Lecture Slides

dingdongboomNetworking and Communications

Oct 27, 2013 (3 years and 10 months ago)

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Computer Networks

Kai
Qian


Network Layer


Transport Layer


Application Layer



The OSI Model

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

Network Layer


The

Network Layer

is Layer 3 of the seven
-
layer

OSI model

of

computer networking.


The Network Layer is responsible for routing
packets delivery

including

routing

through
intermediate routers, whereas the

Data Link
Layer

is responsible for Media Access Control,
Flow Control and Error Checking.

Network Layer


The Network Layer provides the functional
and procedural means of transferring variable
length

data sequences from a source to a
destination host via one or more networks
while maintaining the

quality of
service

functions.

Functions of the Network Layer


Connection
model:

connectionless

communication


For example,

IP

is connectionless, in that a
frame can travel from a sender to a recipient
without the recipient having to send an
acknowledgement. Connection
-
oriented
protocols exist at other higher layers of that
model.

Functions of the Network Layer


Host addressing


Every host in the network needs to have a unique
address which determines where it is. This
address will normally be assigned from a
hierarchical system, so you can be "Fred Murphy"
to people in your house, "Fred Murphy, Main
Street 1" to Dubliners, or "Fred Murphy, Main
Street 1, Dublin" to people in Ireland, or "Fred
Murphy, Main Street 1, Dublin, Ireland" to people
anywhere in the world. On the Internet,
addresses are known as Internet Protocol (IP)
addresses.

Functions of the Network Layer


Message forwarding


Since many networks are partitioned into sub
networks and connect to other networks for
wide
-
area communications, networks use
specialized hosts, called gateways or

routers

to
forward packets between networks. This is also of
interest to mobile applications, where a user may
move from one location to another, and it must
be arranged that his messages follow him.
Version 4 of the

Internet Protocol

(IPv4) was not
designed with this feature in mind, although
mobility extensions exist.

IPv6

has a better
designed solution.

Network Layer


Within the service layering semantics of the
OSI network architecture the Network Layer
responds to service requests from
the

Transport Layer

and issues service
requests to the

Data Link Layer.

Network Layer: Protocols


IPv4/IPv6,

Internet Protocol


DVMRP,

Distance Vector Multicast Routing Protocol


ICMP,

Internet Control Message Protocol


IGMP,

Internet Group Multicast Protocol


PIM
-
SM,

Protocol Independent Multicast Sparse Mode


PIM
-
DM,

Protocol Independent Multicast Dense Mode


IPsec
,

Internet Protocol Security


IPX,

Internetwork Packet Exchange


RIP,

Routing Information Protocol


DDP,

Datagram Delivery Protocol


BGP,

Border Gateway Protocol


Relation to TCP/IP
model


The TCP/IP model describes the

protocol suite

of
the

Internet

(RFC 1122). This model has a layer
called the

Internet Layer, located above the

Link
Layer. In many text books and other secondary
references the Internet Layer is often equated
with OSI's Network Layer. However, this is
misleading as the allowed characteristics of
protocols (e.g., whether they are connection
-
oriented or connection
-
less) placed into these
layer are different in the two models. The
Internet Layer of TCP/IP is in fact only a subset of
functionality of the Network Layer. It only
describes one type of network architecture, the
Internet.

Transport Layer


In

computer networking, the

Transport Layer
provides end
-
to
-
end communication services
for applications[1]

within a layered
architecture of network components and
protocols. The transport layer provides
convenient services such as

connection
-
oriented

data stream

support,

reliability,

flow
control, and

multiplexing.

Introduction


To eliminate the diversity and unreliability of
the network layer, we introduced the concept
of transport layer.


The transport layer provides reliable,
inexpensive information transferring service
from source host to destination host.


Transport Layer


Transport layers are contained in both the

TCP/IP
model

(RFC 1122),[2]

which is the foundation of
the Internet, and the

Open Systems
Interconnection

(OSI) model

of general
networking. The definitions of the Transport
Layer are slightly different in these two models.
This article primarily refers to the TCP/IP model,
in which TCP is largely for a
convenient

application programming interface

to
internet hosts, as opposed to the

OSI model
definition of the Transport Layer.

Transport Layer


The most well
-
known transport protocol is
the

Transmission Control Protocol

(TCP). It lent its
name to the title of the entire

Internet Protocol
Suite,

TCP/IP. It is used for connection
-
oriented
transmissions, whereas the connectionless

User
Datagram Protocol

(UDP) is used for simpler
messaging transmissions. TCP is the more
complex protocol, due to its
stateful

design
incorporating reliable transmission and data
stream services. Other prominent protocols in
this group are the

Datagram Congestion Control
Protocol

(DCCP) and the

Stream Control
Transmission Protocol(SCTP).

Transport Layer: Services


There are many services that can be optionally
provided by a Transport Layer protocol, and
different protocols may or may not implement
them
.


Transport Layer: Services


Connection
-
oriented communication


Byte orientation


Same order delivery


Reliability


Flow
control


Congestion
avoidance


Multiplexing


Transport Layer


The Transport Layer is responsible for delivering
data to the appropriate application process on
the host computers. This involves

statistical
multiplexing

of data from different application
processes, i.e. forming data packets, and adding
source and destination port numbers in the
header of each Transport Layer data packet.
Together with the source and destination IP
address, the port numbers constitutes a

network
socket, i.e. an identification address of the
process
-
to
-
process communication. In the OSI
model, this function is supported by the

Session
Layer.

Transport Layer


Some Transport Layer protocols, for example
TCP, but not UDP, support

virtual circuits, i.e.
provide

connection oriented

communication
over an underlying packet
oriented

datagram

network. A byte
-
stream is
delivered while hiding the packet mode
communication for the application processes.
This involves connection establishment,
dividing of the data stream into packets called
segments, segment numbering and reordering
of out
-
of order data.

Transport Layer


Finally, some Transport Layer protocols, for
example TCP, but not UDP, provide end
-
to
-
end
reliable communication, i.e.

error recovery

by
means of

error detecting code

and

automatic
repeat request

(ARQ) protocol. The ARQ
protocol also provides

flow control, which may
be combined with

congestion avoidance.

Transport Layer: UDP


UDP is a very simple protocol, and does not
provide virtual circuits, nor reliable
communication, delegating these functions to
the

application

program. UDP packets are
called

datagram, rather than segments.

Transport Layer: TCP


TCP is used for many protocols,
including

HTTP

web browsing and email
transfer. UDP may be used
for

multicasting

and

broadcasting, since
retransmissions are not possible to a large
amount of hosts. UDP typically gives
higher

throughput

and shorter latency, and is
therefore often used for real
-
time multimedia
communication where packet loss occasionally
can be accepted, for example IP
-
TV and IP
-
telephony, and for online computer games.

Transport Layer: Protocols


The exact definition of what qualifies as a transport layer protocol is not
firm. The following is a short list:


ATP,

AppleTalk Transaction Protocol


CUDP,

Cyclic UDP


DCCP,

Datagram Congestion Control Protocol


FCP,

Fiber Channel Protocol


IL,

IL Protocol


NBF,

NetBIOS Frames protocol


RDP,

Reliable Datagram Protocol


SCTP,

Stream Control Transmission Protocol


SPX,

Sequenced Packet Exchange


SST,

Structured Stream Transport


TCP,

Transmission Control Protocol


UDP,

User Datagram Protocol


UDP
Lite


µTP,

Micro Transport Protocol

Application Layer


The

Internet Protocol Suite

(TCP/IP) and the

Open
Systems Interconnection

model (OSI model)
of

computer networking

each specify a group of
protocols and methods identified by the name
Application Layer.


In TCP/IP, the Application Layer contains all protocols
and methods that fall into the realm of process
-
to
-
process communications across an Internet Protocol (IP)
network. Application Layer methods use the
underlying

Transport Layer

protocols to establish host
-
to
-
host connections.


Application Layer


In the OSI model, the definition of its
Application Layer is narrower in scope,
explicitly distinguishing additional
functionality above the Transport Layer at two
additional levels, the

Session Layer

and the
Presentation Layer. OSI specifies strict
modular separation of functionality at these
layers and provides

protocol
implementations

for each layer.


Application Layer:
TCP/IP
protocols


Remote Login category


Telnet


File Transfer category


FTP


TFTP


Electronic Mail category


SMTP


IMAP


POP


Support Services category


DNS


RARP


BOOTP


SNMP


CMOT


Application Layer: TCP/IP


The

Internet Protocol Suite

is the set
of

communications protocols

used for the

Internet

and
other similar networks. It is commonly also known
as

TCP/IP named from two of the most important
protocols in it: the

Transmission Control Protocol

(TCP)
and the

Internet Protocol

(IP), which were the first two
networking protocols defined in this standard. Modern
IP networking represents a synthesis of several
developments that began to evolve in the 1960s and
1970s, namely the

Internet

and

local area networks,
which emerged during the 1980s, together with the
advent of the

World Wide Web

in the early 1990s.

Computer Networks


Ends

Reference from Wikipedia.org