Store and Forward vs. Pipeline
Shared RAM adapters derive their name from the fact that they carry on-board RAM and share that RAM with the system processor. The memory on the adapter card is mapped into an unused block of system memory above the 640 KB line in the upper memory area. The upper memory area is the 384 KB of memory immediately above the 640 KB line. The UMB area is reserved for I/O adapters.
The server processor can access this memory in the adapter in the same manner in which it accesses system memory. The starting address of the shared RAM area is determined by the adapter device driver unless the adapter is an MCA Adapter, in which case the address is determined by the setting of the reference diskette.
In size, shared RAM can be 8, 16, 32, or 64 KB depending on which adapter is used and how it is configured. Adapter cards with 64 KB support RAM paging which allows the system to view the 64 KB of memory on the card in four 16 KB pages. This scenario only requires 16 KB of contiguous system memory insteadof the 64 KB required when not using RAM paging. RAM paging will not work unless the adapter's device driver supports it. All IBM NetBIOS products support RAM paging.
The shared RAM area itself contains various status and request blocks, service access points and link station control blocks, receive buffers, and transmit buffers. It is possible to alter the size and number of the transmit and receive buffers by altering parameters associated with adapter device drivers. A shared RAM adapter is the Short IBM Token-Ring 16/4 /A (16-bit).
Primary advantages of the shared RAM architecture:
Main disadvantage of the shared RAM architecture
On lightly loaded servers providing traditional productivity
apps such as word-processing, spreadsheets, and print sharing, this is
not really a problem. But for applications such as databases or for
more heavily loaded file servers, this can be a major source of performance
Bus Master/DMA Adapters
The TR Network 16/4 Busmaster was the first generation of bus master LAN adapters from IBM. It employed the 64 KB on-board adapter memory as a frame buffer to assemble frames before they were sent to the server or sent from the server to the network. The time elasticity provided by this buffer allowed the token-ring chip set to complete its processing and forwarding of the frame before the frame was lost; known as overrun (receive) or underrun (transmit).
The 16-bit MCA bus master was capable of burst mode DMA. It was limited to using only the first 16 MB of system address memory because of it's 24-bit addressing capabilities . Bus master/DMA adapters utilize on-board DMA controllers to transfer data directly between the adapter and system memory without involving the system processor.
Bus master/DMA adapters do not use the shared RAM mechanism to transfer data to system memory. However, bus master/DMA adapters do use shared ROM when they are performing the remote initial program load (RIPL) function.
Primary advantages of the bus master/DMA adapter:
Primary disadvantages of the bus master/DMA
· Poor performance in certain DOS environments: In a DOS environment the 16/4 Adapter II and LANStreamer are supported with NDIS and ODI drivers. Poor performance may occur in an NDIS environment when using LAN Support Program's DXME0MOD.SYS which is an 802.2 NDIS protocol driver. This driver must be used when running 802.2 applications such as PC/3270, AS/400 PC Support, DOS APPN, and TCP/IP V2.X for DOS when using the ASI (802.2) interface.
· No on-board logical link control (LLC): Since the adapter itself does not implement an LLC stack, one must be written into the NDIS MAC driver or protocol driver if one is needed. This means that additional system memory will be needed to implement the LLC stack. This is not much of a consideration in the OS/2 environment, but it may affect a memory constrained environment like that of DOS. Novell NetWare users will have to add a NetWare Loadable Module (NLM), LLC8022.NLM, for example, to add LLC support to the configurations of their server machines. The primary reason for doing so would be to enable the server adapter to be monitored as a critical resource from LAN Network Manager.
· Can't address >16 MB when bus master
card only has 24 address lines:
32-Bit Bus Master Interface:
The LANStreamers provide a 32-bit bus master interface to the Micro Channel
supporting both 32-bit addressing and 32-bit data moves. LAN Streamer's
bus mastering capabilities free the system CPU from having to move data
between the LAN adapter and system memory, freeing the system CPU for other
work and resulting in significantly lower system CPU utilization than shared
Pipelined Frame Processing: LANStreamer
achieves superior performance by changing how token-ring adapters
transmit and receive frames.
In contrast, LANStreamer uses a pipelined architecture.
Frames are streamed directly between the token-ring and attaching system
memory without being stored on the adapter and without any adapter processor
intervention. Rather than first moving frames from system memory to the
adapter, and then moving them from the adapter to the ring, LANStreamer
simultaneously moves the frame from the system onto the adapter and out
onto the ring. This new architecture is made possible by the implementation
in VLSI of the functions previously done in software by the adapter processor.
This dramatically improves performance, because the processing time required
for each frame is the major bottleneck in the store-and-forward architecture.
The result of the pipelined approach is that the adapter
is never the bottleneck for throughput. If the system can handle it, LANStreamer
can transfer or receive frames at 16 Mbps, even at small frame sizes. This
means LANStreamer is capable of up to 48,000 frames
per second throughput. By comparison, the bus
master adapter has a throughput capacity approaching 3,000 frames per second.
In a server such as the PS/2 Model 95-0MF, with a fast 50 MHz 80486 processor,
a high bandwidth Micro Channel bus, and a LANStreamer token-ring adapter,
each critical server component is optimized to provide high LAN I/O throughput
Multiple Group Addressing: Group addressing
is part of the token-ring architecture, but today's token-ring adapters
only implement one group address, which is not very useful for most applications.
By implementing multiple group addressing, LANStreamer offers complete
hardware support for multicasting. Multicasting can be thought of as a
limited broadcast. Rather than sending a frame to either a single destination
station or broadcasting it to every station on the network, multicasting
allows a user to send frames to a limited group of destinations. Stations
may assign themselves to a particular group by setting one of the 256 hardware
group addresses available on LANStreamer. These 256 addresses allow each
LANStreamer station to belong to up to 256 groups, but there can be more
than 256 groups on a network.
Today's implementation can be described as follows: frames
are sent to every station on the network using broadcast. Each station's
CPU sorts each frame using the functional address, and discards frames
not intended for it. There are obvious disadvantages to this approach.
Each station's CPU must sort every broadcast frame (whether it is intended
for the local station or not) tying it up for significant amounts of time.
In one case, where TCP/IP was being used on the network, users reported
that even stations that did not use TCP/IP were spending 40%-50% of their
CPU cycles decoding ARP frames.
Priority Mechanisms: The LANStreamer chip
set provides two mechanisms for prioritizing frames passing through the
token-ring adapter. These are priority queueing in the adapter, and priority
tokens on the ring. LANStreamer implements two prioritized transmit queues.
High priority frames can be placed on the higher priority queue to be processed
ahead of lower priority frames. The LANStreamer adapter will reserve priority
tokens on the ring for these high priority frames.
Both these priority mechanisms transparently coexist with current token-ring implementations. The priority token is part of the token-ring architecture, and is already used in certain applications such as bridging. With LANStreamer, IBM has provided a mechanism, in conjunction with the priority queue, for making priority token reservation available to user applications. The priority queue is a system interface implementation that does not affect token-ring operation.
On-Card STP and UTP Support: The LANStreamer adapters include on-card filters for both STP and UTP media. LANStreamer MC 32 includes RIPL support for both LAN Server (all levels) and NetWare (V3.X and beyond). LANStreamer provides full network management support, and is fully compatible with LAN Network Manager. The LANStreamer MC 32 adapter is available for the 3172 Interconnect Controller.
Another advantage of this technology is that since adapter memory buffers are no longer required, the adapter is less expensive to produce.
The LANStreamer technology is used in the IBM Auto LANStreamer Adapters for PCI and MCA as well as the EtherStreamer and Dual EtherStreamer MC 32 LAN adapters.
The EtherStreamer LAN adapter supports duplex
mode, which allows the adapter to transmit as well as receive at the same
time. This provides an effective throughput of 20 Mbps (10 Mbps on
the receive channel and 10 Mbps on the transmit channel). To implement
this feature, an external switching unit is required.
The PeerMaster technology takes LAN adapters one step forward by incorporating an on-board Intel i960 processor. This processing power is used to implement per port switching on the adapter without the need for an external switch. With this capability, frames can be switched between ports on the adapter, bypassing the file server CPU totally.
If more than one card is installed, packets can be switched both within cards and between cards. The adapters utilize the Micro Channel to switch inter-card and can transfer data at the very high speed of 640 Mbps.
The IBM Quad PeerMaster Adapter is a four-port Ethernet adapter that utilizes this technology. It is a 32-bit Micro Channel bus master adapter capable of utilizing the 80 MBps data streaming mode across the bus either to/from system memory or peer-to-peer with another PeerMaster adapter.
The Quad PeerMaster is a type 5 Micro Channel adapter. This refers to the physical size of the adapter. A type 5 adapter is 13.1 x 4.825 inches and is larger than normal MCA adapters (11.5 x 3.475 inches). It fits in specific servers and only in certain slots. Servers that support the type 5 adapters include the Server 320, 500 and 520. Refer to Server Products for more information on these servers.
It ships with 1 MB of memory. Each port on an adapter serves a separate Ethernet segment. Up to six of these adapters can reside on a single server and up to 24 segments can be defined in a single server.
This adapter can also be used to create virtual networks (VNETs). a single network, eliminating the need to implement the traditional router function either internal or external to the file server.
The Ethernet Quad PeerMaster Adapter is particularly appropriate when there is a need for:
Switching/Bridging traffic among multiple
An add-on to NetFinity provides an advanced Ethernet subsystem management tool. Parameters such as packets/second or total throughput can be monitored for each port, for traffic within an adapter, or for traffic between adapters.
By using NetFinity, you can graphically view the data, monitor
for predefined thresholds, and optionally generate SNMP alerts.