1. Vocabulary
Prototype: A preliminary sketch of an idea or model for something new. It’s the original drawing from which something real might be built or created.
Binary - A way of representing information using only two options.
Bit - A contraction of "Binary Digit". A bit is the single unit of information in a computer, typically represented as a 0 or 1.
Bandwidth - Transmission capacity measure by bit rate
Bit rate - (sometimes written bitrate) the number of bits that are conveyed or processed per unit of time. e.g. 8 bits/sec.
Latency - Time it takes for a bit to travel from its sender to its receiver.
Protocol - A set of rules governing the exchange or transmission of data between devices.
ASCII - ASCII - American Standard Code for Information Interchange. ASCII is the universally recognized raw text format that any computer can understand.
code - (v) to write code, or to write instructions for a computer.
IETF - Internet Engineering Task Force - develops and promotes voluntary Internet standards and protocols, in particular the standards that comprise the Internet protocol suite (TCP/IP).
Internet - A group of computers and servers that are connected to each other.
Net Neutrality - the principle that all Internet traffic should be treated equally by Internet Service Providers. To / From Address: Like an IP address, included on every message sent over the Internet.
Dropped Messages: Poorly formed messages cannot be delivered and so are dropped, just like a letter with a bad address on it. Tomorrow you’ll discuss more technical reasons messages are dropped.
Multiple Hops: A message travelling across the Internet will visit many routers as each tries to forward it along the most efficient path to its destination.
Different Paths: Routers respond to traffic on the Internet in real time. The best path at one moment might be backed up a few seconds later. Routers choose the current best path to get the message through
Router: a computer designed to receive and redirect packets of information based upon the addressing information (e.g. an IP address) contained in the packet.
Packets - Small chunks of information that have been carefully formed from larger chunks of information.
TCP - Transmission Control Protocol - provides reliable, ordered, and error-checked delivery of a stream of packets on the internet. TCP is tightly linked with IP and usually seen as TCP/IP in writing.

2. U1L11 Making the Internet Reliable
CS Principles
U1L11 Making the Internet Reliable

3. U1L11 Making the Internet Reliable Objectives
SWBAT:
Explain why protocols are necessary to overcome the underlying unreliability of the Internet.
Justify the need for acknowledgements and packet numbering in TCP.
Develop a protocol for reliable communication on the Internet.

4. U1L11 Vocab
Packets - Small chunks of information that have been carefully formed from larger chunks of information.
TCP - Transmission Control Protocol - provides reliable, ordered, and error-checked delivery of a stream of packets on the internet. TCP is tightly linked with IP and usually seen as TCP/IP in writing.

5. U1L11 Prompt:
Your friend sent you a message on the Internet, but you never received it. Based on what you already know about routers and the physical Internet, list what reasons might explain this fact.

6. Prompt Discussion
Potential flaws that could lead to a message getting dropped. Some example points of discussion:
Wires are cut
Interference on a radio channel
Router malfunctions or cannot keep up with traffic being directed to it

7. TCP- Transmission Control Protocol
TCP was designed to overcome the inherent unreliability of the Internet.
A small but non-negligible percentage of packets are lost in transmission because of faults in the infrastructure of the Internet.
In order to constrain the extent of these errors, larger messages are divided into many packets which are individually routed to their recipient.
The receiving computer will send an acknowledgement confirming the receipt of that packet. If the sending computer does not receive an acknowledgement, it will resend the packet until all packets have been acknowledged.
Since packets may arrive out of order, additional data must be included to indicate the order in which the packets should be arranged. Thus, while individual packets cannot be guaranteed to arrive, eventually an entire message can be accurately reconstructed.

8. U1L11 Activity
On the real Internet packet sizes are limited, and transmission is unreliable.
In this lesson we have setup the Internet simulator to restrict packet-size to be very small bits for the to and from addresses plus only 8 ASCII characters.
Also, the Simulator drops packets pretty regularly.
In a set of 10 messages it’s very likely one or two will be dropped.
These types of constraints are a very real problem on the Internet.
The problem you have to solve is how to use the 8-ASCII-characters-worth of data to include both a piece of message you’re trying to send, as well as information about how many messages (packets) there are in the whole message, and which number this packet is.

9. Guidelines for Protocol
All communication can only be done through the Internet Simulator.
The full message sent will be at least 80 characters long - broken into at least 10 packets - and might be entirely random (i.e. there’s no way to use human intuition to reconstruct the message).
The message is not known beforehand.
The sender and receiver must be confident the full message was successfully transmitted and reconstructed.