GL Communications Inc.
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Multi-link Frame Relay (MFR)Emulation
with Client-Server


Multi-Link Frame Relay, or MFR, is similar to Multi-Link PPP, and both are a form of inverse multiplexing. Users rely on inverse multiplexing when access line capacity does not scale smoothly, i.e. notice the big jumps in bandwidth from 56kbps, 1.544 Mbps, and 45 Mbps. In such cases, intermediate bandwidth must be derived by aggregating a number of smaller access lines into larger ones. MFR is used to derive a larger frame relay pipe by aggregating smaller frame relay pipes. For example, 5 T1 frame relay pipes could be bundled to appear as a single 7.5 Mbps frame relay pipe. Some of the advantages of using MFR are: better bandwidth sizing according to customer traffic requirements and potentially better QOS by minimizing delay.

User's Guide
Command Ref. Guide
Product Brochure
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MFR works by bundling multiple T1 circuits into a multilink bundle and fragmenting the individual frame relay frames into fragments. These fragments are then transported in parallel over the multiple T1 circuits. At the other end, the fragments are reassembled into the original frame relay frames. The protocol includes the use of sequence numbers to allow the fragments to be reassembled correctly and to ensure that the reconstructed frames are sent out in the original order in which they entered the network.

FR and MFR can be emulated and analyzed using GL's client-server based Multi-Link Frame Relay Emulator and Multi -Link Frame Relay Analysis software modules.

Multi-Link Frame Relay Emulator can be configured as a router or as a bridge to establish connection and route traffic between LANs. The application may be accessed through a GUI or through command line scripts.

Screen Shot of MFR Simulation in GUI

Screen Shot of MFR Simulation in CLI

Main Features:

  • Performs MFR as well as FR simulation on up to 16 T1/E1 lines
  • Adheres to FRF.12 standards
  • Support two simulation modes - FR and MFR
  • FR links can be created on Full or Fractional Timeslots
  • Group FR links to create a MFR bundle
  • Dynamically add/remove (open/close) of Frame Relay links without loss in data
  • Multiple MFR Bundles/FR links can be created with each bundle/link configured with multiple virtual channels for traffic tx/rx
  • Generate and verify end to end traffic on each Virtual Channel
  • Transmit and receive Ethernet traffic over T1E1 links by operating either in bridge or router mode
  • User configurable FR/MFR packet and fragment size, bandwidth using flags, and maximum link differential delay
  • Supports both Interface (UNI and NNI) and End-to-End fragmentation
  • Supports various traffic source/sink types namely, Sequence Number, Binary File, Hex String, and pre-captured HDL files
  • Supports various Byte level, Frame level , CRC error, and Frame error impairments at link level
  • Supports various Byte level and Frame level impairments at Fragment/Packet level for each Virtual Channel
  • Provides detailed statistics for each bundle and virtual channels associated with a bundle

Simulating Frame Relay links

Various links (of any bandwidth varying from 64Kbps to n*64Kpbs or sub channels) can be added in FR Simulation .Two or more than two timeslots can be grouped to constitute a Hyper-channel.

Each of the added links can be configured with Fragmentation size, Flags between HDLC Frames, and Impairments.

Screen Shot of Links in FR Simulation

Link Configuration

This feature provides Frame Fragmentation configuration adhering to FRF.12 standard for traffic generation on selected FR links. The application supports two types of fragmentation: UNI NNI Fragmentation and End-to-End Fragmentation on a FR link. If fragmentation configuration is not enabled then the generated FR traffic will have 2 byte frame relay header only. The application also allows to configure the bandwidth using flags.

Screen Shot of Link Config Layer

Simulating MFR Bundle

MFR bundles multiple link-layer channels into a single network-layer channel. The MFR Simulation allows to create a virtual interface referred as ‘bundle’ interface. An MFR bundle can consist of multiple physical links of the same type or physical links of different types. Data sent through this channel will be distributed among all the links. MFR bundles technique is used to derive larger bandwidth pipe by aggregating smaller bandwidth pipes e.g. from multiple T1s or E1s.

Screen Shot of MFR Bundles and Links

Bundle Configuration and Statistics

Similar to a link, Fragmentation Size and Maximum Differential Delay can be configured for a selected bundle in the Bundle Config screen. Bundle Statistics will show statistics of transmitted frames, received frames, transmitted octets, and received octets for a selected bundle.

Screen Shot of Bundle Config & Statistics


Impairments enable the user to intentionally introduce errors in data transmission. Impairments can be applied at different levels, i.e.

  • Impair all packets sent over a Physical Link
  • Impair frames on a particular Virtual Channel [VC may be on a physical link or on the MFR bundle].
  • Impair frames on a particular Aggregated Virtual Channel
  • Impair all packets on the MFR bundle

Impairments can be applied to a link either before data transmission or during the process of data transmission. Different kinds of impairments are available to perform the task. Bytes can be modified through Delete bytes, Insert bytes, and AND/OR/XOR options. An entire FR frame can also be impaired through Delete, Insert, Duplicate, CRC errors, and Frame errors. Following impairment types are supported:

  • DELETE – Delete few bytes in a frame or the delete the full frame itself
  • INSERT- Insert few bytes in a frame or insert the full frame itself
  • DUPLICATE – Duplicate a frame given number of times
  • AND, OR, XOR – Logically And/Or/Xor an octet in the frame
  • CRC – Introduce CRC error.
  • FRAME ERROR – Introduce frame error.
  • DELAY – Delay transmission on a physical link by x msec.

For selected links, differential delay can be introduced between links. The delayed links in the links can also be brought back to sync with the Synchronize option.

Screen Shot of Impairment Types

Tx and Rx Action

A virtual channel is created for selected links or bundle to perform traffic actions. In FR simulation the VC will be created on the selected link from the ‘Links’ dropdown menu. In case of MFR simulation VC will be created on the selected bundle. Multiple Virtual Channels (VC) can be created on the same physical link with same fragmentation format and fragment size.

Tx parameters will generate the FR traffic. Received data is verified with respect to the selected Rx parameters and results of verification are available in Tx/Rx verification tab. The parameters for each VC are independently set. The Tx/Rx parameter includes:

  • Data Type (Sequence No, Packets from HDL or BIN files, HEX string, or Network Traffic). Network traffic allows users to receive traffic from Ethernet LAN, convert to FR traffic and send through T1/E1 line and vice versa. MFR emulator can be configured to work as router or bridge to establish connection between two systems residing in two different LANs.
  • Data Type Parameters
  • Prefix Header
  • Duration Specification
  • Payload length
  • Impairments

Screen Shot of FR – VCs on a Selected Link

Screen Shot of MFR – VCs on a Selected Bundle

TxRx Verification

The results of the verification for each of the added VCs are available in Tx/Rx Verification. The statistics include:

  • The number of VCs created.
  • The number of frames transmitted successfully
  • The number of frames received successfully
  • If a received frame is verified successfully, then it will be included in "Matched" Frame Count
  • If a received frame does not match, it will be included in the "Modified" Frame Count
  • If the frame is lost then it will be included in "Deleted" Frame Count
  • If extra frames have been received which were not expected then they will be included in Inserted Frame Count

Screen Shot of Tx/Rx Verification for Each VC

MFR Emulator as a Router

The MFR Emulator allows user to setup routing table by configuring IP Address and Mask. Once configured, the emulator forwards the IP packets which match routing criteria over MFR links. The emulator responds to all ARP requests whose IP addresses present in routing table. Shown above, are two networks, Subnet1 and Subnet2, connected through T1/E1 lines using MFR Emulator that is configured to work as router.

MFR Emulator as a Bridge

When the MFR Emulator is configured to act as bridge between two networks, all ARP and traffic received from the network is encapsulated as bridged IP and streamed over T1/E1 links. The Emulator on another network removes bridging header, converts to Ethernet and streams to the destination.

Link Statistics

Provides important statistics information for the selected link such as such as the Number of frames transmitted, Received frames, Octets Transmitted, and Octets Received.

Screen Shot of HDLC Statistics Layer

VC Statistics

The statistics for each of the added VCs are available and these include number of Transmitted and received frames, Fragments, Octets, and Lost fragments.

Screen Shot of Tx/Rx Statistics for Each VC

HDLC Statistics

Errors that occur during transmission / reception like the Tx Under/Over Runs, Rx Under/Over Runs, number of FR packets with bad FCS, and number of packets with Frame Errors is recorded in the HDLC Statistics fields.

Screen Shot of Statistic Layer

MFR Emulation using CLI

Adding and Activating Frame Relay links (streams)

Syntax: inform task n "TS [HC|SC] 'Link Name'";
Syntax: inform task n "ACTIVATE TS [HC|SC] ‘Link Name’";

It is used to add new frame relay links (streams) to the task. In FR simulation the added links are independent of each other, and Virtual Channels will be created on each individual link. In MFR simulation all the added links will constitute one MFR bundle, and Virtual Channels will be created on the bundle but not the constituent bundle links.

The activate command is used to activate /deactivate the individual bundle links in the MFR bundle. Provides an option to dynamically activate/deactivate the links, deactivated links are not be used for Tx/Rx.

Creating/deleting Virtual Channels on the links

FR simulation:

Syntax: inform task n "CREATE VC HC #1:0..23 DLCI x FRAG FORMAT UNI NNI [END TO END] FRAGSIZE n";

MFR simulation:

Syntax: inform task n "CREATE VC DLCI x [y z …] FRAGSIZE n";

This is used to create or delete virtual channels on the FR links. In case of MFR simulation, virtual channels are created on the MFR bundle.

Traffic Generation and Verification

FR Simulation

Syntax: inform task n "Tx[Rx]: HC #1:0..23 DLCI x CONT [FRAMES n |EOF] FIXLEN 1500 SEQNUM MSB4 [MSB|LSB 8|2|1]";

MFR Simulation:

Syntax: inform task n "Rx:[Tx:] DLCI x CONT FIXLEN 1500 SEQNUM MSB4";

Aggregated Virtual Channel

Syntax: inform task n "Rx [t]: HC #1:0..23 AVC x CONT [FRAMES n|EOF] FIXLEN 1500 SEQNUM MSB4 [MSB|LSB 8|2|1]";

In MFR Simulation the traffic is generated and received on the entire MFR bundle. But in FR simulation, traffic can be generated and received on each individual FR link. Transmission parameters are used to generate traffic and receiving parameters are used as reference to verify the received frames.

Applying Impairments on Frame transmission

Syntax: inform task n "ERROR REP n [CONT] SKIP m #1:0..23 DLCI x OFFS x DEL x";

Click here to download the Multi-link Frame Relay Client-Server E1/T1 scripts.

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 ETA or EEA (Octal/Quad Boards), PTA or PEA (tProbe Units), UTA or UEA (USB Units), HUT or HUE (Universal Cards), and HDT or HDE (HD cards) depending upon the hardware.

Item No. Item Description
XX655 Multi-link Frame Relay Emulation w/ Tx/Rx Test (requires XX634)
  Related Software
XX635, XX636 Multi-link Multi-Class PPP Emulator
XX634 Multi-Channel HDLC Emulation and Analysis & File based High Throughput HDLC Record/Playback
XX610 Transmit and Receive File Capability
XX620 Transmit/Detect digits
XX640 File based HDLC Record/Playback
XX641 File based HDLC Remote Record/Playback
XX130 T1 or E1 Real-Time Frame Relay Protocol Analyzer
OLV130 Offline/ Remote Frame Relay Analyzer
XX135 T1 or E1 Real-time MLPPP Protocol Analyzer
XX136 Real-time Packet Data Analysis for MLPPP Protocol Analyzer
  Related Hardware
XTE001 Dual Express (PCIe) T1 E1 Boards
PTE001 tProbe™ Dual T1 E1 Laptop Analyzer with Basic Analyzer Software
HDT001/HDE001 Legacy HD T1 or E1 (PCI) Cards with Basic Analyzer Software
HTE001 Universal T1/E1 Card with Basic Analyzer Software
UTE001 Portable USB based Dual T1 or E1 Laptop Analyzer with Basic Analyzer Software

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