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toc:faq Introduction Recently there were few discussions in CSC on Implementing PSTN gateways in CUCM with queries related to configuration and troubleshooting. To help the users, I have decided to write this blog and provide configuration and troubleshooting steps to make the gateway implementation easy in the Service Provider (SP) network.
Also I have been trying to capture all the day to day issues we face in the SP network and address the common issues in implementing the PSTN gateways in CUCM. I have created this blog based on my work experience in implementing PSTN Gateways in the Service Providers (SP) network and I will cover the Basics, Configuration and Troubleshooting part. Pl share your inputs and the issues you have faced in your network in the comments section and also let us know if you are looking for any further information or solution related to this topic. To help all types of readers I will start from Basics and then I will cover the Network design, Configuration and Troubleshooting part. PSTN Gateways in CUCM To place external calls, Cisco Unified Communications Network (CUCM) deployment needs a connection the Public Switched Telephone Network (PSTN). PSTN connections are provided through Gateways, which connect traditional time-division-multiplexing (TDM) telephony interface (digital T1/E1 or analog FXO port) and VOIP domains.
Gateways can be integrated in CUCM by using different protocols such as Media Gateway Control Protocol (MGCP), H.323 or Session Initiation Protocol (SIP) for signaling on VOIP call legs. Gateway Protocol functions for CUCM Integration Three main signaling protocols - MGCP, H.323 and SIP provides different feature support.
There are Pros and Cons in each protocol. MGCP: Centralized dial plan configuration and Centralized gateway configuration hence it will be easy to implement in a large SP network. H.323: Dial plan configured directly on the gateway. More specific call routing and it support third-party integration on SP network. SIP: Dial plan configured directly on the gateway. It supports third-party telephony integration and end devices. MGCP Gateway Considerations A constant logical IP session (connection) must be present between the Cisco IOS MGCP gateway and CUCM.
If the connection between CUCM and the MGCP gateway isunavailable, the following can happen:. If the gateway was configured for failover (by using the ccm-manager fallback-mgcp command), the MGCP gateway can fail over to local call control mode.
All active calls are dropped (no call survivability/call preservation), and a complete local dial plan must be present. Fallback-MGCP functionality is normally enabled on branch gateway routers configured with SRST in centralized call-processing architectures.Fallback-MGCP can be configured on headquarters routers as well, but this functionality is normally not present because the MGCP gateway’s CUCM group defined in the gateway’s device pool can include up to three CUCM servers to register the MGCP gateway to. Local MGCP registration failovers will not result in disconnected calls at the headquarters because of the graceful switchover feature that enables call survivability. No softkey features will be available during the duration of the survived calls, and new inbound and/or outbound calls will not work until the gateway reregisters with a CUCM server.
Cisco Ios Service Selection Gateway Configuration Guide Guide
If no failover configuration is present, all calls are dropped, and the PRI interface goes down. Gateway Integration with CUCM In this blog I will be discussing the following Gateway integration. 1) Integrating MGCP gateways with CUCM 2) Integrating H.323 gateways with CUCM 3) Integrating SIP gateways with CUCM A gateway is a device that can translate between different types of signaling and media. One type of gateway is a voice gateway.
Voice gateways are used anytime that a Cisco IP Phone communicates with TDM interface. For example, PSTN, traditional PBX, Analog phone, fax and so on. 1) Integrating MGCP gateways with CUCM. MGCP is a plain-text protocol that call-control devices use to manage the IP telephony gateways. MGCP is a client/server protocol that allows the call agent (CA) to take control of a specific gateway endpoint (port).
MGCP has the advantage of centralized gateway administration in the CUCM. CUCM controls the state of each port on the gateway endpoint. MGCP gateway can be controlled on a per endpoint (TDM port) level but H.323 and SIP cannot.
Note: MGCP gateway must be supported in CUCM. Use the Cisco software advisor Tool to make sure that the platform and version of Cisco IOS software or Cisco Catalyst Operating system is compatible with MGCP for CUCM.
MGCP Gateway Support: MGCP support in CUCM includes a wide range of analog and digital interfaces that can be used ton several Cisco router and switch platforms. FXO, FXS, T1-CAS, T1-PRI, E1-CAS, E1-PRI but some voice ports are not supported by MGCP say, E&M voice ports. CUCM pushes the Cisco IOS MGCP gateway configuration from the Cisco TFTP server to the gateway when automatic configuration is configured. CUCM also supports Q.931 backhaul.
Q.931 backhaul is only supported on ISDN voice ports. MGCP backhaul allows CUCM to process the Q.931 messaging from the ISDN circuit. The gateway router encapsulates the Q.931 signaling from the gateway over TCP port 2727.
MGCP Call flow: MGCP communication is used between the CUCM and the MGCP Gateway. MGCP Configuration Server: Configuration Server feature allows all MGCP configurations to be administered through the GUI in CUCM. Cisco IOS commands are downloaded automatically from the TFTP server to the MGCP gateway. Figure shows the MGCP configuration sever communication. Q.931 Backhaul: Q.931 backhaul is a reliable TCP transport layer TCP/IP connection between CUCM and Cisco MGCP gateway. Q.931 backhaul is an encapsulation of the Q.931 signaling in the D channel of the ISDN TDM interface. Q.931 backhaul carries the raw Q.931 signaling to CUCM to be processed natively.
The Gateway is still responsible for the termination of the Layer 2 Q.921 Link Access Protocol D-Channel (LAPD) signaling, but all ISDN layer 3 call setup/call tear down signaling (Q.931) is sent to CUCM for processing. 1.1) MGCP Gateway Configuration: CUCM Add an MGCP Gateway to CUCM Step1: In CUCM Administration, Choose Device Gateway. Step2: Click the Add New button. Step3: Choose the Appropriate MGCP gateway by gateway or router name Gateway Type. Cisco IAD2400/Cisco 1751/Cisco 1760/Cisco 1861/Cisco 269x/Cisco 26xx/Cisco 2801/Cisco 2811/Cisco 2821/Cisco 2821/Cisco 2851/Cisco 2901/Cisco 2811/Cisco 2821/Cisco 2851/Cisco 2901/Cisco 2911/Cisco 2921/Cisco 2951/Cisco 362x/Cisco 364x/Cisco 366x/Cisco 3725/Cisco 3745 etc) Say in this case, Gateway Type: Cisco 2811 Step4: Click Next.
I am in the process of moving the PSTN gateways for my organization from CMM's controlled by MGCP (CUCM v7.1(3) to 3 - 3945 routers. We have 18 - T1 PRI circuits supporting PSTN calling. We will be moving the enterprise to SIP in the near future, but I have to accomodate the multiple PRI environment in the interim.
The circuits will be divided evenly between the routers (6 each). I would like to use H.323, for stability sake, but cannot devise a non-complicated plan to spread the priority circuits across the 3 routers rather than landing the top 6 priority circuits on a single router. Question: Should I stay with MGCP for the simplicity and granular routing control, or go with H.323?
Hello Josh I would suggest you to stay with MGCP with centralized dial plan configuration and centralized gateway configuration. It will be easy to implement since you have multiple PRI circuits connected and obviously more dial plans. As you said in H.323 gateways you need to do lot of ground work for the dial-peer based routing with complex translation pattern.
Hope I answered your query. Pl revert if you are looking for any specific information. I will be updating my blog with more information on implementing the PSTN network using MGCP and H.323 gateways shortly. Regards Lavanya.