DC 7 - 1 DATACOMM John Abbott College JPC Architectures & Protocols M. E. Kabay, PhD, CISSP Director...
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Transcript of DC 7 - 1 DATACOMM John Abbott College JPC Architectures & Protocols M. E. Kabay, PhD, CISSP Director...
DC 7 - 1
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 - 2
Architectures & Protocols
Architectures OSI Model OSI Applications SNA Protocols Common Link-Level Protocols TCP/IP
DC 7 - 3
Architectures
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
DC 7 - 4
OSI Model
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
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OSI Model
The 7 layers Application (7) Presentation (6) Session (5) Transport (4) Network (3) Data Link (2) Physical (1)
UPPERLAYERS
LOWERLAYERS
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OSI Model
Physical Layer (1) Transmits bits I/F to outside world Always hardware Connectors, voltages, amplitudes…. E.g., RS-232-C
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OSI Model
Data Link Layer (2) Error-free data transmission
– examines bits for errors– error recovery– flow control
E.g., bisync, SDLC, HDLCIEEE 802.3, 802.5 (see later)
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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 - 9
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 - 10
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
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OSI Model
Presentation Layer (6) Data interpretation Format & code transformations Appearance of output E.g., ASCII, EBCDIC,
TELNET, printer drivers,e-mail formats
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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 - 13
OSI Applications
OUTPUT INPUT
DC 7 - 14
SNA
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
DC 7 - 15
Protocols
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
DC 7 - 16
Common Link-Level Protocols 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)
DC 7 - 17
Common Link-Level ProtocolsBSC 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 - 18
Common Link-Level ProtocolsBSC 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
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Common Link-Level ProtocolsSDLC 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 - 20
Common Link-Level ProtocolsSDLC 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 - 21
Common Link-Level ProtocolsProtocol 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 - 22
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
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TCP/IP
IP Works at layer 3 (network) Best-effort delivery only Packets called datagrams Connectionless because every packet routed
individually
DC 7 - 24
TCP/IP
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)
DC 7 - 25
Homework
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).