Transcript Chapter Six

Business Data Communications
Chapter Six
Backbone and Metropolitan Area
Network Fundamentals
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
Chapter Six
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Primary Learning Objectives
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone and Metropolitan Area
Networks
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A backbone network (BN):
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Connects other networks of an organization
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Generally spans a building or campus
Has its own address
A metropolitan area network (MAN):
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Networks connected are typically LANs
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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Horizontal and
Vertical Networks
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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A Horizontal Network
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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A Vertical Network
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Connecting to a backbone
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone Network
Protocols
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BNs most often support high traffic demand for
connected LANs
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Gigabit Ethernet:
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Therefore a BN generally uses a protocol that provides
higher throughput than the protocol used by the
connected LANs
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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed and
Collapsed Backbones
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In addition to having a protocol, BNs have an
architecture
Two common types of BN architecture are:
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Distributed
Collapsed
Factors that influence the BN architecture choice include:
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Business need
Condition of the facility or physical plant
The way that users need to communicate
Budget
Placement of networked devices
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed Backbones
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“Distributed” implies “in more than one location”
A Distributed Backbone:
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed Backbones
Each router
will have two
network
addresses
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed Backbones
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When configured with multiple routers, may need to
pass traffic through several routers for that traffic to
reach its final destination
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed Backbones
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Are generally more complex than collapsed backbones,
resulting in more complicated:
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed Backbone with
a Directly Connected DB Server
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Collapsed Backbones
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Use a single central device, namely a router or switch,
to which network segments are connected
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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:
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Collapsed Backbones
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Do not require a protocol different from that of
connected network segments
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Collapsed Backbones
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Use fiber optic cabling to connect network segments to
a collapsed backbone’s backplane
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Collapsed
Backbones
Internetwork traffic
passes through only one
connecting device, in this
example a switch, to its
ultimate destination
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Distributed versus Collapsed
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone Fault Tolerance
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“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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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A Simplified Redundant Backbone
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone Fault Tolerance
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone Design
Considerations
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Internal versus external wiring
Identification and labeling of all backbone networks,
devices, wiring
Knowledge of collision domain boundaries
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An enterprise with a mix of Ethernet networks (such as
Standard, Fast, Gigabit) might have a mix of collision
domains
Wiring closets
Data centers
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone Design
Considerations
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Backbone Design
Considerations
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Wiring Closet Design
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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A few Good Tools
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Common Gigabit
Backbone Problems
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Packet errors
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Early collision
Late collision
Runts
Giants and jabbering
Broadcast storms
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Common Gigabit
Backbone Problems
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Cable errors:
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Near-end cross talk
Attenuation
Impedance
Attenuation to cross talk
Capacitance
Cable length
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Common Gigabit
Backbone Problems
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Network Interface Card errors:
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Improper configuration – diagnostic software
Physical failure
Connectivity testing with ping:
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Based on ICMP
Various vendor implementations
Echo_Request
Echo_Reply
Time-to-live
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Common Gigabit
Backbone Problems
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Switched Multimegabit
Data Services - SMDS
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Were designed specifically for MANs
Support exchanging data between:
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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In Summary
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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:
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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
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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