[ Note: please first read the following 500 words and answer the
question below]

Q1.) Evaluate current transmission methods and media and assess
suitability of each for a particular cummunications channel?


The broad criteria for selection of any network component are
explained below:
1. Strategic criteria: 
1.1 Organization Fit – define and match the features, benefits, and
risks inherent in network technology to the needs and capacities of
the organization and people it serves
1.2 Appropriate Technology – choose and use the type of network
technology that meets a given application in the most efficient and
effective manner
1.3 Usable Design – select, modify, and use technology that meets the
need of the users and the organization
2. Tactical criteria: 
2.1 Manageable and Supportable Technology – this means that the
networks or systems can be managed and supported by the people using
the technology.
  
2.2 Interoperable – it should be possible for one type of network or
system to communicate or work with another regardless of vendor
2.3 Scalable – minimal change should be effected in current
configurations to accommodate growth
2.4 Flexible Management – the network resources should be monitored
and managed strategies that leverage software-based remote management
tools with other resources
2.5 Portable – the products should support several hardware platforms
with different versions or should have built-in capabilities for
switching between them
2.6 Secure – the security of the LAN should not be compromised by flaw
in the interconnection device
 
The generic guidelines for selecting any of the interconnection
devices are as follows:
1. Switch or router? A router supports only one communication at a
time; a switch, on the other hand, enables simultaneous multiple
communications by allowing messages to be routed from one port to
another
2. Bridge or router? Routers are more intelligent than bridges in that
they can constantly adjust to the changing network conditions.
However, this also makes them more processing-intensive and also
slower than bridges
3. Hub or switch? The bandwidth available to network users is the
major differentiating factor between hubs and switches. For small
networks, a hub may be the best choice. If the users of the network
require more bandwidth, using a switch will increase the efficiency of
the network.
 
The specific criteria in choosing LAN interconnection devices are as
follows:
a.) Hub  
Hubs are used to extend the reach of your network. They should satisfy
the following evaluation criteria:
Multiple topology/media support – a hub should be able to support
mix-and-match of various LAN technologies, e.g., Ethernet, ATM, etc.
Fault tolerance – the system and the productivity of the network
should not be negatively affected if any hub component fails
Slot independence – the hub should not impose any limitations as far
as installation of a module in a slot is concerned, i.e., we should be
able to install any module in any slot
High-speed backplanes – their capacity determine the overall capacity
of the hub as they can carry a large amount of data, address, etc.
Routing and bridging – the ability to integrate bridging and routing
plays an important role in smaller networks, as it eliminates a need
for external components
Latency – by latency, we mean the time taken by a hub to forward a
data packet that it has received. Common sense suggests that a lower
latency rate will lead to a faster performance
Management – these advanced management facilities (generally found in
modular hubs) allow the networks to managed with more control and
greater flexibility. The features to be compared include utilities,
monitoring functionality, and training costs
Scalability – it refers to the capability to expand a network with
minimal changes. We should be able to integrate products from previous
with new model lines; it should also be easy for us to migrate to new
platforms with minimal disruption to existing operations
 
b.) Repeater  
Repeaters are nowadays embedded in the other LAN interconnection
devices and therefore their selection criteria are not covered here.
 
c.) Switch   
The following criteria should be kept in mind while selecting a
switch:
1. Ensure that it doesn't drop frames 
2. Check the switch latency 
3. Use cut-through switches for time-sensitive applications; otherwise
store-and-forward switches will suffice
4. Use dedicated switched ports for multimedia stations 
5. Try to keep a 1:1 ratio between demand and resource. Or, provide
multiple lines into one server
6. Determine, in advance, the percentage of bad frames in the network
(baselining) before installing switch
7. Get switches with remote monitoring capability embedded in ports to
save time and money in the long run
8. Be careful while placing switches having “back pressure” control
mechanism into the network
 
d.) Bridge  
Bridges transmit data between dissimilar networks. 
 
e.) Gateway   
 
f.) Router 
Routers increase the speed and the efficiency of data transmission.
The following are the evaluation criteria for choosing routers:
1. WAN Ports – a WAN port is required for each physical connection to
a service provider. The number of WAN ports on the router should be
adequate for satisfying the present needs keeping in mind scalability.
A single port is adequate to connect to the Internet, but a second
port is required to establish a backup link for reliability. For
connecting multiple sites with leased lines, you will need a port for
each link
2. Bandwidth (Line Speed) – the router must be able to support the
expected traffic, with some room for growth or expansion. The
aggregation of traffic at regional or central sites resulting from
connections to multiple remote locations should be taken into
consideration. Also take into account the compression capabilities of
the router
3. Supported Protocols – choose a router that supports all the
protocols needed for the protocols and the services chosen for the
network

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Request for Question Clarification by aditya2k-ga on 28 Apr 2003 13:20 PDT

Hi vergita,

I've worked on your answer for a couple of hours now, and would like
to know if I am on the right track. By transmission methods, I'm
presuming you mean broadband & baseband. By media : coaxial cable,
twisted pair copper wires etc... As far as communication channels are
concerned....FDM and TDM. Specifically, which communication channel
are you interested in?

Cheers,
Aditya.

---

Request for Question Clarification by aditya2k-ga on 28 Apr 2003 13:24 PDT

A request to other researchers ... my answer to this question is 60%
done, so please allow me to complete it, just in case the lock expires
before me refreshing it.

---

Clarification of Question by vergita-ga on 30 Apr 2003 08:39 PDT

all i want is a good eveluation from the 500 hundred words that ive
noted
what ever is neccessary even send me the 60% that u have completed i
will be great full with that if u could do it before 1/5/03.

thanks
 vergita

---

Request for Question Clarification by dogbite-ga on 30 Apr 2003 13:24 PDT

I'm curious about the status of this
  question.  Are you still working on
  it, aditya2k-ga?  If not, I might
  want to look into it.

            dogbite-ga

---

Request for Question Clarification by richard-ga on 30 Apr 2003 14:31 PDT

Dogbite:

aditya2k is in a much different timezone than yours.
You should assume that he will renew his lock and complete the
question later this evening.

-Richard

---

Request for Question Clarification by dogbite-ga on 30 Apr 2003 15:34 PDT

Sure thing -- I was just checking
because vertiga seemed to be
anxious for an answer.

        dogbite-ga

Hi Vergita,

Good day and thanks for your question. 
You are one of the prolific customers of this service.

Two methods are used to transmit signals between nodes - 
baseband (digital transmission of digital signals) and 
broadband (analog transmission of digital signals). 
Majority of networks use banseband transmission except for 
B-ISDN networks (fiber optics as the medium of transmission), 
which use broadband transmission.

Broadband is frequently used as a synonym for "high-speed" 
when discussing connectivity ways to the Intetnet. However, 
baseband is no slower. There is nothing to suggest that one 
is faster than the other.

The main advantage of baseband transmission is that it is 
simple. Digital signals are typically represented using a 
scheme much like on-off keying within a computer. To convert 
such signals into baseband form for transmission is relatively 
simple. Reception is also simple. In contrast, broadband 
transmission requires circuitry to generate and modulate a 
carrier wave for transmission and extraction of the desired 
signal on reception. 

The advantage of broadband transmission is that several signals 
can be simultaneously sent through a single medium without 
interference, because the range of frequencies in the signal 
can be altered by varying the carrier wave frequency. This makes 
Frequency Division Multiplexing (FDM) possible.

When FDM is used, bandwidth is not increased. It divides it up 
among a large number of signals. FDM is NOT possible in 
baseband. Using FDM, multiple transmissions may be concurrently 
sent over a single cable/fiber.

Transmission using baseband involves using more electronic 
equipment along it's path. The signals is evidently attenuated 
after 1km. However, broadband signals can be transmitted for 
long distances before attenuation. 

If an organization uses the tree topology, broadband is 
recommended. Both baseband and broadband can be used for bus 
topologies.

There is a new type of transmission - wireless transmission 
(using radio waves, microwaves etc..). However, availability of 
the same is very limited and it's still in the infant stage.

In a nutshell, baseband is typically used for networks where a 
high bandwidth is not required. Equipments has been standardized 
based on widespread use, and data is transported in a standardized 
common digital format. However, its bandwidth is less than that of 
a broadband  network. Broadband transmission is used in networks 
that transport information-intensive signals that require great 
bandwidth. Typically, these are networks which maintain large 
pictures and files, and electronic libraries. It allows full 
interactivity. It has a much greater LAN cost when compared to 
baseband. Furthermore, since this is a relatively new technology 
which is not widely used, equipment is not standardized, thus 
making way for potential equipment compatibility problems.

The various media through which we can transmit information are
* Conducted/Guided Media
  - Electrical Conductors: Wires and Coaxial Cable
  - Light Conductors: Fiber Optic Cable 
* Radiated/Unguided Media
  - Low Frequency: Radio
  - Microwave Frequency:  Microwave & Satellite
  - High Frequency: Infrared Transmission 

In the wire types, we have single conductor, twisted pair, & 
shielded multiconductor bundles. The have a large installation 
base and are available at reasonable cost. They have a relatively 
low bandwidth, however, recent LAN speeds in the 100 Mbps range 
have been achieved. They are susceptible to external interference, 
however, shielding can reduce external interference. Both analog 
and digital signals can be transmitted. An amplifier is required 
every 5 to 6 km for analog signals and every 2 to 3 km for digital 
signals.

Coaxial cables fall at the low end of the cost spectrum. Typical 
bandwidth is 10Mbps. All copper media are sensitive to EMI, although 
the shield in coax makes the cable fairly resistant. Coaxial cables, 
however, do radiate a portion of their signal, and electronic 
eavesdropping equipment can detect this radiated signal.

Shielded Twisted Pair (STP) cables cost more than thin coaxial or 
unshielded twisted-pair cable. It is less costly, however, than thick
coax or fiber-optic cable. STP cable has a theoretical capacity of 
500 Mbps, although few implementations exceed 155 Mbps with 100-meter
cable runs. The most common data rate for STP cable is 16 Mbps, which
is the top data rate for Token Ring networks. The shield in STP cable
results in good EMI characteristics for copper cable, comparable to 
the EMI characteristics of coaxial cable. This is one reason STP 
might be preferred to unshielded twisted-pair cable in some 
situations. As with all copper cables, STP is sensitive to 
interference and vulnerable to electronic eavesdropping.

The cost of the fiber optic cable and connectors has fallen 
significantly in recent years. However, the electronic devices
required
are significantly more expensive than comparable devices for copper 
cable. Fiber-optic cable is also the most expensive cable type to 
install. Fiber-optic cable can support high data rates (as high as 
200,000 Mbps) even with long cable runs. Although UTP cable runs are 
limited to less than 100 meters with 100 Mbps data rates, fiber-optic
cables can transmit 100 Mbps signals for several kilometers. Because 
fiber-optic cables don't use electrical signals to transmit data, they
are totally immune to electromagnetic interference. The cables also
are
immune to a variety of electrical effects that must be taken into
account
when designing copper cabling systems.

The following are typical characteristics of wireless media:
- High bandwidth (~45 Mbps).
- No cabling between sites.
- Clear line-of-sight required (30 miles).
- Susceptible to radio interference.
- Attenuation increases with rainfall
- Lack of security.
- Up-front investment in towers & repeaters.
- Low power used to minimize effects on people


References:

Network Fundamentals
http://crash.umm.com.my/westnet/Fundamentals/units/unit4_sec3.html

Limits on Baseband Transmission
http://www.cs.williams.edu/~cs105/f01/text/ch3/DigitalTrans_19.html

Baseband Transmission
http://trurl.npac.syr.edu/cps600/cps640/PPTmmnetintro/foilsephtmldir/005HTML.html

Choosing the right computer network
http://www.foothill.fhda.edu/cfi/smart/tgsguide/chapter3.htm

Transmission Media
http://www.coba.usf.edu/departments/isds/faculty/chari/ism_6225/lect4.ppt

Selecting the right transmission media
http://www.corning.com/opticalfiber/products__services/reprints/r1075.asp

Comparison of Wireless Transmission Media
http://216.239.53.100/search?sourceid=navclient&q=cache:http%3A%2F%2Fabc.eznettools.net%2Fetrades%2FCS290%2Fmedia.html

Communication Networks : A First Course, by Jean Walrand, 
Aksen Associates Incorporated Publishers (1991)
ISBN 0-256-08864-0


In case you have any clarifications on the answer, please do not 
hesitate to ask. Thank you for using this service and have a nice day.

Regards,
aditya2k

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