The ten metres everybody forgets
An installer measures a run of 90 metres and tests it. It passes. Later the office adds a long patch cord at each end. The link is now over the limit and users complain.
The test and the real use measured different things. Standards give each a name.
Key words
| Word | What it means |
|---|---|
| Permanent link | the fixed cable from the patch panel to the wall outlet, with its connectors |
| Channel | the whole path from one device to the other, with every patch cord |
| Patch cord | a short flexible cable with a plug on each end |
| Campus | a group of buildings on one site |
| Backbone | the main cables that join buildings or floors |
| Horizontal cabling | the cable from a floor's patch panel to each outlet |
| Passive | kit with no power, such as cable, panels and connectors |
| Active | kit that needs power, such as a switch or a router |
| Switch | a device that sends each frame only to the right port |
| Router | a device that passes data between networks |
| Network | devices joined so they can share data |
| Standard | an agreed set of rules for how work is done |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can tell a permanent link from a channel, work out channel length, and explain campus, passive and active design.
Starter: shapes
Have a go
Starter: shapes
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Permanent link and channel
The permanent link is the fixed part: cable in the walls, with the outlet and the patch panel connector. It is at most 90 metres for twisted pair.
The channel is the whole path, including a patch cord at the desk and another in the rack. A channel is at most 100 metres. So the cords share the last 10 metres.
Worked example: is the channel too long?
| Permanent link | Desk cord | Rack cord | Channel total | Result |
|---|---|---|---|---|
| 80 m | 3 m | 2 m | 85 m | Within 100 m. Pass |
| 90 m | 5 m | 5 m | 100 m | Exactly at the limit. Pass |
| 90 m | 8 m | 5 m | 103 m | Over 100 m. Fail |
| 93 m | 1 m | 1 m | 95 m | Link over 90 m. Fail |
The cells students fill in are left blank in this preview.
Campus distribution
A campus is several buildings. A backbone cable joins them, often fibre, because it carries far and ignores electrical noise. Inside each building a backbone joins floors. On each floor, horizontal cabling reaches each outlet.
So the design has three levels: campus, building and floor.