2. Internet Architecture
Application layer – HTTP, SMTP etc W3C
Transport layer – TCP, UDP
IETF
Network layer - IP
Data link & Physical layers – ITU
the territory of the LANs/Telcos/ISPs IEEE
3. Variables in Internet service
• Bandwidth
• Latency – delay sensitivity
• Error free – loss tolerance
4. Application requirements
Application Loss Delay Band-
Tolerant Sensitive Width
Web None No Medium
E-Mail None No Low
Video streaming Some Some High
Telephone calls Some Yes Low
Video conferencing Some Yes Medium/
high
7. Multicast routing
• We have only talked about single host to
single destination messages
• Some applications require a host to send
messages to many destinations:
– Upgrade of software
– Streaming of an on-line lecture or movie
– Stock price information to subscribers
8. Three approaches
• At the application level where the application
establishes a separate unicast transport connection
to each receiver. This is not usually efficient and
not scalable
• Broadcast – controlled – reverse path & spanning
tree
• An explicit multicast where the network layer
makes copies of the message as close to the
recipient as possible
10. How does it address the one
message to all receivers?
• It is not practicable to:
– Attach a list of addressees to the message
– The addressees may not be known
• Uses a broadcast and subscribe approach
• Subscribers are added to a D class address
• See Kurose for more details
• IGMP (Internet Group Management Protocol)
provides services for managing the group
11. Video and audio Streaming
• Streaming stored video
• Streaming live video
• Real time interactive video - video
conferencing
• Voice over IP
12. Streaming stored video
• Media pre-recorded and held on server
• Ideally server near client (remember WEB caching
discussion)
• Important that it plays at recorded speed
• Uses buffering to prevent jitter – effect of delays
and loss packets
• Because of buffering and one way (predominantly)
latency not as big a problem as with live video
streaming
• Can fast forward and rewind (not usually multicast)
13. Streaming live video
• Can still buffer and build in a delay
• Because it is live, cannot fast forward but
some software will allow rewind
• Can be multicast or unicast
• Multicast overlay – uses servers scattered
through the broadcast area
14. Protocols for streaming
• WEB http uses TCP to make the request
• But TCP not satisfactory for streaming
• Browser kicks off a media player process
• Web server then instructs Steaming server
to send to the media player post on the
browser host probably using RTP
WEB TCP WEB
Browser server
Media
UDP Streaming
player server
15. Control streaming stored video
• Real Time Streaming Protocol (RTSP)
• The equivalent of the Remote control
• Allows the Media player and the Streaming server
to communicate over two additional ports
• RTSP keeps track of the state of the streaming
process including the session number and
sequence number of the segment
16. Compression
• Video and audio must be compressed before
transmission
– Speech normally requires 64kbps
– Stereo CD requires 1.4mbps
– Video much more again
• Various standards (codecs) for compression
– GSM for voice
– MP3 for stereo music
– MP1 and MP4 and others for video
– H.323 for Video conferencing
17. Voice over IP
• Delay sensitive but large bandwidth not
required
• Range of user facilities required to simulate
facilities available in PBX
18. Private WAN PSTN
Call Manager Gateway
Office 1
Private link
Office 2 Public
Internet
Gateway
19. Advantages
• Maintain one network instead of two
• One British bank estimate gives 25% cost saving
• Inter-office calls over own network – fixed cost
• Application extensions
– On-line office directory
– Single messaging system
– Display product information
– Telephony options on screen
– Video conferencing
20. Risks
• Security – could be open to Public internet
• New technology
• QoS over IP – not totally standardised
• Power failure etc, not just network but
phone system as well – all eggs in one
basket
21. Techniques for avoiding jitter in VoIP
• Three problems
– Variable latency
– Lost packets
– Packets out of order
• Approaches
– Sequence numbers & timestamps
– Fixed play out delay
– Error correction
• Redundant data to allow reconstruction of one packet
• Two audio streams- normal and a back-up low resolution
• Interleaving
22. Video conferencing
• Like a phone call, delays must be less than
½ second
• Places real constraints – delay sensitive and
needs bandwidth
