Modems

Fax and Voice

Almost all modems manufactured today are capable of sending and receiving fax data at 14.4 Kbps. The manufacturer may include demo software.  Windows 98 no longer supports Microsoft Fax although the program can be found and installed from the CD. Other programs can receive faxes and convert ASCII text by an OCR (optical character recognition) to be edited.

Modems are full-duplex. Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. If you have speakerphone capabilities you can use headphones (plugs directly to the back of the modem or sound card) or microphone and speaker to talk through your computer.  If you have voice capabilities you can use your computer for voice mail. These capabilities require additional software.

ITU Standard

V.92 is the new dial-up modem specification from the ITU (International Telecommunications Union) that introduces three new features that will add convenience and performance for the modem user. The three features are quick connect, modem-on-hold and PCM Upstream. 

QuickConnect
QuickConnect will shorten the time it takes to make a connection by remembering ("training") the phone line characteristics and storing them for later usage. Typically, the modem handshake (all that noise you hear) takes from 25 to 27 seconds. Surveys indicate that people are quite irritated at this length of time. QuickConnect will cut the modem handshake time in half for most calls, a significant improvement.

Modem-on-Hold
Many households use the same phone line for both voice calls and data (Internet), so when the user is browsing the Internet, an incoming call cannot get through. Modem-on-Hold allows you to receive an incoming call and stay connected to the Internet (Call-Waiting service from your phone company is all that is required). When you hang up the phone you can resume browsing. It also works in reverse; you can initiate a voice call while connected and keep the modem connection. The "hold" time is defined by your ISP. The V.92 specification allows for hold times to be anywhere from 10 seconds to infinite.

PCM Upstream
PCM Upstream boosts the upstream data rates between the user and ISP to reduce upload times for large files and email attachments. A maximum of 48 Kbps upstream rate is supported. PCM Upstream will work particularly well with new equipment such as Internet-connected digital cameras, which primarily upload rather than download information.

V.90 was the standard for 56K modems approved by the ITU members in September '98.  K56flex technology by Lucent and Rockwell and x2 technology by 3COM were incorporated into V.90.  Lucent and 3Com/USR began to working together to ensure that both companies' V.90 products would be interoperable (Lucent & 3Com press release).  Most K56flex and x2 modems can be upgraded to V.90 with software. You can visit Upgrade Central to check to see when your modem manufacturer has the V.90 software upgrade for your modem. V.90 works on a 33.6Kps (kilobytes per second) modem by taking converting analog signals for a through conventional copper twisted-pair telephone line to a digital signal. In recent years, the 2400 bps (bytes per second) modem that could carry e-mail has become obsolete. 14.4 Kbps and 28.8 Kbps modems were temporary landing places on the way to the much higher bandwidth devices and carriers of tomorrow. From early 1998, most new personal computers came with 56 Kbps modems. By comparison, using a digital ISDN adapter instead of a conventional modem, the same telephone wire can now carry up to 128 Kbps. With Digital Subscriber Line (DSL) and cable television systems, now being deployed in a number of communities, bandwidth on twisted-pair can be in the megabit range.

Bandwidth

The bandwidth of a transmitted communications signal is a measure of the range of frequencies the signal occupies. The term is also used in reference to the frequency-response characteristics of a communications receiving system. All transmitted and receiving signals, whether analog or digital, have a certain bandwidth. Bandwidth is directly proportional to the amount of data transmitted or received per unit time.. In analog systems, bandwidth is defined in terms of the difference between the highest-frequency signal component and the lowest-frequency signal component. Frequency is measured in cycles per second (hertz). A typical voice signal has a bandwidth of approximately three kilohertz (3 kHz).

Modem Protocols

The protocols that modems agree on and use for checking and correcting transmission errors have evolved toward accuracy, speed, and efficiency since 1978 when the Xmodem protocol became a standard.  Protocol data is chunked into "blocks" of a certain byte size and sent to the destination modem which checks each block for errors and, depending on the results and the protocol, returns a positive (ACK) or negative (NAK) acknowledgement, the latter usually resulting in a retransmission. The type of checking (checksum or cyclic redundancy check) and the frequency at which a response is sent vary by protocol. A new link-layer compression standard based on technology developed by Hughes Network Systems, V.44 will replace the current V.42bis compression technology. V.44 offers a higher compression ratio than V.42bis. Higher compression ratios mean that more data can be downloaded in the same amount of time. The most significant improvement will be noticed when you are browsing and searching the web, since HTML text files are highly compressible. For most users, data throughput will be increased by 20 to 60%.

Network Protocols

TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in the private networks called intranets and in extranets. When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from.

TCP/IP is a two-layered program. The higher layer, TCP, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message. The lower layer, IP, handles the address part of each packet so that it gets to the right destination. Each gateway computer on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, they'll be reassembled at the destination.

TCP/IP uses the client/server model of communication in which a computer user, a client, requests and is provided a service, such as sending a Web page by a server in the network. TCP/IP communication is primarily point-to-point. Other network protocols your dial up connection may support are IPX/SPX and NetBEUI, but are not supported on the World Wide Web

Internet Protocols

Many Internet users are familiar with the even higher layer application protocols that use TCP/IP to get to the Internet. These include the World Wide Web's Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail Transfer Protocol (SMTP). These and other protocols are often packaged together with TCP/IP as a "suite."

Personal computer users usually get to the Internet through the Serial Line Internet Protocol (SLIP) or the Point-to-Point Protocol (PPP). These protocols encapsulate the IP packets so that they can be sent over a dial-up phone connection to an access provider's modem.