Transcript PPT - ME Kabay

DATACOMM
John Abbott College JPC
Architectures &
Protocols
M. E. Kabay, PhD, CISSP
Director of Education, ICSA
President, JINBU Corp
Copyright © 1998 JINBU Corp.
All rights reserved
DC 7 - 1
Architectures & Protocols







DC 7 - 2
Architectures
OSI Model
OSI Applications
SNA
Protocols
Common Link-Level Protocols
TCP/IP
Architectures




DC 7 - 3
Strategy for connecting information
technology equipment into functional
systems
Communications functions kept modular:
– stratified
– isolated
– segregated from each other
Allows changes in functions without affecting
other aspects of computing
E.g., shape of datacomm connectors can be
modified without affecting application
programs
OSI Model






DC 7 - 4
Open Systems Interconnection Model
Intl Std Organization (ISO)
Universal architecture for datacomm
Allow interoperability of equipment from all
manufacturers
Defines 7 layers for specific functions
Number of layers is arbitrary
OSI Model
The 7 layers
 Application (7)
 Presentation (6)
 Session (5)
 Transport (4)
 Network (3)
 Data Link (2)
 Physical (1)
DC 7 - 5
}
UPPER
LAYERS
}
LOWER
LAYERS
OSI Model
Physical Layer (1)
 Transmits bits
 I/F to outside world
 Always hardware
 Connectors, voltages, amplitudes….
 E.g., RS-232-C
DC 7 - 6
OSI Model
Data Link Layer (2)
 Error-free data transmission
– examines bits for errors
– error recovery
– flow control
 E.g., bisync, SDLC, HDLC
IEEE 802.3, 802.5 (see later)
DC 7 - 7
OSI Model
Network Layer (3)
 Routing messages through networks
 Switching messages among nodes
 Segmenting data into packets
 Blocking data
 Error recovery
 Flow control
 E.g., X.25, ISDN (see later)
DC 7 - 8
OSI Model
Transport Layer (4)
 Data transfer
 Takes messages from upper layers and
breaks into pieces for lower layers
 Blocking
 End-to-end control
 Multiplexing
 Mapping
 E.g., TCP, UDP
DC 7 - 9
OSI Model
Session Layer (5)
 Administration & control of sessions
 Logon/logoff (login/logout)
 I/F to host and remote file systems
 E.g., Berkeley Sockets, NET IPC
DC 7 - 10
OSI Model
Presentation Layer (6)
 Data interpretation
 Format & code transformations
 Appearance of output
 E.g., ASCII, EBCDIC,
TELNET, printer drivers,
e-mail formats
DC 7 - 11
OSI Model
Application Layer (7)
 User application programs/processes
 Management functions
 E.g., terminal emulators,
Mosaic, Netscape, ARPA,
NS/3000, SMTP, X.400, rlogin,
XWINDOWS
DC 7 - 12
OSI Applications
OUTPUT
DC 7 - 13
INPUT
SNA







DC 7 - 14
Systems Network Architecture
IBM proprietary architecture
De facto standard — but declining in use
Complex terminology
Read section on SNA in text (pp. 136-143)
Omit review questions 7-5 through 7-10 on
page 156
Not discussed further in this course
Protocols



DC 7 - 15
Polling
– Host: Ready to Send?
– Terminal: Yes / No
Selecting
– Host: Ready to Receive (ENQ)?
– Terminal: Yes, Acknowledge (ACK)
– No, Negative Acknowledge (NAK)
Automatic Repeat Request (ARQ)
– Check each block for correctness
– Stop-and-wait ARQ
– Go-back-N continuous ARQ
Common Link-Level
Protocols




DC 7 - 16
Let devices share communications link
Define queries/responses for polling &
selecting
Byte-oriented protocols (character-oriented)
– control sequences in whole bytes
– e.g., BSC (Binary Synchronous
Communications)
Bit-oriented protocols
– single bits for control information
– e.g., SDLC (Synchronous Data Link
Control)
Common Link-Level
Protocols
BSC
 IBM proprietary and de facto standard
– half-duplex
– stop-and-wait ARQ
– point-to-point and multipoint datacomm
 Designed for ASCII, EBCDIC (and rarely used
Transcode)
 Not suitable for satellite or other long-delay
transmission modes
 Data transmitted in frames
DC 7 - 17
Common Link-Level
Protocols
BSC frames
 Data frames
– user data
– headers allow specific addressing
 Control information frames
– terminal and host communicate without
user involvement
– terminal buffers transmissions until receipt
of acknowledgement
DC 7 - 18
Common Link-Level
Protocols
SDLC
 IBM proprietary
– but de facto standard
– used in SNA
 Similar protocols:
– ISO HDLC (High-Level Data Link Control)
– CCITT Link Access Procedure-Balanced
(LAP-B)
DC 7 - 19
Common Link-Level
Protocols
SDLC
 Full duplex (usually)
 Go-back-N continuous ARQ
 Suitable for channels even with long delays
 SDLC Frames
– Information frames (I-Frames)
• data
– Supervisory frames (S-Frames)
• control
– Unnumbered frames (U-Frames)
• specialized applications
DC 7 - 20
Common Link-Level
Protocols
Protocol Converters
 Adapt data flow to link systems using
dissimilar link-level protocols
 Code converters translate ASCII and EBCDIC
 E.g., asynchronous terminal linked to SDLC
host
DC 7 - 21
TCP/IP
Transmission Control Protocol / Internet
Protocol
 Originally designed for ARPANET
 Eventually became part of the definition for
being part of the Internet
 TCP
– works at layer 4 (transport) of OSI stack
– ensures reliable delivery
DC 7 - 22
TCP/IP
IP
 Works at layer 3 (network)
 Best-effort delivery only
 Packets called datagrams
 Connectionless because every packet routed
individually
DC 7 - 23
TCP/IP




DC 7 - 24
SMTP (Simple Mail Transfer Protocol)
– universal format for e-mail exchange
Telnet
– allows access to remote host
– simulates terminal
FTP (File Transfer Protocol)
– remote viewing of directories
– file transfers
SNMP (Simple Network Mgmt Protocol)
– see later (Chapter / Section 9)
Homework



DC 7 - 25
Read Chapter 7 of your textbook in detail,
adding to your workbook notes as
appropriate.
Review and be prepared to define or expand
all the terms listed at the end of Chapter 7 of
your textbook except for those relating to
SNA (no hand-in required)
Answer exercises 7-1 through 7-4 and 7-11
through 7-17 on pages 156 of the textbook
using a computer word-processing program
or absolutely legible handwriting (hand in
after quiz tomorrow morning).