Nailed PGW solution - RLM/NFAS question

[tominatornz]

I have a question about NFAS groups and RLM groups.

We run a PGW (9.4.1) in nailed mode.

We connect via SS7 to Telco_X through 2 Signaling Points (DPC's), via a single AS5400.

Consider an E1 from each SP, carrying the same type of type traffic (determined by digit string).

All traffic prefixed with 123 is to terminate via these E1's.

I think I have 2 options for the AS5400 configuration, diagrams outlining each option are attached...

Option 1

trunk group Service_A

!

controller E1 6/0

pri-group timeslots 1-31 nfas_d primary nfas_int 0 nfas_group 0 rlm-group 0

description Switch A - cic's 1 <->31

!

controller E1 6/1

pri-group timeslots 1-31 nfas_d none nfas_int 1 nfas_group 0

description Switch B - cic's 1 <->31

!

interface Dchannel6/0

trunk-group Service_A

!

rlm group 0

server PGW-A

link address x.x.x.x source GigabitEthernet0/0.1 weight 2

link address x.x.x.x source GigabitEthernet0/0.1 weight 1

!

dial-peer voice123 pots

trunkgroup Service_A

destination-pattern123.%

Will the above approach work, or will I need a separate RLM/NFAS group for each switch (DPC), I connect to... as shown below

i.e; Option 2

trunk group Service_A

!

controller E1 6/0

pri-group timeslots 1-31 nfas_d primary nfas_int 0 nfas_group 0 rlm-group 0

description Switch A - cic's 1 <->31

!

controller E1 6/1

pri-group timeslots 1-31 nfas_d primary nfas_int 1 nfas_group 1 rlm-group 1

description Switch B - cic's 1 <->31

!

interface Dchannel6/0

trunk-group Service_A

!

interface Dchannel6/1

trunk-group Service_A

!

rlm group 0

server PGW-A

link address x.x.x.x source GigabitEthernet0/0.1 weight 2

link address x.x.x.x source GigabitEthernet0/0.1 weight 1

!

rlm group 1

protocol rlm port 3002

server PGW-A

link address x.x.x.x source GigabitEthernet0/0.1 weight 2

link address x.x.x.x source GigabitEthernet0/0.1 weight 1

!

dial-peer voice123 pots

trunkgroup Service_A

destination-pattern123.%

I am figuring that the 1st option will work, as the PGW can determine the relationship between the source and destination signaling services and span/timeslots through the nailed trunk provisioning (trunk.dat file)

If I then add 2 more E1's to each switch, and then route calls prefixed with 123 to cic's 1-31, calls with 246 to cics 33-63, and calls with 357 to cics 65-95, I will require a separate RLM/NFAS group for each terminating prefix.

If the second option above is correct, I am going to need 6 RLM groups on the GW. The PGW/GW spec's say that 8 are supported, however, I have read that in practice, you really dont want to go past 5. I believe this was due to an IOS limitation.

Any pointers as to whether "option 1" will fly are greatly appreciated.

[anikas]

Option one will not work. Only the first E1 will work. If you have only 1 RLM group you only have 1 D-Channel between the PGW and that gateway.

Hope this helps answer your question.

[tominatornz]

Thanks,

It looks like I am going to need 6, possibly 7 RLM Groups on the GW.

Can you tell me whether the operational limit of 5 RLM's per GW still exists. I have this info from a training course I did 3 years ago, so it may now not be a problem. It is in the documentation I have from the "Building Cisco SS7 Interconnect & VOIP Networks for Voice and Dial Traffic" course.

[anikas]

If you are running a 9.X release of PGW you can run 8 RLM groups. Again you only need one RLM group per DPC that is connecting to this gateway. If you need 7 as you say that mean that you have 7 DPCs connecting their E1/T1s to the same gateway.

Andreas

[tominatornz]

I may be missing something very basic here, but I am still struggling to see how I can route various digit strings at specific E1's.

eg;

service_a

dest-patt 123.......goes to cic's 01-31 at both SSP's

service_b

dest-patt 246.......goes to cic's 33-63 at both SSP's

service_c

dest-patt 357.......goes to cic's 65-95 at both SSP's

In the past I have created a trunk group for each service type, and then a separate RLM/NFAS group for each, and then associated the dchannel created for each nfas group with the required trunk-group. The pots dial-peer then matches the specific digit strings to the trunk-group.

How can I achieve the same result with only 1 RLM group per DPC?

[anikas]

Sorry, I forgot to respond to the second part of your question.

If you add more E1s to the same switch (SSP/DPC) then you have no need of adding additional RLM groups as you already have the D-channel for those 2 SSPs. If however you plan on going to additional SSPs and want their E1s to terminate on this same gateway only then would you need to add addition RLM groups.

Regards

Andreas