Examples of Communication Systems -Messaging

Refer to pages 274 – 292

1.       Which part of the PSTN network is digital, which part is analog?

Apart from the connections between telephones and their local exchange, the remainder of the PSTN is essentitally digital.

2.       Define multiplexing and identify how it increases efficiency on a digital network. Is a method by which multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred.
-multiple conversations on a single wire

3.       What other features does a digital PSTN offer?
-call waiting, caller ID,

4.       Describe the basic principle of a Facsimile machine (FAX), use the words – scan, light source, sensor, transmission.

The basic principle of a FAX machine us to transmit data from one location to another. like morse code the message is sent as a serius of tones, one for white and another for black, these tomes were converted to an image using heat sensitive paper.
-scanner with a light source that the document is fed through, dark adn light area's are detected by sensor and are coded and transmitted to the receiver.

5.       Complete group task from page 277 – create DFD for voicemail system.

6.       Describe what is meant by a Phone Information Service – give four examples of a service they may provide. Where have you encountered such a system
-phone information service-  computerised service e.g. calling up phone centre's such as vodafone for information and you are met with a computerised voice.
-direct the caller to an extension of the system
-recording voice mail.
-text to speech/speech to text -> either u speak or write and an information system will either repeat what u have written or write in text what you have said.
-Fax
-Call logging to databases.
-Support for multiple incoming and outgoing lines

7.       According to the commonly used standard for IVR (Interactive voice response) identify the numeric key suggested for each of the following actions;

·         Conclude data input - - #

·         Indicating yes/no 1, 2/0

·         Cancel and return to previous step

8.       Both VOIP (Voice over Internet Protocol) and Instant messaging allow for the transmission of audio over the internet. How does VOIP differ from instant messaging? What are the cost components of a VOIP to VOIP call?
- instant messaging is pc to pc

-VOIP transfers voice calls over the public internet -> uses IP datagrams, makes a jump from the internet protocol to computers and telelphones.

9.       VOIP relies on several protocols in the communication and control layer. One is RTP – identify its role. Others are   UDP/IP – why is UDP used and not TCP?
-VOIP - communication control
-RTP -
-UDP/IP instead of TCP/IP - not lagging, speed, compression of data, doesnt perform error checking whereas TCP checks and makes sure data is intact. TCP is slower than UDP but UDP data does get corrupted.
UDP doesnt have processing overheads involved in error checking and therefore can stream teh data more quickly compared to TCP -> downside, some datagrams will be  corrupt.

10.   Typically what hardware would be used to enable the use of VOIP in a home?

11.   Summarise the advantages and disadvantages of VOIP.
Advantages:
-low costs for long distance calls.
-no additional cabaling required.
-requires an internet question
can originate from any location with an internet connection.
portability
Disadvatages:
- IP and internet form a packet switched network, which was not designed for continous delivery of real time data
-emergency calls cannot be made when there is a power failure.
-broadband connections are unreliable in terms of quality of service compared to the PSTN.

12.   Describe the role of the email Destination address fields, To:, CC: and BCC:.
-contains the address of the primary recipients of the message.
- these are the people who the message is directly written to.
-Cc: is short for carbon copy - they receive a copy however the message is not directed at them.
-Bcc: blind carbon copy - those who also recieve the message but their addresses are not to be revealed to any other recipient.

13.   Describe the Date:, From: and Sender: Originator fields.
-Date: must be included and is used to specify the date and time that the user indicated that the message was complete and ready to send.
-From: contains multiple emal addresses, it is possible for a message to be sent from more than one person.
-Sender: used to specify the single email address that actually sent the message.
e.g senior management may formulate an email message that is actually send by a secretary. the From field would then contain each managers email address whilst the Sender field would contain the secretary's email address.

14.   What is the general purpose of Identification Fields?
-used to identify individual messages and to allow email application to maintain links between a thread of messages. they are designed for machines to read rather than humans ->3 possible indentification fields - MessageID, In Reply tp and Reference

15.   Informational Fields in emails are optional, however one is typically used. Name this field.
Subject field

16.   “MIME (Multipurpose Internet Mail Extensions) is a protocol used to code non-textual data” – what does this mean? Give examples of the non-textual data.
-protocol used to code non-textual (not text) data and attachments into ASCII (characters on the keyboard) so that it can be transmitted within email messages.
-transmission of many foreign language characters that cannot be represented using the 127 7-bit ASCII characters.
-type of extention
-coding nontext data as ASCII code text

17.   What code does the MIME format use to transmit data?
ASCII