Shuffling and Hairpinning

From Jaymzworld

Contents 1 Introduction 2 Shuffling 2.1 Determining if shuffling is possible 3 Hairpinning 3.1 Determining if hairpinning is possible 4 Timing

Introduction

Hairpinning and shuffling are similar because they preserve connection and conversion resources that might not be needed, depending on the compatibility of the endpoints that are attempting to interconnect. These two techniques differ in the way that they bypass the unnecessary call-path resources.

Shuffled or hairpinned connections:

• Conserve channels on the TN2302AP IP Media Processor
• Bypass the TDM bus, conserving timeslots
• Improve voice quality by bypassing the codec on the TN2302AP MedPro

Because shuffling frees up more resources on the TN2302AP MedPro circuit pack than hairpinning does, CM checks both endpoints to determine whether they can shuffle, and if they can't, hairpins the call.

If more than one possible type of connection would be possible between 2 endpoints, the order of preference is:

1. ip-ip direct
2. ip-prowler-ip hairpin
3. ip-tdm-ip

Shuffling

Shuffling an audio connection between two IP endpoints means rerouting voice channels away from the usual TDM bus connection and creating a direct IP-to-IP connection. Shuffling saves such resources as TN2302AP or TN2602AP channels and TDM bus time slots and improves voice quality because the shuffled connection bypasses the TN2302AP’s or TN2602AP’s codec. Both endpoints must be capable of shuffling (support H.245 protocol) before Communication Manager can shuffle a call.

Determining if shuffling is possible

Communication Manager uses the following criteria to determine whether a shuffled audio connection is possible:

• A point-to-point voice connection exists between two endpoints.
• No other active call (in-use or held) that requires TDM connectivity (for example, applying tones, announcement, conferencing, and others) exists on either endpoint.
• The endpoints are in the same network region or in different, interconnected regions.
• Both endpoints or connection segments are administered for shuffling by setting the Direct IP-IP Audio Connections field on the Station screen or the Signaling group screen to y.
• If the Direct IP-IP Audio Connections field is y (yes), but during registration the endpoint indicates that it does not support audio shuffling, then a call cannot be shuffled. If the Direct IP-IP Audio Connections field is n (no), but during registration the endpoint indicates that it can support audio shuffling, then calls to that endpoint cannot be shuffled, giving precedence to the endpoint administration.
• The rules for Inter-network region connection management are met.
• There is at least one common codec between the endpoints involved and the Inter-network region Connection Management codec list.
• The endpoints have at least one codec in common as shown in their current codec negotiations between the endpoint and the switch.
• Both endpoints can connect through the same TN2302AP MedPro or TN2602AP MedPro circuit packs.

Hairpinning

Hairpinning means rerouting the voice channel connecting two IP endpoints so that the voice channel goes through the TN2302AP MedPro and TN2602AP MedPro circuit packs in IP format instead of through the TDM bus. Communication Manager provides only shallow hairpinning, meaning that only the IP and Real Time Protocol (RTP) packet headers are changed as the voice packets go through the TN2302AP or TN2602AP circuit pack. This requires that both endpoints use the same codec (coder/decoder), a circuit that takes a varying-voltage analog signal through a digital conversion algorithm to its digital equivalent or vice-versa (digital to analog).

Determining if hairpinning is possible

Communication Manager uses the following criteria to determine whether to hairpin the connection:

• A point-to-point voice connection exists between two endpoints.
• The endpoints are in the same network region, or in different, interconnected regions.
• A single TN2302AP MedPro or TN2602AP MedPro circuit pack serves both endpoints.
• The endpoints use a single, common codec.
• The endpoints are administered for hairpinning: the Direct IP-IP Audio Connections field on the Station screen or the Signaling group screen is y.
• If the IP Audio Hairpinning field is y (yes), but during registration the endpoint indicates that it does not hairpinning, then a call cannot be hairpinned. If the IP Audio Hairpinning field is n (no), but during registration the endpoint indicates that it can support hairpinning, then calls to that endpoint cannot be hairpinned, giving precedence to the endpoint administration.
• The conditions for shuffling are not met.
• Both endpoints can connect through the same TN2302AP MedPro or TN2602AP MedPro circuit pack.

Timing

Any features that could be affected by a 50 to 200 ms break in the speech path will have a feature interaction with hairpinning and shuffling. 50 ms is approximately how long it takes for a hairpin to rearrange the audio path, and 200 ms is approximately how long it takes for a shuffle to rearrange the audio path.

200 ms is a typical upper bound for rearranging the audio path if only one switch is involved; the number will be about 100 ms more for each switch involved. While there is no absolute upper bound on how long the rearrangement can take, if the LAN performance is really bad, the two ip-ip directly connected users will probably go on-hook.