SPECIFICATION
SIMSIMETH simulates an x-kernel ethernet driver by sending and receiving messages using any x-kernel protocol that accepts UDP addresses. SIMSIMETH is platform independent. SIMSIMETH interoperates with SIMETH ( and itself). SIMSIMETH's primary purpose is to support the testing of protocols between x-kernel simulators such as the SunOS simulator and native mode x-kernel implementations such as the Mach 3.0 implementation.

SYNOPSIS
Each instantiation of SIMSIMETH is associates a simulated Ethernet address with a specific UDP address and simulates an Ethernet driver for a single interface. SIMSIMETH reads the UDP port from the ROM file and gets its IP address by performing a GETMYHOST control operation on the protocol configured below it.

The mapping between Unix UDP ports and SIMSIMETH Ethernet addresses is very simple. The six bytes of SIMSIMETH Ethernet address are formed by the concatenation of the four byte IP host number for the Unix host on which the simulator is running and the two byte UDP port used by the SIMSIMETH instantiation. Note that this IP host must be valid and defined by the protocol graph below SIMSIMETH. Since one generally runs two copies of ARP when SIMSIMETH is configured keeping your IP addresses straight is sometimes difficult. See the CONFIGURATION section below.

When a message is sent using SIMSIMETH a map is checked to see if a lower level session exists for that destination address. If no lower level session exists one is created by performing an open on the protocol configured below SIMSIMETH (most probably) UDP. Once SIMSIMETH has opened a lower level session it is never closed. SIMSIMETH then pushes an Ethernet header on the message and pushes the message using the lower level session. When a packet arrives at SIMSIMETH the Ethernet header is removed and SIMSIMETH presents the packet received as an incoming Ethernet packet.

Note that an x-kernel may be configured with multiple instantiations of SIMSIMETH, each with its own UDP port, to simulate a multihomed host. SIMSIMETH can awkwardly simulate Ethernet broadcast messages. When an outgoing broadcast message is sent to SIMSIMETH, SIMSIMETH asks its corresponding ARP protocol for a dump of all hosts in its table. SIMSIMETH then sends the message to each of these hosts in a point-to-point fashion. Note that for a reasonable simulation of Ethernet broadcast, all x-kernels in communication should have the same ARP table (see the ARP appendix.)

The primary purpose of SIMSIMETH is to allow simulated x-kernels and native x-kernels to interoperate. This is possible because SIMSIMETH interoperates with the SIMETH protocol. Interoperability is achieved as follows. The graph.comp file for the simulated x-kernel is unchanged and is rooted at SIMETH the simulated Ethernet driver. The graph.comp for the machine running a native x-kernel must contain the same graph in the simulated version accept that SIMSIMETH is configured instead of SIMETH and SIMSIMETH is configured on top of the standard Internet protocol graph. If the following was the graph.comp on the SunOS simulator:

#SunOS Graph.comp
@;
name=simeth;
name=eth protocols=simeth;
name=arp protocols=eth; 
name=vnet protocols=eth,arp; 
name=ip protocols=vnet; 
name=udp protocols=ip;
name=udptest protocols=udp;
@;
prottbl = ../prottbl.simsimeth;

The corresponding graph for the native mode x-kernel would be:

#Mach 3.0 Graph.comp
@;
name=ethdrv/SE0;
name=eth/lower protocols=ethdrv/SE0;
name=arp/lower protocols=eth/lower;
name=vnet/lower protocols=eth/lower,arp/lower;
name=ip/lower protocols=vnet/lower;
name=icmp/lower protocols=ip/lower;
name=udp/lower protocols=ip/lower;
name=simsimeth protocols=udp/lower;
name=eth/upper protocols=simsimeth;
name=arp/upper protocols=eth/upper;
name=vnet/upper protocols=eth/upper,arp/upper;
name=ip/upper protocols=vnet/upper;
name=udp/upper protocols=ip/upper;
name=udptest protocols=udp/upper;
@;
prottbl = ../prottbl.simsimeth;

The /lower protocols in the above graph.comp correspond to the Internet protocol suite implemented in the SunOS kernel. The /upper protocols correspond the protocols running on the simulated x-kernel. Note that a user defined protocol table is needed. This is done because the protocol table must define the correct (800) relative ETH protocol id for IP for this technique to work. The default protocol table defined by the x-kernel defines the IP protocol number as 3900 to avoid interference when testing new protocols. Note also that if you use SIMSIMETH please make sure that your versions of UDP, IP, ARP, VNET, and ETH are at least as new as SIMSIMETH.

There must be a similar correspondence between the ROM files on the SunOS side and the native Mach 3.0 side. For example the following is an example ROM file for the SunOS platform:

simeth 9875
eth mtu 1400
arp 192.12.69.1 192.12.69.67 9875
arp 192.12.69.2 192.12.69.99 1234

While the following is an example ROM file for the Mach 3 platform:

arp/lower     192.12.69.99    08:00:2b:23:6d:ec # mozart 
simsimeth 1234
eth/upper mtu 1400
arp/upper 192.12.69.1 c0:0c:45:43:26:93 # translation:  192.12.69.67 9875
arp/upper 192.12.69.2 c0:0c:45:63:04:d2 # translation:  192.12.69.99 1234

The SunOS ROM file is identical to the standard ROM file except for the addition of a line to set the Ethernet MTU to 1400 bytes. If the default MTU of 1500 bytes were to be used SunOS IP would fragment the outgoing simulated Ethernet packets into two real Ethernet packets of 1500 bytes and 64 bytes respectively. This pattern of packets can result in a serious increase in the number of dropped packets. The MTU of the simulated Ethernet driver on the Mach platform (eth/upper) is also set to 1400 bytes to avoid the same problem. Note you should always manually set the MTU's of the simulated Ethernet drivers to the same number!

The ROM for Mach 3.0 must be changed to set the appropriate IP to Ethernet address correspondence for the real ARP (ARP/lower). While the simulated ARP (ARP/upper) must be configured with the same information as given in the SunOS ROM file. This is made more complex because ARP on Mach 3.0 platforms expects real Ethernet addresses while the ARP on the SunOS platform expects to find simulated Ethernet address. Therefore the user must manually convert a port IP address pair into an Ethernet address using the algorithm given above. For example the "Ethernet address": c0:0c:45:43:26:93 is simply the hex translation of 192.12.69.67 9875.

Note that when the client is started it should be passed the simulated IP address of the server (192.12.69.1or2) not the real IP address of the server.

Working graph.comp, ROM, and protocol table files can be found in the Template directory.

REALM
SIMSIMETH is in the ASYNC realm, supporting the Ethernet driver interface described in the ETH appendix.

PARTICIPANTS
SIMSIMETH supports the Ethernet driver interface rather than a standard xkernel UPI interface and thus makes no use of participant stacks.

CONTROL OPERATIONS

ETH_REGISTER_ARP:

Used by an ARP instantiation to register itself with its corresponding SIMSIMETH driver. This is used to simulate Ethernet broadcasts as described above. If no ARP protocol registers with a SIMSIMETH instantiation, broadcasts on that instantiation will not be possible.

Input:

XObj /* ARP protocol object */

Output:

none

EXTERNAL INTERFACE
SIMSIMETH supports the Ethernet driver interface described in the ETH appendix.

CONFIGURATION
SIMSIMETH should be configured on top of any protocol that takes UDP addresses and below any protocol which supports the ETH lower level driver interface. It can be configured in either the driver section or the protocol section of graph.comp.

SIMSIMETH recognizes the following ROM options:

simsimeth nnnn: This instantiation of simsimeth should use UDP port nnnn. There must be such a line for each instantiation of SIMSIMETH in the x-kernel.

AUTHOR
Sean O'Malley