Computer Network Overview

[What is the internet?]

"internet" and "the Internet"

• internet (as a common noun)
  • inter + network(s)     <- any set of inter-connected networks
  • regardless of the use of TCP/IP
• the Internet (as a proper noun)
  • network of networks     <- network of globally interconnected computer networks
  • based on TCP/IP

 

Internet of X

1. The Internet -> IoC(Internet of Computers)
2. World Wide Web(WWW) -> IoD(Internet of Documents)
3. Social Media / Web 2.0 -> IoP(Internet of People)
4. Cloud Computing -> IoR(Internet of Resources)
5. Things / Objects -> IoT(Internet of Things)

   => IoE(Internet of Everything)

 

X2X(Any to Any)

1. X=Peer -> P2P(Peer-to-Peer)   #전통적
2. X=Machine -> M2M(Machine-to-Machine)
3. X=Human -> H2X(Human-to-Any)
4. X=Vehicle -> V2X(Vehicle-to-Vehicle)
5. X=Online/Offline -> O2O(Online-to-Offline)
6. X=AI -> AIoT(AI-to-Any, AI of Things or AI+X)

   => X2X(Any-to-Any)

 

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[Internet Networking Architecture]

General Network Reference Model

• Core network
  • mesh of interconnected routers
  • network of networks
  • two key core functions: forwarding, routing
• Access network
  • connecting home/enterprise networks and end systems to core network
  • use of various physical media
• Home/Enterprise network
  • connecting end systems or hosts
  • ecah host runs network applications

 

Internet Networking Architecture

1. 초기: full-mesh connection

2. ISP(Internet Service Provider)

• an organization that provides services for accessing, using, the Internet

3. Network of Networks

• Networks are interconnected through multiple ISPs
• End systems connect to Internet via access ISPs
• Each regional ISP then connects to tier-1 ISPs

   # IXP: operated by third party company to provide a meeting point to multiple ISPs

 

 

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[Definition of Protocol]

Various definition on protocols

• Society
  • etiquette
  • politics: a formal agreement between nation states
• Science
  • science: a predefined written procedural method of conducting experiments
  • clinical trial: a document that plans a clinical trial
• Communications(통신)
  • a defined set of rules and regulations that determine how data is transmitted
  • in telecommunications and computer networking

 

Definition of Communication Protocol

• the set of conventions for the communicating entities to exchange information successfully
• What must confrom to successfully communicate for two entities?
  • 주제: what is communicate
  • 수단: how it is communicated
  • 시간: when it is communicated

 

Key Elements of a Protocol

• Syntax     #data format
  • data formats
  • encoding/defoding information
  • signal level
• Semantics     #actions taken on message transmission and receipt
  • response
  • control information
  • error handling
• Timing     #order of messages
  • timeout
  • sequence number
  • speed matching

 

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[Layered Protocol Models]

Benefits of a Layered Model

• changes in one layer do not affect other layers => independence
• assists in protocol design and implementation easy
• fosters competition among vendors at each layer
• better learning and understanding protocols

 

Requirements for successful communications 

• Same number of layers at two entities
• Same protocol on each peer layer
• Same interface between upper & lower layers

 

Layered Protocol Reference Model

• Standardized Reference Protocol Architectures
  • Any device can communicate with others
  • Any vendors can provide marketable products
  • Customers can choose communication devices independent of vendors
• OSI(Open Systems interconnection) Reference Model
  • Official standard by ISO
  • Seven layers
  • delivered too late
• TCP/IP protocol suite
  • The de facto standard
  • Five layers
  • Most widely used

 

OSI 7 Layers Model

•  Application layer: means for application to access OSI environment
• Presentation layer 
  • define data formats to applications
  • Example services
    • Data formats
    • coding
    • Data compression
    • Encryption
• Session  layer : control od fialogues between applications
• Transport  layer
  • logical communcation to exchange data
    
    • between application layer processes
    • running on different hosts(end systems)
  • common transport layer services
    • error free, in sequence
    • no losses, no duplications
    • quality of service
• Network  layer
  • logical communication to transport packets
    • between identified (addressed) end systems
    • not needed on direct links
  • Basic network layer services
    • routing
    • forwarding
• Data Link  layer
  • Reliable delicery of frames between terminals
    • over a physically connected common local media
  • Datalink layer services
    • framing
    • MAC(Media Access Control)
    • error detection and control
    • flow contro
• Physical  layer : physical interface between devices

 

TCP/IP Model

• Five layers
  • Application
    • supporting network applications
    • FTP, SMTP, HTTP, e-mail, P2P
  • Transport
    • data transfer between app.processes
    • TCP(Transmission Control Protocol)
    • UDP(User Datagram Protocol)
  • Network
    • routing of datagrams from source to destination
    • IP(Internet Protocol)
    • optionally, ICMP, IGMP, ARP
  • Link: frame delivery between neighboring network elelments
  • Physical: bits "on the wire"
• Encapsulation
  • interfacing towards lower layers
  • each layer takes SDU(Service Data Unit) from its upper layer -> appends header -> delivers PDU(header+SDU, Protocol Data Unit) to its lower layer
  • does not modify any bit of the message(SDU)

• Decapsulation
  • interfacing towards upper layers
  • each layer has a specific field in its header to indicate the upper layer protocol for the SDU to be delivered.

 

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[Why All-IP?]

IP(Internet Protocol)

• the only one protocol at network layer of TCP/IP model

   # many protocols exist at other layers.

 

Role of IP Layer

• Internetworking heterogeneous networks <- integration tool
• Solution for the integration of network applications
• a Unified viewpoint of the Internet users