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Business Data Communications. Chapter Six Backbone and Metropolitan Area Network Fundamentals. Primary Learning Objectives. Define backbone and metropolitan area networks Differentiate between horizontal and vertical network segments Recognize the function of a backbone network protocol

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business data communications

Business Data Communications

Chapter Six

Backbone and Metropolitan Area

Network Fundamentals

primary learning objectives
Primary Learning Objectives
  • Define backbone and metropolitan area networks
  • Differentiate between horizontal and vertical network segments
  • Recognize the function of a backbone network protocol
  • Understand the advantages and disadvantages of distributed and collapsed backbones
  • Explain the concept of backbone fault tolerance
  • List examples of backbone design considerations
  • Identify common backbone problems
  • Describe Switched Multimegabit Data Services
backbone and metropolitan area networks
Backbone and Metropolitan Area Networks
  • A backbone network (BN):
    • Connects other networks of an organization
      • Networks connected are typically LANs
    • Generally spans a building or campus
    • Has its own address
  • A metropolitan area network (MAN):
    • Is often used to connects BNs
    • Generally spans a city
    • Is sometimes viewed as a citywide backbone
    • Has its own address
  • The distinction between BNs and MANs is blurring
horizontal and vertical networks
Horizontal and Vertical Networks
  • Each individual LAN is called a network segment
  • A network segment may be horizontal or vertical
  • Horizontal networks are configured on a single floor
  • Vertical networks are configured on multiple floors
  • Whether horizontal or vertical, network segments are usually connected to each other by means of a backbone network
backbone network protocols
Backbone Network Protocols
  • BNs most often support high traffic demand for connected LANs
    • Therefore a BN generally uses a protocol that provides higher throughput than the protocol used by the connected LANs
  • Gigabit Ethernet:
    • Is a common protocol choice for BNs
    • In its initial form was labeled 802.3z by the IEEE
    • Supports 1 Gbps (billion bits per second)
    • Does not change the underlying Ethernet format
    • Is both half- and full-duplex capable
  • ATM and Frame Relay are also possible BN protocols
distributed and collapsed backbones
Distributed and Collapsed Backbones
  • In addition to having a protocol, BNs have an architecture
  • Two common types of BN architecture are:
    • Distributed
    • Collapsed
  • Factors that influence the BN architecture choice include:
    • Business need
    • Condition of the facility or physical plant
    • The way that users need to communicate
    • Budget
    • Placement of networked devices
distributed backbones
Distributed Backbones
  • “Distributed” implies “in more than one location”
  • A Distributed Backbone:
    • Runs throughout the entire facility
    • Uses a central cable
    • Requires its own protocol
    • Is its own network
    • Is usually connected to network segments, LANs, by switches and/or routers
    • Can have directly connected devices that are part of the BN
distributed backbones1
Distributed Backbones

Each router will have two network addresses

distributed backbones2
Distributed Backbones
  • When configured with multiple routers, may need to pass traffic through several routers for that traffic to reach its final destination
    • Going through several routers can result in traffic delay
    • Internetwork traffic can be expected to increase when more routers are used
  • Require that each network segment have its own cabling and connecting device to the distributed backbone, adding to expense
distributed backbones3
Distributed Backbones
  • Are generally more complex than collapsed backbones, resulting in more complicated:
    • Security
    • Maintenance
    • Monitoring
  • Allow the placing of commonly needed networked devices or resources directly onto the backbone
  • May be the only viable solution for a business, depending on the facility and layout of network segments
collapsed backbones
Collapsed Backbones
  • Use a single central device, namely a router or switch, to which network segments are connected
    • This central router or switch is in essence the backbone
  • Connect network segments to the collapsed backbone, using other hubs, switches, or routers
  • Generally reduce cabling needs, however:
    • Connected devices must be able to support cable segment lengths that span the distance to the collapsed backbone
    • Legacy networks using lower grade UTP may not be collapsed-backbone compatible
collapsed backbones1
Collapsed Backbones
  • Do not require a protocol different from that of connected network segments
    • Having one protocol can make network administration easier
    • However, depending on how the backbone needs to be used relative to traffic demands, having one protocol may not be an advantage
  • Utilize a “backplane”--a high-speed communications bus--in the switch or router
collapsed backbones2
Collapsed Backbones
  • Use fiber optic cabling to connect network segments to a collapsed backbone’s backplane
    • Fiber allows network segments to be widely scattered across a building or campus
  • Might not allow legacy Ethernet networks to utilize the collapsed backbone architecture
  • Pass internetwork traffic through only one device
  • Centralize security, monitoring, and maintenance
  • Can achieve significant cost savings
collapsed backbones3
Collapsed Backbones

Internetwork traffic passes through only one connecting device, in this example a switch, to its ultimate destination

backbone fault tolerance
Backbone Fault Tolerance
  • “Fault tolerance” is the capability of a technology to recover in the event of an error, failure, or some other unexpected event
  • Backbones, because they connect and provide communication to various segments of an enterprise, must be fault tolerant
  • Resource redundancy is a common means of providing fault tolerance
backbone fault tolerance1
Backbone Fault Tolerance
  • Redundant backbones also allow for traffic load balancing
  • By permitting placement of half of all network segments onto one or the other backbone, duplicate backbones allow internetworking traffic to be shared or balanced
  • Duplicating the backbone can be done in whole or in part, based on cost and need
  • Documentation is also part of recovery procedures
backbone design considerations
Backbone Design Considerations
  • Internal versus external wiring
  • Identification and labeling of all backbone networks, devices, wiring
  • Knowledge of collision domain boundaries
    • An enterprise with a mix of Ethernet networks (such as Standard, Fast, Gigabit) might have a mix of collision domains
  • Wiring closets
  • Data centers
common gigabit backbone problems
Common Gigabit Backbone Problems
  • Packet errors
    • Early collision
    • Late collision
    • Runts
    • Giants and jabbering
    • Broadcast storms
common gigabit backbone problems1
Common Gigabit Backbone Problems
  • Cable errors:
    • Near-end cross talk
    • Attenuation
    • Impedance
    • Attenuation to cross talk
    • Capacitance
    • Cable length
common gigabit backbone problems2
Common Gigabit Backbone Problems
  • Network Interface Card errors:
    • Improper configuration – diagnostic software
    • Physical failure
  • Connectivity testing with ping:
    • Based on ICMP
    • Various vendor implementations
    • Echo_Request
    • Echo_Reply
    • Time-to-live
switched multimegabit data services smds
Switched Multimegabit Data Services - SMDS
  • Were designed specifically for MANs
  • Support exchanging data between:
    • LANs in different parts of a city
    • Network segments over a large campus
  • Provide packet-switched datagram delivery
  • Are associated with a common carrier’s SMDS network
  • Require subscribers to pay only when they use the common carrier’s network
in summary
In Summary
  • The distinction between BNs and MANs is blurring
  • BNs are critical in connecting the various network segments of an organization
  • BNs have both a protocol and architecture:
    • Gigabit Ethernet is a popular BN protocol
    • Two BN architectures are distributed or collapsed
  • Fault tolerance is important for the backbone
  • Common Gigabit backbone problems include packet, cable, and NIC errors
  • SMDS is associated particularly with MANs