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Unit 1: Introduction. Layering     What is a (communications) network?

• An interconnected structure that allows attached devices to communicate with each other

       Network Applications        Client/Server Model        Example Applications: WWW etc.

       Protocols and Standardizations        Network Classifications

       LAN, MAN, WAN etc.        Internetwork

       Internetworking devices        The Internet as an example

       Brief history        Structure of the Internet        RFC (Request for Comments)

       Network Architectures        Protocol v.s. Services        OSI and TCP/IP 

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Network Protocols =agreed-upon ways in which computers exchange information

Syntax: structure or format of the dataSemantics: meaningsTiming/Procedrue: when data should be sent and how fast it can be sent.

Request ServiceProvide Service

v.s. peer-to-peer model

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MAN

LAN

WAN

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Internetwork

Internetworking devices: bridges, routers, brouters, gateways

 

Figure 1-4 The Internet

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The Internet:A collection of networks and routers that span many countries and uses the TCP/IP protocols to form a single, cooperative virtual network. Intranet: connection of different LANs within an organization. Main players in the Internet:Started by U.S. research/military organizations:(D)ARPA: (Defense) Advanced Research Projects Agency funds technology with military usefulness DoD: U.S. Department of Defense early adaptor of Internet technology NSF: National Science Foundations funds university research

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Today:National backbone providers (NBPs) interconnected through exchange points: NAPs (Network Access Points) and MAEs (Metropolitan Area Exchanges) Regional ISPs connects to the NBPs 

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Brief History of the Internet1830: telegraph 1876: telephone (circuit-switching) Development of Early Packet Switching Principles:early 1960's concept of packet switching (Paul Baran) 1965: MIT's Lincoln Laboratory commissions Thomas Marill to study computer networking 1968: ARPAnet contract awarded to Bolt Beranek and Newman (BBN) 1969: ARPAnet has 4 nodes (UCLA, SRI, UCSB, U. Utah), connected by IMPs (Interface message processors); connected by 50 kbps lines 1971: 15 nodes and 23 hosts

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Internetworking, and New and Proprietary Networks1973: TCP/IP design. First satellite link from California to Hawaii First international connections to the ARPANET:England and Norway 1979: ARPAnet had about 100 nodes 1980s: DARPA funded Berkeley Unix, with TCP/IP 1980-81: BITNET (IBM protocols) and CSNET (NSF-funded) Early 1980's: split ARPnet (research), MILNET (Military) Proliferation of Networks:1984: Domain Name Services (Mapping Domain names into IP addresses) 1986: NSFNET created (56kbps backbone) 1989: Internet passes 100,000 nodes First proposal for World Wide Web NSFNET backbone upgraded to T1 (1.544 Mbps)

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Commercialization and the Web:1990: Original ARPAnet disbanded

Fall 1991: CSNET discontinued1991: Gopher released by University of Minnesota 1992: NSFNET backbone upgraded to T3 (44.736 Mbps)March 1992: First MBONE (Multicast Backbone) video multicastNovember 1992: First MBONE video multicast Februray 1993: 1,776,000 hostsMay 1993: NSF solicited for bids and designated a series of NAPs (e.g. Chicago NAP is run by Ameritech)  April 30, 1995: NSFNet backbone disbanded (See http://www.navigators.com/isp.html for excellent information and links about the architecture of the Internet)

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Some Internet-related organizationsISOC: http://www.isoc.org The Internet SOCiety (ISOC) is a professional membership society with more than 150 organizational and 6,000 individual members in over 100 countries. It provides leadership in addressing issues that confront the future of the Internet, and is the organization home for the groups responsible for Internet infrastructure standards, including the Internet Engineering Task Force (IETF) and the Internet Architecture Board (IAB).

IAB: http://www.iab.org The IAB (Internet Architecture Board) is the Internet Society overseer of the technical evolution of the Internet. The IAB supervises the Internet Engineering Task Force (IETF), which oversees the evolution of TCP/IP, and the Internet Research Task Force (IRTF), which works on network technology.

IETF: http://www.ietf.orgThe Internet Engineering Task Force (IETF) is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. Responsible for RFCs (Request for Comments, Internet Standards/drafts) which can be located at http://www.ietf.org/rfc.html ICANN: http://www.icann.orgThe Internet Corporation for Assigned Names and Numbers (ICANN) is the non-profit corporation that was formed to assume responsibility for the IP address space allocation, protocol parameter assignment, domain name system management, and root server system management function previously performed under U.S. Government contract by IANA (Internet Assigned Numbers Authority) and other entities.

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Figure 1-1 Maturity levels of an RFC

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Analogy:

Application = boss

Transport = secretary

Network Access = post office

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ISO OSI Model

(ISO = International Standard Organization, OSI = Open Systems Interconnection)

Bits

Frames

Packets

Error and Flow Control over a single link

End-to-end Error and Flow Control

Also data compression and encryption

• Synchronization – mechanism for inserting check points

• Dialog control – half-duplex or full-duplex

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Figure 2-2 OSI Layers

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Figure 2-3 An exchange using the OSI model

Layer 5 PDU (Protocol Data Unit) = Layer 6 PDU + Layer 5 header

Virtual communication between layer 5 entities (software implementation)

Encapsulation Decapsulation

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Figure 2-7 Transport Layer

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Figure 2-8 Session Layer

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Figure 2-10 Application Layer

Directory ServiceFile transfer and management

email

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Service: What is provided?

Protocol: How is the service provided?

Layer N+1 entity Layer N+1 entity

Layer N entity Layer N entity

Interface. Passing Service Primitives (e.g. request and parameters)

Exchange Layer N PDUs

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Services

 • A connection is set up first Full addresses needed to set up.

• May use connection number for exchanging data and connection release

• Data delivered in sequence.

• Full addresses with all data units

• Data may be delivered out of sequence.

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1. = connection.request

2. = connection.indication

3. = connection.response

4. = connection.confirm

5. = data.request

6. = data.indication

7. = disconnection.request

8. = disconnection.indication

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Figure 2-11 TCP/IP and OSI Model Connection-oriented

Connectionless

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Figure 2-13 Relationship of layers and addresses in TCP/IP

Example: web browser implementing HTTP

Implemented in TCP and UDP software. HTTP uses TCP.

Interface. Eg. WINSOCK on PCs

Implemented in IP software

Eg. Ethernet Medium Access Control (MAC) implemented in NIC card (Network Interface Card) and driver software

Eg. Ethernet PHY layer. Implemented in NIC card

Eg. TCP port 80 for web server

Eg. 140.192.33.37 (32-

bit)

Eg. Ethernet address (48-bit)

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Figure 2-14 Physical addresses: identify and interface card (Link address, MAC address)

• Usually contains a checksum/Frame check sequence for detecting errors.

• Calculated based on the rest of the frame.

• CRC (Cyclic redundancy check) is commonly used.

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Figure 2-15 IP addresses (A logical address necessary for universal communication over the internet, and is independent of the underlying physical networks)

Note: We commonly uses names such as www.cs.depaul.edu (called Domain Names). To translate from names to IP addresses, needs to use DNS (Domain Name Service) implemented at the Application level.

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Figure 2-16 Port addresses (Different processes communicate through different ports)