Exam 350-801 topic 1 question 80 discussion

B. same document iLBC: iLBC provides audio quality between that of G.711 and G.729 at bit rates of 15.2 kbps (38-bytes or 20msec) and 13.3 kbps (50 bytes or 30 msec). iLBC handles lossy networks in better way than G729 because it treats each packet independently. G729 depends on the previous packet to handle packet loss, jitter and delay which doesn't tolerate well in lossy networks.

iLBC handles jitter and packet loss better

D - correct Bandwidth estimation becomes an issue when voice is included in the calculation. Because WAN links are usually the lowest-speed circuits in an IP Telephony network, particular attention must be given to reducing packet loss, delay, and jitter where voice traffic is sent across these links. G.729 is the preferred codec for use over the WAN because the G.729 method forsampling audio introducesthe least latency (only 30 milliseconds) in addition to any other delays caused by the network. ref: https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_11_5/design/guide/uccx_b_soldg-for-unified-ccx/uccx_b_soldg-for-unified-ccx_chapter_0111.pdf

iLBC: iLBC provides audio quality between that of G.711 and G.729 at bit rates of 15.2 kbps (38-bytes or 20msec) and 13.3 kbps (50 bytes or 30 msec). iLBC handles lossy networks in better way than G729 because it treats each packet independently. G729 depends on the previous packet to handle packet loss, jitter and delay which doesn't tolerate well in lossy networks.

The correct answer is B. iLBC no bandwidth issue, the quality issue packet loss, delay, and jitter. G.729 is good for bandwidth and iLBC for bad Qos. There is similar question and only mention about bandwidth and the answer for that question is G.729.

Handles packet loss better than g729 & g711

I will go with ILBC guys (information is captured from Cisco SRND) https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab10/collab10/netstruc.html "When deploying voice in a WAN environment, Cisco recommends that you use the lower-bandwidth G.729 codec for any voice calls that will traverse WAN links because this practice will provide bandwidth savings on these lower-speed links. Where calls are made over best-effort networks with no QoS guarantees for voice, consider using Internet Low Bit Rate Codec (iLBC), which enables graceful speech quality degradation and good error resilience characteristics in networks where frames can get lost."

G729A & AB are medium Complexity iLBC - High Complexity I go with G729A

Tricky question, as CollabGuy says. I don't think there is any arguement that iLBC is a marginally better codec for this kind of scenario. So it comes down to choosing between g729 and iLBC. Minimising transcoder usage should definitely be a factor. Since newer Cisco phones (8865 and 7975) support iLBC, in the exam I would answer B (iLBC) but how Cisco mark this question is hard to predict. As DEFAULTNERD says, Cisco may prefer g729.

Cisco does not like ILBC it did not create it and does not like it.

As says at this referenced link I believes iLBC is the best option: iLBC handles lossy networks in better way than G729 because it treats each packet independently. G729 depends on the previous packet to handle packet loss, jitter and delay which doesn't tolerate well in lossy networks.

IMHO it has to be iLBC. I think this is a very tricky question and almost evil to ask in an exam. G729 and iLBC are both low bandwidth codecs (everybody knows that). However, as they say that the network has jitter, delay and packet loss we have to use iLBC as "iLBC handles lossy networks in better way than G729 because it treats each packet independently. G729 depends on the previous packet to handle packet loss, jitter and delay which doesn't tolerate well in lossy networks."

Cisco wants g.729 because no trans-coding is needed