Month: May 2013

IEEE 802.3af PoE and IEEE 802.3at PoE+

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(Summary from Deploying Brocade FastIron-based PoE and PoE+ Solutions in the Campus Network)

The IEEE 802.3af and 802.3at specifications define the standards for delivering power over existing network cabling infrastructure and providing multicast-enabled full streaming audio and video applications for converged services, such as Voice over IP (VoIP), WLAN access points, IP surveillance cameras, and other IP technology devices.

PoE technology eliminates the need for an electrical outlet and a dedicated Uninterrupted Power Supply (UPS) near IP-powered devices.

PoE capability is needed in the campus network access layer only. Distribution and core switches do not need PoE capability. Read the rest of this entry »

IEEE 802.1q

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The IEEE 802.1Q specification establishes a standard method for tagging Ethernet frames with VLAN membership information.

The header has 4 parts:

Tag Protocol Identifier (TPID) – 16-bit
The TPID includes an Ethernet Type value that is used to identify the frame as a tagged frame and to select the correct tag decoding functions
This is set to a value of 0x8100 in order to identify the frame as an IEEE 802.1Q-tagged frame

Priority (802.1p): – 3 bit
This value refers to IEEE 802.1p priority. The field is used by 802.1Q to implement Layer 2 quality of service (QoS). It indicates the frame priority level. Values are from 0 (best effort) to 7 (highest)

Canonical Format Indicator (CFI) – 1 bit
This bit is used for compatibility purposes between Ethernet and Token Ring. 0 – Ethernet, 1 – Token Ring

VLAN Identifier (VID) – 12 bit
The VID field is used to distinguish between VLANs on the link. It has 12 bits allowing identification of 4096 (2^12) VLANs. It can be any number between 1 and 4,095 (zero has been reserved to mean that the frame is not a member of any VLAN).


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sFlow is a technology for monitoring traffic in data networks containing switches and routers.

The sFlow monitoring system consists of an sFlow Agent (embedded in a switch or router or in a standalone probe) and a central sFlow Collector.

The sFlow Agent uses sampling technology to capture traffic statistics from the device it is monitoring. sFlow Datagrams are used to immediately forward the sampled traffic statistics to an sFlow Collector for analysis.

An sFlow Collector receives sFlow Datagrams from one or more sFlow Agents.

The current version is 5. It has superceded RFC 3176 that describes v.4

OSI Summary

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Application Layer 7
The Application Layer is where the data is created.

Presentation Layer 6
It takes information from the Application Layer and presents it in its
proper format.

Session Layer 5
The Session Layer’s job is keeping track of conversations.

Transport Layer 4
Makes sure that data gets there reliably

Network Layer 3
The Network Layer’s job is to decide how to get there

Data Link Layer 2
make sure the data gets to the physical devices it needs to

Physical Layer 1
Physical Layer is the layer that does the actual transmitting of data.