1.2 The network edge

Introduction to Network Edge and Access Networks

In this section, we will explore the network edge and focus on access networks. We will discuss how access networks connect edge devices to the larger internet and examine different types of physical media used for transmission.

Understanding the Network Edge and Access Networks

• The network edge refers to the devices that are connected to a network, such as computers, smartphones, and home devices.

• These edge devices are sometimes called hosts because they host or run network applications.

• Access networks connect these edge devices to the first hop router and ultimately to the larger internet.

• There are three main types of access networks: residential access networks, institutional access networks, and mobile access networks.

Residential Access Networks

• Cable access networks use a physical cable to connect multiple homes to a single cable head end.

• Signals are sent at different frequencies on the cable, allowing multiple users to transmit without interference.

• However, users often have to share frequencies with their neighbors due to limited available frequencies.

• Cable access networks typically offer higher downstream transmission rates compared to upstream rates.

Digital Subscriber Line (DSL) Networks

• DSL networks utilize existing phone lines (twisted pair) for connectivity between homes and central offices.

• Users have dedicated transmission capacity without sharing bandwidth with neighbors until reaching the central office.

• DSL lines also have asymmetric transmission rates with faster downstream rates than upstream rates.

• Transmission rates depend on the distance between the central office and user's home.

Home Network Setup

• A typical home network consists of a cable or DSL link from a local telco or cable network provider.

• A modem (modulator-demodulator) is used at the house end of the link for connecting cable modems or DSL modems.

• Routers provide wired (Ethernet) and wireless (Wi-Fi) connections to devices within the home.

• Ethernet typically runs at 100 Mbps or gigabit per second, while Wi-Fi operates at tens or hundreds of megabits per second.

Cable Access Networks

In this section, we will delve deeper into cable access networks and their standard known as DOCSIS. We will discuss transmission rates, asymmetry, and the shared nature of cable networks.

Cable Access Networks

• Cable access networks use frequency division multiplexing (FDM) to transmit signals at different frequencies on a shared cable.

• Users share frequencies with their neighbors, which can impact data transmission rates.

• Typical cable transmission rates are 40 Mbps to 1.2 Gbps downstream and 30 Mbps to 100 Mbps upstream.

• The actual transmission rate may vary based on factors such as the user's subscription plan and modem limitations.

Asymmetry in Cable Access Networks

• Cable access networks are designed to provide faster downstream transmission rates compared to upstream rates.

• This reflects the fact that users tend to consume more data than they produce.

• Asymmetric transmission is optimized for activities like streaming videos and downloading files.

Shared Nature of Cable Networks

• Cable networks are shared networks where multiple users share the same wire or cable infrastructure.

• If a neighbor is transmitting or receiving a lot of data, it may affect the available bandwidth for other users on the same frequency.

Digital Subscriber Line (DSL) Networks

In this section, we will explore DSL networks that utilize existing phone lines for connectivity. We will discuss transmission rates, asymmetry, and distance limitations.

Digital Subscriber Line (DSL)

• DSL networks use existing phone lines (twisted pair) to connect homes directly to central offices without sharing bandwidth with neighbors.

• DSL lines have asymmetric transmission rates, with faster downstream rates than upstream rates.

• Transmission rates depend on the distance between the central office and the user's home.

• If the distance exceeds approximately three miles, DSL may not be feasible.

Home Network Setup

• A typical home network setup includes a DSL or cable link from a local telco or cable network provider.

• A modem (modulator-demodulator) is used at the house end of the link to connect to DSL modems or cable modems.

• Routers provide wired (Ethernet) and wireless (Wi-Fi) connections within the home.

Conclusion

In this section, we concluded our discussion on access networks and their role in connecting edge devices to the larger internet. We also briefly touched upon home network setups.

Key Takeaways

• Access networks connect edge devices to first hop routers and ultimately to the larger internet.

• Residential access networks include cable access networks and DSL networks, each with their own characteristics and transmission rates.

• Cable access networks utilize frequency division multiplexing (FDM) and offer higher downstream rates compared to upstream rates.

• DSL networks use existing phone lines for connectivity, providing dedicated transmission capacity without sharing bandwidth with neighbors until reaching the central office.

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Wireless Networks Overview

This section provides an overview of the two classes of wireless networks: local wireless networks (Wi-Fi) and wide area networks (3G, 4G, and soon 5G cellular networks).

Local Wireless Networks (Wi-Fi)

• Wi-Fi or Wireless LAN (WLAN) networks are widely deployed within municipalities, companies, and institutions.

• They operate in the range of 10 to 100 meters and have different speeds ranging from 11 to 450 megabits per second.

• These protocols are standardized by the IEEE under the family of 802.11 protocols.

Wide Area Networks (Cellular Networks)

• Cellular networks such as 3G, 4G, and soon 5G are operated by mobile cellular operators.

• They have a transmission distance measured in tens of kilometers and can have transmission rates ranging from one to multiple tens of megabits per second per user.

Enterprise Networks

• Enterprise networks are similar to home networks but on a larger scale with multiple switches and routers.

• Data center networks connect massive numbers of servers to each other and the internet at high speeds.

Packet Transmission

This section explains how data is transmitted in packets over access networks.

• Hosts break data into smaller chunks known as packets before transmitting them into the access network.

• Each packet consists of data along with additional information added in a packet header.

• The length of a packet is typically around 1500 bytes (l bits).

• The transmission rate (r) varies depending on the type of access network.

• The time it takes to send l bits into a link at transmission rate r is calculated as l/r.

Physical Characteristics of Transmission Media

This section provides an overview of different types of physical transmission media.

• Physical media can be guided (wires or cables) or unguided (radio or acoustical waves).

• Guided media include twisted pair, which is used for ethernet and ADSL, and coaxial cable used for cable network access.

• Different physical media have different bit loss characteristics, susceptibility to electromagnetic noise, and propagation delays.

The coverage of physical transmission media in this course is limited. For more in-depth knowledge, additional resources are recommended.

Conclusion

This summary provides an overview of wireless networks, including local wireless networks (Wi-Fi), wide area networks (cellular networks), and enterprise networks. It also explains the concept of packet transmission and the physical characteristics of different transmission media.

Wireless Transmission and Concerns

This section discusses wireless transmission and the concerns associated with it.

Wireless Transmission

• Wireless transmission involves carrying signals in the electromagnetic spectrum without the need for physical wires.

• Transmissions are typically broadcasted, allowing any device near the transmitting device to receive the signals.

• This raises concerns about eavesdropping and interference.

Challenges of Wireless Environment

• Wireless transmission is a challenging environment due to various factors:

• Radio signals fade over distance.

• Signals can be reflected off objects or blocked by them.

• Different frequencies have different penetration capabilities through objects like walls.

• Noise generated by motors, microwaves, and other devices can interfere with wireless signals.

Types of Wireless Links

• There are several types of wireless links:

• Wi-Fi networks: Transmit at high speeds (up to hundreds of megabits per second) over short distances (tens of meters).

• 4G cellular networks: Transmit data at rates of tens of megabits per second over longer distances (up to around 10 miles).

• Bluetooth: Used as a cable replacement technology, operates at lower data rates (around one or two megabits per second) over short ranges (5 or 10 meters).

• Terrestrial microwave: Operates at tens of megabits per second for point-to-point communication.

• Satellites: Transmit data at similar rates as terrestrial microwave but with noticeable propagation delay (e.g., geosynchronous satellites have a delay of around 270 milliseconds).

Conclusion

This section concludes the discussion on what happens at the network edge.

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