week2 lec2-bscs1
DESCRIPTION
Computer NetworksTRANSCRIPT
Chapter 1:Introduction Computer
Networking: A Top Down Approach ,
4th edition. Jim Kurose, Keith Ross
Computer Networks
Today’s Lecture
Layered Architecture Brief description of Five Layers
Internet Protocol Stack
To provide structure to design of network protocols, network designers organize protocols in layers
Service – says what a layer doesProtocol – says how the service is
implementedAdvantages DrawbacksWhen taken together the protocols
of various layers are called the Protocol Stack.
Internet Protocol Stack consists of Five layers
Physical, Link, Network, Transport and Application layers .
Organization of Book
Internet Protocol Stack
To provide structure to design of network protocols, network designers organize protocols in layers
Service – says what a layer doesProtocol – says how the service is
implementedAdvantages DrawbacksWhen taken together the protocols
of various layers are called the Protocol Stack.
Internet Protocol Stack consists of Five layers
Physical, Link, Network, Transport and Application layers .
Organization of Book
Internet Protocol Stack
• Application Layer:
Network applications and their application layer protocols reside.
Provides user interfaces and support for services such as e-mail, file transfer etc.
Hyper Text Transfer Protocol (HTTP)File Transfer Protocol (FTP)Session Initiation Protocol (SIP)
An application layer protocol is distributed over multiple end systems
The packets of information at the application layer is called as a message.
Internet Protocol Stack• Transport Layer:
Transports application-layer messages between application end points.
Transport layer packet is called as a segment Breaks long messages into shorter segments There are two Transport Layer Protocols Transmission Control Protocol (TCP)
Connection Oriented serviceGuaranteed delivery of application layer messagesFlow controlCongestion Control
User Datagram Protocol (UDP)Connectionless serviceNo reliability, flow control and congestion control
Internet Protocol Stack• Network Layer:
Responsible for moving network layer packets known as datagrams from one host to another.
Transport layer passes a transport layer segment and a destination address to the network layer.
Network layer includes IP ProtocolDefines the fields in the datagram as well
as how end systems and routers act on these fields
Commonly referred as IP layer.Different routing protocols.
Determine the route that datagrams take between source and destination
Internet Protocol Stack• Link Layer:
Moves a packet from one node (host or router) to the next node in the route.
Divide the stream of bits received from the network layer into manageable data units called frames.
Transforms a raw transmission facility to a reliable link.Mechanism to detect and retransmit
damaged or lost framesExample of link layer protocols include
WiFi, Ethernet etc.
Internet Protocol Stack• Physical Layer:
The job of this layer is to move the individual bits with in frames from one node to next.
Representation of bitsPhysical Layer data consists of a stream of
bits (0 or 1)To be transmitted bits must be encoded
into signals. The physical layer defines the type of encoding.
The protocol in this layer depend on the actual transmission medium of the link.
Internet Protocol Stack Application: Provides user interfaces
and support for services such as e-mail, file transfer etc. FTP, HTTP
Transport: Transports application-layer messages between application end points. Segmentation and reassembly TCP, UDP
Network: Routing of Datagrams from source to destination IP, routing protocols
Link: Move a packet from one node (host or router) to the next node in the route. Ethernet, WiFi
Physical: Move the individual bits with in frames from one node to next
Application
Transport
Network
Link
Physical
OSI Reference Model In 1970 International Organization for
Standardization proposed a seven layered model called Open Systems Interconnection (OSI) model.
Presentation Layer: Provide services such as data encryption, compression.
Session Layer: Synchronization points (checkpointing) and recovery of data exchange.
Internet stack “missing” these layers! these services, if needed, must be
implemented in the application by the application developer.
source
application
transportnetwork
linkphysical
segment
datagram
destination
application
transportnetwork
linkphysical
router
switch
Encapsulationmessage
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networklink
physical
linkphysical
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HtHn M HtHn M
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frame
Throughput The rate (bits/sec) at which bits are transferred
between sender/receiver Difference between Bandwidth and Throughput?
ISPs sell bandwidth In computer networks, the throughput is less
than the bandwidth for several reasons • The channel may be shared by other users• Packet loss due to congestion• Packet loss due to bit errors• Noise in the channel• Transmission rates of the link over which
the data flows.
Throughput
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Throughput is min {Rs,Rc} Transmission Rate of the bottleneck link
Throughput
10 connections share bottleneck link R
Rs
Rs
Rs
Rc
Rc
Rc
R
10 clients/servers pairs, Common link R traversed
by all 10. Rate of the link R is very
large then the throughput is min {Rs , Rc}
Rs=2Mbps, Rc=1Mbps,
R=5Mbps Common link divides
transmission rate equally among the 10 downloads
500kbps to each download
Shared Link R is now the bottleneck.