Make before break and Break before make

Make before break and break before make. I shared many posts so far which was covering the terms used in different field of networking. This one is one of them. Also I will introduce, probably to many of you, a new terminology ‘ Break before make ‘ 

 

If you are from the IP/MPLS background , probably you know what is ‘ Make Before Break ‘

 

For those who don’t know, Make Before Break is a mechanism to establish a new LSP instance and transfer traffic from an old LSP instance onto the new LSP instance before tearing down the old one.

Mostly, we use ‘ Make Before Break ‘ in RSVP-TE LSPs. When there is a failure (Link or Node Failure), traffic is forwarded through the backup path when MPLS Traffic Engineering Fast Reroute is enabled.

 

At the same time, head end node of the Traffic Engineering tunnel, calculates a new tunnel with the constraints, CSPF (Constraint Shortest Path First) tries to find an optimal path, during this period, backup path is used.

 

When new path is found by CSPF , RSVP is used to signal a new LSP before tearing down the old one which passes through the backup path. That’s why it is called Make Before Break.

 

In Cellular networking , Make Before Break is used in a similar way. But it is used for the ‘ Handover (eq : Handoff) ‘ procedure. Handover is required for mobility. You don’t talk on the phone while you are driving I know but maybe the passengers do ?

 

When you travel with your phone , your mobile phone uses many base stations (Towers with mobile equipments). When stronger signal is received from the different tower, connections is not dropped. This is known as Soft handover and fits into our Make Before Break definition. This is important for real-time services.

 

On the other hand, there is a hard handover procedure as well. In this case, mobile device (Commonly referred as UE (User Equipment)) and the base station link is broken. New session is established with the new based station. Communication is lost during this period but this might be okay for some applications.

With the Make Before Break procedure, double booking is a problem in general. Which mean, more than one node reserve capacity for some period of time for the same node/networking entity.

Now you know that Make Before Break is not only used in IP/MPLS networks for the LSP (Label Switch Path) but also used in Mobile/Cellular networking for Handover (Handoff) procedure.

 

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