Network and Telecomm Notes

TCP/IP Stack 

Higher layers of the TCP stack needed.  Lower levels similar to vocal communication, higher similar to independant languages.

Three highest layers: Session, Presentation, Application.

Session

Most likely to be not implemented. 

Establishes who gets to trasnmit when and how much.  Failure to properly do this causes buffer overflow.  Also handles what happens when this error occurs.

Also handles connection termination and resuming on unexpected termination.

Presentation

Handles the formatting of data in the communication (or in files).  Allows either end to transmit and interpret transmitted data.

Standards are put in place to help ensure compatibility between different devices communicating with each other.

Both compression and encryption can also be implemented in this layer transparently to the application on either end.

SSL (HTTPS) uses certificates to help verify website identity.

S/MIME (Secure Multipurpose Internet Mail Extentions) sometimes has encryption on top of it such as RSA and PGP (Pretty Good Privacy).

WWW / HTTP, FTP, LDAP, SMTP, IMAP, POP3 are all on this layer.

Summary: Packages up stuff app spits out. 

Application

Allows the user to control the data sent and received, and otherwise interact with the remote computer.

IP Subneting

Scares people.  Scared the prof.  We need to know it.  Likely to encounter in Cisco/MS networking exams.

Is the process of breaking up the IP address space into chunks for the purpose of more efficient routing.

Wasting IP addresses is bad, so subnets are used to break a space into the smallest needed chunk. 

Four classes of IP addresses: A, B, C, and D.

Class A uses one octet for network address, and three for node address. 128 exist.

Class B uses two octets for each. 65k exist.

Class C uses three and one octect.  254 addresses (remember 0 is null, 255 is broadcast).

Class D is a "last resort" class.

Subnet masks mask the network bits.

Class A: 255.0.0.0, B: 255.255.0.0, C: 255.255.255.0

2 to the power of the number of 0 bits in the subnet minus 2 gives the number of possible addresses.