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Interoperability Between the Two Algorithms

The main interoperability issues of importance to network integrators are the following:

  If the peer entities use logical link control type 1 service, how should the routes be maintained?
  What type or types of frame will be needed to determine the route?
  How can it be guaranteed that all media access control layers support the discovery frames and that they are replicated across the border?
  How is a broadcast frame propagated in a multiring source-routing network?
  How will and end station be notified that the source station is using a source-routing or spanning tree algorithm?
  Will there be support for configurations that place spanning tree bridges in parallel with source-routing bridges?

IEEE 802.9 Local and Metropolitan Area Networks Integrated Services

This standard covers a unified access method that offers integrated services such as voice and data applications to the desktop for a variety of publicly and privately administered backbone networks such as FDDI, ISDN, and the IEEE 802 standards. It specifies interfaces at the media access control and physical layers.

IEEE 802.9a iso-Ethernet (Isochronous Ethernet Integrated Services)

This standard that offers real-time voice, video, and data communications (including ISDN) over existing 10Base-T cable. In IEEE 802.3 Ethernet, a 20 MHz reference clock provides a 10M bps bit stream using Manchester encoding. Instead, IEEE 802.9a iso-Ethernet uses a 4B/5B encoding scheme on the same 20 MHz clock reference to obtain a bit stream of 16.144M bps. The 4B/5B symbol encoding is the same type used by FDDI. It is coupled with an nonreturn to zero inverted (NRZI) linecoding algorithm. This provides an 80% average utilization of the bandwidth, compared with 50% for Manchester encoding.

The 16.144M-bps stream is divided into a 10M-bps ISDN channel for Ethernet traffic (using standard CSMA/CD), called a P channel, and a 6.144M-bps ISDN C channel. The C-channel typically contains 96 64K-bps ISDN B-channels, one of which is used as a D-channel for ITU-T Q.931 signaling. It uses the standard 8 kHz clocking mechanism of the public telephone network.

IEEE 802.9a requires two pairs of Category 3 UTP (unshielded twisted pair) or Category 5 UTP cabling of the type typically already installed in most offices. The maximum allowed wiring distance is 100 meters (330 feet).

The IEEE 802.9a standard offers three modes of operations to allow for a wide range of capabilities and for interoperability with terminal equipment conforming to 10Base-T. These are 10Base-T mode, multiservice mode, and all-isochronous mode.

In the 10Base-T mode, the physical layer operates like an IEEE 802.3 Ethernet using the 10M-bps P channel for packet data traffic. In the multiservice mode, the available bandwidth is divided into a 10M-bps P channel for 10Base-T data traffic and a 6.144M-bps ISDN C channel of full duplex switched ISDN circuits, including a D signaling channel. Various iso-Ethernet ISTEs and standard 802.3 10Base-T stations can be linked within the same LAN using a common iso-Ethernet access unit (AU). In the all-isochronous mode, the total bandwidth of 16.144M bps is used for circuit switched C-channel services providing 248 64K-bps ISDN B channels. It is particularly suitable for videoconferencing.

Exhibit 1-1-34 shows a layout of a network with iso-Ethernet features. Terminals with iso-Ethernet network interface cards (NICs) can handle both standard 10Base-T packet traffic and switched ISDN traffic. Terminals with standard Ethernet 10Base-T adapters can handle shared 10Base-T traffic, only. The terminals are connected to a network that provides ISDN service by means of an iso-Ethernet access unit (AU). Each cluster of terminals are connected to its own AU.


Exhibit 1-1-34.  IEEE 802.9a Network with Iso-Ethernet

Terminals, i.e. PCs and workstations, equipped with iso-Ethernet adapter cards and connected to an AU are called integrated services terminal equipment (ISTE) stations. Isochronous time-division-multiplexing (TDM) is used on the links between the AUs.


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