The OpenNET Project / Index page

[ новости /+++ | форум | теги | ]

Интерактивная система просмотра системных руководств (man-ов)

 ТемаНаборКатегория 
 
 [Cписок руководств | Печать]

ng_vjc (4)
  • >> ng_vjc (4) ( FreeBSD man: Специальные файлы /dev/* )

  • BSD mandoc
     

    NAME

    
    
    ng_vjc
    
     - Van Jacobson compression netgraph node type
    
     
    

    SYNOPSIS

       #include <sys/types.h>
       #include <netinet/in.h>
       #include <netinet/in_systm.h>
       #include <netinet/ip.h>
       #include <net/slcompress.h>
       #include <netgraph/ng_vjc.h>
     

    DESCRIPTION

    The vjc node type performs Van Jacobson compression, which is used over PPP, SLIP, and other point-to-point IP connections to compress TCP packet headers. The ip hook represents the uncompressed side of the node, while the vjcomp vjuncomp and vjip hooks represent the compressed side of the node. Packets received on the ip will be compressed or passed through as appropriate. Packets received on the other three hooks will be uncompressed as appropriate. This node also supports ``always pass through'' mode in either direction.

    Van Jacobson compression only applies to TCP packets. Only ``normal'' (i.e., common case) TCP packets are actually compressed. These are output on the vjcomp hook. Other TCP packets are run through the state machine but not compressed; these appear on the vjuncomp hook. Other non-TCP IP packets are forwarded unchanged to vjip

    When connecting to a ng_ppp4 node, the ip vjuncomp vjcomp and vjip hooks should be connected to the ng_ppp4 node's vjc_ip vjc_vjcomp vjc_vjuncomp and vjc_ip hooks, respectively.  

    HOOKS

    This node type supports the following hooks:

    ip
    Upstream (uncompressed) IP packets.
    vjcomp
    Downstream compressed TCP packets.
    vjuncomp
    Downstream uncompressed TCP packets.
    vjip
    Downstream uncompressed IP packets.

     

    CONTROL MESSAGES

    This node type supports the generic control messages, plus the following:

    NGM_VJC_SET_CONFIG
    This command resets the compression state and configures it according to the supplied struct ngm_vjc_config argument. This structure contains the following fields:
    struct ngm_vjc_config {
      u_char   enableComp;    /* Enable compression */
      u_char   enableDecomp;  /* Enable decompression */
      u_char   maxChannel;    /* Number of outgoing channels - 1 */
      u_char   compressCID;   /* OK to compress outgoing CID's */
    };
    

    When enableComp is set to zero, all packets received on the ip hook are forwarded unchanged out the vjip hook. Similarly, when enableDecomp is set to zero, all packets received on the vjip hook are forwarded unchanged out the ip hook, and packets are not accepted on the vjcomp and vjuncomp hooks. When a node is first created, both compression and decompression are disabled and the node is therefore operating in bi-directional ``pass through'' mode.

    When enabling compression, maxChannel should be set to the number of outgoing compression channels minus one, and is a value between 3 and 15, inclusive. The compressCID field indicates whether it is OK to compress the CID header field for outgoing compressed TCP packets. This value should be zero unless either (a) it is not possible for an outgoing frame to be lost, or (b) lost frames can be reliably detected and immediately reported to the peer's decompression engine (see NGM_VJC_RECV_ERROR below).

    NGM_VJC_GET_STATE
    This command returns the node's current state described by the struct slcompress structure, which is defined in In net/slcompress.h .
    NGM_VJC_CLR_STATS
    Clears the node statistics counters. Statistics are also cleared whenever the enableComp or enableDecomp fields are changed from zero to one by a NGM_VJC_SET_CONFIG control message.
    NGM_VJC_RECV_ERROR
    When the peer has CID header field compression enabled, this message must be sent to the local vjc node immediately after detecting that a received frame has been lost, due to a bad checksum or for any other reason. Failing to do this can result in corrupted TCP stream data.

     

    SHUTDOWN

    This node shuts down upon receipt of a NGM_SHUTDOWN control message, or when all hooks have been disconnected.  

    SEE ALSO

    netgraph(4), ng_iface4, ng_ppp4, ngctl(8)
    V. Jacobson "Compressing TCP/IP Headers" RFC 1144
    G. McGregor "The PPP Internet Control Protocol (IPCP)" RFC 1332
     

    HISTORY

    The node type was implemented in Fx 4.0 .  

    AUTHORS

    An Archie Cobbs Aq [email protected]  

    BUGS

    As the initialization routine in the kernel implementation of Van Jacobson compression initializes both compression and decompression at once, this node does not allow compression and decompression to be enabled in separate operations. In order to enable one when the other is already enabled, first both must be disabled, then both enabled. This of course resets the node state. This restriction may be lifted in a later version.

    When built as a loadable kernel module, this module includes the file net/slcompress.c Although loading the module should fail if net/slcompress.c already exists in the kernel, currently it does not, and the duplicate copies of the file do not interfere. However, this may change in the future.


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    HOOKS
    CONTROL MESSAGES
    SHUTDOWN
    SEE ALSO
    HISTORY
    AUTHORS
    BUGS


    Поиск по тексту MAN-ов: 




    Партнёры:
    PostgresPro
    Inferno Solutions
    Hosting by Hoster.ru
    Хостинг:

    Закладки на сайте
    Проследить за страницей
    Created 1996-2024 by Maxim Chirkov
    Добавить, Поддержать, Вебмастеру