Transcript lecture1-stu

EE4272: Computer Networks
Instructor: Dr. Tricia Chigan
Dept.: Elec. & Comp. Eng.
EE4272
Spring 2004
Introduction of Computer
Networks
Communication & Computer/Data Networks
 Applications of Computer Networks
 Requirements
 Network Architectures
 Implementing Network Software
 Network Performance

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Communication & Computer/Data
Networks

What are the differences between…
 Applications
 Underline
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technologies
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Applications of Computer
Networks (e.g. …)

Surfing the Web


of Client/Server
Streaming Audio & Video
 Video-on-demand:
(
 Video Conference: (

)
)
Different requirements for various
applications

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Requirements from Perspectives…

Application programmer: services that their
applications need, e.g.,

Network designers: cost-effective design
e.g.,

Network providers: system that is easy to
administer and manage e.g.,
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High-level Major Requirements
- Network Designers’ Perspectives
Connectivity
 Cost-Effective Resource Sharing
 Reliability

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Building Blocks & Connectivity

Nodes: PC, special-purpose hardware…
 Host:
edge node for
.
 Switch: node to
.
 Router/Gateway: node connects two/more
different
.


Links: coaxial cable,
Direct connectivity
(a)
 point-to-point
 multiple
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access
(b)
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…

Indirect Connectivity

Switched networks


Internetworks


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switch
router
gateway
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Issues Related to Connectivity

Switching Strategies
 circuit
switching (
send/receive
.
 packet switching (
shared channel; send/receive

): dedicated circuit;
): store-and-forward;
.
Addressing and Routing
 address:
byte-string that
 routing: process of
destination node based on its
 types of addresses



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a node; usually unique
messages towards the
cast: node-specific
cast: all nodes on the network
cast: some subset of nodes on the network
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Cost-Effective Resource Sharing

Must share (multiplex) network resources
(nodes and links) among multiple users
L1
R1
L2
R2
Sw itch 1
Sw itch 2
R3
L3
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Conventional Multiplexing
Strategies

Synchronous Time-Division Multiplexing
(STDM)

Frequency-Division Multiplexing (FDM)
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Statistical Multiplexing



On-demand (not predetermined) time-division
Schedule link on a
basis (fairness): FIFO,
Round-robin…
.
Packets from different sources
on link


What about if only one source has data?
Why


is needed?
Buffer packets that are contending for the link:
Buffer (queue) overflow is called
.
.
■■■
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Spring 2004
What Goes Wrong in the Network?
-Reliability Issue

(light, power,
microwave interference -> error
detection/correction): single or burst error
 depend
on transmission med.: coaxial cable, optical
fiber?
(congestion control)
(network survivability)


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Spring 2004
Network Architecture



Use abstractions (unified model)
Abstraction naturally lead to
Can have
.
.
at each layer
Application programs
Client
Server
Request/reply Message stream
channel
channel
Host-to-host connectivity
Hardware
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Spring 2004
process-to-process
Layering & Protocols

Advantages of Layering
 Manageable
 Modular

design
Protocols
 building
blocks of a network architecture layer
 Each protocol object has two different interfaces


service interface: operations
.
peer-to-peer interface: messages exchanged with
 Term


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“protocol” is overloaded
Module (various) that implements this interface:
specification of peer-to-peer interface (
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)
Interfaces
Host 1
Host 2
High-level
object
High-level
object
Protocol
Protocol
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Protocol Machinery

Protocol Graph
 most peer-to-peer
 peer-to-peer is
communication is
.
only at hardware level
Host 1
File
application
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Digital
library
application
Video
application
Host 2
File
application
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Digital
library
application
Video
application
Protocol Machinery (cont)


Encapsulation (
: control infor., e.g. seq. num)
Multiplexing & Demultiplexing (
): share logical
channel at each protocol layer
Host 1
Host 2
Application
Application
program
program
Application
Application
program
program
Data
Data
RRP
RRP
RRP
Data
RRP
HHP
HHP
HHP
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RRP
Data
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Data
OSI (open systems interconnection)
Architecture
End host
End host
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Netw ork
/aggregation
Data link
Physical
Netw ork
Netw ork
Data link
Data link
Physical
Physical
One or more nodes
w ithin the netw ork
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Netw ork
Data link
Physical
Internet Architecture

Defined by

Design
Application vs Application Protocol (e.g.,HTTP)

FTP
HTTP
(
NV
TFTP
TCP
UDP
TCP
Application
IP
NET 1
NET 2
IP
■■■
NET n
Ethernet, ATM, FDDI…
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UDP
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Network
)
Some Protocols in TCP/IP Suite
Source: book by William Stallings
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Software Protocol Implementation

Service Interface (e.g. Socket API)

socket: the point where a local applications process attaches to the
network


built in most of the Unix OS, common library routines (socket, listen,
accept, client, server, connect, send, recv…)
reference: W. Richard Stevens, Unix Network Programming, 2nd edition,
Prentice Hall 1998

Protocol Implementation Issues (difference
between Socket & protocol- protocol interface)


Process Model
Message Buffers
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Performance Metrics

Bandwidth (throughput) :
 data
transmitted per time unit
 link vs. end-to-end

Latency (delay)
 time
to send message from point A to point B
 one-way versus round-trip time (RTT)
 components

Latency = Propagation + Transmit + Queue




Propagation =
Transmit =
.
.
Throughput (end-to-end) = TransferSize / TransferTime
TransferTime = RTT + 1/Bandwidth x TransferSize (w/o
queue)
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Delay x Bandwidth Product


Amount of data “in flight” or “in the pipe”
Example: 100ms x 45Mbps = 560KB
Delay
Bandw idth

Application Needs

requirements (
): burst with
peak rate

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: variance in latency (
Spring 2004
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