Topic 4 4.1 Anatomy of Data Frame (Ethernet Frames)

4.2 The Open Systems Interconnection Reference Model (OSI)4.3 Transmission Control Protocol/Internet Protocol TCP/IP Suite4.4 Internet Address4.5 Network Services

 

4.1 Anatomy of Data Frame (Ethernet Frames)

Ethernet frame. Frames are the format of data packets on the wire. There are several types of Ethernet frame: Original Ethernet Version I (no longer used) The Ethernet Version 2 or Ethernet II frame, the so-

called DIX frame (named after DEC, Intel, and Xerox), this is the most common today, as it is often used directly by the Internet Protocol.

Novell's homegrown Variation of IEEE 802.3 ("raw 802.3 frame") without LLC

IEEE 802.2 LLC frame IEEE 802.2 LLC/SNAP frame

4 sections in Ethernet Frames

Frame Header SectionIn a data packet sent through the internet, the data (payload) are preceded by header information such as the sender's and the recipient's IP addresses, the protocol governing the format of the payload and several other formats. The header's format is specified in the Internet Protocol.

Frame check sequence (FCS)A frame check sequence (FCS) refers to the extra checksum characters added to a Frame in a communication protocol for error detection and correction.

4 sections in Ethernet Frames

Basic ethernet frame forms.

Address Resolution Protocol (ARP)

Address Resolution Protocol (ARP) can determine the IP address associated with that name. ARP maintains tables of address resolution data and can broadcast packets to discover addresses on the internetwork. The IP addresses discovered by ARP can be provided to Data Link layer protocols.

4.3 Transmission Control Protocol/Internet Protocol TCP/IP Suite

The Internet protocol suite The Internet protocol suite is the set of communications protocols that implement the protocol stack on which the Internet runs. It is sometimes called the TCP/IP protocol suite, after the two most important protocols in it: the Transmission Control Protocol (TCP) and the Internet Protocol (IP), which were also the first two defined.

The internet protocol suite can be described by analogy with the OSI model, which describes the layers of a protocol stack, not all of which correspond well with internet practice. In a protocol stack, each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the higher layers. Higher layers are logically closer to the user and deal with more abstract data, relying on lower layers to translate data into forms that can eventually be physically manipulated.

The internet model was produced as the solution to a practical engineering problem. The OSI model, on the other hand, was a more theoretical approach, and was also produced at an earlier stage in the evolution of networks. Therefore, the OSI model is easier to understand, but the TCP/IP model is the one in actual use. It is helpful to have an understanding of the OSI model before learning TCP/IP, as the same principles apply, but are easier to understand in the OSI model.Insert contents.

The Internet protocol suite

Internet protocol suite   Application layer - HTTP, HTTPS, SMTP, FTP,

UUCP, NNTP,SSH, IRC, SNMP, SIP, RTP, Telnet ,...

Transport layer- TCP, UDP, SCTP, DCCP, ... Network layer - IPv4, IPv6, ICMP, ARP, IGMP, ... Data link layer- Ethernet, Wi-Fi, Token ring, FDDI,

PPP, ... Physical layerRS-232, EIA-422, RS-449, EIA-485...

4.4 Internet AddressIP address

An IP address (Internet Protocol address) is a unique number, similar in concept to a telephone number, used by machines (usually computers) to refer to each other when sending information through the Internet. This allows machines passing the information onwards on behalf of the sender to know where to send it next, and for the machine receiving the information to know that it is the intended destination.

An example IP address is 207.142.131.236. Converting to such numbers from the more human-readable form of domain addresses, such as www.puo.edu.my, is done via the Domain Name System. The process of conversion is known as resolution of the domain name.

3 methods of assigning IP addresses

Manual - asigning using a specified IP address from the TCP/IP properties in the computer it self

Automatic- Set detect IP address by default if working in a local area networks.

Dynamic - IP address that been use for certain time on certain application such as chat program where a dynamic address will be provide every time login

Example of IP addressing

IP Address : 192.168.0.0 Subnet Mask : 255.255.255.0 Default Gateway : 192.168.0.1

IP address classes

4.5 Network Services

Network services are the foundation of a networked computing environment. Generally network services are installed on one or more servers. Common network services include:

authentication servers directory services DHCP DNS e-mail Printing Web hosting (Http servers)

The File Transfer Protocol (FTP)

The File Transfer Protocol (FTP) is a protocol for sharing files between networked hosts. FTP enables users to log on to remote hosts. Logged-on users can inspect directories, manipulate files, execute commands, and perform other commands on the host. FTP also has the capability of transferring files between dissimilar hosts by supporting a file request structure that is independent of specific operating systems.

Objectives and disadvantages

The objectives of FTP, as outlined by its RFC, are: To promote sharing of files (computer programs and/or data). To encourage indirect or implicit use of remote computers. To shield a user from variations in file storage systems among different hosts. To transfer data reliably and efficiently. Disadvantages are: Passwords and file contents are sent in clear text, which can be intercepted by

eavesdroppers. Multiple TCP/IP connections are used, one for the control connection, and one

for each download, upload, or directory listing. Firewall software needs additional logic to account for these connections.

It is hard to filter active mode FTP traffic on the client side by using a firewall, since the client must open an arbitrary port in order to receive the connection. This problem is largely resolved by using passive mode FTP.

It is possible to abuse the protocol's built-in proxy features to tell a server to send data to an arbitrary port of a third computer.

Dynamic Host Configuration Protocol (DHCP)

Dynamic Host Configuration Protocol (DHCP) is a client-server networking protocol. Most organizations use DHCP. A DHCP server provides configuration parameters specific to the DHCP client host requesting, generally, information required by the host to participate on the Internet network. DHCP also provides a mechanism for allocation of IP addresses to hosts.

3 methods of IP address allocation

Manual allocation, where the allocation is based on a table with MAC address - IP address pairs manually filled by the server admin. Only requesting clients with a MAC address listed in this table get the IP address according to the table.

Automatic allocation, where a free IP address of a range given by the admin is permanently assigned to a requesting client.

Dynamic allocation, the only method which provides dynamic reuse of IP addresses. A network administrator assigns a range of IP addresses to DHCP, and each client computer on the LAN has its TCP/IP software configured to request an IP address from the DHCP server when that client computer's network interface card starts up. The request-and-grant process uses a lease concept with a controllable time period. This eases the network installation procedure on the client computer side considerably.

Domain Name System or DNS

The Domain Name System or DNS is a system that stores information about hostnames and domain names in a kind of distributed database on networks, such as the Internet. Most importantly, it provides a physical location (IP address) for each hostname, and lists the mail exchange servers accepting e-mail for each domain.

HTTP (for HyperText Transfer Protocol)

HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. The original purpose was to provide a way to publish and receive HTML pages.

Post Office Protocol version 3 (POP3)

Post Office Protocol version 3 (POP3) is an application layer Internet standard protocol used to retrieve email from a remote server to a local client over a TCP/IP connection. Nearly all individual Internet service provider email accounts are accessed via POP3.

Network File System (NFS)

Network File System (NFS) is a protocol originally developed by Sun Microsystems in 1984 and defined in RFCs 1094, 1813, (3010) and 3530, as a file system which allows a computer to access files over a network as easily as if they were on its local disks.

User Datagram Protocol (UDP)

The User Datagram Protocol (UDP) is a connectionless Transport (host-to-host) layer protocol. UDP does not provide message acknowledgments; rather, it simply transports datagrams.