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New Member

Understanding the call Flow through VCS c/e

Hi Geeks,

I am posting this to understand "How stuff works". Below is the Design.

i have a VCSc configured with SIP domain of example.com   (we have internal DNS server to resolve it)

i have a VCSe configured with SIP domain of cisco.com   (we have external DNS server to make it globally routable)

i create a traversal link bw VCSc and VCSe.

how will the call flow  between Ep A and Ep B 

Scenario A

My Ep A is   Ex90@example.com  dials a Ep B Jabber client (home user) registered on VCSe jabber@cisco.com

how will call flow; i want to understand the flow from beginning ie Ex 90 will send an register message to VCSc etc etc.

Scenario B :

if Ep A Ex90@example.com call a 3rd party (seperate company) =  ( inter business calling ) End point ie stranger@Dell.com

how will the call flow.

Please excuse me for asking Layman Explanation:

Thanks in advance

// Vikram

1 ACCEPTED SOLUTION

Accepted Solutions

Understanding the call Flow through VCS c/e

Hi Vikram,

First thing to note is in most of the scenario customer prefers same sip domain on control and expressway so that they can aviod transform and simplify the dial-plan.

Now  coming to your scenario.

Scenario A

Ep A <--SIP-->VCS-contrl<--traversal-->VCS-Ex<--sip-->Ep B (assumptions made endpoints using SIP protocol)

Ep A starts with sending a SIP invite message to VCS-cntrol which gets forwarded to VCS-exp by VCS-cntrl provided you have setup search rules properly on vcs control.

VCS-exp sends this call to Ep B and call connects. You can google for SIP call flow, so nothing diff happens in this case.

Scenario B

Ep A<--SIP-->VCS-cntrl<--traversal-->VCS-Exp<-->public cloud<-->Ep B (dell.com)

Now to make a calls to external party VCS-exp requires a DNS zone, which uses the dns configured on exp to do srv records query to outside domain like "dell.com"

in this scenario again Ep A starts wtih sending an invite message to VCS-cntrl which gets forwarded to vcs-exp based on search rules. VCS-exp starts looking for address again based on search rule and since it can't find the URI ending with "dell.com" and exp starts to send srv record query for domain "dell.com". DNS configured on exp in company A sends srv record query and get a reply for that domain with company B VCS-exp ip-address and then vcs-exp in company A starts the call setup to remote ip-address.

now in this you can have multiple scenario's and i would recommend you to check the deployment guide for VCS- control and VCS-exp traversal solution.

Rgds,

Alok

5 REPLIES
Cisco Employee

Understanding the call Flow through VCS c/e

Hi Vikram,

You can capture network log from VCS C & VCS E . It will have all detail for call flow , serch rule used , Domain reolution .

If you are doing interworking call then H323 to SIP conversion detail .

hth

Kind regards,

Dharmmesh

New Member

Understanding the call Flow through VCS c/e

Hi Sir,

i tried however, to read those one has to understand the call flow . so that is the reason i posted a question:

if someone can give a step by step explaination.

Kind Regards:

Vikram

Understanding the call Flow through VCS c/e

Hi Vikram,

First thing to note is in most of the scenario customer prefers same sip domain on control and expressway so that they can aviod transform and simplify the dial-plan.

Now  coming to your scenario.

Scenario A

Ep A <--SIP-->VCS-contrl<--traversal-->VCS-Ex<--sip-->Ep B (assumptions made endpoints using SIP protocol)

Ep A starts with sending a SIP invite message to VCS-cntrol which gets forwarded to VCS-exp by VCS-cntrl provided you have setup search rules properly on vcs control.

VCS-exp sends this call to Ep B and call connects. You can google for SIP call flow, so nothing diff happens in this case.

Scenario B

Ep A<--SIP-->VCS-cntrl<--traversal-->VCS-Exp<-->public cloud<-->Ep B (dell.com)

Now to make a calls to external party VCS-exp requires a DNS zone, which uses the dns configured on exp to do srv records query to outside domain like "dell.com"

in this scenario again Ep A starts wtih sending an invite message to VCS-cntrl which gets forwarded to vcs-exp based on search rules. VCS-exp starts looking for address again based on search rule and since it can't find the URI ending with "dell.com" and exp starts to send srv record query for domain "dell.com". DNS configured on exp in company A sends srv record query and get a reply for that domain with company B VCS-exp ip-address and then vcs-exp in company A starts the call setup to remote ip-address.

now in this you can have multiple scenario's and i would recommend you to check the deployment guide for VCS- control and VCS-exp traversal solution.

Rgds,

Alok

New Member

Understanding the call Flow through VCS c/e

Thank you alok .. that helps

Reason for 2 seperate domain was to hide internal domain.

which alternatively can be done through Transform as well.

but i understand now.

Thanks again

// Vikram

Re: Understanding the call Flow through VCS c/e

Hi Vikram,

In addition, there is an old document from Tandberg that helped me a lot when I begun to deploy VCSe topologies. This document describes all the SIP and H323 signalling involved in the communication depending upon whether the endpints are registered to VCS or not.

Take a look at the document starting on page 98:

http://www.cisco.com/en/US/docs/telepresence/endpoint/mxp-series/white_papers/tandberg_h323.pdf

Although this is an old and Tandberg document, don't worry, cause the concept remains exactly the same.

An overview:

VCS Expressway firewall traversall.png

I hope this help.

Paulo Souza

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Paulo Souza Was my response helpful? Please rate useful replies and remember to mark any solved questions as "answered".
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