TCP/IP Networks

Table of Contents

• Computer networks, layers, protocols, interfaces; • OSI reference model; • TCP/IP reference model; • Internet Protocol (operations, addresses, classes); • Routing; • Transmission Control Protocol (TCP); • User Datagram Protocol (UDP); • Applications; • Sockets.

Computer Networks

•Hosts; •Routers - Gateways; •Bridges - Repeaters; •Data packets networks, ISDN, leased lines;

Computer networks classification

NETW ORK CHARACTERIS TICS S iz e S p e e d LAN's

C a m p u s O ffic e 1 0 Mb p s -1 0 0 Mb p s

To p o lo g y

S h a re d m e d ia

MAN's

C ity , To wn 1 0 0 Mb p s S h a re d m e d ia

W AN's

C o u n ty , C o u n try 1 Mb p s , (4 5 Mb p s S MDS ) m e s h Shared media: Workstation Workstation Workstation Bus Workstation Backbone network Vs local access network Workstation Workstation Token-ring Ring Workstation Workstation

Switching Techniques

• Circuit switching; • Message switching; • Packet switching.

Protocol Hierarchies

Host A Layer 5 Layer 4/5 interface Layer 4 Layer 3/4 interface Layer 3 Layer 2/3 interface Layer 2 Layer 1/2 interface Layer 1 Layer 5 protocol Layer 4 protocol Layer 3 protocol Layer 2 protocol Layer 1 protocol Host A Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Physical medium

Layer 5 Layer 4 M

Information Flow

Layer 5 protocol H4 M Layer 4 protocol M H4 M Layer 3 H3 H4 M1 H3 M2 H3 H4 M1 H3 M2 Layer 2 H2 H3 H4 M1 T2 H2 H3 M2 T2 H2 H3 H4 M1 T2 H2 H3 M2 T2 Layer 1 Source machine destination machine

OSI Reference Model

The

OSI reference model

based on a proposal developed by

ISO

has

seven layers

. The

principles

that were applied to arrive at the seven layers are as follows: • A layer should be created where a different level of abstraction is needed; • Each layer should perform a well defined function; • The function of each layer should be chosen with an eye toward defining internationally standardised protocols; • The layer boundaries should be chosen to minimise the information flow across the interfaces; • The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity, and small enough that the architecture does not become unwieldy.

Application Presentation Session Transport Network Data link Physical

OSI Layers Functions

Application

: provides user access to an OSI environment.

Presentation

:hides from the application layer differences in representation of information.

Session

:provides facilities for synchronization.

Transport

: enables QoS network facilities.

Network

: establishes, maintains and terminates connections.

Data Link

: controls data transfer over physical link, including error detection.

Physical

: provides electrical and mechanical control to transmit data bits onto communication medium.

TCP/IP Reference Model

Application Transport Internet Host-to Network • The protocols came first and model is just a description of existing protocols; • The TCP/IP reference model can not describe non-TCP/IP networks; •The layers 5 and 6 are not present in this model.

Application Presentation Session Transport Network Data link Physical

OSI vs TCP/IP

Application TCP UDP IP Host-to Network

TCP/IP Detailed View

FTP, WWW,CMOT Telnet, rlogin, SMTP, TFTP, DNS, SNMP NFS, yp, etc.

PING ARP RARP TCP IEEE 802.3

MAC Ethernet UDP IP ICMP IEEE 802.2, 802.1

IEEE 802.4

MAC Token bus IEEE 802.5

MAC Token ring IEEE 802.6

MAC MAN HDLC/X.25, PPP, SLIP WAN

Internet Protocol (IP)

• Connectionless (i.e., each packet it treated independently, with no reference to packets that have long gone before); •Cannot guarantee reliable, in-order delivery; •PDU: IP datagram, which contains user data, source-destination IP addresses, other inf. (such as its length, time-to-live, etc.); • IP main operations:

Fragmentation/Reassembly

and

Routing

Fragmentation/Reassembly

Reassembly

Two options: either in host B, or in router G2.

It is preferred the first option.

Gain: Simpler routers (no buffering of fragments) Loss:decrement of network utilisation and increment of packet loss probability.

IP Addresses

       An IP address defines both the network and the host on the particular network; An IP address has 4 bytes, so there are 4 billion addresses; There is one-to-one correspondence between IP and physical addresses; Example of an IP address : 147.102.7.1; An IP address includes two parts: a network identifier (netid) and a host identifier (hostid); The netid defines the network, while the hostid differentiate a host of the network from the others; The length of netid depends on the address class: there are three address classes, namely A,B and C;

Address Classes

Class Α: Class B: Class C:

0 + 7bits (netid=1byte) + 3bytes (hostid); 10 + 14bits (netid=2byte) + 2bytes (hostid); 110 + 21bits (netid=3byte) + 1bytes (hostid);     When a network is separated into subnetworks, the hostid defines both the host and the subnetwork of the host.

= A subnet mask (32-bit) indicates the split of hostid to subnetid and new hostid; A subnet mask contains 1 for bits of netid and subnetid and 0 for bits of hostid; Example: The mask 255.255.255.0 defines 14 subnetorks and 4094 hosts for each subnetwork.

Domain Name Service (DNS)

  The DNS servers correspond names such as “swpc94.telecom.ece.ntua.gr” in IP addresses like “147.102.7.94”; However, the traffic of TCP/IP packets uses IP addresses and not names;  Before an Internet process, there is a dialogue (approx. 1/10 sec) between the source host and the local DNS server for finding the IP address of the target host.

Routing

• Direct routing: In the same network, usage of the

Address Resolution Protocol (ARP)

and

Reserve Address Resolution Protocol (RARP)

• Indirect routing: Between different networks, usage of the routers

Routers

• They can manipulate packets from all the interconnected networks; • They communicate with all the interconnected networks; • They are “multihomed”, i.e., they have multiple IP addresses referring to all the interconnected networks; • They perform routing algorithms using the netid of the IP datagrams.

1 I A

Indirect Routing Example

B  Β 2  2 C II  ii 3 3 separate physical networks, with their own addresses, packet size and pattern.

III

1 I A

Indirect Routing Example

B  Β D 4 2  2 C The networks are connected via two routers. The routers can send/receive packets to/from both networks.

4 IV II  ii 3 III

2.1

1.1

1 A

1.4

2.4

Indirect Routing Example

B  Β

1.2

1.3

D 4 2  2

2.2

C Introduction of the unique IP address for each host and the IP datagram as common transfer unit.

2.3

3.1

2.5

I

3.4

5 IV 3 II  ii

3.2



3.3

III

Indirect Routing Example

D 5

A B  Β

1.2

1.1

3.3

2.1

3.3

1

3.1

I

iii data

D 4

1.4

2.4

C 2  2

2.2

2.3

data 3.3

5 IV

2.5

3

3.4

II  ii

3.2

data



3.3

III

1.3

• Each host or router forwards the datagram per one hop towards its destination. For each hop, the datagram is encapsulated into a specific physical layer packet with a local physical address. The datagram keeps the IP address of its destination.

• The routers firstly exams the netid.

• Only at the last hop of routing, the hostid is mapped to the physical address.

• In case of fragmentation, the destination takes over the reassembly.

Indirect Routing Example

• Both hosts and routers keep

routing tables

for leading the IP datagrams to destinations and

physical addresses tables

for mapping the IP addresses to corresponding physical addresses.

• Routing Table: It contains pairs of the form

(N,R)

, where

N

is the IP address of the destination network and

R

is the IP address of the next router towards the destination.

• Examples: Host 1.1

N R N Router 1.4/2.4

R 1.x

2.x

3.x

Computation of the physical address 1.4

1.4

1.1

Physical Addresses Table: 1.2

1.3

1.3

A B C D 1.x

2.x

3.x

direct connection direct connection 2.5

Transmission Control Protocol (TCP)

• Connection-oriented (i.e., a connection is established before the data transmission); • Can guarantee reliable stream delivery services; A 1500 21 FTP B 1501 128.10.0.3

Telnet 23 128.10.0.7

• reserved TCP port numbers (16 bits): FTP 21 Telnet 23 Finger HTTP 79 80

Transmission Control Protocol (TCP)

   Sliding Window Technique; Multiplicative Decrease Congestion Avoidance; Slow Start Recovery;

Allowed_window = min (Receiver_Advertisement, Congestion_Window)

User Datagram Protocol (UDP)

• Connectionless; • No confirmations, packets numbering, flow control; • No error detection/recovery; •Cannot guarantee reliable in order delivery services; • reserved UDP port numbers (16 bits): DNS TFTP 53 69 SNMP 161 • Mainly, broadcasting applications use UDP.

Applications

     FTP; SMTP; WWW; Telnet; Many others

Sockets

A 1500 B 1501 128.10.0.3

21 FTP Telnet 23 128.10.0.7

  The combination of an IP address with a port number identifies a socket; A socket defines an application service;