Networking Tips Tricks

Quadrature Phase-shift Keying Sometimes known as quaternary or quadriphase PSK or 4-PSK, QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol-twice the rate of BPSK. This is used either to double the data rate compared to a BPSK system while maintaining the bandwidth of the signal or to maintain the data-rate of BPSK but halve the bandwidth needed. Although QPSK can be viewed as a quaternary modulation, it is easier to see it as two independently modulated quadrature carriers. With this interpretation, the even (or odd) bits are used to modulate the in-phase component of the carrier, while the odd (or even) bits are used to modulate the quadrature -phase component of the carrier. BPSK is used on both carriers and they can be independently demodulated.

BPSK is the simplest form of PSK. It uses two phases which are separated by 180° and so can also be termed 2-PSK. It does not particularly matter exactly where the constellation points are positioned It is, only able to modulate at 1bit/symbol and so is unsuitable for high data-rate applications.

Modulation is the process by which a carrier wave is able to carry the message or digital signal (series of ones and zeroes). There are three basic methods to this:- Amplitude, Frequency Phase shift keying. Higher orders of modulation allow us to encode more bits per symbol or period (time).

Technical details Schema of a typical DHCP session DHCP uses the same two IANA assigned ports as BOOTP: 67/udp for the server side, and 68/udp for the client side. DHCP operations fall into four basic phases. These phases are IP lease request, IP lease offer, IP lease selection, and IP lease acknowledgement. After the client obtained an IP address, the client may start an address resolution query to prevent IP conflicts caused by address poll overlapping of DHCP servers. DHCP discovery The client broadcasts on the local physical subnet to find available servers. Network administrators can configure a local router to forward DHCP packets to a DHCP server on a different subnet. This client-implementation creates a UDP packet with the broadcast destination of 255.255.255.255 or subnet broadcast address. A client can also request its last-known IP address (in the example below, 192.168.1.100). If the client is still in a network where this IP is valid, the server might grant the request. O...

Requirement Cisco Command Enable debug for RIP debug ip rip Enable summary IGRP debug information debug ip igrp events Enable detailed IGRP debug information debug ip igrp transactions Debug IPX RIP debug ipx routing activity Debug IPX SAP debug IPX SAP Enable debug for CHAP or PAP debug ppp authentication Switch all debugging off no debug all undebug all

Requirement Cisco Command Save the current configuration from DRAM to NVRAM copy running-config startup-config Merge NVRAM configuration to DRAM copy startup-config running-config Copy DRAM configuration to a TFTP server copy runing-config tftp Merge TFTP configuration with current router configuration held in DRAM copy tftp runing-config Backup the IOS onto a TFTP server copy flash tftp Upgrade the router IOS from a TFTP server copy tftp flash

Requirement Cisco Command Enter privileged mode Enable Return to user mode from privileged disable Exit Router Logout or exit or quit Recall last command up arrow or Recall next command down arrow or Suspend or abort and 6 then x Complete Command TAB