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Review of Important Networking Concepts. Introductory material using Prof. Liebeherr on-line notes Review of important networking concepts: protocol architecture, protocol layers, encapsulation, demultiplexing, network abstractions. Networking Concepts .

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review of important networking concepts

Review of Important Networking Concepts

Introductory material using Prof. Liebeherr on-line notes

Review of important networking concepts: protocol architecture, protocol layers, encapsulation, demultiplexing, network abstractions.

networking concepts
Networking Concepts
  • Layered Architecture to reduce complexity
    • Encapsulation
    • Abstractions
sending a packet from argon to neon1
Sending a packet from Argon to Neon

DNS: What is the IP address of “”?

DNS: The IP address of “” is

ARP: What is the MAC address of

ARP: What is the MAC address of

ARP: The MAC address of is 00:20:af:03:98:28

ARP: The MAC address of is 00:e0:f9:23:a8:20 is not on my local network.

Therefore, I need to send the packet to my

default gateway with address is on my local network.

Therefore, I can send the packet directly.



what s a protocol
What’s a protocol?

human protocols:

“what’s the time?”

“I have a question”


… 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 msgs sent and received among network entities, and actions taken on msg transmission, receipt

what s a protocol1
What’s a protocol?

a human protocol and a computer network protocol:

TCP connection



Got the






TCP connection



Q: Other human protocols?

communications architecture
Communications Architecture
  • The complexity of the communication task is reduced by using multiple protocol layers:
      • Each protocol is implemented independently
      • Each protocol is responsible for a specific subtask
      • Protocols are grouped in a hierarchy
  • A structured set of protocols is called a communicationsarchitectureorprotocol suite
tcp ip protocol suite
TCP/IP Protocol Suite

The TCP/IP protocol suite is the protocol architecture of the Internet

The TCP/IP suite has four layers: Application, Transport, Network, and Data Link Layer

End systems (hosts) implement all four layers. Gateways (Routers) only have the bottom two layers.

functions of the layers
Functions of the Layers
  • Data Link Layer:
    • Service: Reliable transfer of frames over a link Media Access Control on a LAN
    • Functions: Framing, media access control, error checking
  • Network Layer:
    • Service: Move packets from source host to destination host
    • Functions: Routing, addressing
  • Transport Layer:
    • Service: Delivery of data between hosts
    • Functions: Connection establishment/termination, error control, flow control
  • Application Layer:
    • Service: Application specific (delivery of email, retrieval of HTML documents, reliable transfer of file)
    • Functions: Application specific
tcp ip suite and osi reference model
TCP/IP Suite and OSI Reference Model

The TCP/IP protocol stack does not define the lower layers of a complete protocol stack

layered communications
Layered Communications
  • An entity of a particular layer can only communicate with:

1. a peer layer entityusing a common protocol (Peer Protocol)

2. adjacent layersto provide services and to receive services

service primitives
Service Primitives

N+1 Layer Peer Protocol

Request Delivery


Communication services are invoked via function calls. The functions are called service primitives

N+1 LayerEntity

N+1 LayerEntity

N LayerEntity

N LayerEntity

service primitives1
Service Primitives

N+1 Layer Peer Protocol

Request Delivery


Recall: A layer N+1 entity sees the lower layers only as a service provider

N+1 LayerEntity

N+1 LayerEntity

Service Provider

layers in the example1
Layers in the Example

Send IP data-gram to

Frame is an IP datagram

Frame is an IP datagram

IP datagram is a TCP segment for port 80

Send HTTP Request to neon

Establish a connection to at port 80

Open TCP connection to port 80

Send IP datagram to

Send a datagram (which contains a connection request) to

Send the datagram to

Send the datagram to

Send Ethernet frame to 00:e0:f9:23:a8:20

Send Ethernet frame to 00:20:af:03:98:28

layers and services
Layers and Services
  • Service provided by TCP to HTTP:
    • reliable transmission of byte streams over a logical connection
  • Service provided by IP to TCP:
    • unreliable transmission of IP datagrams across an IP network
  • Service provided by Ethernet to IP:
    • transmission of a frame across an Ethernet segment
  • Other services:
    • DNS: translation between domain names and IP addresses
    • ARP: Translation between IP addresses and MAC addresses
encapsulation demultiplexing
Encapsulation & Demultiplexing
  • As data is moving down the protocol stack, each protocol is adding layer-specific control information
encapsulation demultiplexing in our example
Encapsulation & Demultiplexing in our Example
  • Let us look in detail at the Ethernet frame between Argon and the Router, which contains the TCP connection request to Neon.
  • This is the frame in hexadecimal notation.

00e0 f923 a820 00a0 2471 e444 0800 4500 002c 9d08 4000 8006 8bff 808f 8990808f 4715 065b 0050 0009 465b 0000 0000 6002 2000 598e 0000 0204 05b4

encapsulation demultiplexing tcp header
Encapsulation & Demultiplexing: TCP Header

Option: maximum segment size

different views of networking
Different Views of Networking
  • Different Layers of the protocol stack have a different view of the network. This is HTTP’s and TCP’s view of the network.
network view of ethernet
Network View of Ethernet
  • Ethernet’s view of the network
the evolution of internet

The Evolution of Internet

Introductory material.

An overview lecture that covers Internet related topics, including a definition of the Internet, an overview of its history and growth, and standardization and naming.

a definition
A Definition
  • On October 24, 1995, the FNC unanimously passed a resolution defining the term Internet.
  • RESOLUTION: The Federal Networking Council (FNC) agrees that the following language reflects our definition of the term "Internet"."Internet" refers to the global information system that --
    • (i) is logically linked together by a globally unique address space based on the Internet Protocol (IP) or its subsequent extensions/follow-ons;
    • (ii) is able to support communications using the Transmission Control Protocol/Internet Protocol (TCP/IP) suite or its subsequent extensions/follow-ons, and/or other IP-compatible protocols; and
    • (iii) provides, uses or makes accessible, either publicly or privately, high level services layered on the communications and related infrastructure described herein.
internet history
Internet History

1961: Kleinrock - queueing theory shows effectiveness of packet-switching

1964: Baran - packet-switching in military nets

1967: ARPAnet conceived by Advanced Research Projects Agency

1969: first ARPAnet node operational


ARPAnet demonstrated publicly

NCP (Network Control Protocol) first host-host protocol

first e-mail program

ARPAnet has 15 nodes

1961-1972: Early packet-switching principles

internet history1
Internet History

1970: ALOHAnet satellite network in Hawaii

1973: Metcalfe’s PhD thesis proposes Ethernet

1974: Cerf and Kahn - architecture for interconnecting networks

late70’s: proprietary architectures: DECnet, SNA, XNA

late 70’s: switching fixed length packets (ATM precursor)

1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles:

minimalism, autonomy - no internal changes required to interconnect networks

best effort service model

stateless routers

decentralized control

define today’s Internet architecture

1972-1980: Internetworking, new and proprietary nets

internet history2
Internet History

Early 1990’s: ARPAnet decommissioned

1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)

early 1990s: Web

hypertext [Bush 1945, Nelson 1960’s]

HTML, HTTP: Berners-Lee

1994: Mosaic, later Netscape

late 1990’s: commercialization of the Web

Late 1990’s – 2000’s:

more killer apps: instant messaging, P2P file sharing

network security to forefront

est. 50 million host, 100 million+ users

backbone links running at Gbps

1990, 2000’s: commercialization, the Web, new apps

applications of the internet
Applications of the Internet
  • Traditional core applications:Email News Remote Login File Transfer
  • The killer application:World-Wide Web (WWW), P2P
  • Future applications:Videoconferencing and Telephony Multimedia Services Internet Broadcast
growth of the internet
Growth of the Internet

Source: Internet Software Consortium

internet infrastructure1
Internet Infrastructure
  • The infrastructure of the Internet consists of a federation of connected networks that are each independently managed (“autonomous system”)
    • Note: Each “autononmous system may consist of multiple IP networks
  • Hierarchy of network service providers
    • Tier-1: nation or worldwide network (US: less than 20)
    • Tier-2: regional networks (in US: less than 100)
    • Tier-3: local Internet service provider (in US: several thousand)
internet infrastructure2
Internet Infrastructure
  • Location where a network (ISP, corporate network, or regional network) gets access to the Internet is called a Point-of-Presence (POP).
  • Locations (Tier-1 or Tier-2) networks are connected for the purpose of exchanging traffic are called peering points.
    • Public peering: Traffic is swapped in a specific location, called Internet exchange points (IXPs)
    • Private peering: Two networks establish a direct link to each other.
tier 1 isp e g sprint
Tier-1 ISP: e.g., Sprint

Sprint US backbone network

who is who on the internet
Who is Who on the Internet ?
  • Internet Society (ISOC):Founded in 1992, an international nonprofit professional organization that provides administrative support for the Internet. Founded in 1992, ISOC is the organizational home for the standardization bodies of the Internet.
  • Internet Engineering Task Force (IETF): Forum that coordinates the development of new protocols and standards. Organized into working groups that are each devoted to a specific topic or protocol. Working groups document their work in reports, called Request For Comments (RFCs).
  • IRTF (Internet Research Task Force):The Internet Research Task Force is a composed of a number of focused, long-term and small Research Groups.
  • Internet Architecture Board (IAB): a technical advisory group of the Internet Society, provides oversight of the architecture for the protocols and the standardization process
  • The Internet Engineering Steering Group (IESG): The IESG is responsible for technical management of IETF activities and the Internet standards process. Standards. Composed of the Area Directors of the IETF working groups.
internet standardization process
Internet Standardization Process
  • Working groups present their work i of the Internet are published as RFC (Request for Comments).
  • RFCs are the basis for Internet standards.
  • Not all RFCs become Internet Standards ! (There are >3000 RFCs and less than 70 Internet standards
  • A typical (but not only) way of standardization is:
    • Internet Drafts
    • RFC
    • Proposed Standard
    • Draft Standard (requires 2 working implementation)
    • Internet Standard (declared by IAB)
assigning identifiers for the internet
Assigning Identifiers for the Internet
  • Who gives University the domain name “” and who assigns it the network prefix “”? Who assigns port 80 as the default port for web servers?
  • The functions associated with the assignment of numbers is referred to as Internet Assigned Number Authority (IANA).
  • Early days of the Internet: IANA functions are administered by a single person (Jon Postel).


  • Internet Corporation for Assigned Names and Numbers (ICANN) assumes the responsibility for the assignment of technical protocol parameters, allocation of the IP address space, management of the domain name system, and others.
  • Management of IP address done by Regional Internet Registries (RIRs):
    • APNIC (Asia Pacific Network Information Centre)
    • RIPE NCC (Réseaux IP Européens Network Coordination Centre)
    • ARIN (American Registry for Internet Numbers)

Domain names are administered by a large number of private organizations that are accredited by ICANN.

  • Layered Internet architecture
    • Reduce complexity
    • Higher layer views lower layer as service provider
    • Application layer, transport layer, network layer, and link layer