Simple Network Management Protocol
Simple Network Management Protocol is an Internet Standard protocol for collecting and organizing information about managed devices on IP networks and for modifying that information to change device behavior. Devices that support SNMP include cable modems, switches, workstations and more. SNMP is used in network management for network monitoring. SNMP exposes management data in the form of variables on the managed systems organized in a management information base which describe the system status and configuration; these variables can be remotely queried by managing applications. Three significant versions of SNMP have been deployed. SNMPv1 is the original version of the protocol. More recent versions, SNMPv2c and SNMPv3, feature improvements in performance and security. SNMP is a component of the Internet Protocol Suite as defined by the Internet Engineering Task Force, it consists of a set of standards for network management, including an application layer protocol, a database schema, a set of data objects.
In typical uses of SNMP, one or more administrative computers called managers have the task of monitoring or managing a group of hosts or devices on a computer network. Each managed system executes a software component called an agent which reports information via SNMP to the manager. An SNMP-managed network consists of three key components: Managed devices Agent – software which runs on managed devices Network management station – software which runs on the managerA managed device is a network node that implements an SNMP interface that allows unidirectional or bidirectional access to node-specific information. Managed devices exchange node-specific information with the NMSs. Sometimes called network elements, the managed devices can be any type of device, but not limited to, access servers, cable modems, hubs, IP telephones, IP video cameras, computer hosts, printers. An agent is a network-management software module. An agent has local knowledge of management information and translates that information to or from an SNMP-specific form.
A network management station executes applications that control managed devices. NMSs provide the bulk of the memory resources required for network management. One or more NMSs may exist on any managed network. SNMP agents expose management data on the managed systems as variables; the protocol permits active management tasks, such as configuration changes, through remote modification of these variables. The variables accessible via SNMP are organized in hierarchies. SNMP itself does not define which variables a managed system should offer. Rather, SNMP uses an extensible design; these hierarchies are described as a management information base. MIBs describe the structure of the management data of a device subsystem; each OID identifies a variable that can be read or set via SNMP. MIBs use the notation defined by Structure of Management Information Version 2.0, a subset of ASN.1. SNMP operates in the application layer of the Internet protocol suite. All SNMP messages are transported via User Datagram Protocol.
The SNMP agent receives requests on UDP port 161. The manager may send requests from any available source port to port 161 in the agent; the agent response is sent back to the source port on the manager. The manager receives notifications on port 162; the agent may generate notifications from any available port. When used with Transport Layer Security or Datagram Transport Layer Security, requests are received on port 10161 and notifications are sent to port 10162. SNMPv1 specifies five core protocol data units. Two other PDUs, GetBulkRequest and InformRequest were added in SNMPv2 and the Report PDU was added in SNMPv3. All SNMP PDUs are constructed as follows: The seven SNMP PDU types as identified by the PDU-type field are as follows: GetRequest A manager-to-agent request to retrieve the value of a variable or list of variables. Desired variables are specified in variable bindings. Retrieval of the specified variable values is to be done as an atomic operation by the agent. A Response with current values is returned.
SetRequest A manager-to-agent request to change the value of a variable or list of variables. Variable bindings are specified in the body of the request. Changes to all specified variables are to be made as an atomic operation by the agent. A Response with new values for the variables is returned. GetNextRequest A manager-to-agent request to discover available variables and their values. Returns a Response with variable binding for the lexicographically next variable in the MIB; the entire MIB of an agent can be walked by iterative application of GetNextRequest starting at OID 0. Rows of a table can be read by specifying column OIDs in the variable bindings of the request. GetBulkRequest A manager-to-agent request for multiple iterations of GetNextRequest. An optimized version of GetNextRequest. Returns a Response with multiple variable bindings walked from the variable binding or bindings in the request. PDU specific non-repeaters and max-repetitions fields are used to control response behavior.
GetBulkRequest was introduced in SNMPv2. Response Returns variable bindings and acknowledgement from agent to manager for GetRequest, SetRequest, GetNextRequest, GetBulkRequest and InformRequest. Error reporting is provided by error-index fields. Although it was used as a response to both gets and sets, this P
A residential gateway is a small consumer-grade router which provides network access between local area network hosts to a wide area network via a modem. The modem may not be integrated into the hardware of the residential gateway; the WAN is a larger computer network operated by an Internet service provider. Multiple devices have been described as "residential gateways": Cable modem DSL modem Wireless router Network switch Voice over internet protocol analog telephone adapter Wireless access point Wired routeror certain combinations of the above. A modem by itself provides none of the functions of a router, it allows ATM or Ethernet or PPP traffic to be transmitted across telephone lines, cable wires, optical fibers, or wireless radio frequencies. On the receiving end is another modem that re-converts the transmission format back into digital data packets; this allows network bridging using telephone, cable and radio connection methods. The modem provides handshake protocols, so that the devices on each end of the connection are able to recognize each other.
However, a modem provides few other network functions. A USB modem plugs into a single PC and allows a connection of that single PC to a WAN. If properly configured, the PC can function as the router for a home LAN. An internal modem can be installed on a single PC allowing that single PC to connect to a WAN. Again, the PC can be configured to function as a router for a home LAN. A wireless access point can function in a similar fashion to a modem, it can allow a direct connection from a home LAN to a WAN, if a wireless router or access point is present on the WAN as well. However, many modems now incorporate the features mentioned below and thus are appropriately described as residential gateways. A residential gateway provides configuration via a web interface, routing between the home network and the Internet, connectivity within the home network like a network switch, network address translation for IPv4, DHCP for IPv4 and router advertisements for IPv6, firewall functions. May have an internal modem, most for DSL or Cable ISP.
It may provide other functions such as Dynamic DNS. Most routers are self-contained components, they are OS-independent, i.e. they can be accessed with any operating system. Wireless routers perform the same functions as a router, but allow connectivity for wireless devices with the LAN, or between the wireless router and another wireless router. Low-cost production and requirement for user friendliness makes the home routers vulnerable to network attacks, which in the past resulted in large clusters of such devices being taken over and used to launch DDoS attacks. A majority of the vulnerabilities were present in the web administration consoles of the routers, allowing unauthorised control either via default passwords, vendor backdoors, or web vulnerabilities; the Residential Gateway Home Gateway Initiative, a group of broadband providers proposing specifications for residential gateways The Residential Home Gateway on About.com
A cable modem is a type of network bridge that provides bi-directional data communication via radio frequency channels on a hybrid fibre-coaxial and radio frequency over glass infrastructure. Cable modems are used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high bandwidth of a HFC and RFoG network, they are deployed in Australia, Europe and America. Internet Experiment Note. From pages 2 and 3 of IEN 96: The Cable-Bus System The MITRE/Washington Cablenet system is based on a technology developed at MITRE/Bedford. Similar cable-bus systems are in operation at a number of government sites, e.g. Walter Reed Army Hospital, the NASA Johnson Space Center, but these are all standalone, local-only networks; the system uses standard Community Antenna Television coaxial cable and microprocessor based Bus Interface Units to connect subscriber computers and terminals to the cable.... The cable bus consists of one inbound and the other outbound; the inbound cable and outbound cable are connected at one end, the headend, electrically terminated at their other ends.
This architecture takes advantage of the well developed unidirectional CATV components. The topology is dendritic.... The BIUs contain Radio Frequency modems which modulate a carrier signal to transmit digital information using 1 MHz of the available bandwidth in the 24 MHz frequency range; the remainder of the 294 MHz bandwidth can be used to carry other communication channels, such as off-the-air TV, FM, closed circuit TV, or a voice telephone system, or, other digital channels. The data rate of our test-bed system is 307.2 kbps. The IEEE 802 Committee defined 10BROAD36 in 802.3b-1985 as a 10 Mbit/s IEEE 802.3/Ethernet broadband system to run up to 3,600 metres over CATV coax network cabling. The word broadband as used in the original IEEE 802.3 specifications implied operation in frequency-division multiplexed channel bands as opposed to digital baseband square-waveform modulations, which begin near zero Hz and theoretically consume infinite frequency bandwidth. In the market 10BROAD36 equipment was not developed by many vendors nor deployed in many user networks as compared to equipment for IEEE 802.3/Ethernet baseband standards such as 10BASE5, 10BASE2, 10BASE-T, etc.
The IEEE 802 Committee specified a broadband CATV digital networking standard in 1989 with 802.7-1989. However, like 10BROAD36, 802.7-1989 saw little commercial success. Hybrid Networks developed and patented the first high-speed, asymmetrical cable modem system in 1990. A key Hybrid Networks insight was that in the nascent days of the Internet, data downloading constitutes the majority of the data traffic, this can be served adequately with a asymmetrical data network; this allowed CATV operators to offer high speed data services without first requiring an expensive system upgrade. Key was that it saw that the upstream and downstream communications could be on the same or different communications media using different protocols working in each direction to establish a closed loop communications system; the speeds and protocols used in each direction would be different. The earliest systems used the public switched telephone network for the return path since few cable systems were bi-directional.
Systems used CATV for the upstream as well as the downstream path. Hybrid's system architecture is used for most cable modem systems today. LANcity was an early pioneer in cable modems, developing a proprietary system, deployed in the U. S. LANcity, led by the Iranian-American engineer Rouzbeh Yassini, was acquired by Nortel, which spun the cable modem business off as ARRIS. ARRIS CMTS equipment compliant with the DOCSIS standard. Zenith offered a cable modem technology using its own protocol which it introduced in 1993, being one of the first cable modem providers; the Zenith Cable Modem technology was used by several cable television systems in the United States and other countries, including Cox Communications San Diego, Knology in the Southeast United States, Ameritech's Americast service, Cogeco in Hamilton Ontario and Cablevision du Nord de Québec in Val-d'Or. Zenith Homeworks used BPSK modulation to achieve 500 Kbit/sec in 4 Mbit/sec in 6 MHz. Com21 was another early pioneer in cable modems, quite successful until proprietary systems were made obsolete by the DOCSIS standardization.
The Com21 system used a ComController as central bridge in CATV network head-ends, the ComPort cable modem in various models and the NMAPS management system using HP OpenView as platform. They introduced a return path multiplexer to overcome noise problems when combining return path signals from multiple areas; the proprietary protocol was based on Asynchronous Transfer Mode. The central ComController switch was a modular system offering one downstream channel and one management module; the remaining slots could be used for upstream receivers, dual Ethernet 10BaseT and also Fast-Ethernet and ATM interfaces. The ATM interface became the most popular, as it supported the increasing bandwidth demands and supported VLANs. Com21 developed a DOCSIS modem; the DOCSIS C
Cable television is a system of delivering television programming to consumers via radio frequency signals transmitted through coaxial cables, or in more recent systems, light pulses through fiber-optic cables. This contrasts with broadcast television, in which the television signal is transmitted over the air by radio waves and received by a television antenna attached to the television. FM radio programming, high-speed Internet, telephone services, similar non-television services may be provided through these cables. Analog television was standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operation. A "cable channel" is a television network available via cable television; when available through satellite television, including direct broadcast satellite providers such as DirecTV, Dish Network and Sky, as well as via IPTV providers such as Verizon FIOS and AT&T U-verse is referred to as a "satellite channel". Alternative terms include "non-broadcast channel" or "programming service", the latter being used in legal contexts.
Examples of cable/satellite channels/cable networks available in many countries are HBO, Cinemax, MTV, Cartoon Network, AXN, E!, FX, Discovery Channel, Canal+, Fox Sports, Disney Channel, Nickelodeon, CNN International, ESPN. The abbreviation CATV is used for cable television, it stood for Community Access Television or Community Antenna Television, from cable television's origins in 1948. In areas where over-the-air TV reception was limited by distance from transmitters or mountainous terrain, large "community antennas" were constructed, cable was run from them to individual homes; the origins of cable broadcasting for radio are older as radio programming was distributed by cable in some European cities as far back as 1924. To receive cable television at a given location, cable distribution lines must be available on the local utility poles or underground utility lines. Coaxial cable brings the signal to the customer's building through a service drop, an overhead or underground cable. If the subscriber's building does not have a cable service drop, the cable company will install one.
The standard cable used in the U. S. is RG-6, which has a 75 ohm impedance, connects with a type F connector. The cable company's portion of the wiring ends at a distribution box on the building exterior, built-in cable wiring in the walls distributes the signal to jacks in different rooms to which televisions are connected. Multiple cables to different rooms are split off the incoming cable with a small device called a splitter. There are two standards for cable television. All cable companies in the United States have switched to or are in the course of switching to digital cable television since it was first introduced in the late 1990s. Most cable companies require a set-top box or a slot on one's TV set for conditional access module cards to view their cable channels on newer televisions with digital cable QAM tuners, because most digital cable channels are now encrypted, or "scrambled", to reduce cable service theft. A cable from the jack in the wall is attached to the input of the box, an output cable from the box is attached to the television the RF-IN or composite input on older TVs.
Since the set-top box only decodes the single channel, being watched, each television in the house requires a separate box. Some unencrypted channels traditional over-the-air broadcast networks, can be displayed without a receiver box; the cable company will provide set top boxes based on the level of service a customer purchases, from basic set top boxes with a standard definition picture connected through the standard coaxial connection on the TV, to high-definition wireless DVR receivers connected via HDMI or component. Older analog television sets are "cable ready" and can receive the old analog cable without a set-top box. To receive digital cable channels on an analog television set unencrypted ones, requires a different type of box, a digital television adapter supplied by the cable company. A new distribution method that takes advantage of the low cost high quality DVB distribution to residential areas, uses TV gateways to convert the DVB-C, DVB-C2 stream to IP for distribution of TV over IP network in the home.
In the most common system, multiple television channels are distributed to subscriber residences through a coaxial cable, which comes from a trunkline supported on utility poles originating at the cable company's local distribution facility, called the "headend". Many channels can be transmitted through one coaxial cable by a technique called frequency division multiplexing. At the headend, each television channel is translated to a different frequency. By giving each channel a different frequency "slot" on the cable, the separate television signals do not interfere with each other. At an outdoor cable box on the subscriber's residence the company's service drop cable is connected to cables distributing the signal to different rooms in the building. At each television, the subscriber's television or a set-top box provided by the cable company translates the desired channel back to its original frequency, it is displayed onscreen. Due to widespread cable theft in earlier analog systems, the signals are encrypted on m
A set-top box or set-top unit is an information appliance device that contains a TV-tuner input and displays output to a television set and an external source of signal, turning the source signal into content in a form that be displayed on the television screen or other display device. They are used in cable television, satellite television, over-the-air television systems, as well as other uses. According to the Los Angeles Times, the cost to a cable provider for a set-top box is between $150 for a basic box to $250 for a more sophisticated box in the United States. In 2016, the average pay-TV subscriber paid $231 per year to lease their set-top box from a cable service provider; the signal source might be an Ethernet cable, a satellite dish, a coaxial cable, a telephone line, broadband over power lines, or an ordinary VHF or UHF antenna. Content, in this context, could mean any or all of video, Internet web pages, interactive video games, or other possibilities. Satellite and microwave-based services require specific external receiver hardware, so the use of set-top boxes of various formats has never disappeared.
Set-top boxes can enhance source signal quality. Before the All-Channel Receiver Act of 1962 required US television receivers to be able to tune the entire VHF and UHF range, a set-top box known as a UHF converter would be installed at the receiver to shift a portion of the UHF-TV spectrum onto low-VHF channels for viewing; as some 1960s-era 12-channel TV sets remained in use for many years, Canada and Mexico were slower than the US to require UHF tuners to be factory-installed in new TVs, a market for these converters continued to exist for much of the 1970s. Cable television represented a possible alternative to deployment of UHF converters as broadcasts could be frequency-shifted to VHF channels at the cable head-end instead of the final viewing location. However, most cable systems could not accommodate the full 54-890 MHz VHF/UHF frequency range and the twelve channels of VHF space were exhausted on most systems. Adding any additional channels therefore needed to be done by inserting the extra signals into cable systems on nonstandard frequencies either below VHF channel 7 or directly above VHF channel 13.
These frequencies corresponded to non-television services over-the-air and were therefore not on standard TV receivers. Before cable-ready TV sets became common in the late 1980s, an electronic tuning device called a cable converter box was needed to receive the additional analog cable TV channels and transpose or convert the selected channel to analog radio frequency for viewing on a regular TV set on a single channel VHF channel 3 or 4; the box allowed an analog non-cable-ready television set to receive analog encrypted cable channels and was a prototype topology for date digital encryption devices. Newer televisions were converted to be analog cypher cable-ready, with the standard converter built-in for selling premium television. Several years and marketed, the advent of digital cable continued and increased the need for various forms of these devices. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCR compatibility and the ability to drive multiple TV sets, albeit with a somewhat nonstandard channel numbering scheme.
Newer television receivers reduced the need for external set-top boxes, although cable converter boxes continue to be used to descramble premium cable channels according to carrier-controlled access restrictions, to receive digital cable channels, along with using interactive services like video on demand, pay per view, home shopping through television. Set-top boxes were made to enable closed captioning on older sets in North America, before this became a mandated inclusion in new TV sets; some have been produced to mute the audio when profanity is detected in the captioning, where the offensive word is blocked. Some include a V-chip that allows only programs of some television content ratings. A function that limits children's time watching TV or playing video games may be built in, though some of these work on main electricity rather than the video signal; the transition to digital terrestrial television after the turn of the millennium left many existing television receivers unable to tune and display the new signal directly.
In the United States, where analog shutdown was completed in 2009 for full-service broadcasters, a federal subsidy was offered for coupon-eligible converter boxes with deliberately limited capability which would restore signals lost to digital transition. Professional set-top boxes are referred to as IRDs or integrated receiver/decoders in the professional broadcast audio/video industry, they are designed for rack mounting environments. IRDs are capable of outputting uncompressed serial digital interface signals, unlike consumer STBs which don't because of copyright reasons. Hybrid set-top boxes, such as those used for Smart TV programming, enable viewers to access multiple TV delivery methods. By integrating varying delivery streams, hybrids enable pay-TV operators more flexible application depl
Cable modem termination system
A cable modem termination system or CMTS is a piece of equipment located in a cable company's headend or hubsite, used to provide high speed data services, such as cable Internet or Voice over Internet Protocol, to cable subscribers. A CMTS provides many of the same functions provided by the DSLAM in a DSL system. In order to provide high speed data services, a cable company will connect its headend to the Internet via high capacity data links to a network service provider. On the subscriber side of the headend, the CMTS enables the communication with subscribers' cable modems. Different CMTSs are capable of serving different cable modem population sizes—ranging from 4,000 cable modems to 150,000 or more, depending in part on traffic. A given headend may have between 1-12 CMTSs to service the cable modem population served by that headend or HFC hub. One way to think of a CMTS is to imagine a router with Ethernet interfaces on one side and coaxial cable RF interfaces on the other side; the RF/coax interfaces carry.
In fact, most CMTSs have both Ethernet interfaces as well as RF interfaces. In this way, traffic, coming from the Internet can be routed through the Ethernet interface, through the CMTS and onto the RF interfaces that are connected to the cable company's hybrid fiber coax; the traffic winds its way through the HFC to end up at the cable modem in the subscriber's home. Traffic from a subscriber's home system goes through the cable modem and out to the Internet in the opposite direction. CMTSs carry only IP traffic. Traffic destined for the cable modem from the Internet, known as downstream traffic, is carried in IP packets encapsulated according to DOCSIS standard; these packets are carried on data streams that are modulated onto a TV channel using either 64-QAM or 256-QAM versions of quadrature amplitude modulation. Upstream data is carried in Ethernet frames encapsulated inside DOCSIS frames modulated with QPSK, 16-QAM, 32-QAM, 64-QAM or 128-QAM using TDMA, ATDMA or S-CDMA frequency sharing mechanisms.
This is done at the "subband" or "return" portion of the cable TV spectrum, a much lower part of the frequency spectrum than the downstream signal 5 - 42 MHz in DOCSIS 2.0 or 5 - 60 MHz in EuroDOCSIS. A typical CMTS allows a subscriber's computer to obtain an IP address by forwarding DHCP requests to the relevant servers; this DHCP server returns, for the most part, what looks like a typical response including an assigned IP address for the computer, gateway/router addresses to use, DNS servers, etc. The CMTS may implement some basic filtering to protect against unauthorized users and various attacks. Traffic shaping is sometimes performed to prioritize application traffic based upon subscribed plan or download usage and to provide guaranteed Quality of service for the cable operator's own PacketCable-based VOIP service. However, the function of traffic shaping is more done by a Cable Modem or policy traffic switch. A CMTS may act as a bridge or router. A customer's cable modem cannot communicate directly with other modems on the line.
In general, cable modem traffic is routed to other cable modems or to the Internet through a series of CMTSs and traditional routers. However, a route could conceivably pass through a single CMTS. A CMTS can be broken down into Integrated CMTS or Modular. There are both cons to each type of architecture; the I-CMTS architecture consists of all components housed in a single chassis. The RF interface and IP Networking components are all integrated in a single device; this makes for much simpler RF combining in the headend. The benefits of an all-in-one solution are less single points of failure, lower costs and ease of deployment. In an M-CMTS solution the architecture is broken up into two components; the first part is the Physical Downstream component, known as the Edge QAM. The second part is the IP networking and DOCSIS MAC Component, referred to as the M-CMTS Core. There are several new protocols and components introduced with this type of architecture. One is the DOCSIS Timing Interface, which provides a reference frequency between the EQAM and M-CMTS Core via a DTI Server.
The second is the Downstream External PHY Interface. The DEPI protocol controls the delivery of DOCSIS frames from the M-CMTS Core to the EQAM devices Some of the challenges that entail an M-CMTS platform are increased complexity in RF combining and an increase in the number of failure points. One of the benefits of an M-CMTS architecture is that it is scalable to larger numbers of downstream channels. ARRIS Group C9 Networks Catapult Technologies Coaxial Networks Inc. Casa Systems Cisco Systems Chongqing Jinghong Damery sa Gainspeed WISI Communications GmbH Kathrein Suma Scientific Huawei Technologies Harmonic Inc. Teleste 3COM Broadband Access Systems ADC Telecommunications BigBand Networks Cadant Com21 RiverDelta Terayon Pacific Broadband Communications Juniper Networks Motorola Daphne sa DOCSIS