Transcript Chapter 8: Internet Operation

Chapter 8: Internet Operation
Business Data Communications, 5e
Network Classes
• Class A: Few networks, each with many
hosts
All addresses begin with binary 0
• Class B: Medium networks, medium hosts
All addresses begin with binary 10
• Class C: Many networks, each with few
hosts
All addresses begin with binary 11
Internet Addressing
• 32-bit global internet address
• Includes network and host identifiers
• Dotted decimal notation
– 11000000 11100100 00010001 00111001
(binary)
– 192.228.17.57 (decimal)
Subnets & Subnet Masks
• Allows for subdivision of internets within
an organization
• Each LAN can have a subnet number,
allowing routing among networks
• Host portion is partitioned into subnet and
host numbers
Subnet Mask Calculations
Internet Routing Protocols
• Responsible for receiving and forwarding
packets between interconnected networks
• Must dynamically adapt to changing
network conditions
• Two key concepts
– Routing information
– Routing algorithm
Autonomous Systems
• Key characteristics
– Set of routers and networks managed by single
organization
– group of routers exchanging information via a
common routing protocol
– connected (in a graph-theoretic sense); that is, there is
a path between any pair of nodes
• Interior Router Protocol (IRP) passes information
between routers in an AP
• Exterior Router Protocol (ERP) passes
information between routers in different Aps
Border Grouping Protocol
(BGP)
• Preferred ERP for the Internet
• Three functional procedures
– Neighbor acquisition
– Neighbor reachability
– Network reachability
Open Shortest Path First (OSPF)
• Widely used as IRP in TCP/IP networks
• Uses link state routing algorithm
• Routers maintain topology database of AS
– Vertices
• Router
• Network
– Transit
– Stub
– Edges
• Connecting router vertices
• Connecting router vertex to network vertex
Autonomous System Example
Directed Graph of Example
The “Need for Speed” and
Quality of Service (QoS)
• Image-based services on the Internet (i.e.,
the Web) have led to increases in users and
traffic volume
– Resulting need for increased speed
– Lack of increased speed reduced demand
• QoS provides for varying application needs
in Internet transmission
Emergence of High-Speed LANs
• Until recently, internal LANs were used primarily
for basic office services
• Two trends in the 1990s changed this
– Increased power of personal computers
– MIS recognition of LAN value for client/server and
intranet computing
• Effect has been to increase volume of traffic over
LANs
• Result exceeds capacity of standard 10mbps and
16mbps networks
Corporate WAN Neds
• Greater dispersal of employee base
• Changing application structures
– Increased client/server and intranet
– Wide deployment of GUIs
– Dependence on Internet access
• More data must be transported off premises
and into the wide area
Digital Electronics
• Major contributors to increased image and
video traffic
• DVD (Digital Versatile Disk)
– Increased storage means more information to
transmit
• Digital cameras
– Camcorders
– Still Image Cameras
Categories of Traffic
• Elastic
– Can adjust to changes in delay and throughput
access
– Examples: File transfer, e-mail, web access
• Inelastic
– Does not adapt well, if at all, to changes
– Examples: Real-time voice, audio and video
Requirements of Inelastic Traffic
• Throughput
– Minimum value may be required
• Delay
– Services like market quotes are delay-sensitive
• Delay variation
– Real-time applications, like teleconferencing, have
upper bounds on delay variation
• Packet loss
– Applictions vary in the amount of packet loss
allowable
Application Delay Sensitivity
Differentiated Services
• Provide QoS on the basis of user needs rather
than data flows
• IP packets labeled for differing QoS treatment
• Service level agreement (SLA) established
between the provider (internet domain) and the
customer prior to the use of DS.
• Provides a built-in aggregation mechanism.
• Implemented in routers by queuing and
forwarding packets based on the DS octet.
• Routers do not have to save state information on
packet flows.
DS Service:
Performance Parameters
•
•
•
•
Service performance parameters
Constraints on ingress/egress points
Traffic profiles
Disposition of excess traffic
DS Services Provided
• Traffic offered at service level A will be delivered with
low latency.
• Traffic offered at service level B will be delivered with
low loss.
• 90% of in-profile traffic delivered at service level C will
experience no more than 50 ms latency.
• 95% of in-profile traffic delivered at service level D will
be delivered.
• Traffic offered at service level E will be allotted twice the
bandwidth of traffic delivered at service level F
• Traffic with drop precedence X has a higher probability
of delivery than traffic with drop precedence Y.
DS Field
• Packets labeled for handling in 6-bit DS field in the IPv4
header, or the IPv6 header
• Value of field is “codepoint”
• 6-bits allows 64 codepoints in 3 pools
– Form xxxxx0 - reserved for assignment as standards.
– Form xxxx11 - reserved for experimental or local use.
– Form xxxx01 - also reserved for experimental or local use, but
may be allocated for future standards action as needed.
• Precedence subfield indicates urgency
– Route selection, Network service, Queuing discipline
• RFC 1812 provides two categories of recommendations
for queuing discipline
– Queue Service
– Congestion Control
DS Configuration Diagram
DS Configuration & Operation
• Routers are boundary or interior nodes
• Forwarding treatment is per-hop behavior (PHB)
• Boundary nodes handle traffic conditioning
–
–
–
–
–
Classifier
Meter
Marker
Shaper
Dropper
Traffic Conditioning Diagram
Token Bucket Scheme