Circuit Switched Networks

Here are some quick facts lifted from a CCNA online quiz

Three accurate descriptions of Circuit Switched Networks
* With circuit switching a dedicated physical circuit is established, maintained and terminated through a carrier network for each communication session
* Circuit switching allows multiple sites to connect to the switched network of a carrier and communicate with each other
* ISDN is a circuit switched network

Three statements for PSTN
* Other than a modem, no additional equipment is required
* Relatively lost cost associated with the implementation of a PSTN connection link
* The maintenance of a public telephone network is very high quality with a few instances in which lines are not available

Three statements describe PPP
* A point to point (or serial) comms link provides a single preestablished WAN communications path from the customer premises through the carrier network ie telephone company to a remote network
* Carriers lease point to point lines usually, so they're often called leased lines
* For a point to point line, the carrier dedicates fixed transport capacity and facility hardware to the line of a customer

Three statements describe WAN bandwidth
* North American standard to describe bandwidth in DS numbers (DS0, DS1...) that refers to the rate and format of the signal
* Bandwidth on a serial connection can be incrementally increased to accommodate the need for faster transmission
* Bandwidth refers to the rate at which data is transferred over the comms link

HDLC
* Includes support for both PPP and multipoint configurations
* Cisco HDLC there is no windowing or flow control
* HDLC specifies an encapsulation method for data on synchronous serial data links using frame character and checksum

Function of PPP
* twist: Authentication phase of PPP session is not necessarily required
* PPP originally emerged as an encapsulation protocol for transporting IP traffic over PPP links
* PPP provides router to router and host to network connections over synchronous and asynchronous circuits
* The LCP in PPP is used for establishment, configuration and testing the data-link connection

Considerations for PPP
* PPP links require minimal expertise to install and maintain
* usually offer a high quality of service
* provide permanent dedicated capacity that is always available

Cisco ICND1 Flashcard: A Brief History of the Internet

The US DOD researchers figured out a way to break up messages into smaller parts, and sending each part to the destination, whereupon reassembly of the original message would be possible. This is called the packet system.

In 1972, ARPANET developers created the first email message software for the purpose of communicating and coordinating projects

In 1984, DNS was introduced to give the world domain endings like .edu, .com, .gov, .org and other country codes.

A 3-way handshake
send-SYN
SYN-ACK
TCP ACK

HVAC and Power Rating Calculators

A quick link to find a Dell Energy Star rating calculator for heat generation and cooling requirements for Dell models for 48U, 42U or 24U Poweredge racks.

I was actually looking for the rating for one machine but it makes sense the application is making the calculations based on an entire rack.  Launch the page for Dell Star Online here.

Another important factor to consider is how many units you can fit into the rack given the power available to the rack. Here is a useful answer for Dell Poweredge Server Power Requirements rated for PE 2950 as a starting point.

Check again for more information about Water Cooled Racks or High Performance Cooling solutions.
Whitepaper for Watts and Volt-Amps

Doing My Own Cisco Tech Support

Cisco has a really good tech support hot line. I put in a TAC request for a pretty simple question about not being able to configure the serial port.

Create Serial Sub Interface Cisco 2811

"Hi. I can't access the serial port, was trying to configure serial 1/0 on my router cisco 2811 but I guess it does not exist?
The cisco online help says to try
Controller t1 0/0/0
Framing esf
Linecode b8zs
Channel-group 0 timeslots 1-24 speed 64
I did show controllers and all kinds of hardware descriptions pop up but not t1 specifically
The router didn't know what to do with the controller command, I checked the hardware but it does not have a serial port. Is that possible?"

I guess I could pause next time, and give the guy a chance to talk or take notes. Anyway I couldn't immediately provide the serial number on the unit cuz I wasn't logged in and I didn't have the service contract searchable right in front of me. So I mention that I will login and write up the TAC online. While clicking online and trying to find the TAC gui, I stumble upon the link for T1 HWIC cards, like the one that is NOT even plugged into to my unit. There is no WAN interface and link connected, the T1 truly does not exist!

I didn't even have a Cisco T1/ E1 WAN Interface Cards
Anywayz I feel rather silly about calling in the first place but now I have confirmed that the show controller command really works! Once again it is the USER error.