free invisible hit counter

Kabel Modem Flap

Kabel Modems can have a problem known in industry jargon as “flap” or “flapping”. A modem flap is when the connection by the modem to the head-end has been dropped (gone offline) and then comes back online. The time offline or rate of flap is not typically recorded, only the incidence. While this is a common occurrence and usually unnoticed, if a modem’s flap is extremely high, these disconnects can cause service to be disrupted. If there are usability problems due to flap the typical cause is a defective modem or very high amounts of traffic on the service provider’s network (upstream utilization too high). Types of flap include reinsertions, hits and misses, and power adjustments.

Network Architectural Functions

In network topology, a kabel modem is a network bridge that conforms to IEEE 802.1D for Ethernet networking (with some modifications). The kabel modem bridges Ethernet frames between a customer LAN and the coax network. Technically, it is a modem because it must modulate data to transmit it over the cable network, and it must demodulate data from the cable network to receive it. With respect to the OSI model of network design, a kabel modem is both Physical Layer (Layer 1) device and a Data Link Layer (Layer 2) forwarder. As an IP addressable network node, kabel modems support functionality at other layers.

Kabel Modem Flap

Kabel Modem Flap

Layer 1 is implemented in the Ethernet PHY on its LAN interface, and a DOCSIS defined cable-specific PHY on its HFC cable interface. The term kabel modem refers to this cable-specific PHY. The Network Layer (Layer 3) is implemented as an IP host in that it has its own IP address used by the network operator to maintain the device. In the Transport Layer (Layer 4) the cable modem supports UDP in association with its own IP address, and it supports filtering based on TCP and UDP port numbers to, for example, block forwarding of NetBIOS traffic out of the customer’s LAN. In the Application Layer (Layer 7), the cable modem supports certain protocols that are used for management and maintenance, notably Dynamic Host Configuration Protocol (DHCP), SNMP, and TFTP.

Some cable modems may incorporate a router and a DHCP server to provide the LAN with IP network addressing. From a data forwarding and network topology perspective, this router functionality is typically kept distinct from the cable modem functionality (at least logically) even though the two may share a single enclosure and appear as one unit, sometimes called a residential gateway. So, the cable modem function will have its own IP address and MAC address as will the router.

source : http://en.wikipedia.org/wiki/Cable_modem


Kabeldeutschlandsky.com is a website that collects various types of cables from various sources on the Internet. There are Kabel Deutschland, BW, HDMI, TV, USB, Receiver, DSL Speedtest

Advertisement

Comments are closed.