Network Architecture - Networking - Lecture Slides, Slides of Computer Networks

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Network Architecture

Outline

Last time: low-level plumbing

Today: top-down architecting of the Internet

• Goals
• Layering
• Protocols
• The end-to-end principle

How would you go about designing the

Internet?

Sit down and…

• List your goals
• Prioritize them
• Hence define the service you will offer
• Architect a solution that implements the service Of course, the original designers of the Internet didn’t do anything of the sort…

Reality

• The lessons accrued over time; many contributors
  • 1961: packet switching (Baran and Kleinrock)
  • 1967: vision of a robust network (ARPANET)
  • 1972: “best effort inter-networking” proposed (Kahn)
  • 1974: TCP/IP paper (Cerf/Kahn)

Reality

• The lessons accrued over time; many contributors
• Many of the lessons were learnt “on the job”
• Consensus didn’t come easy
  • 1961: packet switching is proposed
  • 1972: best-effort communication is advocated
  • 1980: IP adopted as the defense standard
  • 1985: NSFnet picks IP
  • 199x: Circuit switching rises (and falls) in the form of ATM
  • 199x: `Quality of Service’ (QoS) rises and falls

Reality

• The lessons accrued over time; many contributors
• Many of the lessons were learnt “on the job”
• Consensus didn’t come easy
• And progress was ad-hoc
  • “rough consensus and running code .”

Internet Design Goals

(from Clark’s SIGCOMM 1988 paper)

• Connect existing networks
• Robust in face of failures
• Support multiple types of delivery services
• Accommodate a variety of networks
• Allow distributed management
• Cost effective
• Easy host attachment
• Allow resource accountability

Connect Existing Networks

Wanted a single unifying interface that could be used to connect any pair of

(existing) networks

Interface to be compatible with existing networks

couldn’t demand performance capabilities not supported by existing networks had to support existing packet switched networks

Led to focus on an inter-networking service based on the best-effort delivery

of packets

Three steps

• Decompose the problem into tasks
• Organize these tasks
• Assign tasks to entities (who does what)

Decomposition

What does it take to send packets across the globe?

• Bits on wire
• Packets on wire
• Delivery packets within a single physical network
• Deliver packets across multiple networks
• Ensure the destination received the data
• Do something with the data

This is decomposition…

Now, how do we organize these tasks?

Datalink Network Transport Application Physical

CEO Aide FedEx CEO Aide FedexLocation Envelope (FE) FedEx

The Path of the Letter

Letter Envelope Semantic Content Identity “Peers” on each side understand the same things No one else needs to Lowest level has most packaging

The Path Through FedEx

Truck Sorting Office Airport FE Sorting Office Airport Truck Sorting Office Airport Crate Crate FE New Crate Crate FE

Deepest Packaging (Envelope+FE+Crate)

at the Lowest Level of Transport

In the context of the Internet

Application Presentation Session Transport Network Data link 1 Physical

The Open Systems Interconnect (OSI) model developed by the ISO included two additional layers that are often implemented as part of the application

Protocols and Layers

Communication between peer layers on

different systems is defined by protocols

Application Transport Network Data link Physical L

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Application Transport Network Data link L1 Physical

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