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v.35 ,dsu/csu, channelized/unchannelized

sarahr202
Level 5
Level 5

Hi everybody

Please consider the following example:

PCs----lan-----R1- s0---v.35----DSU/CSU----T1 (TELCO)---------CSU/DSU---V.35-----s0-R2----lan--PCs

Above, V.35 cable is under 15 meters, so  we can have maximum 1.54Mbps between router and DSU.

1)Our telco terminates T1 line at CSU. So if we look at the data rate between DSU and our router ( which is 1.5 Mbps) and data rate between CSU and Telco (( which is 1.5 Mbps as well).  In this case no multiplexing is happening.  Because multiplexing is defined as to combines many lower speed signals to generate one composite signal of higher speed. In our case both data rates at DSU site and CSU site are same.

So in this case our DSU/CSU is just changing line coding  for data received from router into coding that our telco understands and vice versa.

I just want to confirm that.

2) Should the above t1 connection be considered as channelized or unchannelized ? ( this is my understanding, since we are just transmiiting data no voice, so no framing is necessary to impart signaling information to receiver. So we can use the whole bandwidth of 1.5 Mbps for data . It should be unchannelized.)

Thanks and have a great day.

4 Accepted Solutions

Accepted Solutions

Reza Sharifi
Hall of Fame
Hall of Fame

Hi Sarah,

I can't see the images, but that is fine.  Your understanding regarding the first question is correct.  The CSU/DSU is just like a converter.

Here is link an CSU/DSU

http://searchnetworking.techtarget.com/definition/CSU-DSU

Correct, a regular T1 is unchannelized.  Although a T1 can be sub-rated using technologies like frame relay.  So, instead of paying for a full T1 of 1.5Mbps, you can have 64, 128 or 512Kb speed circuits which is somewhat cheaper if you don't need the full speed.  On the other hand a channelized T1 or PRI is usually used to voice communication.

HTH

View solution in original post

Hi Sarah,

Congratulations on your new job. I am sure, you will do just fine in your new position. My advice to you is to learn as much as you can by practicing on equipment if you have the opportunely.  If they have a lab take a advantage of it and get yourself familiar with equipment on how to cable and configure them. Overall, don't be afraid to get your hands dirty, as that is an invaluable experience.

Regarding CSU/DSUs, in the older days of 2500 and 2600 routers, you would need an external CSU/DSU with serial interface to connect the T1, or a sub-rate frame relay circuits that telco would bring to your space.  These days, all CSU/DSUs are all build into the WIC and there is no more need for an external CSU/DSU.

here is a link with a pichture of a WIC with built in CSU/DSU.

http://www.cisco.com/en/US/prod/collateral/routers/ps221/product_data_sheet09186a00801a9184.html

and here is a picture of an external CSU/DSU and how it would connect to the router.

http://www.google.com/imgres?imgurl=https://learningnetwork.cisco.com/servlet/JiveServlet/showImage/2-136969-36023/dsu-router-connection.jpg&imgrefurl=https://learningnetwork.cisco.com/thread/28073&h=480&w=640&sz=68&tbnid=lC5Q8_LqH9co4M:&tbnh=90&tbnw...

As for your first question, you are correct, there is no TDM, voice, etc.. it just data.

Regarding your second question, it depends on the environment and setup. If it is a small voip deployment, to save money businesses use a small router like 2800 or 2900 series as call manage and also gateway.  If the environment is large, they usually have a cluster of servers as call managers and then the call manage connects to the router (gateway) and the gateway routes the calls between the voip systems and the PSTN using PRIs or BRI. 

HTH

Reza

View solution in original post

I agree with Reza in saying congratulations on your new job. I hope that you will continue to be an active participant in the forum.

Unfortunately you can not do that. The T1 is channelized or it is not channelized. When you separate slots 13 through 24 you are using a channelized feature. You can treat those combined slots as a single data stream. But the T1 must still provide the signaling to support the various slots.

HTH

Rick

HTH

Rick

View solution in original post

Basically that is what you do - along with configuring the serial interface with encapsulation, IP address etc.

As Reza comments in a post earlier in this thread, it is quite common in recent routers that the DSU/CSU will be integrated into the serial WIC so there is not an external device to configure and that configuration is now done on the router.

HTH

Rick

HTH

Rick

View solution in original post

7 Replies 7

Reza Sharifi
Hall of Fame
Hall of Fame

Hi Sarah,

I can't see the images, but that is fine.  Your understanding regarding the first question is correct.  The CSU/DSU is just like a converter.

Here is link an CSU/DSU

http://searchnetworking.techtarget.com/definition/CSU-DSU

Correct, a regular T1 is unchannelized.  Although a T1 can be sub-rated using technologies like frame relay.  So, instead of paying for a full T1 of 1.5Mbps, you can have 64, 128 or 512Kb speed circuits which is somewhat cheaper if you don't need the full speed.  On the other hand a channelized T1 or PRI is usually used to voice communication.

HTH

Thanks Reza.

I just got out of military after serving 4 years and luckily got my first job in networking starting next month at a big service provider.  I really appreciate your guys help for getting me to this point from nowhere.

CCNA( R/S),CCNP (R/S) do not delve into details of T lines.  . I was told I would be working on from layer1 to layer 3.  I am trying to fill up the gap between certification and practical experience.  I am new to T lines, never seen  DSU/CSU or smart jack in my life.

I have few weeks off so I am trying to understand T lines something my study for Cisco certs did not cover.

I really appreciate if you can help me understand it.  I am also reading Cisco book " Telecommunications technologies reference".

Quote from the link you provided.

The Data Service Unit (DSU) manages line control, and converts input and output between

RS-232C RS-449, or V.xx frames from the LAN and the time-division multiplexed (TDM) DSX frames on the T-1 line

.

In our example, we have unchannelised T1, and we are not usuing TDM ( are we?)  R1 sending data 1.5 Mbps, DSU receives it and conditions it so CSU can understands it. CSU then conditions it so telco can understands it and transmits it to telco.  Here we do no see TDM being used. We have single stream of data from one source R1 entering DSU and exiting CSU towards telco. It is just like having a connection of 1.5 Mbps without requiring any  framing. It is simply unchannelized.

am I correct ?

-------------------------------------------------------

On the contrary if  we have

IP phones--LAN--CUCME ( Build in DSU/CSU)----------t1-----------------T1(MUX) at CO

In above case,  our built-in CSU/DSU has also T1 multiplexer functionality.  So when our CME routers receives voice streams from different channels ( Ip phones). Our CSU multiplexes using TDM and sends the frames to T1 mux at CO where they get demultiplexed and calls are routed .

Am I correct ?

Thanks and have a great day.

Hi Sarah,

Congratulations on your new job. I am sure, you will do just fine in your new position. My advice to you is to learn as much as you can by practicing on equipment if you have the opportunely.  If they have a lab take a advantage of it and get yourself familiar with equipment on how to cable and configure them. Overall, don't be afraid to get your hands dirty, as that is an invaluable experience.

Regarding CSU/DSUs, in the older days of 2500 and 2600 routers, you would need an external CSU/DSU with serial interface to connect the T1, or a sub-rate frame relay circuits that telco would bring to your space.  These days, all CSU/DSUs are all build into the WIC and there is no more need for an external CSU/DSU.

here is a link with a pichture of a WIC with built in CSU/DSU.

http://www.cisco.com/en/US/prod/collateral/routers/ps221/product_data_sheet09186a00801a9184.html

and here is a picture of an external CSU/DSU and how it would connect to the router.

http://www.google.com/imgres?imgurl=https://learningnetwork.cisco.com/servlet/JiveServlet/showImage/2-136969-36023/dsu-router-connection.jpg&imgrefurl=https://learningnetwork.cisco.com/thread/28073&h=480&w=640&sz=68&tbnid=lC5Q8_LqH9co4M:&tbnh=90&tbnw...

As for your first question, you are correct, there is no TDM, voice, etc.. it just data.

Regarding your second question, it depends on the environment and setup. If it is a small voip deployment, to save money businesses use a small router like 2800 or 2900 series as call manage and also gateway.  If the environment is large, they usually have a cluster of servers as call managers and then the call manage connects to the router (gateway) and the gateway routes the calls between the voip systems and the PSTN using PRIs or BRI. 

HTH

Reza

Thanks Reza

Can we use unchannelized and channelised t1  at the same time?

For example

       ipphoes, Computers--- router( CSU/DSU)-------t1--------provider------Internet

                                                                                                            |_______PSTN

Suppose  we made arrangement with the provider that slots 1 through 12 will be used for voice calls, and slots 13 through slots  24 will be used for Internet connectivity.    we configure our csu/dsu controller on our router with two groups.

group1 uses slots s1 through s12 for voice

group 2 uses slots 13 through s24 for data

Group 1 uses channelized t1 slots 1 through slots 12 while group 2 uses unchannelized slots s13 through s24 for data.

can we do that?

Thanks and have a great day

( I am hoping they have lab if they do I will spend my off days practicing different scenarios)

I agree with Reza in saying congratulations on your new job. I hope that you will continue to be an active participant in the forum.

Unfortunately you can not do that. The T1 is channelized or it is not channelized. When you separate slots 13 through 24 you are using a channelized feature. You can treat those combined slots as a single data stream. But the T1 must still provide the signaling to support the various slots.

HTH

Rick

HTH

Rick

Thanks Rick for your kind words.

Let say we want to connect two sites with t1 from a telco .  

1) Ask the telco to provide unchannelized T1.

2) configure our DSU/CSU on both sites.

Is that what we do?

Thanks and have a great weekend.

Basically that is what you do - along with configuring the serial interface with encapsulation, IP address etc.

As Reza comments in a post earlier in this thread, it is quite common in recent routers that the DSU/CSU will be integrated into the serial WIC so there is not an external device to configure and that configuration is now done on the router.

HTH

Rick

HTH

Rick
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