Basics of communication and Internet

Basics of Communication 

and the Internet 

Circle Lecture Communication Systems 

Winter Term 2004/2005 

Outline 

Communication trends and scalability 

Basics of data communication 

How the Internet works 

Prof. Dr. M. Zitterbart 

Institute of Telematics 

Dr.-Ing. Roland Bless 

Design Principles and threats for the Internet architecture 

Communication Systems – Basics of communication and Internet – 1.1 04/05 www.tm.uka.de 

Mobile Communications 

 

 

Communication Trends 

Paradigm: anybody, anytime, anywhere 

Expected: more mobile phone subscribers than POTS subscribers 

(Germany: already 48 Mio. at the end of 2000) 

Technical Communications 

 

 

Today: communication between users 

Tomorrow: communication between machines, e.g. 

Production infrastructure: tele-metrics, tele-diagnosis, tele-operations 

Communications between vehicles: 

Home networks: sensors, security, appliances 

IP-based Communications 

 

 

 

Internet Protocol IP as media independent access 

Voice-Over-IP technology is rolling out 

“All-IP” networks: Telcos will switch to IP for voice calls 

Communication Systems – Basics of communication and Internet – 1.2 04/05 www.tm.uka.de

„Everything goes IP” 

IP 

IP 

IP 


Internet Growth 

Survey based on #hosts registered in DNS 

#Hosts worldwide (Mio.) 

300 

250 

200 

150 

100 

50 

0 

91 92 93 94 95 96 97 98 99 00 01 02 03 04 

Year 


Growth and Scalability 

Constant change is presumably the only constant in the Internet 

Internet survived the tremendous growth: it still works! 

One says: it is “scalable” 

What means scalability? 

Scalability 

A scalable system works even when there is tremendous growth (e.g., by 

several orders of magnitude, i.e., over several scales) of certain system 

parameters 

Why important? Technological development shows often leaps in order of a 

magnitude (c.f. Moore‘s Law, CPU, bandwidth, memory) 

Example for no or bad scalability: 

X(t) 

System 

performance 

t 

Performance of a non-scalable system decreases (strongly) as certain 

parameter values increase, possibly until the whole system fails 


X(t) 

Evolving Internet – important aspects 

Past 

Data communication between research institutions 

Common goals 

Trust relationships between users 

Technically skilled users 

Consistent and coherent architecture 

Presence 

Global infrastructure of the information society 

New interest groups and commercialization (ISPs, service providers) 

Loss of trust relationships 

Average consumers, technically unskilled 

Out of own interests, technologies and extensions are realized, which 

• are used for short-time fulfillment of demand 

• are largely done without architectural thinking 

• are not consistent with the Internet architecture 

• endanger the coherence of the internet 


Data Communications 

Communication (original meaning): 

„Exchange of data between human communication partners.“ 

Every concrete communication is data communication 

N.B.: Information is extracted from data by the process of interpretation 

Data communication 

(more narrow definition in literature and habitual language use): 

„Transmission of digital data between telecommunication devices“ 

Communication (Usage of the term in this lecture): 

„Data (tele)communication is is the the generic term term for for each data data 

exchange using immaterial media and and greater distances 

between men men and/or machines 

(abbreviated: Data communication = communication).“ 

immaterial media: 

• Energy flows, usually electric currents, electromagnetic waves 

• Opposite: material data transport (e.g. letters, shipping of disks) 


Basic model of telecommunication 

sender 

service interface 

service 

access point 

receiver 

message 

medium 

spatial distance 

Participants act as senders or receivers 

The service usage by participants occurs at a special service interface, using 

a service access point 

Different service primitive types: Request, Indication, Response, Confirmation 

The Medium bridges the spatial distance 


What is a protocol? 

A communication protocol describes a set of rules, according to which the 

communication between two or more parties must be performed. 

Communication protocols 

e.g. discussion, conversation 

Computer communication protocols 

e.g. file transfer, electronic mail 

ISO/OSI protocols 

IPX 

TCP/IP protocols 

Ethernet AppleTalk 

WLAN 

DECnet 


Service and Protocol 

Service User 1 Service User 2 

Service 

Service 

Service 

Provider 1 

Protocol 

Service 

Provider 2 


A Model for Telecommunication Systems 

Sender 

Receiver 

telecommunication system 

entity n 

layer n 

entity n 

entity n-1 

layer n-1 

entity n-1 

. . . 

. . . 

entity 1 

layer 1 

Physical medium 

entity 1 

A layer offers a service to its upper layer 

The service is provided by the cooperation of the layer entities 

according to a specified protocol 


ISO/OSI and Internet Model 

7 

6 

5 

4 

3 

2 

1 

ISO/OSI Basic 

Reference Model 

Application 

Presentation 

Session 

Transport 

Network 

Data Link 

Physical 

Internet 

Reference Model 

Application 

Transport 


Media Access 

 

ISO/OSI too complex, but OK as logical model 

Too restrictive (no cross-layer information exchange) 

Redundant functionality in different layers 

Too heavy-weight for simple network devices like printers, etc. 

 

Internet model similar, but simplified (esp. Application layer) 


Physical Layer 

Tasks 

Accesses the physical medium directly (e.g. cable) 

Unsecured connection between systems 

Transport of unstructured bit sequences via a physical medium 

Comprises (among other things) physical link, conversion data ⇔ signals 

Signal Transmission Modes 

Baseband Transmission 

t 

Native and fully digital: 

discrete signal levels, periodic and discrete transition intervals 

Maximum data rate for channel with bandwidth B according to 

• Nyquist: r max [bit/s] =2 B log 2 n, (n=number of discrete levels, noise-less channel) 

• Shannon: r max [bit/s] = B log 2 (1 + S/N) (noisy channel, S/N=Signal-to-noise ratio) 

Broadband Transmission 

Modulation (amplitude, frequency, phase or combination thereof) 

Modem (modulator/demodulator) required 

S(t) 

S(t) 


t 

Tasks 

 

 

Medium-Access/Data Link Layer 

Structuring the data stream 

Synchronization, Framing, Code Transparency 

Protection against errors and loss 

Use of checksum to detect bit errors (e.g., CRC: Cyclic Redundancy Check) 

Reliable link layers use sequence numbers, timers and acknowledgments to 

detect loss of data packets and to recover by automatic retransmission 

Flow control 

Media access control in case of shared media 

Network Access 

Local Area Networks, e.g., Ethernet, Token-Ring, Token-Bus, Wireless 

LANs, .... 

Ethernet-Frame 

Preambel 

StartDel StartDel DestAddr 

SrcAddr 

Length Length Data Data PAD PAD FCS FCS 

56 56 bit bit (8 (8 bit) bit) (16/48 (16/48 bit) bit) (16/48 (16/48 bit) bit) (16 (16 bit) bit) (≤12.000 bit) bit) (0-368 (0-368 bit) bit) (32 (32 bit) bit) 

Metropolitan Area and Wide-Area Networks: Modems, Fiber, DSL, ... 


Tasks 

 

 

 

 

 

 

Network Layer 

Concatenation of point-to-point 

connections to end-system connections 

Uniform addressing of nodes 

Address mapping to 

data link layer addresses 

Transmission quality possibly 

selectable 

Routing 

Flow control, congestion control 

Applicationoriented 

Layers 

Transport 

Layer 

Network 

Layer 

Media Access 

End-system A 

TCP 

IP 

IP 

IEEE 802.3 

Intermediate System 

IEEE 802.3 

IP 

IP 

End-system B 

TCP 

IP 

IP 

IEEE 802.5 IEEE 802.5 

Switching concepts 

 

 

 

 

Physical Medium 

Circuit Switching (Classical telephony, e.g. ISDN) 

Packet Switching (Internet) 

Virtual Connections (ATM: Asynchronous Transfer Mode) 

Message Relaying 

Physical Medium 


Network Layer: Internet Protocol 

 

 

 

 

IP layer enables 

Bigger network 

Global addressing 

Hide network details and changes 

from end-to-end protocols 

A single protocol (Hourglass Model) 

maximizes interoperability 

minimizes the number of service interfaces 

Lean protocol 

Requires minimal common network functionality 

in order to maximize the number 

of usable networks 

End-to-End principle 

Robustness by stateless operation 

See also: 

http://www.iab.org/Documents/hourglass-london-ietf.pdf 

E-Mail, WWW, Telephony .... 

SMTP, HTTP, RTP, BEEP, ... 

UDP, TCP, 

SCTP, ... 

IP 

Ethernet, 

PPP, ... 

CSMA, CDMA, Asynch., SDH, ... 

Copper, Glass Fibre, Radio, ... 


Problem 

Routing in the Internet 

How are data packets forwarded in the Internet? 

Method 

Routing table gives information about the next hop 

The protocol IP 

(Internet Protocol) conducts the 

forwarding of data 

Routing 

Routing 

protocols 

protocols 

• 

• 

RIP, 

RIP, 

OSPF, 

OSPF, 

BGP 

BGP 

Datagram protocol 

• connectionless 

Address 

Address 

resolution 

resolution 

• unreliable 

• ARP, RARP 

• ARP, RARP 

• segmentation and 

reassembly 

Uses Internet addressing 

Uses further protocols like 

• ICMP (Internet Control Message Protocol) 

• ARP (Address Resolution Protocol) 

• IGMP (Internet Group Management Protocol) 

Transport layer: UDP, TCP 

Protocol 

Protocol 

IP 

IP 

• 

• 

Addressing 

Addressing 

• 

• 

Datagram 

Datagram 

format 

format 

•„Packet 

•„Packet 

handling“ 

handling“ 

Protocol 

Protocol 

ICMP 

ICMP 

• 

• 

error 

error 

reports 

reports 

Routing • 

• 

Signalling 

Signalling 

between 

between 

table routers 

routers 

Data link layer 

Physical layer 


Format of an IPv4 data unit 

Version (4) Header Length (4) 

Type of Service (8) 

Total Length (16) 

Identifier (16) 

Flags (3) Fragment Offset (13) 

Time to Live (8) 

Protocol (8) 

Header Checksum (16) 

Source Address (32) 

Destination Address (32) 

Options and Padding (variable) 

Data (variable) 

According to 

RFC 791 

(obsolete) 

0 1 2 3 4 5 6 7 

P P P D T R 0 0 

Precedence 

111 Network Control 

110 Internetwork Control 

101 CRITIC/ECP 

100 Flash Override 

011 Flash 

Delay: 

010 Immediate 

001 Priority 

000 Routine 

Reliability: 

NEW: 

0 1 2 3 4 5 

reserved 

0 normal 

1 low 

Throughput: 0 normal 

DS Field 

Differentiated Services 

1 high 

0 normal 

1 high 

6 7 

R 

ECN 

Explicit 

Congestion 

Notification 


IP addresses 

Structure of IPv4 addresses 

network part part 

local localpart 

network part part 

subnet subnetpart 

end end system system 

Subnet masks mark the area of the IP address describing the network and the subnetwork. 

This area is marked as ones („1“) in the binary form of the subnet mask. 

Example 

IP address: 129. 13. 3. 64 

Subnet mask: 255. 255. 255. 0 = 

1111 1111 1111 1111 1111 1111 0000 0000 

 

 

Network written in prefix notation: 129.13.3.0/24 

Globally visible network is only 129.13.0.0/16 (formerly Class B network) 

Network: 129. 13. 

Subnet: 3. 

End system: 64 

If the subnet mask only covers the network part, there is no subnet part 

(e.g. subnet mask 255.255.0.0 in case of class B) 

Note: Systems attached to several networks (e.g. routers), have several, network-specific 

IP addresses! 


Mapping of IP and MAC addresses 

If (Destination IP address AND Subnet mask) 

= (Own IP address AND Subnet mask) 

Receiver is in the same IP subnet! So I can use a link layer connection... 

Problem: 

Which MAC address does the next system on the route to the target have? 

Scheme 

Application 

Application 

TCP 

Connect with 

12 . 0 . 0 . 21 

TCP 

TCP 

IP 

12 . 0 . 0 . 34 

12 . 0 . 0 . 21 

IP 

MAC 

08002B90102456 

???????????????? 

MAC 



Forwarding in an IP router 

End system A 

129.13.3.108 

MAC-A 

IP-Router 1 

129. 

13. 

3. 

60 

132. 

2. 

2. 

3 

132. 

2. 

2. 

7 

145. 

5. 

9. 

19 

End system B 

145.5.9.27 

MAC-B 

Routing table (Routing Information Base) IP-Router 2 

Constructed by routing protocols: contains several alternative routes to the destination 

Forwarding table (Forwarding Information Base) 

Only selected/active routes: IP address of next hop and identification of the interface used 

Address resolution table 

Built by ARP: MAC address of the next system for the IP address of the end system 

Example 

Destination: end system B; Source: end system A 

Data packet on the way from router 1 to router 2: 

• MAC addresses: MAC address IP-Router 2 (dest) and MAC address IP-Router 1 

(source) 

• IP addresses: end system B (destination), end system A (source) 


Forwarding in an IP router 

Network scenario with router 

End system A 

129.13.3.108 

End system B 

145.5.9.27 

MAC-A 

Router 1 

Router 2 

129.13.3.60 132.2.2.7 

132.2.2.3 145.5.9.19 

If A If B If A If B 

MAC-B 

... 

129.13. 145.5. 

3.108 9.27 

... 

MAC- 

R1-B 

MAC- 

R2-A 

Router functions 

IP addresses MAC addresses 

Determine the IP address of the subsequent system (Next Hop) 

Simple routers have often only a routing table for their subnets and a default route for all 

other destinations 

Mapping of this IP address to the connection point address (MAC address) 

Sending the IP data unit to the next hop on the corresponding interface via layer 2 

IP addresses (Source/Destination) in the IP packet remain unchanged! 


Routing in the Internet 

Network layer protocols 

IP (Internet Protocol) 

ARP (Address Resolution Protocol) 

RARP (Reverse ARP) 

ICMP (Internet Control Message Protocol) 

IGMP (Internet Group Management 

Protocol) 

SNAP (Subnetwork Access Protocol) 

Routing protocols 

RIP (Routing Information Protocol) 

BGP (Border Gateway Protocol) 

EGP (External Gateway Protocol) 

OSPF (Open Shortest Path First) 

Network management 

SNMP (Systems Network Management 

Protocol) 

Transport protocols: 

UDP (Universal Datagram Protocol) 

TCP (Transmission Control Protocol) 

Protocols in an IP router 

ICMP IGMP 

BGP RIP SNMP 

TCP 

Internet Protokoll 

ARP RARP 

SNAP 

LLC-1 

UDP 

EGP / 

IGP 

OSPF 


Routing Hierarchy: View from 10,000m 

AS 100 

AS 111 

AS 112 

AS 120 

AS 110 

AS 114 

AS 121 

AS 101 AS 113 

AS 122 

Splitting networks into „Autonomous Systems“ (AS) 

Otherwise entries in routing tables and amount of exchanged routing 

information not scalable 

Routers within AS have usually only detailed routing information about own AS 

There is at least one designated router that acts as interface to other ASes 

Advantages 

• Scalability 

– Internal routing table size depends on size of AS 

– Changes within AS are usually only propagated within the AS if external connectivity is not 

affected 

• Autonomy 

– Internet = Network of networks 

– Routing is controlled by own organization 

» Unique routing strategy within own system 

» Internal routing protocols can vary between ASes 


AS and prefix number growth 

 

 

Each AS has a unique number 

(currently 16 bit, extension to 32 bit 

planned) 

Currently (Oct. 2004) ~18,000 ASes 

 

Currently (Oct. 2004) ~180,000 different 

IPv4 network prefixes (= best routes) 

Source: http://bgp.potaroo.net 


Routing und Autonomous Systems 

Autonomous Systems are interconnected 

Stub-AS 

• Small companies 

• Connection to exactly one provider 

Multihomed Stub-AS 

• Big companies 

• Connection to several providers (resilience) 

• No transit traffic 

Transit-AS 

Transit AS 

• Provider 

ISP ISP A 

ISP ISP B 

ISP ISP A 

ISP ISP 

Stub-AS 

Stub-AS 

ISP ISP B 

Two different levels of routing 

Intra-AS 

• Administrator is responsible for selecting a routing protocol 

Inter-AS 

• Uniform standards (BGP) 

• AS announces which networks (prefixes) can be reached through it 

– Own networks located/homed in this AS (Origin AS) 

– Networks in other foreign ASes (then the AS is willing to be transit AS for these destinations) 


Why Intra- and Inter-AS routing protocols? 

Policy 

Political question: which transit traffic is allowed to traverse the AS? 

Inter-AS: policies are selected by the provider 

Intra-AS: one organization, few policies necessary 

Scalability 

Inter-AS: further abstraction level; 

Size of routing tables and number of updates can be reduced, as failures within 

one AS can mostly remain hidden 

Intra-AS: higher stability 

Performance 

Inter-AS: Policies are necessary and more important than performance metrics 

Intra-AS: Concentration on performance metrics 


Intra-AS Routing 

Well-known protocols for Intra-AS routing are 

RIP (Routing Information Protocol) Distance Vector Protocol 

OSPF (Open Shortest Path First) Link State Protocol 

IS-IS (Intra-Domain Intermediate System to Intermediate System Routing 

Protocol) Link State Protocol 

• originally ISO/OSI routing protocol 

• used for IP by big providers 

EIGRP (Enhanced Interior Gateway Routing Protocol) 

• CISCO proprietary 

Intra-AS routing protocols are often called Interior Gateway Protocols (IGP) 

OSPF: 

Connectivity and link states are flooded through the network 

Every router has the same view of the network 

Network is mapped to Graph (V,E) 

Calculates shortest paths 

with Dijkstra’s algorithm 

Edge=Link 

Vertex=Node 

(router/ 

subnet) 


OSPF hierarchy in an Autonomous System 

N1 

interior Router 

N2 

R1 

R2 

R4 

(ABR) 

R3 

(ABR) 

R13 

(ASBR) 

R12 

(BBR) 

border router 

virtual 

connection 

Routing Area 

(OSPF Area) 

N: Network 

Autonomous System 

R: Router 

N3 

R5 

R6 

R7 

(ABR) 

ASBR/ 

ABR 

R9 

R8 

ASBR/ 

ABR 

R11 

ABR: Area Border Router 

ASBR: AS Boundary Router 

BBR: Backbone Router 

N4 

R10 

ASBR/ 

ABR 


Inter-AS Routing: Exterior BGP (EBGP) 

Exterior BGP is used between the BGP routers (also called BGP 

speakers) connecting two ASes 

Path Vector protocol (AS path) 

Learn all destination prefixes that can be reached through the other AS 

An AS can prevent to receive traffic for certain destination by not 

announcing any route to it (i.e., policy by route filtering) 

These BGP routers should be directly connected 

Internal information will NEVER be forwarded directly to other BGP 

speakers 

AS 1 AS 2 

BGP Speaker 


Example for BGP topology 

I want to send data to AS122! 

Which route should I use? 

AS 112 

AS 120 

100.0.0.0/8 

111.0.0.0/8 

112.0.0.0/8 

120.0.0.0/8 

AS 121 

AS 100 

AS 111 

AS 101 

110.0.0.0/8 

114.0.0.0/8 

121.0.0.0/8 

AS 110 

101.0.0.0/8 AS 113 

113.0.0.0/8 

AS 114 

AS 122 

122.0.0.0/8 

Routing table AS100 

Routing table AS110 

Network Next Hop Metric LocPrf Weight Path 

… 

Network Next Hop Metric LocPrf Weight Path 

*> 121.0.0.0 10.1.1.110 0 110 114 121 i 

* 

Routing 

121.0.0.0 

table AS114 

10.1.1.111 0 111 112 114 121 i 

*> 122.0.0.0 10.1.1.110 0 110 114 122 i 

* 

Network Next 

10.1.1.113 

Hop Metric LocPrf Weight 

0 

Path 

113 114 121 i 

*> 

*> 112.0.0.0 

10.1.1.114 

10.1.1.112 0 

0 

0 

114 

112 

121 

i 

i 

*> 

* 

122.0.0.0 10.1.1.114 

10.1.1.110 

0 

0 

114 

110 

122 

111 

i 

112 i 

* 

… 

10.1.1.111 0 111 112 114 122 i 

* 

*> 122.0.0.0 

10.1.1.113 

10.1.1.122 0 

0 

0 

113 

122 

114 

i 

122 i 


Routing in "Default-Free-Zones" 

Two modes of operation of BGP (same protocol, 

but different rules) for the distribution 

of routing information 

Between two AS: with EBGP (External BGP) 

Within one AS: with IBGP (Internal BGP) 

Internal full mesh of 

TCP connections necessary 

No distribution of routes learnt with 

IBGP to IBGP neighbors 

IBGP 

EBGP 

IBGP 

EBGP 

AS Y 

EBGP 

AS X 

IBGP 

EBGP 

EBGP 

EBGP 

Full mesh unsuitable for big AS, 

possible solution lies in the implementation of 

Route reflectors (dedicated routers as 

peering points) 

Confederations (private sub-AS) 


Interior BGP (IBGP) 

BGP routers within one AS are connected with IBGP 

IBGP routers have to be fully meshed 

• To learn routes for all external prefixes 

• They inform about new networks (e.g. LANs) 

• They do not propagate internal prefixes outwards 

No direct physical connections (but logical connections) between routers 

necessary 

Each IBGP router must be able to communicate with each other IBGP 

router 

IBGP messages are never forwarded to other BGP routers (to prevent 

loops) 


Tasks 

 

 

Transport Layer 

End-to-end service 

application-based addressing (Ports) 

reliable/unreliable 

Reliable protocol 

Error and loss detection 

Retransmission 

Segmentation/Reassembly 

Flow control 

Congestion control 

Examples 

 

 

 

 

TCP (Transmission Control Protocol) 

UDP (User Datagram Protocol) 

SCTP (Stream Control Transmission Protocol) 

DCCP (Datagram Congestion Control Protocol) 


Application Layer 

Protocols depend on the particular application 

This is also end-to-end 

Examples of protocols above the transport layer: 

 

 

 

 

 

 

 

 

 

telnet (Remote Login) 

SSH (Secure Shell, secure replacement for telnet) 

FTP (File Transfer Protocol) 

HTTP (Hypertext Transfer Protocol, HTML/Web Content Transport, 

Server/Client) 

BEEP (Blocks Extensible Exchange Protocol, Peer-to-Peer, many features) 

SSL/TLS (Transport Layer Security) 

SMTP (Mail Transport) 

DNS (Domain Name System) 

RTP (Streaming) 

Routing Protocols (OSPF, BGP, ...) 

 

...many more... 


Internet architecture: Design goals 

Paper by D. Clark “The Design Philosophy of the DARPA Internet Protocols” 

(SIGCOMM '88) names: 

Fundamental goal: Internetworking (Connection of existing networks) 

 

 

Further goals (ordered by their importance): 

Robustness: sustain internet communication despite failure of networks and 

routers 

Support of multiple types of communication services 

Heterogeneity: Accommodation of a variety of networks 

Distributed resource management 

Cost effectiveness 

Host attachment with a low level of effort 

Resources used must be accountable 

Robustness against failures 

„Fate-Sharing“: acceptable to loose the state information associated with an 

entity if, at the same time, the entity itself is lost 

Do not store state in the network, but in the end systems instead 

Datagram concept as a consequence 


Design principles: End-to-End Argument 

Decisions necessary in system design 

Which functionality is needed? 

Where should certain functions be placed? 

In the end systems or applications? 

In the network? 

Important design principle 

(explicitly expressed as recently as 1981 by Saltzer, Reed and Clark) 

The End-to-End-Argument (E2E argument): 

„The function in question can completely and correctly be 

implemented only with the knowledge and help of the application standing 

at the end points of the communication system. Therefore, providing that 

questioned function as a feature of the communication system itself is not 

possible. (Sometimes an incomplete version of the function provided by the 

communication system may be useful as a performance enhancement.)“ 


Discussion End-to-End-Argument 

 

 

 

This means especially: 

specific functionality of the application layer usually can and should 

preferably not be placed in the network itself 

Minimality principle: 

Avoid integrating more than the essential and necessary functionality into the 

network 

Keep unnecessary functionality out of the network Keep it simple 

Not a strict law, rather a guideline 

Further goals and consequences of the E2E argument: 

Protection of innovation 

Simple to add new services 

Hard to change the infrastructure (see introduction of Multicast, IPv6, ECN, etc.) 

 

Reliability and robustness 

against failure and malfunction of end systems and network components 

If network components have to store state, the probability of connection failures 

grows with increasing network size 


Consequences End-to-End-Argument 

Examples: 

 

Reliable file transfer 

Possible sources of error: 

Read errors in the end system 

Software errors during copying or buffering of data by the file system or file 

transfer program 

Hardware errors during these processes in CPU, memory, bus, etc. 

Loss, bit errors or duplicates in the communication system 

Crash/Failure of end systems (sender or receiver) during or after transfer 

Reliability of the communication system does not eliminate all errors 

Division of TCP/IP into TCP and IP in the late 70’s 

End-to-End security 

Suppression of duplicates (e.g. caused by the application itself) 


Internet Architecture: Principles 

RFC 1958: „Architectural Principles of the Internet“ 

 

 

Independence of the Internet Protocol of the medium and of hardware 

addressing 

If states have to be stored (e.g. routes, QoS-guarantees, Header 

Compression, ...), they should be “self-healing” 

Adaptive procedures and protocols for deriving and maintaining states 

„Soft-State“ concept: State is periodically renewed („refreshed“) 

Reduction of state information to a minimum 

Manually configured states should be reduced to an absolute minimum 


Further design aspects 

RFC 3426 „General Architectural and Policy Considerations“ 

(Internet Architecture Board) 

basic issues concerning protocol and system design 

 

 

no guidelines, no checklist 

Discussion and explanation on the basis of numerous 

case studies (e.g. ECN) 

RFC 1122 „Requirements for Internet Hosts -- Communication Layers“ 

 

 

Good documentation and discussion of design decisions 

Robustness principle (Jon Postel, see also http://www.postel.org): 

“Be liberal in what you accept, and conservative in what you send” 

Software should be able to react appropriately to every error – even if it 

is highly unlikely 

Incoming packet can contain any combination of faults and attributes 

Assumption of intended/malicious generation of such packets 


Many aspects have changed since the outset of the internet 

„Threats“ to the End-to-End-Argument? [RFC 3724] 

Loss of trust between end systems 

Introduction of security technologies 

 

 

 

 

Trends opposed to the E2E principle (1) 

Middlebox 

Middleboxes (Proxies/NATs/Firewalls/Caches/...) 

Break of the End-to-End Principle (esp. security mechanisms) 

New service models: Quality of service becomes part of the service 

(Streaming A/V) Servers are distributed and placed closer to the user 

(e.g. Akamai, Realnetworks...) 

New parties involved: Internet Service Provider, Administrators of company 

networks, governments 

Restriction of services, interest of interposing (e.g. as a Trusted Third 

Party or for eavesdropping/taxation/censorship...) 

Technically uninterested users 

Context and configuration information is placed in the network in order to 

disburden the user 


Trends opposed to the E2E principle (2) 

 

Example: negative effects by security technologies 

Elimination of PATH-MTU-Discovery mechanisms by rigorous filtering 

of ICMP packets 

Filtering of packets with their ToS-Bits set prevents the usage of Explicit 

Congestion Notification 

Limitation of accessibility and available services by private addressing 

in “Intranets” 

 

Possible procedure for future mechanisms which seem to infringe upon the 

End-to-End principle: 

Split E2E-Argument into the components 

Protection of innovation 

• Introduction of new mechanisms is easier in end systems 

Reliability/Robustness and trust 

• add security, where necessary 


Loss of internet transparency 

Internet Transparency [RFC 2775]: 

 

original concept of a single universal logical addressing scheme 

Mechanisms which allow packets to flow essentially unchanged from 

source to destination 

Loss of transparency by: 

Intranets („Security“, Restriction of applications and address transparency, 

network administrator has control) 

Dynamic addresses (SLIP/PPP, DHCP) 

Firewalls (Restriction of services and accessibility) 

SOCKS/Application Level Gateways 

Private addresses (not unique, restriction of accessibility and global 

communication) 

Network Address Translators (NATs) 

Application Level Gateways, Proxies, Caches 

Voluntary isolation (e.g. WAP-Proxies) and partner networks 

Split-DNS 

Tricks for load balancing 


Conclusions 

Today we have networks everywhere, and, they are a critical part of the IT 

infrastructure 

Most network systems and architectures use Internet protocols 

The Internet is a very scalable system 

Accommodated the tremendous growth in the past 

Thanks to the wise design decisions and architectural principles 

 

 

 

 

But for how long will its success continue? 

Requirements for more connectivity, machine-to-machine communication 

etc. lead to the use of IPv6 

Current Inter-Domain routing scheme will probably fail to cope with growth 

of the next two decades... 

Tussle and conflicts in the Internet caused by parties with different interests

Basics of communication and Internet

Create successful ePaper yourself

Delete template?

Save as template?