🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
[Crossbar Switching Fabric]
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
If a switching decision can be made on individual line cards—such as when the line cards
have specialized hardware or a separate processor—copying the packet into shared memory
of any type between interfaces isn’t necessary. Instead, the packet can be transferred
directly from the local memory on one line card to the local memory on another line card.
Figure below illustrates an example of a crossbar switching fabric
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

Ali Mobasheri

Crossbar Switching Fabric @geekgap

🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
In a crossbar switching fabric, each line card has two connections to a fabric. At each cycle
(or point in time), any given line card’s output can be connected to any other line card’s
input. So, if Line Card 2 receives a packet that it determines needs to be transmitted out a
port on Line Card 3, it can ask the switch fabric controller to connect its output to the input
of Line Card 3 and transfer the packet directly.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
For multicast, the inbound line card can request a connection to multiple line card inputs.
For example, in the Figure, Line Card 5’s output is connected to both Line Card 6’s and
Line Card 4’s input, so any packets Line Card 5 transmits will be received by both of these
line cards at the same time.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
The primary advantage of a crossbar switching fabric is that it can be scaled along with the
number of line cards installed in a system; each new line card installed represents a new set
of input and output connections that can be used in parallel with the other existing
connections. As long as each individual connection has enough bandwidth to carry line-rate
traffic between any pair of line cards, the entire router can carry line-rate traffic between
multiple pairs of line cards.
The bandwidth of the individual lines in the crossbar switching mesh will not help in one
instance: if two line cards want to transmit packets to a third line card at the same time. For
example, in the Figure, if both Line Cards 1 and 2 want to transmit a packet to Line Card
3, they can’t; Line Card 3 has only one input.
This problem has several solutions, any and all of which are used in Cisco routers. The first
is to schedule the connections in a way that no line card is expected to receive from two
other line cards at once. Cisco routers provide various scheduling algorithms and systems
to ensure that no line card is starved for transmission, so packets don’t bottleneck on the
inbound line card.
Another possibility, used on some high-speed line cards on some platforms, is to provide
two connections into a given line card so that it can receive packets from two different line
cards at the same time. This doesn’t completely resolve the problem—scheduling is still
required—but it does relieve some of the pressure on line cards that are often used as
uplinks to higher-speed networks.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

Ali Mobasheri

🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
[Bus Backplanes]
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
The last type of connection used between line cards is a bus backplane. This is different in
a few ways from a shared memory architecture with a bus. Figure below illustrates such a
backplane.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

Ali Mobasheri

Bus Backplane @geekgap

🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

Packets that are received by a line card are transmitted onto the backplane as they are
received. When the switching engine has received and processed enough of the packet to
decide which interface the packet needs to be transmitted out of, the line card with that
interface connected is instructed to continue copying the packet off the backplane and is
given information about which port the packet should be transmitted out.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

The remainder of the line cards is instructed to flush this packet from their buffers and
prepare to receive the next packet, or do other work as needed.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷


Ali Mobasheri

Packet Receipt and Transmission Across a Bus Backplane @geekgap

🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
The following list explains the process illustrated in Figure :
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
1 Line Card 1 begins receiving the packet and copies it onto the backplane; all the other
line cards begin to store the packet in local buffers.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
2 When Line Card 1 has put the packet headers up the IP header onto the backplane, the
switching engine consults its local tables to determine the correct output port.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
3 The switching engine now signals Line Card 4 that it should continue accepting and
storing this packet, and it informs the remaining line cards that there is no reason for
them to continue receiving or storing this packet.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
4 After Line Card 1 has finished transmitting the packet onto the backplane, Line Card
4 transmits the packet onto the locally connected physical media.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
Switching multicast packets over a backplane bus is relatively simple; the switching engine
signals several line cards to accept and transmit the packet, rather than just one. Scheduling
algorithms and local buffers are used to prevent several line cards from sending packets
onto the backplane at the same time.
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

Ali Mobasheri

🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
دوستان گیک گپی عزیز شبتون بخیر و خوشی باشه انشاالله
مبحث فردا شب راجع به :
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
[Cisco IOS Software: The Brains]
🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷
به طور کامل راجع به IOS دستگاه های Cisco صحبت میکنیم

هرروزتون گیک گپی

Ali Mobasheri —---> 🇮🇷🇮🇷🇮🇷@geekgap🇮🇷🇮🇷🇮🇷

🎄🎊
آغاز کریسمس را به هموطنان عزیز مسیحی تبریک میگیم و امیدواریم سالی توام با سلامتی،خوشی و خوشبختی و موفقیت داشته باشيد
🌸🌹🌼🌻🌷🌺🌼🌹❤️☃⛄️❄️
@geekgap

نقشه کامل و جامع مدل لایه ای #شبکه #OSI https://t.iss.one/geekgap

تفاوتهای #Hub#switch#
https://t.iss.one/joinchat/AAAAAD-MEmy_zkJAc1J8-g

قست اول سوالات مصاحبه ای CCNA https://geekgap.ir/cisco-interview-question-part1/ @geekgap

جواب های سوالات به زودی منتشر میشود
@geekgap

قسمت اول سوالات شامل ۳۰ مورد میشود
@geekgap

دقایقی پیش تهران دوباره لرزید. بذارید ببینیم چند ریشتر بوده

ساعت 12:55 نیمه شب تهرانی ها این زلزله رو حس کردن

@geekgap

دقایقی پیش تهران دوباره لرزید. بذارید ببینیم چند ریشتر بوده

ساعت 12:55 نیمه شب تهرانی ها این زلزله رو حس کردن

@geekgap

گزارش مقدماتی زمین‌لرزه

بزرگی: 4.2
محل وقوع: مرز استانهای تهران و البرز - حوالی ملارد(تهران)
تاریخ و زمان وقوع به وقت محلی: 1396/10/06 00:54:33
طول جغرافیایی: 50.93
عرض جغرافیایی: 35.68
عمق زمین‌لرزه: 12 کیلومتر

نزدیک‌ترین شهرها:
4 کیلومتری ملارد (تهران)
7 کیلومتری مشكين دشت (البرز)
7 کیلومتری صفا دشت (تهران)

نزدیکترین مراکز استان:
17 کیلومتری كرج
42 کیلومتری تهران

@geekgap

هنگام زلزله چه باید کرد ؟
@geekgap

#فوری / نقشه تخلیه امن تهران

🔹شهرداری تهران نقشه تخلیه امن مناطق تهران را در وبسایت خود منتشر کرد. با مراجعه به آدرس

https://www.tehran.ir/Default.aspx?tabid=401

و جستجوی نام محله خود می‌توانید از نقاط امن در محله خود که در زمان اضطراری (مانند #زلزله) می‌توان به آن مراجعه کرد اطلاع یابید.
@geekgap