Computer Networks
Course Outline:
Lectures
Voice over IP
Wireless LANs
Security
Practicals
Setting up a Windows 2000 LAN
Setting up a DNS server
Setting up an email gateway
Anti Virus (Server and Client)
Network Design software e.g. NetViz
Network Management software e.g. Web boy
Firewall
Email Encryption
Case study Project
Produce a network design document for a small company implementing a LAN:
Hardware
Software
Plans
Labour
Description
The report should include details of price, specifications and sources of all expenses including.
Course Assessment
Continuous assessment:
Practicals 10%
Midway Exam 10%
Project 20%
Final Written Exam 60%
Voice over IP
Introduction
Often for an application user to experience ___________ and ___________ in computing there is a ________________________________.
e.g. Apple computers
Currently in the US alone, there are more than 4,000 telephone service providers.
Global ___________________ of the telephone markets mean:
new often __________________ e.g. DigiPhone, O2
and old _____________ owned carriers e.g. Eircom
______________- for customers
This means that new carriers frequently use ____________________________________, because:
of __________________________________ to the customer
they deploy ______________________ and faster
e.g. WAP, text messaging etc.
Many of these carriers use Voice over IP (______________).
VoIP is used because of:
the ________________ being prevalent
IP (__________________________) is the de facto standard for _____________________________
_______________________________design their applications to use IP
This makes VoIP a powerful service platform for "________________________________".
What is VoIP then?
VoIP allows the sound of your _______________ to be broken up into small pieces or ____________ and places them into an _____________________.
The movement of your voice "_____________" is then handled in the same manner as any other network ____________.
The "voice" IP packet ______________ the network, so the network is used more __________, and so saves _______________.
Overview of the Public Switched Telephone Network (PSTN)
Before we can examine VoIP, we need to understand how the present state of telephone communication developed.
The First Telephone
Alexander Bell made the first ________________________ in 1876.
This transmission had _________________ of numbers
One person picked up the phone
The other person spoke
There was no "_____________"
Over time, the telephone developed from a _____________ voice transmission to a _________ communication.
The voices moved down the wire electrically by:
a carbon microphone
a battery
an electromagnet
an iron diaphragm
a physical cable
Each telephone is physically connected to each of the others in the telephone network.
For example, a four-telephone network would look like:
However to build such a telephone network over a country or large area would not be practical, due to the ____________ and _____________.
The number of lines would be: N x (N - 1) / 2
An 8-telephone network requires 28 separate lines. We have a problem!
The solution
A mechanism was developed to overcome this problem of physically connecting each telephone to each of the others in the telephone network.
This device was called a ___________.
The switch is located _____________ in the telephone network and connects ______ telephones when ___________.
Initially the switch was a __________________:
but nowadays is an _______________________.
Understanding PSTN Basics
Analogue and Digital Signalling:
Everything that you hear, including human speech is in analogue form.
Analogue Waveform
Until several decades ago, the telephone network was based on an analogue __________________.
Although analogue communication is ideal for human and animal interaction, it is not:
____________
efficient at _______________ from line noise
________________ is normally caused by the introduction of _____________ into a voice network.
Long distance analogue transmissions need to be _____________, as the signal ____________ (strength) fades with ____________.
Unfortunately, amplification tends to increase the ______________ as well.
The may lead to an _________________ connection...
Analogue Line Distortion
In digital networks line noise is less of an issue because:
amplifiers or ___________ not only amplify the signal
but ________ it as well
This is possible because the repeater only has to decide whether to regenerate a ___ or a ___.
Digital Line Distortion
When signals are repeated, a clean sound is _______________.
This lead to telephone networks to change to __________________________________ (PCM).Digital Voice Signals:
Pulse Code Modulation (__________) is the most common method of changing, or encoding, an analogue voice signal into a ____________ of 0s and 1s. All ___________ techniques use the Nyquist theorem.
The Nyquist Theorem
"__________________________________________________________________________________________________________________________________________________________________________"
The PCM process:
1. The analogue signal is __________ e.g. cut out high-pitched sounds > 4000 Hz. This limits the amount of "_________________" in the voice network.
2. According to Nyquist the filtered analogue signal should then be _______________ at 2 x 4,000 i.e. 8,000 samples per second to achieve a ___________________________.
3. The sampled signal is then converted to a ____________________-. This sample is represented by a code (or numerical value) indicating the ________________ of the waveform at the __________ the sample was taken.
PCM uses 8 bits for the code for each sample. If your sample is taken at 8,000 times per second, this gives you 8 x 8000 i.e. 64,000 bits per second or 64 kbps.
Note that the industry standard for ____________ at present i.e. 56 kbps will not support the required __________________.
Local loops, Trunks and Interswitch Communication:
The telephone infrastructure begins with a simple pair of ________________ running to your home. The physical cabling is called the ________________.
The local loop connects your home phone to the _________________________________ (Class 5 switch or end office switch).
The communication path between the central office switch and your home is the ________________________. Communication between several central office switches is a _________________ (hence the term “trunk call”).
Just as it is not cost effective to connect all users by a physical wire, it is also not cost effective to connect all central office switches.
A ___________________ of switches is a better model:
Call ___________ and _______________ determine the number of interconnections, switches etc. Some portions of PSTNs may have up to 5 levels of hierarchy.
PSTN Signalling:
Signalling methods are broken into 2 groups:
_____________________ signalling
_____________________ signalling
User-to-Network Signalling
When using twisted copper pair as the transport, a user generally connects to the PSTN via:
____________
Integrated Services Digital Network (__________)
_______ carrier (USA, Japan digital transmission link @ 1.544 Mbps)
Dual Tone Multi-Frequency (DTMF)
The most common signalling method of _________ communication is DTMF. This is also known an ______________ signalling as the tones are carried _____________________:
Dual Tone Multi-Frequency
When you dial a number on your phone, the tone that passes down the line to the central office switch tells the switch what number you want to “dial”.
Out-of-band
ISDN uses another method of signalling known as ______________. There are 2 separate channels with ISDN:
The _____________ carries the voice (64 kbps)
The _____________ (D channel) carries the signal (16 kbps)
There are a number of advantages to out-of-band signalling:
__________ bandwidth realised
less post-dialling _________
more ______________ connections (less line noise than DTMF)
Network-to-Network Signalling
Network-to-network signalling may use:
______________ e.g. Multi-frequency (MF)
or
______________ methods e.g. Signalling System 7 (SS7 or C7)
over a variety of transmission media:
from ______________
through to _________________
depending on the carrier type e.g. T1, E1 etc.
PSTN Call Flow to `Granny's House'
Let's walk through the flow of a telephone call:
1. I pick up the phone, and an "___________" indication is sent to the end office switch.
2. The switch sends back a "____________".
3. I _______ the number for Granny's house (in-band using DTMF).
4. The switch interprets the digits and sends an ___________________ (IAM) or "set-up" message to the SS7 network.
5. The SS7 network _________ the incoming IAM and __________ a new IAM to Granny's switch.
6. Granny's switch sends a ________ to Granny's house, her phone __________.
7. An alerting message is sent from Granny's switch (not phone) _________ to the SS7 network via an ________________________ (ACM).
8. The SS7 network ________ the incoming ACM and ____________ an ACM to my switch.
9. I now _____________ and know that Granny's phone _____________ (the ringing is not synchronised).
10. Granny picks up her phone, sending an "______________" indication to her switch.
11. Granny's switch __________ an ANswer Message (ANM) that is read by the SS7, and a new ANM is _______ to my switch.
12. I can now ________ to Granny until I hang up my phone, giving an "____________" indication.
Note: If Granny's phone had been busy I would have received the "__________" tone, and depending on the kind of service, I could possibly wait on the line or leave a message etc.
PSTN Call Flow to Granny's House
1. Connection
2. Disconnection
PSTN Services and Applications
Many services are available these days, they come in two main groups:
_______________ features
_______________ features
Custom Calling Features
These depend on the ________________ and include:
_______________ - Notifies the customer that another incoming call is on the line
_______________ - Enables the customer to forward incoming calls to a different destination
_______________ - Enables conference calling between 3 parties
CLASS features
This depends on the SS7 network and include:
Display - Displays the calling parties directory number.
Call blocking - Blocks specific incoming numbers.
Call line ID blocking - Stops the customer's directory number from being shown on another phone's "display".
Automatic callback - Enables an automatic recall on a busy number after that line is free.
call return - Enables users to reply quickly to missed calls.
etc.
Drawbacks to PSTN:
Whilst PSTN has done a good job at switching voice calls, there are forces wishing to make voice an application on top of a ____________________.
This is because:
1. ____________________________________________________________________________________
That is data is running on top of networks built for _____________.
However, data has different characteristics:
variable use of ______________
need for higher ______________
Soon voice will run on data networks, built from a “_________________” approach.
Data will be differentiated based on _______________ rather than physical circuits.
New technologies will be used to carry the high-speed networks:
Fast Ethernet
Gigabit Ethernet
optical networking
2. ____________________________________________________________________________________
However, with increasing competition following deregulation of the markets companies are looking at ways to entice new customers. PSTN is dominated by companies with one-stop shopping applications. The architecture is not ______ to adding new applications.
It is the same as Microsoft with Internet explorer vs. Netscape etc.
3. ___________________________________________________________________________________
Analogue lines are the most common domestic connection giving a limit of up to 56 kbps (at best). This bandwidth is not large enough to support high-speed access required for voice and video. After these bandwidth issues are resolved, convergence will follow.
Note that the ___________ of the PSTN has already begun to converge.
4. ___________________________________________________________________________________
Because the applications and switches are bound in to one closed platform it is not possible to make minor changes to improve audio quality.
Note
Circuit-switched calls required the _____________ use of a line, whereas data networks only require the bandwidth ______________________ etc. This affects the whole area of _____________ for use of resources.
VoIP vs. PSTN Conclusions
1. Cost
Comparing a ______________ costing of VoIP vs. PSTN may not be large enough to justify the implementation costs.
This depends on ________________ location i.e. the relative cost of an Internet connection vs. a PSTN local call.
2. Dynamic Host Configuration Protocol (DHCP)
This allows a host or ____________ to be moved anywhere and keep the same phone number.
This is an advantage in a world where it may cost a minimum of €100 to simply move a phone by a technician.
3. Information Services Dept.
A company may have one dept. to cover both voice and data networks.
This may be difficult to implement, as with many new technologies.
4. Voice Mail
It is much cheaper to store voice mail on a hard drive on a PC than on a remote server 3 - 4p per MB compared to 50p - Ł 1.50 .
If your voice mail was on the same server as your email, it would be much easier to access remotely.
5. Call centres
Packet Telephony Call Centre (PTCC) vs. Circuit-Switching Call Centres (CSCC)
These are much more flexible with VoIP.
Home working is easy to implement with no extra equipment costs and a general lower overhead costing advantage.
“Virtual agents” may be located anywhere.
Overall Conclusion
Integrating voice and data networks allows cost savings and new applications for the user and service provider.