WAN Protocol and Technology Details

1. Technologies that are readily available for home based Internet access include SDSL, ADSL, Broadband Cable, PSTN and wireless broadband. Each has particular strengths and not all solutions are available in all areas. Of the above solutions, PSTN or Public Switched Telephone Networks are the most common and least expensive. They are primarily analogue and require a modem that translates analogue to digital signals in order for a computer to connect to the Internet through an Internet Service Provider or ISP. PSTN is also the slowest of the above offerings, supporting a total of 64K in bandwidth of which a maximum of 56K can be used for Internet access traffic (and due to overhead with the connection, the actual bandwidth available is somewhere between 44K and 53K on the best connections).

Like PSTN, ADSL or Asymmetric Digital Subscriber Line uses phone lines to provide Internet access. However, ADSL delivers much higher speeds, in some cases over 8 Mbps download speed. ADSL is supported by an ADSL modem at the house that may also serve as a router and firewall and also uses digital only (unlike PSTN). The modem connects to a DSLAM unit at the telephone company. ADSL is limited in distance from the PoP or Point of Presence to 18,000 feet (also unlike PSTN) and is called asynchronous because the download speed is always much greater than the upload speed (for example, 384K upload and 1.5Mbps download is a typical bandwidth setting).

SDSL or Symmetric Digital Subscriber Line is quite similar in most respects to ADSL with a few exceptions. First, SDSL is synchronous because the upload and download speeds are the same (important if the service will be used to serve web pages and other services over the Internet). SDSL also has a much shorter distance tolerance from the house to the PoP (typically around 15,000 feet or less). SDSL service costs more than ADSL and the bandwidth is usually not as high as ADSL (although this does depend upon the service provider).

Broadband Cable service is quite popular because it generally provides much higher bandwidth that the xDSL variants (over 20 Mbps in some cases depending upon the subscribed service and service provider). However, Broadband Cable upload access is shared with neighbors that are also using Broadband Cable. So when others are also accessing the Internet, Broadband Cable speed will decrease due to shared access. It is important to note that shared access is also a security concern. Broadband Cable uses the cable television network to deliver access to the Internet as compared to PSTN and xDSL, which does not make much of a difference in newer buildings however, if residing in an older building, the building is more likely to be pre-wired for phones but not for television cable, which could increase the cost to install Broadband Cable in the older building.

People that live in rural areas where Broadband Cable and xDSL technologies are not available primarily use wireless Broadband. Wireless Broadband typically uses the IEEE 802.16 standard that is also referred to as WiMax. Wireless Broadband is capable of speeds beyond 100 Mbps, but this is dependent upon the distance between wireless transmitter and receiver. Wireless Broadband does cost more than other broadband services, and is susceptible to service fluctuations due to environmental conditions, which is typical of any wireless service.

2. Frame Relay and ATM or Asynchronous Transfer Mode have a fundamentally different structure at OSI layer 2. Frame Relay transports data using variable length frames to encapsulate data. Unlike X.25 (from which Frame Relay technology was derived), Frame Relay frames do not include error correction information, and instead rely on the network endpoints to provide error correction information in addition to other network management information such as congestion notification using BECN (Backward Explicit Congestion Notification) and FECN (Forward Explicit Congestion Notification) frames that are sent from one endpoint to another to control data flow. Frame Relay subscriptions also usually include a CIR or Committed Information Rate that is the guaranteed bandwidth rate the service provide is committed to delivering. When required and if available, users can exceed the CIR however they will be charged extra for the additional bandwidth. In contrast, ATM addresses congestion issues by framing data in 53 bytes “cells” and not allowing in variance in size. By keeping all cells the same size, ATM is able to forego the typical fragment and reassembly overhead and avoid congestion because the network devices in ATM networks handle only small, predictable size frames. ATM also operates at much higher speeds (155 to 622 Mbps typical with a top end speed of 10 Gbps) whereas Frame Relay offers a mid-range bandwidth typical of a T1 line (1.4 to 1.5 Mbps).

However, Frame Relay and ATM are both considered WAN or Wide Area Network technologies, and both share the same non-broadcast characteristic on OSI layer 2.  In addition, both can be configured with a CIR or Committed Information Rate and can support protocols such as TCP/IP that reside above OSI layer 2. Also, even though Frame Relay is a packet switching technology, both ATM and Frame Relay establish virtual circuits between two points before transporting data.
3. Prior to the breakup of AT&T (Ma Bell), the telephone infrastructure was controlled by a single entity. This means that the configuration decisions, upgrade decisions, and decisions regarding when to adopt new technologies (such as fiber optics infrastructure) would start including a competitive element that did not previously exist. Each of the individual telephone network entities essentially had to be more aggressive in adopting new technologies than they would have otherwise under the single AT&T organization. The result included the adoption of digital technologies much sooner than would have otherwise occurred, the deployment of fiber optic networks, the adoption of wireless services including the use of both cellular technologies and satellite services that a single entity would have or could have afforded to delay to allow for technology maturity, or for simple cost cutting. If AT&T had continued without the breakup, most likely, many of the technologies that we currently enjoy today would not be as advanced or even if they advanced to the same level, may not have been as widely available to the public as they are today.

4. For networks that use Broadband Cable service for establishing connections to the Internet and Internet services, the media used is a coaxial cable type that uses an aluminum shield rather than the RG6 or RG58 cables used in older Ethernet networks. A cable modem receives the signal sent by the Broadband cable company. A router connects to an Ethernet port on the Broadband cable modem using a 6 foot Ethernet patch cord (CAT6 UTP). On the LAN side, Ethernet is used at layer 2, while on the cable company side OSI layer 2 uses a DOCSIS protocol that is similar to ATM in characteristics and function. The upper layers of the OSI are essentially the same on both sides of the modem and the firewall, implementing TCP/IPv4 for layer 3 on up to layer 7 of the OSI. So protocols such as HTTP, FTP, DNS, ICMP are used routinely over this type of network connection.