NIU

Posts Tagged ‘NIU’

postheadericon Are You VoIP Ready? – Glossary

Bandwidth Saturation The point in which all available bandwidth on an Internet

connection is used up.

Bandwidth The amount of data passing through a connection over a given time.
It is usually measured in bps (bits-per-second) or Mbps (Megabits
per Second). As a general rule, get as much as you can afford – and
the make sure you are getting it.
Content Filtering On the Internet, content filtering (also known as information

filtering) is the use of a program to screen and exclude from access

or availability Web pages or e-mail that is deemed objectionable.

Content filtering is used by corporations and governments as part of

Internet firewall computers and also by home computer owners,

especially by parents to screen the content their children have access

to from a computer

Dropped Packets Packets (i.e. small data “packages”) are occasionally dropped, or

lost, on the network for various reasons. For instance, two nodes

may be communicating at widely disparate transfer rates. TCP

packets are resent, UDP s are not.

Hop In a packet-switching network, a hop is the trip a data packet takes

from one router or intermediate point to another in the network. On

the Internet (or a network that uses TCP/IP), the number of hops a

packet has taken toward its destination (called the “hop count”) is

kept in the packet header.

ICMP Internet Control Message Protocol is a message control and

error-reporting protocol between a host server and a gateway to the

Internet. ICMP uses Internet Protocol (IP) datagrams, but the

messages are processed by the IP software and are not directly

apparent to the application user.

ISP An ISP (Internet Service Provider) aka Carrier, aka Provider, is a

company that collects a monthly or yearly fee in exchange for

providing the subscriber with Internet access.

Jitter The difference in latency from one packet to the next measured in

milliseconds.

LAN A Local Area Network is a computer network that spans a

relatively small area. Most LANs are confined to a single building or

group of buildings. However, one LAN can be connected to other

LANs over any distance via telephone lines and radio waves. A

system of LANs connected in this way is called a wide-area network

(WAN).

Latency In a network, latency, a synonym for delay, is an expression of how

much time it takes for a packet of data to get from one designated

point to another. Typically, latency is measured by sending a packet

that is returned to the sender. The round-trip time – measured in

milliseconds – is considered the latency.

NIU A Network Interface Unit (sometimes called a network interface

device) is a device that serves as a common interface for various

other devices within a LAN , or as an interface to allow networked

computers to connect to an outside network.

Ping Loosely, ping means “to get the attention of” or “to check for the

presence of” another party online. Ping operates by sending a packet
to a designated address and waiting for a response. The computer
acronym (for Packet Internet or Inter-Network Groper) was
contrived to match the submariners’ term for the sound of a returned
sonar pulse.

Point to Point Point-to-point telecommunications generally refers to a connection

restricted to two endpoints, usually host computers.

PSTN Public Switched Telephone Network is the world’s collection of

interconnected voice-oriented public telephone networks, both

commercial and government-owned

QoS Quality of Service. Describes the ability of a e.g. router to prioritize

certain packets

SIP Session Initiation Protocol is an application-layer control

(signaling) protocol for creating, modifying, and terminating

sessions with one or more participants. It can be used to create

two-party, multiparty, or multicast sessions that include Internet

telephone calls, multimedia distribution, and multimedia

conferences.

TDM Short for Time Division Multiplexing, a type of multiplexing that

combines data streams by assigning each stream a different time slot

in a set. TDM telephone sets (often referred to as digital  sets)

differ from IP sets in that they do not go on a LAN s infrastucture

are compatible with analogue wiring schemes and can work on cable

runs oup to 1,600 feet.

VPN (pronounced as separate letters) Short for Virtual Private Network,

is a private network that uses a public network (usually the Internet)

to connect remote sites or users together. VPNs use “virtual”

connections routed through the Internet from a company’s private

network , a remote site or employee.

WIC WAN Interface Card is installed in a router and is the component

that a Internet T-1 will physically plug in to.

postheadericon Are You VoIP Ready? – Latency

Every IT staff member knows that when you ping something, in addition to confirming that a device is connected to the network, the reply will give you the round trip time in milliseconds from the device you are pinging. A ping is a type of ICMP packet (along with the commonly used trace route command) that you can use to determine just how much delay your packets will experience from point A to point B and back. All of the graphs you see in this article are latency based and bandwidth availability – or lack thereof – has to be extrapolated from that.
Realistically, there is no way to know how much bandwidth some one has by simply looking at their connection from the outside  unless you are
sitting in the Central office looking directly at the connection. That said, there are several things that latency will tell you. I usually try to get a week s worth of data before I m comfortable with the circuit – if there is a problem, it will likely show up within that sample.
The magic latency number I like to see when testing for VoIP usability between sites is 80ms or lower. Another term that is directly related to latency is jitter . Jitter is caused when packets leaving a source in a certain order and spacing, arrive at the destination in the same order
(usually) but with different spacing. It is essentially the difference in latency time from one packet to the next. When jitter is high – anything over 15% variance between samples – it usually points to bandwidth problem. To get an idea of the impact of high jitter, imagine the sound of an
audio CD that is played while alternating between pause and fast-forward. The garbled sound is characteristic of jitter.
If you are going to network offices within the same city, you should see ping times of around 30ms or less and jitter under 5ms. The further across the country you go, the higher the latency tends to get. As of this article, a typical ping time from Houston to Los Angeles is
between 54ms and 67ms. Surprisingly, latency from Houston to Hong Kong is only 62ms to 87ms. I was in Switzerland not too long ago and the ping time was only 75ms from Bern to Los Angeles. My point is that, while geographical distance is an issue, it is not going to be the
determining factor of whether your VoIP project is going to work or not. Things that will affect whether your voice packets will get there in reasonable time or not is QOS (which stands for Quality of Service), the ISP or Carrier, bandwidth, hardware and hardware configuration.
To get an idea of what mis-configured hardware looks like, take a look at Figure 3. The IT manager had just moved into a new facility and users were complaining to him about slow Internet speed. As you can see, the latency is pretty good but the amount of dropped packets was
very high. The poor guy spent the better part of 3 weeks arguing with the carrier about the problem. Their contention was that the source of the problem was at his end as they showed everything good when they tested up to the NIU. They also ran diagnostics on the router – that
they supplied – and that also produced nothing. Technically, they were right except for one important setting that would not show up on any diagnostic. The Clock Source  setting for the router was configured as Internal  – i.e. it was referencing itself as a clock source – instead of
clocking off the network (sometimes referred to as Recovered  mode). For the most part, it worked but any time the router or carrier s clock drifted slightly, packets would be dropped.