Table 115 Do You Need a Straight Through or Crossover Cable

Straight-Through (Unlike Devices)

Crossover (Like Devices)

Rollover

T1

1-1

1-3

1-8

1-

2-2

2-6

2-7

3-3

3-1

3-6

4-4

4-4

4-5

2-

5-5

5-5

5-4

6-6

6-2

6-3

7-7

7-7

7-2

8-8

8-8

8-1

PC to hub

PC to PC (PC to server)

Console cable

T1

PC to switch

Hub to hub

Switch to router

Switch to switch Hub to switch1*! Ronte r to router PC to routerl*

Doesn't fcllcw the gnenrul rule of like hnvicn" tse cro""ovnr cubln ueh teli<n tse straight-through cable. The d with an u"rnri"< require a cro""ovnri

Doesn't fcllcw the gnenrul rule of like hnvicn" tse cro""ovnr cubln ueh teli<n tse straight-through cable. The d with an u"rnri"< require a cro""ovnri bhe examples marked with an asterisk are exceptions to the general rule of like devices needing u cable and uni ike requiring a s traight-throtg h cab le. my ou dra w a rine between Layer 2 and Layer 3 any device on the same side of the line uses crossover cables.

NOTE

I think oh h ubs and switches as Access Layer devices; because you use them to connect users, cabling respect they are the same. I think of PCs and routers as being the same for cabling pu because both can route us ing routing protoco ls.

Wireless m ed la ie hot these days and Is going to get hotte-. It )s great aor places where wires are n (when you can!t d^ up the street because you don't have the right-of-way, for instance, or over a I where you choose not to lay cable or cable is just not feasible). It is becoming conveniently populu Fn|vgtsities, and hom es. So me eeamples follow. Infrared technologies en able yod to ur-l^nsfer files t easily as you ^p TV chanuels. Spread-spebtrum radio is a coet-e1:fect|ce way to divide frequencies instead oh leasin g lines; from the service providers. En cryp yed fuN-du plex data is ca rried at o fractio Cellular digital packet data (CDsD) uses the setwo ak for da ta when not used for voice. M 1 crowave i widespread. Take a trip ta Maryland's NASA Goddard Space flight Tenter sometime or check out th Thincoteague Island, Virginia. New cars are coming out with what rental cars have had for some ti feositioning systems (GPSs) are more po pular than ever. Ih you are out: on a boat, your latitude and location is pretty significant to your whereabouts on the bay.

Table 1-16 provides a concise yet comprehensive review of the OSI model.

Table 1-16. The OSI Reference Model

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Table 1-16. The OSI Reference Model

[View full size image]

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As you work through this book, you will encounter more detailed information and investigate sped troublesh ooting targets. At all times, remember thataltho ug hi it is certainly helpful to understand h work when you are shooting trouble, a methodical approach to troubleshooting is actually more im

Troubleshooting lay/ Layers»

You must train yourself to systematically analyze, resolve, and escalate problems. Troubleshooting is certainly one way to accomplish thi s. The OSI layers are bei lt and stacded for a reason. For troul start at the Physical Layer and work your way up to the Application Layer. A layer problem will lead and a solution. It is pretty frustrating to just compare what works to what doesn't (the swap-til-yoi approach), especially when you don't ha ve anything left to swap. Use Table 1 -177 to help yon troub layeos.

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