CST311 - Week 5

 

CST311 – Intro to Computer Networks 

The network layer is the central topic for this week. We are moving down from the top application layer to the transport layer and now to the network layer with its two components, the data plane and the control plane. The primary role of this layer is to hand over the data packets from the sender to the receiver through the forwarding and routing mechanisms. In the data plane, forwarding is implemented to process packets by the router and send (or block) to the next router in the path. On the other hand, Routing utilizes routing algorithms in the control plane to determine the end-to-end path for a packet to reach the final destination.

This week's module also covered the basic components of a router: input ports, switching fabric, routing processor, and output ports. Each component has its own function that handles arriving packets as they enter the input ports. Packets are routed to the corresponding output ports determined by the forwarding table. The switching fabric connects the input and output ports and executes link layer and physical layer functions using the longest prefix matching rule. In the data plane, switching could be done via memory, bus, and an interconnection network. The latter offers faster switching through 2N buses for every N port, allowing other packets to forward simultaneously. Packets that reach the output ports are queued accordingly for transmission to the outgoing link.

The equation above calculate the buffer needed for N TCP flowing through a link with Capacity C.

We also examined the IPv4 and IPv6 datagram format and the key fields associated with each version. Where the IPv4 is formatted in dotted-decimal notation, 32 bits long, divided into 4 groups of 8 bits each. For example, the IPv4 address 192.168.1.1 is written in dotted-decimal notation, where each part corresponds to an 8-bit binary value. The IPv6, on the other hand, is 128 bits long divided into 8 groups of 16 bits written in hexadecimal. A Dynamic Host Configuration Protocol (DHCP) automatically assigns a unique IP address from a pool to the requesting host.

NAT or network address translation, offers a way to efficiently manage IPs allocations in a network. For example, a NAT-enabled router translates multiple devices (IP addresses) in a home network to face the public Internet as only one IP address.

In this week, we also covered software-defined networking (SDN), where software-based networking interactively calculates the values of forwarding tables for routing.