Download Structured Systems Analysis and Design

Computer Fundamentals
Northern College Diploma
Philip Bird
Data Communications
0
1
0
0
0
0
0
1
Parallel
Faster over
short distances.
Data sent a byte
at a time.
Serial
More common
that parallel.
Data sent a bit
at a time.
Computer Fundamentals
01000001
Philip Bird
Interface Framing
0010000010100100001111
Start
Bit
8 Data
Bits ‘A’
Computer Fundamentals
Parity
Bit
Stop
Bit
8 Data
Bits ‘C’
Philip Bird
Switching
Packet
Circuit
Message
Computer Fundamentals
Philip Bird
Protocols, Packets and Errors
Packets enable messages to be split into many smaller sections.
Computers need sets of rules (protocols) on how to handle
these packets – how big they should be, what to do if a
transmission error occurs.
Header
Payload
TCP – is responsible for
breaking up the message
into
datagrams, reassembling them at the other end, resending
anything Source
that IP
gets
lost, and putting things back in
the right
Dest IP Packet# Size Checksum
Data
order
IP – is responsible for routing individual datagrams across
networks.
Other protocols determine how the data is handled once it is
put back into a complete message. HTTP, SMTP, POP3, FTP etc.
Computer Fundamentals
Philip Bird
Network Topologies
Computer Fundamentals
Philip Bird
Northern College & JANET
SC
RVC
RC
AT
BC
DC
DVC
TRC
100 Mb
Yorkshire and
Humberside
Metropolitan
Network (YHMAN)
Doncaster Router
Hub
Hub
Sheffield Router
Rotherham Router
Bridge
Switch
Web
Host
Email
Host
10 Mb
Firewall
Northern
College Local
Area Network
Barnsley Router
South
Yorkshire FE
Consortium
Sheffield Hallam
Telewest
8 Mb
NC Router
Leeds Metropolitan
Sheffield
MAN
MAN
1 Gb
Huddersfield
Hull
Bradford
Glasgow
Edinburgh
MAN
2.5 Gb
MAN
York
Leeds
Manchester
Joint Academic
Network (JANET)
1 Gb
LINX
Reading
London
MAN
Other ISP's
Bristol
MAN
Computer Fundamentals
Portsmouth
MAN
MAN
Philip Bird
Summary
Why is most data communicated in
serial rather than parallel form?
Why are standards so important in data
communications?
Computer Fundamentals
Philip Bird