introduction to computer networks · 2 4 copyright© dr. miguel a. labrador intro – 4 what’s...

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Introduction to Computer Networks

Miguel A. Labrador

Department of Computer Science & Engineering

[email protected]

http://www.csee.usf.edu/~labrador

Dr. Miguel A. Labrador

2Copyright© Dr. Miguel A. Labrador

Intro – 22

Copyright© Dr. Miguel A. Labrador

Roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Network access and physical media

1.5 Internet structure and ISPs

1.6 Protocol layers, service models


Intro – 33


What’s the Internet: “nuts and bolts” view

• Millions of connected computing devices: hosts = end systems

• Running network protocols and applications

• Communication links– Fiber, copper, radio, satellite

– Transmission rate = bandwidth

• Routers: forward packets (chunks of data)

local ISP

companynetwork

regional ISP

router workstationserver

mobile

2


Intro – 44


What’s the Internet: “nuts and bolts” view

• Protocols control sending, receiving of messages– e.g., TCP, IP, HTTP, FTP, PPP

• Internet: “network of networks”– Loosely hierarchical

– Public Internet versus private intranet

• Internet standards– RFC: Request for comments

– IETF: Internet Engineering Task Force

local ISP

companynetwork

regional ISP

router workstationserver

mobile


Intro – 55


What’s the Internet: a service view

• Communication infrastructure enables distributed applications:– Web, email, games, e-

commerce, file sharing

• Communication services provided to applications:– Connectionless unreliable

– Connection-oriented reliable


Intro – 66


What’s a protocol?

• Human protocols:

• “What’s the time?”

• “I have a question”

• Introductions

• … specific msgs sent

• … specific actions taken when msgs received, or other events

• Network protocols:

• Machines rather than humans

• All communication activity in Internet governed by protocols

Protocols define format, order of messages sent and received among network entities,

and actions taken on message transmission, receipt

3


Intro – 77


What’s a protocol?

A human protocol and a computer network protocol:

Hi

HiGot thetime?2:00

TCP connectionreq

TCP connectionresponse

Get http://www.csee.usf.edu/~labrador

<file>time


Intro – 88


Roadmap


1.2 Network edge

1.3 Network core





Intro – 99


A closer look at network structure

• Network edge: applications and hosts

• Network core:– Routers

– Network of networks

• Access networks, physical media: communication links

4


Intro – 1010


The network edge

• End systems (hosts)– Run application programs– e.g. Web, email– At “edge of network”

• Client/server model– Client host requests, receives

service from always-on server– e.g. Web browser/server; email

client/server

• Peer-peer model– Minimal (or no) use of dedicated

servers– e.g. Skype, BitTorrent

• Two types of services– Connection-oriented– Connectionless


Intro – 1111


Network edge: connection-oriented service

Goal: data transfer between end systems

• Handshaking: setup (prepare for) data transfer ahead of time

– Hello, hello back human protocol

– Set up “state” in two communicating hosts

• TCP - Transmission Control Protocol

– Internet’s connection-oriented service

TCP service [RFC 793]

• Reliable, in-order byte-stream data transfer

– Loss: acknowledgements and retransmissions

• Flow control:– Sender won’t overwhelm receiver

• Congestion control:– Senders “slow down sending rate”

when network congested


Intro – 1212


Network edge: connectionless service

Goal: data transfer between end systems

– Same as before!

• UDP - User Datagram Protocol [RFC 768]:

– Connectionless

– Unreliable data transfer

– No flow control

– No congestion control

App’s using TCP:• HTTP (Web), FTP (file transfer),

Telnet (remote login), SMTP (email)

App’s using UDP:• Streaming media,

teleconferencing, DNS, Internet telephony

5


Intro – 1313


Roadmap


1.2 Network edge

1.3 Network core





Intro – 1414


The network core

• Mesh of interconnected routers• The fundamental question: how is data

transferred through the network?– Circuit switching: dedicated circuit

per call: telephone network– Packet-switching: data sent

through the network in discrete “chunks”

• As a result, we have:– Circuit-switched networks– Packet-switched networks


Intro – 1515


Delay, loss and throughput in packet switched networks

• A parenthesis to look at three important metrics in networks

• Analyze the performance of switching technologies

6


Intro – 1616


How do loss and delay occur?

Packets queue in router buffers• Packet arrival rate to link exceeds output link capacity

• Packets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay)free (available) buffers: arriving packets dropped (loss) if no free buffers


Intro – 1717


Four sources of packet delay

• 1. Nodal processing:– Check bit errors

– Determine output link

A

B

propagation

transmission

nodalprocessing queueing

• 2. Queueing– Time waiting at output link for

transmission

– Depends on congestion level of router


Intro – 1818


Delay in packet-switched networks

3. Transmission delay:

• R=link bandwidth (bps)

• L=packet length (bits)

• Time to send bits into link = L/R

4. Propagation delay:

• d = length of physical link

• s = propagation speed in medium (~2x108 m/sec)

• Propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queueing

7


Intro – 1919


Nodal delay

• dproc = processing delay– Typically a few microsecs or less

• dqueue = queuing delay– Depends on congestion

• dtrans = transmission delay– = L/R, significant for low-speed links

• dprop = propagation delay– A few microsecs to hundreds of msecs

proptransqueueprocnodal ddddd +++=


Intro – 2020


Queueing delay (revisited)

• R=link bandwidth (bps)

• L=packet length (bits)

• a=average packet arrival rate

traffic intensity = La/R

• La/R ~ 0: average queueing delay small

• La/R -> 1: delays become large

• La/R > 1: more “work” arriving than can be serviced, average delay infinite!


Intro – 2121


“Real” Internet delays and routes

• What do “real” Internet delay & loss look like?

• Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:– Sends three packets that will reach router i on path towards

destination

– Router i will return packets to sender

– Sender times interval between transmission and reply.

3 probes

3 probes

3 probes

8


Intro – 2222


“Real” Internet delays and routes

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu

* means no reponse (probe lost, router not replying)

trans-oceaniclink


Intro – 2323


Packet loss

• Queue (aka buffer) preceding link has finite capacity

• When packet arrives to full queue, packet is dropped (aka lost)

• Lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

A

B

packet being transmitted

packet arriving tofull buffer is lost

buffer (waiting area)


Intro – 2424


Throughput

• Throughput: rate (bits/time unit) at which bits are transferred between sender/receiver– Instantaneous: rate at given point in time

– Average: rate over longer period of time

server, withfile of F bits

to send to client

link capacityRs bits/sec

link capacityRc bits/sec

pipe that can carryfluid at rateRs bits/sec)

pipe that can carryfluid at rateRc bits/sec)

9


Intro – 2525


Throughput (more)

• 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

link on end-end path that constrains end-end throughput

bottleneck link


Intro – 2626


Network Core: Circuit Switching

End-to-end resources reserved for “call”

• Link bandwidth, switch capacity

• Dedicated resources: no sharing

• Circuit-like (guaranteed) performance

• Call setup (signaling mechanism) required

• Three phases– Circuit connection phase

– Transmission phase

– Circuit termination phase

• Telephone network is a typical example


Intro – 2727


Network Core: Circuit Switching

Network resources (e.g., bandwidth) divided into “pieces”

• Pieces allocated to calls

• Resource piece idle if not used by owning call (no sharing)

• Dividing link bandwidth into “pieces”

– Frequency division

– Time division

10


Intro – 2828


Circuit Switching: FDM and TDM

FDM

Frequency

time

TDM

Frequency

time

4 users

Example:


Intro – 2929


Circuit Switching Example


Intro – 3030


Circuit Switching Performance Analysis

• Total Time (T), given by:

• S: Set up time

• M: Message Size

• B: Bit rate

• K: Number of links

• D: Propagation delay per link

KDB

MST ++=

Time

Dat

a

Call request signal

Call accept signal

Queueing delay

Propagation delay

LinkA

LinkB

LinkC

TotalTime

Transmission delay

S N1 N2 N3L1 L2

N4 DL3

11


Intro – 3131


Circuit Switching Performance

• Advantages– Constant delay for all frames belonging to the same message

• Incoming data are switched to the appropriate outgoing channel without delay

– Efficient for transmitting large amounts of data• Elimination of the per packet header overhead

• No queueing delay at intermediate nodes

– Good if traffic is constant

• Disadvantages– Circuit set up overhead

– Inefficient use of the available bandwidth• Not good if station is idle most of the time


Intro – 3232


Network Core: Packet Switching

Each end-end data stream divided into packets

• User A, B packets share network resources

• Each packet uses full link bandwidth

• Resources used as needed

Resource contention:

• Aggregate resource demand can exceed amount available

• Congestion: packets queue, wait for link use

• Store and forward: packets move one hop at a time

– Node receives complete packet before forwarding

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation


Intro – 3333


Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern statistical multiplexing

In TDM each host gets same slot in revolving TDM frame

A

B

C10 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link

12


Intro – 3434


Network Core: Packet Switching

• Packet switching technology can be further subdivided– Connection oriented

• A circuit is established but link can still be shared– Virtual circuit

• All packets follow the same route

• Delay at intermediate node is possible

• Each packet carries tag (virtual circuit ID), tag determines next hop

• Fixed path determined at call setup time, remains fixed through the call

• Routers maintain per-call state

– Connectionless• No connection is made a priori

– Datagrams

• Packets can take any route; Routes may change during session

• Delay at intermediate node is possible

• Destination address in packet determines next hop

• Analogy: driving, asking directions


Intro – 3535


Packet SwitchingConnection-Oriented or Virtual Circuit Service

• Multiple packets of a single message take the same path, although no dedicated physical path is set up

– The virtual circuit has to be set up though

• Each virtual circuit is identified by a Virtual Circuit Identifier (VCI)

• Delays are more variable than with a dedicated circuit

• Guaranteed, reliable, in-sequence delivery, with suppression of duplicates

• Best example: ATM networks

1

2

4

6

3

5

A C

B

VC 1

VC 2


Intro – 3636


Packet Switching - VC Service

• Combination of Circuit Switching and Datagrams

• Total Time (T), given by:• M: Message Size• P:Packet size (contains

overhead)• S: Set up time• B: Bit rate• K: Number of links• D: Propagation delay per link• Q: Queueing delay• N: Number of nodes

KDB

MNQ

B

PKST +++−+=

*

)1(

P Queueing delay

Propagationdelay

LinkA

LinkB

LinkC

Time

TotalTime

PP

PP

P

PP

P

S N1 N2 N3L1 L2

N4 DL3

Call request signal

Call accept signal

* In packets

13


Intro – 3737


Packet Switching PerformanceVirtual Circuit Service

• Advantages– Can provide QoS guarantees to different types of applications

– Efficient use of the available bandwidth, since data from other sources may use the same link

– Flow control can be exercised by each intermediate node or end-to-end

– No packets out of order

• Disadvantages– Complex

• Signaling, resource reservations

• Mechanism to offer bounded delay and loss

• Access control and policing


Intro – 3838


Packet SwitchingConnectionless or Datagram Service

• Multiple packets of a single message are treated individually, and may take different routes– This causes different delays for each packet

– Packets may be lost or duplicated, or arrive out of order

– Best Effort Service• It is the user application that is responsible for enhancing the

quality of the basic service

• Best example: IP networks (TCP/IP), the Internet

1

2

4

6

3

5

A C

B


Intro – 3939


Packet Switching - Datagram Service

• Total Time (T), given by:

• M: Message Size

• P:Packet size (contains overhead)

• B: Bit rate

• K: Number of links

• D: Propagation delay per link

• Q: Queueing delay

• N: Number of nodes

KDB

MNQ

B

PKT +++−=

*

)1(

P

Queueing delay

Propagationdelay

LinkA

LinkB

LinkC

Time

TotalTime

PP

PP

P

PP

P

S N1 N2 N3L1 L2

N4 DL3

* In packets

14


Intro – 4040


Packet Switching PerformanceDatagram Service

• Advantages– Very simple

– Efficient use of the available bandwidth, since data from other sources may use the same link

– Low delay for interactive data

– Flow control can be exercised by each intermediate node or end-to-end

• Disadvantages– Two packets from the same message may take different routes,

and experience different delays

– No reservation of resources• Packets are dropped

– Packets can reach the destination out of order


Intro – 4141


Circuit Switching vs. Packet Switching

• Interesting questions can be asked:– What applications are better off with which service?

• Short and long lived applications

– Under what circumstances one is better than the other?• Which one offers shorter T?

– What is the optimal packet size that maximizes the pipeline effect?

– Which one is better for bursty traffic or constant bit rate traffic?

– Which one offers better and easier QoS guarantees?

• Now, you can answer some of these questions; the others will be answered during the course


Intro – 4242


Packet switching versus circuit switching

• 1 Mb/s link

• Each user: – 100 kb/s when “active”

– Active 10% of time

• Circuit-switching: – 10 users

• Packet switching: – with 35 users, probability > 10

active less than .0004

Packet switching allows more users to use network!

N users1 Mbps link

15


Intro – 4343


Network Taxonomy

Telecommunicationnetworks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

• Datagram network is not either connection-oriented or connectionless• Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps


Intro – 4444


Roadmap


1.2 Network edge

1.3 Network core





Intro – 4545


Access networks and physical media

Q: How to connect end systems to edge router?

• Residential access networks

• Institutional access networks (school, company)

• Mobile access networks

Keep in mind

• Bandwidth (bits per second) of access network?

• Shared or dedicated?

16


Intro – 4646


Residential access: Dial-up Modem

• Dialup via modem

– Uses existing telephony infrastructure– Home is connected to central office

– Up to 56Kbps direct access to router (often less)

– Can’t surf and phone at same time: can’t be “always on”

telephonenetwork Internet

homedial-upmodem

ISPmodem(e.g., AOL)

homePC

central office


Intro – 4747


Asymmetric Digital Subscriber Line (DSL)

• ADSL: Asymmetric Digital Subscriber Line

– Also uses telephone infrastructure

– Dedicated physical line to telephone central office

– Up to 1 Mbps upstream (today typically < 256 kbps)

– Up to 8 Mbps downstream (today typically < 1 Mbps)

telephonenetwork

DSLmodem

homePC

homephone

Internet

DSLAM

Existing phone line:0-4KHz phone; 4-50KHz upstream data; 50KHz-1MHz downstream data

splitter

centraloffice


Intro – 4848


Residential access: cable modems

• Does not use telephone infrastructure– Instead uses cable TV infrastructure

• HFC: Hybrid Fiber Coax

– Asymmetric: up to 30Mbps downstream, 2 Mbps upstream

• Network of cable and fiber attaches homes to ISP router

– Homes share access to router

– Unlike DSL, which has dedicated access

17


Intro – 4949


Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html


Intro – 5050


Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes


Intro – 5151



home

cable headend

cable distributionnetwork (simplified)

18


Intro – 5252



home

cable headend

cable distributionnetwork

server(s)


Intro – 5353



home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM:


Intro – 5454


Fiber to the Home

• Optical links from central office to the home

• Two competing optical technologies– Passive Optical Network (PON)

– Active Optical Networks (PAN)

• Much higher Internet rates; fiber also carries television and phone services

ONT

OLT

central office

opticalsplitter

ONT

ONT

opticalfiber

opticalfibers

Internet

19


Intro – 5555


Ethernet Internet access

• Typically used in companies, universities, etc. – Company/univ local area network (LAN) connects end system to edge router

• Ethernet:

– 10 Mbs, 100Mbps, 1 Gbps, 10 Gbps Ethernet

– Today, end systems typically connect into Ethernet switch

100 Mbps

100 Mbps

100 Mbps1 Gbps

server

Ethernetswitch

Institutionalrouter

To Institution’sISP


Intro – 5656


Wireless access networks

• Shared wireless access network connects end system to router

– Via base station aka “access point”

• Wireless LANs:– 802.11b/g (WiFi): 11 or 54 Mbps

• Wider-area wireless access– Provided by telco operator

– ~1Mbps over cellular system (EVDO, HSDPA)

– Next up (?): WiMAX (10’s Mbps) over wide area

basestation

mobilehosts

router


Intro – 5757


Home networks

Typical home network components:

• ADSL or cable modem

• Router/firewall/NAT

• Ethernet

• Wireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet

20


Intro – 5858


Physical Media

• Bit: propagates betweentransmitter/receiver pairs

• Physical link: what lies between transmitter & receiver

• Guided media:– Signals propagate in solid media:

copper, fiber, coax

• Unguided media:– Signals propagate freely, e.g., radio

Twisted Pair (TP)

• Two insulated copper wires– Category 3: traditional phone

wires, 10 Mbps Ethernet

– Category 5: 100Mbps Ethernet


Intro – 5959


Physical Media: coax, fiber

Coaxial cable:• Two concentric copper

conductors

• Bidirectional

• Baseband:– Single channel on cable

– Legacy Ethernet

• Broadband:– Multiple channel on cable

– HFC

Fiber optic cable:• Glass fiber carrying light pulses,

each pulse a bit

• High-speed operation:– High-speed point-to-point

transmission (e.g., 10 Gbps)

• Low error rate: repeaters spaced far apart ; immune to electromagnetic noise


Intro – 6060


Physical media: radio

• Signal carried in electromagnetic spectrum

• No physical “wire”

• Bidirectional

• Propagation environment effects:– Reflection

– Obstruction by objects

– Interference

Radio link types:• Terrestrial microwave

– e.g. up to 45 Mbps channels

• LAN (e.g., Wifi)– 2Mbps, 11Mbps

• Wide-area (e.g., cellular)– e.g. 3G: hundreds of kbps

• Satellite– Up to 50Mbps channel (or multiple

smaller channels)

– 270 msec end-end delay

– Geosynchronous versus low altitude

21


Intro – 6161


Roadmap


1.2 Network edge

1.3 Network core





Intro – 6262


Internet structure: network of networks

• Roughly hierarchical

• At center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T), national/international coverage

– Treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

NAP

Tier-1 providers also interconnect at public network access points (NAPs)


Intro – 6363



• “Tier-2” ISPs: smaller (often regional) ISPs– Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customerof tier-1 provider

Tier-2 ISPs also peer privately with each other, interconnect at NAP

22


Intro – 6464



• “Tier-3” ISPs and local ISPs – Last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier-3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet


Intro – 6565



• A packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP


Intro – 6666


Roadmap


1.2 Network edge

1.3 Network core




23


Intro – 6767


Protocol “Layers”

Networks are complex!

• Many “pieces”:

– Hosts

– Routers

– Links of various media

– Applications

– Protocols

– Hardware, software

Question:Is there any hope of organizing

structure of network?

Or at least our discussion of networks?


Intro – 6868


Network Design• To reduce design complexity, task of communication broken up into

modules

• Most networks are organized into layers– Each layer is like a module implementing some functions or services

– Each layer enhances the service of the layer below• Added value service

• Two layer “n” entities in different computers use a peer-to-peer layer “n” protocol to communicate with each other

• Two adjacent layers within the same computer communicate through an interface

– The interface defines the primitive operations and services the lower layer provides to the upper layer

• Modularization eases maintenance, updating of system

– Change of implementation of layer’s service transparent to rest of system


Intro – 6969


Network Architecture

Layer N

Layer N-1

Layer 2

Layer 1

Layer N

Layer N-1

Layer 2

Layer 1

Physical Medium

Layer N Protocol

Layer N-1 Protocol

Layer 2 Protocol

Layer 1 Protocol

Layer N<->N-1 Interface

Layer N-1<->N-2 Interface

Layer 2<->1 Interface

24


Intro – 7070


Information Flow

Data

DataH

DataHH

DataHHH

Data

DataH

DataHH

DataHHH

Layer N Protocol

Layer N-1 Protocol

Layer 2 Protocol

Layer 1 Protocol

Physical Medium


Intro – 7171


Interfaces and Services

• Layer N entity implements a service used by Layer N+1– Layer N is the service provider

– Layer N+1 is the service user

• At each layer, protocols are used to communicate

• Control information is added to user data at each layer

• Services are available through Service Access Points (SAPs)– SAPs are uniquely identified by their addresses

– Example: Telephone network• A SAP is the wall socket

• The SAP address is the phone number


Intro – 7272


ISO/OSI Communication Model

25


Intro – 7373


Internet protocol stack

• Application: supporting network applications– FTP, SMTP, STTP

• Transport: End-to-End data transfer (segments)– TCP (CO), reliable, flow and congestion control

– UDP (CL), unreliable, no flow and congestion control

– Socket interface

• Network: routing of datagrams from source to destination (packets)

– IP, routing protocols

• Link: data transfer between neighboring network elements (frames)

– Point-to-Point, reliable service

– PPP, Ethernet

• Physical: bits “on the wire”

application

transport

network

link

physical


Intro – 7474


messagesegment

datagramframe

sourceapplicationtransportnetwork

linkphysical

HtHnHl MHtHn M

Ht MM

destinationapplicationtransportnetwork

linkphysical

HtHnHl MHtHn M

Ht MM

networklink

physical

linkphysical

HtHnHl MHtHn M

HtHnHl M

HtHn M

HtHnHl M HtHnHl M

router

switch

Encapsulation


Intro – 7575


LAN Interconnection and OSI

Presentation

Session

Transport

Network

Link

Physical

Repeater Bridge Router

Application

Presentation

Session

Transport

Network

Link

Physical

Application

MACLLC

Focus of the course

26


Intro – 7676


Some Protocols in TCP/IP Suite

introduction to computer networks · 2 4 copyright© dr. miguel a. labrador intro – 4 what’s...

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