Packet and Circuit Switched Networks: Core Concepts

Packet Switched Networks

IP Protocol

The IP protocol is a connectionless protocol used by both the origin and the destination for data communication over a packet-switched network.

IP Address

An IP address is a 32-bit integer that identifies a network interface. It is classified by type according to the value of the first byte.

Available Private Addresses

• Class A: 10.0.0.0
• Class B: 172.16.0.0 - 172.31.0.0
• Class C: 192.168.0.0 - 192.168.255.0

Netmask

A 32-bit integer associated with an IP address that indicates which bits belong to the network portion (binary 1) and which belong to the host (binary 0).

Fragmentation

The IP protocol includes fragmentation to fit the Maximum Transmission Unit (MTU). This divides an IP packet into smaller segments using the FRAGMENT OFFSET, IS LAST FRAGMENT, and IDENTIFICATION flags. Fragmented packets are reassembled at the receiver, not at intermediate routers, and data sizes are always multiples of 8.

Ethernet

Encodings

• 10BaseT: Manchester encoding using up or down slopes.
• 100BaseTx: Block coding, mapping 4 bits to 5 bits using a dictionary.
• 1000BaseTX: Data scrambling through XOR functions.

Transmission Frame

• Full-duplex: The physical environment is not shared with any other transmitter.
• Half-duplex: Shared physical medium requiring coordination between transmitters using the CSMA/CD protocol.

Flow Control

Ethernet flow control allows two network devices to operate at different speeds and incorporates auto-negotiation mechanisms to select the optimal transmission speed.

ARP Protocol

The ARP protocol is responsible for translating a network address (IP) to its corresponding physical address (MAC).

Standard 802.1Q (VLAN)

The 802.1Q protocol allows multiple networks to share the same physical environment without interference by separating them into virtual networks. VLAN membership is determined by:

• Tagged frames: The VLAN ID is included in the Ethernet frame.
• Conventional methods: The switch determines the VLAN via:
  • Port-based: Associates each input port with a specific VLAN.
  • MAC-based: Associates the frame's MAC address with a specific VLAN.
  • Protocol-based: Associates based on the network protocol.

When sending a frame, the switch generates a list of eligible ports, which is then filtered using the member-set table to ensure the frame reaches the correct VLAN.

Circuit Switched Networks

Basic Telephone Network

Path Selection Algorithms in Space Switching

• Random: Intermediate matrices are tested at random until a valid path is found.
• Rotation: Cycles through intermediate matrices sequentially.
• Sequential: Attempts to complete intermediate matrices in a fixed, orderly manner.