IP in Cable: When Two Worlds Collide
With Internet protocol (IP) playing an increasingly important role in advanced broadband networks, Communications Technology’s editors and advisory board thought it critical that we take an in-depth look at it. In this issue, we present a three-part special report that includes: A quick look at the basics of IP; how IP works specifically for voice, data and video services; and how to use IP over cable—the role of edge devices, CMTS requirements, routing issues, and transport options.
There’s no doubt about it; the RF and Internet protocol (IP) worlds are on a collision course. And if they haven’t bumped up against each other already at your plant, they will be colliding in the not too distant future.
For denizens of the RF world, IP can seem like an alien concept, so what follows is a look at some of the basics of IP.
According to Newton’s Telecom Dictionary, IP is a data communications protocol that keeps track of the Internet’s addresses for different nodes, routes outgoing messages and recognizes incoming messages. It allows packets to traverse multiple networks on the way to their final destination. IP isn’t limited to the Internet, though. The protocol can be used on many types of networks.
The postal delivery service is an often-used analogy to explain IP’s function: An IP packet, or "chunk" of data, is a way of communicating between two hosts—or two intelligent two-way devices connected to a network. The two hosts can be located on the same network or can reside on separate physical networks.
IP is used in conjunction with TCP (transmission control protocol). The TCP/IP protocol routes messages on the Internet and other networks, based on the IP address of the final destination. TCP/IP is what keeps the Internet from turning into a tangled gnarl every time an item is sent. There are five classes of IP addresses: A, B, C, D and E.
The IP address
"Those classes are delineation marks," Steve Lee, Cisco’s manager of engineering, explains. "If you look at an IP address, it’s usually four octets separated by a period. For example, if you have 10.10.10.10, you have an address that’s basically four octets, 32 bits in length that is four bytes long, so that address is a unique IP address that would identify a given host anywhere in the network."
Every device that communicates over the Internet is assigned an IP address, which identifies that device and distinguishes it from other devices on the Internet. The four numbers in an IP address are used in different ways to identify a particular network or a host on that network. Three regional Internet registries, ARIN, RIPE NCC and APNIC, assign Internet addresses.
The class of the address determines which part is the network address and which part is the node address. All nodes—or network connection points—on a given network share the same network prefix but must have a unique host number.
"The way you differentiate between the different classes of addresses is by looking at the first octet head of an IP address range," Lee says.
Identifying classes
Class A Network: Binary addresses start with 0, so the decimal number can be anywhere from 1 to 126. The first eight bits (the first octet) identify the network, and the remaining 24 bits indicate the host within the network.
Class B Network: From 128 to 191. (Lee says the number 127 is a loopback address used by every host that is IP aware.) The first 16 bits (the first two octets) identify the network and the remaining 16 bits indicate the host within the network.
Class C Network: From 192 to 223. The first 24 bits (the first three octets) identify the network, and the remaining 8 bits indicate the host within the network.
Class D Network: From 224 to 239. Class D networks are used to support multicasting.
Class E Network: Binary addresses start with 1111; therefore, the decimal number can be anywhere from 240 to 255. Lee says Class E addresses have never been assigned, instead they are held in reserve by the IETF (Internet Engineering Task Force).
"You can’t really understand IP until you understand how host A speaks with host B. That’s done under the auspices of this IP addressing infrastructure," Lee notes. "Once you understand those basics, then you can move onto things like routing protocols, subnet mask and default gateways."
To get a better understanding of how IP addresses work, look at the IETF’s request for comments (RFCs), specifically RFC 1900 and 1918. Detailed discussions of the Internet protocol can be found in RFCs 1122 and 2600.
"When the Internet started out, it wasn’t based on standards," says Dave Devereaux-Weber, a network engineer at the University of Wisconsin- Madison, division of information technology (DoIT), network services group, and also Webmaster of the SCTE-List. "There was a need for a centralized set of standards so they came up with the IETF, and now that body acts as the central agency for approving all of the RFCs."
Mike Robuck is an associate editor with Communications Technology.
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Boning up on IP
The Internet hosts a wealth of information related to IP, from simple explanations to detailed diagrams of routing protocols.
"Cisco has an incredibly rich Web site," says Dave Devereaux-Weber, a network engineer at the University of Wisconsin-Madison. "There’s also a lot of information from universities such as Rutgers, which I don’t think the cable industry utilizes enough. And there are some good books out there, but there’s so much information online that you can read for free."
For keep-in-the-office references, check out these books on IP:
* Internetworking with TCP/IP: Principles, Protocols, and Architectures, (4th Edition), by Douglas E. Comer. Prentice Hall, 2000.
* Illustrated TCP/IP, by Matthew Naugle. Wiley Computer Publishing, 1999.
Some Internet links for IP include:
* www.cisco.com/univercd/cc/td/ doc/cisintwk/ito_doc/ip.htm#xtocid2
* www.acm.org/crossroads/ columns/connector/july2000.html
