Title: Beyda, W. J., DATA COMMUNICATIONS FROM BASICS TO BROADBAND, 2000
1Beyda, W. J., DATA COMMUNICATIONS FROM BASICS TO
BROADBAND, 2000
- Electronically reproduced by permission of
Prentice Hall, Upper Saddle River, New Jersey.
2Architectures and Protocols
- What is a communication architecture?
3Architectures and Protocols
- A (manufacturers) strategy for connecting (its)
host computers, terminals, and communication
equipment. - Specifically, it can describe special functions
that the host computers hardware and software
must perform to allow application programs to
communicate amongst themselves and the outside
world.
4Architectures and Protocols
- Thus far in this course and in the book, we have
only considered computer-to-terminal
communications. We will now consider
computer-to-computer communications..
5Architectures and Protocols
- Why do we want computers to be able to
communicate with other computers?
6Architectures and Protocols
- So that like computers can share data.
- So that like computers can share resources.
- So that unlike computers can share data.
- So that unlike computers can share resources.
7Architectures and Protocols
- How many operating systems are there in use today?
8Architectures and Protocols
- Some common ones
- Windows NT
- Unix (HP-UX, SunOS, AIX,BSDI,SCO)
- LiNUX
- Windows 95
- Windows 98
- OpenVMS
- Novell
- Proprietary
9Architectures and Protocols
- Year 2001.
- 40 Will be Windows NT
- 40 Will be Unix
- 20 Will be others
- 95 of all businesses will be mixed environment!
- Source 1999 Oracle presentation, Jacksonville,
Florida.
10Architectures and Protocols
- In the past, if you wanted unlike systems to
communicate, you would have to purchase something
(hardware/software/both) to perform the
conversions. - Why not have common communications to solve this
problem?
11Architectures and Protocols
- Enter International Standards Organization (ISO)
and the Open Systems Interconnect Model (OSI
model). - (Dont get ISO and OSI confused!)
12Architectures and Protocols
13Architectures and Protocols
- It is a universal architecture for computer
communications. - It is non-proprietary.
- It breaks down the task of communications into
seven independent layers, each with its own tasks
and responsibilities.
14Architectures and Protocols
- In 1985 the Corporation for Open Systems, COS
formed. - It was non-profit.
- It consisted of representatives of major host
computer manufacturers at the time, including
Control Data, DEC, HP, Honeywell, IBM, NCR,
Tandem, Unisys, Wang, Xerox, and others.
15Architectures and Protocols
- Seven Layers of the ISO model defined
- Layer 7 (Higher Layer) Away Layer
- Layer 6 (Higher Layer) Pizza Layer
- Layer 5 (Higher Layer) Sausage Layer
- Layer 4 (Higher Layer) Throw Layer
- Layer 3 (Lower Layer) Not Layer
- Layer 2 (Lower Layer) Do Layer
- Layer 1 (Lower Layer) Please Layer
16Architectures and Protocols
- Seven Layers of the ISO model defined
- Layer 7 (Higher Layer) Application Layer
- Layer 6 (Higher Layer) Presentation Layer
- Layer 5 (Higher Layer) Session Layer
- Layer 4 (Higher Layer) Transport Layer
- Layer 3 (Lower Layer) Network Layer
- Layer 2 (Lower Layer) Data Link Layer
- Layer 1 (Lower Layer) Physical Layer
17Architectures and Protocols
- Away -gt Application Layer
- Pizza -gt Presentation Layer
- Sausage -gt Session Layer
- Throw -gt Transport Layer
- Not -gt Network Layer
- Do -gt Data Link Layer
- Please -gt Physical Layer
18Architectures and Protocols
- More on the OSI model...
- Each layer represents a particular function.
- Sometimes, each function is performed by a
separate piece of hardware or software. - Sometimes a single program can perform the
functions of several layers.
19Architectures and Protocols
20Architectures and Protocols
- Layer 1 Physical Layer
- responsible for transmission of bits.
- Implemented in hardware and software drivers
encompasses the mechanical, electrical, and
functional interface. - Examples RS-232-C (Sync and Async), ethernet,
X.25, twisted-pair, coaxial cable, fiber optic
cable, satellites, microwave towers, and radio
waves.
21Architectures and Protocols
- Layer 2 Data Link Layer
- responsible for ensuring error-free, reliable
transmission of data. - establishes the communication link between
devices over the physical channel. - Responsible for framing, error control, time-out
levels, and data formatting can request
retransmissions at this level. - Maintains sequence control for frames on the
communication link. - OSI uses the High-level data link control (HDLC)
protocol for these services. IBM uses Binary
Synchronous Protocol (BSC) and Synchronous Data
Link Control (SDLC). DEC uses DDCMP.
22Architectures and Protocols
- Layer 3 Network Layer
- responsible for routing messages throughout a
network. - Internodal traffic control.
- OSI utilizes Internetwork Protocol (IP) at this
level.
23Architectures and Protocols
- Layers 1-3 (Physical, Data Link, and Network) are
referred to as the lower levels
- Layers 4-7 (Transport, Session, Presentation,
Application) are referred to as the higher or
upper levels.
24Architectures and Protocols
- Layer 4 Transport Layer
- Responsible for isolating the functions of the
higher and lower levels. This level will accept
messages from the higher levels and break them
down for the lower layers. - Two popular protocols have been developed to
provide transport services Transmission Control
Protocol (TCP), which as of 1997 was not an
official OSI protocol, and the OSI Transport
Protocol (TP).
25Architectures and Protocols
- Layer 5 Session Control
- Formats the data for transfer between end nodes
of the network. - Security (login/passwords) is handled at this
level. - Provides session-to-session restart and recovery,
and is responsible for maintaining the end-to-end
connection until a termination request is
received from either system.
26Architectures and Protocols
- Layer 6 Presentation
- takes data and translates it into a format that
will enable it to be processed by the receiving
system(terminal, printer, host computer). - Functions include data formatting, code set
conversions (e.g. ASCII to EBCDIC), text
compression for higher throughput efficiency, and
encryption services.
27Architectures and Protocols
- Layer 7 Application
- Provides access to the network for the end user.
- Some application software may permit remote
terminals to access a host computer some may
allow file transfers. - Network management, resource sharing, and
database management services also reside within
this layer.
28Architectures and Protocols