hop

Posts Tagged ‘hop’

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? – The Road to China: Content Filtering to the Max

ChinaNET is managed by the Data Communications Bureau of the Ministry for Posts and Telecommunications, and provides Internet service in all 31 provincial capitals in mainland China. It is one of the two major commercial networks approved by the State Council, the other being ChinaBGN. For this reason, Figure 6 is one of my favorite sites to watch, not because it has great VoIP possibilities – because it does not – but because you can capture the business heart beat of a nation along with the ideology of a government just by viewing this graph over a week s
time. The target site is in a town just south of Shanghai called Hangzhou. The part I find most interesting is that you can tell the moment you hit mainland China (hop 13) because the latency skyrockets from 62ms to 449ms. This is a classic example of Content Filtering  that ChinaNet does in order to keep certain things out of their country. Fortunately, ICMP packets are not one of them, so once we get past the censors, you can see that even within the mainland, there is an overall increase in latency to the final destination – this hints at content filtering within the borders as well. Overall, you can see what the average Chinese Internet user experiences in terms of latency over a weeks time. The graph shows a 7 day cycle and within each day cycle you can see a consistent dip just a little past half way which I found out later was when they – you guessed it – took the equivalent of lunch. This also shows that the basic internal data-transport infrastructure is under a severe load and the chances of VoIP running well WITHIN China are slim if you have to go more than a handful of hops. This might be another reason the Chinese government blocks most of the incoming Internet traffic – the network just could not handle it!
As an aside, when I first started watching this site about a year ago, I was able to see ChinaNet  in the DNSName column. About 7 months ago they removed any identification other than the IP address.
The client originally asked me to see if they could have a telephone connected via VoIP from California to this site and the answer was an emphatic No! . We considered a satellite solution but found out that there were restrictions on this as well. Besides, satellite in general,
has very high latency (too high for decent voice, in my opinion) and is susceptible to bad weather. So as of this article, they are simply resorting to email and regular PSTN connections to communicate.

postheadericon Are You VoIP Ready? – QoS (Quality of Service)

Normally, when packets are serialized out the router to the Internet, they are sent in a first come first serve  fashion. If your router is equipped with QOS, packets from your PBX or SIP server* can be prioritized ahead of the other non-voice packets thereby keeping the flow of
voice traffic relatively smooth. Most carriers that offer a combined package of voice and data services do just that. RonEK is a partner with several ISPs and one of the first questions on the vendor check list is the IP address of the PBX. Most of the higher end carriers will provide an
end to end managed circuit  which means that they can control the connection from your office to their space in the central office. From there, packets are routed out on their backbone or someone else s backbone depending on the carrier s capacity and the final destination.
Keep in mind that QOS prioritizes packets going out to the other end. Once a packet leaves your premise or your provider s backbone, it is no longer prioritized and subject to the winds and tides of the Internet just like all the other packets. So, when designing a multi-site
network, try to stick with one provider and, if possible, try to do it on an MPLS platform. Usually if you stay within a provider s backbone from end to end, the prioritization will be maintained throughout the connection. Also, there is no way to prioritize packets coming to you until they actually get to you. Many times customers think that if they simply implement QOS that all their voice issues will go away not realizing that they only addressed half of the potential problem. Your connection and QOS is just part of the overall voice session that YOU control. The rest is in the hands of the intermediary (often there is more than one) that controls the path of the packets and then finally, the ISP and equipment at the final destination.
* More about SIP servers in coming articles.

postheadericon Are You VoIP Ready?

If you are considering VoIP for your company – or more to the point, if YOU are responsible for the implementation of VoIP for your company – here are the basics you will need to understand.

Voice over IP performance is a function of:

a) Bandwidth

b) Latency

Both components have to be within a certain tolerance  in order to be usable and there are a multitude of factors that can adversely affect either. Many IT professionals who are first time VoIP-ers  often think that given enough bandwidth, you can do anything – including voice. This is only half true. A lack of bandwidth can cause latency, but an abundance of bandwidth is not a guarantee of a clear conversation. Of the two, latency is not only a show stopper, it is also the hardest one to find and correct because there are many causes that are often times not within your control. Figure 1 is a great example of a company with a bonded 6M T-1 connection with such erratic latency – and jitter  – that it is virtually unusable for

voice applications. In many cases like this, the most natural scapegoat is the carrier, however, in this case, hop 14 is the WAN side of the customer s router and hop 15 is a device behind it which implies a problem with the hardware. Here, the problem turned out to be one of the 4 T-1′s were in a permanent Admin Down  mode and needed to have the WIC replaced.

WARNING TO THOSE JUST GETTING INTO VoIP – Voice is real time  – using primarily UDP packets – and therefore much more affected by things like dropped packets, jitter and high latency than regular  data. If there are issues on your Internet connections with these items, you will probably not realize it unless you specifically – and continuously – test for it. Most carriers only guarantee bandwidth and NOT latency. Trust me, the CEO, CFO, Customer Service manager and Sales manager will get upset if the email server or Internet is a little slow, but they will absolutely FREAK if their phones don’t work.