Wassim

Introduction The first thing to know about IP is that it is unreliable. It is fast and simple to build and maintain. It provides no guarantee. So packets can be dropped when necessary and can be corrupted. Idea behind IPv4 It is said that IP provides best effort and out-of-order delivery of datagrams. It is a connectionless protocol because there is no prior connection to communicate and IP does not retain the state of the communication. Figure 1: The thin waist IP is also called the “ thin waist ” because it is a requirement for communication on the internet. However, the upper layers and bottom layers provide a variety of choices. To make a routing decision, routers need to learn the IP DA field of the datagram header. Datagrams are routed hop by hop. Network engineers designed IP as a simple protocol because they believed it will allow the network to run fast on routers scattered worldwide. IPv4 service model IP tries to limit packets stuck in a loop, with the TTL field provides a ...

The most famous communication model on the Internet is the bidirectional byte stream model. Some of the applications that use bidirectional byte stream model are: HTTP, Bittorrent and Skype. We explore the three of them in this blog post. Local applications vs networked applications We must distinguish between networked applications vs local applications. Local applications manipulate data on the local computers. Networked applications manipulate data that we can share across an IP network. Describing the Byte Stream model The following points describe the byte stream model: Two nodes A and B want to communicate with each other. First a connection is established. Then, if A wants to communicate with B, it writes date to the connection. B reads data from the connection. A or B can tear down the connection. For example, “connection reset by peer” in HTTP means that the web server closed the connection. Let’s review three famous applications that use the bidirectional byte stream commun...

Firefox is a popular browser used by more than 11% of the Internet users around the world according to Wikipedia . I still use it for regular Internet surfing. A nice Firefox feature I like is window tabbing. However, a while ago I noticed that, each time I press “CTRL-T” to open a new tab, I get “www.google.com” in it. And that’s annoying because I often times copy a URL and quickly want to paste it in the new tab URL field. Restoring the default blank page on Firefox I tried to change the settings in the Options menu –> Options. But it seemed like Firefox did not take it into account. The solution I found was to play with Firefox variables: In the Firefox URL field, type about:config A warning message displays. Hit “ I’ll be careful, I promise ” In the Search field, type “ browser.newtab.url ” and hit Enter. You’ll see that the value field displays “www.google.com” double-click on the entry. In the Enter String Value , type “ about:blank ” and hit Enter. Now the browser.newtabl.ur...

You’ve taken beautiful photos in your vacation and you want to go straight to the photo where you have the Eiffel Tour behind you. But all your photos are named SAM_xxxx and you don’t know which one you must click on. What’s happening? It’s not a problem on your machine. It’s simply a Windows default behaviour. In fact, Windows 7, by default, does not display picture thumbnails. Instead, it displays icons. It’s not really a useful setting from Microsoft. But it can be corrected. Hopefully this little trick helps you display thumbnails of your photos and videos. Here’s how: Go to Start –> Control Panel, In Control Panel, go to System In System, go to Advanced System Settings Go to Performances and click on Parameters Under Visual Effects tab, search for Show thumbnails instead of icons and check the box Click on Apply Once you have done that, all your pictures will be visible in thumbnails.    

Here I sampled a list of useful commands that you will encounter at least once, in your ilfe as a network engineer: cd /tmp    : go to the /tmp folder Commands related to storage and disks df -h    : check available disk space Commands related to network ethtool -s eth0 speed 1000 autoneg off   : changes the speed and the autonegotiation mode of the Ethernet0 interface. ifconfig eth0 192.168.1.252 netmask 255.255.255.0 up  sets the IP address of a NIC card Eth0 and brings it up. ip route add default via 192.168.1.1 dev Eth0  sets the default gateway of 192.168.1.1 to interface Eth0. ip route add 172.16.1.0/28 via 172.16.2.55 dev eth0   : adds a static route to network 172.16.1.0/28, using gateway 172.16.2.55, across the Ethernet0 interface.   ip route del 172.16.1.0/28 via 172.16.2.55 dev eth0   : deletes the static route to network 172.16.1.0/28, using gateway 172.16.2.55, across the Ethernet0 interface. Other commands ls -alh /bin/ls    : displays permissions on a file. ...

A converged network is a network that transports not only data but also voice and video. Unlike data which is generally delivered in a best effort fashion, voice and video traffic need special care. When data, voice and video share the same network, they are sharing the media bandwidth. This situation may lead to a lack of bandwidth, whose impact on regular data applications is not as hard as it is on voice and video applications. In fact, we can tolerate some delay in email delivery or a server response. But, to hear a choppy sound or a video conference where sound and picture are asynchronous is not appreciated. Talking about bandwidth, we need to distinguish maximum bandwidth and available bandwidth . Maximum bandwidth, on a network path, is equal to the bandwidth of the slowest link. Available bandwidth of a network path is equal to the maximum bandwidth divided by the number of flows. Why? because there are many flows that traverse the network links, and each flow needs its own b...

There are instances where you need to collect logs on the Cisco Unity Connection. For example, your appliance no longer lets you enter the GUI interface. So you raise a TAC ticket and the Cisco team asks you to collect some logs. You will have to do it on the CLI interface. There are two parts in the CLI log collection: You need to have an SFTP server. This server will receive the logs from the Cisco Unity Connection device. In fact, you will see, in the copy process, that you have to specify an IP address, which is the SFTP IP address. You need to know how to get a file on a Cisco Unity Connection device. Preparing the SFTP server You can download a free SFTP server from the web. I have a preference for Solarwinds products. So I recommend their free tool. Getting the logs from Cisco Unity Connection There is a simple command to get files on CLI, from a Cisco Unity Connection: file get {file}. For example, here is how we collect the logs that begin with “CiscoSyslog”: admin:...

Back in 2011 Cisco introduced MediaSense – the call recording solution for Cisco UC environment. Unfortunately, from the users’ perspective it only provides the basic “Search and Play” web-interface that is not as convenient as most MediaSense users require. Cisco MediaSense Search’n’Play Interface But, thanks to Aurus, an authorized Cisco Solution Partner, any company that deployed MediaSense can now get the free user interface on top of it . How does it work and what is actually free? Aurus flagship product is PhoneUP – a bundle of applications designed for Cisco Unified Communications Manager. The “Record” module of PhoneUP is a complete recording solution for CUCM that supports SPAN-recording (port mirroring), BiB-recording (using the conference bridge embedded in Cisco IP-phone) and integrated with Cisco MediaSense to obtain the records. So, what you can get for free is the PhoneUP promo-license that only allows 3 devices to be recorded w...

Call forwarding is one of the features of the call coverage in Cisco CUCM. Call Hunting is when CUCM distributes a call on more than one Directory Number (DN), whether consecutively or simultaneously, depending on the algorithm. Hunt Pilot A Hunt Pilot is the entry point for the whole call hunting process. It is hit by a Call. The Hunt Pilot number is a dialable entity and has many similarities with Route Patterns : We can configure Route Filters with Hunt Pilots, Hunt Pilots can Provide Outside Dial Tone , We can set Hunt Pilots with the Urgent Priority flag, They can route or block calls, They can apply Calling and Called Party Transformations. Hunt Lists After hitting the Hunt Pilot, the call is presented by CUCM to the Hunt List. Each Hunt List contains one or more ordered Line Groups. A Hunt List can be pointed by one or more Hunt Pilots. Line Groups Each Line Group contains one or more member (we’ll refer to them as Hunt members, hunt parties or Line Group members). A Line Grou...

Here is a list of questions that Cisco CCNP Collaboration test takes may need answers for. Question: I have passed CVOICE exam,  does it count towards CCNP Collaboration? Answer: short answer: No Question: I have passed CIPT2 exam,  does it count towards CCNP Collaboration? Answer: short answer: No Question: I am CCNA Voice certified. I want to earn the CCNP Collaboration status. Do I need to be CCNA Collaboration certified? Answer: Yes. You need to have CCNA Collaboration in order to qualify for the CCNP Collaboration title. However, you can pass any CCNP Collaboration exam. Question: I have passed all CCNP Collaboration exams but I’m not CCNA Collaboration certified. Can I earn the CCNP Collaboration title? Answer: No. You need to earn the CCNA Collaboration certification first. Then, you will earn the CCNP Collaboration status. Question: I have CCNP Voice certification and I need to become CCNP Collaboration certified. What should I do? Answer: Pass the CIPTV2 exam Question: Other t...