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Fall 2005

Internetworking: Concepts, Architecture and TCP/IP

Layering

Qutaibah MalluhiCSE DepartmentQatar University

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Motivation

There are many different LAN and WAN technologies

LAN– Low cost

– Limited distance

WAN– High cost

– Unlimited distance

No single networking technology best for all needs

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Universal Service

Arbitrary pair of computers can communicate Fundamental concept in networking Desirable but difficult in a heterogeneous world

of incompatible networks– Electrical properties– Signaling and data encoding– Packet formats– Addresses– Link capacity mismatch– Different administrative authorities

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The Bottom Line

Although universal service is highly desirable, incompatibilities among network hardware

and physical addressing prevent an organization from building a bridged

network that includes arbitrary technologies

Although universal service is highly desirable, incompatibilities among network hardware

and physical addressing prevent an organization from building a bridged

network that includes arbitrary technologies

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Internetworking

Internetworking is a scheme for interconnecting multiple networks of dissimilar technologies

Uses both hardware and software – Extra hardware positioned between networks – Software on each attached computer

System called an internetwork or an internet

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Routers

A router is a hardware component used to interconnect networks

Can interconnect networks that use different technologies– different media and media access techniques, physical

addressing schemes, or frame formats. A router has multiple interfaces on multiple

networks Router forwards packets between networks

– Transforms packets as necessary to meet standards for each network

Some times called internet gatewayRouter

Two net. interfaces

Network 2Network 1

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Internet Architecture

Can have multiple networks with routers interconnecting them.

A host computer connects to a network A router may have multiple network interfaces

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Multiple Routers

Would be possible to interconnect all networks in an organization with a single router?

Most organizations use multiple routers – Router has finite capacity (CPU speed and memory) –

can not handle all traffic – Reliability -- ability to route around failures

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Create a Virtual Network

Internetworking software builds a single, seamless virtual network out of multiple physical networks – Universal addressing

scheme – Universal service

All details of physical networks hidden from users and applications

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Routing

Routers use routing tables Typically, routing tables specify the next hop for

each destination Network ID– Routing table may contain next hop for a destination

host (not a whole network)– Network routs simplify the routing table (dramatically

reduce the number of entries in the routing table Routing table typically have a default route

entry Route command in windows (netstat –r in

unix) to check the routing table

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Routing Table Example

R1

R2

R3

R4

N1

N2

N4

N3

R5

Internet

Destination Network Next Hop

N1 Local interface

N2 Local interface

N4 R4 (address of R4 on N1)

N3 R2 (address of R2 on N2)

Default R5 (address of R5 on N1

Routing table for R1

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TCP/IP Internet Protocols

Most widely used internetworking protocol suite Suite used in the public Internet First internetworking protocol suite

– Work began in 1970’s– Research originally funded by ARPA (currently DARPA)

and other government agencies followed Others internetworking protocol suites include

IPX, VINES, AppleTalk TCP/IP is vendor and platform independent

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TCP/IP Stack

Unlike ISO 7-layers model, TCP/IP has 5 conceptual layers

(Internet)

(Network Interface)

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Peer-to-Peer and Hop-to-Hop Processes

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Sending Data in the Internet model

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The physical layer is responsible for transmitting individual bits from one node to

the next.

The physical layer is responsible for transmitting individual bits from one node to

the next.

Physical Layer

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The data link layer is responsible for transmitting frames on the same network

from one node to the next.

The data link layer is responsible for transmitting frames on the same network

from one node to the next.

Data Link Layer

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Hop-to-Hop Delivery

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A node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by one network. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level (e.g. frame type). The trailer contains error detection (CRC) bits.

Example 1

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Network Layer

The network layer is responsible for the delivery of packets from the original source

to the final destination.

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End-to-End Delivery

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Example 2 We want to send data from a

node with internetwork (IP) address A (e.g. and physical address 10, located on one LAN, to a node with a internetwork (IP) address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The internetwork (logical) addresses have this characteristic.

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Transport Layer

The transport layer is responsible for delivery of a message from one process

to another.

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Reliable Process-to-Process Delivery

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Example 3

Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, internetwork addresses (A and P) are added to each packet.

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Application Layer

The application layer is responsible for providing services to the user.

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Summary of TCP/IP Layer’s Responsibilities

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TCP/IP Layers (1)

Layer 1: Physical Layer– Corresponds to layer 1 in the ISO model– Defines basic networking hardware

Layer 2: Network Interface (Data Link)– Corresponds to layer 2 in the ISO model– Hardware (MAC) frame format– MAC addressing– Interface between computer and network (NIC)

Layer 3: Internetwork (Network) – Defines uniform format of packets forwarded across

networks– Rules for forwarding packets in routers

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TCP/IP Layers

Layer 4: Transport – Corresponds to layers 4 and 5 in the ISO model– Provides reliable delivery of data

Layer 5: Application – Corresponds to ISO model layers 6 and 7– Used for communication among applications

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TCP/IP Vs. OSI

OSI Model TCP/IP

(Internet)

(Network Interface)

ApplicationApplication5

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Internet (Layer 3) Protocols

IP: combined with TCP they are known as the TCP/IP suite

ICMP (error-handling protocol) OSPF, RIP, BGP (routing protocols) IGMP (multicast protocol) MOSPF, DVMRP, PIM (multicast routing

protocols) ARP, RARP (addressing protocols)

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UDP

MIME

OSPFICMP

SNMPTELNETSMTPHTTPFTPBGP

TCP

IP

Some Protocols in the TCP/IP suite

Application Layer

Transport Layer

Internet Layer

SNMP

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Summary

An internet is a collection of possibly heterogeneous physical networks interconnected into a single virtual network

Routers provide the physical interconnection and forward packets between networks

TCP/IP is the most widely used internetworking protocol suite