Dis­cover how your net­worked de­vices com­mu­ni­cate with each other

Mac|Life - - FEATURE -

How does data travel from one part of your network to another? The an­swer lies in the TCP/IP model. TCP (Trans­mis­sion Con­trol Pro­to­col) is the method used by com­put­ers to con­nect over net­works, while IP (In­ter­net Pro­to­col) is the way in which data is bro­ken down into ‘pack­ets’ of in­for­ma­tion and trans­ferred. Each packet is la­belled in such a way as to make it clear where it’s come from and what its des­ti­na­tion is. When data is trans­ferred, the TCP part of the process is re­spon­si­ble for en­sur­ing that the data is checked for er­rors dur­ing trans­mis­sion — if er­rors are found, the data is trans­ferred again. This model can be bro­ken down into four ba­sic lay­ers: Ap­pli­ca­tion, Trans­port, In­ter­net and Link — see the ex­pla­na­tion op­po­site for a ba­sic break­down of what hap­pens on each of those lay­ers. At the lo­cal network level, your de­vices are typ­i­cally linked and man­aged through a sin­gle de­vice — your router — in what’s termed a Lo­cal Area Network (LAN). De­vices are uniquely iden­ti­fied on your network by their IP ad­dress, which con­sists of four sep­a­rate dig­its, each of which can be a num­ber from 0 to 255. The first two re­fer to the network ad­dress and are al­most al­ways 192.168. The last two re­fer to the host ad­dress. Of th­ese, the first num­ber (the sub­net) is shared be­tween all net­worked de­vices, while the fi­nal num­ber (host) is what uniquely iden­ti­fies that de­vice on the network. For ex­am­ple, your Mac might be as­signed and your iPhone might be

One IP ad­dress on your network — of­ten or — is re­served for your router, and this ad­dress is known as the ‘gate­way’, through which all other de­vices com­mu­ni­cate. You’ll also see a ref­er­ence to a sub­net mask, which is usu­ally, and can be safely ig­nored.

By de­fault, IP ad­dresses are handed out au­to­mat­i­cally by your router us­ing a fea­ture called DHCP (Dy­namic Host Con­fig­u­ra­tion Pro­to­col), but you can set them man­u­ally for de­vices whose IP ad­dress needs to re­main con­stant, though this is un­usual in a home set­ting.

Wire­less con­cerns

Data trans­ferred over wires is gen­er­ally con­sid­ered se­cure, but data sent wire­lessly can be in­ter­cepted, which is why wire­less net­works sup­port var­i­ous forms of en­cryp­tion, the most se­cure of which, cur­rently, is WPA-PSK2.

One way to se­cure your in­ter­net con­nec­tion on an in­se­cure wire­less network is to use a Vir­tual Pri­vate Network (VPN), which ef­fec­tively cre­ates an en­crypted ‘tun­nel’ through which data is sent and re­ceived.

1. Ap­pli­ca­tion layer This layer is split into three main el­e­ments: at the top of this layer is the soft­ware you’re us­ing to ac­cess the in­ter­net, such as a web browser. Next is the ‘pre­sen­ta­tion’ el­e­ment, where data is trans­lated into a for­mat for send­ing — for ex­am­ple, if it’s to be en­crypted or com­pressed. Fi­nally, the ‘ses­sion’ el­e­ment de­ter­mines the type of con­nec­tion made — HTTP or HTTPS for the web, and SMTP for email, say. 2. Trans­port layer (TCP) This man­ages how the data will be de­liv­ered by con­vert­ing it into ‘pack­ets’ for send­ing, then mak­ing sure they’re safely de­liv­ered and re­assem­bled at the other end in the cor­rect or­der. It also works in re­verse for pack­ets which have been re­ceived by your com­puter. 3. In­ter­net (or Network) layer This is the layer that cov­ers how the data will be ad­dressed and then routed be­tween de­vices. This means de­ter­min­ing where the data is to be trans­mit­ted to on its route be­tween your com­puter and its des­ti­na­tion. It’s also where the ac­tual de­liv­ery of data oc­curs, us­ing IP packet switch­ing, as de­scribed ear­lier. 4. Link layer The low­est layer, also known as the network ac­cess layer, is where er­ror de­tec­tion and cor­rec­tion take place as the data is pack­aged and trans­ported. It’s also where you’ll find the phys­i­cal hard­ware (typ­i­cally Eth­er­net or Wi-Fi) that con­nects your de­vice to your network and, ul­ti­mately, the in­ter­net.

Vir­tual Pri­vate Net­works (VPNs) work by ‘tun­nelling’ an en­crypted con­nec­tion through an un­en­crypted network, such as a pub­lic Wi-Fi spot.

If you want to ap­ply a static IP ad­dress to your Mac, se­lect your con­nec­tion method in Sys­tem Pref­er­ences > Network, click Ad­vanced, choose ‘Us­ing DHCP with man­ual ad­dress’ and as­sign one that isn’t al­ready in use.

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