Can someone make clear these 2 terms CSU/DSU & demarcati

kadshah

The demarcation point is still unclear to me even though i've read todd's
explanation a million times. Is this the device in my closet that plugs into the phone jack or is this device in my service providers telecommunication closet? Also CSU/DSU i still can't visualize what this is.
Todd says its 1 device (what is this device?) that plugs into a RJ-45.
These 2 terms are so frustrating to understand i'm sure it's something extremely simple.
thanks

keenon

demarc = the point where carrier jack interface is at (smart jack)

csu/dsu = your equipment that will connect to their equipment also called CPE (customer premises equipment)

reloaded

Demarcation point - where your shop's maintenance responsibility ends and where the WAN provider or Telco's responsibility begins...often separated by a DSX (digital cross connect) panel or some type of Telco router, patch panel, etc.

CSU/DSU - basically a line formatter for 56K, T-1, etc...T-1 often comes into a facility from the Telco with different framing than your equipment is set up for, so a CSU/DSU will change the framing, allowing your equipment to interface or connect to the T-1 or WAN link, it also adds/removes framing or "stuff" bits used for additional data (addressing, flow control, etc)

If you've ever seen a rack mounted modem, a CSU/DSU kinda looks like that depending on the model...but don't confuse them with a modem! They do two entirely different operations!

kjpou1

Demarcation point is a concept more than a physical device. It depends on the needs of the company and thus forms the responsibilities of the two parties.

In the U.S. from what I have read this point is usually where the physical cable supplied from the Telco is terminated.

router

---

CSU/DSU

---

|---- WAN/Switch
.......................................demarc

It can also move, like with our local PT&T, where it can also include the CSU/DSU. In the larger clients it is more like the U.S. demarc.

router

---

|

---

CSU/DSU

---

WAN/Switch
..............demarc

Also in one of my smaller clients the PT&T also provides and manages the routers, so again the demarc moves.

Regards

Kenneth

kadshah

thanks for the explanation. It' slowly begining to sink in.