---
title: Intoduction network
tag: NPTU
---

# net work

- appliaction layer
- transport layer
- network layer
- link layer
- physical layer

http(hyper text transfer protocol)
ISP(internet service provider)
VoIP(voice over IP)
bandwidth頻寬
ADSL(Asymmetric digital subscriber line)
NAT(network address translator)
TDM(Time-division multiplexing)

# data transport

packet switch

message switching
- store-and-forward
---
# Internet

- portocals
> portocols define **format**, order of messgaes sent and received among network entities and action taken on message transmission receipt
>
- eg. TCP IP HTTP

## network edge
- hosts: clients nad severs
- servers often in data centers

## access networks and physical media

## network core

# physical media
- bit
- physical link
- guided media
- unguided media
- twisted pair(TP)

# pyhosical media: coax, fiber
- coaxial cable
- fiber optic cable

# circuit switching and packet switching

> FDM: frequency division multiplexing
> TDM: time division multiplexing

- packet switching allow more users to use network
- circuit has banrdwidth guarante

# Internet Structure: network of networks

## four sources of packet delay

- processing delay
- queueing delay
- propagation delay
- transmission delay

# throughput

- bottlenck link:
- link on end-end path that constrains end-end throughtput

- internet scenario:
- per-connection end-end throighput min
- in practice

# internet protocol stack

- application
- supporting network applications
- transport
- process-process data transfer
- network
- routing of datagrams from source to destination
- link
- data teansfer between neighboring network
- phyical
- bits "on the wire"

# rdt
| 版本 | 基本假設 | 缺點 | 改進版本 ｜
| --- | --- | --- | --- |
| 1.0 | perfect reliable | unrelidable | |
| 2.0 | with errors | ack/nak也會錯 | 加入checksum |
| 2.1 | with errors | packet loss | 加入 seguence |
| 3.0 | with errors/packet loss | 速度慢 | 加入 timer |