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Network chapter

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Fathy salah

on 15 February 2013

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Transcript of Network chapter

overview network Network models Network devices internetworking protocoles
transportation protocols encapsulation A network consists of two or more devices that are linked in order to provide a service Network types: LAN: local area network MAN:Metropolitan Area Networks wan:Wide Area Network Osi model TCP/IP model Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) The OSI model defines the communications process into 7 layers, which divides the tasks involved with moving information between networked computers into seven smaller 7) Application Layer : provide services like file transfer, electronic messaging e-mail, virtual terminal access and network management. 6) Presentation Layer : responsible for protocol conversion, date encryption/decryption, Expanding graphics command and the date compression. This layer makes the communications between two host possible. 5) Session Layer : responsible for establishing the process-to-process communication between the host in the network. establishing and ending the sessions across the network. The interactive login is an example of services provided by this layer in which the connective are re-connected in care of any interruption. 4) Transport Layer : responsible for end-to-end delivers of messages between the networked hosts. It first divides the streams of data into chunks or packets before transmission and then the receiving computer re-assembles the packets. It also guarantee error free data delivery without loss or duplications. 3) Network Layer : responsible for translating the logical network address and names into their physical address ( MAC address). addressing, determining routes for sending and managing network problems such as packet switching, data congestion and routines. 2) Data Link Layer : responsible for controlling the error between adjacent nodes and transfer the frames to other computer via physical layer. Data link layer is used by hubs and switches for their operation. 1) Physical Layer :responsible for transmitting row bit stream over the physical cable. The physical layer defines the hardware items such as cables, cards, voltages etc. The TCP/IP protocol suite is so named for two of its most important protocols:
Transmission Control Protocol (TCP) and Internet Protocol (IP). Application layer
The application layer is provided by the program that uses TCP/IP for communication. An application is a user process cooperating with another process usually on a different host (there is also a benefit to application communication within a single host). Examples of applications include Telnet and the File Transfer Protocol (FTP). The interface between the application and transport layers is defined by port numbers and sockets, Transport layer
The transport layer provides the end-to-end data transfer by delivering data from an application to its
remote peer. Multiple applications can be supported simultaneously. The most-used transport layer
protocol is the Transmission Control Protocol (TCP), which provides connection-oriented reliable data
delivery, duplicate data suppression, congestion control, and flow control.
Another transport layer protocol is the User Datagram Protocol ( “User Datagram Protocol (UDP)”
. It provides connectionless, unreliable, best-effort service. As a result, applications using UDP
as the transport protocol have to provide their own end-to-end integrity, flow control, and congestion
control, if desired. Usually, UDP is used by applications that need a fast transport mechanism and
can tolerate the loss of some data. Internetwork layer
The internetwork layer, also called the internet layer or the network layer, provides the “virtual network”
image of an internet (this layer shields the higher levels from the physical network architecture below
it). Internet Protocol (IP) is the most important protocol in this layer. It is a connectionless protocol
that does not assume reliability from lower layers. IP does not provide reliability, flow control, or error
recovery. These functions must be provided at a higher level.
IP provides a routing function that attempts to deliver transmitted messages to their . A message unit in an IP network is called an IP datagram. This is the basic unit of information transmitted across TCP/IP networks. Other internetwork-layer protocols are IP, ICMP, IGMP, ARP, and RARP. Network interface layer
The network interface layer, also called the link layer or the data-link layer, is the interface to the actual
network hardware. This interface may or may not provide reliable delivery, and may be packet or stream
oriented. In fact, TCP/IP does not specify any protocol here, but can use almost any network interface
available, which illustrates the flexibility of the IP layer. Examples are IEEE 802.2, X.25 (which is reliable in itself), ATM, FDDI, and even SNA.
TCP/IP specifications do not describe or standardize any network-layer protocols; they only standardize ways of accessing those protocols from the internetwork layer. bridge:
Interconnects LAN and forwards frames between them. A bridge performs the function of a MAC relay, and is independent of any higher layer protocol (including the logical link protocol).
A bridge is said to be transparent to IP. That is, when an IP host sends an IP datagram to another host on a network connected by a bridge, it sends the datagram directly to the host and the datagram “crosses” the bridge without the sending IP host being aware of it. Router:
Interconnects networks at the internetwork layer level and routes packets between them. The router must
understand the addressing structure associated with the networking protocols it supports and take decisions on whether, or how, to forward packets.
Routers are able to select the best transmission paths and optimal packet sizes.

A router is said to be visible to IP. That is, when a host sends an IP datagram to another host on a network connected by a router, it sends the datagram to the router so that it can forward it to the target host. Gateway
Interconnects networks at higher layers than bridges and routers. A gateway usually supports address mapping from one network to another, and might also provide transformation of the data between the environments to support end-to-end application connectivity. Gateways typically limit the interconnectivity of two networks to a subset of the application protocols supported on either one. For example, a VM host running TCP/IP can be used as an SMTP/RSCS mail gateway. Hubs
Hubs enable computers on a network to communicate. A hub can't identify the source or intended destination of the information it receives, so it sends the information to all of the computers connected to it, including the one that sent it. A hub can send or receive information, but it can't do both at the same time. This makes hubs slower than switches. Hubs are the least complex and the least expensive of these devices. Switches
Switches work the same way as hubs, but they can identify the intended destination of the information that they receive, so they send that information to only the computers that are supposed to receive it. Switches can send and receive information at the same time, so they can send information faster than hubs can. Switches cost a little more than hubs. Access points
Access points (also called base stations) provide wireless access to a wired Ethernet network. An access point plugs into a hub, switch, or wired router and sends out wireless signals. This enables computers and devices to connect to a wired network wirelessly.
Access points act a lot like cellular phone towers: you can move from one location to another and continue to have wireless access to a network. If you want to connect your computers wirelessly and you have a router that provides wireless capability, you don't need an access point. Access points don't have built-in technology for sharing Internet connections. To share an Internet connection, you must plug an access point into a router or a modem with a built-in router. _ Internet Protocol (IP)
_ Internet Control Message Protocol (ICMP)
_ Address Resolution Protocol (ARP)
_ Dynamic Host Configuration Protocol (DHCP) Encapsulation is a process to hide or protect a process from the possibility of outside interference or misuse of the system,
Encapsulation process varies in each layer, in the following process: Decapsulation process
Decapsulation is the inverse of the encapsulation process. Encapsulation is the process of wrapping the data while the decapsulation process is a process of opening packs. Internet Protocol (IP): IP addressing IP routing IP subnets Network Address Translation (NAT) Internet Control Message Protocol (ICMP) Address Resolution Protocol (ARP) Dynamic Host Configuration Protocol (DHCP) Ports and sockets sockets Ports The concept of ports and sockets provides a way to uniformly and uniquely identify connections and the programs and hosts that are engaged in them A port is a 16-bit number used by the host-to-host protocol to identify to which higher-level protocol or application program (process) it must deliver incoming messages There are two types of ports: •Well-known •Ephemeral Well-known ports belong to standard servers for example:
Telnet uses port 23
FTP server which uses two: 20 and 21 port numbers range between 1 and 1023 port numbers have values greater than 1023, normally in the range of 1024 to 65535 Each client process is allocated a port number, for as long as it needs. socket is a special type of file handle.
uses the same port principle to provide multiplexing. If two processes are communicating over TCP, they have a logical connection(port) that is uniquely identifiable by the two sockets User Datagram Protocol (UDP): Transmission Control Protocol (TCP) Real-Time Transport Protocol (RTP) ports & sockets
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
Real-Time Transport Protocol (RTP) for small data units transfer or those which can afford to lose a little amount of data (such as multimedia streaming) will include UDP.
Be aware that UDP and IP do not provide guaranteed delivery, flow-control, or error recovery, so these must be provided by the application .
.connectionless protocol (no feed back) TCP provides considerably more facilities for applications than UDP. Specifically this includes error recovery, flow control, and reliability.
applications using it:
Flow control
Stream data transfer

connection-oriented protocol. provides the transport of real-time data packets. To accommodate new real-time applications.

RTP is often implemented to support multicast applications. are represented by a 32-bit unsigned binary value. It is usually expressed in a dotted decimal format. For example, is a valid IP address.
consists of a pair of numbers
IP address = <network number><host number> Class-based IP addresses Class A addresses:These addresses use 7 bits for the <network> and 24 bits for the <host> Class B addresses :
These addresses use 14 bits for the <network> and 16 bits for the <host> portion of the IP address Class C addresses :
These addresses use 21 bits for the <network> and 8 bits for the <host> portion of the IP address. Class D addresses :
These addresses are reserved for multicasting (a sort of broadcasting, but in a limited area, and only to hosts using the same Class D address). Class E addresses :
These addresses are reserved for future or experimental use. Special use IP addresses:
All bits 0: When a host wants to communicate over a network, but does not yet know the network IP address

All bits 1:
This is called a directed broadcast

The Class A network is defined as the loopback network. Addresses from that network are assigned to interfaces that process data within the local system. These loopback interfaces do not access a physical network. Private IP addresses:
It reserves part of the global address space for use in networks that do not require connectivity to the Internet A single Class A network through 256 contiguous Class C networks
Any organization can use any address in these ranges. Due to the explosive growth of the Internet, the principle of assigned IP addresses became too inflexible .

To avoid having to request additional IP network addresses, the concept of IP subnetting was introduced.
The IP address is interpreted as:
<network number><subnet number><host number>

Any bits in the local portion can be used to form the subnet. The division is done using a 32-bit subnet mask.
Like IP addresses, subnet masks are usually written in dotted decimal form. This provides the basic mechanism for routers to interconnect different physical networks.
The router only has information about four kinds of destinations:
_ Hosts that are directly attached to one of the physical networks to which the router is attached.
_ Hosts or networks for which the router has been given explicit definitions.
_ Hosts or networks for which the router has received an ICMP redirect message.
_ A default for all other destinations. NAT is also known as IP masquerading. It provides a mapping between internal IP addresses and
officially assigned external addresses. Originally, NAT was suggested as a short-term solution to the IP address

exhaustion problem When a router or a destination host must inform the source host about errors in datagram processing, it uses the Internet Control Message Protocol (ICMP).

ICMP can be characterized as follows:
ICMP is used to report errors, not to make IP reliable.
ICMP cannot be used to report errors with ICMP messages. This avoids infinite repetitions. ICMP responses are sent in response to ICMP query messages
•ICMP messages are never sent in response to datagrams with a broadcast or a multicast destination address. ICMP applications :
Ping is the simplest of all TCP/IP applications. It sends IP datagrams to a specified destination host and measures the round trip time to receive a response. The word ping is an abbreviation for Packet InterNet Groper.
The Traceroute program is used to determine the route IP datagrams follow through the network.Traceroute is based on ICMP and UDP is responsible for converting the higher-level protocol addresses (IP addresses) to physical network addresses.

It uses a lookup table (sometimes referred to as the ARP cache) to perform this translation.
When the address is not found in the ARP cache, a broadcast is sent out in the network with a special format called the ARP request. If one of the machines in the network recognizes its own IP address in the request, it will send an ARP reply back to the requesting host. provides a framework for passing configuration information to hosts on a TCP/IP network.
DHCP supports three mechanisms for IP address allocation:
•Automatic allocation: DHCP assigns a permanent IP address to the host.
•Dynamic allocation: DHCP assigns an IP address for a limited period of time. Such a network address is called a lease. This is the only mechanism that allows automatic reuse of adresses that are no longer needed by the host to which it was assigned.
•Manual allocation: The host's address is assigned by a network administrator. 1-network overview
2-network models
3-network devices
4-internetworking protocoles
5-network transportation protocols
6-Encapsulation bridge
switch router gateway switches THANK YOU
Fathy El sharkawy. El sherouck academy
communication & electronic department IP TV
New vision
DR/Salah El Agooz Network topology:
Physical – actual layout of the computer cables and other network devices
Logical – the way in which the network appears to the devices that use it
Common topologies:
– Bus, ring, star, mesh and wireless

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