Networking and Internetworking

1
Networking and Internetworking

• Chapter 3

2
Roadmap

• Terminology and networking issues
• Types of network
• Network principles
• Internet protocols
• Case studies Ethernet, wireless LAN and ATM

3
Roadmap

• Terminology and networking issues
• Types of network
• Network principles
• Internet protocols
• Case studies Ethernet, wireless LAN and ATM

4
Basic Terminology

• Communication subsystem
• Hosts (purposeful) vs. nodes (devices)
• Routing delivering data from one part of the
  (wide area) network to another
• Subnet unit of routing (cf. the Internet being
  constructed from many subnets)

5
Networking Issues for Distr. Systems (1)

• Performance
• Latency (caused by software overhead, routing
  delays, conflicting demands for access to
  transmission channels)
• Data transfer rate (unit bits/sec, caused by
  mainly physical characteristics)
• time required for a network to transfer a message
  with length bits between two computers is
• message transmission time latency
  length/data transfer rate

6
Networking Issues for Distr. Systems (2)

• Performance (cont.)
• Total system bandwidth (measure of throughput)
  total volume of traffic that can be transferred
  across the network in a given time (cf. network
  flow algorithm) in local area network vs. in
  wide area network
• Scalability
• The ability to grow
• The impact of traffic on performance can be
  gauged from common latencies (world wide wait?)

7
Networking Issues for Distr. Systems (3)

• Reliability
• Possible errors are usually due to software
  errors (e.g., receiving computer unable to accept
  a packet, buffer overflow, etc.)
• Security
• Firewall protection boundary between the
  organizations intranet the rest of the
  Internet.
• Purpose to protect the resources inside the
  organization from access by external users, to
  control the access.
• Runs on a gateway (entry point to an intranet).
• Cryptographic techniques are needed (Ch. 7).

8
Networking Issues for Distr. Systems (4)

• Mobility
• More and more in demand
• Quality of service
• The ability to meet deadlines when transmitting
  processing streams of real-time multimedia data
  (require guaranteed bandwidth bounded latency)
• Multicasting
• One-to-many communication (simultaneous
  transmission of messages to several recipients)
• Simulated one-to-one is not good (fault-tolerance
  reason)

9
Roadmap

• Terminology and networking issues
• Types of network
• Network principles
• Internet protocols
• Case studies Ethernet, wireless LAN and ATM

10
Types of Network (1)

• Local area networks (LANs)
• Technologies Ethernet, token rings, etc.
• Bandwidth (b/w) gigabits/sec
• Wide area networks (WANs)
• Routing is needed routers, routing algorithms
• B/w varies from 1-2Mbps ( 10-100Kbps)

11
Types of Network (2)

• Metropolitan area networks (MANs)
• High b/w copper fiber optic cables
• Up to 50 km
• Technologies from Ethernet to ATM
• IEEE 802.6 protocol, 1994
• E.g. DSL (Digital subscriber line), cable modem
  connections

12
Types of Network (3)

• Wireless networks
• IEEE 802.11 (WaveLAN) 2-11Mbps over 150m
• Wireless local area networks (WLANs)
• Wireless personal area networks (WPANs)
• E.g. infra-red links in palmtop laptop
  computers, BlueTooth low-power radio network
  technology (1-2Mbps over 10m)
• Internetworks
• The Internet
• TCP/IP protocols

13
Types of Network (4)
14
Roadmap

• Terminology and networking issues
• Types of network
• Network principles
• Internet protocols
• Case studies Ethernet, wireless LAN and ATM

15
Network Principles (1)

• Packet transmission
• Message logical unit of information. Sequence
  of data items of arbitrary length.
• Packet subdivisions of a message. Sequence of
  binary data of restricted length ( regulated,
  predictable). Carry information of source
  destination computers.
• Data streaming
• Multimedia data streams

16
Network Principles (2)

• Switching schemes
• Broadcast involves no switching. LAN
  technologies (Ethernet), wireless networking.
• Circuit switching telephone networks
• Packet switching store--forward network.
  Postal system.
• Frame relay (small packets) brings advantages of
  circuit switching to packet switching networks.
  ATM networks.

17
Network Principles (3)

• Protocols
• Well-known set of rules
• Communication protocol
• Spec. of the seq. of messages that must be
  exchanged
• Spec. of the format of the data in the messages

Message received
Message sent
Layer n
Layer 2
Layer 1
Communication
medium
Sender
Recipient
18
Network Principles (4)
Encapsulation as it is applied in layered
protocols
19
Network Principles (5)

• Protocol layers in the ISO Open Systems
  Interconnection (OSI) model

20
OSI protocol summary
21
Internetwork layers
22
Network Principles (6)

• Packet delivery
• Datagram packet delivery
• A seq. of packets may follow different routers
• The Internets network layer (IP)
• Ethernet and most local network technologies
• Virtual circuit packet delivery
• A virtual circuit must be set up before packets
  can be delivered.
• Virtual circuit number instead of source
  destination addresses in each packet
• ATM
• Benefits from lower latencies
• Relation with the Internet transport protocols
  UDP (connectionless) TCP (connection-oriented).
  Each can be implemented over either type of
  network layer.

23
Network Principles (7)

• Routing
• Adaptive routing find the best route taking into
  account the current traffic in the network and
  any faults (broken connections or routers).
• Routing algorithm
• Make decisions to determine the route taken by
  each packet.
• Dynamically update its knowledge of the network
  (link-state algorithms) Routing Information
  Protocol (RIP)
• Routing in network finding paths in graphs
• Bellman-Ford protocol distance-vector algorithm

24
Routing in a wide area network
25
Routing tables for the network in the previous
slide
26
Pseudo-code for RIP routing algorithm
Send Each t seconds or when Tl changes, send Tl
on each non-faulty outgoing link. Receive
Whenever a routing table Tr is received on link
n for all rows Rr in Tr if (Rr.link ! n)
Rr.cost Rr.cost 1 Rr.link n if
(Rr.destination is not in Tl) add Rr to Tl// add
new destination to Tl else for all rows Rl in Tl
if (Rr.destination Rl.destination and
(Rr.cost lt Rl.cost or Rl.link n)) Rl Rr //
Rr.cost lt Rl.cost remote node has better
route // Rl.link n remote node is more
authoritative (closer)
27
RIP routing algorithm (cont.)

• Frequency t stabilizing purpose (e.g., if some
  RIP packets are lost). For the Internet t 30
  sec.
• Broken link set cost to infinity for all entries
  in the Tl that refer to the faulty link and
  perform Send action.
• RIP-1 (RFC 1058) improved version of RIP
• Costs can be based on actual b/w of the links.
• Algorithm can be modified to increase its speed
  of convergence and to avoid some undesirable
  intermediate states, such as loops.

28
Network Principles (8)

• Congestion control
• Network congested drop packets
• 80 of its capacity the total throughput tends
  to drop as a result of packet losses
• Internetworking
• Tunnelling protocol tunnel software layer that
  transmits packets through an alien network
  environment
• E.g. IPv6 encapsulated in IPv4 packets, Mobile
  IP, IP multicast protocol, etc.

29
Tunnelling for IPv6 migration
30
Roadmap

• Terminology and networking issues
• Types of network
• Network principles
• Internet protocols
• Case studies Ethernet, wireless LAN and ATM

31
Internet Protocols

• Internet
• ARPANET the first large-scale computer network
  (early 70s)
• TCP/IP (Transmission Control Protocol/Internet
  Protocol)
• Currently more than 60 million hosts
• Applications Web (HTTP), email (SMTP, POP),
  netnews (NNTP), file transfer (FTP), telnet
• TLS (Transport Layer Security) on top of TCP to
  produce secure channels (e.g. for secure HTTP)

32
TCP/IP layers
33
Encapsulation in a message transmitted via TCP
over an Ethernet
34
The programmer's conceptual view of a TCP/IP
Internet(Universality of IP packets)
35
IP AddressingFigure 3.15 Internet address
structure, showing field sizes in bits
36
Figure 3.16 Decimal representation of Internet
addresses(network identifiers allocated by
Internet Network Information Center)
octet 1
octet 2
octet 3
Range of addresses
Network ID
Host ID
1.0.0.0 to
Class A
1 to 127
0 to 255
0 to 255
0 to 255
127.255.255.255
Network ID
Host ID
128.0.0.0 to
Class B
128 to 191
0 to 255
0 to 255
0 to 255
191.255.255.255
Network ID
Host ID
192.0.0.0 to
Class C
0 to 255
0 to 255
1 to 254
192 to 223
223.255.255.255
Multicast address
Multicast address
224.0.0.0 to
Class D (multicast)
0 to 255
0 to 255
1 to 254
224 to 239
239.255.255.255
240.0.0.0 to
Class E (reserved)
0 to 255
0 to 255
1 to 254
240 to 255
255.255.255.255
37
The IP Protocol (1)

• Unreliable (best-effort) delivery semantics no
  guarantee of delivery only header checksum
  (detecting corruptions in the addressing packet
  management data), no data checksum (leaving it to
  the higher-level protocols TCP UDP
  end-to-end argument)
• Address resolution by Address Resolution Protocol
• IP Spoofing malicious sender substitutes address
  (source address) that is different from its own

38
The IP Protocol (2)

• DDoS attacks
• (Example February 2000) Issue many ping
  (checking the availability of a host) service
  requests to a large of computers at several
  sites. These malicious ping requests all
  contained the IP address of a target computer in
  their sender address field. The ping responses
  were therefore all directed to the target -gt
  input buffer overflow -gt preventing legitimate IP
  packets from getting serviced.

39
DDoS Attack
A malicious attacker subverts a number of
machines, known as zombies
remote control
40
DDoS Attack ExampleSMURF Attack Exhausting
Resources
BOB
EVE
x.y.z.w
41
The IP Routing (1)

• Backbones topological map is partitioned
  conceptually into two parts
• Autonomous systems (AS)
• Areas (subdivisions)
• Every AS in the topological map has a backbone
  area
• Routing protocols
• RIP-1 (distance-vector algorithm)
• RIP-2 (in the next slide)
• Link-state algorithms (Open Shortest Path First)
  based on Dijkstras algorithm 1959

42
The IP Routing (2)

• RIP-2
• Classless interdomain routing (CIDR)
• Better multicast routing
• Authentication of RIP packets to prevent attacks
  on the routers
• Solutions to overcome the infeasibility (every
  router maintaining a full routing table w/ the
  route to every destination in the Internet is
  infeasible)
• Topological grouping of IP addresses (1993)
• 194.0.0.0 to 195.255.255.255 Europe
• 198.0.0.0 to 199.255.255.255 North America
• 200.0.0.0 to 201.255.255.255 Central South
  America
• 202.0.0.0 to 203.255.255.255 Asia the Pacific

43
The IP Routing (3)

• Solutions to overcome the infeasibility (cont.)
• Default route specifies a route to be used for
  all IP packets whose destination is not included
  in the routing table (trading routing efficiency
  for table size).
• (E.g.) From figures in slides
• 24 25
• (Esp. useful when all outward messages must pass
  through a single point.)

Routings from C
To
Link
Cost
B
2
1
C
local
0
E
5
1
Default
5
-
44
The IP Routing (5)

• IPv6 (IETF 1994) to overcome the potential
  problem of IPv4 w/ 32-bit addresses
• Fig 3.17 IP packet layout
• Fig 3.19 IPv6 header layout

45
The IP Routing (6)

• IPv6 (cont.)
• Address space 2128 ( 3 x 1038)
• 1000 IP addresses/ m2 of the earth surface in the
  worst case assignments of IP addresses Huitema
• Anycast delivers a packet to at least one of the
  hosts that subscribes to the relevant address
• Security authentication encrypted security
  payload extension header types. IPSec
  specification (RFC 2411)

46
Mobile IP (1)

• DHCP (Dynamic Host Configuration Protocol)
• Enables a newly connected computer to acquire a
  temporary IP address the addresses of local
  resources such as a DNS server from the local
  DHCP server.
• Discovery services discover what local services
  such as printing, mail delivery, etc, are
  available.
• What if the service itself is moving around?
• Need MobileIP (cf. cellular phone network)

47
Mobile IP (2) The MobileIP routing mechanism
Subsequent IP packets
Sender
tunnelled to FA
Mobile host MH
Address of FA
returned to sender
First IP packet
addressed to MH
Internet
Foreign agent FA
Home
First IP packet
agent
tunnelled to FA
48
TCP and UDP

• Use of ports port number for addressing
  messages to processes within a computer. 16-bit
  integer.
• UDP ( transport-level replica of IP) messages
  of up to 64 kbytes in size (the max. packet
  permitted by IP)
• TCP features
• Sequencing (by sequence numbers)
• Flow control (by buffering and variable window
  size)
• Retransmission (by acknowledgement)
• Buffering (by incoming buffer at the receiver)
• Checksum (for error checking in data)

49
Domain Names and Firewalls

• Domain name system (DNS)
• Firewalls security policy
• Service control
• Behavior control
• User control
• Filtering operations
• IP packet filtering
• TCP gateway checks all TCP connection requests
• Application-level gateway acts as proxy for
  application process

50
Firewall configurations
51
Roadmap

• Terminology and networking issues
• Types of network
• Network principles
• Internet protocols
• Case studies Ethernet, wireless LAN and ATM

52
IEEE 802 network standards
53
Ethernet (1)

• Developed at the Xerox Palo Alto Research Center
  in 1973.
• Original prototype Ethernet ran at 3 Mbps now
  ranging from 10 Mbps to 1000 Mbps.
• Method of operation carrier sensing multiple
  access w/ collision detection (CSMA/CD)
  contention bus network
• Packet broadcasting all stations are
  continuously listening to the medium for packets
  that are addressed to them. Packets (frames) are
  broadcast.
• Packets vary in length between 64 and 1518 (MTU
  in the IEEE standard).

54
Ethernet (2)

• Packet layout
• Prefix used for h/w timing purposes
• S start frame delimiter
• Checksum packets w/ incorrect checksums are
  dropped (by the datalink layer in the receiving
  station) end-to-end argument

bytes 7 1 6 6
2 46 1500
4
Preamble S Destination Source
Length Data for transmission Checksum
address address
of data
55
Ethernet (3)

• Packet collisions
• Collision detection
• Jamming signal (all stations recognize the
  collision)
• Back-off (wait random amount of time bounded by
  constant L before retransmitting up to 10
  attempts (each time doubling L)

56
IEEE 802.11 Wireless LAN

• Wireless LAN configuration

57
Asynchronous Transfer Mode Networks (1)

• To carry a wide variety of data incl. multimedia
  data.
• Data-switching technology over telephone networks
  (synchronous), synchronous optical network
  (SONET).
• Virtual connection b/w and latency guarantees
• Low latency switching delay 25 microseconds
• Gigabits per second are attainable in pure ATM
  networks.
• ATM cell layout

58
Asynchronous Transfer Mode Networks (2)

• ATM protocol layers

59
Asynchronous Transfer Mode Networks (3)

• Switching virtual paths in an ATM network

60
Homework 2A

• Please solve the following exercise questions
• Chapter 3 exercises 3.1, 3.3, 3.7, 3.12, and
  3.18.
• Due date
• 4/25/2007 (Wednesday)
• at the beginning of class.