EECS 3213 Lecture 1: Communication Networks, Switching and Topologies

Posted on Nov 4, 2026 in Computer Engineering

EECS 3213 ā€” Lecture 1: Introduction

Communication Networks

Communication network: Equipment (computers, routers, switches, modems, servers, software) and facilities (copper, coaxial, fiber, air) that enable information transfer.

  • Direct-link: One physical link with no intermediate devices.
  • Networked: Multiple links and intermediate devices.
  • LAN (Local Area Network): Small area, privately owned, high-speed, resource sharing.
  • WAN (Wide Area Network): Large geographical area, long-distance communication.

Full Mesh and Switched Networks

Full mesh: Every user is directly connected to every other user. The number of links is N(Nāˆ’1)/2, where N is the number of users. For N = 10 there are 45 links; for N = 100 there are 4,950 links. Full mesh is expensive, complex, and not scalable.

Switched network: Users connect through switches or routers. A single central switch needs only N subscriber lines, giving lower cost and better scalability.

Circuit Switching

Circuit switching: A dedicated end-to-end path is established before transmission, with reserved bandwidth and a fixed rate.

  • Advantages: Predictable delay and jitter, strong QoS, low congestion-related loss.
  • Disadvantages: Wasted bandwidth during idle periods, complex signaling, initial setup delay.
  • Example: PSTN.

Packet Switching

Packet switching: No dedicated path is reserved. The message is divided into independent packets transmitted over shared links.

  • Advantages: Efficient bandwidth use, dynamic sharing, handles bursty traffic, supports alternative routes.
  • Disadvantages: Congestion, variable delay, jitter, packet loss, header overhead, no guaranteed QoS.
  • Examples: ARPANET, the Internet, 4G/5G.

Quality of Service (QoS) terms:

  • Loss: Undelivered data.
  • Delay: Travel time of data.
  • Jitter: Variation in delay.

3G: Circuit and packet switching. 4G: All-IP packet switching.

ARPANET and Packet Concepts

ARPANET: An early WAN and predecessor of the Internet. The first packet was sent on October 29, 1969, and by December 1969 there were four nodes (UCLA, SRI, UCSB, and Utah).

  • Packet: A header (destination and control information) plus a payload (data).
  • Packetization: Dividing long messages into smaller packets.
  • Router / packet switch: Examines the destination address, consults the routing table, and forwards the packet.
  • Routing table: Determines the next hop.
  • Connectionless: No circuit setup before sending; packets are independent.
  • Buffering: Temporarily stores packets awaiting transmission.
  • Multiplexing: Multiple users share communication links.
  • Bursty traffic: Irregular transmissions with idle intervals.
  • Alternative paths: Improve fault tolerance.

Network Topologies

Bus Topology

All devices are connected to a single backbone, and frames are broadcast through the shared medium. A NIC checks the destination address, and the sender listens before transmitting. Simultaneous transmissions cause a collision, after which the sender aborts and retries.

  • Advantages: Simple and cheap.
  • Disadvantages: The backbone is a single point of failure, and collisions reduce capacity.
  • Example: Older Ethernet.

Ring Topology

Each device is connected to two neighbours, forming a closed loop. A token circulates, and only the token holder may transmit.

  • Advantages: Fair access and no contention collisions.
  • Disadvantages: A failure in a link or the token mechanism can disrupt the ring.

Star Topology

Every device is connected to a central hub or switch.

  • Hub: Broadcasts or repeats traffic to other ports. It is a physical star but a logical bus, so collisions are possible.
  • Switch: Forwards unicast frames toward the destination, allowing efficient simultaneous transmissions.

The central device is a possible single point of failure. NIC (Network Interface Card): Connects a device to the network.

Telephone Networks

Bell (1876): A microphone converts voice into an electrical signal, and a loudspeaker converts the electrical signal back into sound. Early telephone networks used dedicated full-mesh lines.

Circuit switching (1878): A central operator connected users on demand, requiring N subscriber lines. Automatic switching later replaced operators. Digital telephony converts analog voice into binary data.

  • PSTN: Public Switched Telephone Network.
  • CO (Central Office): Serves local subscribers.
  • Tandem: Interconnects COs.
  • Toll: Long-distance interconnection.