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Fabric and fiber

Arjun Dabol
Level 1
Level 1

I am new to high end routing / switching and I hear all the high-end routers (CRS/ASR9K)  and switches (nexus) has fabric cards in them ?

 

can someone help in understanding  what is this fabric thing ? And what  is the use of them in high end devices ?

 

Does fabric and fiber has any relation ? is it same what we have at our home internet as finer internet ?

Thanks

1 Accepted Solution

Accepted Solutions

funny website name that is Mark :)

Another set of good detail can be found in Cisco Live id 2904 from orlando 2013, sanfran 2014 and sandiego 2015. or the breakout session ID 2003.

Fiber is merely a transmission media

Fabric is a mechanism to create a "2 stage" forwarding model whereby an ingress "engine" does a lot of the input processing of a packet, hands it over to a fabric for switching to a destination linecard where it receives all its egress processing.

the beauty of a switch fabric is the ability to have multiple entities talking to each other at the same time. See it as a class room. Normally, all the students if they want to talk or ask something they have to go via the teacher. If multiple students talk at the same time the message gets garbled (aka collision) the teacher needs to tell Joe to hold off and let mary speak for the moment, process mary's message, provide a response and go over to Joe. In this case the teacher is a centralized cpu.

Now think about the ability that when bill wants to speak with mary, and joe with harry, the teacher can create to "separate lanes" isolating them from each other and see when one conversation is done to connect another student to let them speak with say bill. In this case the teacher becomes a "fabric arbiter" whereby certain lanes are created for communication.

It goes even further because if there is one person that has something important to say for all students, the arbiter/teacher can tell everyone to listen up to what this person has to say (eg flooding). This so that person doesn't have to tell 2 or 3 or multiple students the same piece of information.

So in so many ways a fabric (with arbiter) provides for a very fast switching mechanism with increased efficiency and extra benefits such as intelligent flooding and replication.

You can also compare a switch fabric to an old school telephone operator plugging cables between two parties that want to connect with each other. In this case the operator is the arbiter of the "Fabric".

The reason why you'd see them generally in higher end devices is because of the price point they have and the fact that if there are only limited students in the class or limited phone lines, does one really need an "expensive operator or teacher" to manage that limited set.

So much more to be said about this all :) Let us know if you like to know more!

cheers

xander

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2 Replies 2

mivens
Level 1
Level 1

The fabric allows a router to scale by distributing the packet forwarding between multiple components, typically multiple linecards. It is essentially a set of switching elements that allow any one linecard to send traffic to any other in a non-blocking fashion without everything needing to go via a single centralised routing processor. Although you can use optic fibre to connect the fabric elements of multiple chassis together to make one logical router, fibre isn't the same thing as a switch fabric.

Take a look at slide 37 from this Cisco Live presentation "Anatomy of Internet Routers".

http://www.anticisco.ru/pubs/ISR_OOO.pdf

There is a nice picture of what a crossbar fabric from a 1960s telephone switch looks like.

If you register you may also be able to watch a video of the presentation.

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=6064

 

 

funny website name that is Mark :)

Another set of good detail can be found in Cisco Live id 2904 from orlando 2013, sanfran 2014 and sandiego 2015. or the breakout session ID 2003.

Fiber is merely a transmission media

Fabric is a mechanism to create a "2 stage" forwarding model whereby an ingress "engine" does a lot of the input processing of a packet, hands it over to a fabric for switching to a destination linecard where it receives all its egress processing.

the beauty of a switch fabric is the ability to have multiple entities talking to each other at the same time. See it as a class room. Normally, all the students if they want to talk or ask something they have to go via the teacher. If multiple students talk at the same time the message gets garbled (aka collision) the teacher needs to tell Joe to hold off and let mary speak for the moment, process mary's message, provide a response and go over to Joe. In this case the teacher is a centralized cpu.

Now think about the ability that when bill wants to speak with mary, and joe with harry, the teacher can create to "separate lanes" isolating them from each other and see when one conversation is done to connect another student to let them speak with say bill. In this case the teacher becomes a "fabric arbiter" whereby certain lanes are created for communication.

It goes even further because if there is one person that has something important to say for all students, the arbiter/teacher can tell everyone to listen up to what this person has to say (eg flooding). This so that person doesn't have to tell 2 or 3 or multiple students the same piece of information.

So in so many ways a fabric (with arbiter) provides for a very fast switching mechanism with increased efficiency and extra benefits such as intelligent flooding and replication.

You can also compare a switch fabric to an old school telephone operator plugging cables between two parties that want to connect with each other. In this case the operator is the arbiter of the "Fabric".

The reason why you'd see them generally in higher end devices is because of the price point they have and the fact that if there are only limited students in the class or limited phone lines, does one really need an "expensive operator or teacher" to manage that limited set.

So much more to be said about this all :) Let us know if you like to know more!

cheers

xander