# 1.2 The Network Edge

* Host
  * Clients
    * Tend to be desktop and mobile PCs, smartphones, and so on 
  * Servers 
    * Tend to be more powerful machines that store and distribute Web pages, stream video, relay e-mail and so on 
    * Most of the servers reside in large data centers 

### 1.2.1 Access Networks 

* Access network: the network that physically connects an end system to the first router ("edge router") on a path from the end system to any other distant end system. 

![](/files/-MZfOLcsM4T-k_CY7tgH)

* Home Access: DSL, Cable, FTTH, Dial-Up, and Satellite 
  * Two most prevalent types of broadband residential access: digital subscriber line (DSL) and cable
  * DSLAM: digital subscriber line access multiplexer 
  * Hybrid fiber coax (HFC): both fiber and coaxial cable are employed 
  * Fiber to the home (FTTH) 
  * Optical network terminator (ONT) 

![](/files/-MZfOv4bgoygNuvCeoWH)

![](/files/-MZfQtyqSCoqobullGf7)

![](/files/-MZi4I3s8_5uuJUqoasQ)

* Access in the Enterprise (and the Home): Ethernet and WiFi 
  * Local area network (LAN) 
    * Ethernet 
  * Wireless LAN 
    * Access based on IEEE 802.11 technology, more colloquially known as WiFi 

![](/files/-MZi4ZOKrCK0IhxLHin4)

![](/files/-MZi4pyF1eGpCt4oLPrO)

* Wide-Area Wireless Access: 3G and LTE 
  * Unlike WiFi, a user need only be within a few tens of kilometers (as opposed to a few tens of meters) of the base station 

### 1.2.2 Physical Media 

* E.x. HFC uses a combo of fiber cable and coaxial cable. DSL and Ethernet use copper wire. Mobile access networks use the radio spectrum. 
* For each transmitter-receiver pair, the bit is sent by propagating electromagnetic waves or optical pulses across a **physical medium**.
  * Can take many shapes and forms and does not have to be of the same type for each transmitter-receiver pair along the path
  * E.x. twisted-pair copper wire, coaxial cable, multimode fiber-optic cable, terrestrial radio spectrum, and satellite radio spectrum 
  * Categories 
    * **guided media**: the waves are guided along a solid medium, such as a fiber-optic cable, a twisted-pair copper wire, or a coaxial cable 
    * **unguided media**: the waves propagate in the atmosphere and in outer space, such as in a wireless LAN or a digital satellite channel 
  * Cost of physical link is relatively minor compared with other networking costs 
* Twisted-Paire Copper Wire 
  * **Unshielded twisted pair (UTP)** 
  * **Rate:** 10 Mbps to 10 Gbps 
  * Dominant solution for high-speed LAN networking 
* Coaxial Cable 
  * Can be used as a guided **shared medium** 
    * A number of end systems can be connected directly to the cable, with each of the end systems receiving whatever is sent by the other end systems 
* Fiber Optics 
  * Thin, flexible medium that conducts pulses of light, with each pulse representing a bit 
  * Preferred for oversea links 
* Terrestrial Radio Channels 
  * Radio channels carry signals in the electromagnetic spectrum. 
  * Classified: short distance, local areas, span from ten to a few hundred meters, wide area, spanning tens of kilometers 
* Satellite Radio Channels 
  * Links two or more Earth-based microwave transmitter/receivers, known as ground stations. The satellite receives transmissions on on frequency band, regenerates the signal using a repeater, and transmits the signal on another frequency. 
  * geostationary satellites 
  * low-earth orbiting (LEO) satellites 


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://sliu583.gitbook.io/blog/networking/index/computer-networking-a-top-down-approach/chapter-1.-computer-network-and-the-internet/1.2-the-network-edge.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.