Networking Tips Tricks

Query: I am little bit confused regarding deploying updates on clients using WSUS server, i have configured some four clients using group policy to point to WSUS server, that clients are shown in WSUS administrationtconsole but how to deploy updtes from server to client i want the procedure , also i want to schedule the client for getting updtes informtion from server. so plz help me out for this problem asap. Solution: Check this Server Side after SUS Installation Synchronizing SUS If you are not already viewing the SUS administration page, open Internet Explorer and navigate to http://yoursusSERVER01/SUSAdmin.  To view the SUS administration site, you might need to add Server01 to the Local Intranet trusted site list to access the site. Open Internet Explorer, and choose Internet Options from the Tools menu. Click the Security Tab. Select Trusted Sites, and click Sites. Add yoursusServer01 and yoursusServer01.contoso.com to the trusted site list...

Query: I need to forward multicast using linux machine. my server lan is on one interface & another interface of the firewall holds local lan, nse server ip is 172.20.20.219 multicast comming from nse server is 233.1.2.3 i need to tansfer same to the local lan to view rates of the NSE EXCHANGE. i am using redhat fedora core 2 eth0 is local lan eth1&eth2 is dsl internet links eth3 is server lan i have tried with ifconfig -allmulti command on server interface, i tried with :- [root@squid all]# echo 1 > /proc/sys/net/ipv4/conf/eth3/ mc_forwarding -bash: /proc/sys/net/ipv4/conf/eth3/ mc_forwarding: Operation not permitted route add -net 233.1.2.3 netmask 255.255.255.255 dev eth0 still i dont get multicast on the local interface. kindly suggest me how can i do this.                                     ...

Problem:   Firewall is applied on my network as given in below diagram; problem is that after configuring the firewall client system didnt get internet ping to firewall on both lan ips. My network flow as follows                 Linux DHCP & Squid Proxy server                                             | Client System---> Switch ------>Firewall ----> Router---->VSNL Leased line My problem is firewall set on linux server my cli Solution: Squid iptables firewall The following  iptables  firewall is suited for a dual-homed Squid proxy server. ssh (TCP port 22), squid (TCP port 3128), and ICMP ECHO requests are allowed on the internal (LAN) interface.  Squid is configured to proxy ftp, http, https, and AOL Instant Messenger traffic. In addition, the server is running a caching/...

Abbreviations used in WiMAX Section AAA Authentication, Authorization and Accounting AAS Adaptive Antenna System also Advanced Antenna System ACK Acknowledgement AMC Adaptive Modulation and Coding ASN Access Service network ASP Application Service Provider BS Base Station BWA Broadband Wireless Access CC Convolutional Coding CP Cyclic Prefix CQI Channel Quality Information CSN Connectivity Service Node CTC Convolutional Turbo Coding DHCP Dynamic Host Configuration Protocol, typically used to assign IP addresses DL Down Link DVB/DAB Digital Video Broadcast/ Digital Audio Broadcast FA Foreign Agent (MIP) FCH Frame Control Header FDD Frequency Division Duplex FFT Fast Fourier Transform FUSC Full Use of Sub-Channels GW Gateway HA Home Agent (MIP) HARQ Hybrid Automatic Repeat reQuest HHO Hard Hand-Off IEEE Institute of Electrical and Electronics Engineers IFFT Inverse Fast Fourier Transform ISI Inter-Symbol...

OFDMA TDD Frame Structure OFDMA is two-dimensional with users sharing in both the time and frequency domains. This allows scheduling and optimum use of finite spectrum. Each user is assigned a burst area that has dimensions of sub-channels and symbols. Key Elements Preamble is broadcast for one symbol period and allows the user devices to acquire the system and synchronize. A known PN code is transmitted. FCH reports the length of the DL-Map. DL-Map contains bandwidth allocation for users and location of the UL-Map. UL-Map contains bandwidth allocation of the UL for the next frame. Both maps contain burst data regions, modulation, and coding type for the user. Allocated regions in UL are available for random access, CQI, and ACKs. Transmit Recieve Transition Gap (TTG) and Receiver Transmit Transition Gap (RTG) are guard times between the transmit and receiver portions of the frame.

Cyclic Prefix (CP) Cyclic prefix (CP) mitigates multipath fading and inter-symbol interference (ISI) at the price of increasing bandwidth. Delay spread exceeds symbol time. ISI is the result. Separate the symbols in time by adding a gap. Transmission must be continuous. To “fill” the gap, append data from the end of the symbol to the beginning of the symbol. CP allows the system to ignore the initial part of each symbol thus avoiding the area that would be most likely impacted by multipath delay. Data in the CP region of the signal is discarded. CP is set to 4-6 times the delay spread. WiMAX Forum profiles use a CP of 1/8, meaning that a section of data equal to 1/8 of the original symbol is used.

Multipath and Fading Each narrow band signal is subject to frequency-selective fading on the radio link. Convolutional Coding (CC) or Convolutional Turbo Coding (CTC) is used to protect the data.

OFDMA Sub-Channels and Permutation Zones The sub-carriers are divided into groups known as sub-channels Sub-carriers may be adjacent or distributed in a sub-channel Sub-carriers are assigned to sub-channels to ensure frequency diversity and interference diversity. Sub-channel Usage Schemes PUSC – Partial Usage of Sub-Channels -        Mandatory mode for sending preambles and allocation messages and all the uplink messages -        Sub-carriers are divided between cells (N=3) and then grouped into sub-channels -        Goal: Reduce RF interference FUSC - Full Usage of Sub-Channels -        Optional and used in the downlink only. -        All sub-carriers are available in every cell (N=1) -        Goal: Maximize throughput AMC – Adaptive Modulation and Coding -        Adjacent sub-c...

OFDM and OFDMA Signal in Frequency Domain The sub-carriers are divided into several types Data Sub-carriers - Use QPSK, 16-QAM, 64-QAM modulation to transport data bits  Pilot Sub-carriers - Data-free symbols used to maintain optimal operation of the receiver  Guard Sub-carriers - Off, no power is generated at these frequencies  DC Sub-carrier - Off to support direct-conversion receivers  Sub-carrier Spacing (1/T) is the reciprocal of the modulation symbol time (T) OFDM - All sub-carriers belong to a single user for some period of time. Multiple users are accommodated at different times. OFDMA - Users share the sub-carriers with a bandwidth dependent on the data service in use. Each color represents a different user.

OFDM Spectral Overlap Conventional Frequency Division Multiplex (FDM) Multi-Carrier Modulation Technique In conventional FDM, each carrier frequency is separated by a guard band to prevent interference. The frequencies in the guard band area cannot be used to carry information. The Transmitter contains an IFFT block and the receiver contains an FFT block. FFT and IFFT are a linear transform pair, defined by the following equations. Orthogonal Frequency Division Multiplex (OFDM) Multi-Carrier Modulation Technique   OFDM sub-carriers have a sinc (sin(x)/x) frequency response resulting in overlapin the frequency domain. This overlap does not cause interference due to the orthogonality of the sub-carriers.   The OFDM receiver uses a time and frequency synchronized FFT to convert the OFDM time waveform back into the frequency domain. In this process the FFT picks up discrete frequency samples, corresponding to the peaks of the carriers. At these frequencies, all other carriers...

IFFTs and FFTs in OFDM The Transmitter contains an IFFT block and the receiver contains an FFT block. FFT and IFFT are a linear transform pair, defined by the following equations.

OFDM Transceiver Block Diagram of OFDM Transmitter & OFDM Receiver

OFDM Basic Principle OFDM is a multi-carrier modulation scheme that transmits data over a number of orthogonal sub-carriers. Conventional transmission uses only a single carrier. OFDM breaks the data to be sent in to multiple data streams. Each data stream is passed to a sub-carrier for modulation. The data streams are sent in parallel on the orthogonal sub-carriers. OFDM Advantages NLOS performance while maintaining a high level of spectral efficiency and maximizing the available spectrum. Simple equalizer design. Supports operation in multi-path propagation environments. Uses a cyclic prefix to provide multi-path immunity and tolerance for time synchronization errors. Scalable bandwidths provide flexibility and potentially reduces capital expense.

WiMAX Network Architecture developed by the WiMAX Forum All IP network Existing IP standards used to avoid creating new network entities WiMAX Forum defines procedures that permit WiMAX to 3GPP and WiMAX to 3GPP2 Access Service Network (ASN) Provides the radio interface that connects the SS with the network Handles the radio interface and contains the base stations Contains the ASN Gateway which has a one-to-many relationship with base stations ASN Gateway handles mobility between base stations Foreign Agent function acts as proxy for authentication and mobile IP Connectivity Service Network (CSN) Provides connectivity between the ASN and the Internet or Application Services Home Agent and AAA provide Authentication Home Agent and DHCP provide IP Address Management AAA provides billing records Home Agent supports mobility Logical Interfaces 802.16 Interfaces R1 interface – SS to BS connection, radio link WiMAX Forum Interfaces - R2 interface – SS to HA, supports roaming - R3 interfa...