202 Practical TCP/IP and Ethernet Networking requires at least a set of 254 Class C IP addresses, either permanently allocated to hosts, or dynamically allocated via a DHCP server, which could run on the same machine. The UNIX/ NT machine is set up with two network adapters, i.e. as a ‘multi-homed’ host. The first adapter is connected to the internal LAN, the second to the Internet. This implies that the second adapter should have the necessary connectivity e.g. X.25 built-in. Each card will need its own permanent IP address, and each card will be configured in such a way that the ‘other’ card’s IP address will be given as its default gateway. In this way, each card will pass on a received message to the other card. 12.3.5 Connection via dedicated router The simplest way of connecting a network to the Internet is via a dedicated 2-port IP router (also referred to as an Internet router). One port of the router will be, for example, an Ethernet port, to be connected to the local area network. The other port could be an X.25 WAN port, which will be connected to a public packet switching network. The X.25 link provides the connection to the ISP. As in the previous case, a set of IP addresses is required, and these are allocated either permanently or via a DHCP server. 13 The Internet for communications Objectives When you have completed study of this chapter you should be able to: • Briefly explain the speed/bandwidth issues • Briefly explain the various options for e-mail • Briefly describe the use of voice over IP • Indicate briefly how voice mail is performed using TCP/IP • Briefly indicate how video conferencing is performed using the Internet 13.1 Introduction The following chapter gives an overview of the current (as of mid 2001) state-of-the-art in Internet communications. This particular area of technology is advancing so rapidly that the only way to keep track of developments is by regularly browsing the Internet. The list of products mentioned in this section is by no means complete, but represents a fair cross-section of what is currently available. A very interesting and significant global development is the changeover from traditional MAN/WAN architectures, used for linking company resources over large geographical areas, to Internet communication because of (a) the much lower cost involved and (b) simplicity of interconnection imposed by the necessity of standardizing on TCP/IP. This tendency is not only manifesting itself in the so-called information technology (IT) environment, but also in commerce and industry, particularly in the manufacturing and process control environments. It is therefore only logical that the Internet will also be used for telecommunications (voice, fax, video etc) on an ever- increasing scale. 13.2 Hardware and software issues The advantage of the current generation of Internet communications products lies therein that they coexist on the already established Internet, PSTN (public switched telephone 204 Practical TCP/IP and Ethernet Networking network) and PBX (private branch exchange) infrastructure. Internet communications products are predominantly software-based and in many cases, they are available either as freeware or shareware. For the top-end products it may be necessary to purchase dedicated Internet interfaces for telephones or fax machines, but in these cases the end-users are typically medium to large enterprises and the capital outlay can be justified in terms of cost savings. 13.3 Speed/bandwidth issues As far as long-distance communication over the Internet is concerned, transmission speed can be a problem. For a modem-connected dial-up user the fastest modem in the world will not improve things much since the bottleneck is imposed by the bandwidth made available to the Internet service provider (ISP) and the number of simultaneous users competing for access to the ISP. In some cases the bandwidth of this data ‘pipe’ feeding the ISP is as little as 64 kbps; with 100 users connected at a given time this translates to only 640 bps per user! When it comes to increasing the available bandwidth within a LAN, however, there are several possibilities open to the LAN owner. Increasing the data transmission speed of the LAN (say, by upgrading from 10BaseT to 100BaseT) is one option, but not the only option. Additional (and in some cases less costly) options are: • Careful segmentation of a large flat network, with bridges, switches and routers. This reduces traffic interference as well as collisions • Cutting down on unnecessary broadcast packets (there are ways to accomplish this • Minimizing the number of routers between a given workstation and the point where the LAN attaches to the WAN leads to fewer ‘hops’ across routers and thus reduces latency (time delays) which adversely affect voice and video transmissions • Tasks which result in heavy network traffic, such as backups and large file transfers can be scheduled for off-peak periods in order to minimize interference with voice/video/fax traffic, which normally takes place during working hours For transmitting voice and video across a WAN there are several options as discussed in the following sections. Some are purely software based; some need hardware; some are hybrids. All approaches have advantages as well as disadvantages, and the prospective user will have to weigh them up against each other. 13.4 Legal issues In certain countries the use of IP services to carry voice traffic over the Internet (referred to as voice over IP, or VoIP) is illegal. Such is the case in South Africa, where the Telecommunications Bill specifically prohibits it. This is in sharp contrast with more enlightened telecommunications regulators, such as Deutsche Telekom, who openly embraced the new Internet telecommunications trend by investing substantially in companies involved in ‘voice over IP’ technology development, and in the process attracting business that would have been lost to competition. The Internet for communications 205 In the USA, ACTA (America’s Carriers Telecommunications Association) tried to ban Internet telephony software but the American FCC (Federal Communications Commission) refuses to have Internet telephony regulated. The fact that there may be a law prohibiting VoIP can hardly deter people from using it. It is difficult to enforce such a law because once a voice call is in progress it is practically impossible to detect it or its origin. Once voice or video has been digitized into packets it is no different from any other data! It is also a fact that Internet telephony is here to stay and the telecommunications regulatory bodies will simply have to find a way to accommodate this reality. 13.5 E-mail 13.5.1 POP and SMTP servers In order to gain a better understanding of the operation of an e-mail program, one has to look at the mechanism of reception and transmission of electronic mail, with reference to the TCP/IP model. Whereas the actual transmission of the mail (in digital format) from end to end is handled by the Internet and host-to-host layers of the TCP/IP (DoD) model, the interface with the user is handled by the SMTP (simple mail transport protocol) and POP (post office protocol) which reside in the process/application layer. As a practical exercise, one can actually connect into POP3 and SMTP servers, using TELNET, and manipulate the contents of the mailboxes as well as send and receive messages. It will soon become evident that although physically possible, this is a very tedious and user- unfriendly process hence a more elegant user friendly interface is required between the actual user on the one hand, and POP3/SMTP on the other hand. This brings us to the popular e-mail programs as discussed in the subsequent paragraphs. 13.5.2 E-mail software residing on the local host (workstation) In this category, we look at popular e-mail programs such as Eudora Lite, Netscape Communicator and Microsoft Internet Mail. The software resides on a PC or Laptop, and enables the user to compose messages, add files as attachments, send, receive and forward messages as well as print mail at leisure. For dial-up users, this category of program offers a particular cost advantage in that mail can be prepared off-line. A connection can then be made, messages sent and received and the user can once again log off resulting in relatively low telephone bills. 13.5.3 E-mail software residing on a remote server This category comprises e-mail programs such Hotmail and Eudora Web mail. Although these services are ostensibly free of charge, the user still needs access e.g. via a dial-up connection to the Internet in order to access mail. To complicate matters, the user needs to remain connected while composing mail and browsing the contents of the mailbox, which becomes costly for dial-up users. The latter problem can be alleviated by composing messages off-line beforehand and then cutting and pasting them into the message setup window before transmitting, minimizing connection time. An advantage of this system is that the user can retain his user ID regardless of where he lives, and can also access E-mail from any site in the world where there is Internet access. For a traveling user without a laptop, a cyber café (Internet café) can fulfill this function. It is also a solution for the corporate user who struggles to get an e-mail user account from a system administrator! It is a particularly ideal solution for university and 206 Practical TCP/IP and Ethernet Networking college students with access to the institutional Internet service since it costs nothing and they retain their e-mail addresses when they leave the institution. 13.5.4 Voice retrieval of e-mail Eudora Webmail is now offering a voice retrieval service whereby a traveling user not having access to a PC or Internet café, can actually dial into the mail server using a regular phone and retrieve mail by voice. At this point in time, this technology is still in its infancy and costly for users not residing in the United States. 13.6 Internet telephony 13.6.1 Introduction This section describes a novel and fast developing aspect of the Internet, namely the transmission of voice over IP. Antagonists of this concept are quick to point out that the Internet was designed to transport data and not voice, video, or other low latency applications. They also insist that the additional voice transmissions will place an unacceptable burden on the existing infrastructure. Fortunately, this has prompted companies such as QualComm to produce ‘smart’ voice compression techniques which utilize less than 10% of the bandwidth of conventional pulse code modulation (PCM) systems, yet achieving a subjectively perceived voice quality that actually exceeds that delivered by normal public telephones! In May 1996, a forum called voice over IP (VoIP) was formed to try maintaining and monitoring an Internet telephony standard. Current members of VoIP include 3Com, Cisco, Microsoft, VocalTec, Netspeak, Intel, IBM and US Robotics. This collaboration should supply substantial impetus to the development of Internet telephony hardware and software. An indication of the legitimacy of Internet telephony is Deutsche Telekom’s $48 million investment in VocalTec, developers of Internet Phone and one of the forerunners in Internet voice systems development. Deutsche Telekom has also committed to using at least $30 million of VocalTec’s products and services in the future, thereby gaining access to VocalTec’s Telephony Gateway, and through that the Internet users and revenue they would otherwise have forfeited to competitors. 13.6.2 PC to PC FreeTel A typical product in this category is FreeTel, which provides real-time voice communication via the Internet. Best of all, this product is free and the only cost involved is the connection to the local ISP. The primary advantage in using the Internet is that one does not incur any long distance telephone charges. Another advantage is the ability to transmit data while talking. On the downside, the Internet introduces a delay of typical 1/2 to one second, similar to the delay present in transcontinental satellite telephone connections. There is also no connectivity with the existing telephone system, so that one can only communicate with other Internet users connected at the time of the call. . telephone 204 Practical TCP/IP and Ethernet Networking network) and PBX (private branch exchange) infrastructure. Internet communications products are predominantly software-based and in many. ideal solution for university and 206 Practical TCP/IP and Ethernet Networking college students with access to the institutional Internet service since it costs nothing and they retain their e-mail. reception and transmission of electronic mail, with reference to the TCP/IP model. Whereas the actual transmission of the mail (in digital format) from end to end is handled by the Internet and host-to-host