Overview
The HDLC is a protocol, which operates at the data link layer specifies data packets standard for serial links. The HDLC protocol
embeds information in a data frame that allows devices to control data flow and correct errors. HDLC data is formatted into frames.
A frame of data is encapsulated by flags. The beginning and end of an HDLC frame are marked by flag characters - 01111110 binary.
At the end of the frame, a Frame Check Sequence (FCS) is used to verify the data integrity. The FCS is a CRC calculated using
polynomial x^16 + x^12 + x^5 + 1. Idle periods in the data channel contain only flags.
GL's HDLC protocol analyzer provides the capability to capture, and analyze HDLC data on a full duplex T1 or E1 line. The data
channel may utilize all or a fractional part of the T1 or E1 line. Also there may be multiple data channels within the T1or E1 line.
After setting the HDLC data channel parameters and starting the decoding process, the main screen displays the received HDLC
frames in hex format. Flags are stripped, all other data is presented, including CRC bytes. GL Communications supports the
following types of HDLC analyzers:
- Real-time HDLC Analyzer (Pre-requisites: GL's field proven E1 or T1 internal cards or USB Laptop E1 or T1 external units,
required licenses and Windows 2000/XP/Vista Operating System)
- Remote/Offline HDLC Analyzer (Pre-requisites: Hardware Dongle and Windows 2000/XP/Vista Operating System)
In addition the following HDLC applications are supported that further help in transmitting and capturing pre-defined HDLC frames:
HDLC Analyzer Main Features
- Displays Summary, detail, hex-dump, statistics, and call trace views.
- Summary view displays timeslot, sub channel, frame#, device#, LAPD, LAPF specific information and IP information like
source/destination IP address, TCP source port, TCP destination port etc.
- Detailed view displays decodes of user-selected frames.
- Statistics view displays statistics based on frame count, byte count, frames/sec, bytes/sec etc for the entire captured data
- Hex dump view displays the frame information in HEX and ASCII format.
- Supports filtering and search features based on C/R, SAPI, TEI, CTL, P/F, N(S), N(R) and FUNC
- Exports detailed and summary information to a comma delimited file for subsequent import into a database or spreadsheet.
- Status bar displaying information regarding running percent utilization, Number of frames captured, CRC errors and Frame errors etc.
- Remote monitoring capability using GL's Network Surveillance System.
Additional features supported by Real-time/Remote HDLC Analyzer:
- Streams can be captured on the selected time slots (contiguous or non-contiguous), sub-channels or full bandwidth. Frames
may also be contained in either one, n x 64 kbps, or n x 56 kbps data channels.
- Other variations accommodated in the software are inverted or non-inverted data, byte reversal or non-reversal.
- Real-time capture filter can be set for filtering frames based on frame length.
- Multiple streams of HDLC traffic on various T1/E1 channels can be simultaneously decoded with different GUI instances.
- Supports decoding of frames with FCS of 16 bits and 32 bits, or none
- Captured frames can later be used for traffic simulation using HDLC Transmit/Receive/Playback application.
- Multiple remote clients may access a single T1/E1 server, the T1/E1 server is fully functional while being accessed as a server.
Thus, a user may perform T1/E1 operations locally on the server while a client is accessing the same server, in real time
(For Remote Analyzers only)
Additional features supported by Offline HDLC Analyzer:
- Trace files for analysis can be loaded through simple command-line arguments
- Multiple trace files can be loaded simultaneously with different GUI instances for offline analysis
Supported Protocols
Following is a description of the protocols supported by GL's HDLC analyzer:
- LAPD: Decodes Layer 2 as Link Access Protocol on the D-channel (LAP-D) as defined in the ITU Q.921
- LAPF: Decodes Layer 2 as Link Access Procedure/Protocol (LAPF) as defined in the ITU Q.922, an
enhanced LAPD (Q.921) with congestion control capabilities, is for Frame Mode Services in the Frame Relay network.
- LAPD+IP: Decodes Layer 2 as Link Access Protocol on the D-channel (LAP-D) as defined in the ITU Q.921 &
Layer 3 as Internet Protocol (IP)
- LAPX+IP: Dumps Layer 2 Link Access Protocol data & decodes Layer 3 as Internet Protocol (IP)
Summary, Detail and Hexdump Views
The HDLC analyzer application is invoked from the main menu of GL's T1/E1 Analyzer for real-time analyzer. The offline HDLC
analyzer is invoked from the installation directory of the offline HDLC Analyzer. The analyzer displays summary, detail and hex
dump view in different panes. The summary pane displays Frame Number, Time, Length, Error, C/R, SAPI, TEI, CTL, P/F, N(S),
N(R), FUNC etc. User can select a frame in summary view to analyze and decode each frame in the detail view. The selected
frame is analyzed and decoded according to HDLC frame specifications. The Hex dump view displays the frame information in
HEX and ASCII.
Screenshot of Summary, Detailed and Hexdump View
Real-time/Remote and Offline Analysis
Users can capture and analyze multi HDLC links in real-time and record all or filtered traffic into a trace file. The recorded
trace file can then be analyzed offline and exported to ASCII file, or printed. Real-time capturing requires user to specify
timeslots, bit inversion, octet bit reversion, user/network side, FCS, and data transmission rate. Recorded trace file can be transmitted
back on T1/E1 using the HDLC File Playback option. Sub channel and N x 56 hyper channel enables user to analyze data captured by
fractional DS0 and DS1 link respectively.
Screenshot of Realtime and Offline Analysis
Filtering and Search
Users can record all or filtered traffic into a trace file. Filtering and search capability adds as another powerful feature to the HDLC
Analyzer. This feature can isolate required frames from all frames in real-time as well as off-line. Users can specify custom values for
frame length to filter frames during real-time capture. The frames can also be filtered after completion of capture according to CTL,
C/R, Modifier Function, N(R), N(S), P, P/ F, SAPI, Supervisory function and TEI. Similarly, search capability helps user to search for a
particular frame based on specific search criteria.
Screenshot of Setting Filtering Criteria
Statistics View
Statistics is an important feature available in HDLC analyzer and can be obtained for all frames both in real-time as well
as offline mode. Numerous statistics can be obtained to study the performance and trend in the HDLC network and it is
based on protocol fields and different parameters e.g. User Type (Key/Total/Field), Statistic type (Frame count, Byte count,
Frames/Sec) and patterns like Range List, Wild card etc.
Screenshot of Statistics View
Enhanced Trace Saving Options
Users can control the captured trace files by saving the trace using different conventions such as trace files with user-defined
prefixes, trace file with date-time prefixes, and slider control to indicate the total number of files, file size, frame count, or time limit.
This feature also allows the captured frames to be saved into a trace file based on the filtering criteria set using display filter feature.
Screen Shot of Enhanced Trace Saving Options Window
Save/Load All Configuration Settings
Protocol Configuration window provides a consolidated interface for all the important settings required in the analyzer. This
includes various options such as protocol selection, startup options, stream/interface selection, filter/search criteria and so on.
All the configuration settings done in any of these options can be saved to a file, loaded from a configuration file, or user may
just revert to the default values using the default option.
Screen Shot of Save/Load All Configuration Setting Window
HDLC Playback Application
The HDLC Playback application is used to transmit HDLC frames in the pre-recorded files over T1/E1 channels. The frames
can be transmitted on selected time slots (contiguous or non-contiguous), sub-channels or full bandwidth. The HDLC frames may
also be transmitted on just one, or n x 64 kbps, or n x 56 kbps hyper channels.
Further, the application also provides the option to reverse or inverse bits in the selected data during transmission.
HDLC Link Impairment Utility
The HDLC Link Impairment Utility (HLIU) offers various options to "impair" (inject errors) specific HDLC frames of a real time
HDLC frame stream. The main objective of this application is to verify the proper working of HDLC protocols by simulating various
scenarios taking place in a real-time network. The HLIU application has the following features:
- Logic Error insertion
- CRC Error insertion
- Drop a Frame
- Change Frame Order
- Duplicate a Frame
- Insert a Frame
- Delay a Frame
The HLIU application works with PCI cards, HD cards and Laptop units, and may be tested with the HDLC Playback File and
HDLC Analysis applications.
Screenshot of HLIU Application Main Window
HDLC Tx/Rx Test Applications
The HDLC Automated Test System consists of two applications: Transmitter application and Receiver application. Each
application has real-time and off-line features.
The Transmitter application generates HDLC test frames, transmits them over T1/E1 or records them to an HDL file for
subsequent use with other applications. Frames are generated using special algorithms that allow subsequent automated
tests that discover frame loss, data modification, frame reordering etc.
The Receiver application can receive frames real-time over T1/E1 or can verify an off-line HDL file for correct frame order and
data integrity.
Screenshot of Tx/Rx Test
Automated HDLC Testing using Client-Server
GL's Windows Client/Server software allows the user of T1/E1 analysis cards, the capability of remote operation, automation, and
multi-site connectivity. Server software can run multiple tasks simultaneously at the request of the Client software. GL provides
client –server based HDLC capture, playback, emulation & analysis modules.
WCS module XX640, XX641-File based HDLC Record/Playback & Remote Capture/Playback
The File based HDLC Record/Playback (Hdlcfunc) module is an optional application that allows HDLC Traffic Capture/Playback.
It also allows transmission/reception of *.HDL frames files located on the server and on client.
Features
- Displays the command syntax.
- Receiving HDLC frames in HDL files located on the server.
- Transmitting HDLC frames from an HDL file located on the server.
- Receiving HDLC frames in HDL files located on the client.
- Transmitting HDLC frames from an HDL file located on the client.
For more information on this application click here
WCS module XX634 - Multi-Channel HDLC Emulation and Analysis; File based High
Throughput HDLC Record/Playback
The HDLCTerr module performs multi-channel HDLC emulation and analysis. It permits frame error testing and transmission
of memory generated sequences of fixed or variable length HDLC frames, GL *.HDL Trace file frames, and various bandwidth
streams.
The HDLCHpio module performs file–based HDLC record and playback actions. It permits receive / transmit of HDLC streams
of various bandwidth (hyper channel, timeslot, and multiple sub-channel streams per timeslot).
For more information on these applications click here
Bridge and Monitor Connections
Buyer's Guide:
Please Note: The XX in the Item No. refers to the hardware platform, listed at the bottom of the Buyer's Guide,
which the software will be running on. Therefore, XX can either be HDT, HDE, HUT, HUE, UTA or UEA depending
upon the hardware.
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