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文章阅读:[转载] Wonderful World of Linux 2.4 (part VIII)
[版面: Linux 操作系统] [作者:ayanami] , 2000年11月26日17:55:07
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发信人: ayanami (发情的蚊子~甲亢中), 信区: Linux
标  题: [转载] Wonderful World of Linux 2.4 (part VIII)
发信站: The unknown SPACE (Sun Nov 26 17:55:07 2000), 转信

【 以下文字转载自 ITnews 讨论区 】
【 原文由 ayanami 所发表 】
Networking and Protocols

Networking and network hardware is one of the major areas
where Linux has always excelled. These devices are neither
"character" nor "block" but inhabit a special space free of
the need for device nodes. Linux 2.4 will include many
improvements to this layer including new drivers,bug fixes,
and new functionality added on to existing drivers.

The Linux model of network sockets is one which is standard
across most UNIX variants. Unfortunately however, the
standard does have some correctable deficiencies. Under
Linux 2.2 and previous versions,if you have a number of
processes all waiting on an event from a network socket (a
web server, for instance), they will all be woken up when
activity is detected. So, for every web page request
received, Linux would wake up a number of processes which
would each try and get at the request. As it does not make
sense for multiple processes to serve the same request, only
one will get to the data; the remainder will discover
nothing to process and fall back asleep. Linux is quite
efficient at making this all happen as quickly as possible,
however it could still be made more efficient by removing
the redundant wakeups. Linux 2.4 includes changes which
implement"wake one" under Linux which will allow us to
completely remove this "stampede effect" of multiple
processes. In short, "wake one" does exactly as its name
indicates: wakes up only one process in the case of
activity. This will allow applications such as Apache to be
even more efficient and make Linux an even better choice as
a web server.

Linux 2.4 also includes a completely rewritten networking
layer. In fact, it has been made as unserialized as possible
so that it will scale far better than any previous version
of Linux. Additionally, the entire subsystem has been
redesigned to be as stable as possible on multiprocessor
systems and many possible crashes have been eliminated. In
addition, it contains optimizations to allow it to work with
the particular quirks of the networking stacks in use in
many common operating systems, including Windows. It should
also be mentioned at this point that Linux is still the only
operating system completely compatible with the letter of
the IPv4 specification (Yes, IPv4; the one we've been using
all this time) and Linux 2.4 boasts an IPv4 implementation
that is much more scalable than its predecessor.

As part of this major rewrite, the firewall and IP
masquerading functionality of the kernel has been completely
rewritten again. (Older users may remember that these same
components were largely rewritten for Linux 2.2 also.) The
new subsystem has been split into two parts: a packet
filtering layer and a network address translation (NAT)
layer. These new subsystems are considerably more generic
than their predecessors, and it is now possible to do most
types of sophisticated (level 3) routing through any Linux
box. Previously, this kind of functionality was largely only
available with dedicated and proprietary routing hardware.
Unfortunately, this major rewrite also includes yet another
new userspace tool to manage the available functionality.
For compatibility, modules exist which will allow you to use
either the Linux 2.0 (ipfwadm) or Linux 2.2 (ipchains) tools
without a major loss of functionality. This will make the
upgrade from either of these kernel versions relatively
seamless.

One major new extension that has now been added to Linux's
networking stack is ECN, Explicit Congestion Notification.
In a nutshell, ENC allows compliant routers to notify a
Linux box that a route is congested. Linux will then respond
by reducing the speed at which packets are being sent. In
the long run, this will allow Linux boxes to drop less
packets over the congested routes and not spend as much time
or bandwidth with dropped packets and retransmits.

For Enterprise-level users, there are a number of features
that will better enable Linux to integrate into older and
newer components of existing network infrastructures. One
important addition in this respect is Linux 2.4's new
(partial) support for the DECNet and ARCNet protocols and
hardware. This allows for better interoperation with
specialized systems, including older Digital/Compaq ones.
Also of special interest to this class of users, Linux 2.4
will include support for ATM network adapters for high-speed
networking.

For the low-end desktop users, PPP is an important part of
day to day life. Linux 2.4 includes some major rewrites and
modularization of much of the code, including a long awaited
combination of the PPP layers from the ISDN layer and the
serial device PPP layer, such as for dial-up connections
with modems. In addition to the modularity, ISDN has been
updated to support many new cards. The PLIP (PPP over
parallel ports) layer has also been improved and uses the
new parallel port abstraction layer. And finally, PPP over
Ethernet (PPPoE, used by some DSL providers) support has
been added to the kernel.

Although not present in Linux 2.4, there is work now on
supporting the NetBEUI protocol used by MS operating
systems. While Microsoft will be moving away from this
protocol in its products and towards TCP/IP, this protocol
is still important for a number of Windows-based network
environments.(Previously, kernel developers had commented
that the protocol is too convoluted and buggy to be
supported in the kernel. Now that an implementation has
surfaced, it remains to be seen whether it will be stable
enough to ever be in an official kernel.)


--
Linux is only free when your time has no value
                                - JWZ

※ 来源:.The unknown SPACE bbs.mit.edu.[FROM: 167.95.252.64.s]
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※ 转载:.The unknown SPACE bbs.mit.edu.[FROM: 64.252.95.167]

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