The HDLC is a protocol operating at the data link layer. The HDLC protocol embeds information in a data frame allowing data flow control and error correction. Each flag consists of eight bits – (01111110).
At the end of the frame, a Frame Check Sequence (FCS) is used to verify the data integrity. The FCS also known as cyclic redundancy check (CRC) is calculated using polynomial xˆ16 + xˆ12 + xˆ5 + 1 (FCS 16 bits) or xˆ0+xˆ1+xˆ2+xˆ4+xˆ5+xˆ7+xˆ 8+xˆ10+xˆ11ˆxˆ12+xˆ16+xˆ22+xˆ23+xˆ26+xˆ32 (FCS 32 bits). 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 XP (or higher) Operating System)
- Remote/Offline HDLC Analyzer (Pre-requisites: Hardware Dongle and Windows XP (or higher) 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
- HDLC Playback
- HDLC Impairment Utility
- HDLC Tx RxTest Application
- Automated HDLC Testing using Client-Server
Additional features supported by Real-time/Remote HDLC Analyzer:
- Displays Summary, Detail, Hex dump, Statistics, and Call Detail Views; the contents of this view can also be copied to clipboard.
- 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.
- Supports decoding of LAPF, LAPD, LAPD+IP, LAPX+IP, X.25, Cisco HDLC Protocols.
- Detail View displays decodes of user-selected frames from the Summary View.
- 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; the contents of this view can also be copied to clipboard.
- Supports filtering and search features based on C/R, SAPI, TEI, CTL, P/F, N(S), N(R) and FUNC
- Any protocol field can be added to the summary view, filtering, and search features providing users more flexibility to monitor required protocol fields.
- Capability to export Summary View details information to a comma delimited file for subsequent import into a database or spreadsheet.
- Capability to export detailed decode information to an ASCII file.
- 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 Offline 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).
- 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.