Transcript 1.introduct
Part 1
1. Introduction to
Computer Networks
Changjin Suh
Soongsil University, School of Computing
820-0686, [email protected]
1
0. Contents
topics
to cover
1. data communication network model : simplified communication
networks
2. famous communication standard organizations
ITU comm. networks
IETF comm. networks
3. protocol stack
TCP/IP model
7-layer OSI model
4. standards
2
1. Data Comm. Network Models
model
o
:
simplified representation consisting of major factors to denote complex
system
communications
model
o
source(송신자) : generates data to be transmitted
o
transmitter(송신기) : Converts data into transmittable signals
o
transmission System : Carries data
used to called “networks”
o
receiver(수신기) : Converts received signal into data
o
destination(수신자) : Takes incoming data
(See the next slide)
3
1. Data Comm. Network Models
simplified
communication model - diagram
4
1. Data Comm. Network Models
Data
Communications Model
o
information : important ideas or contents (abstract)
o
data
o
signal
o
analog/digital
(image)
abstract
5
1011011
s(t)
1. Data Comm. Network Models
Network
o
Model1
transmission system : may includes LAN, MAN, WAN, internet,
ADSL, …
6
1. Data Comm. Network Models
network
o
o
component
links (medium) : 링크
transmission medium like
cable, fiber optics
router
server
workstation
mobile
local ISP
nodes : two types
host : PCs, servers,
network devices : routers,
switches
regional ISP
path(경로)
: line connecting
source and destination node
o
consists of a sequence of links
company
network
7
1. Data Comm. Network Models
Internet
x
w
y
z
8
2.1. ITU Comm. networks
ISDN
(Integrated Services Digital Network)
o
Designed to replace public telecom system
o
Wide variety of services
o
Entirely digital domain
o
the first network that can send telephone and data transfer together
Frame
Relay
Most overhead for error control is stripped out from ISDN or ATM
o
Packet switching systems had large overheads to compensate for errors
o
Modern systems are more reliable, so that simple error recovery is
enough
Only end systems (server and PC) can check errors.
o
only for data transfer used in late 1990 ~ early 2000
9
2.1. ITU Comm. networks
ATM
(Asynchronous Transfer Mode)
o
Evolution of frame relay
o
Little overhead for error control (same as frame relay)
o
Fixed packet (called cell) length
o
fast : basic rate = 155Mbps
o
for data, telephone, and realtime multimedia services
xDSL
o
begun as a family of broadband network(=ATM)
o
for high speed access network used with telephone lines.
10
2.2. IETF Comm. networks
Local
Area Networks by IEEE802
o
Smaller scope
Building or small campus
o
Usually owned by same organization
o
Data rates much higher (10Mbps to 10Gbps)
o
(previously) broadcast system, but currently changes to non-broadcast
o
more than 90% is Ethernet, wireless LAN, Wibro, metro (Ethernet)
Internet
o
by IETF
TCP/IP, SIP, …
size
wire .
LAN
LAN
extension
wired
Ethernet
metro
wireless
wireless WIMAX or
LAN
WIBRO
11
3.1. TCP/IP Model by IETF
TCP/IP
Protocol Architecture Model
12
3.1. TCP/IP Model by IETF
core
actions of 5-layer model
layer
roles
application
Generate message for users’ convenience
transport
Make sure the message at the destination and source identical.
(If transmission error occurs, retransmission is required)
network
provides how to reach the destination node (Internet only gives
navigation information : no action!)
If necessary, do interworking!
network access Generate frames and send it to the peer node (action!). + LAN
physical
Send a bit to the peer node.
analogy of L2 and L4
o L2 in charge of link transmission (one-hop transmission) and
o L4 in charge of end-to-end(source to destination) transmission
13
3.1. TCP/IP Model by IETF
Application
Layer
o
Support for user applications
o
e.g. http, SMTP
Transport
Layer (TCP)
o
Reliable delivery of data
o
Ordering of delivery
Internet
Layer (IP)
o
Systems may be attached to different networks
o
Routing functions across multiple networks
o
Implemented in end systems and routers
14
3.1. TCP/IP Model by IETF
Network
Access Layer
o
Exchange of data between end system and network
o
Destination address provision : IP address
o
Invoking services like priority
Physical
Layer
o
Physical interface between data transmission device (e.g. computer)
and transmission medium or network
o
Characteristics of transmission medium
o
Signal levels
o
Data rates
15
Data Transfer
data
application
transport
network
link
physical
application
transport
network
link
physical
network
link
physical
application
transport
network
link
physical
data
application
transport
network
link
physical
16
3.2. OSI 7 Layer Model by ITU
OSI
Model (Open Systems Interconnection)
o
Developed by the International Organization for Standardization (ISO)
o
A theoretical system : currently not used
TCP/IP model
OSI
(not OSI 7 layer model) is the de facto standard.
7 Layers : Please Do Not Touch (the) Sexy Pamela Anderson !
o
Application
o
Presentation
o
Session
o
Transport
o
Network
o
Data Link
o
Physical :
17
3.3. 5-Layer and 7-Layer Model
OSI
v TCP/IP
18
4. Standards
Standards
o
required to allow for interoperability between equipment
define protocols and suggest the way of desirable primitives
o
advantages
low cost : (See next slides)
convenience : easy inter-operability between many
communication vendors
o
disadvantages
It freezes technology and research.
may be multiple standards for the same thing
19
4. Standards
comparison
of standard/non-standard
o
condition : K sources and L destinations (See next slide)
o
non-standard : K*L protocols and K*L implementations
o
standard
:
1 protoco and K + L implementations
20
4. Standards
Use
of Standard Protocols (k=4, L=3)
21
5. Connection Oriented vs Connectionless
CO(Connection
Oriented)
o
자신이 수행할 기능을 고품위로 매우 정성스럽게 처리함.
이를 이루다 보니 다음과 같은 특성을 갖게 되었다.
o
상대방에게 여러 차례 세부사항을 문의함.
상대방이 여러 번에 걸쳐서(질의 sequence가 존재함) 요청함.
state-oriented : state를 잘 제어하여 동작시퀀스를 만들고 있음.
o
상대방이 요청한 세부사항을 기억하고 있음.
o
프로토콜과 프로그램이 복잡함
o
CPU power가 많이 소요됨(사용자 1인당 서비스 비용이 높음)
22
5. Connection Oriented vs Connectionless
CL(Connectionless)
o
정의 : 자신이 수행할 기능을 간단하고 신속하게 처리함.
이를 이루다 보니 다음과 같은 특성을 갖게 되었다.
o
상대방의 하나의 요구 사항을 당장 한번에 처리함. (처리가 불가할
경우 서비스가 안됨을 상대방에게 통보함.)
o
memoryless : 일단 작업이 끝나면 서비스와 관련된 모든 사항을
폐기함.
o
프로토콜과 프로그램이 간단함.
o
CPU power가 적게 소요됨(사용자 1인당 서비스 비용이 저렴함)
23
5. Connection Oriented vs Connectionless
connection-oriented
o
vs connectionless
Every layer are both implemented as CO or CL.
connection-oriented
connectionless
complexity
complicated
simple
cost
expensive
cheap
1-state
(called stateless)
multi-state
state
1. pre, 2.main, 3.
ending ,,,,
only main state
memory
sequence control
possible
memory-less
reliability
reliable
un-reliable
service quality
good
poor (“best effort”)
24
5. Connection Oriented vs Connectionless
typical
o
behavior of CO service
client
3. connection
release
un-connected
state
1. connection
establishment
connected state
2. main routine
o
server
3. connection
release
un-connected
state
ready state
1. connection
establishment
connected state
2. main routine
25
5. Connection Oriented vs Connectionless
적응계층에서의 CO
o
smtp : 수신자 측은 송신자 측에서 올바른 account와 사용자id를
언급한 경우에만 메일의 내용을 송신하도록 허락함.
o
ftp : 요청자가 올바른 account와 passwd를 올바르게 입력한
경우에만 file transfer를 허용함.
적응계층에서의 CL
o
http : http request를 보내면 그에 해당하는 내용을 전달하고 종료함.
그 외의 프로토콜
o
html, xml : 통신 프로토콜이 아니어서 혼자서 전달된 내용만으로
일을 처리함. 따라서 CO, CL의 구분도 없음.
26
5. Connection Oriented vs Connectionless
every
o
layer has connection-oriented & connectionless
transport L : for a path
the same content at the source = the same content at the destination
CO
: TCP
CL : UDP
o
IP L : routing along a predetermined path
CO : ATM routing (virtual circuit),
telephone routing (Circuit switching, Signal No.7)
CL : IP routing (OSPF, RIP, …)
27
5. Connection Oriented vs Connectionless
every
o
layer has connection-oriented & connectionless (2/2)
network access L : for a link
the same content at the source = the same content at the destination
CO
: X.25,
CL : Ethernet (most LANs)
CO/CL의 조합1
o
browser는 http(CL) - TCP(CO) - 인터넷(CL)로 동작함.
o
VoIP는 RTP(CO) - UDP(CL) – 인터넷(CL)로 동작함(자세한 사항은
다음 참조)
28
5. Connection Oriented vs Connectionless
자세한 멀티미디어 서비스의 프로토콜 스택
IP
29
6. Addresses
Every
layer has addresses or Id.
layer
protocols
address
application
E-mail
[email protected]
transport
TCP, UDP
port addr.
network
IP
IP addr.
network access
Ethernet
Ethernet addr. or
(mac addr., NIC addr.)
physical
usually combined with N.A.
(not famous)
30