Comparing VoFR and VoIP Packet Overhead

The main handicap is the greater packet overhead required by IP. Both FR and IP packets are constructed with packet header information, voice/fax header information, and the digitized, compressed voice and fax information (the payload).
Each payload represents a fragment of speech called a ‘talk spurt.’ Representing a long talk spurt requires the VDID (Voice/Data Integration Device) to accumulate the speech information over an extended period of time, and possibly introducing delay into the conversation. Conversations with added delay sound unnatural and cause the corporate telephony user to bypass the VDN (Voice/Data Network), defeating any hoped-for cost savings. This delay-limiting requirement dictates a maximum talk spurt size for voice (and consequently, fax) of 50 bytes at a compressed data rate of 8Kbps (1000 bytes per second, or one byte per millisecond). Fifty bytes represent 50 milliseconds of speech activity, the longest practical period without contributing too much to the overall delay.
Tables A and B show the bandwidth consumed in Kbps for FR and IP telephony packets. The speech compression CODEC is assumed to need 8Kbps. The sum of the CODEC bandwidth and the packet overhead is the peak bandwidth consumed by an active conversation. The peak only occurs for a few seconds and is replaced by 0Kbps during the natural periods of silence in a typical conversation. While one person talks, the other listens, yielding silence about 50% of the time over a 20-30 second period. Pauses and interruptions in the conversation contribute another 10%. The net bandwidth consumption averaged over the 20-30 second period is about 40% of the peak bandwidth.
The method in which silence suppression is implemented can affect both the perception of voice quality and bandwidth consumed. Absence of sound is often perceived as a broken connection because the listener is accustomed to hearing a certain minimal level of background noise or ‘comfort noise’. There are two methods of solving this problem. The first is to inject white noise generated by the VDID at either end of the connection to let the listener know that the connection is alive. The advantage of this method is that it does not consume any bandwidth over the WAN link. However, it results in a reduced level of perceived voice quality. The other method involves actually sampling the background noise. This method produces a significant improvement in voice quality, but consumes more bandwidth. The way that the comfort noise feature is implemented differs with each vendor and can often be configured by the network manager. Bandwidth consumption can vary from 0 to 2Kbps, plus overhead.

COMPARING VoFR AND VoIP PACKET TECHNOLOGIES

There are four main areas of material differences between VoIP and VoFR packet management technologies:
· Packet overhead
· WAN access-line carrying capacities and associated cost implications
· Packet prioritization
· Packet segmentation or fragmentation and its effect on data packet sizes

Each area of difference presents more of a challenge to the VoIP gateway approach than the VoFR approach, both because VoFR is more mature and because VoIP has a few inherent technological handicaps.

What is Packet Data Networks

There are a several different types of wide area packet data networks that can support integrated voice/fax traffic, with varying degrees of success. The principal data network technologies in use today are X.25, Frame Relay, ATM, SNA, Novell/IPX, TDM, and TCP/IP. Because TDM is not a packet technology, it is much less efficient than the other technologies, and is rapidly being replaced by them. X.25 and SNA, based on older packet technologies, are too slow and delay-prone to effectively carry voice and fax traffic. The Novell/IPX technology was designed primarily for LAN applications and does poorly in the WAN environment; it is quickly being replaced by TCP/IP.


The remaining packet technologies – Frame Relay, ATM, and TCP/IP – are the principal networking techniques companies use today to build new wide area data networks. Today’s WANs are constructed using leased lines running these three technologies, and using public data network services based on them. By a substantial margin, Frame Relay and TCP/IP are used the most, both over leased lines and as public data services.


ATM, Frame Relay, and TCP/IP are each able to carry voice and fax traffic. ATM has been designed from the beginning to carry voice/fax traffic, while Frame Relay and TCP/IP were originally designed to carry only data. Because adding voice and fax to Frame Relay and TCP/IP has been an ‘after market’ activity, there are areas of caution and even concern that must be addressed when building integrated WANs using Frame Relay or TCP/IP.

Network Address Translation (NAT)

Network Address Translation (NAT)
• NAT is a router function where IP addresses (and possibly
port numbers) of IP datagrams are replaced at the boundary
of a private network
• NAT is a method that enables hosts on private networks to
communicate with hosts on the Internet
• NAT is run on routers that connect private networks to the
public Internet, to replace the IP address-port pair of an IP
packet with another IP address-port pair.

Microsoft Excel Cheat Sheet

Error Codes
1. #VALUE! – Wrong type of data.
2. #NAME? – Incorrect function name.
3. #NUM – Problem with one of the numbers you’re using.
4. #REF! – Incorrect cell reference.
5. ##### - Formula cannot be displayed in the cell using the current number format.
Math and Statistical Functions
1. ROUND( number to round, #of digits)
a) (3.987, 2) = 3.99
b) (3.987, 0) = 4
c) (34655.7, -2) = 34,700
2. ROUNDDOWN
a) (1.1, 0) = 2
3. ROUNDDOWN
a) (1.9, 0) = 1
4. MROUND (number to round, multiple)
a) (653, 5) = 655
5. COUNT – Find out how many items there are in a list.
6. COUNTBLANK – Counts the number of empty cells in a specified range of cells.
7. RANK – Returns the rank of a number in a list of numbers: its size relative to the other
values in the list.
8. REPT – Repeats text a given number of times.
9. SQRT – Returns the square root of a number.
10.STDEV – Estimates the standard deviation of a sample.
11.PERMUT – Returns the number of permutations for a given number of objects that can
be selected from the total objects.
12. COMBIN – Returns the number of combinations for a given number of items.
13.WEEKDAY – The WEEKDAY function takes a date, and returns a number that
represents which day of the week that date falls on. For example, if the date occurs on
Sunday, the number’s 1, on Monday it’s 2, right up to Saturday, which is 7.
a. WEEKDAY( date, (return-type)
I. (DATE (2007, 1, 6) = 7.
14.MAX ( ), MIN ( ) – “ pick the largest or smallest value out of a series of cells.
15. LARGE, SMALL – (range, position)

HOw Virus Load in System

AppInit_DLLs: All the DLLs that are specified in this value are loaded by each Microsoft Windows-based application that is running in the current log on session. The AppInit DLLs are loaded by using the LoadLibrary() function during the DLL_PROCESS_ATTACH process of User32.dll. Therefore, executables that do not link with User32.dll do not load the AppInit DLLs. Therefore one of the 16 imports was user32.dll (Import table (libraries: 16))Because of their early loading, only API functions that are exported from Kernel32.dll are safe to use in the initialization of the AppInit DLLs. So murka.dat registers itself in the "AppInit_DLLs" as a load point for the beep.sys so that every time the computer starts, the RootKit driver can load itself with the kernel...

Example:
Trojan.Virantix.B---------------------------------------------------------------------------------------------------------------------------------------------When the Trojan is executed, it creates following files:%System%\user32.dat%Windir%\medichi.exe%Windir%\medichi2.exe%Windir%\murka.datIt then overwrites following files:%System%\beep.sys %System%\dllcache\beep.sys <---- Actual driver that later on uses RootKit feature to hide the process medichi.exe Next, the Trojan creates the following registry entries so that it executes whenever Windows starts:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\"AppInit_DLLs" = "%Windir%\murka.dat"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\"Medichi" = %Windir%\medichi.exe"HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\"Medichi2" = "%Windir%\medichi2"It then hooks the following API and hides itself: <--- RootKit activityZwQuerySystemInformation <--- Hooks the Native subsystems funftion callThe Trojan then connects to the following location, which displays a fake security alert:hxxp://gomyhit.com/MTc3MTY=/2/6018/852/It also opens the following URL, which may contain another program:hxxp://81.13.38.39/alerThe Trojan monitors the browser on the compromised computer and steals search keywords that can be used on certain search engines and submits it to following remote location:hxxp://werdagoniotu.com/searcIt attempts to download updates of itself from the following locations:hxxp://globalmenu.net/1/serthxxp://softinfoway.info/1/serthxxp://getupdate.info/1/sert

Live Match Score Card Pakistan Vs SriLanka

SL: 138/6 (20.0 Ovs)
Angelo Mathews *
35(24)
Kumar Sangakkara
65(52)
Pak
Umar Gul *
4-0-30-1
Mohammad Aamer
4-1-30-1
RR : 6.90 Curr P'ship: 68(43)
Last Wkt: Isuru Udana b Afridi 1(5) - 70/6 in 12.6 ov.
Prev Ovs: 4 1 2 1 N1 1 4 . . 1 4 1 4 1 4 1 1 . 1 2 4 6 2 1 2