Tag Archives: technology
Working of a CAM
Let us see how CAM works in hardware. As mentioned earlier CAM can be binary or ternary.
Binary CAM cell
CAM logic will simply have the storage circuitry and comparator logic to provide the match information for the searches performed. In this case a XOR gate is used to compare between the stored data and the searched data.
Ternary CAM cell
A Ternary cam as the name indicates has three states 0,1 and X. A “don’t care” condition exists in a ternary CAM to mask off certain bits for a partial match. The possibility of masking off of certain bits of the data opens up a wide range of applications where partial match is necessary; for instances at the edge of a router, where the router only worries about the destination network address and not the host ID.( An IP address consists of two fields: network ID and host ID).
Software and Hardware CAM
Hardware search engines are faster than algorithmic approaches for search intensive applications. Also, the turnaround time of a hardware CAM would be highly deterministic while that of software would depend on how efficiently the search-tree balancing algorithm is implemented. However, software would results in low costs. Hybrid CAMS integrate the robustness of a hardware CAM while providing the flexibility of high degree of software programming.
Types of CAMs
Fundamentally, CAM’s are of two types binary and ternary. As the name indicates a binary CAM has two bit states (’1′ and a ’0′), while a ternary CAM has ’1′, ’0′ and a third state called “don’t care”, so a search-hit on a ternary CAM would be an exact match or a partial match.
Currently, ternary CAMs are defacto in the industry. These bring the possibility of multiple match in a lookup table. All the access list tables for packet forwarding use a popular address resolution algorithm called the longest prefix match where the addresses are placed in the CAM based on certain priorities and the CAM by itself has priority encoder that helps in resolving the winning address.
CAM's : Memories Faster then RAM's
Content Addressable Memorys (CAM’s) in their most trivial form, work in a way opposite to conventional memories. While a random access memory (RAM) returns data upon providing the address, a CAM provides address when data is supplied. So effectively a CAM is a search tool that looks for the data in question within its data base.
CAM’s commonly work as hardware search engines in routers and switches to accelerate forwarding of packets on the destination route. We will talk about the various other applications that consider a CAM as an important processing engine as we proceed engine as we proceed in this article.
As indicated in its definition, CAM holds the address to be looked up for and returns the route associated information to the host processor to perform the successive tasks of forwarding the incoming packet. So we can also define a CAM as a network coprocessor to the central processor.
Note that TCP/IP and /or OSI models are taken here as reference to explain the concepts similar analogies may be drawn with other protocols like IPX/SPX, Apple Talk and UDP.
What is IPTV
IPTV delivers television programs to households via a broadband connection using internet protocols. Since it is in digital format, all analogue TVs require an IPTV set-top box (STB). IPTV is clubbed with other services like video on demand (VoD), voice over IP (VOIP) or digital phone and web access, collectively referred to as triple play. Triple play implies high speed internet and television/telephone service over a single broadband connection. With wireless, it is called quadruple play and grouped services (triple and quadruple) are called multi-play. Accordingly, IPTV comprises TV series provided over network, controlled by service operators such as telecom, cable or internet service providers.
IPTV vs DTH, digital.cable TV
A common question is being often asked:does IPTV score over digital TV, cable TV and DTH? It will not be appropriate to compare IPTV with other modes of broadcast. IPTV as a service will further augment what is available on DTH and other traditional forms. Thus IPTV will complement them and to compete with them.
Static phase converters and their different types
Static phase converters are used for operating three phase equipment with single phase power supply. With the help of a three phase generating rotary phase converter, you can operative three phase equipment from normal residential single phase power supply. Static phase converters operate by charging and discharging capacitors to temporarily produce a third phase of power for only a matter of seconds during the startup of electric motors. It then drops out forcing the motor to continue to run on just one phase.
Static phase converters do not actually convert single phase power into three phase power, nor do these generate three phase power. Due to their technology, they do not properly power a three phase machinery or equipment. They have limited utility as they are unable to power all types of machinery with three phase circuitry. They also reliability scale.
The performance of static phase converter is inferior to a true rotary phase converter built with a three phase generator that provides true three phase power.
