Data Communications Exam 1
The Physical Layer - ANS-The Physical Layer is the layer that interacts with the real world. It
specifies how to transmit bits across different kinds of medium as electrical (or other analog)
signals.
PDU: Signal/Bit
Ex. 100BASE-T, 802.11n
The Data Link Layer - ANS-The Data Link Layer is used to deliver data across some physical
network, typically a local area network. It is also responsible for error checking transmissions. A
common medium for the data link layer is Ethernet. It is not really a layer at all, in the normal
sense of the term, but rather an interface between hosts and transmission links.
PDU: Frame
Ex. Ethernet
The Network Layer - ANS-The Network Layer holds the entire architecture together by providing
routing and addressing for packets. Its job is to permit hosts to inject packets into the network
and have them travel independently to the destination, which could be on a different network.
The network layer defines an official packet format and protocol called IP (Internet Protocol),
and each host computer should have a different IP address. Essentially, the job of the network
layer is to deliver IP packets where they are supposed to go.
PDU: Packet/Datagram
Ex. IP, ICMP
The Transport Layer - ANS-The Transport Layer is designed to allow peer entities on the source
and destination hosts to carry on a conversation. Two end-to-end transport protocols are
defined here: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP is
a reliable connection-oriented protocol that allows a byte stream originating from one machine
to be delivered to any other machine on the internet without error. It segments the byte stream
into discrete messages and passes them to the network layer. The receiving TCP process
reassembles the messages into the output stream. UDP, on the other hand, is an unreliable
connectionless protocol for applications that want to provide their own sequencing or flow
control instead of using TCP's.
PDU: Segment
Ex. TCP, UDP
, The Application Layer - ANS-The Application Layer provides services to the application software
running on a computer and contains all the higher-level protocols. It does not define the
application itself, but it defines services that applications need. Some of the early protocols
included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP), but many
other protocols have been added to these over the years.
PDU: Message/Packet/Data
Ex. HTTP, SMTP, DNS, FTP, DHCP, IMAP, POP, SSL
Interface - ANS-Area between each pair of adjacent layers which defines the primitive
operations and services the lower layer makes available to the upper one
Connection Oriented Service - ANS-A service that required a connection setup (handshaking)
phase prior to data exchange
Ex. Telephone
Connection-less Service - ANS-A service that doesn't require a connection setup phase prior to
data exchange.
Ex. P.O. Box
Protocol (Other) - ANS-A set of rules both the sender and receiver comply to achieve successful
communication.
Network Service - ANS-A set of primitives (operations) that a layer provides to the layer above
it.
- The service defines what operations the layer is prepared to perform on behalf of its users, but
it says nothing at all about how these operations are implemented
- A service relates to an interface between two layers, with the lower layer being the service
provider and the upper layer being the service user.
Networking application - ANS-An implementation of a protocol
PDU Layers - ANS-Application Layer: Message/Packet/Data
Transport Layer: Segment
Network Layer: Datagram/Packet
Data Link Layer: Frame
Physical Layer: Signal/bit
DNS - ANS-Domain Name System
Converting a domain name to an IP address
UDP (Connection-less Service)
The Physical Layer - ANS-The Physical Layer is the layer that interacts with the real world. It
specifies how to transmit bits across different kinds of medium as electrical (or other analog)
signals.
PDU: Signal/Bit
Ex. 100BASE-T, 802.11n
The Data Link Layer - ANS-The Data Link Layer is used to deliver data across some physical
network, typically a local area network. It is also responsible for error checking transmissions. A
common medium for the data link layer is Ethernet. It is not really a layer at all, in the normal
sense of the term, but rather an interface between hosts and transmission links.
PDU: Frame
Ex. Ethernet
The Network Layer - ANS-The Network Layer holds the entire architecture together by providing
routing and addressing for packets. Its job is to permit hosts to inject packets into the network
and have them travel independently to the destination, which could be on a different network.
The network layer defines an official packet format and protocol called IP (Internet Protocol),
and each host computer should have a different IP address. Essentially, the job of the network
layer is to deliver IP packets where they are supposed to go.
PDU: Packet/Datagram
Ex. IP, ICMP
The Transport Layer - ANS-The Transport Layer is designed to allow peer entities on the source
and destination hosts to carry on a conversation. Two end-to-end transport protocols are
defined here: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP is
a reliable connection-oriented protocol that allows a byte stream originating from one machine
to be delivered to any other machine on the internet without error. It segments the byte stream
into discrete messages and passes them to the network layer. The receiving TCP process
reassembles the messages into the output stream. UDP, on the other hand, is an unreliable
connectionless protocol for applications that want to provide their own sequencing or flow
control instead of using TCP's.
PDU: Segment
Ex. TCP, UDP
, The Application Layer - ANS-The Application Layer provides services to the application software
running on a computer and contains all the higher-level protocols. It does not define the
application itself, but it defines services that applications need. Some of the early protocols
included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP), but many
other protocols have been added to these over the years.
PDU: Message/Packet/Data
Ex. HTTP, SMTP, DNS, FTP, DHCP, IMAP, POP, SSL
Interface - ANS-Area between each pair of adjacent layers which defines the primitive
operations and services the lower layer makes available to the upper one
Connection Oriented Service - ANS-A service that required a connection setup (handshaking)
phase prior to data exchange
Ex. Telephone
Connection-less Service - ANS-A service that doesn't require a connection setup phase prior to
data exchange.
Ex. P.O. Box
Protocol (Other) - ANS-A set of rules both the sender and receiver comply to achieve successful
communication.
Network Service - ANS-A set of primitives (operations) that a layer provides to the layer above
it.
- The service defines what operations the layer is prepared to perform on behalf of its users, but
it says nothing at all about how these operations are implemented
- A service relates to an interface between two layers, with the lower layer being the service
provider and the upper layer being the service user.
Networking application - ANS-An implementation of a protocol
PDU Layers - ANS-Application Layer: Message/Packet/Data
Transport Layer: Segment
Network Layer: Datagram/Packet
Data Link Layer: Frame
Physical Layer: Signal/bit
DNS - ANS-Domain Name System
Converting a domain name to an IP address
UDP (Connection-less Service)
