Congestion Control Algorithm

1
Congestion Control Algorithm

• Preallocation of Buffers e.g.,
• Allocate Buffer to Each Virtual Circuit in Each
  IMP.
• Note This May be Expensive, and Only Used Where
  Low Delay High Bandwidth are Essential (e.g.,
  Digitized Voice)

2
Packet Discarding

• Datagram Service Packet Discard at Will
• Virtual Circuit Service A Copy of Packet Must be
  Kept
• Note If Congestion is to be Avoided by
  Discarding Packets, A Rule is Needed

Input Lines
Output Lines
Free Buffer
Congestion can be reduced by putting an upper
bound on the number of buffers queued on an
output file
3
Packet Discarding (cont.)

• (Irland) Discovered Simple Rule of Thumb
• (Not Optimal) for Determining Max Q Length, m,
  for an IMP With k Buffers
• m k / Ö s, Where s º of Output Lines

4
Internetworking

• Many Different Networks Exist
• Different Networks Have Radically Different
  Technology
• Still Desirable to Connect These
  Networks Examples of This Follow
• 1. LAN-LAN A Computer Scientist Downloading a
  File to Engineering
• 2. LAN-WAN A Computer Scientist Sending Mail to
  a Distant Physicist
• 3. WAN-WAN Two poets Exchanging Sonnets
• 4. LAN-WAN-LAN Engineers at Different
  Universities Communicating

5
Four Common Types of Relays

• Layer 1 Repeaters Copy Individual Bits Between
  Cable Segments
• Layer 2 Bridges Store and Forward Frames Between
  LANs
• Layer 3 Gateways Store and Forward Packets
  Between Dissimilar Networks
• Layer 4 Protocol Converters Provide Interfacing
  in Higher Layers

6
Network interconnection
7
Gateways

• Operate at The Network Level
• Two Styles
• Connection-Oriented e.g., Virtual Circuit
• Connectionless-Oriented e.g., Datagram

8
Internetworking(A Full Gateway)
Network 1
Network 2
B U F F E R
Net 1 to Internet Internet to Net 1
Net 2 to Internet Internet to Net 2
1
2
Machine owned jointly by both network
9
Internetworking(Two half-Gateways)
Communication Line
Network 1
Network 2
Net 1 to Internet Internet to Net 1
Net 2 to Internet Internet to Net 2
1
2
Machine owned by Network 1
Machine owned by Network 2
10
The Network Layer
11
The Network Layer (cont)
12
A datagram moving fromnetwork to network
13
A datagram moving fromnetwork to network (cont.)
DHX Data link Header for network
X DTX Data link Trailer for network
X IP Internet Protocol header TH
Transport Header
Frame 1 DH1 IP TH DT1
Frame 2 DH2 IP TH DT2
Frame 3 DH3 IP TH DT3
Internet packet
14
Transparent Fragmentation
15
Non-transparent Fragmentation
16
Firewall

• A dedicated gateway machine with special security
  precautions on it.
• Out-going/in-coming packets may be blocked.
• IP address and a port number may be used to block
  the packets.

17
The IP Protocol
32 Bits
Version
IHL
Type of Service
Total Length
D F
Identification
Fragment Offset
M F
Header Checksum
Time to Live
Protocol
Source Address
Destination Address
Options (0 or more words)
The IP (Internet Protocol) header
18
The IP Addresses
32 Bits
Range of host address
Class
1.0.0.0 to 127.255.255.255
0
Network
Host
A
128.0.0.0 to 191.255.255.255
10
Network
Host
B
192.0.0.0 to 223.255.255.255
110
Network
Host
C
224.0.0.0 to 239.255.255.255
1110
Multicast Address
D
240.0.0.0 to 247.255.255.255
11110
Reserved for Future use
E
IP address formats
19
The IP Addresses
20
The IP Addresses
21
ARP
Provides a mapping between the two forms of
addresses 32-bit IP addresses and data link
addresses (e.g., 48-bit Ethernet addr.)
22
ARP Request/Reply
23
ARP (contd)
Fund. Concept The network interface has a
hardware address, and frames exchanged at the
hardware level must be addressed to the correct
interface. TCP/IP works with its own addresses
(i.e., 32-bit IP addresses). Knowing a hosts
IP addresses does not let the kernel (i.e.,
Ethernet driver) must know the hardware address
to send the data.
24
Summary
Protocol addresses cannot be used when
transmitting frames across physical network
hardware, because the hardware does not
understand IP addressing. So, a frame sent across
a given physical network must use hard wares
frame format, and all addresses in the frame
must be hardware address
25
Three interconnected class C networks two
Ethernets and an FDDI ring
26
Internet Control Protocols

• ICMP (Internet Control Message Protocol)
• ARP (Address Resolution Protocol)
• RARP (Reverse Address Resolution Protocol)
• BOOTP (Bootstrap Protocol)

27
BOOTP (contd)
BOOTP uses UDP and is intended as an alternative
to RARP For bootstrapping a diskless system to
find its IP address. Bootp can also return
additional information such as the IP address of
a router, the clients subnet mask, and the IP
address of a name server.
28
BOOTP (contd)
BOOTP ? DHCP (Dynamic Host Configuration
Protocol) Unlike BOOTP, DHCP does not require an
administrator to add an entry for each computer
to the database that a server uses. Instead,
DHCP provides a mechanism that allows a computer
to join a new network and obtain an IP address
without manual intervention. Note An
administrator can configure a DHCP server to have
2 types of addresses Permanent addresses and a
pool of addresses to be allocated on demand.
29
Operation of ARP
FTP
TCP
IP
(2)
(3)
establish connection with IP address
send IP datagram to IP address
(4)
Host Name
IP addr
(1)
Resolver
ARP
(5)
(6)
(8)
(9)
Ethernet Driver
ARP request (Ethernet broadcast)
Ethernet Driver
Ethernet Driver
(7)
ARP
IP
ARP
TCP
Operation of ARP when user types ftp hostname
30
Goals IPv6

1. Support billions of hosts, even with inefficient
   address space allocation
2. Reduce the size of the routing tables
3. Simplify the protocol, to allow routers to
   process packets faster
4. Provide better security (authentication and
   privacy) than current IP
5. Pay more attention to type of service,
   particularly for real-time data

31
IPv6 (contd)

1. Aid multicasting by allowing scopes to be
   specified
2. Make it possible for a host to roam without
   changing its address
3. Allow the protocol to evolve in the future
4. Permit the old and new protocols to coexist for
   years

32
The IPv6 fixed header (required)
33
Examples of The Network Layer
7 6 5 4 3 2 1
7 6 5 4 3 2 1
Application protocol (not defined by X.25)
Presentation protocol (not defined by X.25)
Session protocol (not defined by X.25)
Transport protocol (not defined by X.25)
X.25 layer 3
X.25 layer 3
3 2 1
3 2 1
3 2 1
X.25 layer 2
X.25 layer 2
X.25 layer 1
X.25 layer 1
DTE
DTE
Internal protocols are not defined by X.25
The place of X.25 in the protocol hierarchy
34
Two Forms of Connections

• Virtual Calls --- A Connection is Established,
  Data Are Transferred, Then The Connection is
  Released
• Permanent Virtual Calls --- Like A Leased Line,
  DTE at Either End LAN Just Send Data Whenever It
  Wants, Without Any Setup
• Note The Choice of Circuit on Outgoing Calls
  is Determined by The DTE, and on Incoming Calls
  by The DCE, May Lead to A Call Collision.

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