To assist
you in quickly comparing the layers of the OSI Reference Model, and
understanding where they are different and how they relate to each other,
I have created the summary chart shown in table below.. It shows each
layer's name and number, describes its key responsibilities, talks about
what type of data is generally handled at each layer, and also what
the scope of each layer is in approximate terms. I also show some of
the more common protocols that are associated with each layer.
I will say here that “standard
disclaimers apply”. I don't want to repeat all of the caveats I mentioned
elsewhere in discussions of the OSI model, but know that they apply
here as well. Namely: the layers aren't always hard-fast, I haven't
listed every single protocol here, some may really fit into more than
one layer, and so on. In particular, note that many of the technologies
listed as being in the data link layer are there because that is the
layer where their primary functionality resides. In reality, most of
these technologies include components in other layers, especially the
physical layer.
OSI Reference Model Layer Summary
Group |
# |
Layer Name |
Key Responsibilities |
Data Type
Handled |
Scope |
Common
Protocols and Technologies |
Lower
Layers |
1 |
Physical |
Encoding
and Signaling; Physical Data Transmission; Hardware Specifications;
Topology and Design |
Bits |
Electrical
or light signals sent between local devices |
(Physical
layers of most of the technologies listed for the data link
layer) |
2 |
Data
Link |
Logical
Link Control; Media Access Control; Data Framing; Addressing;
Error Detection and Handling; Defining Requirements of Physical
Layer |
Frames |
Low-level
data messages between local devices |
IEEE
802.2 LLC, Ethernet Family; Token Ring; FDDI and CDDI; IEEE
802.11 (WLAN, Wi-Fi); HomePNA; HomeRF; ATM; SLIP and PPP |
3 |
Network |
Logical
Addressing; Routing; Datagram Encapsulation; Fragmentation and
Reassembly; Error Handling and Diagnostics |
Datagrams
/ Packets |
Messages
between local or remote devices |
IP;
IPv6; IP NAT; IPsec; Mobile IP; ICMP; IPX; DLC; PLP; Routing
protocols such as RIP and BGP |
4 |
Transport |
Process-Level
Addressing; Multiplexing/Demultiplexing; Connections; Segmentation
and Reassembly;
Acknowledgments and Retransmissions;
Flow Control |
Datarams
/ Segments |
Communication
between software processes |
TCP
and UDP; SPX; NetBEUI/NBF |
Upper
Layers |
5 |
Session |
Session
Establishment, Management and Termination |
Sessions |
Sessions
between local or remote devices |
NetBIOS,
Sockets, Named Pipes, RPC |
6 |
Presentation |
Data
Translation; Compression and Encryption |
Encoded
User Data |
Application
data representations |
SSL;
Shells and Redirectors; MIME |
7 |
Application |
User
Application Services |
User
Data |
Application
data |
DNS;
NFS; BOOTP; DHCP; SNMP; RMON; FTP; TFTP; SMTP; POP3; IMAP; NNTP;
HTTP; Telnet |
|
|