Network Access

Network access to three types:

•Residential access: family, the system and network connected.

•Specific access: will, business or education institutions of terminal system and network connected.

• mobile access: will move end system and network connected.

A, residential access

Will family end system (such as PC) and edge router connections.

1, through dial-up modem (dial - up modem)

Will family end system through common simulated using dial-up modem line with your ISP connected. Is a kind of common, popular form.

• end system square: household modems will PC output of digital signals into analog form, in order to simulate the twisted-pair phone line (on) the transmission.

• ISP square: modems to analog signal conversion back to digital form, as ISP router input.

 analog signal: with continuous variation of electromagnetic waves representing data, can according to different frequency transport across the link.

 digital signal: with a series of voltage pulse data is represented, usable positive and negative two level says "1", "0". Usually, modems rate can reach 56kbit/s.

Faults:

Because twisted-pair cable, with low quality, users get the effective rate far below 56kbit/s, download time long.

Such as, download a 3 minutes MP3 songs needs about 8 minutes.

• user Internet and dialed the ordinary telephone not simultaneously.

2, new bandwidth access technology

For residential users provide higher bitrate, Users can also access Internet and telephone.

Two commonly used types: digital subscriber line (DSL line, digital subsscriber and HFC (hybrid fiber coaxial cable, HFC coaxial cable).

(1) digital subscriber line DSL access

By telephone company or with independent ISP partnership company offers.

Features:

 new dial-up modem technology: with modem similar,

 high rate transmit and receive data: the user and the ISP modems between short transmission;

 download speed over upload rate:

• download: from the ISP router to family, such as rate more than l0Mbit/s,

Upload: from family, to the ISP, such as rate more than 1Mbit/s

The actual realization at a faster rate is low.

 use frequency division multiplexing: family and the ISP communications link between divided into three overlap band:

High-speed download channel, medium-speed upload channel, ordinary two-way telephone channels.

(2) HFC

Is the traditional radio and TV cable system improvement.

Traditional way: cable head end (head end) broadcast through coaxial cable and the amplifier's distribution network to housing.

HFC structure: adopting coaxial cable and optical fiber mixed the access method

By cables, head end connected to adjacent domain level the endplates (optical fiber node), then use traditional cable reach each family homes.

Each adjacent domain join-point support, 500 to 500 home users.

Features:

 adopt special modems (cable modems) : the family PC connected to a is the maximum distance that 10base-t Ethernet (Ethernet) port.

 divided into two channels: namely downlink channel and uplink channel.

Downlink channel bandwidth is bigger, the transmission rate faster, by all family share,

 sharing broadcast media:

Send the head end, each packet down through each segment of link to every family,

If several users to download, individual users receive the actual rate drops greatly.

Every family, send each grouping the uplink channel to head the transmission.

Several users simultaneously send packet will conflict, reduce the effectiveness of uplink bandwidths.

(3) is more

• DSL in family and between the ISP, established a point-to-point connections, all special no sharing bandwidth,

Higher than DSL bandwidth, HFC,

• DSL and HFC can offer the service: the user to open the computer, and have been with your ISP connection and can simultaneously dials and answer the ordinary telephone.

Second, the company access

Using a local area network (LAN) connected end users and edge router.

First, multiple end system connected into LAN: if the Ethernet technology (high rate can reach 10Mbps, 100Mbps, 1GMbps, 10Gbps), with twisted pair or coaxial cable will end system are connected with each other;

• again with edge router connection: edge router destination is not responsible for the grouping of choose this LAN road.

Ethernet technology:

• Shared Ethernet: end system Shared Ethernet transmission rate,

• switch Ethernet: use multiple twisted-pair Ethernet segments and switches connected, makes the Ethernet full bandwidth can simultaneously for the same LAN different users relay messages.

Three, mobile access

For mobile computers, mobile phones and pdas etc of mobile devices access.

In two ways:

 wireless LAN:

Mobile users, with a dozen meters radius bs (wireless access points) between transmitting/receiving grouping,

The base station, cable and wireless Internet connections, for users with connecting cable network services.

Typical technology:

Based on IEEE802. J, LLB technology of wireless local area network (wireless Ethernet or Wi - Fi); Provide the llMbps share bandwidth,

• family hybrid network: the bandwidth residential access (cable modems or DSL) and wireless LAN technology with the wide area wireless access a: -

Base, by telecommunications providers management, for dozens of km radius of users provide services;

• roaming user available mobile phone base stations access.

Typical technology:

• wireless access protocol (WAP)

• i.mode