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Network Architecture Layered system with alternative abstractions available at a given layer.

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Presentation on theme: "Network Architecture Layered system with alternative abstractions available at a given layer."— Presentation transcript:

1 Network Architecture Layered system with alternative abstractions available at a given layer

2 Abstraction and Layering
The University of Adelaide, School of Computer Science 9 June 2018 Abstraction and Layering Abstraction The hiding of details behind a well-defined interface Define a model Capture important aspects of the system Abstractions naturally leads to layering The general idea Start from services offered by the underlying hardware Add a sequence of layers, each providing a higher (i.e., more abstract) level of service. Manageability and Mudularity Chapter 2 — Instructions: Language of the Computer

3 Protocols The abstract objects the make up the layers of a network system are called protocols Building blocks of a network architecture Each protocol object has two different interfaces service interface: operations on this protocol peer-to-peer interface: messages exchanged with peer (indirect communication, except for the hardware)

4 Interfaces Service and Peer Interfaces

5 The University of Adelaide, School of Computer Science
9 June 2018 Protocols Protocol Specification: Written description (prose) pseudo-code state transition diagram Packet format RFCs: Request For Comments IETF: Internet Engineering Task Force Standardization body Ex. RFC 2616 for HTTP protocol Interoperable: when two or more protocols that implement the specification accurately Chapter 2 — Instructions: Language of the Computer

6 Protocol Graph Example of a protocol graph
nodes are the protocols and links the “depends-on” relation

7 High-level messages are encapsulated inside of low-level messages
Encapsulation High-level messages are encapsulated inside of low-level messages

8 Packets General Format
Header Payload Trailer Peers talk to each other through Headers and Trailers

9 OSI – Open Systems Interconnection
OSI Architecture The OSI 7-layer Model OSI – Open Systems Interconnection

10 The University of Adelaide, School of Computer Science
9 June 2018 Description of Layers Physical Layer Handles the transmission of raw bits over a communication link Data Link Layer Collects a stream of bits into a larger aggregate called a frame Network adaptor along with device driver in OS implement the protocol in this layer Frames are actually delivered to hosts Network Layer Handles routing among nodes within a packet-switched network Provides Host-to-Host connectivity Unit of data exchanged between nodes in this layer is called a packet The lower three layers are implemented on all network nodes Chapter 2 — Instructions: Language of the Computer

11 Description of Layers Transport Layer
Implements a process-to-process channel Unit of data exchanges in this layer is called a message There is a disagreement on the top three Session, Presentation, and Application Mainly because the are not always present

12 The University of Adelaide, School of Computer Science
9 June 2018 Description of Layers Session Layer Provides a name space that is used to tie together the potentially different transport streams that are part of a single application Ex., tie the audio and video together in videoconference Presentation Layer Concerned about the format of data exchanged between peers Ex., integer formats, audio/video format, most/least significant Application Layer Include things like the Hypertext Transfer Protocol Basis the world wide web Used by web browsers The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers Chapter 2 — Instructions: Language of the Computer


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