CS 598 Quiz 1

CS 598, Internet Telephony

Quiz 1, 10 June 2008

What is the objective of smart routing techniques in an IP network, and why do they sometimes fail to achieve their objectives?
The smart routing techniques are looking for low-delay routes through the Internet to improve VoIP quality of service. They sometimes fail because Internet conditions change more rapidly than smart routing techniques are able to adapt.
The answers, in no particular order and approximately verbatim:
1. The objective of smart routing techniques in an IP network is to reduce delay. They can fail when there is traffic congestion, buffer overflow, or if there is a loop/network and packet keeps moving in the same loop of routers.
2. To find the best path between two nodes A & B in network is the objective of smart routing techniques. Best path can be based on low cost, or less time to travel, etc. Sometimes, these routine techniques fail due to congestion in the network. Routers doesn't know that the path they decided might be congested. An hence packets are dropped.
3. The objective of smart routing is to reduce delay. It has problems when routers in the path are unavailable, for whatever reason. Being smart also requires overhead. Overhead itself is expensive.
4. Objective:
  1. Transfer packets fast with minimum packet loss.
  2. Route packets through less congested link to reach at destination quickly.
  Internet telephony is a best-effort technique and there is no guarantee that all the packets will reach to destination. If network is a shared resource and can not predict traffic volume and flow. That's the reason some times fail to achieve objectives by smart routing technique.
You have created a voice rope and embedded it in an e-mail message, which you've sent to a colleague. After sending the message, you realized you used a wrong name in the rope. You try to fix the problem by editing the voice rope to include the proper name. Does this fix the problem? Explain.
It does not. Voice ropes are immutable; when you edited the old voice rope, you actually created a new voice rope, one with a new reference. The e-mail message still contains a reference to the original voice rope.
The answers, in no particular order and approximately verbatim:
1. Voice rope's are immutable. So, just editing will not work. I have to reattach the *newly edited voice rope and resend it. *(Create new voice rope from previous voice rope.)
2. If the name is part of the voice recoding, no. You can't modify the voice string. If the name of the rope is not the unique id, but part of the management info, then you are fine. If you edit the voice string, you must save it as a new string and then create a new voice rope.
3. No, you cannot fix the problem as the voice rope is ‘embedded’ in the e-mail message. Had it been ‘embedded’ the friend would have heard the edited rope.
4. No. Embedding a voice rope in an e-mail means you created a copy of the voice rope and send via an email. By editing the voice rope to include proper name does not edit embedded voice rope in email. If you included a reference of particular voice rope in an email, by editing voice rope can solve the problem.
Give two trade-offs that might be used in deciding when to use voice ropes versus embedding voice directly into a document.

One trade-off is space: references to voice ropes are small, while the voice itself is large, orders of magnitude larger. Embedding a reference to a voice rope uses much less space than embedding the voice itself.

Another trade-off is time: accessing a voice rope for playback takes much longer than accessing embedded voice because the voice rope has to be retrieved from the voice server while the embedded voice is present for play.

The answers, in no particular order and approximately verbatim:
1. Voice takes up lot of space. When you want lots of people to share a common voice rope it is better not to embed it in the document. This will consume less space as references will be used to access the voice rope. But referencing a document from a server takes time. As against when it was embedded in the document you get the copy on your end and time required to access it from server is saved. But if you have to send the same voice rope to say 50 friends you make 50 copies of same and this consumes lot of space. If voice rope is to be shared with few embedding it directly in document is a good choice. But as the number of people accessing it grows sharing is a better option. So space and time are two parameters which should be considered.
2. 1. Future reference and/or editing.
  2. Document's size.
  3. Access control.
3. Voice ropes help reduce storage size. They contain more data than embedded voice, such as security info, accounting, and usage. voice ropes take more time to access. and require more storage size in the message itself.
4. 1. Space utilization — Voice ropes utilizes the space where as into a document wakes more space. Ex: Same voice is to be embedded in two different documents.
  2. Finding an unused voice rope is easier than finding a document where voice is directly embedded. After finding unused voice rope, we can delete it.
What is the principle difference between a VoIP architecture and the proposed Voice over Packet (VoP) architecture?
The VoP architecture is designed to exploit the existing PSTN, while a VoIP architecture exploits any IP overlay network.
The answers, in no particular order and approximately verbatim:
1. The proposed Voice over Packet (VoP) architecture will use the PSTN network. The principal difference between these two architectures is that there will be a dedicated path (PSTN) formed for VoP while VoIP doesn't have any dedicated path. Packets in VoIP will take the dynamic path decided by router.
2. In VoIP voice packets one enclosed in Internet Protocol packet. VoIP use connectionless, unreliable
3. VoIP architecture divides a voice message into packets that arrive at different times. Only the end points are smart. There is no guarantee of delivery. It uses heterogeneous networks. I would guess that VoP differs in some way on one of these points.
4. VoP flood packets over Internet and VoIP sends packet to destination IP address.