Transcript MIS 430 Part III Chapter 6

MIS 430 Part III
Local Area Networks
Chapter 6
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Background
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95+% of LANs are Ethernet
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Traditional (802.3)
Switched
Wireless (802.11 etc)
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Use LANs for
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Information Sharing
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Data Files, Email, Web pages
Resource Sharing
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Printers, access to specialty hardware
Access to software applications
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We use Keyserver to “meter” software to users
Beware illegal activities: SPA “software police”
http://www.spa.org/piracy/default.asp SW Publishers
Association
Gateway to other networks
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Types of LAN
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Dedicated Server
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File, Web, Email, Database, Print servers
Remote access server (RAS) for ISP
Sophisticated Network SW
Peer to peer server
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Regular client PC serves files and printers
Internet Connection Sharing (ICS)
Limit to < 10 computers unless inactive
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Day in the Life: LAN Admin
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Arrive before others: check network
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Run routine diagnostics
Check daily logs
Do daily backup (incremental is short)
Check for Windows critical security updates, antivirus updates
Respond to user emails about problems
Plan for future upgrades, SW rollouts, security
improvements
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I. Basic LAN Components
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NIC-network interface card
Network cables
Network hub (switch or router)
Network operating system (client,
server versions)
Client computers
Server (can be a client)
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Network Interface Card (NIC)
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Built into motherboard or as an add in card
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PCI bus versus ISA bus (expansion slot)
PC Card – plugs into laptop PC Card slot on side
and sticks out (remove when putting in the case)
miniPCI card – fits inside a laptop (~wireless)
Speed: 10 vs 10/100 vs 100 Mbps
Connector: RJ-45 vs BNC or AUI
Plug and Play – computer configures NIC
vs. program via SW vs. set jumper switches
Boot PROM – allows booting from server
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Network Cables
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Most use UTP – unshielded twisted pair
Also have coax (BNC) and fiber optic
See Tech Focus 6-1 p. 192 for cables
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Cat 5 and 5e: 100 Mbps twisted pair
Cat 6: 250 up to 1000 Mbps (1 “gigabit”)
RG-58 coax 802.2 (RG-59 is TV cable)
RG-8 coax 802.5 (more expensive than RG-58)
X3T9.5 fiber optic (FDDI)
Price/foot in table; add cost of connectors
Cat 5 wire: 123 6 (Bl, Bl/Wh, Or, Or/Wh)
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Cable Management, p. 193
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Terry College of Bus, U of Georgia
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No cable plan; a mess!
Nobody knew where the cables and hubs
were: had to crawl around ceiling wires
Found asbestos in ceiling! Had to fix it …
…Univ spent $400K to install Cat 5 to every
office; installed fiber-optic BN between
network segments
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Network Hub: Fig 6.2 p. 193
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Hub repeats signal to other nodes
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Dumb hub: only repeats
Smart hub: managed (SNMP) and program
Switching Hub: switches signal only to
destination (aka switch)
Measure: # of ports
Hub speed: 10, 10/100, or 100 Mbps
Router often combines switched hub
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Network Operating System
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NOS – controls the network
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One set runs on server (Novell Netware; Windows
Server: NT, 2000, 2003; Unix)
One set runs on client (Windows 9x, ME, 2000, XP,
Mac, etc.)
NOS (server) replaces regular server
operating system
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Provides file sharing, print sharing, web service,
FTP service, email service, etc.
Windows 2003 looks remarkably like Windows XP
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Network Profiles
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Gives the resources that are shared on
the network
User profile for each person shows what
resources can be accessed
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II. Ethernet (IEEE 802.3)
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Traditional (shared) Ethernet
Topology – layout of network
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Logical versus physical topology
Bus
Star – most prevalent
Loop or ring
Hybrid
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Ethernet Media Access Control
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Contention: CSMA/CD – carrier sense
multiple access with collision detection
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So long as nobody is broadcasting on
network, a node can transmit
If two packets collide, jamming occurs and
the two parties wait a random time and
redo
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Types of Ethernet
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See figure 6-5 p. 199
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10Base-2 (10=10 Mbps, Base=baseband, and –2
is coaxial cable
10Base-T = 10 Mbps twisted pair
100Base-T= 100 Mbps UTP
1000Base-T = 1 Gbps Ethernet
40GbE = 40 Gbps fiber
Some use 10/100 which switches to match speed
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III. Switched Ethernet
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Switch replaces hub – only transmits packet
to desired node, not all nodes
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Greatly enhances the capacity of cable because
switch buffers packets, allowing transmissions on
all lines ~ simultaneously
Helpful as #users increases
10/100 switch allows mixture of 10 and 100 Mbps
Switch uses forwarding table (like routing
table) which builds dynamically
This is a layer-2 switch (at data link layer)
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Switching Modes
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For first few minutes, works like a hub until it
identifies where clients connect
Cut through switching
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Store and forward switching
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Sends pack immediately before checking CRC
Process packet normally after CRC
Fragment-free switching
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Send after reading 1st 64 bytes
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V. Best Practice LAN Design
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Effective Data Rates depend on ..
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Nominal data rate in physical layer
Error rate (# of retransmissions)
Efficiency of data link layer protocols used
Efficiency of media access control methods
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CSMA/CD work well in low-volume subnets (the elbow
curve – fig 6.7 p. 205)
Thus keep utilization < 50-60%!
Switched ethernet works better than hub
See Fig 6.8 p. 207 for effective data
rates/user
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Recommendations
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Costs drop after new technology appears –
10BaseT and 100BaseT are now cheap!
Very small networks: 10BaseT
Switched 10BaseT over Cat 5e cable is fine
unless high volume data (streaming) is done
Hi vol: switched 100BaseT on Cat 5e or fiber
optic cables
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VI. Improve Network Performance
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Software –
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Basically fine tune network settings in NOS: disk
cache, buffer space, etc.
Add a new protocol that is faster
Hardware –
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Buy another (or faster) server
Increase memory in server
RAID drive or higher performance disk
NIC: get server version NIC with high performance
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Improve Network Performance
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Improve circuit capacity
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Upgrade to 100 Mbps hub
Upgrade to switched hub
Split into 2 or more subnets and add a
server NIC for each network segment
Move high demand clients to different
segments
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Improve Network Performance
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Reduce network demand
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Move files to client computers (e.g., heavily
used applications)
Use disk cache SW on clients to reduce
need to access files on servers
Adjust time when users work – busiest
times are 9 AM and right after lunch:
FlexTime is very popular in IT
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