Networks Tutorial A
Q. Differentiate between guided and unguided media.
Guided: signals propagate in solid media eg : copper, fiber, coax.
Unguided: signals propagate freely eg : radio.
Q. Outline the operation of two types of communcation technologies using guided media and a single type using unguided media.
Guided - Coax cable
Two concentric copper conductors, outerconductor serves to shield inner from
electromagnetic interference
Bidirectional, broadband, multiple channels on cable.
Guided - Fiber optic cable
Glass fiber carrying light pulses, each pulse a bit
High-speed point-to-point transmission (e.g., 10s-100s Gpbs transmission
rate)
Low error rate: repeaters spaced far apart,immune to electromagnetic noise
Unguided - Radio
Signal carried in electromagnetic spectrum, no physical wire,bidirectional
Propagation environment effects:reflection,obstruction by objects,interference
Q. Give concise definitions for the following terms: link bandwidth,
throughput, latency, router, protocol
Link bandwidth a measurement of bit rate of available or consumed data
communication resource expressed in bits per second ( ie the amount of data
that can be transmitted in a fixed amount of time.
Throughput The rate of successful end to end message delivery over a communications channel.
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Latency The amount of time it takes a packet to travel from source to destination. Together latency and bandwidth define the speed and capacity of a
network.
Router A router is a device that forwards data packets along networks. A
router is connected to at least two networks, commonly two LANs or WANs
or a LAN and its ISP’s network. Routers are located at gateways, the places
where two or more networks connect.
Protocol Communicating systems use well-defined formats (protocol) for exchanging messages. Each message has an exact meaning intended to elicit
a response from a range of possible responses pre-determined for that particular situation. Thus, a protocol must define the syntax, semantics, and
synchronization of communication
Q. Explain the terms network core, network edge
The network core is the central part of a telecommunications network
that provides various services to customers who are connected by the access
network.The network core usually deploys a mesh topology that provides
any-to-any connections among devices on the network. Many main service
providers would have their own core/backbone networks, that are interconnected. Some large enterprises have their own core/backbone network, which
are typically connected to the public networks
The devices and facilities in the core / backbone networks are switches and
routers. The trend is to push the intelligence and decision making into access and network edge devices and keep the core devices dumb and fast. As a
result, switches are more and more often used in the core/backbone network
facilities. Technologies used in the core and backbone facilities are data link
layer and network layer technologies such as SONET, DWDM, ATM, IP, etc.
For enterprise backbone network, Gigabit Ethernet or 10 Gigabit Ethernet
technologies are also often used.
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Q. List the five layers of the Internet protocol architecture, giving
the principal responsibilties of each layer and an example of a protocol at each layer.
application supporting network applications : FTP, SMTP, HTTP
transport process-process data transfer : TCP, UDP
network routing of datagrams from source to destination: IP, routing protocols
link data transfer between neighboring network elements: Ethernet, 802.111
(WiFi), PPP
physical bits on the wire
Q. Define four sources of delay encountered by a packet as it traverses the internet from source to destination.
Total delay = dproc + dqueue + dtrans + dprop
dproc: nodal processing
check bit errors
determine output link
typically less than msec
dqueue: queueing delay
time waiting at output link for transmission
depends on congestion level of router
dtrans: transmission delay:
L: packet length (bits)
R: link bandwidth (bps)
dtrans = L/R
dprop: propagation delay:
d: length of physical link
s: propagation speed in medium ( 200000k m/sec)
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dprop = d/s
Q. Calculate the transmission delay and the propagation delay for
sending a packet of 1000 bytes over a link that is 2000 km long
and operates at 2 Mb/second. Assume bits propagate at 200,000
km/second. Give the answer in milliseconds
d = distance of link = 2000km
s = propagation speed = 200000km/sec
dprop = propagation delay = d/s = 0.01 sec
dtrans = transmission delay = L/r = (1000 x 8 ) / (2000 x8 ) = 500 ms
Q. Why is packet switching more suitable than circuit switching
for data networking?
In packet-switched networks, the message gets broken into small data packets. These packets are sent out from the computer and they travel around
the network seeking out the most efficient route to travel as circuits become
available. This does not necessarily mean that they seek out the shortest
route. Each packet may go a different route from the others
Advantages
Security
Bandwidth used to full potential
Devices of different speeds can communicate
Not affected by line failure (redirects signal)
Availability no waiting for a direct connection to become available
Disadvantages
Under heavy use there can be a delay
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Data packets can get lost or become corrupted
Protocols are needed for a reliable transfer
Poor for some types data streams (e.g. real-time video streams can lose
frames due to the way packets arrive out of sequence
In circuit-switched networks, electronic signals pass through several switches
before a connection is established. During a call no other network traffic can
use those switches. The resources remain dedicated to the circuit during the
entire data transfer and the entire message follows the same path.
Advantages
Circuit is dedicated to the call no interference, no sharing
Guaranteed the full bandwidth for the duration of the call
Guaranteed quality of service
Disadvantages
Inefficient the equipment may be unused for a lot of the call; if no data is
being sent, the dedicated line still remains open.
It takes a relatively long time to set up the circuit.
During a crisis or disaster, the network may become unstable or unavailable.
It was primarily developed for voice traffic rather than data traffic.
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