Ocd lec networks_10-11 (1)

www.bournemouth.ac.uk
Online Content Distribution
Lecture: Networking for Content
Delivery
Andres Ibarra Lobo

www.bournemouth.ac.uk 2
Objectives
This lecture aims to help you:
1. Understand network topologies.
2. Understand network communication basics.
3. Understand packet switching mechanism.
4. Understand addressing/routing methodologies.
5. Understand communication protocols for streaming.

Computing Network Topology
Definition:
• The way in which the connections within a computing network are
made (e.g., the shape or the layout).
Types:
• Physical refers to the physical design of a network. That is, how
different systems of a network are actually connected with cables
and wires.
• Logical refers to the data communication over the physical network.
That is, how systems communicate across the physical topologies.

Physical Topologies
Bus
• Each of the systems in the network connects to a “line” (backbone).
Ring
• Each of the systems in the network is connected to its two respective
neighbours forming a ring.
Star
• Each of the systems in the network connects to a “central device” (hub).
Mesh
• Each of the systems in the network has a dedicated point-to-point link to
every other system.
Tree
• Like its name implies, it is a mix use of other types topologies with the
concept of hierarchy (root, nodes, branches, children etc.).

Bus Topology
Advantages:
• Inexpensive, very low cost
• Easy installation/implementation
(adding/removing)
• Ideal for small networks (netcafe, studios)
Disadvantages:
• Speed/distance limitations.
• Highly depends on the
availability/robustness of the “line”
• Security issues
• Difficulty in troubleshooting
• Unmanageable for large networks

Ring Topology
Advantages:
• Relatively low cost
• Easy installation
• Token-ring is secure
• Support to form larger network (e.g., small
enterprise intranet)
Disadvantages:
• Speed/distance limitations.
• Difficulties in change (moving, adding,
removing systems) and maintenance.
• One system would fail the entire network!
• Low efficiency

Star Topology
Advantages:
• Easy installation/upgrading support
• Easy troubleshooting and maintenance
• Simplicities of operation
• Good security
• Ideal for larger networks
Disadvantages:
• Expensive (for long distance)
• Hub dependency – central hub is everything!
• Sometimes not efficient

Mesh Topology
Advantages:
• Good connection possibility so no traffic
problem
• Security
• Robust
• Fault tolerant
Disadvantages:
• Difficult cabling
• Complex installation
• Connection redundancy
• Cost

Tree Topology
Advantages:
• Best possible solution for large network
(WAN)
• Point-to-point communication is possible.
• Best topology for branched out networks.
• Each of systems get access to larger
networks in the hierarchy.
Disadvantages:
• Not suitable for smaller networks as it
wastes resources
• Highly depends on the root “backbone”.
• Difficult to configure after a certain point.
Root
Mesh Mesh Mesh
Mesh Star Bus Star Mesh
Star
Bus
Ring
Ring
Ring

Logical Topology
Shared media (current Ethernet topology)
• Each of systems has the ability to access the physical layout whenever they need it
(unrestricted access).
• However, it could easily cause collisions when two or more systems send information
at the same time. A solution is to add a traffic detection mechanism to monitoring
current traffic.
• It is typically deployed in a bus, star, or hybrid physical topology.
Token based (old-fashioned technology from IBM)
• Use of a token to provide access to the physical media.
• The biggest problem of token is latency as systems have to wait until they get an
available token.
• It is typically deployed in a ring physical topology.

Network Communication
Network communication
• Communication happens
between different nodes.
• Communication has to be
initialised by a node.
• The node knows which other
nodes it wants to
communicate.
• The node has to let other
nodes aware if they want to
communicate to them (e.g.,
make a link).
Human communication
• Communication happens
between different people.
• Communication has to be
initialised by someone.
• The person knows whom they
want to communicate.
• The person has to let other
people aware if they want to
talk to them (e.g., call their
names).

Network Communication (cont.)
Network communication
• There are some controls to
make sure only the intended
receiver(s) will receive the
message.
• There are also some
mechanism to ensure the
smooth communication.
• Any of the two sides can end
the communication.
• A communication can not be
forced.
Human communication
• There are some controls to
make sure only the intended
person(s) will receive the
message.
• There are also some
mechanism to ensure the
smooth communication.
• Any of the people can end the
communication.
• A communication cannot be
forced.

Network Communication (cont.)
Have you realised something important?
• Sender and receiver: important indeed.
• Make connections: switching.
• Know where to go: addressing/routing.
• Smooth communication: protocols.

Switching
• Switching is the way to create communicational
channel to allow network nodes communicate with
each other in a network.
• In a traditional telephony network, switch
boards/exchanges are used to establish a direct &
physical dedicated connection between two nodes. This
process is normally called circuit switching.
• In a modern digital network (Ethernet or Internet), data
sending from one node are divided into a number of
blocks (packets) which are then transmitted individually
to another node through the network. This process is
normally called packet switching.

Addressing & Routing
• Routing is a process of selecting paths to send
network traffic.
• Routing is the act of moving information across a
network from a source to a destination.
• The main activities of routing is to 1) determine optimal
(best possible) routing paths and 2) forward packages.
• Routing paths are pre-configured in static routing.
• Routing paths are selected by routing algorithms in non-
static (adaptive or dynamic) routing.

Addressing/Routing Semantics
Unicast:
• Deliver a message to a single specified node in the network (one to one).
Broadcast:
• Deliver a message to all nodes in the network (one to many).
Multicast:
• Deliver a message to a group of nodes which are receivers (one to many).
Anycast:
• Deliver a message to the topologically nearest node in a group of potential
receivers (one to one of many).

Unicast
sender router
dest

Multicast
sender router
dest
dest

Broadcast
sender router
dest
dest
dest
dest
dest

Anycast
sender router
dest
dest

Network Switches, Hubs & Routers
Switches vs. hubs vs. routers:
• Switches and hubs create a network.
Routers join networks.
• Switches are more intelligent and they
have higher performance than hubs.

Protocols
What is a communication protocol:
• It is a set of rules for exchanging messages in or
between systems.
• A protocol describes the syntax, semantics, and
synchronisation of communication.
• Protocols can be implemented in hardware or software.
• A data transmission in or between systems normally
requires a set of protocols (for example, Internet Protocol
Suite).

Common Protocols
TCP (Transmission Control Protocol)
• A reliable but complex data exchange protocol used
for major Internet applications (e.g., emails).
• TCP operation is divided into three handshake
phases, connection establishment, data
transmission & connection termination.
UDP (User Datagram Protocol)
• An unreliable but simple data exchange protocol
commonly used for most contemporary Internet
applications (e.g., online games, streaming etc.).

TCP
TCP header structure
Source port Destination port
Sequence number
Acknowledge number
Data offset Reserved Flags Window Size
Checksum Urgent pointer
Options
Data

UDP
UDP header structure
Source port Destination port
Length Checksum
Data

Research Tasks
• Give real-life examples of network topologies.
• What will be the best Ethernet topology for a small studio
with 20 staff & draw the diagram?
• Give real-life examples of different routing semantics.
• Draw the diagram of how multicast and unicast protocols
are used for video on demand.
• Compare TCP and UDP in terms of streaming.

Ocd lec networks_10-11 (1)

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