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[lwip-users] TCP Window and Memory Allocation


From: Caglar Akyuz
Subject: [lwip-users] TCP Window and Memory Allocation
Date: Wed, 30 May 2007 10:35:22 +0300
User-agent: Thunderbird 1.5.0.8 (X11/20060911)

Hi,

When I was playing with my lwipopts.h file, I realized that increasing
TCP_WND size does not effect my memory allocation. Is this the case?

If it is, then what should I do to assure correct operation for the
stack? I think I should adjust my memory allocation accordingly, but I
don't know what should be the policy. How much memory should I allocate
for a given size of TCP Window?

Excuse me if I'm asking something trivial but I'm having hard-time
understanding lwIP's memory allocation scheme on my embedded system.

Kind Regards
Caglar Akyuz

P.S: I'm attaching my options file for convenience.


=======================================================================================


#ifndef __LWIPOPTS_H__
#define __LWIPOPTS_H__

#define LWIP_NOASSERT 1 // To suppress some errors for now (no debug output)
#define SYS_LIGHTWEIGHT_PROT            1

#define TCPIP_THREAD_PRIO       3

/* ---------- Memory options ---------- */
/* MEM_ALIGNMENT: should be set to the alignment of the CPU for which
   lwIP is compiled. 4 byte alignment -> define MEM_ALIGNMENT to 4, 2
   byte alignment -> define MEM_ALIGNMENT to 2. */
#define MEM_ALIGNMENT           4

/* MEM_SIZE: the size of the heap memory. If the application will send
a lot of data that needs to be copied, this should be set high. */
#define MEM_SIZE                2000

/* MEMP_NUM_PBUF: the number of memp struct pbufs. If the application
   sends a lot of data out of ROM (or other static memory), this
   should be set high. */
#define MEMP_NUM_PBUF           5
/* MEMP_NUM_UDP_PCB: the number of UDP protocol control blocks. One
   per active UDP "connection". */
#define MEMP_NUM_UDP_PCB        4
/* MEMP_NUM_TCP_PCB: the number of simulatenously active TCP
   connections. */
#define MEMP_NUM_TCP_PCB        10
/* MEMP_NUM_TCP_PCB_LISTEN: the number of listening TCP
   connections. */
#define MEMP_NUM_TCP_PCB_LISTEN 8
/* MEMP_NUM_TCP_SEG: the number of simultaneously queued TCP
   segments. */
#define MEMP_NUM_TCP_SEG        8
/* MEMP_NUM_SYS_TIMEOUT: the number of simulateously active
   timeouts. */
#define MEMP_NUM_SYS_TIMEOUT    3


/* The following four are used only with the sequential API and can be
   set to 0 if the application only will use the raw API. */
/* MEMP_NUM_NETBUF: the number of struct netbufs. */
#define MEMP_NUM_NETBUF         4
/* MEMP_NUM_NETCONN: the number of struct netconns. */
#define MEMP_NUM_NETCONN        4
/* MEMP_NUM_APIMSG: the number of struct api_msg, used for
   communication between the TCP/IP stack and the sequential
   programs. */
#define MEMP_NUM_API_MSG        8
/* MEMP_NUM_TCPIPMSG: the number of struct tcpip_msg, which is used
   for sequential API communication and incoming packets. Used in
   src/api/tcpip.c. */
#define MEMP_NUM_TCPIP_MSG      8

/* These two control is reclaimer functions should be compiled
   in. Should always be turned on (1). */
#define MEM_RECLAIM             1
#define MEMP_RECLAIM            1

/* ---------- Pbuf options ---------- */
/* PBUF_POOL_SIZE: the number of buffers in the pbuf pool. */
#define PBUF_POOL_SIZE          8

/* PBUF_POOL_BUFSIZE: the size of each pbuf in the pbuf pool. */
#define PBUF_POOL_BUFSIZE       2048

/* PBUF_LINK_HLEN: the number of bytes that should be allocated for a
   link level header. */
#define PBUF_LINK_HLEN          16

/* ---------- TCP options ---------- */
#define LWIP_TCP                1
#define TCP_TTL                 255

/* Controls if TCP should queue segments that arrive out of
   order. Define to 0 if your device is low on memory. */
#define TCP_QUEUE_OOSEQ         1

/* TCP Maximum segment size. */
#define TCP_MSS                 1490

/* TCP sender buffer space (bytes). */
#define TCP_SND_BUF             4 * TCP_MSS

/* TCP sender buffer space (pbufs). This must be at least = 2 *
   TCP_SND_BUF/TCP_MSS for things to work. */
#define TCP_SND_QUEUELEN        6 * TCP_SND_BUF/TCP_MSS

/* TCP receive window. */
#define TCP_WND                 10000

/* Maximum number of retransmissions of data segments. */
#define TCP_MAXRTX              12

/* Maximum number of retransmissions of SYN segments. */
#define TCP_SYNMAXRTX           4

/* ---------- ARP options ---------- */
#define ARP_TABLE_SIZE 10
#define ARP_QUEUEING 1

/* ---------- IP options ---------- */
/* Define IP_FORWARD to 1 if you wish to have the ability to forward
   IP packets across network interfaces. If you are going to run lwIP
   on a device with only one network interface, define this to 0. */
#define IP_FORWARD              1

/* If defined to 1, IP options are allowed (but not parsed). If
   defined to 0, all packets with IP options are dropped. */
#define IP_OPTIONS              1

/* ---------- ICMP options ---------- */
#define ICMP_TTL                255


/* ---------- DHCP options ---------- */
/* Define LWIP_DHCP to 1 if you want DHCP configuration of
   interfaces. DHCP is not implemented in lwIP 0.5.1, however, so
   turning this on does currently not work. */
#define LWIP_DHCP               0

/* 1 if you want to do an ARP check on the offered address
   (recommended). */
#define DHCP_DOES_ARP_CHECK     1

/* ---------- UDP options ---------- */
#define LWIP_UDP                1
#define UDP_TTL                 255


/* ---------- Statistics options ---------- */
#define STATS

#ifdef STATS
#define LINK_STATS 0
#define IP_STATS   0
#define ICMP_STATS 0
#define UDP_STATS  0
#define TCP_STATS  0
#define MEM_STATS  0
#define MEMP_STATS 0
#define PBUF_STATS 0
#define SYS_STATS  0
#endif /* STATS */

#define LWIP_PROVIDE_ERRNO 1

#endif /* __LWIPOPTS_H__ */


=======================================================================================




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