ATM in a T3 (DS3)/E3 Network
Overview
Asynchronous Transfer Mode (ATM) is a flexible network, which carries voice, video, and data in the same way, i.e. fixed length cells. It has generated a
number of revenue opportunities because of its different classes of service support for multimedia traffic, efficient bandwidth management for burst traffic,
support for LAN/WAN architecture and high performance via hardware switching.
ATM network basically has two kinds of interfaces i.e. UNI (Interface between ATM User and Public ATM switch) and NNI (Interface between two Public
ATM switches). Similar to the OSI Protocol model, ATM has an ATM Layer as Layer 2, ATM Adaptation Layer (AAL) as Layer 3 and other higher layers
depending on C-Plane, U-Plane or Layer Management Plane. User information is transferred across U-Plane and Signaling messages is transferred across
C-Plane. ATM-UNI signaling is used to create and release SVCs along with a particular QoS attached to it depending bandwidth on demand.
GL's T3 ATM Analyzer is used to analyze and decode different ATM protocols like ATM, AAL2 Protocols (CPS-SDU, SSSAR-SDU, and SSCS), AAL5 (CPCS),
UNI and others across U plane and C plane of UNI and NNI interface.
ATM Analyzer Main Features
- Displays Summary, detail, hex-dump, statistics, and call trace views.
- Summary View displays Dev #, Frame #, VPI/VCI, PT (Payload Type), HEC, OSF, AAL Type, Frame Type, CID, LI, CPI, UUI, SSSAR CID and SSCS
message type etc.
- Detailed view displays decodes of user-selected frames.
- Hex dump view displays raw frame data as hexadecimal and ASCII octet dump.
- Statistics view displays statistics based on frame count, byte count, frames/sec, bytes/sec etc for the entire capture data.
- Call trace capability based on UNI signaling parameters, VPI/VCI etc.
- CRC verification for AAL5 carrying packet data.
- Support of various UNI Signaling Protocols i.e. UNI 4.0, UNI 3.1 and UNI Q-2931.
- Supports search and filtering capabilities.
- Ability to configure .ini file for PVC carrying UNI signaling messages to get the proper decoding options
- Capability to export summary as well as detail view information to an ASCII file for subsequent import into a database or spreadsheet
- Captures, decodes, filters, and reassembles AAL-2 and AAL-5 frames in real-time, from within the ATM cells according to user defined VPI/VCI.
- Unscrambling of ATM cells based on SDH X^43 + 1 algorithm.
- Multiple streams of ATM traffic on various T3/E3 ports can be simultaneously decoded
- Streams may be captured on the selected ports
Protocols Supported
The list of protocols that are supported by GL's T3 (DS3) /E3 ATM analyzer are as given below
Supported Protocols Structure for ATM Protocol Analysis
- ATM Layer- B-ISDN ATM LAYER SPECIFICATION, ITU-T Recommendation I.361
ATM layer is responsible for transporting the information in the form of a fixed length cells (53 bytes) across the network using several virtual
connections identified by VPI/VCI values. The connection isn't assigned a dedicated bandwidth. Depending on the QoS of involved parties, the
connection is assigned a bandwidth and traffic is actually sent.
- ATM Adaptation Layer (AAL)
ATM adaptation layer performs the necessary mapping between higher layer protocols and ATM layer. It multiplexes the higher layer info in the
fixed length ATM cells. Because of different quality of service parameters, different types of AAL starting from AAL0 to AAL5 are defined. AAL0 is
nothing but ATM cells itself. Different classes of service are mapped to individual AAL type. Among these, GL's T3 ATM analyzer supports AAL2 and
AAL5 as specified below:
AAL 2- Class B (ITU-T Recommendation I.363.2)
AAL 5- Class C & D (ITU-T Recommendation I.363.5)
AAL includes the following sublayers :
- SSCS (Service Specific Convergence Sublayer): ITU-T Recommendation I.366.2
It uses AAL2 connection for transporting different narrowband traffic like Voice, CAS bits, DTMF digits, circuit mode and frame mode data etc.
- SSSAR (Service Specific Segmentation and Reassembly Sublayer): ITU-T Recommendation I.366.1
It multiplexes frame mode data in an AAL2 connection. It fragments very large amount of data of a frame and packed in an AAL2 connection thus
can assure assigned QOS for the service.
- UNI
GL's T3 ATM analyzer can be configured to support following UNI interfaces:
- ITU-T Standard Interfaces (UNIQ.2931):
Q.931 based UNI signaling is an ITU-T UNI signaling standard used to establish and release of SVC. SVC is switched virtual channel created using
signaling protocol when it is needed and then later on released. Various variants of UNI signaling are available.
- ATM Forum Standard Interfaces (UNI 3.0, UNI 3.1, UNI 4.0):
Similar to Q.2931, ATM forum has defined it's own recommendations for establishment and release of SVC across ATM User-Network interface. The
procedures described in these recommendations apply to both public UNI as well as private UNI.
Summary, Detail and Hexdump Views
The T3 ATM analyzer application is invoked from the main menu of GL's T3/E3 Analyzer for real-time analyzer. The offline ATM analyzer is invoked
from the installation directory of the offline ATM Analyzer. The analyzer displays summary, detail, call trace, statistics, and hex dump views in different
panes. The summary pane displays Dev#, Frame#, Time, Length, Error, VPI/VCI, PT and so on. User can select a frame in summary view to analyze and
decode each frame in the detail view. The Hex dump view displays the frame information in HEX and ASCII format.
Protocol Summary, Detailed, and Hexdump Views in ATM Protocol Analysis
Real-time and Offline Analysis
Users can capture and analyze UNI and NNI interfaces 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 Recorded trace file can be opened later for offline analysis. User can capture raw ATM data
and can then transmit using playback file application.
ATM raw data capturing requires user to specify ports, user/network side, and scrambling options. Captured trace files can later be used for offline analysis
Port Selection for real-time capture
Filtering and Search
Users can record all or filtered traffic into a trace file. Filtering and search capability adds a powerful dimension to the ATM Analyzer. This feature
can isolate required frames from all the captured frames in real-time, as well as offline. Users can specify custom VPI, VCI, and PT type values to filter
frames during real-time capture. The frames can also be filtered after completion of capture according to Dev#, Frame #, Time, Length, Error, VPI/VCI,
PT (Payload Type), HEC, OSF, AAL Type, Frame Type, CID, LI, CPI, UUI, and more. Similarly, search capability helps user to search for a particular frame
based on specific search criteria.
Offline Filtering and Search Criteria for ATM Protocol Analysis
Real-time/pre-capture Filtering and Search Criteria for ATM Protocol Analysis
Reassembly
Using reassembly option user can specify VPI /VCI value to reassemble as per the Segmentation and Reassembly rules defined by the specified
AAL type. It multiplexes ATM cells as per the user specified VPI/VCI/AAL type into CPS or SAR frames. ATM cells not satisfying the user specification
will be reassembled as per the default specification.
Reassembly Options for ATM Protocol Analysis
Call Trace and Statistics View
Call trace defining important call specific parameters like Call ID, Call disposition, Call duration, VPI/VCI, Call type (point-to-point/point-to-multipoint
etc) calculated based on UNI signaling messages are displayed in Call Trace view.
Statistics is an important feature available in ATM analyzer and can be obtained for all frames both in real-time as well as offline mode. Various
statistics can be obtained in statistics view to study the performance and trend in the ATM network based on different parameters e.g. Use Type,
Statistic type and various patterns.
Statistics Options for ATM Protocol Analysis
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.
Protocol Trace Saving Options for ATM Protocol Analysis
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