Networking Notes 5 - Switching

Pactket-Switched Networks: Routing

Two Main approaches to implement packet switching

• Datagram approach
• Virtual circuit approach

Datagram Network

• connection-less network
• destination address determines next hop
• routes may changee during session

Datagram Approach

• Connectionless switching
• Each packet(datagram) is treateed indeependently
• Packets may go by different paths across the network
• May arrive out of order, the transport layer neeeds to reorder them

Virtual circuit network

• Connection-oriented switching
• Call request and call accept packets are used to establish the connection between sender and receiver
• Each packet carries tag(virtual circuit ID), tag determines next hop
• fixed path determined at call setup time, remains fixed thru call
• routers maintain per-call state
• Path is fixed

Virtual Circuit approach

• All packets of the same message are transferred via a preplanned route(same route)
• Arrive in order
• Eatablish between sender and receiver at the beginning

There are two main virtual circuit

Permanent virtual circuit(PVC)

• Set up by the network provider
• No need to terminate the VC after transmission, and no need to set up the VC before it(because it is already seted up by network provider)

Switch virtual circuit

• Setup everytime when a VC is needed, and terminate after the transmission
• May get different VC according to network conditions
• More flexible, but required extra set up time before data transfer begins

1. Connection establishment
2. Data transfer
3. Connection release

VC vs Datagram

VC

• sequencing and error control
• No routing decisions to make -> Packets are forwarded more quickly
• Less reliable

Datagram

• No call setup phase - Good for bursty data
• More flexible
  • can have alternate route
  • can avoid congested parts of the network

Switching

Switching in computer network helps in deciding the best route for data transmission if there are multiple paths in a larger network
One-to-One connection

Packet Switching

• The internet is a packet switched network
• Message is broken into individual (Packets)
• Each packet is sent individually
• Each packet will have source and destination IP address with sequence number.
• sequence number will help receiver
  • Reorder the packets
  • Detect missing packets
  • Send acknowledgments