Computer Networks

Summary

Prof. Dr. Oliver Hahm

2024-02-09

Exam

Organizational

  • The exam will take place at 4-111/112 on February 20, 2024 at 14:00 CET
  • You will be allowed to bring a single-sided cheat sheet and a calculator
  • Note the exam regulations, in particular …
    • You have to be registered for exam via HIS.
    • You can authenticate yourself with an photo ID and your student identity card.
    • In case of delay no additional time will be granted.

Content

  • All necessary formulas, concrete numbers, and some conversion tables will be given in the exam (see mock exam)
  • The exam will consist of similar tasks as in the exercise sheets and look similar to the mock exam

Reminder

  • What is necessary to pass the exam?
  • You should be able to …
    • explain main concepts and ideas with your own words,
    • select a suitable solution for a given problem,
    • analyze a given solution and detect (potential) problems, and
    • explain your answers.

Overview

Being online

  • Being online means to be connected to the Internet
    • You can use the WWW via HTTP
    • Your browser can communicate end-to-end to a webserver over TCP
    • The IP datagrams find the best way towards the server
    • You connect towards your local gateway via WLAN or Ethernet

How does the Internet work?

  • How do you access videos on YouTube?
  • Access the YouTube server via IP, allow high throughput via TCP, stream the video via HTTP
  • What’s the deal with a lag in online gaming?
  • Use UDP for low latency, deal with end-to-end delay
  • Who can read my mails?
  • Everyone – Unless you use TLS for encrypting the transport and use PGP/GPG or S/MIME to encrypt the mail itself
  • How can we transmit data through the air (aka wireless networking)?
  • Use of radio waves as unguided transmission media and coordinate the access via CSMA/CA

Objective

Now you should …

  • understand what the term “online” means,
  • be able to explain what the Internet is,
  • know how computers communicate,
  • know what protocols are,
  • be familiar with the layers of a network stack,
  • understand how the data finds its way, and
  • be conscious of security and privacy concerns of computer networks.

Key Terms

  • Host, Client, Server, Peer
  • Network service
  • Network protocol
  • Transmission medium
  • PAN/BAN, LAN, MAN, WAN
  • Synchronous vs. asynchronous communication
  • Unicast, broadcast, multicast, anycast
  • Connection-oriented vs. connectionless
  • Simplex, half-duplex, full-duplex
  • Topology
  • Bandwidth, Throughput, Goodput, and Latency/Delay
  • Reference models and layers
  • Analog and digital signals
  • Quantization and Sampling
  • Frequency, period, amplitude, phase
  • Bandwidth, symbol rate, and date rate
  • Line encoding, baseline wander, clock recovery, and modulation
  • Coaxial cables, twisted pair, and fiber optic cables
  • Ethernet (IEEE 802.3), Token Ring (IEEE 802.5), WLAN (IEEE 802.11), and Bluetooth
  • Frames, byte/bit stuffing
  • Physical network addresses AKA MAC addresses
  • Bridges, switches, forwarding, and Spanning Tree Protocol
  • ALOHA, CSMA (CD and CA), MACA, TDMA, FDMA, CDMA
  • Error control, error detection, error correction
  • Hamming distance, parity check, CRC
  • ARP and NDP
  • IPv4 and IPv6, packet header
  • IP addresses, ranges, classes, network ID, subnet ID, host ID
  • Private or unique local addresses, link-local addresses, and NAT
  • IP fragmentation, MTU
  • ICMP, ping, and traceroute
  • Address autoconfiguration, DHCP, SLAAC
  • Internetworking, router, forwarding, and routing
  • Autonomous systems, Inter and intra domain routing
  • Routing algorithms and metrics
  • Distance vector routing and link state routing
  • Bellman-Ford and Dijkstra algorithm, RIP, OSPF, IS-IS, and BGP
  • Count-to-infinity and split horizon
  • End-to-end transport, multiplexing, and (well-known) ports
  • Reliability, ordering, flow control, and congestion control
  • TCP, UDP, and QUIC
  • Sockets
  • TCP sequence numbers and acknowledgement numbers
  • Three-way handshake, data transmission, and connection termination
  • AIMD, Slow start, congestion avoidance, sliding window, silly window syndrome, (duplicate) ACKs, fast retransmit, and fast recvovery
  • SYN flood DOS attack
  • Head of line blocking
  • DNS, domain, resource record, zone, label, TTL, FQDN
  • Telnet, and SSH
  • HTTP, HTTP methods and status codes
  • SMTP, IMAP, POP, MUA, MTA, Spam

Computer Networks - Summary - WS 23/24