AT&T MicroCell Troubleshoot Manual

MicroCell
™
Informational Document for
Technical, Operational, and Troubleshooting Issues v1.7
by Otto Pylot
Page 3 of 23
Unfortunately, the end user has no control over these issues and they can be
on-going or temporary.
Jitter – this is defined as a variation in the delay of received packets. Data packets
are sent as a continuous stream evenly spaced apart. Due to network congestion,
improper queing, or configuration issues, the steady stream may be interrupted
such that the delay between each packet can vary instead of remaining constant.
When the router receives the RTP (Real-Time Protocol) audio stream, it has to
compensate for any jitter that is encountered. This basically means that the RTP has
to be buffered and then put back together in a steady stream to be sent to the DSP
(Digital Signal Processor) and re-converted back to an analog signal. This buffer is
either called the playout delay buffer or the de-jitter buffer.
If the jitter is too large to be buffered adequately, packets are discarded which
results in audio dropouts. Sometimes the dropouts are not noticeable if the DSP can
insert packets that it thinks should be there (predictive insertion). If they are too
large, audio quality deteriorates or the connection is dropped.
Jitter can only be fixed by your ISP.
Packet Loss – this is simply data packets that just get lost in transit. Not an
uncommon event on the internet. Causes can include signal degradation, channel
congestion, corrupted packets being rejected in-transit, faulty network hardware,
faulty network drivers, or home network/wiring issues. Sometimes packet loss can
be intentional by your ISP for operational management purposes.
Excessive packet loss can result in voice dropouts or loss of connectivity. Packets
are transmitted using either TCP (Transmission Control Protocol) or UDP (User
Datagram Protocol) protocols on specific ports designated by AT&T. The exact
function of those protocols will not be discussed in this document.
Insufficient Bandwidth – it’s nice to have a 50Mbps download speed but that is
rarely a sustained speed (100% of the time). It will vary for lots of reasons and are
not guaranteed by your ISP (the term usually given is “up to”). Most of the time one
is close to that but variations will occur with sometimes very drastic speed
fluctuations. All of which can affect the MicroCell voice quality and connectivity.
You home network will also affect the bandwidth if you are sharing multiple devices
that can all connect to the internet.
There are various applications that you can use to test for latency, jitter, packet loss,
and speed. But these only take snapshots at that point in time. To get a more

AT&T MicroCell Specifications

General

Device Type	Femtocell
Network Connectivity	Ethernet
Frequency Bands	850 MHz, 1900 MHz
GPS	Yes
Compatible Networks	AT&T
Internet Connection	Broadband
Maximum Users	4 simultaneous users
Ports	1 x Ethernet
Model Numbers	DPH151, DPH153, DPH154
Cellular Technology	3G
Supported Devices	3G phones
GPS Requirement	Required
Range	Up to 5000 square feet

Summary

Introduction

Document Purpose

Explains technical workings of the MicroCell to help users with problems.

VoIP Basics

Latency

Time for a voice packet to travel over the internet; affects call quality.

Jitter

Variation in packet delay; can cause audio dropouts or connection issues.

Packet Loss

Data packets lost in transit, causing dropouts or connectivity loss.

Insufficient Bandwidth

Low internet speed affecting MicroCell voice quality and connectivity.

Requirements

AT&T Equipment and SIM

Requires 3G, 4G, or LTE-capable AT&T equipment and an AT&T SIM card.

Internet Service Requirements

Requires ISP service (not satellite/wireless broadband) with minimum speeds.

Coverage Area and Account

Location must be within AT&T coverage and require an active postpaid account.

Setup Configurations

Nominal Setup

Modem -> Router -> MicroCell connection; requires proximity to a window for GPS.

Alternate Setup

Modem -> MicroCell -> Router connection; used for troubleshooting by bypassing the router.

Router Configuration

Minimum router requirements include specific ports and settings like DHCP and IPSec Pass-Through.

U-verse Basics

AT&T HSIA Technologies

Explains ADSL2+ and VDSL technologies used by AT&T for internet service.

VDSL Characteristics

VDSL is distance-limited, uses fiber optics, and can be sensitive to line faults.

Residential Gateway (RG)

RG choice depends on VDSL type and distance from VRAD; bonded pairs may be used.

Wireless Home Phone (WHP)

WHP Overview

Standalone device using AT&T Mobility network for calls via corded/cordless handset.

WHP and MicroCell Interaction

WHP connects to MicroCell for GSM connection if cellular coverage is poor.

Ethernet Conditions

Physical Connection and Wiring

MicroCell requires Ethernet connection; cable type, installation, and grounding affect performance.

GPS Lock

Importance for E911 and Timing

Maintains GPS lock for E911 services and timing packet synchronization with towers.

Signal Acquisition and Placement

GPS signal requires window proximity or external antenna; address verification is key.

Initial Activation

Activation Process Steps

Unit acquires DHCP license, syncs time, DNS query, establishes IPsec VPN.

AT&T Address Verification

AT&T verifies physical address via online registration for service.

Handing Over

Cellular Handover Types

Explains soft and hard handovers, and how MicroCells use hard, vertical handovers.

Handoff Challenges

Handoff issues arise if local tower is far away, impacting calls outside the home.

Technical Information

Processor, Range, and Frequencies

Details on processor, range, UMTS, HSPA+, and LTE frequencies used.

Data Speeds and HD Voice

Information on 3G data speeds, HSPA+, and HD Voice (VoLTE) technology.

IMSI and IMEI

IMSI Number Function

Identifies subscriber on the network; stored on SIM card, used for interconnectivity.

IMEI Number Function

Unique 15-digit number identifying the device, used for registration and tracking.

Phone Compatibility Issues

Non-AT&T phones may not work if IMSI is not recognized by the MicroCell.

Connection Issues

System Design and Limitations

MicroCell is a closed system; no firmware access or modification is allowed.

Troubleshooting Context

Suggestions assume proper setup; success varies due to diverse LAN setups and macrocell locations.

Troubleshooting - Blinking Red 3G Light

Cause and Resolution

May indicate hardware failure or update issue; power cycling or hard reset might fix.

Troubleshooting - Power and Ethernet Lights

Power Light Status

Red or no light indicates power problem; check connections or replace adapter.

Ethernet Light Status

Blinking light signifies no or bad Ethernet connection; check cables and reset.

Troubleshooting - GPS and Green 3G Lights

GPS Light Status

Blinking GPS light requires Power/Internet lights to be solid green first.

Blinking Green 3G Light

Indicates no connection to AT&T servers or pending activation; complete reset/activation recommended.

Troubleshooting - Phone Connectivity

Phone Connectivity Problems

If MicroCell is operational, issue is likely the phone; check guest list, reset settings.

Second-Hand MicroCell Activation

Requires deactivation by original owner; serial number tied to account.

Call Quality Issues

Internet Speed Impact

Variable internet speed is a main cause; faster, stable speeds improve call quality.

Latency, Jitter, and Packet Loss

Technical factors affecting VoIP calls and causing issues.

Signal Strength Interference

Stronger tower signal than MicroCell can cause issues; disabling handout might help.

Environmental Impact on Signals

Stucco houses, terrain, weather, and buildings can affect tower signal strength.

Service Conflicts and Alternatives

Vonage VoIP and SIP ALG

Vonage VoIP and poor router SIP ALG implementation can disrupt MicroCell traffic.

General Troubleshooting Advice

MicroCell may not work due to variables; contacting support is necessary.

Phone-Specific Connection Issues

Some phones have issues due to software/hardware compatibility.

Error Codes and Alternatives

Identifies error codes and suggests signal boosters as alternatives.

Disclaimer

Additions/Changes