CIPT2 Notes


Quality Issues
Availability Issues
Dailplan Issues
Nat and Security Issues


Quality Issues
  • Packet by packet delivery
    • No guarantee for correct order
    • RTP fills in gaps with sequence numbers
  • Bandwidth shared by multiple users and applications
    • Peaks and buffer queues
    • Jitter
    • Packet drops in case of buffer congestion
** When queue fills up packets are dropped so QoS needs to be implemented

Quality Issues in multisite deployment generally are:
 1. Buffer delays and packet drops
 2. Bandwidth shared by multiple streams
 3. Packets can be delivered out of sequence

Bandwidth Issues
  • All inter-site traffic ( voice data video) competing for availability
  • Voice causes lots of overhead
  • No unnecessary traffic should be sent over the IP WAN

Voice Packet :
  • Small size
  • High Packet Rate
  • Large Overhead
Data Packet :
  • Large Size
  • Lower Packet Rate
  • Small Overhead

Availability Issues
 - Signaling
 - Media Transmission
 - Phone Services ( ie XML)


Dial Plan Issues:

DID versus attendants
Overlapping DN's
Nonconsecutive DN's
Optimized Call Routing
  • Toll Bypass
  • Tail-end hop-off
  • PSTN Backup
PSTN Requirements
    • Access codes, national and international dialing

Three ways to detect end of dialing in variable length numbering plans

    • Interdigit Timeout

    • Use of # Key

    • Use over overlap and overlap receiving ( could get complex and has to be supported)

 QOS Review
  1. Traffic identification
  1. Traffic divided into classes
  2. QoS Policy is applied per class

QOS Advantages
  1. Prevent Jitter
  2. Ensure Enough Bandwidth for signaling
  3. Prevent Packet Loss caused by tail drops in queues



cRTP reduces the bandwidth requirements of a call on a WAN Link but its not true header compression because we are caching.

Header compression does not pay off on links above 768k



Mixed Conference Bridging allows multiple bandwidth codecs used by remote participants



Deploying Transcoders or Mixed Conference Bridges
  • Hardware only devices that support multiple codecs
  • Used where low-bandwidth codecs are not supported by all endpoints

Deploying Local Conference Bridges
  • Keeps voice traffic off IP WAN


Deploying Low-Bandwidth Codecs
  • Compresses 64kb/s voice streams to 8kb/s


Using RTP-Header Compression
  • Can be used on selectively slow WAN interfaces



Multicast MOH from branch router flash is a feature for multisite deployments with centralized call processing
  • Based on MOH capabilities of SRST

Configuration for Branch Router with MOH SRST
Call-manager-fallback
Max-ephone 1
Max-dn 1
Ip source-address x.x.x.x
Moh moh-file.au
Multicast moh 239.1.1.1

CAC is used to limit the number of calls
Locations
  • Bandwidth limit
RSVP Enable Locations
  • Special implementation of locations
  • Allows calls to flow through two routers
  • Call leg between routers uses RSVP to limit bandwidth

SIP Precondition
  • Like RSVP-enabled locations but between SIP domains (e.g. two clusters interconnected via a SIP trunk)


SURVIVABILITY and AVAILABILITY

Options
  • PSTN Backup
  • MGCP Fallback
    • Falls back to a default application using either h323 or sip
  • Fallback for IP Phones
    • SRST
    • CUCME SRST
  • CFUR ( Call forward unregistered )
  • AAR and CFNB ( automated alternate routing / call forward no busy)
  • Mobility Solutions
    • Extension Mobility
    • Device Mobility
    • Unified Mobility


DIAL PLAN SOLUTIONS

Overlapping and nonconsecutive numbers
  • Access / site codes fix this
  • Allow routing independent of DN
  • Appropriate digit manipulation
Variable length numbering
  • Dial string length determined by timeout or use of # key
  • Overlap sending and receiving
DID ranges and PSTN addressing
  • User of IVR or attendant required if no DID numbers
  • Directory numbers appended to PSTN number
Number presentation ( ISDN TON )
Least cost routing , TEHO, PSTN Backup
  • Call routing and path selection based on prioritzed paths


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