Guide to Networking Essentials Fifth Edition by 3n5ulPE

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									Guide to Networking Essentials
         Fifth Edition


           Chapter 7
      Network Architectures
                                           Objectives

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




Guide to Networking Essentials, Fifth Edition           2
                         Objectives (continued)

• Describe the token ring architecture and its
  components
• Describe the AppleTalk network architecture
• Explain the function of Fiber Distributed Data
  Interface
• Describe other LAN and WAN architectures and their
  role in today’s networks




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       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




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                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 collisions
• 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
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                        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



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                                          Contention

• 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
  again
• To organize contention-based networks, two carrier
  access methods were created
      – CSMA/CD
      – CSMA/CA


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      Carrier Sense Multiple Access with
       Collision Detection (CSMA/CD)




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      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 transmit
      – 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 transmit
      – Access point hears transmissions from all devices,
        so it can determine whether it’s okay to transmit
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                                            Switching

• 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
        switch’s capability to handle multiple connections
• Advantages: fairer, centralized management
  (enables QoS), switch can have connection ports
  that operate at different speeds
• Disadvantage: higher cost

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                                    Token Passing




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                                  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 fashion
             • 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
Guide to Networking Essentials, Fifth Edition                      12
                                                Polling




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               Choosing an Access Method




Guide to Networking Essentials, Fifth Edition   14
               Choosing an Access Method
                      (continued)




Guide to Networking Essentials, Fifth Edition   15
               Choosing an Access Method
                      (continued)




Guide to Networking Essentials, Fifth Edition   16
                    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 Hawaii
      – 1972: Robert Metcalf and David Boggs, from Xerox’s
        PARC, developed an early version of Ethernet
             • 1975: PARC released first commercial version (3
               Mbps, up to 100 computers, max. 1 km of total cable)
• DIX developed standard based on Xerox’s Ethernet
  (10 Mbps)
• 1990: IEEE defined the 802.3 specification
      – Defines how Ethernet networks operate at layers 1-2
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                           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 NIC’s MAC address to address frames
      – Ethernet variations are compatible with one another
             • Basic operation and frame formatting is the same
             • Cabling, speed of transmission, and method by which
               bits are encoded on the medium differ



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                              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 important:
      –    How Ethernet accesses network media
      –    Collisions and collision domains
      –    How Ethernet handles errors
      –    Half-duplex and full-duplex communications


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                   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



Guide to Networking Essentials, Fifth Edition                 20
         Collisions and Collision Domains




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                       Ethernet Error Handling

• Collisions are the only type of error for which
  Ethernet automatically attempts to resend the data
• Errors can occur when data is altered in medium
      – Usually caused by noise or faulty media connections
      – 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 don’t match, the data was corrupted
             • Destination computer discards the frame
             • No notice is given to the sender
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           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
  communication)
      – The collision detection circuitry is turned off because
        collisions aren’t possible
      – Results in a considerable performance advantage




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                             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


Guide to Networking Essentials, Fifth Edition      24
                  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
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                                         100BaseTX

• 100BaseTX is the standard that’s 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



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                                         100BaseT4

• 100BaseT4 Ethernet uses all four pairs of wires
  bundled in a UTP cable
• Advantage: capability to run over Category 3 cable
      – 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




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                                         100BaseFX
• 100BaseFX uses two strands of fiber-optic cable
      – Advantages:
             • Impervious to electrical noise and electronic
               eavesdropping
             • Can span much greater distances between devices
      – Disadvantage: far more expensive than twisted-pair
      – Rarely used as a complete 100BaseTX replacement
             • Used as backbone cabling between hubs or switches
               and to connect wiring closets between floors or
               buildings
             • Connect client or server computers to the network
               when immunity to noise and eavesdropping is
               required
Guide to Networking Essentials, Fifth Edition                      28
        100BaseT Design Considerations




Guide to Networking Essentials, Fifth Edition   29
        100BaseT Design Considerations
                 (continued)




Guide to Networking Essentials, Fifth Edition   30
                    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



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                                                10BaseT




Guide to Networking Essentials, Fifth Edition             32
                                                10BaseF




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    Gigabit Ethernet: IEEE 802.3ab and
             802.3z Standards
• 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




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                                         1000BaseT




Guide to Networking Essentials, Fifth Edition        35
                                       1000BaseLX




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                                       1000BaseSX




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                                      1000BaseCX




Guide to Networking Essentials, Fifth Edition      38
      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 (SANs)
      – Will be the interface for enterprise-level servers


Guide to Networking Essentials, Fifth Edition               39
      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
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                   What’s 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 today’s CPUs can transfer data to memory
      – This level of speed has major implications for the
        entertainment industry and many other areas
Guide to Networking Essentials, Fifth Edition                     41
                         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

Guide to Networking Essentials, Fifth Edition             42
                                    Ethernet 802.3




Guide to Networking Essentials, Fifth Edition        43
                                    Ethernet 802.2

• Ethernet 802.2 frames comply completely with the
  Ethernet 802.3 standard
• The IEEE 802.2 group didn’t address Ethernet,
  only the LLC sublayer of the OSI model’s layer 2
      – Since Novell had already decided to use the term
        Ethernet 802.3 to describe Ethernet raw, it’s
        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

Guide to Networking Essentials, Fifth Edition              44
                                   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 frame’s data section




Guide to Networking Essentials, Fifth Edition        45
                                           Ethernet II




Guide to Networking Essentials, Fifth Edition            46
    Wireless Ethernet: IEEE 802.11b, a,
                  and g
• AP serves as the center of a star topology network
• Stations can’t 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
Guide to Networking Essentials, Fifth Edition                      47
               The Token Ring Architecture




Guide to Networking Essentials, Fifth Edition   48
                           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 protocols
                  – 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
Guide to Networking Essentials, Fifth Edition                         49
                                          Beaconing




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                       Hardware Components
• A hub can be a multistation access unit (MSAU)
  or smart multistation access unit (SMAU)
• IBM’s 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 hubs
             • IBM allows connecting 33 hubs
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  Cabling in a Token Ring Environment




Guide to Networking Essentials, Fifth Edition   52
               The Token Ring Architecture
                       (summary)




Guide to Networking Essentials, Fifth Edition   53
                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 device’s
  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
Guide to Networking Essentials, Fifth Edition              54
                                            LocalTalk

• 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




Guide to Networking Essentials, Fifth Edition                         55
                    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 NIC
      – 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


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    The Fiber Distributed Data Interface
           (FDDI) Architecture




Guide to Networking Essentials, Fifth Edition   57
    The Fiber Distributed Data Interface
      (FDDI) Architecture (continued)




Guide to Networking Essentials, Fifth Edition   58
                        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)


Guide to Networking Essentials, Fifth Edition             59
                     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

Guide to Networking Essentials, Fifth Edition              60
                   Cable Modem Technology




Guide to Networking Essentials, Fifth Edition   61
               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

Guide to Networking Essentials, Fifth Edition                     62
                      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 user’s computer sends very little traffic
      – User connects to service provider through a modem
      – Service provider sends data by satellite to the user’s
        home at speeds up to 400 Kbps
      – E.g., service offered by DirectTV, through its
        DirectPC add-on products
Guide to Networking Essentials, Fifth Edition                63
   Asynchronous Transfer Mode (ATM)

• High-speed network technology for LANs and WANs
      – Connection-oriented switches
             • Dedicated circuits are set up before communicating
      – Data travels in fixed-size 53-byte cells (5 byte-header)
             • 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
Guide to Networking Essentials, Fifth Edition                       64
       ATM and SONET Signaling Rates




Guide to Networking Essentials, Fifth Edition   65
    High Performance Parallel Interface
                 (HIPPI)
• HIPPI (late 1980s): high-speed interface developed
  for supercomputers and high-end workstations
      – 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 aren’t often found in typical corporate networks
Guide to Networking Essentials, Fifth Edition                                66
                                            Summary
• 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 mediums
           • 10 Gigabit Ethernet runs only over fiber-optic cable and
             only in full-duplex mode
Guide to Networking Essentials, Fifth Edition                       67
                           Summary (continued)

• Token ring networks are reliable, fast, and efficient
     – 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 rings
• 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
  switches
 Guide to Networking Essentials, Fifth Edition            68

								
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