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Easy Learn Java: Programming Articles, Examples and Tips - Page 203


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In Socket class exists method ''getOOBInline'' that checks if OOBINLINE is enabl

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Question: In Socket class exists method "getOOBInline" that checks if OOBINLINE is enabled. What is "OOBINLINE" and can I do with it?

Answer: OOB stands for Out-Of-Band Data.

The TCP/IP protocol allows users to send data asynchronously, otherwise known as OUT-OF-BAND data. When using this feature, the operating system interrupts the receiving process if this process has chosen to be notified about out-of-band data. The receiver can grab this input without affecting any information currently queued on the socket.
Therefore, you can use this without interfering with any current activity due to other wire and remote interfaces.

Unfortunately, most implementations of TCP/IP are broken, so use of out-of-band data is limited for safety reasons. You can only reliably send one character at a time.
What is about safety? Let's look at this scenario: While a server is working on a task, the server is sensitive to interrupts. An interrupt will cause the server to abort the current task and begin listening for new instructions.
Interrupts can be sent to the server by sending an interrupt ("INT") to the process number of the server with the Unix kill command. The server socket will also raise an interrupt if out of band (OOB) data are received. Thus, the client can send a single arbitrary byte of OOB data to generate an interrupt. So, if someone will send much OOB data to a server it can seriously decrease performance of server...

On one of hackers web sites I found "OOB Attack Program" that described like this:
"This is a good program that exploits the oob attack on port 139 of any Windows machine running MS TCP/IP.
Allows for multiple IP addresses to be attacked.
Coded for fun by: Hiro Protagonist "

If you are developing a server that will be exposed to Internet remember that some people "for fun" can take it down because OOBINLINE is enabled.


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16 comments | Printer Friendly Page  Send to a Friend | Score: 4
Posted by jalex on Tuesday, May 18, 2004 (00:00:00) (5744 reads)

Does Java support QoS (Quality of Service) for packets that are sent over the In

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Question: Does Java support QoS (Quality of Service) for packets that are sent over the Internet?

Answer: Yes, Java supports although it also depends on network configuration...
Paths through the Internet vary widely in the quality of service they provide. Some paths are more reliable than others. Some impose high call setup or per-packet charges, while others do not do usage-based charging. Throughput and delay also vary widely. Often there are tradeoffs: the path that provides the highest throughput may well not be the one that provides the lowest delay or the lowest monetary cost. Therefore, the "optimal" path for a packet to follow through the Internet may depend on the needs of the application and its user.

Because the Internet itself has no direct knowledge of how to optimize the path for a particular application or user, the IP protocol provides a (rather limited) facility for upper layer protocols to convey hints to the Internet Layer about how the tradeoffs should be made for the particular packet. This facility is the "Type of Service" facility, abbreviated as the "TOS facility" here.
Although the TOS facility has been a part of the IP specification since the beginning, it has been little used in the past. However, the Internet host specification now mandates that hosts use the TOS facility. Additionally, routing protocols (including OSPF and Integrated IS-IS) have been developed which can compute routes separately for each type of service. These new routing protocols make it practical for routers to consider the requested type of service when making routing decisions.

So, in Java you can try use the method setTrafficClass(int tc) of Socket class. As the underlying network implementation may ignore this value applications should consider it a hint.
For Internet Protocol v4 the value consists of an octet with precedence and TOS fields as detailed in RFC 1349. The TOS field is bitset created by bitwise-or'ing values such the following:-

IPTOS_LOWCOST (0x02)
IPTOS_RELIABILITY (0x04)
IPTOS_THROUGHPUT (0x08)
IPTOS_LOWDELAY (0x10)
read more in RFC 1349 and Java API


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7 comments | Printer Friendly Page  Send to a Friend | Score: 0
Posted by jalex on Thursday, May 13, 2004 (00:00:00) (5203 reads)

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