1. 4.1 Fundamentals COMMUNICATION: Advanced Operating Systems (CSc 8320)
Presented by: Azim Ahmadzadeh
September 8, 2017

2. The Problem → (ISO OSI) Protocols
In distributed systems, there is no shared memory;
When two processes need to communicate, they should rely on sending and receiving messages;
To avoid chaos, some agreements are needed:
How many volts to signal a O-bit and I-bit?
What is the last bit of the incoming message?
How to know if a message is damaged or lost?
→ (ISO OSI)
International Standards Organization developed a reference model called Open System Interconnection model.
Protocols

3. Connection Oriented Protocols;
Generally, there are 2 types of protocols:
Connection Oriented Protocols;
First, establish a connection;
(Possibly) negotiate the protocols;
Communicate;
Finally, terminate the connection;
Exp: Telephone
Connectionless Protocols;
No established connection is required;
Transmit the message when the “sender” is ready.
Exp: Mailbox

4. OSI Communication Model The Seven Layers
A group of protocols from a communication model.
Any open system needs to follow this model to be able to communicate with other open systems.
“Each layer deals with one specific aspect of the communication.”
“Each layer provides an interface to the one above it.”
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

5. Physical Layer OSI Communication Model
It is concerned with transmitting the O’s and I’s.
How many bits per seconds can be sent?
Can transmission take place in both directions simultaneously?
It makes sure that when a machine sends a 0 bit, it is actually received as a 0 bit and not a 1 bit;
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

6. Data Link Layer OSI Communication Model
It divides packets into frames;
0’s and 1’s will not always be received as they were sent. Data link layer has to detect and correct such mistakes.
An error is detected when the two sides of the communication do not agree on the checksum;
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

7. Network Layer OSI Communication Model
It is to find the best route from sender to receiver;
The shortest route is not necessarily the best route, but the one with the minimum number of queued messages;
IP is the most popular network protocol;
Each IP packet is routed to its destination independent of all others. No internal path is selected and remembered
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

8. Transport Layer OSI Communication Model
Upon receiving a message, transport layer breaks it into smaller pieces called Segments (Windowing);
“Which packets have been sent?”
“Which packets have been received?”
“How many more the receiver has room to receive?”
Protocols: TCP, TCPIIP, UDP, RTP;
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

9. Session Layer OSI Communication Model
For any system-to-system communication, a session has to be established (Handshaking);
It controls which party is talking now (synchronization);
Only a few applications are interested in the session layer;
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

10. Presentation Layer OSI Communication Model It is in the OS layer;
Not concerned with the bits, but their meaning;
Responsible for tasks like encryption (Security protocols);
Compatibility of systems with different internal representations on the opposite sides;
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

11. Application Layer OSI Communication Model
Applications such as Firefox, Skype, etc.
“It is practically the container for all applications and protocols that do not fit into one of the underlying layers”;
Protocols such as HTTP, FTP.
Physical layer: Cable layer; Systems need to be physically connected to the network; Transmission of raw bits;
Data Link: Every networking device need a MAC address; How switches operate; It divides packets into frames; error detection and correction;
Network Layer: Anything related to IP addresses; DNS; Routing -> finding the path and making sure the message reaches the other end;
Transport Layer: Windowing (divides messages into smaller pieces); Decides how large a block of info should be; how long a computer should wait (acknowledgement);
Session Layer: A computer to communicate to any other system, a session has to be established; (Handshaking)
Presentation Layer: In the OS layer; encryption; Security protocol; conversion;
Application Layer: Skype; chrome; firefox; ...
Illustration from:

12. Moving Through Stacks
Data chunks becoming enveloped with more data as headers.
At each layer, a header will be added to the message containing the corresponding protocols.
E.g. “Data link layer header” is added to the message on the “Data link” layer.
Illustration from:

13. Persistent vs Transient
Persistent communication
A message is stored at a communication server as long as it takes to deliver it at the receiver.
Transient communication
A message is discarded by a communication server as soon as it cannot be delivered at the next server or at the receiver.
Source:

14. Synchronous vs Asynchronous
Asynchronous Communication
Sender continues immediately after it has submitted its message for transmission.
Something that is happening in real time.
Instant Messaging, Video Conference
synchronous communication
Sender blocked until its message is stored in a local buffer at the receiving host or actually delivered to the receiver.
Something that is not happening in real time.
senders ship off their messages for recipients to open at their convenience.
Text Message, , Facebook, Youtube
Source:

15. See chapter 4.1 and copy all the references here …
DAY, J. and ZIMMERMAN, H.: "The OSI Reference Model." Proceedings of the IEEE, (71)12: , Dec
COMER, D.: lnternet working with TCPIIP, Volume I: Principles, Protocols, and Architecture. Upper Saddle River, NJ: Prentice Hall, 5th ed., Cited on page 121.
SCHULZRINNE, H., CASNER, S., FREDERICK, R.. and JACOBSON, V.: "RTP: A Transport Protocol for Real-Time Applications." RFC 3550, July 2003.
POSTEL, J. and REYNOLDS, J.: "File Transfer Protocol." RFC 995, Oct
FIELDING, R., GETTYS, J., MOGUL, J., FRYSTYK, H., MASINTER. L., LEACH, P., and BERNERS-LEE, T.: "Hypertext Transfer Protocol - HTTP/1.1." RFC 2616, June 1999.

16. Synchronous vs Asynchronous
Persistent Asynchronous
Persistent Synchronous
Source: