Transcript LAN Wiring & Physical Interfaces

LAN Wiring & Physical
Interfaces
Lecture 6
Network Interfaces
Every device has some form of a
network interfaces.
A PC has a Network Interface Card
(NIC).
The Cisco 2501 routers have an
Attachment Unit Interface (AUI)
connection.
NICs
NICs are dependent on what type of
topology exists in the LAN.
For example, an Ethernet NIC can’t be
used with a Token Ring NIC, and viceversa.
NICs (cont.)
A NIC performs most of the network-level
operations in order to reduce CPU overhead.
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Receives incoming packets
Storage of frames
Actively listens on the network
A NIC is exactly the same as any other I/O
device to the CPU. Read and write from the
data bus with certain addressing.
NIC (cont.)
Ethernet NIC
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RJ-25
BNC (British Naval
Connector)
AUI
ST/SC for fiber
The NICs pictured at
the right have RJ-45
(top) and ST (bottom)
connectors.
NIC (cont.)
In addition to providing the physical
connection to the network, the NIC also
deals with hardware addressing.
All LAN traffic ultimately deals with
hardware addresses. The NIC will only
read (copy) packets destined for it’s
own address.
Broadcasted packets are also read.
Physical Hardware Addressing
Three separate types of addressing occur:
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Static – hardware manufacture specifies the
address, and it is unchangeable.
 Advantages: Ease of use, and permanence.
 Disadvantages: manufactures must keep track of usage.
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Configurable – the end user can modify the
address through software or switches on the card.
 Advantages & Disadvantages: A mix of above and below.
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Dynamic – random numbers are tried until one is
found that is unused.
 Advantages: smaller HW addresses!
 Disadvantages: lack of permanence, potential conflict.
Broadcasting
Broadcasting refers to the concept that
a certain type of packet can be
generated that is received by all
hardware attached on the network.
Useful for finding printers, file shares,
etc.
Broadcasting usually uses a specific
broadcast address for such schemes.
Thick Ethernet Wiring
Thick Ethernet Specifications
50 Ohm coaxial cable, 0.4” thick.
10base5 – 10Mbps, 500m segments.
Ends must be terminated.
AUI connectors.
“Vampire” taps / Transceivers.
Thin Ethernet Wiring
Thin Ethernet Specifications
50 Ohm coaxial cable, 0.2” thick.
10base2 – 10Mbps, 185m segments.
Ends must be terminated.
BNC connectors.
Transceivers are integrated into the
NIC.
Twisted-Pair Ethernet Wiring
Twisted-Pair Ethernet
Specifications
Twisted-pair cable.
10baseT- 10Mbps, 100m segments.
100baseT – 100Mbps, 100m segments.
RJ-45 connectors.
Hubs/Switches required.
Extending the LAN
Hardware has been developed that
“boosts” the signal so you can create
larger LAN segments.
Fiber Extensions
Repeaters
Bridges
Switches
Hubs
Why Extend the LAN?
Distance limitation is the most common
hurdle for LAN design.
You always want more. More computers,
more people, more access to shared
resources.
Users want access to shared resources. It
doesn’t make economical sense to have a
single printer for each segment, for example.
Fiber Modems
Fiber modems are used to connect a
single remote computer to an
established LAN.
Effective, since fiber is low latency, high
bandwidth.
Repeaters
Repeaters are just as they sound. They
connect two segments together as one,
and just repeat the traffic of one
segment and forward it on to the
second.
Repeaters are unintelligent. What you
get on one segment is what you get on
the other. No more, no less.
Repeaters (cont.)
A repeater as it’s commonly used. Hubs
and switches have repeaters built-in, so
you can connect multiple segments
together.
IEEE designates how many segments
may be connected together.
Repeaters (cont.)
Repeaters have several drawbacks:
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They expand the collision domain.
Noise from one segment flows on to the
second segment.
Any electrical problems that occur on one
segment will be sent to the second
segment!
Another Common Use of
Repeaters
Bridges
Bridges are smarter repeaters.
Main difference: bridges verify that the
frame is intact and valid before it is
forwarded on to the second segment.
This provides a higher quality of
service. Problems on one segment do
not affect the other segment.
Bridges (cont.)
Bridges also have the attractive feature of
“frame filtering.”
A frame will only be forwarded to the second
frame if the destination computer is not on
the first frame. This reduces chatter on the
combined segments.
Bridges that learn which computers are on
which segments are called “adaptive” or
“learning” bridges.
Adaptive Bridges
When a bridge boots, it does not have any
information about computers on the
segments that it connects.
After a long time, the bridge reaches a
steady-state where it has developed a
mapping of which computers are on which
segments.
At this steady-state, extra frames on the
segments is cut to a minimum. In this state,
maximum parallelism is achieved.
Bridging Between Buildings
Switching
Switches (cont.)
Switches allow for independent, parallel
communications between ports on the
switch.
Switches are combined with hubs for a
cost-effective method of providing
equal-access for all users.