COM-1006: Device and Network (Lecture 3: Circuit and Packet Switching)

Switching networks facilitate long-distance transmission using circuit switching and packet switching.

• Circuit Switching: Requires a dedicated communication path between two stations with allocated and reserved resources.

  • Requires three steps: connection establishment, data transfer, and connection termination.

  • Channel capacity is dedicated, which is inefficient for bursty traffic, and involves an initial connection delay.

• Packet Switching: Shares network resources without dedicated links, allocating resources on demand.

  • Data is transmitted in short packets, each containing a header for routing based on the store-and-forward concept.

  • Offers better link utilization and is suitable for bursty traffic; can prioritize packets.

  • Two approaches: virtual circuits and datagrams.

  • Virtual Circuit: Establishes a route before packet transmission, but links aren't dedicated.

  • Uses virtual circuit identifiers (VCI) for packet forwarding. Setting up a VCI involves setup request, acknowledgment, and teardown phases.

  • Datagram: Transmits each packet independently without a pre-established route.

  • Requires dynamic routing decisions at each node, with packets possibly delivered out of order.

  • Faster for fewer packets and more flexible in handling congestion.

• Essential Maths for Networking

  • $bit = binary\ digit = {0, 1}, 1\ byte = 8\ bits$

  • $GB: gigabyte = 2^{30} bytes = 2^{33} bits$

  • $MB: megabyte = 2^{20} bytes = 2^{23} bits$

  • $KB: kilobyte = 2^{10} bytes = 2^{13} bits$

  • $1 KB = 1024 bytes (NOT 1000 bytes) = 8 \times 1024 bits$

  • $1 MB = 1024 \times 1024 bytes = 8 \times 1024 \times 1024 bits$

  • $Gbps: gigabit\ per\ second = 10^9 bits\ per\ second$

  • $Mbps: megabit\ per\ second = 10^6 bits\ per\ second$

  • $Kbps: kilobit\ per\ second = 10^3 bits\ per\ second$

  • The bandwidth of a link/channel is the number of bits per unit time that can be transmitted over the link/channel. It is measured in bps (bits per second).

• Converting Binary to Decimal

  • To find the answer as a decimal, add up the powers of two for all the positions containing a 1

• Converting Decimal to Binary

  • Is X (strictly) smaller than the power of two above the position?

  • If yes, write 0

  • If no, write 1 and subtract the power of two from X

• Bitwise AND

  • The AND operation is performed on individual bits and is tabulated below:

  • 0 AND 0 = 0

  • 0 AND 1 = 0

  • 1 AND 0 = 0

  • 1 AND 1 = 1

• Bitwise OR

  • The OR operation is performed on individual bits and is tabulated below

  • 0 OR 0 = 0

  • 0 OR 1 = 1

  • 1 OR 0 = 1

  • 1 OR 1 = 1

• Bitwise XOR

  • The XOR (exclusive OR) operation is performed on individual bits and is tabulated below. XOR stands for exclusive or and means 'one or the other, not both'

  • 0 XOR 0 = 0

  • 0 XOR 1 = 1

  • 1 XOR 0 = 1

  • 1 XOR 1 = 0