R&M Data Center Handbook

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Although the OSI model is recognized worldwide, TCP/IP represents the technically open standard on whose
base the Internet was developed. The TCP/IP reference model and the TCP/IP protocol stack enable the exchange
of data between any two computers located anywhere in the world.
The TCP/IP model is historically just as significant as those standards which are the basis for successful developments
in the telephone, electrical engineering, rail transportation, television and video industries.
No general agreement exists on how TCP/IP should be described in a layer model. While the OSI model has an
academic character, the TCP/IP model is closer to programmer reality and leans to the structure of existing protocols.
However, both models – OSI as well as TCP/IP – have one thing in common: Data are passed down in the stack
during transmission. When receiving data from the network, the path through the stack again leads to the top.
A comparison of both models appears below.
OSI layers TCP/IP layers Protocol examples Coupling elements
7
Application
6 Presentation
5 Session
4 Application
HTTP, FTP, SMTP,
POP, DNS, DHCP,
Telnet
4 Transport 3 Computer TCP, UDP
TCP/IP-protocol-stack
Gateway, Content
Switch, Layer 4 to 7
Switch
3 Network 2 Internet IP, ICMP, IGMP Router, Layer 3 Switch
2 Data Link
1
Bit transfer
(physical)
1 Network access
Ethernet, Token Ring,
Token Bus, FDDI
Bridge, switch
Cabling, repeater, hub,
media converter
The best known use of protocols takes place around the Internet, where they take care of:
• Loading websites – (HTTP or HTTPS)
• Sending and receiving e-mails – (SMTP & POP3/IMAP)
• File uploads and downloads – (FTP, HTTP or HTTPS)
3.8.2. Ethernet IEEE 802.3
The IEEE (Institute of Electrical and Electronics Engineers) is a professional organization that has been active
worldwide since 1884 and currently has more than 380,000 members from over 150 countries (2007). This largest
technical organization with headquarters in New York is divided up into numerous so-called societies that concentrate
in the special fields of electrical and information technology. Project work is concentrated into approximately
300 country-based groups. Through publications like its journal IEEE Spectrum, the organization also contributes
to providing interdisciplinary information on and discussion of the social consequences of new technologies.
IEEE 802 is an IEEE project which started in February 1980, therefore the designation 802. This project concerns
itself with standards in the area of local networks (LAN) and establishes network standards for layers 1 and 2 of
the OSI model. However, IEEE 802 teams also give tips for sensibly integrating systems into one overall view
(network management, internetworking, ISO interaction).
Different teams were formed within the 802 project, and also deal with new project aspects as needed. The oldest
study group is the CSMA/CD group IEEE 802.3 for Ethernet. CSMA/CD is a description of the original access
method (Carrier Sense Multiple Access with Collision Detection). The central topic for this study group is the
discussion of high-speed protocols. The group is divided up into various other groups which concentrate their
effects on optical fibers in the backbone, InterRepeater links, layer management, and other topics.
Page 98 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0