Nuts & Bolts
High Speed Access takes the form of a specially engineered Phone line, TV Cable, or Wireless connection. This guide is broken up into sections so that you can jump to the topics that interest you now. The bottom of this guide provides a glossary of terms. Click on a topic below, or read to your heart's content.
DSL | IP, Network Addressing | ISDN | Wireless
:::. DSL (Digital Subscriber Line) uses an ordinary copper phone line, but is subject to distance restrictions and line quality requirements. Distance, as measured in total cable length from the Telephone CO to your location, is limited to 20,500 feet for the lowest data rate. The closer you are to the CO within this range, the higher the rate you can get. This distance figure is not your distance "as the crow flies". The telephone cable running to your area does not travel in a straight line from the CO to you, it may in fact run to another area, and then run to your area.
Line quality and line integrity are also limiting factors. If a bridge-tap, loading coil, pair gain unit, or gauge transition, appear anywhere on the line you will be unable to order DSL from most providers. Some providers will agree to condition the line so that you may order the service, in exchange for a contract term of one year or more.
The basic questions, assuming you qualify for DSL service, are:
- How much bandwidth do you need?
- Are you an end user or a provider?
- How many computers are you connecting to the Internet?
The bandwidth question can be a little tricky to answer. A single computer used for casual Internet use can certainly use a 256k without any doubts. ZiaNet has many business offices, including Travel Agencies, Insurance Agencies, Law Offices, and Banks, that have up to 14 computers networked to a single 256K DSL connection. As long as the users are not engaged in heavy downloading or file transfers this is not a problem; 256K is more than adequate. However, if some users on the connection are going to be doing heavy file transfers or regularly streaming audio or video content, it may be wise to consider a higher bandwidth DSL interface. Upgrading the bandwidth on Qwest DSL costs only $30.
An End User is an Internet user who does email, web surfing, and downloading or uploading of files to other servers. A Provider runs a server (a computer that provides services such as email, web, FTP, or file sharing services to other users on the Internet). If you are a provider, you may wish to consider both a higher bandwidth, and possibly selecting an SDSL service.
ADSL versus SDSL :::. ADSL is Asymmetric Digital Subscriber Line, where the Downlink bandwidth is higher than the Uplink bandwidth. This type of service is just fine for the end user, because they spend most of their time downloading (or receiving) data. A Provider spends most of it's time uploading (or serving) data to other systems. SDSL is Symmetric, meaning that the rated bandwidth is equal for both uplink and downlink. Determining what bandwidth a provider may require is beyond the scope of this article. Here is a useful reference from Dell, Web server sizing: see Calculating the network transfer rate.
Router versus Modem :::. Some DSL services allow you to select between a router or modem. A router is more expensive than a modem, but it gives you options, flexibility and even services, that a modem will not provide. A DSL modem is intended to connect a single computer to the DSL connection. It is possible to set that single computer up as a Gateway machine that will route requests from other computers on your network, but this requires some skill. A modem connection is a direct connection, in the sense that the IP address assigned to the connection is the IP address of the computer on the network. This makes it easier for a malicious hacker to get direct access to your machine. A router uses NAT, so that network requests are translated through the router as a gateway. A hacker might gain access to the router itself, but you may shut off the vulnerable services (web, TELNET, FTP) so that is would be difficult or impossible to tamper with your system. If you have a several computers networked together via TCP/IP, connecting a DSL router to the hub or switch on your network will provide seamless Internet connectivity for all. If you have a larger network of computers, many of the routers even provide DHCP service for automatic allocation of addresses on your network. This simplifies your network configuration and management.
For the end user, the simplicity and lower cost of a modem often makes sense. For the provider, or for anyone connecting a network of end users to the DSL connection, the router is the very best investment.
:::. IP, Network Addressing. Most DSL and ISDN services in New Mexico use dynamic IP address assignment. An Internet service provider does not need to have a unique IP address for every customer. Since not all customers are connected to the network at once, IP addresses are handed out as needed, from a pool of addresses that are not currently in use. Some connections require a static IP address; the same address at all times, so that the computer may get access to systems on the other side of a firewall, or so that other users may access the system from the Internet. ZiaNet can provide a single Static IP address, or a CIDR block of addresses if needed.
Please submit your request for a static IP or CIDR to Requests. If you need help determining your needs, please call our Tech support number.
Charges for Additional IP Addresses :::. All requests for additional IP addresses must follow ARIN (American
Registry of Internet Numbers) guidelines as shown at:
Requests for additional IP addresses may require Customer to renumber
from previously issued IP address space to conform to accepted routing guidelines. All pricing for IP addresses is subject to change.
Please submit your request for a static IP or CIDR to Requests. If you need help determining your needs, please call our Tech support number.
:::. ISDN service is like dial-up service, but it uses a specially engineered telephone circuit. ISDN uses a regular phone line, but each end of the line has a special device attached so that the line may be used to transfer digital data. Basic Rate ISDN is supported in many ZiaNet communities. The service provides two 64Kbs circuits. Both may be used for both data and voice.
An ISDN modem will connect the first channel when ever a network connection is requested (by your PC). The second channel is connected automatically when the first channel fills up. It may be set to disconnect when demand falls off again. Either channel will disconnect if someone calls the phone number associated with that channel, or if you pick up that phone line to make an outgoing call.
ISDN is not a negotiated rate. You get 64Kbs on one channel, two channels, or none at all. Connect negotiation (and username/password authentication) takes a few tenths of a second. This means that your ISDN service may be set to completely disconnect when idle for several minutes. The connection is a established only as needed, and the delay in the connect process is too brief to be noticed.
Equipment considerations :::. The equipment at the customer end of the circuit is commonly called a terminal adaptor (TA). An ISDN TA may take one of two forms:
- An Ethernet device that connects to a single computer, or to a switch or hub to connect a Local Area Network of computers.
- A "modem" type device that connects to a serial port on a single computer.
In order to utilize one or both of the ISDN Channels, the TA that you buy must have a jack to plug in one or more telephone circuits. Typical TA's include a single phone jack that uses the second channel only. Some TA's, especially the Ethernet variety, do not provide any phone jack. You should figure out your needs before you purchase a terminal adaptor.
The TA is the only interface that can provide voice circuit(s) at your end of the ISDN line. If you intend to use one or both of the ISDN channels for voice, you may need to modify the phone wiring at your location. If you have one or more phones that you wish to use, the line for those phones will need to be connected to the back of the TA. This is not a problem if you will only be using a single phone plugged directly into the back of the TA. However, if you have several phones in different rooms, this would require some special wiring changes: the line that feeds those phones will need to be connected to the back of the TA, not at the phone company access point on an outside wall of the building.
Limitations :::. Casual use ISDN service from ZiaNet is $40 per month. It is a connect on demand service with very high availability (in most towns, a 5 to 1 user to modem ratio) but this service is not intended for 24 hour continuous connection. As explained above, the connection can be established in less than a second, on demand, 24 hours a day. A continuous ISDN connection is billed by ZiaNet for $300 per month. If you intend to run services such as FTP, web or mail, you may need to be connected 24 hours a day in order to be available to others who use your service. ISDN is a costly way to provide such services.
Wireless service :::. ZiaNet offers two Wireless services in Las Cruces and Doña Anna County: Wisper Wireless, and ZiaNet Wireless. Wisper Wireless is also available in Las Vegas and Santa Fe. These services are point-to-point low power radio interfaces using 802.11b. These are not roaming access services. An antennae mounted on the customer's building connects to the base radio. There must be a line-of-site path from the customer's building to the base station. The distance cannot exceed 7 miles.
Speeds range from 256/128kb to 1024/1024kb.
- Asymmetric Digital Subscriber Line. The download speeds are
different than the upload speed.
- Asynchronous Transfer Mode. A high speed shared
transport service offered by US West and other phone companies that allows voice, video, and data services to be simultaneously carried over the same physical lines.
ATM Cell Cloud
- ATM services are typically made of multiple ATM switches, also
referred to as an ATM Cell Cloud. DSL service provides the transport from the customers site to the ATM Cell Cloud based on the Qos
being purchased. Leased line services between ZiaNet and the ATM Cell Cloud provide high speed transport to the ATM Cell Cloud based on a CBR Qos.
- A bridge is a product that connects a local area network (LAN) to
another local area network that uses the same protocol (for example, Ethernet or Token Ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN(s).
- Bridge Tap refers to line that is cut short but continues to be
physically connected to the pairs that continue beyond the new termination point. Think of a "T" intersection on a road.
- Committed Bit Rate. Its an ATM Qos (quality of service) that guarantees delivery of the speed
being contracted for on communication services. For example, if purchase
a 256k service, under CBR you are guaranteed 256k based on the Qos being provisioned in the ATM cell cloud.
- A routable block of IP addresses, (Classless Inter-Domain Routing) assigned by your network provider (in this case, ZiaNet) so that your systems may communicate with, and be available to, other systems on the Internet.
CO (Central Office)
- The Telephone Central Office is a facility where the switch equipment that switches phone calls is located. Most towns have several of these facilities, and large towns have many.
- Customer Premises Equipment.
- DHCP (Dynamic Host Configuration Protocol) is a protocol that lets
network administrators manage centrally and automate the assignment of Internet Protocol (IP) addresses in an organization's network.
- Digital Subscriber Line. A phone company offering that
allows up to 7.0 Mbs of bandwidth to be utilized over a single traditional phone line. The typical offering for both practical and technical reasons is generally in the 144k to 768k range. Like ISDN, this service requires substantial equipment investment by the phone company and has even more stringent distance, quality-of-line, and equipment restrictions. Most phone companies are making this service available only in densely populated, higher income areas. DSL is an ATM service, i.e. all DSL traffic uses ATM encapsulation.
- Digital subscriber lines access multiplexer. This is the gizmo that
allows your phone line to carry both voice and data by splitting the voice and data signals.
- Gauge is the measure of the circumference (or thickness) of wire. The AC wiring in your home is 14 or 16 gauge, whereas phone wire is 24 or 26 gauge (the bigger the number, the smaller the wire). Telephone wire is terminated on blocks of metal pins where it comes out of a large cable (200-600 pairs of wires), where it then runs on smaller cables to individual blocks or buildings. If different gauge wire was used from one cable to the next, DSL service is not possible: different gauge wires have different impedance (or resistance) characteristics, and this makes DSL signaling impossible.
- IDSL is ISDN over DSL.
- In order to communicate and exchange data through a network, each computer must have a unique address. IP addresses are numeric assignments in the form of four blocks of numbers, e.g. 188.8.131.52.
- Integrated Services Digital Network. A phone company offering that allows up to 128 Kbps bandwidth to be utilized over a single traditional phone line. This is digital service, not analog service.
The standard voice telephone network is an analog service. Dial-tone service using digital signaling is widely available in larger telephone company central offices, but not in central offices serving smaller communities. ISDN has distance limitations that prevent its use beyond about 3.5 miles. There are quality-of-line (literally, the condition of
the copper line), intervening equipment (such as multiplexors, signal splitters), and interference issues that also affect where the service can be offered.
- Also called Voice coils, these inductive devices used to be installed on weak phone lines in order to boost the loudness of frequencies in the range of the voice. On voice-only circuits the benefit is obvious. On modem and data circuits this device cuts the data rate of the connection. These devices are no longer used, but may be present on older lines, especially in areas that are distant from the CO.
- The local loop is the facility (wire) between the phone switch and the customers location (i.e., house, office, etc.). The local loop is also referred to as The Last Mile.
- In order to DSL to work a customer must have a local loop that can
qualify (loop qualify) for the service being ordered by the customer. One of the limiting factors is the distance factors based on various speed ratings. There are other line quality issues that can prevent a line from loop qualifying. An example is bridge tap.
- NAT (Network Address Translation) is the translation of an Internet
Protocol address (IP address) used within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside. Typically, a company maps its local inside network addresses to one or more global outside IP addresses and translates the global IP addresses on incoming packets back into local IP addresses.
- Pair Gain devices are used to increase the number of telephone circuits available without laying additional cable. If an area is running out of copper pairs for telephone circuits, pair gain units may be installed to multiply the number of lines. A pair gain unit is an analog to digital device that takes 2 or more phone wires, converts them into data signals, and runs them through a single phone line back to the CO. Pair gain devices typically limit the modem connection to 28,000Kbs or less.
- A PVC (Permanent Virtual Circuit) is a software-defined logical
connection in a frame relay network. A feature of frame relay that makes it a highly flexible network technology is that users (companies or clients of network providers) can define logical connections and required bandwidths between end points and let the frame relay network technology worry about how the physical network is used to achieve the defined connections and manage the traffic.
- Quality of service, i.e., CBR, UBR, etc.
- A router is a device that determines the next network point to
which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any juncture of networks or gateway, including each Internet point-of-presence.
- Symmetric Digital Subscriber Line. The download speeds are the
same as the upload speeds.
- Uncommitted Bit Rate. Its an ATM Qos (quality of service) that as no guaranteed delivery of the
speed being contracted for on communication services. For example, you may purchase a 256k service, however, under UBR there is zero guarantee that you will see 256k based on the Qos being provisioned in the ATM cell cloud.