-Linux (and Unix) concepts of packetized data networks have changed human interaction with tech forever.
-The most prominent example of this is the Internet.
-Ethernet is the most ubiquitous network layer protocol.
-it began as a research project in MIT, Xerox in the 70s. it used coaxial cables then.
-ethernet works on the principle of csma/cd.
-csma/cd = carrier sense, multiple access, collision detect.
-its like a dinner party where guest wait for a lull in chatter, before they speak.
-if two guest talk simultaneously, they both stop, wait a bit and try again.
-switches help in detecting and reducing collision.
-ethernet packets can travel only in one direction.
-ethernet packets can be of 3 types - unicast, multicast or broadcast.
-unicast=> 1dest, multicast=> many dest, broadcast=> all hosts on a segment are dest.
-a single segment can have hosts talking at different speeds.
-ethernet runs on various media - coax, unshielded twisted pair (utp), fiber etc. it started out on coaxial in 70s.
-unshielded twisted pair or utp is the chosen medium for ethernet. they hv RJ45 terminators.
-utp works on star topology. utp is cheap, simple install and easy debug than coax and fiber.
-the common type of utp cable is cat5e or cat 6. These transmit data at 100Mbps to 1Gbps.
-utp has 4 pairs of wires (total 8), orange, green and brown paired with white.
-ethernet devices and tcp/ip layers:
. hubs - physical - not smart, dont analyze packets
. switch - link - smarter, analyze pkts, std devices for conn two n/w into one big n/w
. router - network - smarter still, analyze pkts, can do prioritization of pkts, security etc.
-autonegotiation: is a feature of ethernet defined by ieee.
-autoneg allows hosts to 'learn' the n/w transmit speed of their neighbors and modulate their own accordingly.
-this is imp bec if two devices talk at diff speeds, their connectivity will not work.
-all dev abv 1Gbps need autoneg. for dev upto 100Mbps, both ends need autoneg and full duplex.
-ethernet can even transmit power on itself to devices like voip, wireless access points etc.
-this is called PoE - power over ethernet.
-ethernet is easy to debug. One can analyze a n/w link by link. Problems can be found in minutes.
-ethernet pkts are usually 1500 bytes in size.
-jumbo pkts are usually 9000 bytes that are set by manufacturers for their devices.
-jumbo pkts are not recognized as a standard by ieee for interoperability reasons but yet they exist.
-nfsv4, smb, cifs etc benefit from jumbo pkts. some jumbo can be 64Kb in size (super jumbo).
-all devices in the n/w need to support jumbo, if jumbo is configured.
-Internet doesnt support jumbo as it is not a standard.
-Wireless is also a type of ethernet.
-wireless has two components - access points and clients.
-access points are also called wireless access points (WAPs).
-waps usually have a radio and stripped down linux kernel.
-beyond 8 clients for a wap, performance degrades.
-common ieee stds for wireless - bgn at 2.4GHz radio and upto 54Mbps.
-Wireless n/w are usually not very secure.
-To make them more secure, wifi protected area (wpa) proto is used along with bgn.
-in wifi enabled areas (like airports, campus etc), a central wireless switch serves several waps.
-dedicated hi speed conn like T1,T3,Sonet,Mpls,Framerelay are expensive and therefore rare.
-'last mile' connections therefore fill the gap.
-dsl and cable modems are two 'last mile' connections.
-dsl works on telephone lines and serves upto 5Mbps (real speed).
-unlike pots(plain old telephone system) & isdn which are dial up, dsl is always on.
-cable compaines provide lastmile conn over their existing fiber optic n/w.
-in conclusion, a network is like a chain -- as good as the weakest/slowest link.
-The most prominent example of this is the Internet.
-Ethernet is the most ubiquitous network layer protocol.
-it began as a research project in MIT, Xerox in the 70s. it used coaxial cables then.
-ethernet works on the principle of csma/cd.
-csma/cd = carrier sense, multiple access, collision detect.
-its like a dinner party where guest wait for a lull in chatter, before they speak.
-if two guest talk simultaneously, they both stop, wait a bit and try again.
-switches help in detecting and reducing collision.
-ethernet packets can travel only in one direction.
-ethernet packets can be of 3 types - unicast, multicast or broadcast.
-unicast=> 1dest, multicast=> many dest, broadcast=> all hosts on a segment are dest.
-a single segment can have hosts talking at different speeds.
-ethernet runs on various media - coax, unshielded twisted pair (utp), fiber etc. it started out on coaxial in 70s.
-unshielded twisted pair or utp is the chosen medium for ethernet. they hv RJ45 terminators.
-utp works on star topology. utp is cheap, simple install and easy debug than coax and fiber.
-the common type of utp cable is cat5e or cat 6. These transmit data at 100Mbps to 1Gbps.
-utp has 4 pairs of wires (total 8), orange, green and brown paired with white.
-ethernet devices and tcp/ip layers:
. hubs - physical - not smart, dont analyze packets
. switch - link - smarter, analyze pkts, std devices for conn two n/w into one big n/w
. router - network - smarter still, analyze pkts, can do prioritization of pkts, security etc.
-autonegotiation: is a feature of ethernet defined by ieee.
-autoneg allows hosts to 'learn' the n/w transmit speed of their neighbors and modulate their own accordingly.
-this is imp bec if two devices talk at diff speeds, their connectivity will not work.
-all dev abv 1Gbps need autoneg. for dev upto 100Mbps, both ends need autoneg and full duplex.
-ethernet can even transmit power on itself to devices like voip, wireless access points etc.
-this is called PoE - power over ethernet.
-ethernet is easy to debug. One can analyze a n/w link by link. Problems can be found in minutes.
-ethernet pkts are usually 1500 bytes in size.
-jumbo pkts are usually 9000 bytes that are set by manufacturers for their devices.
-jumbo pkts are not recognized as a standard by ieee for interoperability reasons but yet they exist.
-nfsv4, smb, cifs etc benefit from jumbo pkts. some jumbo can be 64Kb in size (super jumbo).
-all devices in the n/w need to support jumbo, if jumbo is configured.
-Internet doesnt support jumbo as it is not a standard.
-Wireless is also a type of ethernet.
-wireless has two components - access points and clients.
-access points are also called wireless access points (WAPs).
-waps usually have a radio and stripped down linux kernel.
-beyond 8 clients for a wap, performance degrades.
-common ieee stds for wireless - bgn at 2.4GHz radio and upto 54Mbps.
-Wireless n/w are usually not very secure.
-To make them more secure, wifi protected area (wpa) proto is used along with bgn.
-in wifi enabled areas (like airports, campus etc), a central wireless switch serves several waps.
-dedicated hi speed conn like T1,T3,Sonet,Mpls,Framerelay are expensive and therefore rare.
-'last mile' connections therefore fill the gap.
-dsl and cable modems are two 'last mile' connections.
-dsl works on telephone lines and serves upto 5Mbps (real speed).
-unlike pots(plain old telephone system) & isdn which are dial up, dsl is always on.
-cable compaines provide lastmile conn over their existing fiber optic n/w.
-in conclusion, a network is like a chain -- as good as the weakest/slowest link.
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