PSTN vs ISP Redundancy

[asingh005]

HI,

I want to know that in VOIP we buy a pstn connection for redundancy in case if our wan connectivity goes down, call flow can go from the pstn connection .But why do we need do we need a pstn connection ? why don't we go for another ISP connection for redundancy ?
I'm new to VOIP . Please help as i'm keen to learn

Regards 
Aateek singh

[Terry Cheema · Accepted solution]

There are 2 scenarios:

1) When an enterprise has a completely converged network - i.e data/voice is routed on a single IP backbone. The enterprise has SIP trunks to Service Provider for PSTN or external Calls. In this scenario some enterprises may reserve partial ISDN services for backup PSTN calls in case of a failure. But the ideal design is always redundant links/ISP etc.

2) Second scenarios is where SIP trunks are not used, primary function of the PSTN is to route external calls. Its mainly for external connectivity. For example, if you want to call a mobile, or any landline etc. thats routed over ISDN. The calls are sent over the ISDN line to the Telco who would know how to reach that number.

Hope that helps.

-Terry

[asingh005]

Thank you Terry 
But can i ask something about dscp values also ?
suppose we define the dscp value for priority in the in the class map and and inpolicy-map also.
I want to know how these values are set ie how a packet gets to know that there dscp value is ef or af31 etc .
who define these value ?

Thank you in advance 
Regards 
Aateek singh

[Terry Cheema · Accepted solution]

Sure no problem. I guess you would need to do some study to get complete understanding but I can try to explain on a high level.

Phones will send the traffic marked with dscp 46 (for media) and CS3 (24), you configure the switch ports to trust these markings. If proper trust is set up at switch level, the marking are sent to router unchanged. On the router you match traffic on various criteria (ip addresses, markings etc in ACLs/Class-maps) and process traffic (prioritize/police/re-mark etc) according to your defined policies at router level.

Router will process traffic according to defined QoS policies and hand over to service provider cloud - which will then process traffic according to agreed SLAs.

Hope it helps.

-Terry

Please rate all helpful posts and mark the thread as answered if you have no more queries.

[asingh005]

Thank you very much Terry:)
You cleared my doubts, now i'm getting the logic .
thank you so much 

Regards
Aateek Singh

[Terry Cheema]

No Worries - glad that helped. Please feel free to post if you have any more questions.

Terry

[asingh005]

Yes sure 

Regards 
Aateek singh

[asingh005]

Hi Terry,
 

i want to know if i have 2 ip phones connected to my ASA 5505 and my network is 10.1.1.0 and i have configured a vpn tunnel with another network who's network is 192.168.1.0 where there resides an Asterisk server .
So i want to know to register the ip phones with the asterisk server what will be the process?
what will be unicast ,multicast.
Please help 

Regards
Aateek singh

[Terry Cheema]

Hi Mate,

Refer to below guides:

http://www.minded.ca/2009-12-16/configure-cisco-ip-phones-with-asterisk/

http://www.voip-info.org/wiki/view/Asterisk+phone+cisco+79xx

From your network side just make sure there is full network connectivity between both sides. 

-Terry

[asingh005]

Thank you Terry 
I'll read the documents from the links which you had mentioned.Thank you for guiding me
 

Regards 
Aateek Singh

[Terry Cheema]

No worries, thanks for the rating. Also try to search from youtube if there is any video on this (sorry i am typing from mobile ), if not these guides should be sufficient.

-Terry

[asingh005]

Sure Terry:)
 

Regards
Aateek singh

[asingh005]

Hi Terry 
Can you give me some alternatives .
We need a Cisco switch that can handle about 96 GigE copper ports. It has to have good performance for a busy network segment.

Regards
Aateek Singh

[Terry Cheema]

Hi Mate,

Depending on your needs if you want an access level switch you can look at stacking two Cisco 3650/3850 48 port switches (poe/non-poe). Then next level up is 4500, a higher end access/core switch. Then Cisco 6800 is another level up core switch.

I believe you are looking at access level 3560/3850 will be a good choice.

http://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3650-series-switches/qa_c67-729531.pdf

I am assuming you dont have Nexus in your environment.

-Terry

[asingh005]

Thank you Terry 
I really appreciate .
Yes i have Nexus also .Can you give me some information so that i can search more?

Regards 
Aateek Singh