Post on 21-Dec-2015
transcript
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
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
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 NetworkProtocols
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
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” 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 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 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
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 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 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 Backbones
Internetwork traffic passes through only one connecting device, in this example a switch, to its ultimate destination
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 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
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
Packet errors Early collision Late collision Runts Giants and jabbering Broadcast storms
Common Gigabit Backbone Problems
Cable errors: Near-end cross talk Attenuation Impedance Attenuation to cross talk Capacitance Cable length
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
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
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