Queue(aka buffer) preceding link in buffer has finitecapacity Packet arriving to full queuedropped (aka lost) Lost packet may beretransmitted by previous node, by source end system, or not at all A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)
Overview Courseoverview Introduction to theInternet TheInternet layered architecture
What is layering?
Layering by analogy with postal services
Why layering? Problem: Without layering, each new application has to be re- implemented for every network technology! Telnet FTP Email Packet radio Coaxial cable Fiber optic Application Transmission Media HTTP
Why layering? (Cont’d) Solution: introducean intermediatelayer that provides a unique abstraction for various network technologies Telnet FTP Email Packet radio Coaxial cable Fiber optic Application Transmission Media HTTP Intermediate Layer
Layering principles A layer should becreated wherea different level of abstraction is needed Each layer should performa well-defined function Thelayer boundaries should bechosen to minimizeinformation flow across theinterfaces Number of layers Largeenough that distinct functions need not be thrown together in the same layer Small enough that thearchitecture does not become unwieldy
Layering: Pros and Cons Advantages Abstract functionality: lower layer can be changed without affecting the upper layer Reuse: upper layer can reuse the functionality provided by lower layer Modularity: protocols easier to manage and maintain • Different vendors and organizations responsible for different layers Disadvantages Information hiding: inefficient implementations
Protocol hierarchy Network protocols form a hierarchy of layers Each protocol falls into a singlelayer Protocol Interfaces Serviceinterface: defines theserviceprovided between layers • Layer N uses service provided by layer N-1 • Layer N-1 provides a service to layer N Peer interface: defines protocol interfacebetween two or morehosts at the samelayer
Protocol interfaces example Node 1 Layer N Layer N-1 Node 2 Layer N Layer N-1 Service Interface Peer Interface
The Internet layered architecture Application Transport Transport Protocol (TCP/UDP) Application Protocols (e.g., Email) Node1 Node2 Router Application Transport Internet/Network Host-to-network IP IP Focus of this class Host-to-network Host-to-network Internet/Network Internet/Network
ISO OSI network architecture Application Presentation Session Transport Network Data Link Physical Node1 Node2 Application Presentation Session Transport Network Data Link Physical Network Data Link Physical Router Host-to-network in Internet arch New layers
Physical layer Moves bits between two systems connected by a physical link
Data link layer Provides thenetwork layer with what appears to bean error-free link for data frames transmitted between machines connected by a physical link
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