flow-control

TCP 数据传输 TCP 的数据传输分为两种，一种是交互式数据，一种是块数据，交互式数据如 Telnet ，一般都是小于 10 个字节的分组，而成块数据如 FTP 传输文件，基本都是大于 512 字节的报文，对于这两种数据， TCP 的处理机制是不一样的，算法也不相同，下面是一个 telnet 的抓包，由于此处讨论的主要是交互数据，而不是 telnet 协议，因此抓包主要集中在交互上 CentOS release 5.3 (Final) Kernel 2.6.18-128.el5 on an x86_64 login: qa Password: Last login: Fri May 13 15:35:27 from 10.103.51.142 [qa@hding ~]$ ls Desktop hello socat-1.7.3.0.tar.gz [qa@hding ~]$ #ls 1. IP 10.103.51.142.57545 > 10.8.116.6.telnet: P 73:74(1) ack 199 win 16375 C->S ‘l’ 2. IP 10.8.116.6.telnet > 10.103.51.142.57545: P 199:200(1) ack 74 win 46 S->C ‘l’ 3. IP 10.103.51.142.57545 > 10.8

I have recently stumbled over a seeming inconsistency in Python's way of dealing with else clauses in different compound statements. Since Python is so well designed, I'm sure that there is a good explanation, but I can't think of it. Consider the following: if condition: do_something() else: do_something_else() Here, do_something_else() is only executed if condition is false, as expected. Similarly, in try: do_something() except someException: pass: else: do_something_else() finally: cleanup() do_something_else() is only executed if no exception occurred. But in for or while loops, an else

I consider it bad style to use try: except: for flow control, but I can't figure out how to write the following code to test if a DB field in Django exists. This is the "dirty" code which works: @receiver(pre_save, sender=UserProfile) def create_user_profile(sender, instance=None, **kwargs): try: print str(instance.bank_account) except: print 'No account' I would rather wanna do something like this, but I get an exception when the if statement is run and the object does not exist: @receiver(pre_save, sender=UserProfile) def create_user_profile(sender, instance=None, **kwargs): if instance.bank

Possible Duplicate: for vs each in Ruby Let's say that we have an array, like sites = %w[stackoverflow stackexchange serverfault] What's the difference between for x in sites do puts x end and sites.each do |x| puts x end ? They seem to do the same exact thing, to me, and the syntax of the for loop is clearer to me. Is there a difference? In what situations would this be a big deal? There is a subtle difference regarding scoping, but I would recommend understanding it well as it reveals some of important aspects of Ruby. for is a syntax construct, somewhat similar to if . Whatever you define

This question already has an answer here: TCP - difference between Congestion window and Receive window 2 answers What is the difference and connection between sliding window in flow control and congestion window in congestion control? I think both are the control size for transmitting, but what are the difference? I do not quite get the difference between flow control and congestion control too. Manoj Pandey Congestion window and flow-control are different features of TCP and their input is fed to the sliding window. The congestion-window is based on an estimation of the network sending rate.