Subject: RE: Shared Risk Link Group (SRLG)

From: [email-masked]
Date: Tue, 13 Feb 2001 08:08:00 -0000

> > In general, if I have a (non-optical) network, can I identify
> > group(s) of links that might fail together ?
> 
> Sure.
> 
> Kireeti.
>
NH=> Only if you have full knowledge of the physical infrastructure (ie duct
layer network).  A client layer link connection (ie 1 element of
connectivity of a client layer trail between 2 adjacent nodes in the client
layer) is created by a server layer trail (ie end-end path in the server
layer, composed of several concatenated server layer link
connections).....this is how one constructs client layer topology and is the
fundamental aspect of network design/TE.  The disjoint degree of
connectivity of the duct network is inherited by all (client) layer networks
above this.....noting that this is a recursive relationship between
server/client layers, and so the actual diversity of a layer N (client)
network is a function of (server) layer N+1, layer N+2, layer N+3, etc to
the duct.  If you lease server layer capacity (at any layer, including the
duct) you may not have this knowledge.

---

From: David Charlap <[email-masked]>
Date: Tue, 13 Feb 2001 10:36:18 -0500

[email-masked] wrote:
>
> Only if you have full knowledge of the physical infrastructure (ie
> duct layer network).  A client layer link connection (ie 1 element of
> connectivity of a client layer trail between 2 adjacent nodes in the
> client layer) is created by a server layer trail (ie end-end path in
> the server layer, composed of several concatenated server layer link
> connections).....this is how one constructs client layer topology and
> is the fundamental aspect of network design/TE.  The disjoint degree
> of connectivity of the duct network is inherited by all (client) layer
> networks above this.....noting that this is a recursive relationship
> between server/client layers, and so the actual diversity of a layer N
> (client) network is a function of (server) layer N+1, layer N+2, layer
> N+3, etc to the duct.  If you lease server layer capacity (at any
> layer, including the duct) you may not have this knowledge.

This is actually a serious problem in the real world.

You may buy a fiber from two different companies for redundant backup,
only to find that they're both going through the same conduit in the
street, so both will get cut at once if a backhoe operator digs into
that conduit.

There's nothing that any protocol can do about this.

-- David