Foundation1
Introduction
packet switching -> store and forwarding 방식 사용
Why do we have 'data loss'?
The size of memory is limited -> it occurs overflow.
1. What is Internet?
A set of networks based on IP protocol.
IP address -> what addresses are required?
A) Source address/Destination address
Internet vs Web(ex. google)
Internet: web+e-mail+online cat+...
Web: Part of internet. A collection of interconnected documnets, linked by URL, hyperlinks.
Packet switching
Circuit switching
* What is wireless's two important meanings?
- Mobility
- Broadcast
2. What is a possible architecture of the Internet?
A network consisting of routers
TCP/IP protocol
L1: Physical layer
bit.
L2: Data Link Layer
hop-to-hop(one-link, one-hop). frame.Reliable
ex) MAC,
CSMA/CA(Carrier Sense Multiple Access/Collision Avoidance) -> ethernet,
CSMA/CD(Carrier Sense Multiple Access/Collision Detection) -> Wifi
LLC(Logical Link Control)
MAC 계층과 Network layer의 접속 담당.
MAC 계층과 독립적으로 위치하지만 L2에 속한 것으로 본다
L3: Network Layer
end-to-end. packet.Unreliable
ex) IP(IPv4, IPv6)
- IP: Best-effort delivery, Unreliable, Connectionless
L4: Transport Layer
process-to-process(port). segment.
ex) TCP(Reliable)/UDP(Unreliable)
- segment: always include AWS(Advertisement Window Size)
L5: Application Layer
message.
ex) HTTP
TCP에서의 ACK
TCP에서 ACK는 Sequence number에 1을 더한 값으로 전송된다.
3. What is the possible communication layers consisting of the Internet architecture?
TCP/IP protocol suite(5 layers)
IP is unreliable. Why?
A) IP의 위아래 계층들이 많아 연결용으로 쉽고 단순한 구조로 구성될 필요가 있음.
OSI 7 Layers
L5가 Session, Presentation, Application으로 구분됨.
- Session: A set of connections for a transaction
- Presentation: encoding, pack, ...
- Application: Manage the session
Reliable - Control
- Error Control(Required)
TCP는 ACK를 통해 Error Control을 진행함. UDP는 ACK 없으므로 Unreliable- Flow Control(TCP standard)
Prevent the receiver from overflow- Congestion Control(Optional)
Reduce the rate of transmitting packets(RTT)
병목 현상- IPv4 does not care about flow/congestion control
4. What is a mininal data unit over the Internet?
Internet is based on IP protocol(L3) -> Network layer's minimal data unit is packet.
Packet: Header+Options+Payload
Internet is a network of networks based on IP.
* What is LAN?
LAN(Local Area Networks)
-> one-hop range area network
* Why do we need router?
Router is required to interconnect different networks.
Router
Router interconnects based on IP.
IP address has network number/host number
- Network number: Identifies a distinguish network.
- Host number: Identifies a distinguish host(End-system)
* What is subnet mask?
A) Network number과 Host number을 구별할 수 있게 해 주는 nubmer.
ex) 192.168.0.3 / 192.168.0.4
-> 192.168.0은 network number, 3,4는 host number
IP packet fragmentation&Reassemble?
Packet fragmentation: Occurs of router
Packet reassembly: At destination system
MTU(Maximum Transmission Unit): 1460bytes(Total 1500bytes - IP headers(20bytes) - TCP(20bytes))
IP header's length: 20bytes
Version(4bit)
Header length(4bit)
Total length(16bit)
Header checksum(16bit)
SRC IP address(32bit)
DST IP address(32bit)
- Router은 Header만 care하고 Payload는 care하지 않음
Fragmentation이 진행되어도 Packet ID는 100으로 동일
Foundation2
How to make networks scalable -> switching technique
Packet switching
Source에서 message를 일정한 크기의 packet으로 분해해서 전송.
Destination에서 모두 받은 후 조립.
- 장점: 고효율, 다른 기종의 단말장치도 통신 가능
- 단점: 경로에서 다소의 지연 발생 가능. 패킷별 헤더 추가로 인한 overhead(헤더 추가로 인한 추가 처리 시간/메모리) 발생 가능
Circuit switching
A와 B 사이 회선이 연결되면, 회선을 독점한다.
- 장점: 전송 지연 없음, Fast and simple transfer
- 단점: 회선 이용률 측면에서 비효율적
ex) Telephone network
1. How to build a scalable network that will support different applications?
Switched networks
2. What is a computer network?
Packet switching networks
3. How is a computer network different from other types of networks?
Circuit vs Packet switcing networks
4. What is a computer network architecture?
Store and forward -> based architecture with TCP/IP protocol suite consisting of 5 layers
