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Bronze

what is switch fabric

hi everybody!

I am trying to understand the term "switch fabric". I googled the term and found the link:

http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci214147,00.html

Based on the above link which defines switch fabric as" combination of software and hardware which moves the data out of correct port in a switch."

I think every switch does the same thing with the help of software and hardware installed.I also noticed this term is usually used in modular switches(4500,6500).

I would really appreciate if anyone help me understand this term.

thanks a lot!

3 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Silver

Re: what is switch fabric

Hello Sarah,

the term switch fabric in modular switches means that there a switching matrix : they are also called crossbar switch that provides N x N high speed links.

Each linecard has a connection or two connection to the fabric.

The advantage of this type of architecture is traffic between slot 1 and slot 2 does not lower resources for traffic between slot 3 and slot 4.

This is a great step in comparison to a bus architecture.

Actually the switching fabric in a modern C6500 is a a daughter card that is part of the supervisor

all supervisors SUP720 XX have a 720Gbps switching fabric.

The switch can host a mix of different type of linecards and only the newer can take advantage of this switching fabric.

The chassis provides also a shared bus used by older linecards

there is a C6500 architecture whitepaper

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html

this can be interesting

Hope to help

Giuseppe

Super Bronze

Re: what is switch fabric

As Giuseppe mentions, "fabric" is often the term for a cross bar matrix. A cross bar allows every end point full bandwidth to any other end point without sharing the bandwidth.

For instance ports 1 and 2 could use their maximum bandwidth regardless of what the other ports are doing. However, if both ports 1 and 2 wanted to pass traffic to/from port 3, they would share port 3's fabric connection.

True port-to-port switch fabrics are very expensive, so many switch fabrics group ports that share a larger quanity of bandwidth to the switch fabric. For instance, the original 4500 series provides 6 GB of switch fabric to each slot. Line cards often allocate this fabric bandwidth equally, but the don't have to. An interesting example is the WS-X4418-GB which provide full gig to two ports and the remaining four gig to 16 ports (see table 2 in http://www.cisco.com/en/US/prod/collateral/modules/ps2710/ps5494/product_data_sheet0900aecd802109ea_ps4324_Products_Data_Sheet.html)

The 6500 supports different methods of bandwidth to the slots. It can support a shared 32 gig using its "classic bus" (sup1/sup-32/sup2(w/o optional SFM); 256 gig fabric (sup2 w/SFM or sup720), 1 or 2 8 gig connections to each slot; or 720 gig fabric (sup720), 1 or 2 20 gig connection to each slot. 6500 line cards are designed for these different backplane connections and how and they share the slot's bandwidth between their ports.

Other switch fabric implementions can differ.

Super Bronze

Re: what is switch fabric

In your Google search, did you see the http://en.wikipedia.org/wiki/Backplane?

In network devices, especially switches, traffic from port-to-port or card-to-card, might transverse a backplane. The backplane could be a bus (sort of similar to original Ethernet sharing a single cable, or a fabric, as discussed within this post's messages. Backplane could be a generic reference for either without further defination of the physical architecture.

5 REPLIES
Silver

Re: what is switch fabric

Even smaller switch has different switch fabric.

since modular switches provides more Layer 2/3/4 feature, so needs to be highlighted the same is the specification.

Like sup1V have 64Gbps switch fabric whereas Sup6E has 320Gbps switch fabric.

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps4324/product_data_sheet0900aecd8035cf2b.html

See attached file

Hall of Fame Super Silver

Re: what is switch fabric

Hello Sarah,

the term switch fabric in modular switches means that there a switching matrix : they are also called crossbar switch that provides N x N high speed links.

Each linecard has a connection or two connection to the fabric.

The advantage of this type of architecture is traffic between slot 1 and slot 2 does not lower resources for traffic between slot 3 and slot 4.

This is a great step in comparison to a bus architecture.

Actually the switching fabric in a modern C6500 is a a daughter card that is part of the supervisor

all supervisors SUP720 XX have a 720Gbps switching fabric.

The switch can host a mix of different type of linecards and only the newer can take advantage of this switching fabric.

The chassis provides also a shared bus used by older linecards

there is a C6500 architecture whitepaper

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd80673385.html

this can be interesting

Hope to help

Giuseppe

Super Bronze

Re: what is switch fabric

As Giuseppe mentions, "fabric" is often the term for a cross bar matrix. A cross bar allows every end point full bandwidth to any other end point without sharing the bandwidth.

For instance ports 1 and 2 could use their maximum bandwidth regardless of what the other ports are doing. However, if both ports 1 and 2 wanted to pass traffic to/from port 3, they would share port 3's fabric connection.

True port-to-port switch fabrics are very expensive, so many switch fabrics group ports that share a larger quanity of bandwidth to the switch fabric. For instance, the original 4500 series provides 6 GB of switch fabric to each slot. Line cards often allocate this fabric bandwidth equally, but the don't have to. An interesting example is the WS-X4418-GB which provide full gig to two ports and the remaining four gig to 16 ports (see table 2 in http://www.cisco.com/en/US/prod/collateral/modules/ps2710/ps5494/product_data_sheet0900aecd802109ea_ps4324_Products_Data_Sheet.html)

The 6500 supports different methods of bandwidth to the slots. It can support a shared 32 gig using its "classic bus" (sup1/sup-32/sup2(w/o optional SFM); 256 gig fabric (sup2 w/SFM or sup720), 1 or 2 8 gig connections to each slot; or 720 gig fabric (sup720), 1 or 2 20 gig connection to each slot. 6500 line cards are designed for these different backplane connections and how and they share the slot's bandwidth between their ports.

Other switch fabric implementions can differ.

Bronze

Re: what is switch fabric

Thanks a lot Joseph and Giuseppe !

The forwarded links were very helpful, but I came across another term" backplane" ,used in i those links frequently which is not defined anywhere.

Now I understand the term" switch fabric", I want to know the term" backplane". I googled it but did not find clear explanation.

Thanks a lot!

Super Bronze

Re: what is switch fabric

In your Google search, did you see the http://en.wikipedia.org/wiki/Backplane?

In network devices, especially switches, traffic from port-to-port or card-to-card, might transverse a backplane. The backplane could be a bus (sort of similar to original Ethernet sharing a single cable, or a fabric, as discussed within this post's messages. Backplane could be a generic reference for either without further defination of the physical architecture.

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