18. Introduction to Networking
with TCP/IP
Networking is sharing and communicating with others. A model is needed for:
compatibility with other programs, computers, etc. It is modular, allowing changes to one
layer without significantly effecting others. It is versatile, allowing upgrading and
additions.
Different layers of TCP/IP model defined:
- Application (or software) layer – (the file is in charge of everything here) this
layer provides the interface between the user through software and the computer (hardware)
- TCP layer – (The kernel takes over) this layer provides multiple transport sessions
over one IP number (i.e. 192.168.0.23). This gives the illusion of 1 session per person
even though there isn’t. (this is because the signal is multiplexed)
- IP layer – Takes all the signals and combines and distributes it according to
address
- Ethernet layer – actual interface between IP layer and Physical layer (through the
Network Interface Card or NIC). These layer controls flow of information, checks for
errors and manages speed of the packets. Flow control is managed by CSMA/CD Carrier Sense
Multiple Access/Collision Detect
- Physical Layer – This layer puts the signal on the wire (translates the bytes into
electrical signals for transmission)
Differences in layer models |
| OSI Model |
TCP/IP Model |
- Application (software)
- Session
- Presentation
|
- Application (software)
|
- Transport
- Network
- Data Link
- Physical
|
- TCP
- IP
- Ethernet
- Physical
|
TCP uses port numbers for TCP layer to forward packet to application layer. IP uses IP
addresses, so router can forward packet and so the destination can recognize it. Ethernet
layer gets the information to first router. All these are encapsulated starting with the
application down to the Ethernet layer. Two protocols are:
- IGRP (Interior Gateway Routed Protocol) is internal to the network and
- EGRP (Exterior Gateway Routed Protocol) is worldwide
There are four ways to receive IP packets
- Promiscuous – you receive all packets (snoop)
- Broadcast – directed to all addresses on a particular network. (address looks like
this (hex) ff:ff:ff:ff:ff)
- Multicast – directed to a multicast group you subscribe to. (address looks like
this (hex) 1:0:5e:x[0-7f]:x:x)
- Unicast – each host has a unique Ethernet address
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