Network&Communication(1&2).pdf

Computer Network & Communication(2) By Eng. Ghifar awadalla  Introduction Because TCP/IP is so central to working with the Internet and intranets, it’s essential for you to understand it in detail. I’ll begin by giving you some background on TCP/IP and how i...

Computer Network & Communication(2) By Eng. Ghifar awadalla  Introduction Because TCP/IP is so central to working with the Internet and intranets, it’s essential for you to understand it in detail. I’ll begin by giving you some background on TCP/IP and how it came about and then move on to describe the important technical goals defined by the original designers. After that, you’ll find out how TCP/IP compares to a theoretical model—the Open Systems Interconnection (OSI) model. Eng.Ghifar awadalla 2 IP Internet Protocol DOD =Department Of Defense model Eng.Ghifar awadalla 3 Eng.Ghifar awadalla 4  4-Application layer (Application , presentation , session layer) Eng.Ghifar awadalla 5 3-Host to Host layer (Transport layer) Eng.Ghifar awadalla 6  TCP Three-Way Handshake/Open Connection Host A Host B Send SYN 1 (seq = 100 ctl = SYN) SYN Received Send SYN, ACK 2 SYN Received (seq = 300 ack = 101 ctl = syn,ack) Established 3 (seq = 101 ack = 301 ctl = ack) 7  2-Internet Layer (Network layer ) Network layer protocol Routing protocols RIP , OSPF. EIGRP , IS-IS Routed protocols Logical address IP, Apple Talk , Internetwork packet exchange IPX Message and control protocol ICMP (Internet Control Message Protocol) , Error Message , Ping Tracert Address Resolution Protocol (ARP) Eng.Ghifar awadalla 8  1-Network Access Layer (physical , datalink layer ) Network Access layer protocol LAN protocols Ethernet , Token ring , ARC-NET WAN protocols HDLC , PPP , ISDN , Frame relay , ATM MAC Address Convert the binary data to signal to fit the network media Eng.Ghifar awadalla 9 Eng.Ghifar awadalla 11 Eng.Ghifar awadalla 12 Eng.Ghifar awadalla 13 1-Source port number :It consists of 2 bytes (16 bit), containing the port number for sender from the range 0 to 65535. 2-Destination port number 2 bytes (16 bit), containing the port number for Receiver from the range 0 to 65535. 3-Total Length : it is a field that shows the length of the segment (header + data) 4-Checksum : this filed make arithmetic operation at the sender and also when segment reaches to the receiver it performs the same arithmetic operation if the same result is obtained that mean the data is correct and there was no modification in it during transmission, but if we get a different number there is a modification to this data so the receiver deletes it and does not look at it. 1. Source port number :It consists of 2 bytes (16 bit), containing the port number for sender from the range 0 to 65535. 2. Destination port number: It consists of 2 bytes (16 bit), containing the port number for Receiver from the range 0 to 65535 3. Sequence number :is 30 bits long Its task numbering the data after dividing it into small part(called segment),The purpose of the numbering is to arrange and if the segment arrives unordered to the receiving device to facilitate its arrangement. 4. Acknowledgment number : confirms the number of segments received from the sender so that the sending device after receiving the confirmation will send the remaining segments. 5. DO : shows the header size (maybe starts from 20 bytes and can be up to 60 bytes) 6. RSV : the sixth field is meant to be reserved for developers for TCP to run tests or when an additional field is added in the future now is not used and its length is 4 bits. 7. Flags : is 8 bits in length, controlling the TCP connection and the type of data disconnection through a specific letter that symbolizes the state of data disconnection, for example, the letter U that it is necessary or a that it has arrived properly , R meaning a request to restore the connection after the interruption of the connection, f meaning to end sending the segments, 8. Window : the sender and receiver determine the number of segments that can be sent continuously without waiting for approval or the acknowledgment process. 9. Checksum : the sender puts a value inside this filed and creates a mathematical operation on this filed before sending , and after sending the receiving device performs the same operation on receiving segments. If you gets the same value, these segments will be approved. If it does not match, the modification has been made to the segments, it will be deleted and requested to be resent. 10.Urgent pointer is called the emergency indicator used in the event of segments was urgent, and it have the control bit symbol is the u meaning urgent. 11.Options : to put additional options, for example some large data, programs and applications You need to increase the head then we use this field 12.Data : original data (message) Preamble An alternating 1,0 pattern provides a clock (synchronization) at the start of each packet, which allows the receiving devices to lock the incoming bit stream. Start of Frame Delimiter (SOF)/Synch The preamble is seven octets, and the start of a frame (SOF) is one octet (synch). The SOF is 10101011, where the last pair of 1s allows the receiver to come into the alternating 1,0 pattern somewhere in the middle and still synch up and detect the beginning of the data. Destination Address (DA) This transmits a 48-bit value using the least significant bit (LSB) first. The DA is used by receiving stations to determine whether an incoming packet is addressed to a particular host and can be an individual address or a broadcast or multicast MAC address. Remember that a broadcast is all 1s (or Fs in hex) and is sent to all devices, but a multicast is sent only to a similar subset of hosts on a network. Source Address (SA) The SA is a 48-bit MAC address used to identify the transmitting device, and it uses the LSB first. Broadcast and multicast address formats are illegal within the SA field. Length or Type 802.3 uses a Length field, but the Ethernet frame uses a Type field to identify the total length of the frame—Internetwork Packet Exchange (IPX), for example. Data This is a packet sent down to the Data Link layer from the Network layer. The size can vary from 64 to 1,500 bytes. Frame Check Sequence (FCS) FCS is a field that is at the end of the frame and is used to store the CRC. Okay—let’s take a minute to look at some frames caught on our trusty network analyzer. You can see that the following frame has only three fields: Destination, Source, and Type. Eng.Ghifar awadalla 18 Eng.Ghifar awadalla 19 token ring network (MAU) is equivalent to a hub or switch on an Ethernet network. The MAU internally performs the token circulation. To create the complete ring, the ring in (RI) port on each MSAU is connected to the ring out (RO) port on another MSAU. The last MAU in the ring is then connected to the first to complete the ring ,pricey because you need several cables to connect each computer, it’s really hard to reconfigure, and as you’ve probably guessed, it’s not fault tolerant, to add to the network, you have no choice but to break the cable ring, which is likely to bring down the entire network! This is one big reason that ring topology isn’t very popular. The number of devices on token ring network is depend on the type of cable like(twistpair 260 devices..) but on 1 MAU have 33 devices 1-Token passing is a protocol responsible for transfer data between all devices over the network on one direction , any device in the network regenerate the weak signal and retransfer it even that token signal arrive to destination 2-Ring topology ARC-net is called IEEE 802.5 Is common between BUS and Token ring ,the cable use are UTP(Unshiled twisted pair) or fiber  1980 IEEE 802.3 Ethernet is a contention media-access method that : allows all hosts on a network to share the same bandwidth of a link. popular because it’s readily scalable, meaning that it’s comparatively easy to integrate new technologies, such as Fast Ethernet and Gigabit Ethernet, into an existing network infrastructure. It’s also relatively simple to implement in the first place, and with it, troubleshooting is reasonably straightforward. Ethernet uses both Data Link and Physical layer specifications The term collision domain is an Ethernet term that refers to a particular network scenario where in one device sends a packet out on a network segment and thereby forces every other device on that same physical network segment to pay attention to it. This is bad because if two devices on one physical segment transmit at the same time, a collision event—a situation where each device’s digital signals interfere with another on the wire—occurs and forces the devices to retransmit later. Collisions have a dramatically negative effect on network performance, so they’re definitely something we want to avoid! The situation I just described is typically found in a hub environment where each host segment connects to a hub that represents only one collision domain and one broadcast domain. This begs the question, What’s a broadcast domain? Ethernet networking uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD), a media access control method that helps devices share the bandwidth evenly without having two devices transmit at the same time on the network medium. CSMA/CD was created to overcome the problem of those collisions that occur when packets are transmitted from different hosts. And trust me—good collision management is crucial because when a host transmits in a CSMA/CD network, all the other hosts on the network receive and examine that transmission. Only bridges, switches, and routers, but not hubs, can effectively prevent a transmission from propagating throughout the entire network CARRIER SENSE MULTIPLE ACCESS COLLISION DETECTION CSMA/CD A star topology’s computers are connected to a central point with their own individual cables or wireless connections. You’ll often find that central spot inhabited by a device like a hub, a switch, or an access point. Star topology offers a lot of advantages over bus topology, making it more widely used even though it obviously requires more physical media. One of its best features is that because each computer or network segment is connected to the central device individually, if the cable fails, it only brings down the machine or network segment related to the point of failure. This makes the network much more fault tolerant as well as a lot easier to troubleshoot. Another great thing about a star topology is that it’s a lot more scalable—all you have to do if you want to add to it is run a new cable and connect to the machine at the core of the star