecture
  • Explain the function of Fiber Distributed Data
  • Describe other LAN and WAN architectures and
    their role in todays networks

Putting Data on the Cable Access Methods
  • Given that network architectures communicate in a
    number of different ways, some factors in network
    communications must be considered
  • How computers put data on the cable
  • How they ensure that the data reaches its
    destination undamaged

Function of Access Methods
  • The way in which computers attached to a network
    share the cable must be defined
  • A collision results from two or more devices
    sending a signal along the same channel at the
    same time
  • Splitting data in small chunks helps prevent
  • Channel access methods specify when computers can
    access the cable or data channel
  • Ensure that data reaches destination by
    preventing computers from sending messages that
    might collide
  • Every computer on a network must use the same
    access method

Major Access Methods
  • Channel access is handled at the MAC sublayer of
    the Data Link layer in the OSI model
  • Five major types of channel access
  • Contention
  • Switching
  • Token passing
  • Demand priority
  • Polling

  • In early networks based on contention, computers
    sent data whenever they had data to send
  • As networks grow, outgoing messages collide more
    frequently, must be sent again, and then collide
  • To organize contention-based networks, two
    carrier access methods were created

Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
Carrier Sense Multiple Access with Collision
Avoidance (CSMA/CA)
  • When the computer senses that no other computer
    is using the network, it signals its intent to
  • Other computers with data to send must wait when
    they receive the intent-to-transmit signal and
    send their intent-to-transmit only when channel
    is free
  • The overhead created by intent-to-transmit
    packets reduces network speed significantly
  • Used in wireless LANs with an access point
  • Wireless NIC tells access point its intents to
  • Access point hears transmissions from all
    devices, so it can determine whether its okay to

  • Switching nodes are interconnected through a a
    switch, which controls access to the media
  • Contention occurs only when multiple senders ask
    to reach the same receiver simultaneously or when
    the simultaneous transmission requests exceed the
    switchs capability to handle multiple
  • Advantages fairer, centralized management
    (enables QoS), switch can have connection ports
    that operate at different speeds
  • Disadvantage higher cost

Token Passing
Demand Priority
  • Demand priority channel access method used
    solely by the 100VG-AnyLAN 100 Mbps Ethernet
    standard (IEEE 802.12)
  • 100VG-AnyLAN runs on a star bus topology
  • Intelligent hubs control access to the network
  • Hub searches all connections in a round-robin
  • When an end node has data to send, it transmits a
    demand signal to the hub
  • The hub then sends an acknowledgement that the
    computer can start transmitting its data
  • The major disadvantage of demand priority is price

Choosing an Access Method
Choosing an Access Method (continued)
Choosing an Access Method (continued)
The Ethernet Architecture
  • 1960s and 1970s many organizations worked on
    methods to connect computers and share data
  • E.g., the ALOHA network at the University of
  • 1972 Robert Metcalf and David Boggs, from
    Xeroxs PARC, developed an early version of
  • 1975 PARC released first commercial version (3
    Mbps, up to 100 computers, max. 1 km of total
  • DIX developed standard based on Xeroxs Ethernet
    (10 Mbps)
  • 1990 IEEE defined the 802.3 specification
  • Defines how Ethernet networks operate at layers

Overview of Ethernet
  • Ethernet is the most popular network architecture
  • Advantages easy to install, scalable, broad
    media support, and low cost
  • Supported transmission speeds 10 Mbps to 10 Gbps
  • Uses the NICs MAC address to address frames
  • Ethernet variations are compatible with one
  • Basic operation and frame formatting is the same
  • Cabling, speed of transmission, and method by
    which bits are encoded on the medium differ

Ethernet Operation
  • Ethernet is a best-effort delivery system
  • It works at the Data Link layer of the OSI model
  • Relies on the upper-layer protocols to ensure
    reliable delivery of data
  • Understanding the following concepts is
  • How Ethernet accesses network media
  • Collisions and collision domains
  • How Ethernet handles errors
  • Half-duplex and full-duplex communications

Accessing Network Media
  • Ethernet uses CSMA/CD in a shared-media
    environment (a logical bus)
  • Ethernet device listens for a signal or carrier
    (carrier sense) on the medium first
  • If no signal is present, no other device is using
    the medium, so a frame can be sent
  • Ethernet devices have circuitry that detects
    collisions and automatically resends the frame
    that was involved in the collision

Collisions and Collision Domains
Ethernet Error Handling
  • Collisions are the only type of error for which
    Ethernet automatically attempts to resend the
  • Errors can occur when data is altered in medium
  • Usually caused by noise or faulty media
  • When the destination computer receives a frame,
    the CRC is recalculated and compared against the
    CRC value in the FCS
  • If values match, the data is assumed to be okay
  • If values dont match, the data was corrupted
  • Destination computer discards the frame
  • No notice is given to the sender

Half-Duplex Versus Full-Duplex Communications
  • When half-duplex communication is used with
    Ethernet, CSMA/CD must also be used
  • When using a switched topology, a computer can
    send and receive data simultaneously (full-duplex
  • The collision detection circuitry is turned off
    because collisions arent possible
  • Results in a considerable performance advantage

Ethernet Standards
  • Each Ethernet variation is associated with an
    IEEE standard
  • The following sections discuss many of the
    standards, some of which are obsolete or had
    limited use
  • Keep in mind that Ethernet over UTP cabling has
    been the dominant technology since the early
    1990s, and will likely to continue to be for the
    foreseeable future

100 Mbps IEEE Standards
  • The most widely accepted Ethernet standard today
    is 100BaseT, which is also called fast Ethernet
  • The current IEEE standard for 100BaseT is 802.3u
  • Subcategories
  • 100BaseTX Two-pair Category 5 or higher UTP
  • 100BaseT4 Four-pair Category 3 or higher UTP
  • 100BaseFX Two-strand fiber-optic cable
  • Because of its widespread use, the cable and
    equipment in fast Ethernet are inexpensive
  • Architecture of choice for all but heavily used
    servers and multimedia applications

  • 100BaseTX is the standard thats usually in mind
    when discussing 100 Mbps Ethernet
  • Requires two of the four pairs bundled in a
    Category 5 twisted-pair cable
  • Although three cable types are available for
    100BaseT, 100BaseTX is the most widely accepted
  • Generally called fast Ethernet

  • 100BaseT4 Ethernet uses all four pairs of wires
    bundled in a UTP cable
  • Advantage capability to run over Category 3
  • One of the biggest expenses of building a network
    is cable installation, so many organizations with
    Category 3 cabling chose to get the higher speed
    with the existing cable plant by using 100BaseT4
    instead of 100BaseTX

  • 100BaseFX uses two strands of fiber-optic cable
  • Advantages
  • Impervious to electrical noise and electronic
  • Can span much greater distances between devices
  • Disadvantage far more expensive than
  • Rarely used as a complete 100BaseTX replacement
  • Used as backbone cabling between hubs or switches
    and to connect wiring closets between floors or
  • Connect client or server computers to the network
    when immunity to noise and eavesdropping is

100BaseT Design Considerations
100BaseT Design Considerations (continued)
10 Mbps IEEE Standards
  • Four major implementations of 10 Mbps Ethernet
  • 10Base5 Ethernet using thicknet coaxial cable
  • 10Base2 Ethernet using thinnet coaxial cable
  • 10BaseT Ethernet over UTP cable
  • 10BaseF Ethernet over fiber-optic cable
  • Of these 10 Mbps standards, only 10BaseT and
    10BaseF are seen today
  • 10Base2 and 10Base5 are essentially obsolete

Gigabit Ethernet IEEE 802.3ab and 802.3z
  • Gigabit Ethernet implementations
  • 802.3z-1998 covers 1000BaseX specifications,
    including the L (long wavelength
    laser/fiber-optic), S (short wavelength
    laser/fiber-optic), and C (copper jumper cables)
  • 802.3ab-1999 covers 1000BaseT specifications,
    which require four pairs of 100 ohm Category 5 or
    higher cable

10 Gigabit Ethernet 10 Gbps IEEE 802.3ae Standard
  • Defined to run only on fiber-optic cabling, both
    SMF and MMF, on a maximum distance of 40 km
  • Provides bandwidth that can transform how WAN
    speeds are thought of
  • Runs in full-duplex mode only
  • CSMA/CD is not necessary
  • Primary use as network backbone
  • It also has its place in storage area networks
  • Will be the interface for enterprise-level servers

10 Gigabit Ethernet 10 Gbps IEEE 802.3ae
Standard (continued)
  • Standards
  • 10GBASE-SR Runs over short lengths (between 26
    and 82 meters) over MMF
  • For high-speed servers, SANs, etc.
  • 10GBASE-LR Runs up to 10 km on SMF
  • For campus backbones and MANs
  • 10GBASE-ER Runs up to 40 km over SMF
  • Primary applications are for MANs
  • 10GBASE-SW Uses MMF for distances up to 300 m
  • 10GBASE-LW Uses SMF for distances up to 10 km
  • 10GBASE-EW Uses SMF for distances up to 40 km

Whats Next for Ethernet?
  • Implementations of 40 Gbps Ethernet are underway
  • Ethernet could increase tenfold every 4-6 years
  • 100 Gbps Ethernet available by 2006 to 2008,
    terabit Ethernet by 2011, and 10 terabit Ethernet
    by 2015
  • In October 2005, Lucent Technologies demonstrated
    for the first time the transmission of Ethernet
    over fiber-optic cable at 100 Gbps
  • It will be able to transfer data across the city
    faster than todays CPUs can transfer data to
  • This level of speed has major implications for
    the entertainment industry and many other areas

Ethernet Frame Types
  • Ethernet supports four non-compatible frame types
  • Ethernet 802.3 used by IPX/SPX on Novell NetWare
    2.x and 3.x networks
  • Ethernet 802.2 used by IPX/SPX on Novell NetWare
    3.12 and 4.x networks
  • Supported by default in Microsoft NWLink
  • Ethernet SNAP used in EtherTalk and mainframes
  • Ethernet II is used by TCP/IP
  • All Ethernet frame types support a packet size
    between 64 and 1518 bytes, and can be used by all
    network architectures mentioned previously

Ethernet 802.3
Ethernet 802.2
  • Ethernet 802.2 frames comply completely with the
    Ethernet 802.3 standard
  • The IEEE 802.2 group didnt address Ethernet,
    only the LLC sublayer of the OSI models layer 2
  • Since Novell had already decided to use the term
    Ethernet 802.3 to describe Ethernet raw, its
    generally accepted that Ethernet 802.2 means a
    fully 802.3- and 802.2-compliant Ethernet frame
  • Ethernet 802.2 frames contain similar fields to
    802.3, with three additional LLC fields

Ethernet SNAP
  • Ethernet SubNetwork Address Protocol (SNAP) is
    generally used on the AppleTalk Phase 2
  • It contains enhancements to the 802.2 frame,
    including a protocol type field, which indicates
    the network protocol used in the frames data

Ethernet II
Wireless Ethernet IEEE 802.11b, a, and g
  • AP serves as the center of a star topology
  • Stations cant send and receive at the same time
  • CSMA/CA is used instead of CSMA/CD
  • 802.11b/a/g use handshaking before transmission
  • Station sends AP an RTS and it responds with CTS
  • Standards define a maximum transmission rate, but
    speeds might be dropped to increase reliability
  • No fixed segment length
  • Maximum of 300 feet without obstructions
  • Can be extended with large, high-quality antennas

The Token Ring Architecture
Token Ring Function
  • A token passes around the ring
  • If an in use token is received from NAUN, and
    the computer has data to send, it attaches its
    data to the token and sends it to its NADN
  • If received token is in use, NIC verifies if it
    is the destination station
  • If not, the computer re-creates the token and the
    data exactly and sends them to its NADN
  • If it is, data is sent to the upper-layer
  • Two bits in data packet are toggled and token is
    sent to NADN when original sender receives it,
    it frees the token and then passes it along

Hardware Components
  • A hub can be a multistation access unit (MSAU) or
    smart multistation access unit (SMAU)
  • IBMs token ring implementation is the most
    popular adaptation of the IEEE 802.5 standard
  • Minor variations but very similar to IEEE specs
  • IBM equipment is most often used
  • 8228 MSAU has 10 connection ports, eight of which
    can be used for connecting computers
  • The RO port on one hub connects to RI port on the
    next hub, and so on, to form a ring among the
  • IBM allows connecting 33 hubs

Cabling in a Token Ring Environment
The Token Ring Architecture (summary)
The AppleTalk Environment
  • Designed for use in Macintosh networks (1983)
  • Can be run over several physical architectures
    commonly run over Ethernet (EtherTalk)
  • Easy to implement
  • Dynamic scheme used to determine devices address
  • AppleTalk Phase 1 supported only 32 computers per
    network, and only with LocalTalk cabling
  • With hubs/repeaters, increased the number to 254
  • AppleTalk Phase 2, EtherTalk, and TokenTalk
    (1989) allow more than 16 million computers

  • LocalTalk uses STP in a bus topology to allow
    users to share peripherals and data in a small
    home or office environment
  • CSMA/CA channel access method
  • Avoids more collisions, but cumbersome
  • Maximum transmission speed of 230.4 Kbps
  • Thus, this architecture was used primarily in
    small, Macintosh-only environments

EtherTalk and TokenTalk
  • EtherTalk is the AppleTalk protocol running over
    a 10 Mbps IEEE 802.3 Ethernet network
  • TokenTalk is the AppleTalk protocol running over
    a 4 or 16 Mbps IEEE 802.5 token ring network
  • Both implementations require using a different
  • Since 1996, Apple Computer has offered systems
    with built-in Ethernet NICs or with options to
    add Ethernet or token ring to its systems at a
    low cost
  • Mac OS X with an Ethernet interface can freely
    participate in a Windows-based network

The Fiber Distributed Data Interface (FDDI)
The Fiber Distributed Data Interface (FDDI)
Architecture (continued)
Networking Alternatives
  • Many other network architectures are available
  • Some are good for specialized applications, and
    others are emerging as new standards
  • Topics
  • Broadband technologies (cable modem and DSL)
  • Broadcast technologies
  • ATM
  • ATM and SONET Signaling Rates
  • High Performance Parallel Interface (HIPPI)

Broadband Technologies
  • Baseband systems use a digital encoding scheme at
    a single fixed frequency
  • Broadband systems use analog techniques to encode
    information across a continuous range of values
  • Signals move across the medium in the form of
    continuous electromagnetic or optical waves
  • Data flows one way only, so two channels are
    necessary for computers to send and receive data
  • E.g., cable TV

Cable Modem Technology
Digital Subscriber Line (DSL)
  • Competes with cable modem for Internet access
  • Broadband technology that uses existing phone
    lines to carry voice and data simultaneously
  • Most prominent variation for home Internet access
    is Asymmetric DSL (ADSL)
  • Splits phone line in two ranges Frequencies
    below 4 KHz are used for voice transmission, and
    frequencies above 4 KHz are used to transmit data
  • Typical connection speeds for downloading data
    range from 256 Kbps to 8 Mbps upload speeds are
    in the range of 16 Kbps to 640 Kbps

Broadcast Technologies
  • By definition one-way transmissions
  • This changed in Internet access by satellite
    television systems
  • Work on the principle that most traffic a user
    generates is to receive files, text, and graphics
  • The average users computer sends very little
  • User connects to service provider through a modem
  • Service provider sends data by satellite to the
    users home at speeds up to 400 Kbps
  • E.g., service offered by DirectTV, through its
    DirectPC add-on products

Asynchronous Transfer Mode (ATM)
  • High-speed network technology for LANs and WANs
  • Connection-oriented switches
  • Dedicated circuits are set up before
  • Data travels in fixed-size 53-byte cells (5
  • Enables ATM to work at extremely high speeds
  • Quick switching
  • Predictable traffic flow
  • Enables ATM to guarantee QoS
  • Used quite heavily for the backbone and
    infrastructure in large communications companies
  • LAN emulation (LANE) required for LAN applications

ATM and SONET Signaling Rates
High Performance Parallel Interface (HIPPI)
  • HIPPI (late 1980s) high-speed interface
    developed for supercomputers and high-end
  • Serial HIPPI is a fiber-optic version that uses
    point-to-point optical links for bandwidth up to
    800 Mbps
  • In early 1990s, it was used as a network backbone
    and for interconnecting supercomputers
  • With the advent of Gigabit Ethernet, interest in
    HIPPI as a LAN backbone decreased
  • HIPPI-6400 (1998) up to 6.4 Gbps transfer rates
  • Known as Gigabyte System Network (GSN)
  • HIPPI and GSN are now exotic networking products
    and arent often found in typical corporate

  • Cable access methods determine how a network
    architecture gains access to the network medium
  • A network architecture defines how data is
    placed, transmitted, and at what speed, and how
    problems in the network are handled
  • DIX introduced Ethernet, which later became the
    IEEE 802.3 standard, transmitting data at 10 Mbps
  • Standards for 10Mbps, 100Mbps, 1000Mbps
    (Gigabit), and 10G indicate the supported network
  • 10 Gigabit Ethernet runs only over fiber-optic
    cable and only in full-duplex mode

Summary (continued)
  • Token ring networks are reliable, fast, and
  • Capable of transmitting at 4 Mbps or 16 Mbps
  • Macintosh computers use AppleTalk to communicate
  • FDDI is an extremely reliable, fast network
    architecture that uses dual counter-rotating
  • Cable modem technology delivers high-speed
    Internet access to homes and businesses
  • ATM, a high-speed network technology designed
    both for LANs and WANs, uses connection-oriented
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