网络基础学习笔记

 Efficiently transmit data between nodes in different segment  Process data in software

 Use IP addresses to identify devices

Devices-Switch/Bridge

 Efficiently forward data from one node to another in the same segment  Bridge process data in software; Switch process data in hardware  Use MAC address to identify devices

Devices – Modem and CSU/DSU

 Modem convert analog to digital and viceversa  CSU/DSU convert LAN data to WAN data.  CSU transmit data, DSU manages data. Devices – AP and WLC

 Access point is a wireless bridge join wired and wireless network  AP can act individually or listen to a master  Wireless LAN Controller manges APs Devices – firewall

 Ensure network security

 Can be hardware or software, can be host based or network based  IDS and IPS are firewall that detect and protect your network

Data encapsulation

Data is prepared by upper layer Encapsulated into segment at layer 4 Encapsulated into packet at layer 3 Encapsulated into frame at layer 2 Encapsulated into bits at layer 1 Data decapsulation

Receive and translate bits at layer 1 Decapsulate into frame at layer 2 Decapsulate into packet at layer 3 Decapsulate into segment at layer 4

Data is passed to upper layers for processing

Tcp/ip protocol

Devices and layers

 Gateway(upper layers) – segment  Router (network layers) –packet  Switch/bridge (data link layer) – frame  Hub (physical layer) – bits

Part II network models OSI model Contains 7 layers

Define functionalitu of protocols in each layer Data pass one layer then next

Protocol receive request from upper layer and pass it to lower layer

Layer – Application

 Provide underlying structure for software programs  Determine protocols used in lower layers  Verify reachability of the other end  Optional authentication Layer – presentation Responsible for:

 Data formatting/translation  Data encryption/decryption  Data compression/decompression

Layer – session

Establish computer to services between of connection.

Manage dialogue requests from presentation and issue service requests to transport.

 Responsible for:  Session authentication  Session permission

 Session checkpointing and recovery Layer – Transport Responsible for: Error checking

 Services addressing  Connection management

 Data segmentation and reassembly Layer – network

Use routed protocol to identify device 可路由协议，特指IP协议，用IP地址标识具体的某台设备。

Routing protocol to define best path 路由协议，为数据查找、选择最佳的path，并转发，

Data fragmentation 数据分片，IP协议中的相关字段

Most popular protocol:IP 网络层被IP协议所统一，就像数链层的局域网协议以太网一样。

Layer – data link Responsible for:  Error detection  Error correction  Hardware addressing  Two sub-layers:MAC and LLC TCP

TCP Maximum Transmission Unit: Depend on data link layer Header format, minimum 20 bytes (max 60 bytes)