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Saturday, 4 February 2017

Introduction to DWDM Technology

DWDM - Dense Wavelength Division Multiplexing

WDM technology is a fiber communication technology transmitting multiple optical carriers with information (analog or digital) on one fiber.

WDM concept was first published in 1978, and by 1980 WDM systems were being realized in the laboratory. The first WDM systems combined only two signals. Modern systems can handle 160 signals and can thus expand a basic 200,100,10 Gbit/s across the metro, regional, long-haul, and ultra-long-haul DWDM system over a single fiber pair to over 16 Tbit/s. A system of 320 channels in also present (12.5 GHz channel spacing). 400G DWDM Prototype for Next Generation Ultra-Broadband Transmission possible also.

Compared to 100-Gbps CP-QPSK, CP-16QAM modulation doubles the spectral efficiency, transmitting 200 Gbps per wavelength at the same baud rate while reducing unregenerated reach up to 10000 KM. 

Dense wavelength division multiplexing Concept:

DWDM Basic System:

Saturday, 25 April 2015

Difference between stp , rstp , mstp , pvst , pvst+ Cisco

Difference between stp ,rstp,mstp,pvst,pvst+

STP (Spanning-tree Protocol):
Layer 2 protocol used in LAN enviroment to Avoid :

Broadcast Storms
Mac-Table Inestability
Multiples copies of frames.

And it is defined in 802.1d Standard.

RSTP(Rapid Spanning Tree Protocol-802.1w Standard):
 it is the enhanced protocol of STP,
the main characteristic of this one is Faster than STP (it converge in less than 6 seconds).

While STP can take 30 to 50 seconds to respond to a topology change, RSTP is typically able to respond to changes within 3 × Hello times (default: 3 times 2 seconds) or within a few milliseconds of a physical link failure. The so-called Hello time is an important and configurable time interval that is used by RSTP for several purposes; its default value is 2 seconds

Limitation :

The default hop count for MST/RSTP is 20

**PVST+ (Per Vlan Spanning Tree Plus) :

In Ethernet switched environments where multiple Virtual LANs exist, it is often desirable to create multiple spanning trees so that traffic from different VLANs uses different links.Cisco's proprietary versions of Spanning Tree Protocol, Per-VLAN Spanning Tree (PVST) and Per-VLAN Spanning Tree Plus (PVST+), create a separate spanning tree for each VLAN. Both PVST and PVST+ protocols are Cisco proprietary protocols, and few switches from other vendors support them

This feature (by cisco) is used to create an instace of STP for each VLAN. e.g.

If you have a switch with 3 vlans you will have a 3 instances of VLANs that you could
modify the parameters (like to make root bridge for a specific VLAN) independiently
accord to your design goals.

***Rapid PVST+ :

This is Cisco's proprietary version of Rapid Spanning Tree Protocol. It creates a spanning tree for each VLAN, just like PVST. Cisco refers to this as Rapid Per-VLAN Spanning Tree (RPVST)

·          Uses Bridge Protocol Data Unit (BPDU) version 2 which is backward compatible with the 802.1D STP, which uses BPDU version 0
·          All the switches generate BPDUs and send out on all the ports every 2 seconds, whereas in 802.1D STP only the root bridge sends the configuration BPDUs
·          Port Roles—Root port, designated port, alternate port and backup port.
·          Port States—Discarding, Learning, and Forwarding.
·          Port Types—Edge Port (PortFast), Point-to-Point and Shared port.
Rapid-PVST uses RSTP to provide faster convergence. When any RSTP port receives legacy 802.1D BPDU, it falls back to legacy STP and the inherent fast convergence benefits of 802.1w are lost when it interacts with legacy bridges.

Limitations :

  • The maximum number of VLANs and ports is 16,000.
  • Only Rapid PVST+ or MST can be active at any time for each VDC.
  • Port channeling—The port-channel bundle is considered as a single port. The port cost is the aggregation of all the configured port costs assigned to that channel.
  • Private VLANs:
    • On a normal VLAN trunk port, the primary and secondary private VLANs are two different logical ports and must have the exact STP topology.
    • On access ports, STP sees only the primary VLAN.
  • We recommend that you configure all ports connected to Layer 2 hosts as STP edge ports.
  • Always leave STP enabled.
  • Do not change timers because changing timers can adversely affect stability.
  • Keep user traffic off the management VLAN; keep the management VLAN separate from the user data.
  • Choose the distribution and core layers as the location of the primary and secondary root switches.
  • When you connect two Cisco devices through 802.1Q trunks, the switches exchange spanning tree BPDUs on each VLAN allowed on the trunks. The BPDUs on the native VLAN of the trunk are sent untagged to the reserved 802.1D spanning tree multicast MAC address (01-80-C2-00-00-00). The BPDUs on all VLANs on the trunk are sent tagged to the reserved Cisco Shared Spanning Tree Protocol (SSTP) multicast MAC address (01-00-0c-cc-cc-cd).

MIST(Multiple Instances of Spaning Tree-802.1s):
This protocol is the equivalent for PVST, however this protocol just can be used in conjunction with RSTP.

ইসলামে প্রশাসক

৪৪২৫. আবূ বাক্রাহ (রাঃ) হতে বর্ণিত। তিনি বলেন, রসূলুল্লাহ সাল্লাল্লাহু ‘আলাইহি ওয়াসাল্লাম থেকে শ্রুত একটি বাণীর দ্বারা আল্লাহ জঙ্গে জামালের (উষ্ট্রের যুদ্ধ) দিন আমার মহা উপকার করেছেন, যে সময় আমি সাহাবায়ে কিরামের সঙ্গে মিলিত হয়ে জামাল যুদ্ধে শারীক হতে প্রায় প্রস্তুত হয়েছিলাম। আবূ বাক্রাহ (রাঃ) বলেন, সে বাণীটি হল, যখন নাবী সাল্লাল্লাহু ‘আলাইহি ওয়াসাল্লাম-এর কাছে এ খবর পৌঁছল যে, পারস্যবাসী কিসরা কন্যাকে তাদের বাদশাহ মনোনীত করেছেন, তখন তিনি বললেন, সে জাতি কক্ষণো সফল হবে না স্ত্রীলোক যাদের প্রশাসক হয়। [৭০৯৯] (আ.প্র. ৪০৭৭, ই.ফা. ৪০৮০)

Source : Hadithbd