+#include <net/slcompress.h>
+#include <net/if_slvar.h>
+
+/*
+ * SLMAX is a hard limit on input packet size. To simplify the code
+ * and improve performance, we require that packets fit in an mbuf
+ * cluster, and if we get a compressed packet, there's enough extra
+ * room to expand the header into a max length tcp/ip header (128
+ * bytes). So, SLMAX can be at most
+ * MCLBYTES - 128
+ *
+ * SLMTU is a hard limit on output packet size. To insure good
+ * interactive response, SLMTU wants to be the smallest size that
+ * amortizes the header cost. (Remember that even with
+ * type-of-service queuing, we have to wait for any in-progress
+ * packet to finish. I.e., we wait, on the average, 1/2 * mtu /
+ * cps, where cps is the line speed in characters per second.
+ * E.g., 533ms wait for a 1024 byte MTU on a 9600 baud line. The
+ * average compressed header size is 6-8 bytes so any MTU > 90
+ * bytes will give us 90% of the line bandwidth. A 100ms wait is
+ * tolerable (500ms is not), so want an MTU around 296. (Since TCP
+ * will send 256 byte segments (to allow for 40 byte headers), the
+ * typical packet size on the wire will be around 260 bytes). In
+ * 4.3tahoe+ systems, we can set an MTU in a route so we do that &
+ * leave the interface MTU relatively high (so we don't IP fragment
+ * when acting as a gateway to someone using a stupid MTU).
+ *
+ * Similar considerations apply to SLIP_HIWAT: It's the amount of
+ * data that will be queued 'downstream' of us (i.e., in clists
+ * waiting to be picked up by the tty output interrupt). If we
+ * queue a lot of data downstream, it's immune to our t.o.s. queuing.
+ * E.g., if SLIP_HIWAT is 1024, the interactive traffic in mixed
+ * telnet/ftp will see a 1 sec wait, independent of the mtu (the
+ * wait is dependent on the ftp window size but that's typically
+ * 1k - 4k). So, we want SLIP_HIWAT just big enough to amortize
+ * the cost (in idle time on the wire) of the tty driver running
+ * off the end of its clists & having to call back slstart for a
+ * new packet. For a tty interface with any buffering at all, this
+ * cost will be zero. Even with a totally brain dead interface (like
+ * the one on a typical workstation), the cost will be <= 1 character
+ * time. So, setting SLIP_HIWAT to ~100 guarantees that we'll lose
+ * at most 1% while maintaining good interactive response.
+ */
+#define BUFOFFSET 128
+#define SLMAX (MCLBYTES - BUFOFFSET)
+#define SLBUFSIZE (SLMAX + BUFOFFSET)
+#define SLMTU 296
+#define SLIP_HIWAT roundup(50,CBSIZE)
+#define CLISTRESERVE 1024 /* Can't let clists get too low */
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