Lesson 1: Intro, History, and Internet Architecture Flashcards
What are the different layers of the Open Systems Interconnection model?
Application Presentation Session Transport Network Data Physical
What are the different layers of the Internet Protocol Stack? And how is this different from the OSI Model?
Application
Transport
Network
Data
Physical
-In the IP stack, the Application Layer includes the Presentation and Sessions Layers from the OSI model.
-The interface between the Application & Transport layer are the sockets.
What are examples of Application protocols? What is a packet of info referred to at this layer?
HTTP, SMTP, FTP, DNS
Referred to as a message
What is the responsibility of the Presentation Layer?
Format data coming from the session layer up to the Application layer.
Ex: Formatting video streams, translating integers from big endian to little endian.
What is the responsibility of the Session Layer?
Responsible for the mechanism that manages different transport level streams that belong to the same session between end-user application processes.
Ex: Tying together the audio and video stream of a teleconference application
What is the responsibility of the Transport Layer?
Responsible for end-to-end communication between hosts. Packet of information is referred to as a “segment”. Leverages two transport protocols: TCP and UDP.
TCP services:
- connection-oriented service to the applications
- guaranteed delivery of application-layer messages
- flow control
- congestion control
UDP services:
- connectionless best-effort service
- no reliability, flow or congestion control
What is the responsibility of the Network Layer?
Packet of information is a datagram. Responsible for moving datagrams from one internet host to another.Specifically, the Network layer is responsible for delivering the datagram to the transport layer in the destination host. The Network Layer protocol is the IP Protocol.
IP Protocol defines:
- The fields int he data gram
- How these fields are used by the hosts/intermediate routers so that the datagrams reach their destination
- Routing protocols that determine the routes used by the datagrams
What is the responsibility of the Data Layer?
Receives the datagram from the network layer, deliver the datagram to the next node, at the next node, the data layer passes the datagram up tot he network layer. Packets of information is referred to as Frames.
Protocol Examples: Ethernet, Wifi
Services: Reliable delivery (different from that provided by the GCP protocol), physical addressing (eg MAC address)
What is the responsibility of the Physical Layer?
Facilitates the interaction with hardware and is responsible for transferring bits within the frame between two nodes that are connected by a physical link.
Example: Coaxial cable, fiber optics, radio frequency transmitters
Describe the Encapsulation & De-Encapsulation process.
The process of taking data from one protocol and translating it into data that is used by another protocol, so that the data can continue across a network.
Encapsulation:
Step 1 - Application layer message is sent to the Transport Layer
Step 2 - Transport layer appends it’s Header Info (eg what the application is, error detection). This is now called a “segment”
Step 3 - Transport layer sends the segment to the Network Layer.
Step 4 - Network Layer appends it’s Header Info (eg source/destination addresses). This is now called a “datagram”.
Step 5 - Network layer sends the datagram to the Data Layer.
Step 6 - Data Layer appends it’s Header Info. This is now called a “frame” and is sent to the Physical layer for transmission.
De-encapsulation: When the receiving host receives the frame, it reverses the Encapsulation process in order to get the message to the appropriate application.
Intermediate Devices: Routers (Layer 3) and Switches (Layer 2): Only de-encapsulate and encapsulate up to their Layer.
What is the End to End (e2e) Principle? What are examples of some exceptions to this princple?
The network core should be simple and minimal (eg, only up to Layer 2 or 3), while the end systems should carry the intelligence (where the applications exist).
Exceptions:
- Firewalls and Traffic Filters
- NAT boxes
Lesson 1 Quiz 1:
Some data link layer protocols, such 802.11 (WiFi), implement some basic error correction as the physical medium used is easily prone to interference and noise (such as a nearby running microwave). Is this a violation of the end-to-end principle?
No, because violations of the e2e principle typically refer to scenarios where it is not possible to implement a functionality entirely at the end hosts, such as NAT and firewalls.
In this question, we have a lower level protocol implementing error checking.
Why does the Internet Architecture have an hourglass figure?
The Evolutionary Architecture Model makes the following argument:
The transport layer (TCP, UDP) acts as an “evolutionary shield” for IP because any new transport layer protocols are unlikely to survive the competition with TCP/UDP which already have multiple products at higher layers. So the stability of these two protocols provides stability for IP by eliminating any potential new transport protocols that could select a competing network layer protocol.
Lesson 1 Quiz 2:
Which of the following are ramifications of the “hourglass shape of the internet”?
A: Many technologies that were not originally designed for the internet have been modified so that they have versions that can communicate over the internet (such as Radio over IP).
B: It has been a difficult and slow process to transition to IPv6, despite the shortage of public IPv4 addresses
C: Applications like BitTorrent leverage peer-to-peer networking instead of a more traditional client-server model for better performance.
- A is correct; Modifying a technology so that it is compatible with the rest of the internet (i.e., by making it compatible with IP) greatly enhances market penetration (from the vendor’s perspective), and/or decreases the amount of extra development that would need to happen.
- B is correct. A big part of the Internet infrastructure uses IPV4 while the cost of transitioning is high. This reflects as a consequence of the narrow waist.
- C is not relevant here. The hourglass shape of the Internet refers to Internet architecture in terms of protocols available at the different layers.
Describe the function of Repeaters/Hubs and Bridges/Layer 2 Switches. What are the limitations?
Repeaters and Hubs: Provide connectivity between hosts that are directly connected in the same network.
- Operate at Layer 1
- Hosts connected to these devices compete for access to the same link
Bridges and Layer 2 Switches: Enable communication between hosts that are not directly connected.
- Operate at Layer 2 based on MAC addresses.
- Limitation: No transmission control. If arrival rate is higher than output rate, a full buffer space could lead to dropped packets.
