Wednesday, April 28, 2010

Broadband Wireless Access Technologies

Broadband Wireless Access Technologies 
  • Local Multipoint Distribution Services (LMDS) 
  • Multi-channel Multipoint Distribution Services (MMDS) 
  • CDMA EvDO/EvDV 
  • W-CDMA 
  • TD-CDMA 
  • WiMAX
What is WiMAX?
  • Worldwide Interoperability for Microwave Access (WiMAX) is the common name associated to the IEEE 802.16a/d/e standards that originally covered the Wireless Local Loop technologies with radio spectrum from 10 to 66 GHz.
Why WiMAX?
  • Standard based 
  • Lower Cost 
  • Ensures compatibility and interoperability 
  • Better Performance & Coverage

Ways of providing Broadband Access

 Ways of providing Broadband Access?
  • Copper Wire (DSL) 
  • Optical Fiber Cable 
  • Wireless Access System. 
  • Satellite Communication System 

Why Broadband Wireless Access ?
  • Lower Capital Expenditure 
  • Lower Operational Expenditure 
  • Faster Deployment Time 
  • Scalable & Easy Relocation

What is Broadband

Q: What is Broadband?
Ans:
  • Broadband comes from the words "broad bandwidth" and is used to describe a high-capacity, two-way link between an end user and access network suppliers capable of supporting full-motion, interactive video applications. 
  • A way of transmitting large amounts of data, voice, and video that is greater than telephony networks.
  • A term for high-speed, high-capacity Internet and data connections. 
  • It is type of data transmission in which a single medium can carry several channels at once including voice, data and video simultaneously. It is also a general term for different types of high-speed, high-bandwidth connections to the Internet, including Cable and DSL. 
  • Broadband" refers to a type of network connection that supports a very high bit rate, as opposed to "narrowband," which supports a lower bit rate. The higher the bit rate, which is a measure of speed of transmission of bits per second (bps), the faster the transmission will occur in a given period of time. Delivered via DSL or cable service, bandwidth: >128 Kilo Bits per second (Kbps) 

Friday, April 16, 2010

16-QAM,64-QAM Modulation

16-QAM,64-QAM

  • The number before QAM (for example 16QAM) refers directly to the number of decision points in the constellation. Meaning, 256QAM has 192 more decision points than 64QAM. The number before QAM is also always a power of two. (EG. 2^6=64QAM) 
  • There are several trade offs to this: 
  • The more Decision points, the more throughput per channel. 
  • The more Decision points, the more susceptible the channel is to noise (as the decision boundaries get smaller to accommodate more decision points, it becomes harder to distinguish which boundary the point was intended to lie in). 
  • More Decision points=More Bandwidth=Higher susceptibility to noise or poor signal (the same applies inversely as well). 
  • At best, it'll enable either to: 
  • Deliver the same number of customers incrementally faster speeds.-or- 
  • Deliver a larger number of customers the same speeds as before.

Sunday, April 11, 2010

NDR (Non-Delivery report) Code List


NDR (Non-Delivery report) List of Codes and their meanings

4.2.2 The recipient has exceeded their mailbox limit. It could also be
that the delivery directory on the Virtual server has exceeded its
limit. (Default 22 MB)

4.3.1 Not enough disk space on the delivery server. Microsoft say this
NDR maybe reported as out-of-memory error.

4.3.2 Classic temporary problem, the Administrator has frozen the
queue.

4.4.1 Intermittent network connection. The server has not yet
responded. Classic temporary problem. If it persists, you will also a
5.4.x status code error.

4.4.2 The server started to deliver the message but then the connection
was broken.

4.4.6 Too many hops. Most likely, the message is looping.

4.4.7 Problem with a timeout. Check receiving server connectors.

4.4.9 A DNS problem. Check your smart host setting on the SMTP
connector. For example, check correct SMTP format. Also, use square
brackets in the IP address [197.89.1.4] You can get this same NDR
error if you have been deleting routing groups.

4.6.5 Multi-language situation. Your server does not have the correct
language code page installed.

5.0.0 SMTP 500 reply code means an unrecognised command. You get this
NDR when you make a typing mistake when you manually try to send email
via telnet.
More likely, a routing group error, no routing connector, or no
suitable address space in the connector. (Try adding * in the address
space)
This status code is a general error message in Exchange 2000. In fact
Microsoft introduced a service pack to make sure now get a more
specific code.

5.1.x Problem with email address.

5.1.0 Often seen with contacts. Check the recipient address.

5.1.1 Another problem with the recipient address. Possibly the user
was moved to another server in Active Directory. Maybe an Outlook
client replied to a message while offline.

5.1.3 Another problem with contacts. Address field maybe empty. Check
the address information.

5.1.4 Two objects have the same address, which confuses the
categorizer.

5.1.5 Destination mailbox address invalid.

5.1.6 Problem with homeMDB or msExchHomeServerName - check how many
users are affected. Sometimes running RUS (Recipient Update Service)
cures this problem. Mailbox may have moved.

5.1.7 Problem with senders mail attribute, check properties sheet in
ADUC.

5.2.x NDR caused by a problem with the large size of the email.

5.2.1 The message is too large. Else it could be a permissions
problem. Check the recipient's mailbox.

5.2.2 Sadly, the recipient has exceeded their mailbox limit.

5.2.3 Recipient cannot receive messages this big. Server or connector
limit exceeded.

5.2.4 Most likely, a distribution list or group is trying to send an
email. Check where the expansion server is situated.

5.3.0 Problem with MTA, maybe someone has been editing the registry to
disable the MTA / Store driver.

5.3.1 Mail system full. Possibly a Standard edition of Exchange
reached the 16 GB limit.

5.3.2 System not accepting network messages. Look outside Exchange for
a connectivity problem.

5.3.3 Remote server has insufficient disk space to hold email. Check
SMTP log.

5.3.4 Message too big. Check limits, System Policy, connector, virtual
server.

5.3.5 Multiple Virtual Servers are using the same IP address and port.
See Microsoft TechNet article: 321721 Sharing SMTP. Email probably
looping.

5.4.0 DNS Problem. Check the Smart host, or check your DNS. It means
that there is no DNS server that can resolve this email address. Could
be Virtual Server SMTP address.

5.4.1 No answer from host. Not Exchange's fault check connections.

5.4.2 Bad connection.

5.4.3 Routing server failure. No available route.

5.4.4 Cannot find the next hop, check the Routing Group Connector.
Perhaps you have Exchange servers in different Routing Groups, but no
connector.

5.4.6 Tricky looping problem, a contact has the same email address as
an Active Directory user. One user is probably using an Alternate
Recipient with the same email address as a contact.

5.4.7 Delivery time-out. Message is taking too long to be delivered.

5.4.8 Microsoft advise, check your recipient policy. SMTP address
should be 
cp.com.
NOT 
server.cp.com.

5.5.0 Underlying SMTP 500 error. Our server tried ehlo, the
recipient's server did not understand and returned a 550 or 500 error.
Set up SMTP logging.

5.5.2 Possibly the disk holding the operating system is full. Or could
be a syntax error if you are executing SMTP from a telnet shell.

5.5.3 More than 5,000 recipients. Check the Global Settings, Message
Delivery properties.

5.5.5 Wrong protocol version

5.6.3 More than 250 attachments.

5.7.1 Permissions problem. For some reason the sender is not allowed
to email this account. Perhaps an anonymous user is trying to send
mail to a distribution list.
Check SMTP Virtual Server Access Tab. Try checking this box: Allow
computers which successfully authenticate to relay
User may have a manually created email address that does not match a
System Policy.

5.7.2 Distribution list cannot expand and so is unable to deliver its
messages.

5.7.3 Check external IP address of ISA server. Make sure it matches the
SMTP publishing rule.

5.7.4 Extra security features not supported. Check delivery server
settings

5.7.5 Cryptographic failure. Try a plain message with encryption.

5.7.6 Certificate problem, encryption level maybe to high.

5.7.7 Message integrity problem

Thursday, April 8, 2010

Squid Configuration file

Squid Configuration file

Requirement: option file which consist of all squid configuration options.

Solution:
Squid Cache: Version 3.0.PRE4-20060804
configure options: '--build=i386-redhat-linux' '--host=i386-redhat-linux' '--target=i386-redhat-linux-gnu' '--program-prefix=' '--prefix=/usr' '--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--includedir=/usr/include' '--libdir=/usr/lib' '--libexecdir=/usr/libexec' '--sharedstatedir=/usr/com' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--exec_prefix=/usr' '--bindir=/usr/sbin' '--libexecdir=/usr/lib/squid' '--localstatedir=/var' '--sysconfdir=/etc/squid' '--enable-poll' '--enable-snmp' '--enable-removal-policies=heap,lru' '--enable-storeio=aufs,coss,diskd,null,ufs' '--enable-ssl' '--with-openssl=/usr/kerberos' '--enable-delay-pools' '--enable-linux-netfilter' '--with-pthreads' '--enable-ntlm-auth-helpers=SMB' '--enable-external-acl-helpers=ip_user,ldap_group,unix_group,wbinfo_group' '--enable-auth=basic,ntlm' '--enable-useragent-log' '--enable-referer-log' '--disable-dependency-tracking' '--enable-cachemgr-hostname=localhost' '--disable-ident-lookups' '--enable-truncate' '--enable-underscores' '--datadir=/usr/share' '--enable-basic-auth-helpers=LDAP,MSNT,NCSA,PAM,SMB,YP,getpwnam,multi-domain-NTLM,SASL' '--enable-arp-acl' 'build_alias=i386-redhat-linux' 'host_alias=i386-redhat-linux' 'target_alias=i386-redhat-linux-gnu'


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