I'm going to build on this post as I come across each of the different types but it can get very confusing talking about the different types of Juniper Line Cards, so here is a reference:
DPC - Dense Port Concentrator
ichip based cards which are available for the MX series routers
They come in 3 variations:
DPCE-R - Routing and Switching, operate as complete L3 router or Full L2 switch
DPCE-X - Limited Scale L3. Cost optimized line case
DPCE-Q - Enhanced Queueing, up to 64,000 queues per card. Per VLAN queueing.
MPC - Modular Port Concentrator
trio based cards for the MX series routers. They support full LS, L2 and application services. MICs are used inside MPCs to provide interfaces.
MPC1 - 32k IFL, port queues, 30Gbps
MPC2 - 64k IFL, port queues, 60Gbps
MPC1-Q - 32k IFL, VLAN queues, 128k I/E queues, 30Gbps
MPC2-Q - 64k IFL, VLAN queues, 256k I/E queues, 60 Gbps
MPC2-E-Q - 64k IFL, VLAN queues, 512k queues, 60Gbps
MX-FPC - MX Flexible Port Concentrator
These are used to add non-Ethernet interfaces to an MX series chassis. They take up 2 slots and have reduced performance (2.5 Gbps Type 2 or 10Gbps Type 3)
More to come as I come across them...
Wednesday, 22 August 2012
Tuesday, 14 August 2012
Calculating Packets Per Second of Devices
So here's a topic which just keeps cropping up and I look it up every time, so I'm sticking it on the blog so that I've got a reference for the future and hopefully I'll remember it a bit better for next time!
You will often have to calculate the required packets per second of a device to make sure it is "powerful enough" to handle the job given to it. Alternatively you may be sizing a device for a link, for example a router for a WAN connection, and you want to make sure it can handle wire speed on the link. Here is my calculations for this.
I'll use the standard example of a 1 gigabit WAN connection 1Gbps, this is 1,000,000,000 bits:
In order to work out the required pps (Packets Per Second) of a device for the WAN link we need to consider the maximum and minimum packet sizes. Bear in mind the packet size in reality will vary so the actual number is anyone's guess but this gives you a great boundary.
The minimum packet size is 84 bytes (46 payload, 4 CRC, 2 MAC type, 6 MAC source address, 6 MAC destination address, 8 preamble, 12 inter frame gap).
The maximum packet size is 1538 bytes (same as above but with 1500 payload instead of 46)
The calculation is:
Convert bits into bytes -- 1,000,000,000 bits per second / 8 = 125,000,000 bytes per second
Convert bytes into packets -- 125,000,000 bytes per second / 84 = 1,488,096 packets per second
The above works out the minimum packets per second, changing 84 to 1538 works out the maximum packets per second:
Convert bytes into packets -- 125,000,000 bytes per second / 1538 = 81,274 packets per second
From this we know if all the packets were the minimum sized we'd need a more powerful device to handle wirespeed, but this is theoretical because you wont be able to guarantee the size of all packets, apart from in very special cases.
If you can work out the average packet size within the environment you will be able to workout more accurately the device requirements, but from here is it a bit of a guessing game do you plan for the lowest possible packet size to ensure the device can handle wirespeed or do you pick a more realistic but unknown value somewhere in the middle. That answer is up to you.
You will often have to calculate the required packets per second of a device to make sure it is "powerful enough" to handle the job given to it. Alternatively you may be sizing a device for a link, for example a router for a WAN connection, and you want to make sure it can handle wire speed on the link. Here is my calculations for this.
I'll use the standard example of a 1 gigabit WAN connection 1Gbps, this is 1,000,000,000 bits:
The minimum packet size is 84 bytes (46 payload, 4 CRC, 2 MAC type, 6 MAC source address, 6 MAC destination address, 8 preamble, 12 inter frame gap).
The maximum packet size is 1538 bytes (same as above but with 1500 payload instead of 46)
The calculation is:
Convert bits into bytes -- 1,000,000,000 bits per second / 8 = 125,000,000 bytes per second
Convert bytes into packets -- 125,000,000 bytes per second / 84 = 1,488,096 packets per second
The above works out the minimum packets per second, changing 84 to 1538 works out the maximum packets per second:
Convert bytes into packets -- 125,000,000 bytes per second / 1538 = 81,274 packets per second
From this we know if all the packets were the minimum sized we'd need a more powerful device to handle wirespeed, but this is theoretical because you wont be able to guarantee the size of all packets, apart from in very special cases.
If you can work out the average packet size within the environment you will be able to workout more accurately the device requirements, but from here is it a bit of a guessing game do you plan for the lowest possible packet size to ensure the device can handle wirespeed or do you pick a more realistic but unknown value somewhere in the middle. That answer is up to you.
Monday, 13 August 2012
450Mbps Wireless. Spatial Streams and 4x4 MIMO
So I've not posted for a while, which is bad and I will definitely start again soon. But in the mean time I've learnt something very interesting about 802.11n wireless, spatial streams and 450Mbps that I want to jot down.
802.11n radios give 300Mbps with 2x2 antennas, this is 2 transmit and 2 receive. They also utilise 2 spatial streams. The maths behind this is that each channel gives 75Mbps, 2 channels (2 x 20MHz channels = 40MHz) gives 150Mbps. 2 spatial thus gives 300Mbps. Note that each side needs the same setup to achieve these rates, this is critical.
MIMO allows multiple datastreams to be sent simultaneously however there are two sides to this coin. Each MIMO stream can be used to send the same data, thus you have multiple redundant copies of the data and the connection is very reliable, this is Diversity. The other extreme is throughput where each stream sends different data but there is no redundancy in the path so it is potentially faster but also less reliable. Most commonly a balance in the middle is used to give you reliable throughput.
Thus APs can theoretically achieve 450Mbps by using 3x3 radios with 3 spatial streams, the problem is this is a extreme throughput situation and you will likely not get the fastest possible speeds due to distances and errors in the transmission. If one of the streams experiences deep fading (low signal) the transmission fails or slows down to a lower transmission rate.
Cisco has a solution to the above in the 3600 AP. It has 4x4 radios and 3 spatial streams meaning that three can send and receive while the remaining is used for diversity to help achieve the reliable throughput needed. It's worth noting that this is custom silicon as well and only available to Cisco, at the time of writing anyway.
References:
There's a fantastic video from techwize tv called 'fundamentals of spatial streams'. Currently on this page:
http://www.cisco.com/en/US/products/ps11983/index.html
802.11n radios give 300Mbps with 2x2 antennas, this is 2 transmit and 2 receive. They also utilise 2 spatial streams. The maths behind this is that each channel gives 75Mbps, 2 channels (2 x 20MHz channels = 40MHz) gives 150Mbps. 2 spatial thus gives 300Mbps. Note that each side needs the same setup to achieve these rates, this is critical.
MIMO allows multiple datastreams to be sent simultaneously however there are two sides to this coin. Each MIMO stream can be used to send the same data, thus you have multiple redundant copies of the data and the connection is very reliable, this is Diversity. The other extreme is throughput where each stream sends different data but there is no redundancy in the path so it is potentially faster but also less reliable. Most commonly a balance in the middle is used to give you reliable throughput.
Thus APs can theoretically achieve 450Mbps by using 3x3 radios with 3 spatial streams, the problem is this is a extreme throughput situation and you will likely not get the fastest possible speeds due to distances and errors in the transmission. If one of the streams experiences deep fading (low signal) the transmission fails or slows down to a lower transmission rate.
Cisco has a solution to the above in the 3600 AP. It has 4x4 radios and 3 spatial streams meaning that three can send and receive while the remaining is used for diversity to help achieve the reliable throughput needed. It's worth noting that this is custom silicon as well and only available to Cisco, at the time of writing anyway.
References:
There's a fantastic video from techwize tv called 'fundamentals of spatial streams'. Currently on this page:
http://www.cisco.com/en/US/products/ps11983/index.html
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