csc 535 communication networks i chapter 1 introduction dr. cheer-sun yang
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CSC 535Communication Networks I
Chapter 1Introduction
Dr. Cheer-Sun Yang
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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
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Network and ServicesA 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.
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Radio and TV NetworksMeans 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
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Telephone NetworksMeans 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.
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The caller picks up the phone triggering the flow of current in wires that connect to the 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.
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.)
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.
The ringing signals are discontinued when the destination phone is picked up and communication can then proceed.
Either of the users terminate the call by putting down a receiver.
Telephone Office
1.
Telephone Office
2.
Telephone Office
3.
4.
Telephone Office
5.
6.
Telephone Office
Telephone Office
Figure 1.1
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Data NetworksMeans 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 real-time (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
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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.
1.
2.
3.
4.
5.
6.
Figure 1.4
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Realplayer example
Figure 1.5
Copyright © 1995-2000, RealNetworks, Inc. All rights reserved. RealPlayer is a trademark of RealNetworks, Inc.
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Network Funcations and Some Design IssuesProvides connectivity between usersSwitching provides a saving on the number of
connectivityMultiplexing provides an efficient way to share
connectivityRouting provides a direction regarding a
destination associated with a connection Addressing identifies source and destinationsTraffic control regulates traffic flowing through a
networkNetwork management monitors network status
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t0t1
Network
Figure 1.6
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Network
(a) A switch provides the network to a cluster of users
(b) A multiplexer connects two access networks
Access network
Figure 1.7
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Metropolitan network A consists of access subnetworks a, b, c, d.
National network consists of regional subnetworks .
Metropolitan network A is part of regional subnetwork .
A
A
Metropolitan
1*
a
c
b
d
(a)
(b)
2
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Figure 1.8
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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 CardHardware: modemSoftware: TCP/IP softwareSoftware: device driverSoftware: operating system that ftp(an
application program) is running onLet’s try “ftp -d taz.cs.wcupa.edu”
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[yang@coyote yang]$ ftp -d taz.cs.wcupa.eduConnected 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 yang331 Password required for yang.Password:---> PASS XXXX230 User yang logged in.---> SYST215 UNIX Type: L8Remote system type is UNIX.Using binary mode to transfer files.ftp>
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ftp> cd public/socket---> CWD public/socket250 CWD command successful. ftp> get server1.clocal: server1.c remote: server1.c---> TYPE I200 Type set to I.ftp: setsockopt (ignored): Permission denied---> PASV227 Entering Passive Mode (144,26,77,43,87,139)---> RETR server1.c150 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.clocal: server1.c remote: server1.cftp: setsockopt (ignored): Permission denied---> PASV227 Entering Passive Mode (144,26,77,43,180,246)---> STOR server1.c150 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---> QUIT221-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.
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C
PS
PS
C
PSPS
C
C
C
PS = packet switch
C = computer
Figure 2.7
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G
G
G
G
G
net 1
net 2
net 3
net 4
net 5
G = gateway/router
G
Figure 2.8
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Net Interface
IP
TCP
HTTP
Net Interface
IP
Net Interface
IP
TCP
HTTP
Ethernet PPP
Router
router
(1,1)
s
(1,2)
w
(2,1)
(1,3) r
(2,2)
PPP
Ethernet
(a)
(b)
Server PC
Figure 2.13
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User Interface
User PI
User DTP
PI = Protocol interpreter
DTP = Data transfer process
User FTP
Server PI
Server DTP
Server FTP
Control
Connection
Data
Connection
Figure 2.19
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Communication ProtocolsA set of rules that is used for “governing” how a
source and a destination communicates. Must speak the same languageEntities
User applications e-mail facilities terminals
Systems Computer Terminal Remote sensor
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Key Elements of a ProtocolSyntax
Data formats Signal levels
Semantics Control information Error handling
Timing Speed matching Sequencing
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Examples of ProtocolsApplications:
HTTP(p.45) SMTP(p. 48) FTP(p.82)
Transportation: TCPNetworking: IPmany 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 ArchitectureDeveloped by the US Defense Advanced
Research Project Agency (DARPA) for its packet switched network (ARPANET)
Used by the global InternetNo 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
communicateControl information is added to user data at
each layerTransport layer may fragment user dataEach fragment has a transport header added
Destination SAP Sequence number Error detection code
This gives a transport protocol data unit
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ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
Application A Application Bdata
data
data
data
data
data
data
ah
ph
sh
th
nh
dh
bits
dt
Figure 2.9
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Physical LayerPhysical interface between data
transmission device (e.g. computer) and transmission medium or network
Characteristics of transmission mediumSignal levelsData ratesetc.
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Network Access LayerExchange of data between end system
and networkDestination address provisionInvoking services like priority
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Internet Layer (IP)Systems may be attached to different
networksRouting functions across multiple
networksImplemented in end systems and routers
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Transport Layer (TCP)Reliable delivery of dataOrdering of delivery
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Application LayerSupport for user applicationse.g. http, SMPT
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OSI ModelOpen Systems InterconnectionDeveloped by the International
Organization for Standardization (ISO)Seven layersA theoretical system delivered too late!TCP/IP is the de facto standard
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ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
ApplicationLayer
PresentationLayer
SessionLayer
TransportLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
NetworkLayer
Electrical and/or Optical Signals
Application A Application B
Data LinkLayer
PhysicalLayer
NetworkLayer
Data LinkLayer
PhysicalLayer
Communication Network
Figure 2.6
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OSI LayersApplicationPresentationSessionTransportNetworkData LinkPhysical
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OSI v TCP/IP
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StandardsRequired to allow for interoperability
between equipmentAdvantages
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
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Who defines standards? International: The International Standards
Organization(ISO)The American National Standards Institute(ANSI)The International Telecommunications Union-
Telecommunication 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
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Further Reading
Sections 1.1, 1.2,(skip pp.14-pp32)Sections 2.1, 2.2, 2.3