Cable internet docsis 2.0 and 3.0. DOCSIS technology: what it is and how to connect. When the DOCSIS standard appeared and who is it useful

Actually, the abbreviation DOCSIS has been heard by many, but not everyone knows what it is and why it is needed. The most curious could even be enlightened by this question in Wikipedia, but as practice shows, quite a lot of questions still remain. So, we begin to tear off the veils, let's deal with the questions:
1. what is it?
2. Who needs it?
3. What is needed for this?
4. how to start?

The faint of heart who do not want to delve into "How it" s made? please do not look under the habrakat - there is nothing interesting there.

So let's start with a general theory.
The abbreviation DOCSIS (Data Over Cable Service Interface Specifications) denotes the data transmission standard for television cable, which was adopted in 98. This standard in the original assumes data transmission up to 42/38 Mbit / s in the downstream (to the user) and up to 10/9 Mbit / s in the upstream (from the user).
Those who are faced with technology for the first time often have a question - is this for everyone? No - the band is shared among all users hanging on these DS / US.

There are several versions of DOCSIS:
- DOCSIS 1.0
- DOCSIS 1.1
- DOCSIS 2.0
- DOCSIS 3.0
- EURODOCSIS
Without going into details, the differences between the two boil down to QoS, frequencies, link aggregation, bandwidth, and modulations. Actually, all this is directly related to the speed and viability in noisy networks.

Who needs it?
Need it first existing to KTV operators to expand the range of services by providing end users with high-speed Internet access and related add-ons (VoIP, IPTV, or whatever the imagination is enough for).
I emphasized the word "existing" and because of the following (I think an obvious consideration).

Deploying a coaxial network just for the sake of providing Internet access to users from scratch is at least stupid and economically unreasonable, since there are much cheaper and fast technologies (e.g. FTTB, ADSL, PON). As an example, if you are not a KTV operator, but let's say a PBX, then again it is not useful to build a coaxial network throughout the city much cheaper to go to ADSL - I think it's understandable.

With the existing well-built coaxial network covering a significant area, DOCSIS can be an optimal start, requiring minimal intervention in physics. Especially in sparsely populated areas such as the private sector, where the density of couplings / switches / boxes per consumer unit can be cosmic in the case of FTTB. Again, in the case of multi-storey buildings (so-called residential areas) with existing competition in the form of "home networks", it may make sense to deploy a parallel coaxial FTTB network, or if you really want to use HCNA, it will be cheaper and more promising.

Equipment
In general terms, a typical diagram would look like this:

Actually, from the googled picture, it immediately becomes clear that in order to provide the end user with the Internet, it is required:
1.the cloud in which the Internet lives;)
2.server with installed DHCP, TFTP services
3.CMTS (Cable Modem Termination System)
4.coaxial network going to the subscriber
5.the user wants to connect to the modem

Let's briefly go over the points indicated above.
1. with the Internet everything is clear - let's say we have it
2. We will use the server on something with which the administrator is familiar. Let's assume he is familiar with FreeBSD / Linux;)
3. CMTS ... there are different black, white dirty. A short list of manufacturers can be found. For those who are completely uninformed, it is (very rude) such a large and expensive modem to which subscriber modems are linked.
4. The main requirement for the network is serviceability and the presence of a reverse channel on the amplifiers. Serviceability is the permanent removal of illegal immigrants and monitoring the signal levels in the forward and reverse channels. A seasonal signal chat can be a big problem for your users and your support team.
5. A short list of modem manufacturers is available. Docsis modem is a rather specific device that provides quite wide opportunities - starting with a limitation bandwidth the subscriber right on his modem and ending with filters (roughly remotely controlled firewall).

Where to begin?
Recently, administrators whose bosses have been knocking on me with enviable regularity, guided by the considerations set forth in "Who needs it?" bought a CMTS (for some reason, most often it is something like used BSR1000, BSR2000, CiscoUBR) and said "put the Internet into the KTV network."
For people already familiar with Ethernet or ADSL scheme work DOCSIS networks it may not be entirely transparent, and the number of gestures necessary for at least one modem to ping is finally stoned. It's quite difficult to do something without understanding the general principles of how it should work. The first thought that comes to mind is to screw the modem directly to the CMTS and see what happens. Naturally, nothing will work out - the modem will simply flicker with light and music lights and that's it. Nothing else will happen.

When trying to connect, the modem scans the entire frequency range for the presence of downstream / upstream and if it finds it tries to get an address via DHCP for the modem, if the address is received, the modem tries to get a specially collected config for itself via TFTP, after which, if the config is normally chewed, it tries to get DHCP address for CPE (customer-provided equipment) which will most likely be a network card or a router.

It should work normally on the test bench like this:
1.CMTS is configured
2. The above services are raised on the server
3. the modem is connected via a pack of tapes to provide nominal signal levels for DS / US.

1. We will not focus on setting up the CMTS, because depending on the manufacturer, the physical realities of the network and the planned network topology, it will vary greatly. I am pleased with the comprehensive documentation that came with all the devices that came into my hands - I think it should be more or less clear for people familiar with the cisco-like interface and the general theory of configuring network devices.

The minimum hand passes over the CMTS to be ready for bench testing are as follows:
- prescribe the DS frequency
- prescribe frequencies and modulations for US
- we register the address of the DHCP server that we will reel
- register a secret key for configs
- we register passwords
- we keep

2. We raise the services we need on the server.

# cd / usr / ports / net / isc-dhcp31-server / && make install (build with Option82 support)
tftpd most likely we have by default, just uncomment it in /etc/inetd.conf
#cd / usr / ports / net-mgmt / docsis && make install
Which we need to generate binary configs for DOCSIS-compatible modems, as pkg-descr says.

Let's say we have configured the CMTS as 10.10.10.9 releasing DHCP rquests to our host's network with an ipish 10.10.10.10 looking at the CMTS. Then our /usr/local/etc/dhcpd.conf should look like this
option domain-name "catv";
option domain-name-servers 10.10.10.10;
default-lease-time 3600;
max-lease-time 43200;
authoritative;
ddns-update-style none;
log-facility local7;
one-lease-per-client true;
deny duplicates;

Subnet 10.10.200.0 netmask 255.255.248.0 (
default-lease-time 3600;
max-lease-time 86400;
option domain-name-servers 10.10.10.10;

option routers 10.10.200.1;

Include "/usr/local/etc/users_dhcp.conf";
}

Subnet 10.10.100.0 netmask 255.255.248.0 (
default-lease-time 3600;
option subnet-mask 255.255.248.0;
option routers 10.10.100.1;
server-name "10.10.10.10";
option tftp-server-name "10.10.10.10";
option bootfile-name "cm_config / other.b";
next-server 10.10.10.10;
filename "cm_config / other.b";
option time-servers 10.10.10.10;
option time-offset 2;

Include "/usr/local/etc/modems_dhcp.conf";

From which it should be clear that we reserve the 10.10.100 / 21 network for modems and 10.10.200 / 21 user CPE networks

For ease of use in the future, we will include hosts for sabets from /usr/local/etc/modems_dhcp.conf and /usr/local/etc/users_dhcp.conf respectively. First, in /usr/local/etc/modems_dhcp.conf, we enter our test modem in the form

Host m1002 (
hardware ethernet 00: ff: ff: 55: ff: f2;
fixed-address 10.10.100.3;
filename "cm_config / testmodem.b";
}

And add your test host to /usr/local/etc/users_dhcp.conf:

Host m10102002 (
hardware ethernet 00: cc: cc: 99: aa: ff;
fixed-address 10.10.200.2;
}

The filename directive should hint that it contains the path (relative to tftp root, which is usually in / tftpboot) to the binary config of the modem. In the simplest case, the modem config (not suitable for real use! For testing purposes only! Achtung!) Will look like this:

#cat / tftpboot / cm_source / testing

Main (
NetworkAccess 1;

GlobalPrivacyEnable 0;
UsServiceFlow
{
UsServiceFlowRef 200;
QosParamSetType 7;
MaxRateSustained 0;
SchedulingType 2;
}
DsServiceFlow
{
DsServiceFlowRef 100;
QosParamSetType 7;
TrafficPriority 3;
MaxRateSustained 0;
}

MaxCPE 16;
}

Now we need to compile it into a form acceptable for the modem using the previously compiled docsis utility using the secret-key specified on the CMTS

#echo "sosecret"\u003e / somewhere / key
#docsis -e / tftpboot / cm_source / testing / somewhere / key /tftpboot/cm_config/testing.b

We register routes for modem networks, and users on CMTS in rc.conf:

Static_routes \u003d "cable modem"
route_cable \u003d "10.10.200.0/21 10.10.10.9"
route_modem \u003d "10.10.100.0/21 10.10.10.9"

3. We collect from matches and acorns, pigtails and tapes, a structure that combines DS and one of the US and ensures the transmission of the signal levels specified in the documentation to the modem.

If we did everything right then at the CMTS at
bsr # show cable modem

We will see something like
Cable 0/0 / D0 / U0 / C0 431 online 1458 26.0 10.10.100.3 00ff.ff55.fff2

And accordingly, our test modem and test host which, as we remember, 10.10.100.3 and 10.10.200.2 should ping.

Do you see how simple and clear everything is? - and you were afraid. \u003d)

In the case of segmenting the network into multiple CMTSs to provide increased resiliency and performance, things look the same. And it boils down to the spreading of different networks for routines.

The above config is not adequate for real use for a number of reasons:

Least:
- no filters to isolate users
- there are no registered snmp for collecting statistics
- there is no binding of the modem to a specific CPE
It would also be nice to do:
- channel shaping directly on the device
- take into account the peculiarities of various devices
- cut off the web face of the modem, the user has nothing to do there
- competently build QoS

Initially, I really wanted to write a step-by-step manual on how to do not just "go the Internet" but also on how to competently sell them to end users, in fact, with examples of configs, ready-made ACP, etc. But since I am a writer, frankly speaking, no one - I'm trite ashamed to show my trash code, which, moreover, is quite narrowly specific and in any case requires deep refinement for a specific operator :)
In general terms, the billing requirements for the DOCSIS network are very simple:
- be able to count traffic
- be able to count money
- make flexible tariffs out of the calculated traffic money
- flexibly limit custom bandwidth
- be able to compile configs for modems for each user on the fly + edit dhcpd hosts.

If everything is clear with the first four points - and actually all the ACPs are mainly engaged in them, then the last one should focus on the latter. Naturally, you can issue one config for all, and then authenticate the user using the internal ACP mechanisms (motley authorizers) or, say, using the PPtP tunnel method, but I think this is just an additional crutch and a deliberate rejection of the very convenient opportunities provided by the technology.

I think now many, many people will say that the technology is dead, expensive, not relevant and poke my face in FTTB, PON, HCNA. Yes, I am aware that there are such and that, for example, in densely populated high-rise buildings, the price / port speed is ten times cheaper with FTTB and that HCNA provides much tastier speeds over the same coaxial with a comparable cost of subscriber hardware and there is no need to purchase a relatively expensive CMTS. If interested, I can explain on my fingers why FTTB is expensive in the private sector, and why HCNA there boils down to "almost FTTB" at the cost of the port, and also why the public is not yet ready for PON. Again, there are always motives for applying any still living technology, from “let's use the existing network” to “otherwise it will be too expensive and time-consuming”. Again, the choice to play dumping and race at home network speeds is not the best a good option with the above performance characteristics and the actual trump card of the DOCSIS provider should be IMHO services provided over one cable and their quality.
At this stage of development, DOCSIS 2.0 can compete more successfully with ADSL, and 3.0 is stepping on the heels of the rest as a promising platform for Triple Play.

As always at the end of the article, I use my weak excuse which sounds like:

“I'm not literate, I know. The language is not native, they were not taught at school, although I guess this is a weak excuse. If you take the missing comma as a personal insult, I apologize in advance. Honestly - I didn't want to "

As a rule, it works;)

The article was written for the special order of the magazine

Let's get acquainted with the peculiarities of the modem operation, as well as the data transfer rates using the DOCSIS 3.0 technology, in the Volia company network. How much does the practical speed correspond to the one declared by the provider? How does the modem "behave" in operation, and what are the conditions for providing the device for home and business users?

Appearance and connection

I will make a reservation right away - there are several types of modems that support DOCSIS 3.0 technology from Volia, and all of them are provided to users on certain terms. But let's not delve into the terms of providing devices to the end consumer for now, but consider the features of a specific model - the device that I had on testing - Thomson TCM 470.

So, the body of the device is made of two colors of matte plastic - black and white. Of course, this combination cannot be called one that "hooks", but the device itself is pretty and it cannot be taken away.

It cannot be said that black or white plastic is dominant in the assembly of the case - both are equally: the lower part of the case, as well as the front and rear walls are made of black plastic, while the upper part, as well as the right and left side walls are white.

Although the top of the modem is white, dust remains noticeably on the surface. Personally, I wiped the outer part of the modem's case almost every third day, along with cleaning the room in which the device is located.

The assembly of the device is wonderful. Despite the fact that the white part of the case is “dressed” on the black one, besides it is already tactilely easy to feel that we are dealing with durable and somewhat massive materials, the gaps in the end turned out to be minimal, not to mention the backlash. Nothing staggers, does not crunch, and does not differ in other examples of negligent assembly.

On all the walls of the case, except for the front one, many small holes are implemented. These are the so-called ventilation grids. The air ventilation system is silent. It should also be noted that the capabilities of the ventilation system implemented in this modem are very modest - when working for at least 9-10 hours in a row, the device case heats up noticeably. It is also good that even a noticeable heating does not affect the functionality of the device at all.

The front panel contains various indicators for displaying the status of processes in the system. It is not necessary to know their clear purpose, it is enough just to understand a simple thing - in order for the device to work correctly, it is necessary that the POWER, DS, US, and also ONLINE indicators light up without winking, and only the indicator with the Link signature blinks. If this task is completed, then the device is working correctly.

If the user connects to the modem Wi-Fi router or another "distributor" of the signal, it must "reset" the basic settings of the modem, which the system automatically assigns to the modem during the previous connection. To do this, just press and release the reset button, which is located on the rear side panel. After that, you only need to restart the computer, during which it is best to connect the router - a matter of several minutes.

In addition to the reset button, on the same panel there is an outlet for connecting a cable coming from a distribution board in a house or business center. There is also a port for connecting a cable that directly connects the modem itself to a computer or laptop, plus a button for switching the device's power supply.

On the lower operating panel, in addition to many ventilation holes, there is a sticker with various technical data about the device, as well as two gaps for fastening the modem with screws to a wall or a vertically located platform.

Practical speed indicators

The NetMeter utility, with the help of which all calculations were carried out, is interesting not only as a speed tester. Before us is a fairly simple and overnight easy-to-learn traffic "recorder" with which any user can keep detailed statistics of consumed traffic for a period - one day, a month, or just a session.

Another, not less interesting feature, this tester is the simplest way testing internet speed in mode various features traffic consumption. For example, I personally really liked the ability to track the speed when playing streaming video in various formats. To do this, I used the VideoLAN VLC Media player 0.8.5, which, as you know, works with almost all formats, besides, it is easy to run a media file in it. All videos were played at 720x576 pixels.

The average traffic consumption for VOB video playback was 1.15 Mbps. During the playback of the DivX file, the maximum speed was 415 Kbps, and during the playback of MPEG4 video, the peak speed for the "stream" was 1.85 Mbps. The size of each of the files did not exceed 1.5 GB.

In this case, the situation with regard to speeds is as follows. On Upload, it was easy to achieve the "up to 3 Mbps" declared by the provider. During the measurement, the speed was in a "floating" state - from 2.2 Mbit / s to 2.9 Mbit / s.

As for Download, in this case the spread in indicators was as follows. During the so-called peak network loads, the speed did not exceed 17-19 Mbit / s, and in the period from 7-8 in the morning to 17-18 hours, the rates fluctuated from 30-35 Mbit / s to 55 Mbit / s.

Terms of provision

For private users, Volia provides modems exclusively on a lease basis - they cannot be redeemed. At least for now.

The rental cost by the provider is included in the price of one or another tariff plan. Depending on what speed the subscriber wants to order, there are several devices to choose from, including the Thomson TCM 470 described above, and some others, in particular Thomson TCW 690/710, Arris WBM750B / NU DOCSIS 3.0, etc.

For business clients, conditions are different. Both the rental of devices and their purchase are allowed here. At the moment the list of devices offered by the provider is limited to two Arris WBM750B / NU and Scientific Atlanta EPC 3000. The price of the first one is 389 hryvnias. The second will cost 699 hryvnia. The cost of renting a modem for a business user is the same as renting a device for a home user.

Some results

Despite the fact that in practice the speed in Download mode does not reach the 150 Mbps declared by the provider, nevertheless, the speed in DOCSIS 3.0 is an order of magnitude higher than the previous standard. Watch a video on the same YouTube in high resolution or an HD movie on-line, as well as perform a lot of other tasks related to the need for high speed internet the user will be able to with clearly greater comfort than in the previous standard mode.

It's a little annoying that for legal entities today this service is still quite expensive. Although its popularity is gaining momentum, and therefore it is possible that at least in the direction of increasing the popularization of the service, the company will reduce prices in the foreseeable future.

pros

• Almost 100% coverage in Kiev;
• The only ISP providing Internet in the DOCSIS 3.0 standard;
• An interesting offer "Volia Absolute" - at a speed of up to 150 Mbps for 200 hryvnia per month for home users. This package is especially interesting when purchasing new service TV + Internet (http://volia.com/bundle/price). In this case, the monthly fee is almost halved. For example, for the same UAH 200 you can buy a so-called "bundle" - a basic TV package (over 80 channels) and an Internet package with a speed of up to 150 Mbps.
• Wide choose tariff plans generally;
• Good speed for streaming video;
• Stable connection

Minuses

• For business clients, the cost is quite high;
• There may be speed limits if the fair use policy is violated for home users. Although there is a plus - less than 1% of users fall into this limitation.

They tested it in Ukraine, and one of the operators is preparing.

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The Internet is transmitted by telephone, television, fiber optic cables and twisted pair. The choice depends on the existing network infrastructure and financial viability. Each option has its own data transmission standard.DOCSIS is one of the standards. In accordance with it, data transmission is carried out through deployed television (coaxial) cables. Often you can see a numerical value next to the standard. It denotes the version of the technology specification. The versions differ from each other in the peculiarities of the organization of the network, and for the user the main difference is in the speed of the Internet.

DOCSIS connectivity technology

The standard for connecting subscribers to the network via coaxial cable uses a downstream channel, that is, it is carried out from top to bottom.

In general terms, the diagram looks like this:

where CMTS is the cable modem termination system. Simply put, it is the operator's modem to which user devices are connected. It encodes and moderates data streams, translating them into the desired frequency range.

Such a scheme assumes distribution of the Internet through the main modem, CMTS, to all connected subscribers at the same time.

When the DOCSIS standard appeared and who is it useful

Doxis has been used since 1998. The objective of the standard is to unify the requirements for data transmission over coaxial cable and to ensure the compatibility of equipment supplied by different manufacturers.

At the time of implementation, the technology was promising. It made it possible to conduct the Internet through existing networks, which means, to reduce the cost of creating a new infrastructure. For cable TV operators, this meant the possibility of expanding the list of services provided, and for users - inexpensive Internet with a fairly high speed.

Now the connection via DOCSIS in terms of data transmission speed is inferior in speed to other options for connecting to the network - FTTB, PON, HCNA.

What are the varieties of Doxis technology

Doxis is divided according to the types of specifications. The division is carried out in the order of the release of updates with additional functions:

• Version 1.0.
• Version 1.1.
• Version 2.0.
• Version 3.0.
• Version 3.1.
• Version 3.1 FD.
• EuroDOCSIS.

The differences between the types are determined by the criteria of quality of service (QoS), flow capacity, modulations, noise immunity. EuroDOCSIS - adaptation of the standard to the European frequency grid.

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What is the speed of Doxis

The very first standard assumed data transmission at a speed of no more than 42 Mbit / s, and in the opposite direction - up to 10 Mbit / s.

Channel asymmetry persisted in subsequent years, when the update was released. Only in the latest version of the specification was it possible to equalize the flow rates.

Starting with DOCSIS 3.0, the data transfer rate was increased to 170 Mbps on the forward channel and to 122 Mbps on the reverse.

The speed is spelled out in the regulations of version 3.1 direct channel up to 10 Gb / s, and the reverse - up to 1 Gb / s. These values \u200b\u200bsignificantly exceed the previous specifications. In addition, the standard provides for energy efficiency reduction through energy management tools. This approach makes the coaxial data industry more economical.

So! Subtleties of buying a router:

If you are looking for best speeds Internet for your home, cable Internet service is still a good choice for most users. But what most users don’t know is that they sometimes pay much more than they owe for cable. broadband - especially if they are using equipment offered by the cable company.

Indeed, many users can save up to $ 5 per month - that's more than $ 60 per year - on their current cable Internet connection. To this end, I have compiled five of the most popular reader questions I usually get about cable Internet. I've included both short and detailed answers to each question, including suggestions on how to save money on your monthly bill (spoiler alert: buy, don't rent your cable modem).

What Cable Modem Do You Really Need?

The short answer is:
choose the one that is able to support the speed of the tariff plan you subscribed to. When in doubt, select one that supports DOCSIS 3.0. Of these, you should choose not the most expensive one, and to be sure - from the list of supported equipment of your provider.

Note: Your actual speed Internet connections depend on the speed of the modem, router, Wi-Fi connection, switches, and the user device itself, and by the way, on the tariff plan that you have chosen. Most of the time, what you pay for is the lowest common denominator, and does not determine real speed Your internet connection.

Long answer:
A cable modem is a device that receives an Internet signal from a cable provider and turns it into a data signal that can be understood by computing devices such as personal computers, tablets, or smartphones. The modem comes with a female coaxial connector - just like the one behind your HDTV - and a LAN port. This means that with a modem, you can only connect one computer to the Internet. To connect more devices, you will need to get your hands on a Wi-Fi router. (More on this below.)

Modems are usually very simple devices, and because of this, most of them are practically indistinguishable from each other. The biggest difference between the two is the standard they support, which defines the internet speeds that it is capable of supporting, both for download and upload. This standard is called d ata over cable service interface specification, or DOCSIS.

There are DOCSIS 1.x, DOCSIS 2.0 and DOCSIS 3.0 modems currently on the market. Both DOCSIS 1.x (mostly now an obsolete standard) and DOCSIS 2.0 only support one channel, which supports 43 Mbps download speeds and 10 Mbps and 31 Mbps upload speeds, respectively.

In DOCSIS 3.0 (which is backward compatible with older standards), the single link speed remains 43 Mbps download and 31 Mbps upload, but modems are now capable of handling multiple links (link bonding) at a time. A typical DOCSIS 3.0 modem typically offers four or eight download channels, giving speeds of 172 Mbps or 344 Mbps, respectively. For upload, they usually support four channels, offering speeds up to 124 Mbps. DOCSIS 3.0 modems that can handle even more channels are coming relatively soon.

Your actual Internet speed also depends on what you are paying for; the faster you want, the larger the monthly payment. If you are paying for an internet plan with download speeds of 30 Mbps or less, chances are that a DOCSIS 2.0 modem will be enough for you, which costs almost half the price of DOCSIS 3.0. Moreover, if your tariff is called: Lightweight, Basic, Starter or Standard, then the DOCSIS 2.0 modem will probably be enough for you, but if you choose more high levelsuch as Turbo, Premier, Super or Extreme, a DOCSIS 3.0 modem with four or even eight download channels is a must.

Please note that all broadband services offer much slower upload speeds than download speeds. Most of the time, most plans offer upload speeds of only 10 Mbps. In addition, you need to check if the modem is DOCSIS compliant and is on the ISP's approved modem list, or it may not work at all. In addition, sometimes you come across one ISP that does not allow the use of consumer modems on their network.

On a typical home network, you need to connect the modem to the WAN port of the Wi-Fi router using the (preferably) short network cable.

Rent or buy?

The short answer is:
Whenever possible, it is best to purchase your own modem. This is a pretty good saving over time.

Long answer:
When you register an application for a connection to the cable Internet service system, the provider often includes a modem in the service package. This device is usually not free; it costs you a monthly rent. Often, the provider does not clearly inform you about this when concluding a contract, and also the fact that you can avoid this by using your own equipment. This fee for renting a modem may not be so big at first, but then it usually increases and sometimes up to $ 10 per month, which may not be entirely interesting for you.

It doesn't seem like a lot, but over time, it adds up to not so little. And if you plan on using the Internet for one year, it is much better to get your own modem, which costs between $ 50 and $ 100, new. You can buy one before signing the contract or any time thereafter. In the latter case, make sure you return the modem provided by the service providers, or else you will be charged for it. From my personal experience, it is best to bring this unit and return it in person at the nearest customer service center to avoid losing it.

Even if you plan to use the Internet from this operator for a short time, it is still a good idea purchase your own modem. You can always use it again for a new connection only if the connection type is the same, or you can sell it and get most of what you paid for it back.

Continuing the conversation about selling an old modem, you can also buy a used one.

New, used, or after a return?

The short answer is:
It never hurts to get a brand new modem, but you can also save a lot and not lose anything if you buy a used one or return it.

Long answer:
Cable modems are simple devices and after initial installation they are usually left alone, they just stay in the same place. You will never change settings or tweak anything again. Also, modems have no moving parts (most of them don't even have fans). Therefore, they can work for a long time and simply become obsolete before they actually stop working. This means that purchasing a brand new modem will do you no more benefit than getting a returned modem of the same type.

In truth, the most common reasons for returning modems are either no further need for them or a mismatch. appearance devices to interior design. And from the inside, they are practically no different from new devices. In many cases, the modem that your ISP offers you may be just after you returned, and this device was used by previous customers. On the market, modems after return cost up to two-thirds of the price of a new one.

The purchase of used modems carries a higher risk associated with previous owners. as long as the modem has not been dropped and there is no visible external damage, it should work well. However, if you buy a used one, make sure that you can return it after a few days, because if it can work for a few days without problems, then there is a chance it will work for a long time. In turn, a used modem tends to cost about a third of the price of a new one.

From my personal experience, the most common problem with a modem is the power adapter, which is fairly easy to replace.

Back of the combo cable internet device. You can see a lot of LAN ports and the absence of a WAN port, which is present in a regular router.

Buy a modem with a built-in router or two separate devices?

The short answer is:
If your provider does not provide you with a modem with a built-in router for free (which is unlikely), always ask for a modem and purchase a router separately. After receiving the modem, simply take one of the routers, not the most expensive one according to your need. If you really want a combo for practical reasons such as fewer wires, the Motorola SBG6782-AC Surfboard eXtreme is your the best choice for now. Make sure you read his full review first.

Long answer:
As mentioned above, you need a router to share the Internet connection from your cable modem on more than one computer; total amount - up to 254 devices for most routers. You just have to connect the LAN port of the modem to the WAN port of the router using a network cable. This is the preferred setup and also the most popular as it gives you the flexibility and ability to customize your network based on your needs and your budget.

Equipment	Per	Vs	The best choice
Separate modem and Wi-Fi router	Flexibility in price, functions, performance features, flexibility to upgrade, replace with a new one.	More wires and need two sockets	ISP approved modem and one of the top routers
Modem / Wi-Fi router two in one	One device, one outlet needed, fewer wires	Lack of flexibility, the built-in router is not always the best, the complexity of updating the device is more expensive and will have to be changed entirely.	Motorola SBG6782-AC Surfboard eXtreme.

There are also combo units that consist of a modem and a router in one box. I generally don't recommend them for two main reasons. First, it is dangerous. If any part of the device, modem or router module, is damaged or out of fashion and out of date, you must replace the entire device. The second reason is that in most of the existing combo devices, the router portion is usually very limited, making your home network less flexible and functional than it could be.

If you are in business, try to avoid purchasing a combo device, because its part of the router probably will not have all the configuration options you need for your business. A capable sysadmin can still get things up and running by adding another router to the network, but that is much more work than just getting a modem and the right router right away.

Do I need to purchase an extended warranty period?

No, not worth it. Cable modems (or combo devices), even returned ones, usually come with a factory warranty ranging from 90 days to two years. Since these are simple devices, if something unusual should happen, for example, a defective device comes across, or you run into problems installing it, this will happen immediately after purchase. After that, it is unlikely that something like this will happen.

Purchase extended term a guarantee is just a waste of money. Instead, it's best to use that money to buy surge protectors for your home network devices, as power surges and lightning are two of the most common causes that damage equipment. It is also best to install the unit in an open space and dry place to avoid damage caused by water or overheating.

Should you try to bring down the price?

Definitely!!

It is true that most of us live in an area that is served by just one cable company, but there are other alternatives such as FDDI, satellite or DSL (which is almost everywhere and is usually cheaper). You should use them as your leverage in negotiations with the cable company for the best deal. You can also get better deals by subscribing to packages with many services such as TV, Internet and telephone, although do not subscribe to what you do not plan to use.

Some cable companies may give you good deals for some time, say six months, and then start charging you the full rate, which is up to 50 percent higher. You can always dial the operator or look on the website when this period ends and ask about current or new promotions, or you can simply terminate the contract and then re-subscribe. It costs nothing and you already have a modem.

Most importantly, check from time to time when there are new ones. promotions or discounts, or just call them to ask for a lower rate. It works. After all, you cannot get what you have not asked for.

That's all for now. If you still have questions, feel free to write to me at,