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IT Basic Concept

2016-09-02 17:24:26   0  举报

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Internet Technology Architecture

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OSI

1. Physical (Bits)

2. Data Link (Frames)

Handling transmission errors

CRC

Data flow regulation

3. Network (Packets)

Routing

Connectionless Network Protocol (CLNP)

does not perform connection setup or termination because paths are determined independently for each packet that is transmitted through a network.

best-effort delivery, which means that no guarantee exists that data will not be lost, corrupted, misordered, or duplicated

relies on transport-layer protocols to perform error detection and correction.

Connectionless Network Service (CLNS). CLNP and CLNS

Connection-Oriented Network Protocol (CONP)

Connection-Mode Network Service (CMNS)

Connectionless Network Protocol (CLNP)

Connectionless Network Service (CLNS)

does not perform connection setup or termination because paths are determined independently for each packet that is transmitted through a network.

provides best-effort delivery, which means that no guarantee exists that data will not be lost, corrupted, misordered, or duplicated.

relies on transport-layer protocols to perform error detection and correction

4. Transport (TPDU)

Combine data into segments

Segments are smaller than packets so they will be wrapped inside packets

connection-oriented transport service

this service is provided to session layer so must be connection-oriented

5. Session (SPDU)

Validate access

Data Transmission Control

6. Presentation (PPDU)

Data Encrypt/Decrypt

Data Decode/Encode/TransCode

Data Compression/Decompression

7. Application (APDU)

Questions

Why it does not take over the world?

Principles of Design

1. A layer should be created where a different abstraction is needed.

2. Each layer should perform a well-defined function.

3. The function of each layer should be chosen with an eye toward defining internationally standardized protocols.

Basic Terms

Network

Type of Networks

Personal Area Network

Local Area Network

Transmission Technology

Physically connected network

Topology

Bus

Only 1 machine can transmit at any pointing time, need to resolve conflicts, Ethernet is the most common practice

Ring

Each transmission bit is propagated individually, FDDI is the most common practice

Metropolitan Area Network

Internt

World Wide Web

Telnet

Euronet

Bitnet

Mechanism

Inherently it is a network of networks

Type of Services

Connection-oriented

Reliable message stream

Sequences of pages

Reliable byte stream

Remote login

Unreliable connection

Digitised voice

Connectionless

Unreliable datagram

Junk mail

Acknowledged datagram

Registered mail

Request reply

Database query

Packet

IP Address

Network Tranmission

Broadcast Link

Broadcasting is a mode of operation which allows a packet to be transmitted that every machine must process.

Multicast Link

Multicasting is a mode of operation which allows a subset of machines to process a given packet.

Point to Point Link

Point to point networks consist of many connections between individual pairs of machines.

Service Primitives

Set of primitives that a layer provides to a layer above it

At the start of the discussion on each layer we talked about the services that the layer provides to the upper layer.

Types

LISTEN

CONNECT

RECEIVE

SEND

DISCONNECT

Protocol

Rules which govern the format and meaning of packets that are exchanged by peers within a layer

Model

TCP/IP

OSI

Overhead

Categories

Headers for each packet

Establishing and ending the connection

Re-transmitted packets

Usage

The overheads/headers are used to allow each layer in the networking architecture perform their particular service.

These headers are part of how data is transferred between the networking layers, as is what we call ENCAPSULATION, and keeps networking functions separate and modular between the layers.

HTTP GET EXAMPLE

SYN and SYN ACK packets at the beginning which establishes a reliable connection between two hosts

the RST or FIN packet at the end when the connection is closed.

The packets in the middle are the transferring of the actual web page.

Between every two or three packets that are received, our computer sends an ACK or acknowledgement packet to communicate to the remote host that the packets sent were successfully received.

Why keep overhead with layering architecture?

A non-layered architecture may be more efficient (less or even zero protocol overhead), but at the cost of flexibility and modularity.

ADV: Information hiding (i.e. if you were a network engineer, you would not need to know detailed information on the physical layer or link layer – remember the interface?)

ADV: Flexibility (the ability to change protocols in a certain layer, without affecting the operation of other layers).

Network Architecture Design Issues

LAN

ADV of LAN over simply using a big time-sharing system

The LAN can be grown INCREMENTALLY. If the the LAN is just a long cable, it cannot be brought down by a single failure (if the servers are replicated). It is probably cheaper. It provides more computing power and better interactive interfaces.

Layering Architecture/Protocols

Breaking up the design problem into smaller, more managable pieces, and layering means that the protocols can be changed without affecting higher to lower ones.

International Standards

One advantage is that if everyone uses the standard, everyone can talk to everyone. Another is the widespread use of any standard will give its economies of scale, as with VLSI chips.

A disadvantage is that the political compromises necessary to achieve standardisation frequently lead to poor standards. Another disadvantage is that once a standard has been widely adopted, it is difficult to change, even if new and better techniques or methods are dicovered.

OSI and TCP/IP Models

Similarities

Stacking of layered protocols

Similar functionalities in each of the layers

Layers above transport layer relate to applications

Differences

TCP/IP does not distinguish between services interfaces and protocols

TCP/IP does not clearly separate physical and data link functions

OSI supports connectionless and connection-oriented at the network layer, while TCP/IP supports only connectionless at the IP layer

OSI supports only connection-oriented at the transport layer while TCP/IP supports both connectionless and connection-oriented at the transport layer(at TCP layer, each packet should receive ACK to finish transmission, while at IP layer it only takes packets as independent segment of data)

Topologies

Linear

Links: N-1 (N is number of nodes)

Ring

Links: N

Full Mesh

Used for connecting military centres, cost not important, reliability is the top priority

Links: C(2)(N)

Quality of Services(QoS)

reliability

delay

jitter