module 1 - networking

what is a network?

two or more computer systems linked by transmission medium, allowing them to exchange data

nodes

devices

links

communication pathways

intermediate nodes

perform forwarding to other nodes

end systems (hosts)

send & receive data traffic

transmission media

the physical or wireless communication channels

client-server networks

server makes resources available, client consumes services, centralized - LAN

peer 2 peer networks

hosts act as client & server, decentralized - WAN

LAN (Local Area Network)

network confined to one geographical location, nodes connected by cable or short wireless, owned by one org, home/residential

WAN (Wide Area Network)

network of networks connected by long-distance links

ex. main office → branch offices, enterprise networks → remote workers

Topology

physical or logical structure of a network

physical topology

placement of nodes, logistics of transmission media

ex. connected cables vs. connecting a switch

logical topology

flow of data through a network

half duplex

point → point links where nodes cannot simultaneously send and receive

full duplex

point → point links where nodes can simultaneously send and receive

star topology

each end point is connected to a central forwarding appliance, most widely used, single point of failure, LAN

Hub and spoke

same physcial layout as star topology, used in different context (WAN)

Full mesh topology

each device is connected to every other device, multiple routes incase nodes fail

impractical for most as it grows exponentially L=(n(n-1))/2

partial mesh topology

hybrid approach where the most important nodes are interconnected, good redundancy, more practical

bus topology

all nodes connect to a single trunk cable, connecting to nodes via drop cables and end nodes are terminators (absorb signal & prevent reflection), travels one node to the other, broken cable can break termination

ring topology

nodes connected to form a ‘ring’ where signals travel in one direction, each device acts as a repeater, one node malfunction disrupts communication

OSI (open system interconnection) model

for understanding network system components, separated hardware & software functions into seven layers

encapsulation

adding headers as data moves down stack of sender

decapsulation

removing headers as data moves up stack of receiver

OSI model: Layer 1 - physical

transmits BITs as signals over a transition medium (copper, fiber, wireless)

BITs → signal → media

devices: transceiver, repeater, hub, media converter

OSI model: Layer 2 - data link

controls how data is placed & received from media through framing which includes error detection

devices: network adpapter (NIC), bridge, switch, wireless access point (AP)

OSI model: Layer 3- network

moves data through internetwork

logical addressing, routing, path determination through IP packet

device: router

OSI model: Layer 4 - transport

manages end → end communication

segmentation, flow control, error control using multiplexing & ports

devices: advanced firewalls, intrusion detection systems (IDSs)

OSI model: Layer 5 - session

manages communication sessions (opens, closes, authentication, authorization)

OSI model: Layer 6 - presentation

translation, data compression, encryption (sending), decryption (receiving)

OSI model: Layer 7 - application

provides interface for software to exchange data; web browsing, email, file transfer

TCP (transmission control protocol) / IP (internet protocol) suite

OSI is perfect theoretically but internet was used with this which uses 4 of the 7 OSI layers

4 application (application & presentation), three transport (session & transport), two network, one data link (data link & physical)

How does a switch work in layer 2 of the OSI model?

Reader the header of the ethernet frame to find the destination MAC, then finds the port that leads to the destination and sends it

How does routing across networks work in layer 3 of the OSI model?

sender creates an IP packet and compares the IP destination to its own. it ends up being on a different network so the IP packet gets sent to the router and the receiver is connected vis intermediate nodes so data link protocol is used to send message to IP address

How does multiplexing & port numbers work in layer 4 of the OSI model?

it combines different data streams on same network at the same time using port numbers & addresses to keep data separate, delivers data to the correct application once received