Explaining Home Network Speeds

How often have you wondered what the kbps really means?  Ever wonder how fast a 10Mbps Ethernet is?  How long SHOULD it take to copy a file from one computer to another over different kinds of networks?  How long should a download take over a modem?  Is a 1mb network like Home PNA fast enough for your home? In this article I will attempt to clarify modem, broadband, and common networking speeds in a practical way.

Definitions

BIT: abreviated to a small b (Kbps), unit of measurement in a computer represneting a 1 or a 0

BYTE:  abreviated to a capital B (KBps), another unit of measurement in a computer, 8 bits are in a single byte.  Other lengths are possible like 16, 32, 64, etc but network communications is based on 8 bit lengths.  

Kbps:   kilobits per second, or 1000 bits per second

Mbps:  Megabits per second or 1,000,000 bits per second

Is It Bytes or Bits? The small b in Kbps lets us know the unit of measurement is bytes.  A capital B would let us know the measurement is in Bytes.

Even though the metric system uses a small k for kilo, the computer industry has chosen to use a capital K in most cases.

Definition Examples:

56Kbps      56 X 1000 bits per second = 56,000 ones and zero's

128Kbps      128 X 1000 bits per second = 128,000 ones or zero's

460Kbps     460 X 1,000,000 bits per second = 460,000 ones or zero's

1Mbps     1 X 1,000,000 bits per second = 1 million one's or zero's

10Mbps     10 X 1,000,000 bits per second = 10 million one's or zero's

Use:

So far so goood.  It would appear that you have enough information to start figuring out how long it takes to transfer files but you have to remember that these speeds are in BITS not BYTES.  When we look at a file size we look at the number of BYTES not the number of bits.  Using this information we can build the chart below.

Theoretical Maximum Speeds

Common Name	Used With	Bits per Second	Bytes per Second
28.8Kbps	Modems	28,800	3,600
56.6Kbps	Modems	56,600	7,200
128Kbps	ISDN	128,000	16,000
460Kbps	Cable Modem	460,000	57,500
1Mbps	Home PNA 1.0	1,000,000	125,000
1.6Mbps	HomeRF	1,600,000	200,000
10Mbps	Ethernet	10,000,000	1,250,000
100Mbps	Fast Ethernet	100,000,000	12,500,000

Approx Theoretical Transfer Times:

Common Name	Used With	Time to Transfer 1 Megabyte	Time to transfer 50 Megabytes
28.8Kbps	Modems	4.5 Min	3.8 Hrs
56.6Kbps	Modems	2.3 Min	2 Hrs
128Kbps	ISDN	1 Min	50 Min
460Kbps	Some Cable Modems	17 Sec	14.5 Min
1Mbps	Home PNA 1.0, Cable Modes	8 Sec	6.5 Min
1.6Mbps	HomeRF	5 Sec	4 Min
10Mbps	Ethernet	1 Sec	40 Sec
100Mbps	Fast Ethernet	1 Sec	4 Sec

Theoretical vs Real times:

So many factors go into real transfer times that it is very dificult to wrap blanket numbers around them.  Once you get over ISDN speeds, network latency, protocol overhead, driver efficiency, and all kinds of other technical things get in the way.  In general, expect transfer speeds of 40 to 80% of the maximum speed. 

Aprox Real Transfer Times:

Common Name	Used With	Time to Transfer 1 Megabyte	Time to transfer 50 Megabytes
28.8Kbps	Modems	6-12 Min	4.8-9.6 Hrs
56.6Kbps	Modems	3-6 Min	2.4-4.8 Hrs
128Kbps	ISDN	1-3 Min	1-2.1 hrs
460Kbps	Some Cable Modems	22-43 Sec	18-36 Min
1Mbps	HomePNA 1.0**, Some Cable Modes	10-20 Sec	8-16  Min
1.6Mbps	HomeRF**	6-13 Sec	5-10 Min
10Mbps	Ethernet, HomePNA 2.0**	1-2 Sec	50-100 Sec
100Mbps	Fast Ethernet	1 Sec	5-10 Sec*

*PCI Bus efficiency can easly make this 9-14 seconds

**Often, these systems run at 1/2 speed because of interference

Explaining DMZ’s and Port forwarding as it pertains to home networking and broadband routers

Ports: Applications running on TCP/IP open connections to other computers using something called ports. Ports allow multiple applications to reside on a single computer - all talking TCP/IP. Ports are another set of numbers AFTER the standard IP address. Applications often hide these port numbers to reduce the complexityof TCP/IP. Example: web services (HTTP) reside on port 80 by default. To reach this web site, you could type http://www.homenethelp.com:80 into your browser. The 80 is the default port number for the HTTP protocol so typing it is not necessary. There are 65535 available ports. Here is a list of some ‘well known ports’. 

Port Forwarding: A broadband router or other NAT application (like ICS) creates a firewall between your internal network and the internet. A firewall keeps unwanted traffic from the internet away from your LAN computers.  A ‘tunnel’ can be created through your firewall so that the computers on the Internet can communicate to one of the computers on your LAN on a single port. This is handy for running web servers, game servers, ftp servers, or even video conferencing. This is called port forwarding. One of your computers could run a web server (port 80) while another computer could run an FTP server (port 23) - both on the same IP address.

DMZ: This is a feature that is included on some routers but is not in Internet sharing software. A DMZ allows a single computer on your LAN to expose ALL of its ports to the Internet. When doing this, the exposed computer is no longer ‘behind’ the firewall.

Port Forwarding vs DMZ

A DMZ is far easier to set up than port forwarding but exposes your entire computer to the Internet. Sometimes TCP/IP applications require very specialized IP configurations that are difficult to set up or are not supported by your router. In this case, placing your computer in the DMZ is the only way to get the application working. Placing a computer in the DMZ should be considered ‘temporary’ because your firewall is no longer able to provide any security to it.

Port forwarding can sometimes be difficult to configure, but provides a relatively safe way of running a server from behind a firewall. Since only a single port (or small series of ports) is exposed to the Internet, the computer is easier to secure. Additionally, port forwarding allows you to run multiple kinds of servers from different computers on your lan. (see above diagram) Many broadband routers have special port forwarding configuration screens for standard applications (FTP, WWW, Mail, etc) and special screens for custom applications.

PORT NUMBERS

(last updated 2001 Jul 02)

The port numbers are divided into three ranges: the Well Known Ports,

the Registered Ports, and the Dynamic and/or Private Ports.

The Well Known Ports are those from 0 through 1023.

The Registered Ports are those from 1024 through 49151

The Dynamic and/or Private Ports are those from 49152 through 65535

WELL KNOWN PORT NUMBERS

The Well Known Ports are assigned by the IANA and on most systems can

only be used by system (or root) processes or by programs executed by

privileged users.

Ports are used in the TCP [RFC793] to name the ends of logical

connections which carry long term conversations.  For the purpose of

providing services to unknown callers, a service contact port is

defined.  This list specifies the port used by the server process as

its contact port.  The contact port is sometimes called the

"well-known port".

To the extent possible, these same port assignments are used with the

UDP [RFC768].

The range for assigned ports managed by the IANA is 0-1023.

http://www.iana.org/assignments/port-numbers