• AS: Autonomous System. A large network or group of networks that share a common a unified routing policy.
  • ASN: An Autonomous System Number. A unique, unsigned, 16 or 32 bit numbers that identify an individual AS.
  • BGP: Border Gateway Protocol: protocol for exchanging routing information between gateway hosts (each with its own router) in a network of autonomous systems.
  • AS Path: Autonomous Systems Path. The path between ASes that data traverses to get to a specific router. BGP uses AS Path for loop detection and best path selection.
  • TDM: time-division multiplex
  • TDMA: time-division multiple access
  • Half Duplex: Provides bi-directional communication, but only one direction at a time.
  • Full Duplex: Provided concurrent bi-directional communication, radios: transmit on one frequency and receive on another. Ethernet connections use two pairs of wires for outbound data, and two pairs of wires for inbound data, making the cable a collision free environment.
  • RIP: Routing Information Protocol.
  • RIB: Routing Information Base. Contains multiple paths to a given destination. Keeps track of routes that could possibly be used.
  • *MED: Multi-exit Discriminator: Makes it possible, via BGP, to tell a remote AS that if there are multiple exit points on to your network, a specific exit point is preferred.
  • OSPF: open shortest path first is a routing protocol for IP networks that falls into the group of interior routing protocols. That means that it distributes routing information between routers that are a part of the same AS.
  • IGPs: Interior Gateway Protocols (RIP, OSPF, IGRP, EIGRP, IS-IS) are used within the network of a single organization
  • EGPs: Exterior Gateway Protocols (EGP, BGP)
  • RTOS: Real-time Operating System. Scheduler in an RTOS is designed to provide a predictable (deterministic) execution pattern. Particularly of interest to embedded systems that must respond to a certain event within a strictly defined time (the deadline).
    • variability in the item it takes to accept and complete a task is ‘jitter’.
    • a ‘hard’ RTOS has less jitter than a ‘soft’ RTOS.
    • chief design goal of an RTOS is a guarantee of a soft or hard performance category.
    • if the OS can meet the deadline deterministically, it is a hard real-time OS.

Big Picture of the Internet

Routing on the Internet is comprised of two parts:

  1. Internal, fine-grained portions managed by an IGP such as an Open Shortest Path First
  2. The interconnections of those autonomous systems (AS) via BGP.


Networking protocols are rules that define how data is encoded and transmitted between different devices so that heterogeneous systems can communicate the “same language” with each other.

There are three primary types of protocols

  1. Communication
  2. Network Management
  3. Security

Protocols are further subdivided by the layer of the OSI model in which they belong.

Common Protocols


Transmission Control Protocol is a “reliable” or “guaranteed delivery” and flow control. Each packet sent has to be positively ack’d. Additional packets will not be sent until the current packet(s) have been sent and verified. It is used in systems where all of the data must be sent.


User Datagram Protocol is an “unreliable” or “not-guaranteed delivery” protocol. It is faster than TCP as there is no form of acknowledgment, flow control, or error correction and resending of data. It is used in systems where the loss of some of the data is tolerated by the application.

ICMP: Internet Control Message Protocol
Network protocol useful in IP network management and administration. ICMP is a required element of IP implementations. Designed to carry not data but information about the status of the network itself.

IGMP: Internet Group Management Protocol: provides a way for an Internet computer to report its multicast group membership to adjacent routers
ARP : Address Resolution Protocol, layer 2
IP addresses are used to figure out the MAC address to send to using ARP.

Systems keep an ARP table to map IP addresses to MAC addresses.

When sending a ping, the first thing that happens is the lookup of the MAC address. If it is not there, an ARP packet is broadcast to the network.

The machine that has that address will respond with an ARP packet indicating that it has that IP and will include the MAC address of the machine.

You can broadcast an ARP update using arping to send a ‘gratuitous ARP’.

OSI Model

Encrypted UDP: DTLS,