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NETWORKING ESSENTIAL
Interconnection of computers
To share resources (files, printers, modems, fax machines)
To share application software (MS Office)
Increase productivity (make it easier to share data amongst users)
Connected using a wide variety of different Cabling types.
Can share files, exchange mail, schedule meetings, send faxes and share printers
LAN- The Local Area Network
The typical characteristics of a LAN
Physically limited (< 2km)
High bandwidth (> 1mbps)
inexpensive cable media (coax or twisted pair)
data and hardware sharing between users
owned by the user
Five Sub-system of Cabling System
Equipment Room
Back Bone Cabling
Telecommunications Closet (TC)
Horizontal Cabling
Work Area
Back Bone Cabling System
100-ohm unshielded twisted pair (not exceeding 100 meters per segment)
150-ohm shielded twisted pair (not exceeding 100 meters per segment)
50-ohm coaxial cable (not exceeding 185 meters per segment)
62.5/125um multi-mode fiber (not exceeding 2,000 meters)
Types of Cables
Cable is used to interconnect computers and network components together.
Twisted Pair – UTP & STP
Coaxial
Fiber Optic
Twisted Pair
Twisted Pair:
cable is readily accepted as the preferred solution to cabling. It provides support for a range of speeds and configurations, and is widely supported by different vendors.
Shielded twisted pair:
Used as a special braided wire which surrounds all the other wires, which helps to reduce unwanted interference.
Twisted Pair - Features
used in token ring (4 or 16MBps), 10BaseT (Ethernet 10MBps), 100BaseT (100Mbps)
reasonably cheap
reasonably easy to terminate [special crimp connector tools are necessary for reliable operation
UTP often already installed in buildings
UTP is prone to interference, which limits speed and distances
low to medium capacity
medium to high loss
Co Axial Cables
medium capacity
Ethernet systems (10Mbps)
slighter dearer than UTP
more difficult to terminate
not as subject to interference as UTP
care when bending and installing is needed
10Base2 uses RG-58AU (also called Thin-Net or Cheaper Net)
10Base5 uses a thicker solid core coaxial cable (also called Thick-Net)
Fiber Optic
expensive
used for backbones [linking LAN’s together] or FDDI rings (100Mbps)
high capacity [100Mbps]
immune to electromagnetic interference
low loss
difficult to join
connectors are expensive
long distance
REPEATERS
EXTEND network segments.
They amplify the incoming signal received from one segment and send it on to all other attached segments.
Allows the distance limitations of network cabling to be extended.
There are limits on the number of repeaters which can be used
allow isolation of segments in the event of failures or fault conditions
increase traffic on segments
have distance limitations
limitations on the number that can be used
propagate errors in the network
cannot be administered or controlled via remote access
cannot loop back to itself (must be unique single paths)
no traffic isolation or filtering
HUBS
There are many types of hubs. Passive hubs are simple splitters or combiners that group workstations into a single segment, whereas active hubs include a repeater function and are thus capable of supporting many more connections.
Nowadays, with the advent of 10BaseT, hub concentrators are being very popular. These are very sophisticated and offer significant features which make them radically different from the older hubs which were available during the 1980's
utilize existing cabling and other network components
becoming a low cost solution
BRIDGES
Bridges interconnect Ethernet segments – FEATURES:
increase the number of attached workstations and network segments
since bridges buffer frames, it is possible to interconnect different segments which use different MAC protocols
since bridges work at the MAC layer, they are transparent to higher level protocols
by subdividing the LAN into smaller segments, overall reliability is increased and the network becomes easier to maintain
used for non routable protocols like NETBEUI which must be bridged
help localize network traffic by only forwarding data onto other segments as required (unlike repeaters)
BRIDGES - Disadvantages
The buffering of frames introduces network delays
Bridges may overload during periods of high traffic
Bridges which combine different MAC protocols require the frames to be modified before transmission onto the new segment. This causes delays
In complex networks, data may be sent over redundant paths, and the shortest path is not always taken
Bridges pass on broadcasts, giving rise to broadcast storms on the network
operate at the MAC layer (layer 2 of the OSI model)
can reduce traffic on other segments
broadcasts are forwarded to every segment
most allow remote access and configuration
often SNMP (Simple Network Management Protocol) enabled
loops can be used (redundant paths) if using spanning tree algorithm small delays introduced
fault tolerant by isolating fault segments and reconfiguring paths in the event of failure
not efficient with complex networks
redundant paths to other networks are not used (would be useful if the major path being used was overloaded)
shortest path is not always chosen by spanning tree algorithm
ROUTERS
Packets are only passed to the network segment they are destined
They work similar to bridges and switches in that they filter out unnecessary network traffic and remove it from network segments
Routers generally work at the protocol level.
Routers were devised in order to separate networks logically.
Example:: A TCP/IP router can segment the network based on groups of TCP/IP addresses. Filtering at this level (on TCP/IP addresses, also known as level 3 switching) will take longer than that of a bridge or switch which only looks at the MAC layer
use dynamic routing
operate at the protocol level
remote administration and configuration via SNMP
support complex networks
the more filtering done, the lower the performance
provides security
segment networks logically
broadcast storms can be isolated
often provide bridge functions also
more complex routing protocols used [RIP]
Network Topology
The choice of topology is dependent upon
Type and number of equipment being used
Planned applications and rate of data transfers
Required response times
Cost
There are FOUR major competing topologies
Bus
Ring
Star
FDDI
Bus Topology
All workstations connect to the same cable segment
Commonly used for implementing Ethernet at 10mbps
The cable is terminated at each end
Wiring is normally done point to point
A faulty cable or workstation will take the entire LAN down
two wire, generally implemented using coaxial cable during the 1980's
Bus Topology
Bus Topology - Comparison
Advantages
Easy to implement
Low cost
Disadvantages
Limits on cable length and Workstation numbers
Difficult to isolate network faults
A cable fault affects all workstations
As the number of workstations increase, the speed of the network slows down
Ring Topology
Workstations connect to the ring
Faulty workstations can be bypassed
More cabling required than bus
The connectors used tend to cause a lot of problems
Commonly used to implement token ring at 4 and 16mbps
Four wire, generally STP or UTP
Ring Topology
Ring Topology - Comparison
Advantages
Cable failures affect limited users
Equal access for all users
Each workstation has full access speed to the ring
As workstation numbers increaseperformance diminishes slightly
Disadvantages
Costly Wiring
Difficult Connections
Expensive Adaptor Cards
Star Topology
All wiring is done from a central point (the server or hub)
Has the greatest cable lengths of any topology (and thus uses the most amount of cable)
Generally STP or UTP, four wire
Star Topology
Star Topology - Comparison
Advantages
Easy to add new workstations
Centralized control
Centralized network/hub monitoring
Disadvantages
Hub failure cripples all workstationsconnected to that hub
Hubs are slightly more expensive than thin-Ethernet
FDDI TopologyFiber Distributed Data Interface
100mbps
Normally implemented over fiber optic
Dual redundancy built in by use of primary and secondary ring
Automatic bypassing and isolation of faulty nodes
FDDI TopologyFiber Distributed Data Interface
Peer To Peer (Windows Workgroups)
The advantages of peer to peer networks are,
Workstations make available their resources
No centralized server required
Security responsibility of each workstation
Each station runs same software
Each computer has its own accounts database
Cheap and easy to set up for small groups
Workgroups
A workgroup is a collection of computers which are logically grouped together for a common purpose. In any organization, logical workgroups exist, like sales, marketing, accounts, salaries and support. By allowing like people to share their files and resources, it assists the way in which people work and leads to increased productivity.
A workgroup is a Peer to Peer network
Resources in a workgroup
Computers in a workgroup make available resources for other members of the workgroup to use. Features of resources are,
a typical resource is a file, directory or printer
resources given names (share names)
resources assigned permissions (like a password)
permissions can be read-only or full
any user knowing the password can access the resource
collection of computers organized for a specific purpose (suits the needs of the group)
is peer to peer
no centralized administration
each computer has its own accounts database and permission lists
share files, printers and applications
each computer identified by unique name (normally person using that computer)
Novell Netware
The features of a Novell Netware network are
workstations communicate with a host computer
security enforced by server
requires a high end machine as a server
resources on workstations (disks) not available
server runs special networking software
each server has its own accounts database
as the number of servers increase, administration becomes more difficult
Domains
A domain is a logical grouping of one or more Windows NT server based computers that allow them to be managed as a single unit. Using domains, the administrator creates one account for each user. Users logon to the domain, not the individual servers in the domain.
are logical groupings of Windows NT Server based computers
provide a single network logon to server based resources
simplify administration by providing a single point of administering user accounts and security policies
provide backup systems [redundancy] to take over in the event of a PDC going off-line
replicate the accounts database to backup domain controllers
Dynamic Host Configuration Protocol DHCP
BOOTP: Disadvantages
The problems with the BOOTP approach is that
it relies upon static entries in a BOOTP table
if there is no entry for the workstation, the workstation cannot connect to the network
it requires administration in keeping the table up to date
IP addresses are allocated and cannot be used for another computer even if not currently in use
easy to run out of available IP addresses as the network grows
DHCP
a user can pick an IP address which conflicts with one already assigned to another computer
wrong values causes the computer to function incorrectly
moving the computer to a different part of the network requires allocation of a new IP address
DHCP - Advantages
IP addresses can be re-used, when the lease expires they are returned to the available pool
eliminates errors in configuration as subnet masks, DNS server and gateway IP addresses can be included in the lease
easy to move computers to another part of the network
require little or no intervention once configured [no tables to maintain]
setting up clients is simple [just enable it as a DHCP client], no need to know what the correct IP addresses are for things like subnet mask, gateway, wins servers or DNS servers
IP addresses conflicts are eliminated
Windows Internet Naming Service - WINS
This service was designed to eliminate the need for broadcasts to resolve computer names to IP addresses. Previously, to find the address of a computer, a network broadcast packet was sent to all computers on the network. This broadcast contained the name of the computer which needed to be contacted. Each computer looked at the broadcast packet. The computer that recognized that the packet was destined for it responded with its IP address.