Ques about interface Bandwidth

Answered Question

Hi Experts,

I have always had this ques in my mind and wanted to clarify...When we do a show interface on a router for a V.35 serial interface, the interface bandwidth shows as 1544 Kbps...is it because these routers are manufactured in the US and are set to default T1 BW or is it so that these interfaces cannot support line speeds of more than 1.544 Mbps. Would appreciate if someone can please clarify the same.

Many thanks in advance.

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Correct Answer by mohammedmahmoud about 9 years 4 months ago

Hi,

The default bandwidth for WIC serial interfaces is 1544kbps as shown in the output of show interface but it can have up to 2.048 Mbps physical speed, but the bandwidth parameter itself can be <1-10000000> kilobits, which as i said doesn't reflect the physical speed in any means.

HTH,

Mohammed Mahmoud.

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Overall Rating: 4.8 (5 ratings)
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mohammedmahmoud Sat, 08/11/2007 - 09:37

Hi,

This is the default value, and please keep in mind that this value doesn't reflect or control the actual speed of the interface this value is used by the IOS features (QoS, routing protocols, ...) and can be changed.

Router(config-if)#bandwidth ?

<1-10000000> Bandwidth in kilobits

HTH,

Mohammed Mahmoud.

Edison Ortiz Sat, 08/11/2007 - 11:14

The bandwidth value on a interface is inherited from the type of card in the slot. If you look at the model of the card, perhaps it's a T1 card not an E1 card. If you were to insert a DS3 card, the interface bandwidth value would be 45Mbps

Correct Answer
mohammedmahmoud Sat, 08/11/2007 - 13:56

Hi,

The default bandwidth for WIC serial interfaces is 1544kbps as shown in the output of show interface but it can have up to 2.048 Mbps physical speed, but the bandwidth parameter itself can be <1-10000000> kilobits, which as i said doesn't reflect the physical speed in any means.

HTH,

Mohammed Mahmoud.

Edison Ortiz Sat, 08/11/2007 - 15:15

I haven't had the pleasure to deal with E1 circuits, but since you do, what's the part number of the card that connects to this type of circuit ?

I never claimed that's the maximum speed, I explained how this default value is derived.

Paolo Bevilacqua Sat, 08/11/2007 - 15:19

Edison, there are many, nowadays the most used are VWIC-xMFT-E1 and VWIC2-xMFT-T1/E1 for the small and medium routers.

Edison Ortiz Sat, 08/11/2007 - 15:21

Thanks Paolo, I was trying to find in the Cisco website and couldn't find a part number hence my query.

What's the default BW for this type of card ?

It can't be 1544Kbps, can it ?

Paolo Bevilacqua Sat, 08/11/2007 - 15:37

It depends on how many timeslots are configured for the channel-group. IOS multiplies that by 64 and result is the default bandwidth. Same logic as for T1 channelized interfaces.

Edison Ortiz Sat, 08/11/2007 - 17:09

If you have an E1 with all timeslots (32), the interface will have a BW value of 2048kbps ?

If that's the case, then the OP was looking at a WIC1T serial card which is for T1 circuits (mostly American circuits) or a E1 serial card with 24 timeslots configured.

mohammedmahmoud Sat, 08/11/2007 - 22:57

Hi Edison,

I think the original poster is talking about a WIC-1T (or maybe also a WIC-2T - it doesn't matter), although the default bandwidth under these interfaces is 1544 (which we all agree that it doesn't reflect the physical speed) but these interfaces can take physically upto E1 speed.

HTH,

Mohammed Mahmoud.

Guys,

Thanks for all those valuable inputs...

The type of interface I am talking about is a V.35 interface which does not allow us to set any timeslots like a G.703 card.

I guess the same WIC2T card can be used for any type of circuit(T1,E1, fractional 256 K), right? The actual speed must be decided by the SP CSU..please correct if I am wrong.

Regards.

Paolo Bevilacqua Sun, 08/12/2007 - 02:27

Ever wondered why serial interfaces are coded as 'T' rather than 'S' in cisco part numbers, causing confusion with T1 interfaces ?

At the beginning of time, cisco routers had no native T1 interfaces, only serial. But invariably these interfaces were connected to T1 circuits by mean of external DSU with V.35 interfaces. So the naming.

mohammedmahmoud Sun, 08/12/2007 - 03:00

Hi Paolo,

I always thought this would be the reason but i couldn't confirm it, thanks for this historical fact, rated indeed :)

BR,

Mohammed Mahmoud.

Paolo Bevilacqua Sun, 08/12/2007 - 02:22

The nitpick here is that because timeslot 0 is always reserved for OAM in E1 world, the most you can get in framed, aka channelized E1 setting is 31 timeslots for a bandwidth of 1.984 Mbps. This way of doing thing is correctly called G.704.

Full 2.048 Mbps requires support for unframed G.703 on both the router card, and the circuit as provisioned by telco. In this case, there is no more timeslot framing in the bitstream, sometime this kind of arrangement is referred as "pure G.703".

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