Understanding the splice tables

You’ve generated a design and downloaded the splice tables, but what does the output mean?

FOND splice tables describe splicing on a per-closure basis. Each row of the csv corresponds to a closure, and describes how a fiber from an incoming cable is spliced to a fiber in an outgoing cable (if at all).

Below is a small example of what the splice tables at a Drop Hub could look like.

closure	cable_in	fibre_in	type	cable_out	fibre_out
DROP_HUB_0210	DIST_CABLE_0219	1	splice	DROP_CABLE_3190	1
DROP_HUB_0210	DIST_CABLE_0219	2	splice	DROP_CABLE_3191	1
DROP_HUB_0210	DIST_CABLE_0219	3	splice	DROP_CABLE_3192	1
DROP_HUB_0210	DIST_CABLE_0219	4	spare	spare
DROP_HUB_0210	DIST_CABLE_0219	5	dead	dead
DROP_HUB_0210	DIST_CABLE_0219	6	dead	dead
DROP_HUB_0210	DIST_CABLE_0219	7	dead	dead
DROP_HUB_0210	DIST_CABLE_0219	8	dead	dead
DROP_HUB_0210	dead		dead	DROP_CABLE_3190	2
DROP_HUB_0210	dead		dead	DROP_CABLE_3191	2
DROP_HUB_0210	dead		dead	DROP_CABLE_3192	2

We’ll have a deeper look at these rows and what they mean

Splice type records

The first type of record we’ll look at are records having the splice type. These are the simplest types of records: each record indicates how a fibre on the incoming cable should be spliced onto an outgoing cable. For example if we look at the splice records in the above example:

closure	cable_in	fibre_in	type	cable_out	fibre_out
DROP_HUB_0210	DIST_CABLE_0219	1	splice	DROP_CABLE_3190	1
DROP_HUB_0210	DIST_CABLE_0219	2	splice	DROP_CABLE_3191	1
DROP_HUB_0210	DIST_CABLE_0219	3	splice	DROP_CABLE_3192	1

Then we can read off that:

Fibre 1 of DIST_CABLE_0219 should be spliced onto fibre 1 of DROP_CABLE_3190
Fibre 2 of DIST_CABLE_0219 should be spliced onto fibre 1 of DROP_CABLE_3191
Fibre 3 of DIST_CABLE_0219 should be spliced onto fibre 1 of DROP_CABLE_3192

Spare type records

A spare record indicates that an active (e.g. lit from the upstream root) fibre is being provided to the device and left as spare there. In the above example we had a single spare fibre left as spare at DROP_HUB_0210:

Spare
closure	cable_in	fibre_in	type	cable_out	fibre_out
DROP_HUB_0210	DIST_CABLE_0219	4	spare	spare

Since the fibre is left at the closure there’s no outgoing cable or fibre.

Incoming dead records

The next type of records are dead records corresponding to the incoming cable. These are the dead records where cable_out is dead. In our example there are four such records:

Incoming dead
closure	cable_in	fibre_in	type	cable_out
DROP_HUB_0210	DIST_CABLE_0219	5	dead	dead
DROP_HUB_0210	DIST_CABLE_0219	6	dead	dead
DROP_HUB_0210	DIST_CABLE_0219	7	dead	dead
DROP_HUB_0210	DIST_CABLE_0219	8	dead	dead

This indicates that fibres 5-8 of DIST_CABLE_0219 are dark (unlit) and don’t have a trace back to the upstream root.

Outgoing dead records

On the other hand we also have dead records corresponding to outgoing cables. These are the dead records where cable_in is dead. In a typical design we don’t connect every fibre in every outgoing cable to the incoming cable: those fibres that aren’t connected result in an outgoing dead record. In our example:

Outgoing dead
closure	cable_in	type	cable_out	fibre_out
DROP_HUB_0210	dead	dead	DROP_CABLE_3190	2
DROP_HUB_0210	dead	dead	DROP_CABLE_3191	2
DROP_HUB_0210	dead	dead	DROP_CABLE_3192	2

there are three of these dead records. This is because the outgoing DROP cables (DROP_CABLE_03190, DROP_CABLE_3191 and DROP_CABLE_3192) in this example have size two but only require one lit fibre.

Split records

Split records indicate where a fibre on the incoming cable has been split into multiple outgoing fibres. From the splice records above you can see that our DROP hub didn’t have any splitters hence there were no split records.

Here are some records for a DIST hub with split records:

A more complicated example
closure	cable_in	fibre_in	type	cable_out	fibre_out
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	1
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	2
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	3
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	4
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	5
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	6
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	7
DIST_HUB_0021	FEEDER_CABLE_0045	1	split	DIST_CABLE_0197	8
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	9
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	10
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	11
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	12
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	13
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	14
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	15
DIST_HUB_0021	FEEDER_CABLE_0045	2	split	DIST_CABLE_0197	16
DIST_HUB_0021	FEEDER_CABLE_0045	3	split	DIST_CABLE_0197	17
DIST_HUB_0021	FEEDER_CABLE_0045	3	split	DIST_CABLE_0197	18
DIST_HUB_0021	FEEDER_CABLE_0045	3	split	DIST_CABLE_0197	19
DIST_HUB_0021	FEEDER_CABLE_0045	3	split	DIST_CABLE_0197	20
DIST_HUB_0021	FEEDER_CABLE_0045	3	split	DIST_CABLE_0197	21
DIST_HUB_0021	FEEDER_CABLE_0045	3	spare	spare
DIST_HUB_0021	FEEDER_CABLE_0045	3	spare	spare
DIST_HUB_0021	FEEDER_CABLE_0045	3	spare	spare
DIST_HUB_0021	FEEDER_CABLE_0045	4	splice	FEEDER_CABLE_0046	4
DIST_HUB_0021	FEEDER_CABLE_0045	5	splice	FEEDER_CABLE_0046	5
DIST_HUB_0021	FEEDER_CABLE_0045	6	splice	FEEDER_CABLE_0046	6
DIST_HUB_0021	FEEDER_CABLE_0045	7	splice	FEEDER_CABLE_0046	7
DIST_HUB_0021	FEEDER_CABLE_0045	8	splice	FEEDER_CABLE_0046	8
DIST_HUB_0021	dead		dead	DIST_CABLE_0197	22
DIST_HUB_0021	dead		dead	DIST_CABLE_0197	23
DIST_HUB_0021	dead		dead	DIST_CABLE_0197	24

We can make a couple of observations here:

There are eight different records corresponding to fibre 1 of `FEEDER_CABLE_0045`.

This tells us that this fibre is passing through a 1:8 splitter at this device. Similarly for fibres two and three.

There are three split spare fibres being left at the device.

This can be seen by looking at the records for fibre 3 of FEEDER_CABLE_0045.

Express records

Express records indicate uncut fibres. Uncut fibres indicate the continuation of a trunk path, while fibres required for laterals (branches) will be cut and spliced. Generally speaking, fibres can be left uncut if

The incoming and outgoing cables are in the same tier (eg. both DIST cables)
The incoming and outgoing cables are the same size

This is not to be confused with the concept of fibres which bypass splitters at a cabinet location in order to service a location with unsplit fiber. Although we often refer to these as 'express' fibers, it is a separate concept to uncut fibers. Unsplit fibers would show as a splice type in the splice records as they involve the connection of cables of two separate tiers.

Here is an example of a DIST splice with express records:

Express
closure	cable_in	fibre_in	type	cable_out	fibre_out
DIST_SPLICE_0004	DIST_CABLE_0004	1	splice	DIST_CABLE_0006	1
DIST_SPLICE_0004	DIST_CABLE_0004	2	express	DIST_CABLE_0005	2
DIST_SPLICE_0004	DIST_CABLE_0004	3	express	DIST_CABLE_0005	3
DIST_SPLICE_0004	DIST_CABLE_0004	4	express	DIST_CABLE_0005	4
DIST_SPLICE_0004	DIST_CABLE_0004	5	express	DIST_CABLE_0005	5
DIST_SPLICE_0004	DIST_CABLE_0004	6	express	DIST_CABLE_0005	6

A trunk of uncut fibers is maintained between DIST_CABLE_0004 and DIST_CABLE_0005. One fiber is spliced into the lateral DIST_CABLE_0006.

Refer to Distribution tier settings for information on the Taper cables parameter. When disabled, express fibers will be encouraged in the design.