Troubleshooting ISDN on Cisco Gateways

• ISDN:

ISDN is a set of communication protocols that enables simultaneous transmission of voice, data, video and other network services over traditional networks like PSTN. The ISDN mainly relies on the following:

  

       Q.921 : Setup of D channel and ensure reliable delivery of Q.931 Signaling.

                    Also known as Link Access Protocol - D channel [LAPD]

       Q.931 : Call Signaling.

Let have a look at the output of a basic troubleshooting command. I have two different scenario outputs shown below. The command is : show isdn status

SCENARIO 1 :

Global ISDN Switchtype = primary-5ess

ISDN Serial1:23 interface
        dsl 1, interface ISDN Switchtype = primary-5ess
    Layer 1 Status:
        ACTIVE
    Layer 2 Status:
        TEI = 0, Ces = 1, SAPI = 0, State = TEI_ASSIGNED
    Layer 3 Status:
        0 Active Layer 3 Call(s)
    Activated dsl 1 CCBs = 0
    The Free Channel Mask:  0x807FFFFF
    Total Allocated ISDN CCBs = 5
The Layer 2 status "TEI_ASSIGNED" indicates that the D channel is not up. 


SCENARIO 2 :

Global ISDN Switchtype = primary-5ess
ISDN Serial0:23 interface
        dsl 0, interface ISDN Switchtype = primary-5ess
    Layer 1 Status:
        ACTIVE
    Layer 2 Status:
        TEI = 0, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED
    Layer 3 Status:
        5 Active Layer 3 Call(s)
    Activated dsl 0 CCBs = 5
        CCB:callid=7D5, sapi=0, ces=0, B-chan=9, calltype=DATA
        CCB:callid=7D6, sapi=0, ces=0, B-chan=10, calltype=DATA
        CCB:callid=7DA, sapi=0, ces=0, B-chan=11, calltype=DATA
        CCB:callid=7DE, sapi=0, ces=0, B-chan=1, calltype=DATA
        CCB:callid=7DF, sapi=0, ces=0, B-chan=2, calltype=DATA
    The Free Channel Mask:  0x807FF8FC


The Layer 2 status "MULTIPLE_FRAME_ESTABLISHED" indicates successful set up of 

D channel and the output also shows 5 active calls on Layer 3.

CCB = Call Control Blocks, appears in the message only when there are active calls..

 Displays the Call ID and B Channel it is occupying.

Layer 1 Status:

If not active, check physical layer connectivity.

Also check : show controllers [ t1 | e1 ]

Layer 2 Status:

• TEI_ASSIGNED : D channel is not up.

1) Check switch-type and PRI timeslots.

2) Check network user side configuration. (On the Serial x:23 interface : NO SHUT, ENCAPSULATION, NO LOOPBACK)

Run the debug ISDN q.921 command.

The actual process of setting up of D channel consists of the following messages (in this case User is the gateway and network is the PSTN) :

UI : Unnumbered Information Frame

SAPI : Service Access Point Identifier. It is used to identify the type of frame by the value it carries.

           0 = Q.931

           63 = TEI Assignment

           16 = X.25

SABME : Set Asynchronous Balanced mode Extended

UA : Unnumbered Acknowledge

Router sends an SABME message and receives a UA frame to synchronize with the TELCO switch.

If the UA frame is received, the D Channel is UP.

When D channel is up, we receive Receive Ready packets (Keepalives) every 10 seconds :

ISDN Se0:23: RX <- RRp sapi=0 tei=0 nr=18

If 4 keepalives are missed, D channel is DOWN and setup begins again.

If instead of UA frame, we receive a BAD FRAME message, then there is a problem with the TELCO.

If we receive nothing, it may be a problem with the Hardwire Plug or the Router itself, contact CISCO TAC.

FOR A TROUBLESHOOTING FLOW CHART REFER :

http://www.cisco.com/en/US/tech/tk713/tk628/technologies_tech_note09186a00800a754a.shtml?referring_site=smartnavRD

-Abhinay Mylavarapu.

CUCM Clustering and Database Replication

What is a CUCM Cluster?

- A CUCM Cluster is a group of CUCM servers running the same version of CUCM working together as a single system to provide high availability of services for clients, transparent sharing of resources, features and enables system scalability.

- When a failure occurs on one server in a cluster, resources are redirected and the workload is redistributed to another server.

- The clustering feature of CUCM also provides a mechanism for distributing call processing and database replication among multiple CUCM servers. - The CUCM can support these two types:

Cluster : 

• Supports upto 30000 IP phones
• Can be scaled to a maximum of 20 Servers in which there can be a maximum of : 1 Publisher, 8 Call Processing Subscribers, 2 TFTP servers, 9 Other Servers.

Supercluster (Mega Cluster) :

• Requires Cisco BU approval via Cisco Accounts Team
• Supports upto 60000 IP phones
• Can be scaled to a maximum of 21 Servers in which there can be a maximum of  : 1 Publisher, 16 Call Processing Subscribers, 2 TFTP Servers, 2 Other servers

There are two types of data communication between CUCM servers :

1) Database Replication :
Replication is the process of copying and maintaining database objects in multiple databases that make up a distributed database system. Replication can improve the performance and protect the availability of applications because alternate data access options exist.
- Read/write copy of the database is with the Publisher.
- This database is located in the IBM-IDS server. (Informix Dynamic Server manufactured by IBM Corp.)
- This is replicated to all Subscribers in a Hub (Publisher) and Spoke (Subscriber) topology i.e in a single direction from the Publisher to all subscribers (as shown in above figure).
- The Database replication is secured using embedded Red Hat Linux, iptables dynamic firewall (within the CUCM) and database security password (given during installation)

2) Cluster Communication :
ICCS Signaling :
- Used to replicate run-time data such as : Registration of devices, Locations bandwidth, Shared Media Resources.
- This signaling runs only between the servers that have the "ccm.exe" service i.e the Call manager service running (Call Processing agents).
- Uses TCP ports 8002-8004.

CDR & CAR :
- Call Detail Records are logged by the Call Processing Engine taking the call.
- These are periodically pushed to the Publisher server.
- The Cisco CAR or any third party billing application server always points to and collects data from the Publisher.

User Facing Features :
These features are two way replicated between Publisher and Subscriber.
These features work even if the publisher is down (from 8.x) :

• Call Forward All (CFA)
• MWI
• Privacy Enabled/Disabled
• DND
• Extension Mobility Login
• Hunt group login
• Device Mobility
• CTI CAPF Status
• Credential Authentication

- Abhinay Mylavarapu.

"Hello World"

Hello World! I've been wanting to start my blog for a while now but time and other constraints have been preventing me, but now I have broken all the shackles and here I am..! Yaaaaayyy!!! This is a STRICTLY NO NONSENSE take on Cisco Voice and Collaboration.

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