Describe, and critique, one application with regard to its transmission requirem
ID: 3875734 • Letter: D
Question
Describe, and critique, one application with regard to its transmission requirements, such as bandwidth, latency, reliable delivery, in-sequence delivery, and jitter. Example applications include:
Stored unicast video
Stored multicast video
Live unicast video
Live multicast video
Live 2-way video phone
Live multi-way video phone
Bulk file transfer (FTP, HTTP download)
Remote desktop (Microsoft RDC, VNC)
Bittorrent
Infrastructure traffic (DNS, DHCP, routing protocols, router hot spare protocol, inter-server heartbeat for clusters)
Client-server database
Storage Area Network (SAN) connections (iSCSI)
SNMP or other management protocols
Choose an application, and evaluate its needs for these requirements.
Propose a way of provisioning an Enterprise LAN so that this application gets the best performance. Do you see areas of possible conflict? Can you think of other parameters to be considered along with the ones mentioned above? These could be any resource or constraint that would affect the behavior of the network.
Explanation / Answer
Live unicast video
A Unicast transmission/stream sends IP packets to a single recipient on a network. A Multicast transmission sends IP packets to a group of hosts on a network. If the streaming video is to be distributed to a single destination, then you would start a Unicast stream by setting the destination IP address and port on the AVN equal to the destination’s values. If you want to view the stream at multiple concurrent locations, then you would set the AVN’s destination IP address to a valid Multicast IP address (224.0.0.0 – 239.255.255.255).
Note that while the Multicast IP address range is from 224.0.0.0 – 239.255.255.255, the first octet (224.xxx.xxx.xxx) is generally reserved for administration. VSI recommends setting the first octet to 225 and the remaining three octets to the AVN’s IP address. For example, if the AVN’s IP address is 192.168.1.53, then set the destination IP address to 225.168.1.53 for Multicast streaming.
Since Multicasting is a relatively new technology, some legacy devices that are part of your network might not support Multicasting.
Before using the AVN encoder in Multicast streaming mode, check the functional specifications of your network infrastructure to ensure that the Multicast stream will not create major traffic on your network. Verify that your backbone switch supports Internet Group Messaging Protocol (IGMP) snooping, which allows the core of your network to ignore the traffic streams that Multicasting may generate.
For more information on IGMP querying and snooping please refer to an AVN encoder’s user manual, available on our website by product, in the chapter titled “Connecting to the Network”.
Unicast
Reliable delivery has been succinctly defined as "Data is accepted at one end of a link in the same order as was transmitted at the other end, without loss and without duplicates." This implies four constraints:
(i) No loss (at least one copy of each PDU is sent)
(ii) No duplication (no more than one copy of each PDU is sent)
(iii) FIFO delivery (the PDUs are forwarded in the original order)
(iv) A PDU must be delivered within a reasonable period
For a communications protocol to support reliability, requires that the protocol identifies each individual PDUs that is transmitted. The protocol implements an error recovery procedure (e.g. Stop and Wait ).
There is very little data which is so important that it must be sent no matter how late. If the links in the network are therefore liable may lead to loss of packets, a reliable protocol should be used. When the under-lying network is very reliable (as in an Ethernet LAN), best effort protocols may be sufficient.
Reliability may be provided at various levels of the OSI reference model. Examples of reliable communications protocols are:
Layered protocols usually also employ timers at each level, governing this interval. The service provided by a protocol layer may be unreliable for various reasons including:
A "Best Effort" service is one which does not provide full reliability. It usually performs some error control (e.g. discarding all frames which may have been corrupted) and may also provided some (limited) retransmission (e.g. CSMA/CD). The delivered data is not however guaranteed. A best effort service, normally requires reliability to be provided by a higher layer protocol.
Examples of best effort services are:
Link Layer - HDLC (UI frames); Ethernet
Network Layer - IP (Datagrams)
Transport Layer - UDP and UDP-Lite.
Services may be better than best effort, for example provide service guarentees or better expectations of the service. The Differentiated Services (diffserv) and Integrated Services (intserv) frameworks provide this type of service at the network-layer.
There has also been work on less than best effort services, specifically services that are designed to operate in the background. The IP Scavenger service is an example network-layer service that allows file transfers to safely operate in the background without impacting other network users. This service has as yet not been widely used.