IEEE 802.11 is a set of standards for wireless local area network (WLAN) computer communication. The terms 802.11 and Wi-Fi are often used interchangeably but there is slight difference between the two.
(A) 802.11a
Frequency- 5 GHz
Typical Data Rate - 23 Mbit/s
Max Data rate – 54 Mbit/s
Range – 115 feet
(B) 802.11b
Frequency - 2.4 GHz
Typical Data Rate - 4.5 Mbit/s
Max Data rate – 11 Mbit/s
Range - 115 feet
(G) 802.11g
Frequency - 2.4 GHz
Typical Data Rate – 19 Mbit/s
Max Data rate - 54 Mbit/s
Range – 125 feet
(N) 802.11n
Frequency - 5GHz and/or 2.4GHz
Typical Data Rate - 74 Mbit/s
Max Data rate - 300 Mbit/s (2 streams)
Range – 230 feet
Thursday, October 20, 2011
Monday, January 31, 2011
How nice are you ?
"If you can't say something nice, don't say anything at all."
We've all heard this saying. It's something our parents reminded us of constantly. In fact, you may very well be cautioning your own children.
Now that you realize how hurtful words can be to others, have you every thought about the effects your own comments have on your self-esteem? Do you ever hear yourself saying nasty things about someone-that someone being you?
No one likes to be called "lazy, " "stupid," or "fat," and calling ourselves these names has a damaging effect on our self-worth. So today, take your own advice and the next time you begin to say something bad about yourself, try to stop. Instead of pointing out how little you have accomplished, why not acknowledge what you have achieved? And try replacing words like "I can't" and "I won't" with "I can" and "I will".
Being churlish never served us when we were young, and that is still true. Be kind to yourself.
We've all heard this saying. It's something our parents reminded us of constantly. In fact, you may very well be cautioning your own children.
Now that you realize how hurtful words can be to others, have you every thought about the effects your own comments have on your self-esteem? Do you ever hear yourself saying nasty things about someone-that someone being you?
No one likes to be called "lazy, " "stupid," or "fat," and calling ourselves these names has a damaging effect on our self-worth. So today, take your own advice and the next time you begin to say something bad about yourself, try to stop. Instead of pointing out how little you have accomplished, why not acknowledge what you have achieved? And try replacing words like "I can't" and "I won't" with "I can" and "I will".
Being churlish never served us when we were young, and that is still true. Be kind to yourself.
Wednesday, December 15, 2010
Tuesday, November 23, 2010
Thanksgiving Quotes
Best of all is it to preserve everything in a pure, still heart, and let there be for every pulse a thanksgiving, and for every breath a song.
- Konrad von Gesner
How wonderful it would be if we could help our children and grandchildren to learn thanksgiving at an early age. Thanksgiving opens the doors. It changes a child's personality. A child is resentful, negative-or thankful. Thankful children want to give, they radiate happiness, they draw people.
- Sir John Templeton
In the past I always thought of gratitude as a spontaneous response to the awareness of gifts received, but now I realize that gratitude can also be lived as a discipline. The discipline of gratitude is the explicit effort to acknowledge that all I am and have is given to me as a gift of love, a gift to be celebrated with joy.
- Henri J. M. Nouwen
As we express our gratitude, we must never forget that the highest appreciation is not to utter words, but to live by them.
- John Fitzgerald Kennedy
- Konrad von Gesner
How wonderful it would be if we could help our children and grandchildren to learn thanksgiving at an early age. Thanksgiving opens the doors. It changes a child's personality. A child is resentful, negative-or thankful. Thankful children want to give, they radiate happiness, they draw people.
- Sir John Templeton
In the past I always thought of gratitude as a spontaneous response to the awareness of gifts received, but now I realize that gratitude can also be lived as a discipline. The discipline of gratitude is the explicit effort to acknowledge that all I am and have is given to me as a gift of love, a gift to be celebrated with joy.
- Henri J. M. Nouwen
As we express our gratitude, we must never forget that the highest appreciation is not to utter words, but to live by them.
- John Fitzgerald Kennedy
Monday, August 23, 2010
Affirmation:
8/25:
"Qualities you see in others, reveal something about you."
You may not realize it, but the characteristics you like or dislike in others delivers a special message.
If you respond to a person that you see as outgoing, positive and energetic, these are most likely qualities you possessed, but have not fully embraced or developed. Likewise, if you react to the overbearing nature of another, then do a self check,you may have tendency to be overbearing yourself.
Either way, turn into what you do and don't admire in others. Take notes of your emotion response. With this new found awareness you can't help but discover something you didn't know about yourself.
Today's affirmation:The qualities I respond to in others reflect who I am.
8/26:
I will waste not even a precious second today in anger or hate or jealousy or selfishness. I know that the seeds I sow I will harvest, because every action, good or bad, is always followed by an equal reaction. I will plant only good seeds this day.
-Og Mandino 1923-1996, Author and Speaker
9/17:
"Happiness is not the destination."
Many people slog for a lifetime looking for happiness. They feel guilty doing things they enjoy. So they take care of their jobs, their families and their children thinking that the time for happiness will come later. In the end, they discover that it doesn't.
Believe that you deserve happiness right now!
You know those early hours in the morning when the house is quiet and the mist is floating outside the window? That is happiness. Remember how it felt to hold your baby for the first time? That is happiness. Remember how you felt when you achieved what seemed like an impossible goal? That is happiness.
Do not defer your happiness to a later date. Find joy in what you do every day.
Today's affirmation: I deserve to be happy right now.
10/5
"Admit your mistake! It's your most empowering choice."
We all make mistakes. It's a fact of life. What matters is what you do afterward.
You have a choice. You can let your mistake torment you, embarrass you, and hold you back. Or, you can admit you made a mistake, learn from it, and move on.
Mistakes are lessons in disguise. You can learn something from each and every one. Next time, you make a mistake, act quickly and decisively. Take responsibility and look for the lesson. Use the lesson to reach greater success and good fortune in your life.
Learn from your mistakes. Only then can they empower you to greater heights.
Today's affirmation: I admit my mistakes and learn from them.
"Qualities you see in others, reveal something about you."
You may not realize it, but the characteristics you like or dislike in others delivers a special message.
If you respond to a person that you see as outgoing, positive and energetic, these are most likely qualities you possessed, but have not fully embraced or developed. Likewise, if you react to the overbearing nature of another, then do a self check,you may have tendency to be overbearing yourself.
Either way, turn into what you do and don't admire in others. Take notes of your emotion response. With this new found awareness you can't help but discover something you didn't know about yourself.
Today's affirmation:The qualities I respond to in others reflect who I am.
8/26:
I will waste not even a precious second today in anger or hate or jealousy or selfishness. I know that the seeds I sow I will harvest, because every action, good or bad, is always followed by an equal reaction. I will plant only good seeds this day.
-Og Mandino 1923-1996, Author and Speaker
9/17:
"Happiness is not the destination."
Many people slog for a lifetime looking for happiness. They feel guilty doing things they enjoy. So they take care of their jobs, their families and their children thinking that the time for happiness will come later. In the end, they discover that it doesn't.
Believe that you deserve happiness right now!
You know those early hours in the morning when the house is quiet and the mist is floating outside the window? That is happiness. Remember how it felt to hold your baby for the first time? That is happiness. Remember how you felt when you achieved what seemed like an impossible goal? That is happiness.
Do not defer your happiness to a later date. Find joy in what you do every day.
Today's affirmation: I deserve to be happy right now.
10/5
"Admit your mistake! It's your most empowering choice."
We all make mistakes. It's a fact of life. What matters is what you do afterward.
You have a choice. You can let your mistake torment you, embarrass you, and hold you back. Or, you can admit you made a mistake, learn from it, and move on.
Mistakes are lessons in disguise. You can learn something from each and every one. Next time, you make a mistake, act quickly and decisively. Take responsibility and look for the lesson. Use the lesson to reach greater success and good fortune in your life.
Learn from your mistakes. Only then can they empower you to greater heights.
Today's affirmation: I admit my mistakes and learn from them.
HA: NSB NSR ISSU
Modern high-performance routers architecturally separate the forwarding plane and the control plane into separate physical components, each with its own memory and processors. The control plane runs the routing protocols, maintains the necessary databases for route processing, and derives a forwarding table (FIB). The FIB is given to the forwarding plane, which is responsible for packet forwarding.
In fact the control plane could stop functioning altogether and because the forwarding plane is a separate entity with its own processors it can continue forwarding packets based on its copy of the FIB. This is Non-Stop Forwarding (NSF): The ability of the forwarding plane to continue running “headless” if the control plane stops.
Of course this is dangerous; if the network topology changes while the control plane is down there is no way to process new route information and the forwarding plane’s FIB can become invalid, resulting in incorrectly forwarded packets. So why would you even want NSF?
The answer is redundant control planes (Cisco calls their control planes Route Processors; Juniper calls them Routing Engines). NSF allows you to switch from a primary to a backup control plane without disrupting forwarding. The FIB could still become invalid during the period between when the primary control plane goes down and the backup control plane takes over, but the risk in this period is usually an acceptable compromise.
So if the backup control plane maintains a copy of the active configuration and current state on system components such as interfaces, it can become active much faster than if it had to learn all this information first. Cisco calls this Stateful Switchover (SSO) and Juniper calls it Graceful Routing Engine Switchover (GRES).
The problem with control plane switchovers as so far described, even if it uses stateful procedures to decrease the switchover time, is that routing protocol adjacencies are broken by the switchover. When a primary control plane goes down any neighboring router that had a peering session with it sees the peering session fail. When the backup control plane becomes active it re-establishes the adjacency, but in the interim the neighbor has advertised to its own neighbors that router X is no longer a valid next hop to any destinations beyond it, and the neighbors should find another path. And of course when the backup control plane comes on-line and reestablishes adjacencies its neighbors advertise the information that router X is again available as a next hop and everyone should again recalculate best paths. All of this is can be highly disruptive to the network.
The objective of NSR is to prevent, or at least minimize, the effect of broken peering sessions.
A first attempt at controlling broken adjacencies during control plane switchovers is Graceful Restart (GR) protocol extensions. Each routing protocol has its own specific GR extensions, but they all work pretty much the same. When a router’s control plane goes down its neighbors, rather than immediately reporting to their own neighbors that the router has become unavailable, wait a certain amount of time (the grace period). If the router’s control plane comes back up and reestablishes its peering sessions before the grace period expires, as would be the case during a control plane switchover, the temporarily broken peering sessions do not effect the network beyond the neighbors.
There are, however, a couple of problems with GR:
.Neighbors are required to support the GR protocol extensions. yet small CE routers are less likely to support GR.
.If there is a complete control plane or router failure rather than just a switchover, the GR grace period can slow network reconvergence.
A newer generation of NSR uses internal processes to keep the backup control plane aware of routing protocol state and adjacency maintenance activities, so that after a switchover the backup control plane can take charge of the existing peering sessions rather than having to establish new ones. The switchover is then transparent to the neighbors, and because the NSR process is internal (and vendor specific) there is no need for the neighbors to support any kind of protocol extension.
Here’s where the confusion comes in: Different vendors use these terms differently. Juniper, for example, calls its graceful restart implementation Graceful Restart, whereas Cisco calls its graceful restart implementation Non-Stop Forwarding Awareness (even though GR applies to routing, not forwarding). Juniper users often confuse GRES and GR: Although the “G” in both acronyms stands for “Graceful,” GRES and GR are two different things. And both Cisco and Juniper have internal NSR capabilities, but the circumstances in which each can be used are quite different.
So enjoy the circus, but be aware that different vendors sometimes use different names for essentially the same act. When a vendor talks about NSF, GR, and NSR, be sure you know that vendor’s.
RPR
RPR enables a quicker switchover between an active and standby RSP if the active RSP experiences a fatal error. When you configure RPR, the standby RSP loads a Cisco IOS image on bootup and initializes itself in standby mode. In the event of a fatal error on the active RSP, the system switches to the standby RSP, which reinitializes itself as the active RSP, reloads all of the line cards, and restarts the system.
RPR+
The RPR+ feature is an enhancement of the RPR feature. RPR+ keeps the VIPs from being reset and reloaded when a switchover occurs between the active and standby RSPs. Because VIPs are not reset and microcode is not reloaded on the VIPs, and the time needed to parse the configuration is eliminated, switchover time is reduced to 30 seconds.
SSO
SSO establishes one of the supervisor engines as active while the other supervisor engine is designated as standby, and then SSO synchronizes information between them. A switchover from the active to the redundant supervisor engine occurs when the active supervisor engine fails, or is removed from the router, or is manually shut down for maintenance. This type of switchover ensures that Layer 2 traffic is not interrupted.
SSO switchover preserves FIB and adjacency entries and can forward Layer 3 traffic after a switchover. Configuration information and data structures are synchronized from the active to the redundant supervisor engine at startup and whenever changes to the active supervisor engine configuration occur.
ISSU: In-Service Software Upgrade (ISSU) CISCO
Requires Dual RE
1. Primary and Standby Supervisors Running Current Image
2. Load New Image on Standby Supervisor
3. Make Standby Supervisor “Active” (<150ms)—Switch Now Running New Image
4. Rapid Rollback Option (<150ms) if Necessary
5. Load New Image on Primary Supervisor and Commit Change
In fact the control plane could stop functioning altogether and because the forwarding plane is a separate entity with its own processors it can continue forwarding packets based on its copy of the FIB. This is Non-Stop Forwarding (NSF): The ability of the forwarding plane to continue running “headless” if the control plane stops.
Of course this is dangerous; if the network topology changes while the control plane is down there is no way to process new route information and the forwarding plane’s FIB can become invalid, resulting in incorrectly forwarded packets. So why would you even want NSF?
The answer is redundant control planes (Cisco calls their control planes Route Processors; Juniper calls them Routing Engines). NSF allows you to switch from a primary to a backup control plane without disrupting forwarding. The FIB could still become invalid during the period between when the primary control plane goes down and the backup control plane takes over, but the risk in this period is usually an acceptable compromise.
So if the backup control plane maintains a copy of the active configuration and current state on system components such as interfaces, it can become active much faster than if it had to learn all this information first. Cisco calls this Stateful Switchover (SSO) and Juniper calls it Graceful Routing Engine Switchover (GRES).
The problem with control plane switchovers as so far described, even if it uses stateful procedures to decrease the switchover time, is that routing protocol adjacencies are broken by the switchover. When a primary control plane goes down any neighboring router that had a peering session with it sees the peering session fail. When the backup control plane becomes active it re-establishes the adjacency, but in the interim the neighbor has advertised to its own neighbors that router X is no longer a valid next hop to any destinations beyond it, and the neighbors should find another path. And of course when the backup control plane comes on-line and reestablishes adjacencies its neighbors advertise the information that router X is again available as a next hop and everyone should again recalculate best paths. All of this is can be highly disruptive to the network.
The objective of NSR is to prevent, or at least minimize, the effect of broken peering sessions.
A first attempt at controlling broken adjacencies during control plane switchovers is Graceful Restart (GR) protocol extensions. Each routing protocol has its own specific GR extensions, but they all work pretty much the same. When a router’s control plane goes down its neighbors, rather than immediately reporting to their own neighbors that the router has become unavailable, wait a certain amount of time (the grace period). If the router’s control plane comes back up and reestablishes its peering sessions before the grace period expires, as would be the case during a control plane switchover, the temporarily broken peering sessions do not effect the network beyond the neighbors.
There are, however, a couple of problems with GR:
.Neighbors are required to support the GR protocol extensions. yet small CE routers are less likely to support GR.
.If there is a complete control plane or router failure rather than just a switchover, the GR grace period can slow network reconvergence.
A newer generation of NSR uses internal processes to keep the backup control plane aware of routing protocol state and adjacency maintenance activities, so that after a switchover the backup control plane can take charge of the existing peering sessions rather than having to establish new ones. The switchover is then transparent to the neighbors, and because the NSR process is internal (and vendor specific) there is no need for the neighbors to support any kind of protocol extension.
Here’s where the confusion comes in: Different vendors use these terms differently. Juniper, for example, calls its graceful restart implementation Graceful Restart, whereas Cisco calls its graceful restart implementation Non-Stop Forwarding Awareness (even though GR applies to routing, not forwarding). Juniper users often confuse GRES and GR: Although the “G” in both acronyms stands for “Graceful,” GRES and GR are two different things. And both Cisco and Juniper have internal NSR capabilities, but the circumstances in which each can be used are quite different.
So enjoy the circus, but be aware that different vendors sometimes use different names for essentially the same act. When a vendor talks about NSF, GR, and NSR, be sure you know that vendor’s.
RPR
RPR enables a quicker switchover between an active and standby RSP if the active RSP experiences a fatal error. When you configure RPR, the standby RSP loads a Cisco IOS image on bootup and initializes itself in standby mode. In the event of a fatal error on the active RSP, the system switches to the standby RSP, which reinitializes itself as the active RSP, reloads all of the line cards, and restarts the system.
RPR+
The RPR+ feature is an enhancement of the RPR feature. RPR+ keeps the VIPs from being reset and reloaded when a switchover occurs between the active and standby RSPs. Because VIPs are not reset and microcode is not reloaded on the VIPs, and the time needed to parse the configuration is eliminated, switchover time is reduced to 30 seconds.
SSO
SSO establishes one of the supervisor engines as active while the other supervisor engine is designated as standby, and then SSO synchronizes information between them. A switchover from the active to the redundant supervisor engine occurs when the active supervisor engine fails, or is removed from the router, or is manually shut down for maintenance. This type of switchover ensures that Layer 2 traffic is not interrupted.
SSO switchover preserves FIB and adjacency entries and can forward Layer 3 traffic after a switchover. Configuration information and data structures are synchronized from the active to the redundant supervisor engine at startup and whenever changes to the active supervisor engine configuration occur.
ISSU: In-Service Software Upgrade (ISSU) CISCO
Requires Dual RE
1. Primary and Standby Supervisors Running Current Image
2. Load New Image on Standby Supervisor
3. Make Standby Supervisor “Active” (<150ms)—Switch Now Running New Image
4. Rapid Rollback Option (<150ms) if Necessary
5. Load New Image on Primary Supervisor and Commit Change
Friday, August 13, 2010
IP Header
Defined at RFC 791
A summary of the contents of the internet header follows:
Version: 4 bits
The Version field indicates the format of the internet header.
4 - ipv4
6 - ipv6
IHL: 4 bits
Internet Header Length is the length of the internet header in 32
bit words, and thus points to the beginning of the data.
5 - minimum value without option
Type of Service: 8 bits
Bits 0-2: Precedence.
Bit 3: 0 = Normal Delay, 1 = Low Delay.
Bits 4: 0 = Normal Throughput, 1 = High Throughput.
Bits 5: 0 = Normal Relibility, 1 = High Relibility.
Bit 6-7: Reserved for Future Use.
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| | | | | | |
| PRECEDENCE | D | T | R | 0 | 0 |
| | | | | | |
+-----+-----+-----+-----+-----+-----+-----+-----+
Precedence
111 - Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
Total Length: 16 bits
Total Length is the length of the datagram, measured in octets, including internet header and data.
Identification: 16 bits
An identifying value assigned by the sender to aid in assembling the
fragments of a datagram.
Flags: 3 bits
Various Control Flags.
Bit 0: reserved, must be zero
Bit 1: (DF) 0 = May Fragment, 1 = Don't Fragment.
Bit 2: (MF) 0 = Last Fragment, 1 = More Fragments.
0 1 2
+---+---+---+
| | D | M |
| 0 | F | F |
+---+---+---+
Fragment Offset: 13 bits
This field indicates where in the datagram this fragment belongs.
The fragment offset is measured in units of 8 octets (64 bits). The
first fragment has offset zero.
Time to Live: 8 bits
This field indicates the maximum time the datagram is allowed to
remain in the internet system.
Protocol: 8 bits
This field indicates the next level protocol used in the data
portion of the internet datagram. The values for various protocols
are specified in "Assigned Numbers" RFC 1700
1 - ICMP
2 - IGMP
6 - tcp
17 - udp
47 - GRE
88 - IGRP
Header Checksum: 16 bits
A checksum on the header only. Since some header fields change
(e.g., time to live), this is recomputed and verified at each point
that the internet header is processed.
Source Address: 32 bits
The source address.
Destination Address: 32 bits
The destination address.
Options: variable
The options may appear or not in datagrams.
A summary of the contents of the internet header follows:
Version: 4 bits
The Version field indicates the format of the internet header.
4 - ipv4
6 - ipv6
IHL: 4 bits
Internet Header Length is the length of the internet header in 32
bit words, and thus points to the beginning of the data.
5 - minimum value without option
Type of Service: 8 bits
Bits 0-2: Precedence.
Bit 3: 0 = Normal Delay, 1 = Low Delay.
Bits 4: 0 = Normal Throughput, 1 = High Throughput.
Bits 5: 0 = Normal Relibility, 1 = High Relibility.
Bit 6-7: Reserved for Future Use.
0 1 2 3 4 5 6 7
+-----+-----+-----+-----+-----+-----+-----+-----+
| | | | | | |
| PRECEDENCE | D | T | R | 0 | 0 |
| | | | | | |
+-----+-----+-----+-----+-----+-----+-----+-----+
Precedence
111 - Network Control
110 - Internetwork Control
101 - CRITIC/ECP
100 - Flash Override
011 - Flash
010 - Immediate
001 - Priority
000 - Routine
Total Length: 16 bits
Total Length is the length of the datagram, measured in octets, including internet header and data.
Identification: 16 bits
An identifying value assigned by the sender to aid in assembling the
fragments of a datagram.
Flags: 3 bits
Various Control Flags.
Bit 0: reserved, must be zero
Bit 1: (DF) 0 = May Fragment, 1 = Don't Fragment.
Bit 2: (MF) 0 = Last Fragment, 1 = More Fragments.
0 1 2
+---+---+---+
| | D | M |
| 0 | F | F |
+---+---+---+
Fragment Offset: 13 bits
This field indicates where in the datagram this fragment belongs.
The fragment offset is measured in units of 8 octets (64 bits). The
first fragment has offset zero.
Time to Live: 8 bits
This field indicates the maximum time the datagram is allowed to
remain in the internet system.
Protocol: 8 bits
This field indicates the next level protocol used in the data
portion of the internet datagram. The values for various protocols
are specified in "Assigned Numbers" RFC 1700
1 - ICMP
2 - IGMP
6 - tcp
17 - udp
47 - GRE
88 - IGRP
Header Checksum: 16 bits
A checksum on the header only. Since some header fields change
(e.g., time to live), this is recomputed and verified at each point
that the internet header is processed.
Source Address: 32 bits
The source address.
Destination Address: 32 bits
The destination address.
Options: variable
The options may appear or not in datagrams.
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