Chapter 2 - Network Standards

4 step handshake closing

Just like 3 way but finishes with a FIN ACK. Host B is finished sending data it sends its own FIN segment and receives an acknowledgment. Then the connection is closed. (FIN ACK ACK FIN)

TCP/IP

Note that TCP/IP is the standards architecture, while TCP and IP are individual standards within the architecture.

Which layers are reliable?

Only Layer 4 TCP is reliable. Because it is Connection-oriented and resends the packet if there's an error. Layer 2 is unreliable because it doesn't automatically resend the bad packet only detects it.

Trailer

Some messages also have trailers, which consist of everything coming after the data field.

OSI standards at 1-7 layers

Almost all switched and wireless networks -both LANs and WANs -follow OSI stnadards at the physical and data link layers, regardless of what upper-layer standards they use.

What happens when a segment is not sent correctly?

Unless a transport process receives a segment correctly, it does not send an acknowledgement.

UDP

User Datagram Protocol (UDP) - does not have openings, closings, or acknowledgements, and so it substantially has less traffic than TCP. Called Datagrams because are very simple.

Port Numbers

Well-know port numbers are between 0-1023.

Vertical Communication on hosts

1. Application creates message HTTP message, hands message to Transport Layer. 2. Transport layer encapsulates with a TCP header then hands that down to the Internet layer 3. Internet layer encapsulates a TCP segment in data field of IP packet then hands it down to data link layer. 4. Data link layer encapsulates and add a data link layer frame. Then hands it to the physical process layer 5. Physical process layer converts bits into signals and transmits its signal out the physical link.

How many bits or octets in a IPv4 address?

32 bits or 4 octets.

Nibble

4 bits.

Codec

A codec converts between analog microphone signals and digital transmitted signals. Co- is compression of analog signal into digital signals called encoding. Dec is converting incoming digital signals into analog signals to cause the earpiece to vibrate is called decoding.

HTML vs. HTTP

HTML - markup language for the web. HTTP - Transport protocol and is used to move stuff.

Basic Binary Math

If a field has N bits, it can represent 2^N alterantives 0 bits = 2^0 = 1 # of alternatives 1 bits = 2^1 = 2 2 bits = 2^2 = 4 4 bits = 2^4 = 16 8 bits = 2^8 = 256 16 bits = 2^16 = 65,536 32 bits = 2^32 = 4,294,967,296

Physical Link vs. Data Link vs. Internet Layers

Physical link is the actually link between host and next switch or switch to switch (next stop). Data link is between host and router (one network). Internet Layer is the Host to the destination host over a router called a route (multiple networks).

Port Number for FTP

Port 20 and 21

Port Number for SMTP

Port 25

Port Number for HTTP

Port 80

OSI standards

Reference Model of Open Systems Interconnection. Reference Model means architecture.

Reliability

Reliable protocol means it detects the error and then finds a way to recover from the error. example: Damaged packet/never reached destination host.

RFC

Requests for comments - Every few years, the IETF publishes a list of RFCs that are official internet protocol Standards.

Semantics vs. Syntax

Semantics is the meaning of a message. Syntax is how a message is organized

TCP/IP standards at 1-7 layers

TCP/IP is dominant at the internet and transport layers. TCP/IP is also dominant in corporate networking at the internet and transport layers.

IETF

The Internet Engineering Task Force - TCP/IP's standards agency.

Data Field

The data field is the heart of the message. It contains the content being delivered by the message.

Fields in headers and trailers

The header and trailer usually contain smaller syntactic sections called fields.

Header

The message header, quite simply, is everything that comes before the data field.

The Hybrid TCP/IP-OSI Standards Architecture

The most common standards pattern in organizations is to use OSI standards at the physical and data link layers, TCP/IP standards at the internet and transport layers, and application standards from several sources. This is the hybrid TCP/IP-OSI standars architecture.

Networking Standards

are rules of operation that govern the exchange of messages between two hardware or software processes. This includes message semantics, syntax, message order, reliability, and connection orientation.

Socket

helps to know what exact application you are trying to connect to: IP address, a colon, and the port number. example - source socket is 60.171.18.22:2707 and the destination is 1.33.17.13:80

3 way hand-shake

if Host A wishes to communicate to Host B then: 1. Host A transmits a TCP SYN to Host B 2. Host B sends back a TCP SYN/ACK segment. They SYN indicates that it also is willing to begin the communication. the ACK part is acknowledgement of Host A's SYN message. 3. Host A sends back a pure TCP ACK segment. This acknowledges Host B's SYN/ACK. In TCP, all segments are acknowledged, with the primarily exception of pure ACKs.

ISO

international Organization for Standardization. OSI is an architecture and ISO is a standards agency.

Encapsulation

is placing a message in the data field of another message

Byte

just like a Octet. A group of 8 bits.

Octets

same term as a byte. Octet is a group of 8 bits.