We recently had an opportunity to add an IP Pool to the Starent 16000 PDSN in our Nortel CDMA network. It is standard procedure that any network activity that has the potential to impact service must be performed during a low traffic period, (aka “the maintenance window”) and must be accompanied by a written method of Procedure (”MOP”.) Writing a MOP is not a very exciting activity, and in fact, takes a significant effort to get right. However, on the few occasions when the procedure went sideways, a well-written MOP was handy for resolving the issue, and in the worst cases, keeping us out of trouble in the post-mortem that followed.

Procedures that are frequently done benefit from a MOP by serving as a guideline for new engineers. Infrequently done procedures benefit by having a detailed reminder of what to, and not, do.

Read on for those details. (more…)

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Today Nortel presented their solution for monitoring and billing high bandwidth users of the wireless broadband network.  Software running directly in the Starent PDSN  basically uses deep packet inspection to implement traffic shaping.  The product is called Enhanced Charging Services (ECS) and it claims to provide integrated content-based billing.  The solution as presently sold might not truly be called “deep” packet inspection.  It only looks as deeply as layer 4, TCP and UDP packets.
(more…)

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Purpose

The purpose of this Method Of Procedure (MOP) is to add ranges of IP Addresses, called “pools”, to the Starent 16000 PDSN. An IP address from an IP pool is assigned to a subscriber by the PDSN when a data session is initiated.

Procedure

Begin this procedure by creating a backup of the PDSN configuration file. Use the copy command to create a new configuration file.

[local]pdsn1# copy /flash/system.cfg /flash/system.backupfile.cfg <CR>

The file called system.backupfile.cfg is created as a contingency in the event a problem occurs during execution of this method.
(more…)

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I’ve been working for a couple months now to create the software infrastructure for allocating wireless data network resources based upon the product purchased by the subscriber. This means granting them access to the purchased resources, and denying access to other resources. This is one of the functions of the PDSN, in cooperation with the AAA server.
I post trouble reports and questions as they arise to the TeleTips Message Board for the Starent PDSN. Here is a step-by-step procedure for testing on the PDSN. (more…)

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We continue working to deploy new Wireless Data plans. This week we’ve stumbled on an issue in the edge router. It does not appear to be properly detecting the OSPF routes. This problem manifests itself when the 4th octet of the IP address assigned by the PDSN to a handset exceeds “128″. Whenever a higher number gets assigned all data calls fail. Doing a stare and compare with other IP address ranges in the router shows the difference. But so far the cause cannot be explained.

Nortel has proposed flushing the OSPF cache on the PDSN with this command:

clear ip ospf process

After the command has been entered, we’ll monitor use of the use of the erring address space to see if data sessions having an IP Address above .128 succeed.

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I was recently asked to provide a parlor brief on Wireless E-9-1-1.

Wireless E-9-1-1 allows a handset to be located.

There are three phases of E-9-1-1:

• Phase 0 provides the call-back number only, no location information.
• Phase I provides the location of the cellular tower from which the 911 call was made.
• Phase II provides the most accurate location, often within a few meters, depending upon the location technology deployed by the service provider. If for some reason a phase II “fix” is not possible during a given call, the system should fallback to Phase I location.

Location accuracy depends on which phase your service provider and the local Public Safety Access Provider (PSAP) have implemented. If phase II has been implemented the accuracy also will depend upon the wireless network technology (such as GSM or CDMA) and on the location technology used by the wireless service provider (such as TDOA, E-TDOA, NAGPS, AOA, etc.  Wikipedia has a good article.) PSAP generally are police departments, fire departments, and other emergency services.

When the PSAP and the service provider each deploy E-9-1-1 the lattitude and longitude of the cellular towers is configured in PSAP location software and equipment. The PSAP will add street address information, and usually both are overlaid on a map of the covered area.

All of the PSAP in a given area agree where the boundary between each PSAP should be drawn on the map. This information is shared with the service provider, or, more commonly, is shared with a wireless location service provider such as TCS or Intrado, who provides location services under contract to the wireless service provider.

At the time an E-9-1-1 call is made, the wireless service provider’s switch (the switch has many names: MSC, MTSO, MTX, Central Office Exchange, there are others) signals the wireless location service provider using SS7 (Signaling System 7, which someone with a poor grip on reality called “The Intelligent Network”.) This signaling provides a way for equipment at the wireless location service provider to determine the location of the caller, which is then compared to the previously agreed map of PSAP boundaries.

When the proper or most likely PSAP is determined then the wireless location service provider signals the switch to route the voice portion of the call to that PSAP, where a call taker will answer and the location of the caller is displayed on the map, and along with other information about the call.

There is much more. But this is just a high-level overview.

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For the last few days I’ve been working on defining new data products in a CDMA network. This is my first foray into wireless data so most of the actions are completely foreign. There seems to be no comprehensive procedural guide. Our vendor has Subject Matter Experts (SME) for each of the various components. But their expertise is defined by the platform for which the are responsible, and no one has been able to provide a cogent over view of the overall process for defining and implementing these product in the network. I plan to take a few posts to try creating a comprehensive guide.

First let’s cover the systems and hardware that’s involved. I’ll emphasize those that must be manipulated as part of the implementation process. We’ll start from the handset and work in towards the cellular switch and then outward towards the service application.

• Handset. Must be capable of interacting with the service application.
• The radio network, aka “Base transceiver Sub-system” (BSS.) Not generally manipulated on a per-product basis, mentioned here only for completeness. We’ll focus on a 1xRTT network for now.
• The Packet Data Serving Node (PDSN.) Basically a router on steroids.  We have a message board on the Starent 16000 PDSN.
• The Authentication Authorization and Accounting server (AAA.) IT folks will recognize this as a RADIUS server.
• Core or Edge router, depending on your perspective. Fire-walled access to the Internet.
• Mobile Telephone Exchange (MTX.) This is the switch, which includes the HLR.
• Service Application. This can be the MMS-C, WAP Gateway, ASP, hosted content, or any of dozens of application servers. Which one depends on the actual data service being deployed.

In this series of posts we’ll detail the roles and configuration requirements of the PDSN, AAA Server and Edge Router. Others will be discussed in support of various examples.

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