[Lecture]Network 3강 : 1.4 delay, loss, throughput in networks

One-Hop(Link) Delay

1. Processing delay(routing table lookup&swiching)

2. Queueing delay(output buffer at router when data be crowed)

3. Transmission delay (bit --> singal depanding on a cable performance)

4. Propagation delay(router to router)

 

Nodal processing

- routing table lookup & switching from input port to output port(store and forward)

1. Check bit erros

2. Determine output link

 

Queueing delay

- queueing delay at outout link for transimission

1. time waiting at outout link for transmission.

2. depends on congestion level of router

tip : traceroute == 목적지로 거치는 라우터를 모두 볼 수 있는 명령어

Transmission delay(L/R)

- transmission delay

1. L : packet length (bits)

2. R : link bandwidth (bits) == Put bits into link by speed

 

Propagation delay(d/s)

- 하나의 bit가 1-Hop을 이동하는데 걸린 시간

1. d : length of physical link

2. s : propagation speed in medium

 

 

Queueing delay(revisited)

data == traffic

a is average packet arriaval rate which is meaning that sometime some packet is longer than average. 0.7 point La/R is to turning point into infinite queueing delay.

 

1. Packet loss

packet arriving to full queue dropped(aka lost)

lost packet may be retransmitte by previous node, by source end system, or not at all

 

2. Throughput(단위 시간당 처리량)

rate(bits/ time unit) at which bits transferred between sender/receiver( End to End)

 

 

1.5 Protocol layers, service models

Why Layer?

해야 할 일이 많기 때문에 시스템 별(일처리 별) 계층을 분리, 모듈화 하여 독립적으로 작업 수행.

 

 

Application  == Message

application 계층 (msg) user가 사용하는 최상단 network application을 support하는 protocol. IETF에서 RFC문건으로 정의

Ex. FTP, SMTP(email이라는, network를 필요로하는 application을 support), HTTP(web, file upload)

Transport == Segment

transport 계층 (segment) dst를 찾아 process to process data transfer(마치 같은 컴퓨터에 있는 것처럼 메시지를 주고 받음) 그러려면? dst에 가 있어야함. 그 역할을 하는 게 routing 하는 밑 계층.(그래서 아래 계층이 윗 계층의 service provider, 윗 계층은 아래 계층이 제공하는 service를 이용하는 user). IETF에서 RFC문건으로 정의

Ex. TCP, UDP

Network == Datagram

network 계층 (packet, datagram) src로부터 dst까지 routing을 수행. IETF에서 RFC문건으로 정의

Ex. IP, routing protocols(OSPF, RIP, BGP)

 

Link == Frame

link 계층 (frame) link, 한 hop을 지나가는 일을 수행. IEEE에서 정의 NIC(Network Interface Card)에 있음. link layer의 두 sublayer 중 윗 계층까지 sw로 개발할 수 있음

Ex. Ethernet, 802.11 (Wifi), PPP

 

physical 계층 물리적인 일 담당. IEEE에서 정의, NIC에 있음

 

Scenario

source's application layer 헤더를 붙여 4계층으로 내려보냄
source's transport layer process2process 해야하니까 dst의 transport layer가 보라고 헤더를 붙여 내려보냄. port 주소 담김
source's network layer 라우팅할 때 보라고 dst address(IP) 등 붙여 내려보냄
source's link layer 1 hop을 이동 (switch는 3계층이 없으니 IP 주소도 없고 2계층의 MAC주소도 없음), 여기서 붙이는 header는 다음 switch의 link layer가 보라고 붙이는 것. 주로 MAC addr 담김

switch's link layer router로 가기 위한 MAC addr가 담김
router's link layer link layer에서 1 hop을 이동한 것
router's network layer 헤더를 떼고 올려줘야 src의 network layer에서 붙인 헤더를 보고 dst addr를 알 수 있음
router's link layer 다시 ****헤더에 다음(여기선 dst) 2계층 주소를 설정

destination's link layer 받음
destination's network layer 헤더의 dst addr를 보고 맞게 왔는지 확인할 수 있음
destination's transport layer 헤더의 port 번호를 보고 맞는 application에 msg 전달

 

한 hop(link)이 길면 중간에 switch가 있을 수 있음

패킷 네트워크에서 패킷이 1-hop을 지나간다고 하는 것은 하나의 네트워크를 지나간다는 의미

보다 구체적으로, “사용자 디바이스(end host)와 라우터” 사이 혹은 “라우터와 라우터” 사이를 이동하는 것을 의미

⇒ 사용자와 라우터 사이에 존재하는 2계층 스위치는 같은 네트워크에 포함되므로 하나의 홉에 포함됨

⇒ 위 그림에서 source에서 router까지가 한 hop. source의 link 계층 헤더는 router의 link 계층에서 봄

link 계층과 network 계층의 차이

network 계층은 최종 목적지를 향한 다음 노드 (라우터 혹은 목적지 호스트)를 결정. → 3계층 헤더에 포함된 목적지 주소는 destination host의 IP 주소

link 계층 헤더에 포함된 목적지 주소는 **다음 노드 까지 가는 2계층 주소**

결과적으로 하나의 패킷이 한 홉을 지나갈 때 3계층 IP 목적지 주소는 변하지 않으나 2계층 목적지 주소는 계속 변함

⇒ 2계층에서 주로 MAC addr 사용, 3계층에서 주로 IP addr 사용

 

 

Netwrok security

 

 

춸처 : 이화여대 컴퓨터 네트워크 (2014년)

https://velog.io/@lychee/%EB%84%A4%ED%8A%B8%EC%9B%8C%ED%81%AC-1.5