Ch2 Communication

1. Benefit of networking devices

WAN Private/Pubilc

  • larger geographic coverage
  • Connect to virtual devicse 虚拟机
  • Able to connect to the cloud
  • Easy to expand users

LAN Private

  • Faster transimate speed
  • Lower latency (safer)
  • Easy to set up
  • Lower cost to set up & maintance

2. Difference between peer-to-peer &client-server

p2p

peer to peer

  • Features

    1. All computers are equal
    2. Data is distributed in many devices
    3. Each device responsible for its own data security (NO FIRE WALLS)

  • Advantages

  • File download separatlly & simultaneously

Client-Server

\[ \text{Client-Server} \Rightarrow \begin{cases} \text{Thick Client} \\ \text{Thin Client} \end{cases} \]

  • Sever run applications,tests given by the client
  • Client request data from server
  • Server process data and send results back
  • Client display results

Thick & Thin Client

  1. Thick: Client do some of the applications work
  2. Thin: Client only display results, server do all the applications work

3. Network Topology

BUS

  • Advantages
    1. Easy to set up & extend
    2. Cheap
    3. One link shared by many devices (LAN)
  • Disadvantages
    1. If one device fails, whole network fails
    2. Limit distance range
    3. Collisions CSMA/CD(见第7点)
    4. Lots of traffic on one spine

Ring

  • Advantages
    1. Higher transimation speed (compare to BUS)
    2. Each device has equal access to the resource
    3. No need for centrol device
  • Disadvantages
    1. Error effect to the whole system
    2. Highly dependent on wire
    3. Transimation speed slower than Star

Mesh

  • Advantages:
    1. Data transmited simultaneasly
    2. Error do not effect the whole system
    3. Extnad with out distrubuting other devices
  • Disadvantages:
    1. Costly
    2. Too much route unused

Star

  • Advantages
    1. Easy to set up & extend
    2. Error do not effect the whole system
    3. Centralized management
  • Disadvantages
    1. Dependent on central device
    2. Central device (Hub/Router) increase cost
  • How packet transmitted in star:
    1. Packet contains destination address (IP)
    2. Sender send packet to central device
    3. Central device locate & send packet only to resever

4. Cloud computing

  • Accessing a resource on a remote device

Advantages

  1. Access any where with internet
  2. Easyer to share
  3. More secure
  4. Muitple users work on one file

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Disadvantages

  1. Can't access with out internet
  2. Reliant on server own security(Firewall)
  3. Can't access when server is down

5. Wired & Wireless networks

Wiredless network

  • Advantage
    1. Devices can be more mobile
    2. No need for physical connection(cable)
    3. Easy set up & extend
    4. Muitple devices can share one connection
  • Disadvantage
    1. Easy hacking
    2. Signal degrades quickly
    3. More interference

Different wires

  • Fibre-optic compare to copper wire
    1. Less interference
    2. Need less signal boosting
    3. Difficult to hack
    4. Bigger bandwidth
  • Disadvantage of Fiber-optic
    1. More expensive
    2. Fragile / Easy broken
    3. Transmit data in one direction
    4. Can't transmit POWER
Type of connection Descriptions
Fibre-optic 1. Transmit data as light signal
2. Made of glass/plastic
Copper wire 1. Transmit data as electrcal signal
2.Connect with twised paires of copper wire
Satellite 1. At Earth's obrit
2. Recives & transmits data
Radio waves 1. Transmit data as electromagnetic waves
2. Carries data wireless(Wi-Fi)

6.Router路由器

  • Router is a device that connects two or more networks
  1. Receove packets from network/devices
  2. Find destination using IP address
  3. Send packets to destination
  4. Assign Private IP to devices on LAN
  5. Update & Maintain a Routing table (Mac- IP table) for faster transimition
  6. Procides the LAN with public IP
  7. Gateway to the internet 网关
  8. Used as Firewall
  9. As control device in some Topology(Star)

7. 以太网Ethernet

  • 有线的LAN, 遵守CSMA/CD和TCP/IP(AS不考)协议
  1. A protocol (Alevel)
  2. Have CSMA/CD
  3. Data transmitted over wired networks
  4. Data transmitted as frames 帧
  5. Frame contains Data & destination IP address
    • Frame header: Data & Destination IP address
    • Frame trailer: Error checking
  6. Check if the frame is corrupted( By frame trailer)

How CSMA/CD works

Carrier Sense Multiple Access with Collision Detection

  1. Work station monitor the communcation channel
  2. If channel is free, send data
  3. Collision occurs when two or more work stations try to send data
  4. Delay for a random time(caculate by CSMA/CD) and try again
  5. Collision occurs again, delay time increases

7.Bit Streamming

  1. Data compressed before transmission
  2. Video/Sound signal transmitted as series of bits(bit stream)
  3. Signal is hosted on a media server
  4. Buffer stores the data in
  5. Binary data is converted to audio/video signal by software in user

8.Differernt between WWW & Internet

  1. Internet is a collection of global networks
  2. WWW is the muitmedia of pages
  3. Wab page of WWW is written in HTML
  4. WWW is accessed over the internet
  5. WWW use HTTP protoal
  6. Internet use HTTP,IP,(SMTP)... protocols

9. Communcation system

PSTN

  • Public Switched Telephone Network 公共交换电话网络
  1. Consists of many different type
  2. Data transmitted in both direction
  3. Communcation pass through different switches 转换机

Other communcation system

  • Dedicated line 专线
    1. Perment connection
    2. Used for SQL & big organizations
    3. Safer than other system
  • Cell phone network
    1. Send data to cell towers 信号塔 over mobile devices
  • Satellite
    1. Send data to satellite over wireless networks

Set up Dedicated lines

  • Advantages
    1. Faster
    2. More consistant transmission speed
  • Disadvantages
    1. Expensive to set up & maintance
    2. No alternative if line is off

10. IP in data transmission

Different between IP in Router & computers

  • Router
    1. Public IP address to be identifiable on internet
    2. Private IP to be identifiable on LAN
  • Computers
    1. Need Public IP only if direct connect to internet
    2. Private IP to be identifiable on LAN
    3. Do not need Public IP if connect to internet through Router
    4. More secure to hide under private IP
    5. Date need to pass through Router before reserve

11. How to loacte resource on WWW

  • DNS, URL , IP

Steps for URL mathcing IP

  1. Broswer translate URL to Domain Name
  2. A list of domain name & comesponding IP is stored in devices
  3. Go to DNS is not found
  4. DNS is a database of domain name - IP
  5. Go to higher DNS untill IP if found
  6. Return the domain name to broswer
  7. Return 404 if not

\[ \begin{aligned} &\text{URL typed in broswer} \rightarrow \text{Broswer send URL to DNS}\rightarrow \text{Client-Server}\rightarrow \begin{cases} \text{Found} \rightarrow \text{DNS return IP to broswer} \\ \\ \text{Not found} \rightarrow \text{Go to other DNS} \\ \end{cases}\\ \end{aligned} \]