Overview of Internet and Networks: How It Works?
Table of Contents
1. Protocol
The networks is developed on top of protocol.
2. What Happens at Network Edge?
2.1. TODO Access Networks
Internet structure consists of three parts: network edge, including hosts and servers; access networks including wired or wireless communication links; network core including routers and network of networks.
There are 3 ways to connect end systems to edge router: residential access nets, institutional access networks and mobile access networks. We usually care about transmission rate of access network, as well as shared or dedicated access among users.
Hosts’ sending function takes application message, breaks it into smaller chunks (packets) of length \(L\) bits and transmits packet into access network at transmission rate \(R\) (or link transmission rate, link capacity, link bandwidth).
2.1.1. Cable-Based Access Networks
Frequency division multiplexing.
Asymmetric. Downstream speed is faster than upstream speed.
Shared access network to cable headend.
2.1.2. Digital Subscriber Line (DSL)
2.1.3. Home Networks
2.1.4. Wireless Access Networks
Shared wireless access networks connects end system to router via base station aka “access point”.
- Wireless Local Area Networks (WLAN).
- Wide-area cellular access networks.
2.1.5. Data Center Networks
2.1.6. Enterprise Networks
2.2. Links: Physical Media
Physical links lie between transmitter and receiver that transmits bits. Links can have different types. We may roughly categorize them into 2 classes: guided media and unguided media.
Typical media include twisted pair (TP), coaxial cable, fiber optic cable, wireless radio, radio link types.
3. What Happens at Network Core?
The network core is mesh of interconnected routers. The most important operation is packet switching.
- Packet switching
- network forwards packets from one router to the next, across links on path from source to destination.
- Circuit switching
- End-to-end resources allocated to (and reserved for) “call” between source and destination. This approach is an alternative to packet switching.
Packet switching involves 2 core operations:
- forwarding (switching), local action that a router moves packets from its input link to appropriate output link;
- routing, global aciton that determine source destination paths taken by packets.
3.1. Packet Forwarding at Router
Store-and-forward. entire packet must arrive at router before it can be transmitted on next link.
Packet queuing and loss. If arrival rate to link exceeds transmission rate of link, then packets will queue, waiting to be transmitted on output link; packets can even be dropped if memory in router fills up.
3.2. Circuit Switching
May cause inefficiency.
Frequency/time division multiplexing.
4. Network of Networks
Hosts connect to Internet via access Internet Service Providers (ISP).
Internet exchange point (IXP) connects different ISPs.
5. Performance: Loss, Delay, Throughput
Packet loss comes from queue overflow in routers.
5.1. Packet Delay
Delay consists of
- node processing. bit checks, determine output link.
- queuing delay. time waiting at output link for transmission.
- transmission delay. \(d_{trans}=L/R\) where \(L=\) packet length in bits, and \(R=\) link transmission rate (bps)
- propagation delay. \(d_{prop}=l/s\), where \(l=\) length of physical link and \(s=\) propagation speed.
5.2. Queuing Delay
traffic intensity.
5.3. Throughput
- Throughput
- Rate at which bits are being sent from sender to receiver.