Technical Library

LAN-ISDN service has been upgraded to allow 128kbps through the use of two ISDN B channels with the Internet Standard MultiLink Protocol (MLP). Customers will now have twice the bandwidth available for use with multimedia applications such as the World Wide Web. No additional fees will be charged by us for using the second B channel.

Availability

Many of the communication servers support this feature. Cities which support two B channels can be found on the Access Numbers web pages.

Required and Certified Hardware

Customers must use certified hardware and software solutions to ensure that the service works correctly. While many vendors are pursuing support for ISDN and MLP, currently only following hardware is certified for use with MLP:

• Ascend
  Pipeline models 100, 50, and 25 with software revisions later than 4.4B
  
  
• Cisco
  IGS 2503, IGS 2504, 1003 and 1004 with software revisions later than 11.0 (4.1)
  
  
• Farallon
  Netopia 430, 440, 630 and 640 with software revision later than 1.1.1
  
  
• Nethopper BRI with software revision later than 4.2

The customer's ISDN service must also be configured with both B channels capable of data service. This can be determined by checking with the telephone company if the two B channel configuration is not functioning.

What is the MultiLink Protocol?

MultiLink Protocol (MLP) is the Internet Standard Point to Point Protocol enhanced to support multiple channels. It is specified in RFC 1990.

When packets are sent over multiple channels, the sending device must choose which of the channels to send each packet on. Because sequential datalink packets are traveling different channels, they may arrive out of order. The receiving end must reorder the packets. While packet order is ensured in single channel connections and relied upon by PPP, it is not ensured in multichannel connections and thus an enhanced protocol is required.

While MLP was inspired by the desire to use multiple ISDN channels, the protocol is more general and could be used to manage connectivity over other multiple channels including asynchronous lines.

MLP is negotiated as an option to PPP using the Link Control Protocol. Most MLP implementations do not provide for dynamic allocation of bandwidth. The number of channels in use is statically configured prior to service.

What is MultiChannel Point to Point Protocol?

MPP is Ascend Communication Company's proprietary enhancement to MLP. When the ISDN connection is between two Ascend devices, they will use MPP. Connections between differing devices will use MLP as described above.

MPP is designed to allow the peer servers to dynamically allocate bandwidth on a connection while preserving packet order and providing management of the remote end system. This system is referred to as Inverse Multiplexing.

Recommended Usage

While bandwidth allocation is theoretically a good idea, bandwidth usage is measured only on outgoing data. Since LAN-ISDN customers initiate all calls, inbound data may not cause the second channel connection to be initiated. For this reason and because most LAN-ISDN customers are consumers of data, it is recommended that customers statically configure their bandwidth usage to meet the needs of their applications rather than relying on the dynamic allocation to provide the appropriate bandwidth.