fundamentals of communication and networking

Serial Transmission

Sends and receives data one bit at a time over a single wire from source to destination. used for long distance communication (\>1m)

Speed of serial transmission depends on...

the type of cabling

Serial transmission pros

Easy to regenerate a signal to prevent signal strength dropping too far -\> successful communication
It also reduces the need for cabling

Parallel data transmission

Use of multiple wires to transmit several bits simultaneously

Cons of parallel data transmission

More wires, more data transmitted -\> more expensive
Signal will degrade as distance increases due to interference between lines
Synchronisation is more difficult as wires are increased

Examples of use of parallel data transmission

printer cables (large amounts of data sent quickly), computer buses

Skew

As each individual wire has slightly different properties, bits might travel/arrive at a slightly different speed/time

Parallel data transmission is reliable over...

short distances

What is crosstalk

EM interference between two parallel wires or adjacent channels

Crosstalk gets more pronounced as..

the speed of transmission increases

Serial transmission is reliable over...

very long distances at very high frequencies

Serial connectors such as USB connectors are ... than parallel connectors

much smaller and cheaper

Synchronous data transmission

all data transfers are timed to coincide with an internal clock pulse

How is the data sent in synchronous data transmission?

One long stream or block of data

What does the receiver do when they receive the data from synchronous transmission?

Counts the bits and reconstructs bytes

Asynchronous data transmission

Each byte is sent separately the moment it is available instead of waiting for a clock signal

What is each byte preceded by and ends with in asynchronous transmission?

a start bit and a stop bit

Asynchronous transmission con:

relatively slow (because of the number of bits being sent)

Asynchronous transmission pros:

Cheap and effective form of serial transmission well suited to low-speed connections (keyboard and mouse)

Aysnchronous serial data transmission

To communicate successfully, two devices
1. need to know that the other device is ready to transmit or receive data
2. need prior knowledge of
- the type of parity checking used and
- on which bits
- The value and number of start and stop bits
3. need to know the communication methods they use
4. need to agree on the protocol to be used
5. must identify the fastest transmission speed both devices are capable of

Handshaking

the process of 2 devices sending signals to each other to indicate that they are ready to send and/or receive data

Why is handshaking necessary?

to allow communication between devices built by different manufacturers

Start bit

In asynchronous communications, the bit that signals the receiver that data is coming.

Stop bit

in asynchronous communications, a bit that indicates that a byte has been transmitted

Bandwidth

measure of the maximum capacity of a comms channel, measured in bps

Latency

time delay between the moment the first byte or packet of a communication starts and when it is received at its destination

Broadband

carries multiple signals on a fixed carrier wave. bits are sent as variations on the wave

baseband

carries one signal at a time. a bit is represented by a high or low voltage in the cable

bit rate

number of bits transmitted in one second over a wired or wireless data link
(volume of data sent)

baud rate

rate at which the signal in a comms channel changes state
(frequency of signals (1 baud \== 1 signal change per sec))

protocol

set of rules relating to communication between devices

Bit rate can be higher than baud rate if...

more than one bit is encoded in each signal change

Bit rate is directly proportional to...

bandwidth

Bit rate \= baud rate * ...

no. of bits per signal

Baseband carries...

one signal at a time.

In baseband a bit (1 or 0) is represented by...

a high or low voltage in the cable

In baseband, bit rate...

\= baud rate; when 1 bit is encoded in each signal change

Signals in baseband are quick but can only be sent over distances up to

300m without booster equipment

Where is baseband generally used

short distances as it can provide speedy communication without a large cost

Broadband carries...

multiple signals on a fixed carrier wave

In broadband, bits are sent as...

variations on the wave

In broadband bit rate...

\> baud rate; when more than 1 bit is encoded in each signal change

What does bandwidth refer to

the range of frequencies that can be transmitted over the medium

The higher the bandwidth,

the higher the bit rate (greater rate at which data can be sent)

What is the medium of transmission for broadband?

Wire or fibre-optic cable for example

what is broadband used for

longer distances

putting it into context

Postman Pat can carry 10 parcels in a van

Increase the baud rate and...

the wheels rotate faster (more cycles)

Increase the bit rate and...

more vans on the road

Increase the bandwidth and..

the road is bigger (more lanes), so it is allowing a higher bit rate (more vans)

Latency and bandwidth together define...

the speed and capacity of a network

Network topology

the arrangement of the various computing devices which make up a computer network

Bus topology

an arrangement where nodes are connected in a daisy chain by a single central communications channel

Star topology

an arrangement where a central node or hub provides a common connection point for all other nodes

in a bus network all the workstations, servers and printers are joined to...

one single backbone cable (the bus)

at the end of the cable a terminator is fitted to...

stop signals reflecting back down the bus

each node in a bus network is

passive

in a bus network data is sent in

one direction at a time only

in a bus network, only ... can transmit successfully at any one time

one computer

what technology is used in a bus network to enable nodes to transmit on the same cable

Carrier Sense Multiple Access (CSMA/CD)

Advantages of a bus network

- easy to install
- cheap to install: doesn't require much cabling
- good for small networks

Disadvantages of a bus network

- if the main cable fails, the whole network will fail
- limited cable length
- more connections, performance will be slower, increases data collisions
- security risks as every workstation on the network 'sees' all of the data on the network

In a star network, each device on the network has its own cable that connects to a central node which is...

a switch

definition of a switch

a switch sends each communication to the specific computer it is intended for
fast and secure

the star network topology is the most popular way of doing what?

settting up a LAN

advantages of a star network

very reliable - if one cable or device fails then all the others will continue to work

high performing as no data collisions can occur

disadvantages of a star network

- expensive to install as this type of network uses the most cable (network cable is expensive)
- extra hardware required (hubs or switches) which adds to cost
- if a hub or switch fails all the devices connected to it will have no network connection

every networked device contains a...

Network Interface Card (NIC)

every NIC has a unique...

Media Access Control (MAC) address

a switch holds all of the...

MAC addresses for each device connected to it

what does the switch use MAC addresses for

switch uses MAC addresses to direct packets of data to the correct device

Physical vs logical topology

physical - how devices are physically connected

logical - how devices communicate across the physical topologies

a network wired in star topology can behave logically as...

a bus network

how can a network wired in star behave logically as bus

by using a bus protocol and appropriate physical switching

operation of a logical bus network

a node broadcasts data to the entire network.

all nodes on the network receive the data

a node examines the received data to check if it is the intended recipient

only one node can successfully transmit data at a time

what does a bridge do

connects two or more LANs together
packets sent to remote LAN cross, other packets do not cross
segments the network on MAC addresses

what does a router do

connects two or more LANs together
packets sent to remote LAN cross
network is segmented by IP address

what does a gateway do

connects two dissimilar networks (LAN, WAN)
connects coaxial to twisted pair

main purpose of networking

share data between computers

how can a file be sent over a network

by breaking a file up into packets

two types of network architecture

client-server
peer-to-peer

client-server network

server is a powerful computer which provides services or resources required by any of the clients (e.g. file server, email server)

client is a computer which requests the services or resources provided by the server

in a client-server network, most computers are nominated as ... and one or more as ...

clients, servers

there can be many ... in a large client-server network

specialised servers

Advantages of a client-server network

- Security is better since all files are stored in a central location
- Backups are done centrally so individual users do not need to back up
- data and resources can be shared

disadvantages of a client-server network

it is expensive to install and manage
professional IT staff are needed to maintain the servers and run the network

a peer-to-peer network has no...

central server

in a peer-to-peer network, each individual computer is...

connected to each other, either over a LAN or WAN so that they can share files

in a peer-to-peer network, each computer has

equal status

where is a peer-to-peer network a good choice and why

in a small LAN, as it is cheap to set up, it enables users to share resources such as a printer or router, and it is not difficult to maintain

downside of peer-to-peer networking

the networking has been widely used for online piracy, since it is impossible to trace the files which are being illegally downloaded

Wi-Fi

a local area wireless technology that enables you to connect to a device such as a PC or smartphone to a network resource or to the Internet via a WAP

main aims of WLAN

seamless roaming
message forwarding
greatest range of operation
support for a large number of users

hotspot

a physical location where people may obtain Internet access, typically using Wi-Fi technology, via a wireless local area network (WLAN) using a router connected to an internet service provider.

what is needed to connect to a wireless network

ISP (Internet Service Provider)
Modem and wireless router (Often combined)
Device with a network interface card (NIC), also known as a network interface controller

wireless components - a station consists of ...

a computer and a wireless network interface card (NIC)

wireless components - stations share a...

radio frequency channel

whats does a WAP and router require

WAP requires connection to a router
router requires connection to a modem

WAP and modem are often...

built into the router
a wireless router performs the functions of a WAP and provides access to the Internet

components for wireless networking

wireless router, WAP, wireless network adapter

Wi-Fi network topologies

peer-to-peer topology

AP-based topology