Transcript William Stallings Data and Computer Communications

CSC 535
Communication Networks I
Chapter 1
Introduction
Dr. Cheer-Sun Yang
Communication and
Networking
What are the differences?
Communication - focuses on the transmission of data
from one end, called the source, to another end,
called the destination.
Networking - focuses on the issues involved when
connecting more communication hosts together and
becoming a network.
CSC535- focuses on point-to-point
communications
CSC581- focuses on networking including LAN
and WAN
2
Network and Services
A communication network connects many hosts
together to provide services.
Some examples:
Radio and television networks
Telephone networks
Cable networks
Data networks such as the Internet and SOHO
networks
Transportation networks - not our focuses but useful
for understanding the services provided by a
network.
3
Radio and TV Networks
Means of commuinication: electrical wave with
various frequencies
Services: carrying signals that encode some
entertaining programs and commercial
information.
Requirements:
Many programs being broadcast simultaneously
Delay in the order of seconds can be tolerated
4
Telephone Networks
Means of commuinication: electrical wave with
various frequencies
Services: carrying signals that encode human
conversations.
Requirements:
Real-time service: delay in the order of seconds can
not be accepted; acceptable delay is around 250
milliseconds
Availability requirement is higher than TV or radio.
The network must be available throughout the
conversations.
More “intelligent services” that users are involved.
5
1.
2.
3.
4.
5.
6.
Telephone
Office
The caller picks up the phone triggering the flow of current in wires
that connect to the telephone office.
Telephone
Office
The current is detected and a dial tone is transmitted by the
telephone office to indicate that it is ready to receive the
destination number.
Telephone
Office
The caller sends this number by pushing the keys on the telephone set.
Each key generates a pair of tones that specify a number. (In the older
phone sets the user dials a number which in turn generates a
corresponding number of pulses.)
Telephone
Office
The equipment in the telephone office then uses the telephone
network to attempt a connection. If the destination telephone busy,
then a busy tone is returned to the caller. If the destination telephone
is idle, then ringing signals are sent to both the originating and
destination telephones.
Telephone
Office
The ringing signals are discontinued when the destination
phone is picked up and communication can then proceed.
Telephone
Office
Either of the users terminate the call by putting down a
receiver.
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
Figure 1.1
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Data Networks
Means of commuinication: electrical wave with
various frequencies
Services: carrying signals that encode
information.
Requirements:
connectionless (e-mail) vs. connection-oriented (ftp,
telnet, www, etc.);
real-time (audio/video conferencing) vs. Non realtime (video on demand)
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Figure 1.2 Retrieving e-mail
Figure 1.3 World Wide Web example
generic examples of each type of application
8
1.
2.
3.
4.
5.
6.
The user clicks on a link to indicate which document is to be
retrieved.
The browser must determine the address that contains the
document. It does this by sending a query to its local name
server.
Once the address is known the browser establishes a connection to the
specified machine, usually a TCP connection. In order for the
connection to be successful, the specified machine must be ready to
accept TCP connections.
The browser runs a client version of HTTP, which issues a request
specifying both the name of the document and the possible document
formats it can handle.
The machine that contains the requested document runs a server
version of HTTP. It reacts to the HTTP request by sending an
HTTP response which contains the desired document in the
appropriate format.
The TCP connection is then closed and the user may view
the document.
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
Figure 1.4
9
Realplayer example
Copyright © 1995-2000, RealNetworks, Inc. All rights reserved. RealPlayer is a trademark
of RealNetworks, Inc.
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
10
Figure 1.5
Network Funcations and Some
Design Issues
Provides connectivity between users
Switching provides a saving on the number of
connectivity
Multiplexing provides an efficient way to share
connectivity
Routing provides a direction regarding a
destination associated with a connection
Addressing identifies source and destinations
Traffic control regulates traffic flowing through a
network
Network management monitors network status 11
t1
t0
Network
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
12
Figure 1.6
(a) A switch provides the network to a cluster of users
Network
Access network
(b) A multiplexer connects two access networks
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
13
Figure 1.7
1*
a
(a)
2
b
4
3
A
c
Metropolitan network A
consists of access
subnetworks a, b, c, d.
d
Metropolitan
(b)
A
a
b
g
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
National network
consists of regional
subnetworks a, b, g.
Metropolitan network
A is part of regional
subnetwork a.
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Figure 1.8
Key Communications Tasks
 Transmission system utilization
 Interfacing
 Signal generation
 Synchronization
 Exchange management
 Error detection and correction
 Addressing and routing
 Switching and multiplexing
 Message formatting
 Security
 Network management
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What happens “In the Cockpit”?
Example: ftp
Hardware: links between source and destination
Hardware: PCs and Network Interface Card
Hardware: modem
Software: TCP/IP software
Software: device driver
Software: operating system that ftp(an
application program) is running on
Let’s try “ftp -d taz.cs.wcupa.edu”
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[yang@coyote yang]$ ftp -d taz.cs.wcupa.edu
Connected to taz.cs.wcupa.edu.
220 taz.cs.wcupa.edu FTP server (Version wu-2.6.1(1) Wed Aug 9
05:54:50 EDT 2000
) ready.
Name (taz.cs.wcupa.edu:yang): yang
---> USER yang
331 Password required for yang.
Password:
---> PASS XXXX
230 User yang logged in.
---> SYST
215 UNIX Type: L8
Remote system type is UNIX.
Using binary mode to transfer files.
ftp>
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ftp> cd public/socket
---> CWD public/socket
250 CWD command successful.
ftp> get server1.c
local: server1.c remote: server1.c
---> TYPE I
200 Type set to I.
ftp: setsockopt (ignored): Permission denied
---> PASV
227 Entering Passive Mode (144,26,77,43,87,139)
---> RETR server1.c
150 Opening BINARY mode data connection for server1.c
(1639 bytes).
226 Transfer complete.
1639 bytes received in 0.0147 secs (1.1e+02 Kbytes/sec)
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ftp> put server1.c
local: server1.c remote: server1.c
ftp: setsockopt (ignored): Permission denied
---> PASV
227 Entering Passive Mode (144,26,77,43,180,246)
---> STOR server1.c
150 Opening BINARY mode data connection for server1.c.
226 Transfer complete.
1639 bytes sent in 0.000157 secs (1e+04 Kbytes/sec)
ftp>
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ftp> quit
---> QUIT
221-You have transferred 3278 bytes in 2 files.
221-Total traffic for this session was 5858 bytes in 5 transfers.
221-Thank you for using the FTP service on taz.cs.wcupa.edu.
221 Goodbye.
20
PS = packet switch
C
PS
C
C = computer
PS
PS
PS
C
C
C
Copyright 2000 McGraw-Hill
Leon-Garcia and Widjaja
Communication Networks
21
Figure 2.7
net 3
G
net 1
G
G
G
net 2
net 5
G
net 4
G
G = gateway/router
Copyright 2000 Leon-Garcia and
Widjaja Communication Networks
22
Figure 2.8
(a)
(1,1)
(2,1)
(2,2)
router
s
Ethernet
PPP
(1,3) r
w
(1,2)
(b)
Server
HTTP
PC
HTTP
TCP
Router
IP
IP
IP
Net Interface
Net Interface
Net Interface
Ethernet
TCP
PPP
Copyright 2000 Leon-Garcia and
Widjaja Communication Networks
23
Figure 2.13
User
Interface
Control
Server PI
Server
DTP
Server FTP
Connection
Data
User PI
User DTP
Connection
User FTP
PI = Protocol interpreter
DTP = Data transfer process
Copyright 2000 Leon-Garcia and
Widjaja Communication Networks
24
Figure 2.19
Communication Protocols
A set of rules that is used for “governing” how a
source and a destination communicates.
Must speak the same language
Entities
User applications
e-mail facilities
terminals
Systems
Computer
Terminal
Remote sensor
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Key Elements of a Protocol
Syntax
Data formats
Signal levels
Semantics
Control information
Error handling
Timing
Speed matching
Sequencing
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Examples of Protocols
Applications:
HTTP(p.45)
SMTP(p. 48)
FTP(p.82)
Transportation: TCP
Networking: IP
many others....almost too many
(skip sections 1.2.2, 1.2.3, 1.2.4,1.2.5, 1.2.6,
1.3.1)
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TCP/IP Protocol Architecture
Developed by the US Defense Advanced
Research Project Agency (DARPA) for its packet
switched network (ARPANET)
Used by the global Internet
No official model but a working one.
Application layer
Host to host or transport layer
Internet layer
Network access layer
Physical layer
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TCP/IP Protocol Architecture
Model
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Protocol Data Units (PDU)
At each layer, protocols are used to
communicate
Control information is added to user data at
each layer
Transport layer may fragment user data
Each fragment has a transport header added
Destination SAP
Sequence number
Error detection code
This gives a transport protocol data unit
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Application A
data
Application
Layer
data
Transport
Layer
data
Network
Layer
Physical
Layer
data
dt
Presentation
Layer
ph
data
Session
Layer
Application
Layer
ah
data
Presentation
Layer
Data Link
Layer
Application B
data
sh
Session
Layer
th
Transport
Layer
Network
Layer
nh
dh
bits
Copyright 2000 Leon-Garcia and
Widjaja Communication Networks
Data Link
Layer
Physical
Layer
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Figure 2.9
Physical Layer
Physical interface between data transmission
device (e.g. computer) and transmission
medium or network
Characteristics of transmission medium
Signal levels
Data rates
etc.
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Network Access Layer
Exchange of data between end system and
network
Destination address provision
Invoking services like priority
33
Internet Layer (IP)
Systems may be attached to different networks
Routing functions across multiple networks
Implemented in end systems and routers
34
Transport Layer (TCP)
Reliable delivery of data
Ordering of delivery
35
Application Layer
Support for user applications
e.g. http, SMPT
36
OSI Model
Open Systems Interconnection
Developed by the International Organization for
Standardization (ISO)
Seven layers
A theoretical system delivered too late!
TCP/IP is the de facto standard
37
Application A
Application B
Application
Layer
Application
Layer
Presentation
Layer
Presentation
Layer
Session
Layer
Session
Layer
Transport
Layer
Communication Network
Transport
Layer
Network
Layer
Network
Layer
Network
Layer
Network
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Data Link
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Physical
Layer
Electrical
and/or Optical
Copyright
2000 Leon-Garcia
andSignals
Widjaja Communication Networks
38
Figure 2.6
OSI Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
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OSI v TCP/IP
40
Standards
Required to allow for interoperability between
equipment
Advantages
Ensures a large market for equipment and software
Allows products from different vendors to
communicate
Disadvantages
Freeze technology
May be multiple standards for the same thing
41
Who defines standards?
International: The International Standards
Organization(ISO)
The American National Standards
Institute(ANSI)
The International Telecommunications UnionTelecommunication Standards Sector (ITU-T,
formally the CCITT)
The Institute of Electrical and Electronics
Engineers (IEEE)
Internet Society (ISOC) and Internet
Engineering Task Force (IETF)
ATM Forum
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What have they defined?
ISO: Open Systems Interconnection(OSI)
ANSI: represents USA in ISO
ITU-T: X.25, X.400, X.500; e-mail; ISDN
IEEE: IEEE 802.2, 802.3, 802.4, 802.5, 802.11
ISOC and IETF: TCP/IP, SNMP, routing protocols
(RIP, OSPF, BGP)
IETF: maintains Request for Comments(RFCs)
ATM: ATM related standards
43
Further Reading
Sections 1.1, 1.2,(skip pp.14-pp32)
Sections 2.1, 2.2, 2.3
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